University of Southern California Dissertations and Theses

Film deposition and optoelectronic properties of low-dimensional hybrid lead halides

(USC Thesis Other)

Film deposition and optoelectronic properties of low-dimensional hybrid lead halides

PDF

Download a page range

Download transcript

Copy asset link

Request this asset

Transcript (if available)

Content FILM DEPOSITION AND OPTOELECTRONIC PROPERTIES OF
LOW-DIMENSIONAL HYBRID LEAD HALIDES
by
Gemma Goh Yang
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(CHEMISTRY)
August 2024
Copyright 2024 Gemma Goh Yang

Acknowledgments
This PhD experience has been more than an intellectual pursuit; it has also been a
profound personal journey. I am grateful to my advisors for the opportunities they
provided, which allowed me to grow as a scientist, as well as to my fellow lab mates
and collaborators for their invaluable intellectual support. I am deeply indebted for
the emotional support I have received from my dear family members and the strong
support system I am fortunate to have in LA, which gave me the courage and strength
to navigate the highs and lows of the PhD process. Thanks to your love and support,
I am proud to share this accomplishment with all of you.
ii

ii
vi
vii
x
xii
Table of Contents
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Curriculum Vitae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1 3D Hybrid Organic–Inorganic Perovskites . . . . . . . . . . . . . . . . 2
1.1.1 Crystal Structure of 3D Perovskites . . . . . . . . . . . . . . . 2
1.1.2 Interest in 3D Hybrid Organic–Inorganic Halide Perovskites for
Photovoltaic Applications . . . . . . . . . . . . . . . . . . . . 3
1.1.3 Beyond Photovoltaics . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Lower-Dimensional Hybrid Metal Halides . . . . . . . . . . . . . . . . 5
1.2.1 Introducing Functional Organic Moieties into the Perovskite
Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.2 Crystal Structure of 2D and 1D Hybrid Halides . . . . . . . . 8
1.3 Thesis Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Chapter 2: Film Deposition Methods of Low-Dimensional Hybrid
Lead Halides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
2.2.1 Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2.2 Substrate Preparation . . . . . . . . . . . . . . . . . . . . . . 13
2.2.3 Structure Determination . . . . . . . . . . . . . . . . . . . . . 14
2.2.4 Photophysical Properties Measurements . . . . . . . . . . . . 14
2.3 Vapor Deposition of 2D Hybrid Lead Halide Films . . . . . . . . . . . 14
iii
12
12

2.3.1 VPD System Setup and Operation . . . . . . . . . . . . . . . 15
2.3.2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . 19
2.4 Spin-Coating of Hybrid Lead Halide Films . . . . . . . . . . . . . . . 24
2.4.1 Precursor Solution . . . . . . . . . . . . . . . . . . . . . . . . 25
2.4.2 Spin-Coating and Annealing . . . . . . . . . . . . . . . . . . . 25
2.4.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . 26
2.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.6 Supplemental Information . . . . . . . . . . . . . . . . . . . . . . . . 28
Chapter 3: Structural Diversity in 2-(2-Aminoethyl)pyridine-Based
Hybrids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
3.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.2.1 Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.2.2 Structure Determination . . . . . . . . . . . . . . . . . . . . . 33
3.2.3 DFT Calculations . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.2.4 Photophysical Properties Measurements . . . . . . . . . . . . 34
3.2.5 Dielectric Properties Measurements . . . . . . . . . . . . . . . 34
3.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.5 Supplemental Information . . . . . . . . . . . . . . . . . . . . . . . . 48
in 1-Naphthylammonium and 1-Methylquinolinium-Based 1D
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
53
4.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.2.1 Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.2.2 Structure Determination . . . . . . . . . . . . . . . . . . . . . 56
4.2.3 DFT Calculations . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.2.4 Photophysical Properties Measurements . . . . . . . . . . . . 59
4.2.5 Dielectric Properties Measurements . . . . . . . . . . . . . . . 60
4.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 60
4.3.1 Structural Characterization . . . . . . . . . . . . . . . . . . . 60
4.3.2 Optoelectronic Properties . . . . . . . . . . . . . . . . . . . . 73
4.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4.5 Supplemental Information . . . . . . . . . . . . . . . . . . . . . . . . 84
4.5.1 Material Characterization . . . . . . . . . . . . . . . . . . . . 84
4.5.2 Solid State NMR . . . . . . . . . . . . . . . . . . . . . . . . . 89
iv
29
Lead Iodide
53
Chapter 4: Probing Donor–Acceptor Charge Transfer Properties
Hybrid Lead Halides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

for the PPMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
5.2 Multipurpose Electrical Probe . . . . . . . . . . . . . . . . . . . . . . 92
5.2.1 Design of Multipurpose Electrical Probe . . . . . . . . . . . . 92
5.2.2 Sample Stage Designs for Dielectric Measurements . . . . . . . 93
5.2.3 Design of Chip for Four-Point Hall Measurements . . . . . . . 98
5.3 Optical Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
0
5.3.1 Design of Optical Probe for Emission and Lifetime Measurements101
5.3.2 Photophysical Measurements with First Probe Design . . . . . 104
5.3.3 Photophysical Measurements with Current Probe Design . . . 106
5.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
Chapter 6: Polarizable Anionic Sublattices Can Screen Molecular
Non-Centrosymmetric Inorganic–Organic Hybrid . . . . .
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
6.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
6.2.1 Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
6.2.2 Structure Determination . . . . . . . . . . . . . . . . . . . . . 115
6.2.3 DFT Calculations . . . . . . . . . . . . . . . . . . . . . . . . . 116
6.2.4 Photophysical Properties Measurements . . . . . . . . . . . . 116
6.2.5 Dielectric Properties Measurements . . . . . . . . . . . . . . . 117
6.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 118
6.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
6.5 Supplemental Information . . . . . . . . . . . . . . . . . . . . . . . . 126
6.5.1 Expanded Photophysics and Optical Measurements . . . . . . 126
6.5.2 Material Characterization . . . . . . . . . . . . . . . . . . . . 128
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
v
Chapter 5: Multipurpose Electrical Probe and Optical Probe Designs
Dipoles in
113
113
100

List of Tables
3.1 Comparison of structural details between (PEA)2PbI4, (2-AEP)2PbI4,
and (2-AEPH)PbI4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2 Effective and reduced masses of charge carriers using SOC-DFT . . . 44
3.3 Crystal data and structure refinement for (2-AEP)2PbI4 . . . . . . . 48
3.4 Fractional atomic coordinates and equivalent isotropic displacement
parameters for (2-AEP)2PbI4 . . . . . . . . . . . . . . . . . . . . . . 49
3.5 Hydrogen atom coordinates and isotropic displacement parameters for
(2-AEP)2PbI4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.1 Crystallographic data for single crystal structure determination of (1-
MQ)PbI3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.2 Crystallographic data for single crystal structure determination of (1-
MQ)(1-NA)Pb2I6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
4.3 Information on the distance between methyl hydrogen and ammonium
hydrogen atoms in 1-NA and 1-MQ in the optimized crystal structure 89
4.4 Experimental solid-state NMR parameters . . . . . . . . . . . . . . . 90
6.1 Integrated intensities of (MDA)Pb2Br6 emission spectra . . . . . . . . 127
6.2 Rietveld refinement results for (MDA)Pb2I6 and (MDA)Pb2Br6 . . . 128
6.3 Crystallographic data for (MDA)Pb2Br6 . . . . . . . . . . . . . . . . 129
vi

List of Figures
1.1 3D ABX3 perovskite structure . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Best research-cell efficiency chart . . . . . . . . . . . . . . . . . . . . 3
1.3 Tolerance factors of halide perovskites . . . . . . . . . . . . . . . . . 6
1.4 Band structure and DOS of MAPbI3 . . . . . . . . . . . . . . . . . . 6
1.5 Main objectives of thesis . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.6 Structural variation in hybrid metal halides . . . . . . . . . . . . . . 9
2.1 VPD system full setup . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2 (PEA)2PbI4 structure and (PEA)(2-AEP)PbI4 model . . . . . . . . . 19
2.3 VPD system chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.4 XRD, absorbance, and emission of vapor deposited (PEA)2PbI4 film . 22
2.5 XRD of vapor deposited (4-AEP)2PbI4 film . . . . . . . . . . . . . . 23
2.6 Spin-coating technique . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.7 XRD, absorbance, and emission of spin-coated (PEA)2PbI4 film . . . 26
3.1 Crystal structures of (PEA)2PbI4, (2-AEPH)PbI4, and (2-AEP)2PbI4 30
3.2 Rietveld refinement of (2-AEP)2PbI4 powder . . . . . . . . . . . . . . 35
3.3 Pawley fits of spin-coated films annealed at 50 and 160 °C . . . . . . 38
3.4 Ex situ XRD of spin-coated films annealed at varying temperatures . 39
3.5 Ex situ absorbance and emission of spin-coated films annealed at varying temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.6 Fluorescence microscopy of spin-coated films from a 0.5 M (2-
AEP)2PbI4 DMF solution, annealed at various temperatures . . . . . 42
3.7 Band structures and DOSs of (PEA)2PbI4, (2-AEP)2PbI4, and (2-
AEPH)PbI4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.8 Dielectric measurements of (2-AEP)2PbI4 pellets . . . . . . . . . . . . 45
3.9 Dielectric measurements of (2-AEPH)PbI4 pellets . . . . . . . . . . . 46
3.10 Dielectric measurements of (PEA)2PbI4 pellets . . . . . . . . . . . . . 46
3.11 Pawley fit of spin-coated film annealed at 100 °C . . . . . . . . . . . 50
3.12 Ex situ XRD of spin-coated films from a 0.1 M (2-AEP)2PbI4 DMF
solution annealed at varying temperatures . . . . . . . . . . . . . . . 51
vii

3.13 TGA and DSC of (2-AEP)2PbI4 powder . . . . . . . . . . . . . . . . 52
4.1 Crystal structures of (1-NA)PbI3, (1-MQ)(1-NA)Pb2I6, and (1-MQ)PbI3 61
4.2 1H spin echo solid-state NMR and 1H{14N} D-HMQC spectra . . . . 63
4.3 1H{14N} D-HMQC spectra . . . . . . . . . . . . . . . . . . . . . . . . 64
4.4 207Pb spin echo solid-state NMR spectra . . . . . . . . . . . . . . . . 65
4.5 1H{207Pb} TONE D-HMQC solid-state NMR spectra . . . . . . . . . 66
4.6 1H→13C CP solid-state NMR spectra . . . . . . . . . . . . . . . . . . 68
4.7 2H spin echo solid-state NMR and 1H{2H} DE-RESPDOR spectra . . 69
4.8 1H{2H} DE-RESPDOR dephasing curves and molecular distance visualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.9 RMSD curve as a function of 1H-2H distances . . . . . . . . . . . . . 70
4.10 Crystal structures with projected dipole vectors of (1-NA)PbI3, (1-
MQ)(1-NA)Pb2I6, and (1-MQ)PbI3 . . . . . . . . . . . . . . . . . . . 71
4.11 Band structures and DOSs of (1-NA)PbI3, (1-MQ)(1-NA)Pb2I6, and
(1-MQ)PbI3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.12 Charge density projections of (1-NA)PbI3, (1-MQ)(1-NA)Pb2I6, and
(1-MQ)PbI3 at the VBM and CBM . . . . . . . . . . . . . . . . . . . 73
4.13 Pawley fits of (1-NA)PbI3, (1-MQ)PbI3, and (1-MQ)(1-NA)Pb2I6 powder XRD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
4.14 XRD of (1-NA)PbI3, (1-MQ)(1-NA)Pb2I6, and (1-MQ)PbI3 films . . . 75
4.15 Absorption of (1-NA)PbI3 and (1-MQ)PbI3 films . . . . . . . . . . . . 76
4.16 Temperature-dependent emission of (1-NA)PbI3 and (1-MQ)PbI3 films 77
4.17 Temperature-dependent powder emission of (1-NA)PbI3, (1-MQ)(1-
NA)Pb2I6, and (1-MQ)PbI3 . . . . . . . . . . . . . . . . . . . . . . . 78
4.18 Integrated emission intensities of (1-NA)PbI3, (1-MQ)(1-NA)Pb2I6,
and (1-MQ)PbI3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4.19 77 K emission and excitation spectra of (1-NA)I and (1-MQ)I in 2-
methylTHF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
4.20 Dielectric measurements of (1-NA)PbI3 and (1-MQ)PbI3 pellets, collected from 2 to 300 K . . . . . . . . . . . . . . . . . . . . . . . . . . 81
4.21 Dielectric measurements of (1-NA)PbI3 and (1-MQ)PbI3 pellets, collected from 300 to 2 K . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5.1 PPMS electrical probe . . . . . . . . . . . . . . . . . . . . . . . . . . 93
5.2 Dielectric setup, version 1 . . . . . . . . . . . . . . . . . . . . . . . . 94
5.3 Dielectric setup, version 2 . . . . . . . . . . . . . . . . . . . . . . . . 95
5.4 Dielectric measurements using the second sample stage setup . . . . . 96
5.5 Dielectric setup, version 3 . . . . . . . . . . . . . . . . . . . . . . . . 96
5.6 Dielectric measurements using the third sample stage setup . . . . . . 97
5.7 Hall effect setup, version 1 . . . . . . . . . . . . . . . . . . . . . . . . 99
5.8 Hall effect setup, version 2 . . . . . . . . . . . . . . . . . . . . . . . . 100
viii

5.9 PPMS optical probe schematic . . . . . . . . . . . . . . . . . . . . . . 102
5.10 PPMS optical probe . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
5.11 Temperature-dependent emission of MAC–Au–Cz film . . . . . . . . . 104
5.12 Temperature-dependent emission of fac-Ir(ppy)3 film . . . . . . . . . 105
5.13 Temperature-dependent lifetime of MAC–Au–Cz film . . . . . . . . . 105
5.14 Temperature-dependent lifetime of fac-Ir(ppy)3 film . . . . . . . . . . 107
5.15 Magnetic field-dependent lifetime of fac-Ir(ppy)3 film . . . . . . . . . 108
5.16 Magnetic field-dependent emission of fac-Ir(ppy)3 film at 3 K . . . . . 109
5.17 Temperature-dependent emission of (1-NA)PbI3 film . . . . . . . . . 110
5.18 Temperature-dependent emission of (2-AEP)2PbI4 film and detector
sensitivity comparison . . . . . . . . . . . . . . . . . . . . . . . . . . 111
6.1 Rietveld refinements of (MDA)Pb2I6 and (MDA)Pb2Br6 . . . . . . . 119
6.2 DOS and band diagrams for (MDA)Pb2I6 and (MDA)Pb2Br6 . . . . . 120
6.3 Kubelka–Munk transform of (MDA)Pb2I6 and (MDA)Pb2Br6 . . . . 120
6.4 Temperature-dependent emission of (MDA)Pb2I6 and (MDA)Pb2Br6 122
6.5 SHG of (MDA)Pb2I6 and (MDA)Pb2Br6 . . . . . . . . . . . . . . . . 123
6.6 Dielectric measurements of (MDA)Pb2I6 and (MDA)Pb2Br6 . . . . . 124
6.7 Kubelka-Munk transforms of MDA and Pb salts . . . . . . . . . . . . 126
ix

Curriculum Vitae
Education
2019-2024 Ph.D., Chemistry
University of Southern California, Los Angeles, CA
2015-2019 B.S., Chemistry
Rochester Institute Technology, Rochester, NY
Publications
1. Goh, Y. G.; Cassingham, M. A.; Zavalij, P. Y.; Djurovich, P. I.; Thompson,
M. E.; Melot, B. C. Structural Diversity in 2-Aminoethylpyridine-based Lead
Iodide Hybrids. Inorg. Chem. 2024, 63 (22), 10160–10166.
2. Cassingham, M. A.*; Lamahewage, S. N. S.*; Goh, Y. G.*; Squires, A. G.;
Ponnekanti, A.; Karabadjakyan, S.; Wapner, A.; Djurovich, P. I.; Scanlon, D.
O.; Rossini, A. J.; Thompson, M. E.; Melot, B. C. Ordered Cationic Mixing in
Novel 1D Organic-Inorganic Hybrid. To be submitted. (*co-first authors)
3. Cassingham, M. A.; Goh, Y. G.; McClure, E. T.; Hodgkins, T. L.; Zhang,
W.; Liang, M.; Dawlaty, J. M.; Djurovich, P. I.; Haiges, R.; Halasyamani, P.
S.; Savory, C. N.; Thompson, M. E.; Melot, B. C. Polarizable Anionic Sublattices Can Screen Molecular Dipoles in Non-centrosymmetric Inorganic-Organic
Hybrids. ACS Appl. Mater. Interfaces 2023, 15 (14), 18006-18011.
4. Chen H.; Zhao B.; Mutch J.; Jung G. Y.; Ren G.; Shabani S.; Seewald E.; Niu
S.; Wu J.; Wang N.; Surendran M.; Singh S.; Luo J.; Ohtomo S.; Goh Y. G..;
x

Chakoumakos B. C.; Teat S. J.; Melot B.; Wang H.; Pasupathy A. N.; Mishra
R.; Chu J.; Ravichandran J. Charge Density Wave Order and Electronic Phase
Transitions in a Dilute d-Band Semiconductor. Adv. Mater. 2023.
5. Goh, Y. G.; Lauro, S.; Barber, S. T.; Williams, S. A.; Trabold, T. A. Cleaner
Production of Flexographic Ink by Substituting Carbon Black with Biochar. J.
Clean. Prod. 2021, 324, 129262.
xi

Abstract
This collection of works presents the knowledge we have gained on the deposition and
optoelectronic properties of low-dimensional hybrid lead halides. Our studies aimed to
understand how integrating larger organic molecules with desired functionalities can
alter the optoelectronic properties of the resulting hybrid systems. A key focus was
on fabricating phase-pure hybrid films, a crucial factor for determining the feasibility
of new materials in optoelectronic devices.
Chapter 2 details the film deposition methods explored in fabricating hybrid
lead halide films. In Chapter 3, we introduce a new hybrid containing 2-(2-
aminoethyl)pyridine, forming a 2D hybrid with the composition (2-AEP)2PbI4. This
chapter demonstrates the structural diversity of 2-(2-aminoethyl)pyridine-based lead
iodide hybrids in solution-processed films, emphasizing the importance of solutionprocessing conditions in obtaining single-phase films of hybrids containing dibasic
organic species. Chapter 4 builds on the knowledge gained from Chapter 3, leading to
successful synthesis of a novel ordered mixed-cation 1D hybrid, (1-MQ)(1-NA)Pb2I6.
This novel hybrid and its end members are characterized for their photophysical and
dielectric properties to better understand their optoelectronic properties.
To conduct dielectric and photophysical measurements on the hybrid materials,
we custom-built a multipurpose electrical probe and an optical probe for the Physical Properties Measurement System (PPMS). Chapter 5 details the work done in
xii

designing and testing these probes, expanding the types of measurements that can be
conducted with the PPMS. Chapter 6 presents early efforts in combining photophysical and dielectric measurements to understand the polar nature of (MDA)Pb2I6 and
(MDA)Pb2Br6. This approach demonstrated its utility in characterizing new hybrid
materials and has been adopted in the other chapters of this thesis.
This thesis expands the knowledge on the design, processing, and characterization
of low-dimensional hybrid lead halides, and aims to aid in future design rules for these
materials in optoelectronic devices.
xiii

Chapter 1
Introduction
This thesis explores the integration of the desired physical properties of organic
molecules and inorganic extended solids to enhance the optoelectronic properties of
the resulting hybrid system. Drawing inspiration from the success of 3D hybrid
halide perovskites in photovoltaic (PV) technology, this work seeks to discover the
next generation of materials for optoelectronic applications. Specifically, it focuses
on lower-dimensional materials derived from 3D hybrid halide perovskites, referred
to as 2D hybrid metal halides and 1D hybrid metal halides.
These materials are attractive as it presents the opportunity to independently
tune the frontier orbitals of organic molecules to the band edge of periodic inorganic
lattices. This enables the retention of the desirable optoelectronic properties of 3D
hybrid halide perovskites, which have been proven effective as solar absorbers, while
leveraging the optical tunability of organic molecules to enhance the overall properties
of the hybrid system.
A significant aspect of this research is the film deposition of these lowerdimensional hybrid materials. The ease of fabrication is a crucial factor in determining the feasibility of new materials for optoelectronic devices, as demonstrated
by the success of 3D hybrid halide perovskites. Film deposition not only showcases
the practicality of these materials but also allows for a more comprehensive study of
their optical properties, which is a key focus of this thesis.
This introductory chapter provides a historical overview of 3D halide perovskites
and outlines the motivation for studying lower-dimensional hybrid metal halides. It
1

1.1. 3D Hybrid Organic–Inorganic Perovskites
also briefly discusses the crystal structure of these hybrid metal halides, setting the
stage for the detailed investigations presented in this thesis.
1.1 3D Hybrid Organic–Inorganic Perovskites
1.1.1 Crystal Structure of 3D Perovskites
Figure 1.1: 3D ABX3 perovskite structure. The structure comprises of cornersharing BX6 octahedra, with A cations filling the cuboctahedral spaces.
The perovskite structure is derived from the perovskite mineral, CaTiO3, that
was first discovered by Gustav Rose in 1839. 1 Perovskite describes a compound with
the general formula of ABX3, where A and B are cations, and X is an anion. Structurally, it is composed of corner-sharing BX6 octahedra, with A cations sitting in the
cuboctahedral sites, as depicted in Figure 1.1. This structure can only accommodate
certain combinations of ions, based on their relative sizes. This is described by the
Goldschmidt tolerance factor, t, given in terms of the ionic radii, rA, rB, and rX:
2
t =
rA + rX
√
2(rB + rX)
2

1.1. 3D Hybrid Organic–Inorganic Perovskites
The optimal bounds for t where a 3D perovskite structure is favored are within the
range 0.825 < t < 1.059.
3 Another criterion that needs to be met for the perovskite
structure is charge balance. As A and B are cations and X is an anion, the sum of
valences of A and B has to be three times that of X. Specifically for halide perovskites,
which were first reported in 1893, 4
it is most common to have the A and B cations
to be monovalent and divalent, respectively.
1.1.2 Interest in 3D Hybrid Organic–Inorganic Halide Perovskites for Photovoltaic Applications
Figure 1.2: Best research-cell efficiency chart. 5
The first hybrid halide perovskites, MAPbX3 (MA = CH3NH3, X = Cl, Br, I)
and MASnBrxI3−x (x = 0–3) were reported in 1978 by Dieter Weber. 6,7 This class
of material was further characterized for its solid-state chemistry and physics over
3

1.1. 3D Hybrid Organic–Inorganic Perovskites
the course of a decade. 8–10 It was not until 2009 when the potential for halide perovskites as a solar absorber was demonstrated by Miyasaka’s group. Their publication
introduced MAPbI3 as an alternative sensitizer in a dye-sensitized solar cell configuration, achieving a power conversion efficiency (PCE) of 3.8%. 11 Research interest
on halide perovskites gained significant momentum in 2012 with the publication of
three coincident reports on all-solid-state perovskite solar cells (PSCs), which demonstrated PCEs of 10–12% and vastly improved stability. 12–14 The subsequent explosion
of research efforts have led to a current certified PCE record of 29.1% for perovskite
tandem cells, all within a span of twenty years. 5
In comparison, PSCs have achieved
PCEs on par with Si-based solar cells in a third of the time it took for Si-based cells
to reach similar efficiency levels, as shown in Figure 1.2. 5
1.1.3 Beyond Photovoltaics
The shot to stardom of halide perovskites in PV technology can be attributed to a
confluence of several ideal semiconductor properties within a single material, including
direct and tunable bandgaps, 15,16 strong light absorption coefficients, 17 high charge
carrier mobilities,18 high defect tolerance, 19,20 long carrier lifetimes and diffusion
lengths.21 In addition, halide perovskites are easy to fabricate via solution processing
or other low-cost fabrication methods. 22 This unique combination of superior optoelectronic properties and ease of fabrication allows for the low-cost production of high
quality optoelectronic devices.
Early research in hybrid halide perovskites explored their potential applications
in thin film transistors 23–25 and light-emitting diodes (LEDs). 26,27 The recent success
of hybrid halide perovskites as PSCs have since rekindled research interest in optoelectronic applications beyond PV technology, such as LEDs, 28 photodetectors, 29 and
4

1.2. Lower-Dimensional Hybrid Metal Halides
lasers.30 In order to discover the full potential of hybrid halide perovskites as optoelectronic devices, a fundamental understanding of how photogenerated charges are
affected by the structure and composition of the material must be established.
1.2 Lower-Dimensional Hybrid Metal Halides
1.2.1 Introducing Functional Organic Moieties into the Perovskite Structure
To commercialize a new PV technology, three main aspects must be considered: efficiency, cost and lifetime (stability). 31 While PSCs offer comparable efficiencies and
low manufacturing cost, their maximum reported lifetime is around one year, 32 significantly shorter than the 25-year lifetime of commercial Si-based PV modules. This
short lifetime is the primary barrier to PSC commercialization. 33–35 MAPbI3 and its
analogous hybrid halide perovskites degrade readily when exposed to moisture, heat,
and light—conditions common for deployed PV modules. The degradation pathways
of these hybrid halide perovskites are attributed to the volatility of MA, ion migration, and halide segregation, processes often accelerated in the presence of moisture,
heat, and light.36,37 While the stability of PSCs have come a long way with device
structure engineering, it has become more pressing from the viewpoint of materials
discovery to find a solution to the inherent instability of the 3D halide perovskites.
Using t = 1 and the maximum values for rB and rX, (i.e., Shannon ionic radii
rPb = 1.19 Å and rI = 2.20 Å),38 the limit of rA for ABX3 perovskites, where B
is a divalent metal and X is a halogen, is approximately 2.6 Å.
39 Due to the size
limitation, MA and formamidinium (FA) are among the few cations that can be
successfully incorporated into the 3D halide perovskite structure. 40 The tolerance
factors for the most popular lead or tin halide perovskites are listed in Figure 1.3. 41
5

1.2. Lower-Dimensional Hybrid Metal Halides
Figure 1.3: Tolerance factors (t) of a series of halide perovskites. 41
Typically, organic cations in these structures act only as structure-directing units
and do not contribute to the frontier electronic structure of the material. 42 This can
be illustrated by the projected density of states (DOS) and band structure of the
prototypical 3D halide perovskite, MAPbI3, shown in Figure 1.4.43 The valence band
maximum (VBM) states primarily comprise I 5p states, while the conduction band
minimum (CBM) states are mainly of Pb 6s character. It is evident that MA does
not contribute to the band edge states of the hybrid perovskite.
Figure 1.4: Left: crystal structure of MAPbI3. Right: band structures of cubic
PbI−
3 1 (green dashed curve) and MAPbI3 (solid black curve), along with the corresponding projected DOS. 43
While introducing larger, more hydrophobic cations can enhance device stability,
it comes at the cost of reduced pathways for charge-carrier transport within the
6

1.2. Lower-Dimensional Hybrid Metal Halides
material, significantly decreasing the PCE of PSCs. 44–47 This is expected, as the
3D connectivity of the inorganic lattices must be reduced to accommodate larger
molecules.
On the flip side, lower-dimensional hybrid metal halides offer the potential to
independently align the frontier molecular orbitals of larger organic molecules to the
band edge of periodic inorganic lattices. 48 By carefully tailoring the HOMO–LUMO
energies of the organics, as well as introducing functional organic molecules within
the hybrid structure, we can further expand the structure–property flexibility of this
class of materials.
Figure 1.5: Three main objectives in exploring how the incorporation of different
organic moieties impacts the structure and property of hybrid lead halide materials.
This collection of works aims to expand the library of 2D and 1D hybrid metal
halide systems with three main objectives in mind, as outlined in Figure 1.5. The first
objective is to incorporate optoelectronically active organic molecules by adjusting the
HOMO—LUMO energies of chromophores. This targets materials that are type IIa
7

1.2. Lower-Dimensional Hybrid Metal Halides
and IIb, where the frontier orbitals of the organic molecules inject charges into the
band edge of the inorganic lattice. The second objective seeks to introduce organic
molecules with strong dipole moments to incorporate local electric fields into the
hybrid structure. This will allow us to study the effects on charge separation and
collection within the hybrid. The third objective builds on the foundation of the
first objective by exploiting the structural similarities of organic molecules to create
hybrids incorporating more than one organic chromophore into the inorganic lattice.
These hybrids will explore the behavior of multiple organic moieties in the excited
state.
Through the knowledge gained from these studies, we aim to better inform the
materials design of hybrids in which the organic moiety contributes to the overall
optoelectronic property of the hybrid.
1.2.2 Crystal Structure of 2D and 1D Hybrid Halides
The dimensionality of hybrid metal halides refers to the connectivity of the inorganic
metal halide octahedra. In 2D hybrid metal halides, cleaving the 3D halide perovskite
along a crystallographic plane forms 2D inorganic sheets. This cleaving can occur
along the 〈100〉-, 〈110〉-, and 〈111〉-planes of the 3D structure, resulting in 〈100〉-,
〈110〉-, and 〈111〉-oriented 2D hybrid metal halides. For 1D hybrid metal halides,
the dimensionality is further reduced, resulting in 1D inorganic octahedral chains
surrounded by organic cations. The octahedra can be connected through corners,
edges, or faces (Figure 1.6).
While the size restrictions for the organic cations in lower-dimensional hybrid
metal halides are relaxed, there are other important features to consider for the successful design of a targeted perovskite-derived structure. The charge balance criterion
still holds, where the organic cations need to balance the overall negative charge of
8

1.3. Thesis Overview
the inorganic octahedra. Additionally, the organic cation must contain a terminal
functional group that can interact with the anionic inorganic lattice without the rest
of the molecule interfering with the components B and X. Most known layered 2D
hybrid metal halides feature mono- or diammonium cations, yielding a general formula of (RNH3)2BX4 or (RNH3)BX4. In 1D hybrid metal halides, while presence
of hydrogen bonding is not as critical, the requirement for charge balance remains
essential.
Figure 1.6: Structural variation in hybrid metal halides. Top: schematic structures
of (a) 3D, (b) 2D, and (b) 1D hybrid metal halides. Bottom: different connectivities
of the octahedra, (d) corner-sharing, (e) edge-sharing, and (f) face-sharing. 49
1.3 Thesis Overview
This thesis presents the knowledge gained on the vapor and solution processing of
hybrid lead halide films, as well as their optical and dielectric properties.
9

1.3. Thesis Overview
Chapter 2 details the two deposition techniques explored—vapor phase deposition
and spin-coating—for fabricating hybrid lead iodide films. The setup and working
principle of the lab-built vapor phase deposition system are described. The advantages
and disadvantages of vapor phase deposition are discussed, along with the rationale
for proceeding with spin-coating for subsequent film depositions.
In Chapter 3, the incorporation of 2-(2-aminoethyl)pyridine (2-AEP) into the
well-studied (PEA)2PbI4 phase is explored, based on the hypothesis that organics
with similar molecular shapes will facilitate the formation of alternating cations in
the interlayer space (ACI) phase. Although an ACI phase was not synthesized, the
structural diversity of 2-AEP-based lead iodide hybrids is investigated. This work also
highlights the importance of optimizing solution processing conditions in achieving
phase pure films.
Building on the knowledge gained from Chapter 3, Chapter 4 discusses the synthesis and structural determination of a 1D mixed-cation lead iodide hybrid, where the
cations are 1-naphthylammonium and 1-methylquinolinium. The optical and dielectric properties of the 1D mixed-cation hybrid are compared with those of its end
member hybrids.
Chapter 5 details the design of two probes for different measurement options in
the Physical Properties Measurement System (PPMS). The design of a multifunction
probe for electrical measurements is presented, along with various sample stages customized for different applications. Additionally, the design of an optical probe made
to collect temperature–field dependent emission and lifetime in the PPMS is discussed. These probes are essential for the characterization of the hybrid lead halides
presented throughout this thesis.
Chapter 6 briefly discusses hybrid lead halides containing 4,4’-methylenedianiline
(MDA), initially targeted to introduce polar functionality into the hybrid system.
10

1.3. Thesis Overview
This chapter highlights the dielectric measurements performed to rationalize the second harmonic generation (SHG) observed in (MDA)Pb2I6 and (MDA)Pb2Br6, contributing to the work done primarily by Dr. Megan Cassingham.
11

Chapter 2
Film Deposition Methods of Low-Dimensional
Hybrid Lead Halides
2.1 Introduction
This chapter describes the deposition techniques used to fabricate hybrid lead halide
films in this dissertation, namely vapor phase deposition (VPD) and spin-coating.
The VPD system, built by Dr. Francisco Navarro, was recommissioned and modified
for the deposition of hybrid lead halide films. The setup and general operation of
the VPD system are discussed, along with our results on depositing a 2D hybrid
lead halide, (PEA)2PbI4, using this system. Due to the thermal stability issues of
other organic cations we were interested in integrating into the organic bilayer of
(PEA)2PbI4, we transitioned to spin-coating methods.
We discuss the benefits of using spin-coating to deposit hybrid lead halide films,
and detail the general procedure for this deposition method. A (PEA)2PbI4 film was
successfully spin-coated and is compared to the vapor-deposited film.
2.2 Experimental
2.2.1 Synthesis
1.0 g portion (8.2 mmol) of 4-(2-aminoethyl)pyridine (4-AEP, >97%, TCI) was added
to 20 mL of ethanol (200 proof, Koptec) in a round-bottom flask. The solution
was bubbled with N2 for 30 min and the head space was flushed out with N2 for
12

2.2. Experimental
10 min to minimize air exposure. While cooling the ethanol solution in an ice
bath, 1.1 mL (8.2 mmol) of hydroiodic acid (HI, 57 wt.% in H2O, stabilized, SigmaAldrich) was added dropwise. After the mixture was stirred under N2 for an hour,
the solvent was removed using a rotary evaporator at 40 °C. The resulting salt, 4-
(2-ammonioethyl)pyridine iodide (4-AEP)I was collected via vacuum filtration and
rinsed with diethyl ether (≥99%, VWR). The solids were then dried under vacuum overnight (1.112 g, 54% yield). 2-(2-ammonioethyl)pyridine iodide (2-AEP)I
was prepared following the same procedure using 1.0 g portion (8.2 mmol) of 2-(2-
aminoethyl)pyridine (2-AEP, 95%, Acros Organics).
2.2.2 Substrate Preparation
1 mm thick plain microscope slides (Fisherbrand) were cut into 20×20 mm squares to
be used as substrates for VPD. The glass substrates were arranged on a substrate rack
and submerged into solvent-specific beakers filled with different solvents for cleaning.
The cleaning procedure is as follows:
1. Sonicate substrates in a beaker filled with a 1:100 dilution of TERGITOLTM
(Sigma-Aldrich, Type NP-10) in DI water for 5 min.
2. Dip substrates into a beaker filled with DI water to rinse off any excess soap
solution.
3. Sonicate substrates in a beaker filled with DI water for 5 min, and repeat twice
more for a total of three times.
4. Sonicate substrates in a beaker filled with acetone (≥99.5%, VWR) for 5 min.
Repeat once more for a total of two times.
13

2.3. Vapor Deposition of 2D Hybrid Lead Halide Films
5. Submerge substrates in a beaker filled with heated isopropyl alcohol (VWR) on
a hot plate for 5 min. Repeat once more for a total of two times.
6. Dry the substrates with pressurized nitrogen gas (N2).
7. Place the substrates in a UVOCS Model T10X10/OES UV ozone cleaner for
10 min.
2.2.3 Structure Determination
The synthesis of the (4-AEP)I and (2-AEP)I salts was confirmed by 1H NMR spectroscopy (Section 2.6). Ex situ XRD characterization of films and powder was carried
out on a Bruker D8 Advance powder diffractometer equipped with a Cu–Kα source
and LynxEye XE—T detector.
2.2.4 Photophysical Properties Measurements
Ex situ UV–vis spectra of films were taken on an Agilent 8453 UV–visible spectrophotometer. Ex situ steady-state emission spectra of films were recorded on a Photon
Technology International QuantaMaster spectrofluorometer.
2.3 Vapor Deposition of 2D Hybrid Lead Halide
Films
One of the main advantages of vapor deposition as a film fabrication technique for
hybrid lead halide materials, compared to the widely adopted spin-coating technique,
is the absence of a solvent. Solvent processing techniques often lead to the formation
of solution-based intermediates instead of the desired phase of the hybrid lead halide
14

2.3. Vapor Deposition of 2D Hybrid Lead Halide Films
material.50,51 Vapor deposition techniques circumvent these issues associated with
solution processing methods.
Since its inception from 1995, 52 Organic Vapor Phase Deposition (OVPD) has
proven to be a versatile, reliable and efficient method for depositing organic materials
in the fabrication of organic light emitting devices (OLEDs), 53 organic photovoltaics
(OPVs),54 and organic thin-film transistors (OTFTs). 55 This success suggests promising potential for the translation of OVPD to the deposition of hybrid organic-inorganic
metal halides.
Compared to vacuum deposition techniques such as vacuum thermal evaporation
(VTE), the OVPD system employs an additional degree of freedom by using carrier
gases to transport source materials to a substrate. This allows for more accurate
control of transport rates and efficient use of materials due to the laminar flow created.
Moreover, the multiple boats in the OVPD system enable the blending of several
precursors during deposition, aligning with our Objective 3 goal of fabricating hybrid
metal halide films with multiple organic moieties.
2.3.1 VPD System Setup and Operation
The OVPD system was first introduced in 1995 to grow thin films of nonlinear optical
organic materials. 52,56 In 1996, a modified version, Low Pressure Organic Vapor Phase
Deposition (LP-OVPD), was developed to grow single heterostructure OLEDs based
on small molecular weight organic thin films. 53 Dr. Francisco Navarro, a former
student in Prof Mark Thompson’s lab, later adopted and improved the OVPD system
to deposit metals and inorganic compounds. 57 This improved system, referred to as
the Vapor Phase Deposition (VPD) system, was recommissioned and modified for the
deposition of hybrid lead halide films, as presented in this chapter.
15

2.3. Vapor Deposition of 2D Hybrid Lead Halide Films
VPD relies on a carrier gas to move sublimed gaseous molecules onto a cooled
substrate by forced convection. The carrier gas can be any inert gas; in the experiments described below, N2 was the carrier gas. Figure 2.1 illustrates the setup used
to deposit hybrid lead halide films.
The VPD system comprises three main components: the chamber, the gas flow
system, and the cooling system. The deposition chamber is made of Pyrex and is
heated by a Carbolite TVS 12/600/2416 CG three zone (1–3) tube furnace, allowing
for a controlled temperature profile during deposition. The chamber is operated at
temperatures below 450 °C, as Pyrex begins to flow around 450–500 °C. Two types of
chambers are used: one with detachable source boat holders for lead compound deposition, and another with fused source boat holders for all other types of deposition,
mainly organic. The detachable holders facilitate easier cleaning after lead deposition. The chamber accommodates four source boat holders, allowing for deposition
of up to four different sources in a single run. Thermocouple probes are placed next
to each source boat to monitor the temperature during deposition.
Each source boat holder is connected to an inlet of carrier gas, with gas flow rates
controlled by MKS mass flow controllers (MFCs) and a multi gas controller (MKS
Type 647C). The multi gas controller also controls the pressure of the chamber,
which is measured by a pressure transducer (Baratron, 10 Torr, Model 626A). The
low vacuum condition (0.1–10 Torr) required for the VPD system is achieved using a
oil-free dry scroll pump (Varian IDP-3). The sources used for deposition are relatively
pure and dry solid compounds that are loaded onto a source boat.
At the opposite end of the Pyrex chamber are a gold-coated quartz crystal
microbalance (INFICON, 6 MHz) and a substrate holder that houses up to two substrates. Both components are cooled by circulating cold water using a water chiller.
This cooling system is simplified from the previous VPD version designed by Dr.
16

2.3. Vapor Deposition of 2D Hybrid Lead Halide Films Figure 2.1: VPD system full setup.
17

2.3. Vapor Deposition of 2D Hybrid Lead Halide Films
Francisco Navarro, 57 as the extremely low temperatures of liquid N2 are not needed
for depositing hybrid lead halide films. The substrate holders have shutters that can
be manually opened or shut, depending on the deposition stage. The quartz crystal microbalance is connected to an INFICON XTC/2 deposition monitor, allowing
real-time monitoring of deposition rate and film thickness.
Prior to starting a deposition, high purity precursors are loaded onto the source
boats and loosely plugged with glass wool. Cleaned substrates are mounted onto the
substrate holder. Once the chamber is properly sealed, the vacuum pump is turned
on and allowed to pull for approximately 30 min. A pressure of around 0.19 Torr
is achieved when there are no leaks in the system. After verifying that there are
no leaks, the water chiller, furnace, thermocouple reader, multi gas controller, and
deposition monitor are turned on and set to the desired parameters.
Once the furnace, substrate, and water temperatures, as well as the chamber
pressure, are stable, a source boat is introduced horizontally into the furnace until
the material starts subliming. With constant pressure and gas flow, the deposition
rate of the material depends on the position of the source boat. Once the desired
deposition rate is achieved, the position of the boat is marked. This step is repeated
for other source boats if performing a co-deposition with more than one precursor.
The source boats are then placed in the marked position, and once a stable deposition
rate is achieved, the shutters are opened to start deposition on the substrates.
The vapors of the precursor material are directed by the carrier gas flow towards
the other end of the chamber, where they condense onto the cooled substrates, forming
a layer of deposited material. Once the desired thickness is achieved, the shutters are
closed. Proper calibration of the crystal monitor can be done by measuring the thickness of the film with an ellipsometer. The tooling factor, TF =
ellipsometer thickness
crystal monitor thickness is
used to calibrate the film thickness reading on the crystal monitor.
18

2.3. Vapor Deposition of 2D Hybrid Lead Halide Films
The VPD system is then cooled to room temperature before it is vented and the
films are retrieved. This cooling step ensures that the deposited films do not oxidize
when exposed to atmospheric conditions and that vapors are not inhaled by the user
while the VPD system is hot.
2.3.2 Results and Discussion
Figure 2.2: (a) Targeted donor–acceptor pairs for synthesizing an alternating cations
in the interlayer space (ACI) phase. (b) Crystal structure of (PEA)2PbI4.
58 (c) A
model of (PEA)(2-AEP)PbI4 phase. Crystal structures depicted using VESTA. 59
19

2.3. Vapor Deposition of 2D Hybrid Lead Halide Films
Phenethylammonium lead iodide [(PEA)2PbI4] is a well-studied 2D hybrid lead
halide material58 that has been intensively researched to improve the moisture stability of perovskite solar cells (PSCs). 60 Figure 2.2b depicts the crystal structure of
(PEA)2PbI4. VPD offers the advantage of fabricating hybrid lead halide films with
multiple organic moieties. In our effort to accomplish Objective 3, we focused on
fabricating (PEA)2PbI4.
Phenethylammonium (PEA) is an attractive organic cation because it serves as an
excellent platform for tuning its HOMO–LUMO energy levels. This tuning is easily
achieved by introducing nitrogen into the phenyl ring, forming various alkylammonium pyridine derivatives, including the organics shown in Figure 2.2a. By using PEA
as a net donor and an alkylammonium pyridine as a net acceptor, we aim to introduce donor–acceptor pairs into the organic bilayer, similar to the (PEA)(2-AEP)PbI4
model depicted in Figure 2.2c. This approach integrates charge transfer properties
into 2D hybrids, ultimately enhancing 3D charge transport pathways in a topologically 2D material. The first step in achieving that is to vapor deposit (PEA)2PbI4
using the VPD system.
Vapor deposition of hybrid metal halide films can be done using either a onestep or two-step process. 22 In the one-step process, the metal halide and organic
halide precursor materials are co-deposited. As for the two-step process, the metal
halide precursor is typically deposited first, followed by the deposition of the organic
halide precursor. A post-annealing step is then carried out to ensure complete phase
transformation and to drive off any excess organic halide precursor.
For the deposition of (PEA)2PbI4, we chose to use the one-step processing method.
This method involves simpler steps, and the VPD system is capable of co-depositing
both phenethylammonium iodide [(PEA)I] and lead (II) iodide (PbI2), despite the
significant difference in their sublimation temperatures.
20

2.3. Vapor Deposition of 2D Hybrid Lead Halide Films
Figure 2.3: VPD system chamber setup.
(PEA)I (98%, Sigma-Aldrich) and PbI2 [99.999% (metal basis), Alfa Aesar] were
loaded into separate source boats in the VPD system. The three zones of the furnace,
from the substrates to the source boats, are set to 380 °C, 410 °C, and 430 °C,
respectively. The water chiller was set to a temperature of 2 °C, resulting in a
substrate holder temperature of around 12 °C. The N2 flow rate for the PbI2 boat
was set to 5 sccm, and the flow rate for the (PEA)I boat was set to 10 sccm. For
the other two unused source boats, N2 gas was flowed at a 5 sccm rate and set to
PID mode to enable the multi gas controller to adjust the flows to maintain the set
pressure of 0.7 Torr. These parameters are summarized in Figure 2.3.
To form (PEA)2PbI4, (PEA)I and PbI2 need to be co-deposited in a 2:1 molar
ratio. The following calculations were done to estimate the deposition rate ratios
needed to achieve this 2:1 molar ratio co-deposition criterion. The density, ρ of each
precursor is calculated using the formula:
ρ =
Z · FW
V · NA
21

2.3. Vapor Deposition of 2D Hybrid Lead Halide Films
Where NA is Avogadro’s constant, and the formula units per unit cell (Z), formula
weight (FW), and volume (V) are extracted from published crystallographic information files. Assuming a volumetric deposition rate of 1 Å3/s, the rate is converted to
mol/s using the calculated ρ and FW.
From these calculations, it is estimated that when (PEA)I and PbI2 are deposited
at a rate of 1:1 Å/s, the rate in mol/s is 1:2. Therefore, to achieve a (PEA)I:PbI2
2:1 molar ratio during co-deposition, the deposition rate in Å/s must be 4:1. (PEA)I
is set to a deposition rate of approximately 4 Å/s, with the source boat temperature
around 200 °C. PbI2 is set to a deposition rate of approximately 1 Å/s, with the
source boat temperature around 350 °C.
Both source boats are placed at the marked positions, and the combined deposition
rate detected by the crystal monitor is allowed to stabilize. Once stabilized, the
film deposition is started by opening the shutters of the substrate holder. The film
Figure 2.4: (a) XRD of vapor deposited (PEA)2PbI4 film, Pawley fitted to
(PEA)2PbI4, with Rwp of 6.5%. Inset: vapor deposited (PEA)2PbI4 film. (b)
Absorbance and emission of vapor deposited (PEA)2PbI4 film.
22

2.3. Vapor Deposition of 2D Hybrid Lead Halide Films
deposition is stopped when the crystal monitor reads a thickness of 300 nm. The
films are retrieved once the VPD system is cooled to room temperature.
A Pawley fit of the XRD pattern of the resulting film, presented in Figure 2.4a,
shows the successful fabrication of (PEA)2PbI4 film. The vapor deposited film
exhibits preferred orientation for the (00l) plane, which corresponds to the 2D inorganic sheets of the hybrid. The (PEA)2PbI4 film displays a strong excitonic absorption
feature at 515 nm, and an emission peak at 528 nm, as shown in Figure 2.4b. Straus
and co-workers also observed an excitonic absorption feature of 515 nm in their spincoated (PEA)2PbI4 film, but the emission peak observed was slightly blue-shifted to
520 nm.61 This discrepancy in emission data could be due to different film defects
or morphology imparted by the differing processing techniques. The XRD pattern
and optical data collected for the vapor deposited (PEA)2PbI4 film demonstrate the
successful vapor deposition of (PEA)2PbI4 via VPD using a one-step co-deposition
method.
Figure 2.5: XRD of vapor deposited (4-AEP)2PbI4 film.
23

2.4. Spin-Coating of Hybrid Lead Halide Films
(PEA)I was then replaced with (4-AEP)I in an attempt to deposit (4-AEP)2PbI4
films. Several different (4-AEP)I and PbI2 deposition rates were tested. However, XRD patterns of the deposited film did not indicate any formation of the
(4-AEP)2PbI4 hybrid. Instead, the XRD reflections indicated formation of PbI2,
as shown in Figure 2.5.
To understand this outcome, (4-AEP)I was sublimed at 240 °C in a sublimator,
and the resulting powder was collected and analyzed with 1H NMR spectroscopy.
The 1H NMR spectrum showed that the (4-AEP)I had decomposed. The thermal
stability under vacuum was also checked for a similar derivative, (2-AEP)I, and it
similarly decomposed.
While the results for (PEA)2PbI4 was promising, the inability to vapor deposit
(4-AEP)I and (2-AEP)I due to thermal instability makes VPD of this class of 2D
hybrid lead halide no longer viable. Consequently, we adopted spin-coating as our
film deposition method moving forward.
2.4 Spin-Coating of Hybrid Lead Halide Films
Figure 2.6: General spin-coating technique and annealing step.
One of the simplest methods of preparing halide perovskite and hybrid metal
halide films is via spin-coating. This method was used in the first report of PSCs by
24

2.4. Spin-Coating of Hybrid Lead Halide Films
Kojima and coworkers. 11 The ease of fabrication via solution processing and the high
defect tolerance are key factors driving the astronomical rise of halide perovskites in
the photovoltaic industry. There are three main components to spin-coating: precursor solution, spin-coating, and annealing. A general schematic of the spin-coating
process is illustrated in Figure 2.6.
2.4.1 Precursor Solution
A precursor solution for spin-coating can be prepared using two main methods,
both of which have been employed to make spin-coated films in this thesis. The
first method involves dissolving a stoichiometric ratio of metal halide and organic
halide in a solvent. The other method involves the dissolution of the hybrid metal
halide in a solvent. Typical solvents used for spin-coating include dimethylformamide
(DMF), dimethyl sulfoxide (DMSO), gamma-butyrolactone (GBL), and N-methyl-2-
pyrrolidone (NMP). If the concentration of the precursor solution is high (>0.5 M),
the solution is filtered through a 0.2 µm PTFE filter prior to spin-coating. This
step filters out any large crystallites that may have formed in the solution, ensuring
uniform grain size distribution in the film.
2.4.2 Spin-Coating and Annealing
1 mm thick plain microscope slides (Fisherbrand), cut into 20×20 mm squares are
used as the main substrate for spin-coating. For temperature-dependent measurements where a good heat conductor is required, a round sapphire disk (Esco Optics,
random orientation, 25.4 mm diameter) is used instead. The substrates are cleaned
as described in the experimental section prior to deposition.
The spin-coating rates used for depositing hybrid films in this work typically range
from 1000 to 5000 rpm, lasting up to 60 s. These rates depend on the surface tension
25

2.4. Spin-Coating of Hybrid Lead Halide Films
and viscosity of the precursor solution, as well as the surface energy of the substrate.
Therefore, spin-coating rates are often adjusted depending on the solvent, substrate,
and concentration of the precursor solution to ensure uniform film coverage.
The annealing temperatures and environments during annealing affect the final
phase of the hybrid lead halide film, as discussed in Chapter 3. The annealing temperature and duration depend on the boiling point of the solvent, as this step evaporates
any remaining solvent post-spin-coating. The choice of environment—whether air or
an inert atmosphere—also influences the final phase of the hybrid film, particularly
if the organic cation is sensitive to air or moisture.
2.4.3 Results and Discussion
Figure 2.7: (a) XRD comparison of spin-coated and vapor deposited (PEA)2PbI4
films. Inset: spin-coated (PEA)2PbI4 film excited under UV light and without. (b)
Comparison of absorbance and emission between spin-coated (solid lines) and vapor
deposited (dashed lines) (PEA)2PbI4 films.
A 0.25 M (PEA)2PbI4 precursor solution was made by dissolving a stoichiometric
ratio of (PEA)I and PbI2 in DMF. The solution was spin-coated on a glass substrate
26

2.5. Summary
at 5000 rpm for 40 s and then annealed under N2 flow for 3 min. The XRD pattern
of the resulting film (Figure 2.7a) matched that of the vapor deposited (PEA)2PbI4
film, albeit with a small impurity of PbI2. This impurity could be due to a slight
exposure to ambient conditions during the annealing step.
The spin-coated film exhibits a strong excitonic absorption feature at 516 nm,
and an emission peak at 532 nm, as shown in Figure 2.7. Both features are slightly
red-shifted to the vapor deposited film, possibly due to the different film defects or
morphology resulting from the differing processing methods. The XRD pattern and
optical data demonstrate the utility of spin-coating hybrid lead halide films, which is
adopted for the subsequent film deposition described in the rest of this thesis.
Efforts were made to fabricate an alternating cation in the interlayer space (ACI)
phase by incorporating 4-AEP or 2-AEP into the organic bilayer of (PEA)2PbI4,
but these attempts were unsuccessful. This failure is attributed to the discrepancy
in organic cation packing and hydrogen bonding of the organic cations, which is
discussed further in Chapter 3.
2.5 Summary
We successfully fabricated (PEA)2PbI4 films using both VPD and spin-coating methods. Ultimately, spin-coating was chosen as the film deposition method for our subsequent studies because most other organic cations decompose during vapor deposition,
making the VPD technique impractical for our purposes.
27

2.6. Supplemental Information
2.6 Supplemental Information
1H NMR of 4-(2-ammonioethyl)pyridine iodide (4-AEP)I salt
1H NMR (400 MHz, DMSO-d6) δ 8.52 (m, 2H), 7.72 (s, 3H), 7.30 (m, 2H), 3.11
(dd, J = 8.7, 6.8 Hz, 2H), 2.87 (dd, J = 8.9, 6.6 Hz, 2H).
1H NMR of 2-(2-ammonioethyl)pyridine iodide (2-AEP)I salt
1H NMR (400 MHz, DMSO-d6) δ 8.54 (d, 1H), 7.81 (td, J = 2.0 Hz, 1H), 7.80
(s, 3H), 7.37 (d, J = 7.8 Hz, 1H), 7.33 (dd, J = 7.6, 4.9 Hz, 1H), 3.22 (q, J = 7.1
Hz, 2H), 3.06 (t, J = 7.2 Hz, 2H).
28

Chapter 3
Structural Diversity in
2-(2-Aminoethyl)pyridine-Based Lead Iodide
Hybrids
3.1 Introduction
Many groups have harnessed the tunable electronic structure of organics to adjust
the HOMO–LUMO energy levels of the organic cations, allowing participation of the
organics in charge transport and charge separation in hybrid materials. 63–70 Similarly,
introducing donor–acceptor pairs into the organic bilayer is a promising direction
for integrating charge transfer properties into 2D hybrids. Inducing charge transfer between the donor–acceptor pairs will allow the organic layer to participate in
charge transport/separation, overall improving 3D charge transport pathways in a
topologically 2D material.
Following this logic, phenethylammonium (PEA)+ was chosen as a net donor and
2-(2-ammonioethyl)pyridine (2-AEP)+ as a net acceptor in an attempt to form alternating cations in the interlayer space (ACI) phase. 71 Several alkylammonium pyridine
derivatives have been incorporated to form new lead iodide hybrids, where unprotonated/protonated pyridines form hybrids with the formula of A2PbI4/APbI4.
72–74
Due to (PEA)+ and (2-AEP)+ having similar molecular geometry, we anticipated
structurally compatible packing in the hybrid form, forming an ACI phase. We found
in our initial experiments that we were not able to achieve an ACI phase in the
film owing to phase separation. The well-known structure (PEA)2PbI4 (Figure 3.1a)
29

3.1. Introduction
Figure 3.1: Crystal structures of (a) (PEA)2PbI4,
58 (b) (2-AEPH)PbI4, and (c)
(2-AEP)2PbI4.
62 Different perspectives of the (2-AEP)+ packing in (2-AEP)2PbI4
are shown. Dipole arrows depict the cancellation of dipoles that drives the π–π
interaction between adjacent (2-AEP)+ cations, where the π–π distance is 3.44 Å.
The N–N distance in (2-AEP)+ is 2.76 Å, showing the presence of intramolecular
hydrogen-bonding. Crystal structures depicted using VESTA. 59
forms if the mixed cation film does not undergo annealing. Upon annealing, the
film phase segregates into three separate phases: (PEA)2PbI4 and two unique 2-(2-
aminoethyl)pyridine (2-AEP)-based lead iodide hybrid phases.
30

3.1. Introduction
In this work,75 we report a new 2D hybrid, (2-AEP)2PbI4, which was originally
targeted to determine if a solid solution could be created with (PEA)2PbI4. Closer
inspection of their crystal structures reveals two different types of organic bilayer
packing, preventing the formation of the ACI phase. The face-to-face packing of
the organic bilayer in (2-AEP)2PbI4 can potentially improve through-layer charge
transport.
We also show evidence of the structural diversity of (2-AEP)-based lead iodide
hybrids in solution-processed films. Structural diversity of lead iodide hybrids based
on a similar organic cation, 4-(2-aminoethyl)pyridine (4-AEP) has been reported previously, where the hybrid structure depends on the protonation state of the organic
cation.72 In this report, we show that a low temperature anneal results in the formation of (2-AEP)2PbI4, while a high temperature anneal results in the formation
of (2-AEPH)PbI4, which was first reported by Febriansyah et al.62 This is particularly relevant in understanding the formation and coordination mechanisms of large
organic molecules in 2D hybrids.
31

3.2. Experimental
3.2 Experimental
3.2.1 Synthesis
1.0 g portion (8.2 mmol) of 2-(2-aminoethyl)pyridine (2-AEP, 95%, Acros Organics)
was added to 20 mL of ethanol (200 proof, Koptec) in a round-bottom flask. The
solution was bubbled with N2 for 30 min and the head space was flushed out with
N2 for 10 min to minimize air exposure. While cooling the ethanol solution in an
ice bath, 1.1 mL (8.2 mmol) of hydroiodic acid (HI, 57 wt.% in H2O, stabilized,
Sigma-Aldrich) was added dropwise. After the mixture was stirred under N2 for an
hour, the solvent was removed using a rotary evaporator at 40 °C. The resulting salt,
2-(2-ammonioethyl)pyridine iodide (2-AEP)I was collected via vacuum filtration and
rinsed with diethyl ether (≥99%, VWR). The solids were then dried under vacuum
overnight (1.112 g, 54% yield).
Films reported were made via spin-coating, with the general procedure as follows.
(2-AEP)2PbI4 precursor solution was made by dissolving a stoichiometric ratio of (2-
AEP)I and lead(II) iodide [PbI2, 99.9985% (metal basis), Thermo Fisher Scientific] in
dry N,N-dimethylformamide (DMF, 99.8%, Acros Organics) using standard Schlenk
techniques. The precursor solution was heated at 70 °C under N2 overnight to ensure
that all solids were dissolved. Once the solution was cooled to room temperature,
it was filtered with a 0.2 µm PTFE filter. A 0.5 M (2-AEP)2PbI4 DMF precursor
solution was used to prepare films for ex situ X-ray diffraction (XRD), steady state
emission, and fluorescence microscopy. A 0.1 M (2-AEP)2PbI4 DMF precursor solution was used to fabricate films for UV-vis absorption to ensure the absorbance for
excitonic peaks fell within a measurable range, i.e. less than 2. In a N2 glovebox,
32

3.2. Experimental
70 µL of precursor solution was then spin-coated on a cleaned 20 × 20 mm glass substrate at 3000 rpm for 40 s. The spin-coated film was subsequently annealed in the
N2 glovebox at varying temperatures for 10 min on a hot plate.
Crystals of (2-AEP)2PbI4 were isolated by the slow evaporation of a 0.5 M (2-
AEP)2PbI4 DMF precursor solution, which resulted in red-orange prismatic crystals.
The resulting single crystals (on the order of 0.3 mm × 0.2 mm × 0.1 mm in dimension) were isolated from its mother liquor for crystal structure determination.
3.2.2 Structure Determination
The synthesis of the (2-AEP)I salt was confirmed by 1H NMR spectroscopy (Section
3.5). Single crystal data of the new 2-AEP-based hybrid, (2-AEP)2PbI4 was collected
using a Bruker Smart APEX II diffractometer with a CCD area detector. Ex situ
XRD characterization of films and powder was carried out on a Bruker D8 Advance
powder diffractometer equipped with a Cu–Kα source and LynxEye XE–T detector.
3.2.3 DFT Calculations
DFT calculations were performed on each of the three systems using the Vienna
Ab initio Simulation Package. 76–79 The projector augmented wave method was used
to describe the interaction between core and valence electrons. 80 Density of states
(DOS) and band diagram plots were visualized using sumo. 81 Sumo was also used
to extract the electron and hole effective masses from the band structures. 81 The
functional of Perdew, Burke, and Ernzerhof adapted for solids (PBEsol) 82 was used
for geometrical relaxation. Spin–orbit coupling (PBEsol + SOC) was included for
electronic structure calculations, including the DOS and electronic band structure.
The total energy for all three compounds converged to within 10 µeV per atom using
a plane wave energy cutoff of 600 eV and a Γ-centered k-point mesh of 2 × 2 × 1.
33

3.2. Experimental
The plane wave energy cutoff was not altered for the geometric relaxation step, and
the calculation was considered converged when the forces on each atom fell below
0.01 eV Å−1
.
3.2.4 Photophysical Properties Measurements
Ex situ UV–vis spectra of films were taken on an Agilent 8453 UV–visible spectrophotometer. Ex situ steady-state emission spectra of films were recorded on a
Photon Technology International QuantaMaster spectrofluorometer. Fluorescence
microscopy of films was taken on a Nikon Eclipse ME600D Inspection Microscope,
with a pco.panda 4.2 M microscope camera.
3.2.5 Dielectric Properties Measurements
The temperature-dependent dielectric properties of (PEA)2PbI4, (2-AEP)2PbI4, and
(2-AEPH)PbI4 were measured in a parallel plate geometry. Each material was ground
using an agate mortar and pestle and pressed into 6 mm diameter pellets. (2-
AEP)2PbI4 pellet was vapor deposited with Au, while (PEA)2PbI4 and (2-AEPH)PbI4
pellets were vapor deposited with Al on both faces of the pellets. Powder XRD patterns were taken before and after metal deposition to ensure that the crystal structures
of the pellets were retained. Dielectric measurements were taken from 10 to 300 K at
frequencies of 1, 2, 5, 10, and 20 kHz. The sample temperature was controlled by using
a Quantum Design Physical Property Measurement System (PPMS) Dynacool. The
dielectric measurements were taken using an Andeen-Hagerling 2700A 50 Hz-20 kHz
Ultra-Precision Capacitance Bridge.
34

3.3. Results and Discussion
3.3 Results and Discussion
Figure 3.2: Rietveld refinement of (2-
AEP)2PbI4 powder against solved crystal
structure of (2-AEP)2PbI4, with Rwp of 14.6%.
Modeling of the powder pattern was unsuccessful due to the prismatic shape of the crystals,
which resulted in preferred orientation that
could not be fit using laboratory XRD data.
The (2-AEP)+ cation has previously
been used as a spacer cation in
3D FA0.92MA0.08PbI3 (MA = methylammonium; FA = formamidinium)
perovskite to form 2D/3D perovskite
solar cells.83 Li et al. noted the presence of a secondary phase of 2-AEP
hybrid, depending on the annealing temperature. Using the methods described above, it was found
that the secondary phase is likely
(2-AEP)2PbI4, which crystallizes in
the orthorhombic space group P bcn
(#60), with the full details of the
atomic positions provided in Table
3.3. As shown in Figure 3.1b, the 2D
inorganic sheet consists of cornersharing [PbI6]
4− octahedra. (2-AEP)+ forms organic cation bilayers that alternate
with the inorganic layers. Rietveld refinement of the powder XRD pattern of (2-
AEP)2PbI4 ground-up crystals (Figure 3.2) shows that the bulk product is a pure
single phase material. Attempts to fit the structure to the data were complicated by
the prismatic shape of the crystals which made modeling of the preferred orientation
not possible due to the low resolution of the laboratory XRD data.
A brief comparison of the structural details among (PEA)2PbI4, (2-AEP)2PbI4,
and (2-AEPH)PbI4 hybrids is given in Table 3.1. The lead iodide octahedra in
35

3.3. Results and Discussion
Table 3.1: Comparison of Structural Details between (PEA)2PbI4,
58 (2-
AEP)2PbI4, and (2-AEPH)PbI4
62a
compound (PEA)2PbI4 (2-AEP)2PbI4 (2-AEPH)PbI4
average Pb–I–Pb (deg) 153.3 167.9 164.5
Db 0.006 0.011 0.013
σ
2c 3.6 11.8 26.2
interlayer distance (Å)d 9.94 7.60 3.75
penetration depth of NH3 (Å)e 0.57 0.32 1.44
a Values were quantified using VESTA. 59 b D is the distortion index based on
bond lengths.84 c σ
2
is the bond angle variance. 85 d The interlayer distance
is defined by the interplanar distance between terminal iodides.
(PEA)2PbI4 are mainly distorted in-plane, resulting in a Pb–I–Pb angle of 153.3°.
Both (2-AEP)2PbI4 and (2-AEPH)PbI4 octahedra are mainly distorted out-of-plane,
resulting in Pb–I–Pb angles of 167.9°and 164.5°, respectively. For both the distortion index, D,84 and bond angle variance, σ
2
,
85 (PEA)2PbI4 has the lowest value,
and (2-AEPH)PbI4 has the highest value. The penetration depth of the ammonium
group, defined by the interplanar distance between the nitrogen on the ammonium
group and the plane of terminal iodides, is the smallest in (2-AEP)2PbI4, followed by
(PEA)2PbI4, and then (2-AEPH)PbI4.
As mentioned previously, the (2-AEP)+ cation was selected due to similar molecular geometry and was intended to alternate with (PEA)+ cation within the interlayer
space to produce an ACI phase, where (2-AEP)+ will act as the net acceptor and
(PEA)+ as the net donor. This was found to be synthetically challenging, and we
were unable to achieve a single-phase film. When looking closer at the (2-AEP)+
interactions in (2-AEP)2PbI4, we observe a face-to-face interaction between the pyridine rings of two adjacent (2-AEP)+ cations in the organic layer, similar to the bilayer
packing observed in (4-AEP)2PbI4.
72 This face-to-face stacking of the organic bilayer
36

3.3. Results and Discussion
is believed to be driven by the cancellation of dipoles in the pyridine rings of (2-
AEP)+, as illustrated in Figure 3.1b. This feature is in contrast with the well-studied
2D hybrid (PEA)2PbI4,
58 illustrated in Figure 3.1a, where the interaction of the rings
across the layer is edge-to-face, a common packing motif for aromatic molecules and
2D hybrids containing aromatic cations. 86,87 Hydrogen bonding is observed between
the ammonium group and the nitrogen in the pyridine of (2-AEP)+ cations in (2-
AEP)2PbI4. Consequently, the folded geometry causes the ethylammonium group to
insert deeper within the A-site pocket of the octahedra plane. This results in a smaller
interlayer distance in (2-AEP)2PbI4 (7.60 Å) compared to (PEA)2PbI4 (9.94 Å). Due
to this disparity in bilayer packing within their respective hybrid phases, it is difficult
to synthetically achieve an ACI phase with (2-AEP)+ and (PEA)+ as the alternating
cations.
Our findings showcase that a similarity in molecular shape cannot be the only
consideration when selecting donor–acceptor pairs. While most known ACI phases
are mixed with organic cations of similar molecular shape, 88–91 Yan et al. were able to
achieve ACI phases by mixing alkyl and aryl cations, which have different molecular
shapes.92 The presence of a dipole and hydrogen bonding should also be considered.
Ideally, the crystal structures of both end members should be closely examined for
structural packing compatibility prior to attempting synthesis of the ACI phase.
The presence of through-layer π–π interactions between the rings of the organic
bilayer in (2-AEP)2PbI4 presents an alternative to achieving 3D charge transport in
a 2D structure. In order to probe the optoelectronic properties of (2-AEP)2PbI4,
spin-coated films were fabricated. (2-AEP)2PbI4 DMF precursor solution was spincoated on a cleaned glass substrate and subsequently annealed in the N2 glovebox
for 10 min on a hot plate. In our initial experiments, XRD of a (2-AEP)2PbI4 film
annealed at 100 °C revealed the presence of a second phase. To achieve a phase-pure
37

3.3. Results and Discussion
Figure 3.3: Top: spin-coated film annealed at 50 °C for 10 min, Pawley fitted
to (2-AEP)2PbI4, with Rwp of 3.2%. Bottom: spin-coated film annealed at 160 °C
for 10 min, Pawley fitted to (2-AEPH)PbI4 and c-axis expanded (2-AEPH)PbI4 [(2-
AEPH)PbI4*], with Rwp of 3.9%.
film, film annealing studies at various temperatures were carried out in a N2 glovebox.
Annealing the spin-coated film at 50 °C results in a phase-pure (2-AEP)2PbI4 film.
Annealing the spin-coated film at 160 °C results in the complete phase transformation
to (2-AEPH)PbI4, which was first reported by Febriansyah et al..
62 Pawley fittings
of the XRD patterns of the films, presented in Figure 3.3, show the fabrication of
(2-AEP)2PbI4 and (2-AEPH)PbI4 films. Annealing at an intermediate temperature
of 100 °C for 10 min resulted in mixed phases of (2-AEP)2PbI4 and (2-AEPH)PbI4,
as shown in Figure 3.11.
For both end members (2-AEP)2PbI4 and (2-AEPH)PbI4, the annealed films
show a preferred orientation for the (00l) plane, which corresponds to the 2D inorganic sheets of the hybrid. For the 160 °C annealed phase, (2-AEPH)PbI4, a c-axis
38

3.3. Results and Discussion
expanded unit cell, (2-AEPH)PbI4*, was added in order to achieve a good Pawley
fit. One possible reason for the presence of the c-axis expanded unit cell is due to
the transformation from the (2-AEP)2PbI4 phase, which has a much larger c-axis
compared to that of the (2-AEPH)PbI4 phase.
Figure 3.4: Ex situ XRD of spin-coated films annealed at varying temperatures for
10 min in N2 atmosphere.
Ten films were spin-coated using 0.5 M (2-AEP)2PbI4 DMF precursor solution
and annealed at different temperatures on the hot plate for 10 min. Ex situ XRD
characterization was carried out on the films. Figure 3.4 illustrates the phase
change from (2-AEP)2PbI4 to (2-AEPH)PbI4 as the anneal temperature increases.
(2-AEPH)PbI4 phase starts growing in at 80 °C and gradually increases in crystallinity until it is the only phase observed with XRD at 160 °C. No intermediate crystalline phases were observed with our in-lab X-ray diffractometer. Due to
39

3.3. Results and Discussion
the dibasic nature of 2-AEP, an equilibrium exists between its protonated species:
2 (2−AEP+
) −−↽−−⇀∆
2−AEP + 2−AEPH2+. Once enough heat is provided to push the
equilibrium to the right, the neutral 2-AEP species evaporates from the film, leaving
the doubly protonated 2-AEPH2+, forming the (2-AEPH)PbI4 phase. Thermogravimetric analysis (TGA) of (2-AEP)2PbI4 powder confirms the loss of 2-AEP to form
(2-AEPH)PbI4 (Figure 3.13). The sum of the first and second mass loss of the TGA
is close to the theoretical mass loss of one equivalent of 2-AEP.
Figure 3.5: Ex situ (a) absorbance and (b) emission of spin-coated films annealed
at varying temperatures for 10 min in N2 atmosphere. The absorption spectra were
taken on films made from 0.1 M (2-AEP)2PbI4 DMF precursor solution. The emission
spectra were taken on films made from 0.5 M (2-AEP)2PbI4 DMF precursor solution
and were excited at 400 nm.
40

3.3. Results and Discussion
Figure 3.5 indicates that the phase transformation can also be tracked by observing
the absorbance and emission of the films. In the 50 °C annealed film, there is a weak
absorption band at 490 nm and a strong excitonic absorption feature at 522 nm. In the
110 °C annealed film, there is an increase in absorbance at 490 nm, and an excitonic
feature shifted to 547 nm. Finally at 160 °C, there is a loss of the 490 nm band,
and a sharp excitonic feature at 559 nm, which is very close to the value reported for
(2-AEPH)PbI4 by Febriansyah et al.
62
Based on prior studies of 2D lead iodide hybrids, 93,94 we presume that the higher
energy absorption feature (490 nm) arises from surface states, and the lower energy
absorption feature arises from the bulk. When the film is annealed above 50 °C, (2-
AEP)2PbI4 crystallites appear in the bulk film, and based on fluorescence microscopy
results, it appears that the (2-AEP)2PbI4 crystallites have the largest surface area
at the 110 °C anneal (Figure 3.6). Thus, we assign the 490 nm band to the surface excitonic absorption of (2-AEP)2PbI4. This is also supported by the absorption
spectra of films annealed at intermediate temperatures (Figure 3.5), which show the
greatest relative intensity for the 490 nm band at 110 °C. The 547 nm band in the
110 °C annealed film is likely due to bulk excitonic absorption of the incipient (2-
AEPH)PbI4. The energy of the bulk excitonic feature in this film is blue-shifted
relative to the 160 °C annealed film because it is present as a shoulder on the more
intense 490 nm band.
The emission peak of the 50 °C annealed film is 554 nm, which steadily decreases
in intensity as the (2-AEPH)PbI4 species grows in. Febriansyah and co-workers
also observe a low emission intensity at room temperature for single crystal (2-
AEPH)PbI4,
62 agreeing with our findings. Fluorescence microscopy (Figure 3.6) at
the excitation wavelengths of 465–495 nm visually depicts the phase transformation
of the film from (2-AEP)2PbI4 to (2-AEPH)PbI4. This can be seen from the decrease
41

3.3. Results and Discussion
in the total area of green emission (515–555 nm) of films as the annealing temperature
increases. It should be noted that a 0.5 M (2-AEP)2PbI4 DMF precursor solution was
used for emission, fluorescence microscopy, and XRD measurements, whereas a 0.1 M
solution was used for absorbance measurements. While there is a difference in ratio of
the two phases at intermediate annealing temperatures between the thicker and thinner films (Figure 3.12), the two phases are present at the intermediate temperatures
for both films.
Figure 3.6: Fluorescence microscopy of spin-coated films from 0.5 M (2-AEP)2PbI4
DMF solution, annealed at various temperatures in N2 atmosphere. The films were
excited at wavelengths of 465–495 nm and a 515–555 nm filter was applied to isolate
green emission from the film. To observe the overall morphology of the film, the films
were also probed under white light.
42

3.3. Results and Discussion
Figure 3.7: Calculated band structures and DOSs (PBEsol + SOC) of (a)
(PEA)2PbI4, (b) (2-AEP)2PbI4, and (c) (2-AEPH)PbI4 visualized using sumo.81 The
energy is displayed from −1 to 2.5 eV to highlight the band dispersion in the stacking
direction (Γ to Z).
The calculated DOS for each hybrid, as shown in Figure 3.7, indicate that the
contribution from the organic component moves closer to the minimum of the conduction band going from PEA2PbI4 to (2-AEP)2PbI4 to (2-AEPH)PbI4. This tracks
with the LUMO energies expected for the organic cations, where (PEA)+ has the
highest LUMO, followed by (2-AEP)+, and then (2-AEPH)2+, which are effectively
the LUMO energies for phenyl, pyridyl, and pyridinium, respectively. The band dispersion of (2-AEP)2PbI4 and (2-AEPH)PbI4 (Figure 3.7) suggests significant electron
mobilities particularly in (2-AEP)2PbI4, as supported by the effective charge carrier
masses shown in Table 3.2. The effective charge carrier masses of (2-AEP)2PbI4 is
comparable to (PEA)2PbI4. Unfortunately, the directions of the charge carrier masses
are all within the 2D lead iodide octahedra sheet, and no through-layer charge transport is observed. Looking closely at the band dispersion in the stacking direction
43

3.3. Results and Discussion
Table 3.2: Effective and Reduced Masses of Charge Carriers Using SOCDFTa
material and direction holes (mh) electrons (me) reduced mass (µ)
PEA2PbI4 0.263 0.197 0.113
Γ → Y
PEA2PbI4 0.258 0.197 0.112
Γ → X
(2-AEP)2PbI4 0.321 0.169 0.111
(−0.1, 0, 0.5) → T
(2-AEP)2PbI4 0.404 0.143 0.106
(−0.1, 0, 0.5) → Z
(2-AEPH)PbI4 3.330 0.407 0.363
(0.43, 0, 0) → Y
(2-AEPH)PbI4 2.440 0.377 0.327
(0.43, 0, 0) → Γ
a Note that (−0.1, 0, 0.5) lies between Z and T for (2-AEP)2PbI4 and
(0.43, 0, 0) lies between Y and Γ for (2-AEPH)PbI4.
(Γ to Z) in Figure 3.7, both (PEA)2PbI4 and (2-AEP)2PbI4 are flat, whereas it is
relatively dispersed in (2-AEPH)PbI4. This is not surprising given that the interplanar distance between terminal iodides decreases when going from (PEA)2PbI4 to
(2-AEP)2PbI4 to (2-AEPH)PbI4.
The dielectric measurements of both (2-AEP)2PbI4 (Figure 3.8) and (2-
AEPH)PbI4 pellets (Figure 3.9) reveal a non-negligible degree of loss, which reflects
the semiconducting character and implies that the polycrystalline pellets exhibit some
degree of electrical conductivity. The capacitance and dielectric loss of both forms of
the 2-AEP hybrids exhibit a feature-less frequency dependence of a dielectric material
that can be attributed to thermal contraction during cooling, with the loss decreasing
significantly at low temperatures. Both the cooling and warming traces are effectively
identical with the random fluctuations between points simply reflecting vibrations of
44

3.3. Results and Discussion
the sample holder and wires, implying no significant structural or electronic transitions at low temperatures. This is contrasted with the overall lower loss observed
in the dielectric measurement of the (PEA)2PbI4 pellet (Figure 3.10), indicating it
has a more insulating behavior compared to the 2-AEP hybrids. However, there is
a significant feature centered around 250 °C in the capacitance and dielectric loss
of (PEA)2PbI4, which could be related to a structural transition near room temperature. The higher loss seen in the 2-AEP hybrids is believed to be related to the
lower LUMO levels of (2-AEP)+ and (2-AEPH)2+ compared to (PEA)+, as well as
the higher organic contribution in the conduction band minimum, as shown in the
DOS plots (Figure 3.7).
The presence of π–π interactions in (2-AEP)2PbI4 should improve through-layer
charge transport but ultimately was not achieved due to the insulating alkylammonium chain. Future improvements to this system would be to incorporate a conjugated
ammonium chain to establish a continuous charge transport from the π–π interaction
in the ring to the chain into the 2D inorganic sheet.
Figure 3.8: Dielectric measurements of (2-AEP)2PbI4 pellets from (a) 300 to 10 K
and (b) 10 to 300 K.
45

3.4. Summary
Figure 3.9: Dielectric measurements of (2-AEPH)PbI4 pellets from (a) 300 to 10 K
and (b) 10 to 300 K.
Figure 3.10: Dielectric measurements of (PEA)2PbI4 pellets from (a) 300 to 10 K
and (b) 10 to 300 K.
3.4 Summary
We have successfully prepared a new 2D hybrid, (2-AEP)2PbI4, that contains faceto-face packing in the organic bilayer. Through a systematic study of spin-coating
conditions, we demonstrated the presence of two competing (2-AEP) phases, and
that the final phase depends on the annealing temperature. This has important
46

3.4. Summary
implications for the film fabrication of any hybrid containing dibasic organic cations,
as achieving a single-phase film will most likely be highly contingent upon optimizing
the solution processing conditions.
47

3.5. Supplemental Information
3.5 Supplemental Information
Table 3.3: Crystal data and structure refinement for (2-AEP)2PbI4.
Parameter (2-AEP)2PbI4
Chemical formula C14H22I4N4Pb
Formula weight 961.14
Temperature (K) 296
Crystal system orthorhombic
Space group P bcn
a (Å) 9.2673(3)
b (Å) 9.1639(3)
c (Å) 27.8083(8)
α (
◦
) 90
β (
◦
) 90
γ (
◦
) 90
Volume (Å3
) 2361.61(13)
Z 4
ρcalc (g/cm3
) 2.703
µ (mm−1
) 12.377
F(000) 1712.0
Crystal size (mm3
) 0.315 × 0.16 × 0.11
Radiation MoKα (λ = 0.71073)
2Θ range for data collection (◦
) 5.282 to 59.998
Index ranges −13 ≤ h ≤ 13, −12 ≤ h ≤ 12, −39 ≤ l ≤ 37
Reflections collected 32160
Independent reflections 3438 [Rint = 0.0304, Rsigma = 0.0172]
Data/restraints/parameters 3438/0/107
Goodness-of-fit on F2 1.069
Final R indexes [I >= 2σ (I)] R1 = 0.0231, wR2 = 0.0532
Largest diff. peak/hole (eÅ−3
) 1.49/-1.01
48

3.5. Supplemental Information
Table 3.4: Fractional atomic coordinates and equivalent isotropic displacement
parameters (Å2 × 103
) for (2-AEP)2PbI4. Ueq is defined as 1/3 of the trace of the
orthogonalised UIJ tensor.
Atom x y z U(eq)
Pb1 0.5 0.60356(2) 0.75 29.69(6)
I1 0.55585(3) 0.60203(3) 0.63656(2) 43.96(8)
I2 0.76504(3) 0.83751(3) 0.76004(2) 43.14(7)
N1 0.5655(4) 0.2047(4) 0.64797(15) 66.6(11)
C2 0.5124(4) 0.0531(5) 0.65015(17) 55.5(10)
C3 0.3662(5) 0.0393(6) 0.62664(15) 61.8(11)
C4 0.3614(4) 0.0738(4) 0.57365(13) 39.1(7)
C5 0.2619(4) 0.0046(5) 0.54432(14) 49.8(9)
C6 0.2574(5) 0.0382(5) 0.49603(14) 57.3(10)
C7 0.3541(5) 0.1374(4) 0.47822(15) 55.8(10)
C8 0.4491(5) 0.2005(4) 0.50924(17) 56.4(10)
N9 0.4542(3) 0.1724(3) 0.55652(12) 45.8(7)
Table 3.5: Hydrogen atom coordinates and isotropic displacement parameters (Å2×
103
) for (2-AEP)2PbI4.
Atom x y z U(eq)
H1A 0.565064 0.235252 0.617592 100
H1B 0.655096 0.208502 0.659467 100
H1C 0.508542 0.261859 0.665548 100
H2A 0.505695 0.022528 0.683473 67
H2B 0.580365 -0.010785 0.634012 67
H3A 0.33183 -0.0597 0.631243 74
H3B 0.299583 0.103902 0.643118 74
H5 0.198556 -0.063896 0.557104 60
H6 0.19003 -0.005697 0.475925 69
H7 0.354862 0.161153 0.445703 67
H8 0.514746 0.267393 0.496828 68
49

3.5. Supplemental Information
1H NMR of 2-(2-ammonioethyl)pyridine iodide (2-AEP)I salt
1H NMR (400 MHz, DMSO-d6) δ 8.54 (d, 1H), 7.81 (td, J = 2.0 Hz, 1H), 7.80
(s, 3H), 7.37 (d, J = 7.8 Hz, 1H), 7.33 (dd, J = 7.6, 4.9 Hz, 1H), 3.22 (q, J = 7.1
Hz, 2H), 3.06 (t, J = 7.2 Hz, 2H).
Figure 3.11: Spin-coated film annealed at 100 °C for 10 min, Pawley fitted to (2-
AEP)2PbI4 and (2-AEPH)PbI4, with Rwp of 4.6%.
50

3.5. Supplemental Information
Figure 3.12: Ex situ XRD of spin-coated films annealed at varying temperatures
for 10 min in N2 atmosphere. The films were deposited using a 0.1 M (2-AEP)2PbI4
DMF precursor solution.
51

3.5. Supplemental Information
Figure 3.13: TGA and DSC of (2-AEP)2PbI4 powder under N2 gas flow.
The first and second mass loss of the TGA sums up to 11.6%, which corresponds to
the mass loss of 2-AEP. The theoretical mass loss of 2-AEP is 12.7%. Thus, there is a
8.7% difference between the experimental and theoretical mass loss. The overall TGA
mass loss is 48.4%, which corresponds to the decomposition of the powder to PbI2.
The theoretical mass loss to form PbI2 is 52.0%. So, the percent difference between
the overall mass loss and the theoretical mass loss to form PbI2 is 6.9%. In the
differential scanning calorimetry (DSC) curve, the first endothermic peak at 117 °C
is attributed to desorption of surface moisture. The second and third endothermic
peaks at 166 °C and 213 °C coincide with the mass loss of 2-AEP, and are assigned
as one equivalent of 2-AEP evaporating. The fourth endothermic peak at 234 °C
is assigned as the second equivalent of 2-AEP evaporating, leading to subsequent
decomposition of the powder to PbI2.
52

Chapter 4
Probing Donor–Acceptor Charge Transfer
Properties in 1-Naphthylammonium and
1-Methylquinolinium-Based 1D Hybrid Lead
Halides
4.1 Introduction
As demonstrated in the previous chapter, similarity in molecular shape cannot be
the sole consideration when selecting donor–acceptor pairs to incorporate within a
hybrid metal halide material. We were interested in (1-NA)PbI3, a 1D hybrid lead
iodide comprising 1-naphthylammonium (1-NA) and face-sharing lead iodide octahedral chains. By varying the nitrogen position, we can obtain 1-NA isomers with different HOMO–LUMO energy levels. Through screening a series of lead iodide hybrids
with 1-NA isomers, we identified (1-MQ)PbI3, a hybrid with the same space group
and organic cation packing, but with 1-methylquinolinium (1-MQ) as the organic
cation. Confirming the structural similarities between (1-NA)PbI3 and (1-MQ)PbI3
enabled us to synthesize of a novel ordered mixed-cation hybrid, (1-MQ)(1-NA)Pb2I6.
(1-MQ)(1-NA)Pb2I6 features ordered organic cations, 1-NA and 1-MQ, surrounded by face-sharing lead iodide octahedral chains. The crystal structure of this
new material was determined using single crystal X-ray diffraction (XRD). Solid-state
NMR techniques confirmed the ordering of the organic cations, and their positions
were rationalized by analyzing the projected dipole moments of the organics within
53

4.2. Experimental
the crystal structure. To our knowledge, this is the first demonstration of a 1D hybrid
metal halide with ordered mixed organic cations.
We further characterized the optoelectronic properties of this series of 1D hybrid
lead halide via DFT calculations, UV-vis absorption, temperature-dependent photoluminescence, and dielectric measurements of powders and films. Despite their structural similarities, we found that the optical properties of the materials are highly
dependent on the LUMO of the organic cation. Additionally, the differing optical
properties of the hybrid materials correlated to the capacitance and dielectric loss
data collected. This work was conducted in close collaboration with Dr. Megan
Cassingham.95
4.2 Experimental
4.2.1 Synthesis
The precursor salt, 1-methylquinolinium iodide [C10H10NI, (1-MQ)I], was synthesized
by mixing two parts quinoline (98%, Sigma Aldrich) with iodomethane (99%, stab.
with Cu, Fisher) in approximately 10 mL of acetonitrile (HPLC, EMD Millipore).
The solution was then heated to 85 °C and stirred for 2 hours. Once the solution
cooled to room temperature, it was transferred to a glass petri dish to allow the solvent
to evaporate. The resulting yellow solid was vacuum filtered and rinsed with diethyl
ether (≥98%, stabilized, VWR). Proton NMR spectra using DMSO-d6 (Cambridge
Isotope Laboratories) were collected to confirm the purity and structure of the product
(reported in Section 4.5).
1-methylquinolinium lead iodide [(1-MQ)PbI3] was prepared by dissolving 0.2 g
(0.43 mmol) of lead (II) iodide (PbI2, 99.9985%, metals basis, Alfa Aesar) and 0.12 g
(0.44 mmol) of the prepared (1-MQ)I salt in 2 mL and 3 mL of hydroiodic acid
54

4.2. Experimental
(HI, 57 wt% stabilized, Sigma Aldrich) in 2 dram and 8 dram scintillation vials,
respectively. The organic salt solution was stirred continuously in an aluminum bead
bath on a hot plate until reaching 100 °C. Once all solids were dissolved in both
solutions, the lead solution was decanted into the organic solution and allowed to
briefly mix before turning off the heat. The resulting yellow crystals were collected
via vacuum filtration and rinsed with acetone (≥99.5%, VWR).
1-naphthylammonium lead iodide [(1-NA)PbI3] was prepared following the same
procedure using 0.2 g of PbI2 (0.43 mmol) and 0.078 g (0.54 mmol) of 1-
naphthylamine (C10H9N, 99%, Sigma Aldrich). The resulting product was vacuum
filtered and rinsed with diethyl ether.
The mixed hybrid, (1-MQ)(1-NA)Pb2I6, was synthesized by using the same procedure. The lead solution was made by dissolving 0.2 g (0.43 mmol) of PbI2 with
2 mL HI in a 2 dram vial. The organic salt solution was made by dissolving 0.038 g
(0.27 mmol) 1-naphthylamine and 0.056 g (0.21 mmol) (1-MQ)I with 5 mL of HI in
an 8 dram vial. The resulting product was vacuum filtered and rinsed with diethyl
ether. (1-NA)PbI3 and (1-MQ)(1-NA)Pb2I6 were both stored in an Ar glove box to
avoid degradation due to atmospheric exposure.
1-naphthylammonium-d3 chloride salt was synthesized to create a deuterated version of the mixed hybrid for solid-state NMR experiments. 100 mg of 1-naphthylamine
was heated and dissolved in 10 mL of deuterium chloride (DCl, 20% w/w in D2O,
99.5% isotopic). The resulting product was analyzed by NMR and used to synthesize
the mixed hybrid. (1-MQ)(1-NA-d3)Pb2I6 was synthesized using the same procedure
outlined above with the expectation that some back conversion of the deuterons to
protons would occur. Any resulting back conversion did not affect the solid-state
NMR experiments significantly.
55

4.2. Experimental
The films discussed were made via spin-coating, mostly on a cleaned 20 × 20 mm
glass substrate. Films made for temperature-dependent emission studies were spincoated on a cleaned, round (25.4 mm diameter) sapphire disk, to ensure the sample
achieves the desired temperatures, especially at sub-zero Kelvin temperatures. The
synthesized (1-NA)PbI3 powder was dissolved in dry N,N-dimethylformamide (DMF,
99.8%, Acros Organics). 30 µL of the precursor solution was spin-coated on a cleaned
substrate at 3000 rpm for 40 s and subsequently annealed at 90 °C for 5 min in a N2
glovebox.
For (1-MQ)PbI3, the precursor solution was made by dissolving synthesized (1-
MQ)PbI3 powder in dimethyl sulfoxide (DMSO, ≥99.9%, EMD Millipore). The following film deposition was done in air. 70 µL of the precursor solution was spin-coated
at 1000 rpm for 30 s. Toluene was then dispensed on top of the film to act as an
antisolvent, and the film was spun for an additional 30 s. The film was subsequently
annealed at 250 °C for 10 min.
4.2.2 Structure Determination
Single crystal data for (1-MQ)PbI3 and (1-MQ)(1-NA)Pb2I6 were collected at 100 K
using a Rigaku XTALab Synergy diffractometer with a CCD area detector. The data
reduction was performed using Crysalis Pro and refined using Olex2 with the ShelXL
program installed.96 Single crystal data was also collected for (1-NA)PbI3 to confirm
the structure first reported by Lemmerer and Billing and later reported with minor
lattice changes by Mitrofanov et al.97,98
Solid-state NMR spectroscopy experiments were performed on a 9.4 T Bruker
wide-bore magnet equipped with a Bruker AVANCE III HD console (1H spin echo,
207Pb spin echo, 1H{14N} D-HMQC, 2H spin echo, 1H{2H} DE-RESPDOR) and
equipped with a Bruker 1.3 mm HX probe with MAS frequency. All experiments
56

4.2. Experimental
utilized N2 gas for spinning. 1H chemical shifts were referenced to neat tetramethylsilane using adamantane (δiso(
1H) = 1.72 ppm) as a secondary chemical shift reference.
207Pb and 2H chemical shifts were indirectly referenced to neat TMS using the IUPAC
recommended relative NMR frequency. 99 NMR spectra were processed and analyzed
with Bruker TopSpin version 3.6.4 (AVANCE III HD data) software.
The following experimental details are with respect to data acquired at B0 =
9.4 T with the 1.3 mm HX NMR probe. 1H spin echo solid-state NMR spectra
of (1-NA)PbI3, (1-MQ)PbI3, and (1-MQ)(1-NA)Pb2I6 were recorded with a 50 kHz
MAS frequency, and the 1H longitudinal relaxation time constants (T1) were ca. 3.3
s, 19.3 s, and 6.9 s, respectively. All experiments utilized a 1.3*T1 s recycle delay.
207Pb spin echo solid-state NMR spectra of (1-NA)PbI3, (1-MQ)PbI3, and (1-MQ)(1-
NA)Pb2I6 were recorded with a 50 kHz MAS frequency, and all experiments utilized
a 0.5 s optimized recycle delay. The 207Pb isotropic chemical shift tensor parameter
(δiso) was determined with the solid line shape analysis (SOLA) module in the Bruker
TopSpin 3.6.4 software.
For the 1H{14N} D-HMQC2
solid-state NMR experiment, the symmetry-based
SR4
2
1 dipolar recoupling sequence 100 was applied on the 1H channel at the 2nd order
rotary resonance recoupling condition. 101–103 The optimum total dipolar recoupling
time used for the (1-MQ)(1-NA)Pb2I6 was 1.28 ms, and the 14N excitation and reconversion pulse lengths had a duration of one rotor period. The 14N RF field was
62.1 kHz. 2H spin echo solid-state NMR spectra of (1-MQ)(1-NA-d3)Pb2I6 were
recorded with a 20 kHz MAS frequency, and all experiments utilized a 0.1 s recycle delay. 1H{2H} DE-RESPDOR9
experiments of (1-MQ)(1-NA-d3)Pb2I6 were performed with 50 kHz MAS and 2H saturation pulses that were 30 µs (1.5 × τ rot)
in duration with 107.5 kHz RF field. The SR4
2
1 heteronuclear dipolar recoupling
sequence was applied to the 1H spins to reintroduce the 1H-2H dipolar interaction
57

4.2. Experimental
under MAS.100 A control (without a 2H saturation pulse) and dephased (with a 2H
saturation pulse) point were recorded at each recoupling time considered in this experiment. The 1H T1 of (1-MQ)(1-NA-d3)Pb2I6 was ca. 6.8 s and 7.1 s for high-frequency
(aromatic protons) and low-frequency (-CH3) signals, respectively; all experiments
utilized a 9.23 s recycle delay and considered the low-frequency signal (-CH3) to construct the RESPDOR dephasing curve. The 2H isotropic chemical shift (δiso), CQ, and
η were determined by extracting side band manifolds from the one-dimensional (1D)
spin echo spectrum and fitting the manifold with the SOLA module in the Bruker
TopSpin 3.6.4 software. A summary of all experimental data is shown in Table S1 in
supplementary information.
SIMPSON v4.1.1 was used to run numerical solid-state NMR simulations. 104–106
The archived data includes the SIMPSON input codes. Except for the 1H π/2 pulses,
all the pulses in the files were finite in duration. The 1H{2H} DE-RESPDOR dephasing curves were simulated using rep678 crystal file, 13 γ-angles, 107.5 kHz 2H RF field.
The 1H{2H} DE-RESPDOR numerical simulations for the (1-MQ)(1-NA-d3)Pb2I6
were done considering a multispin 1H-2Hn (n=3) system and corresponding Euler
angles.
XRD characterization of films and powder was carried out on a Bruker D8 Advance
powder diffractometer equipped with a Cu–Kα source and LynxEye XE–T detector.
The patterns for each of the hybrid materials were evaluated using the Pawley method
as implemented in the TOPAS-Academic (v6). 107
4.2.3 DFT Calculations
Density functional theory (DFT) calculations were performed using the projectoraugmented wave method within the Vienna Ab initio Simulation Package
(VASP).76,77 The density of states (DOS) and band diagram plots were plotted
58

4.2. Experimental
using sumo.81 Due to the size of the unit cells, the functional of Perdew, Burke,
and Ernzerhof108 was used for geometrical relaxation, while the functional of Heyd,
Scuseria, and Ernzerhof (HSE06), 109,110 with the explicit inclusion of spin–orbit coupling (HSE06+SOC), was used for electronic structure calculations, including DOS
and electronic band structure, performed using the PBEsol-relaxed structures. Iterative convergence testing was used before performing the geometric relaxations to
determine the optimal ENCUT and KPOINT values for the INCAR files. Geometry
optimization was considered to have converged when the forces on each atom fell
below 0.01 eV Å˘1, and the plane wave cutoff was increased to 600 eV during relaxation to avoid Pulay stress. Partial charge density information was generated using
pymatgen.111
4.2.4 Photophysical Properties Measurements
UV-vis absorption spectra of films were taken on an Agilent 8453 UV-visible spectrophotometer. Temperature-dependent emission data were collected from 3–300 K
using neat solid samples and spin-coated films. Each powder sample was sandwiched
between two 1 mm thick, 25.4 mm diameter sapphire disks before being placed into
the cryostat system. The film samples were deposited on two 1 mm thick, 25.4 mm
diameter sapphire disks, which were then sandwiched and mounted onto the cryostat system. The samples were excited at 365 nm and data was collected from
400–800 nm for the steady-state emission spectra using a Photon Technology International QuantaMaster model C-60SE spectrofluorimeter in tandem with a Janis
model SHI-4-2 optical He cryostat equipped with a Lakeshore model 335 temperature controller. Steady-state emission and excitation spectra for the organic salts in
2-methyltetrahydrofuran (2-methylTHF, stabilized, Fisher Scientific) were collected
59

4.3. Results and Discussion
using the Photon Technology International QuantaMaster model C-60SE spectrofluorimeter at 77 K.
4.2.5 Dielectric Properties Measurements
The temperature-dependent dielectric properties of the 1D hybrid materials were
measured in a parallel plate geometry. Each material was ground using an agate
mortar and pestle and pressed into 6 mm diameter pellets. The pellets were vapor
deposited with Al, on both faces of the pellets. Powder XRDs were taken before and
after metal deposition to ensure that the crystal structures of the pellets were retained.
Dielectric measurements were taken from 10 to 300 K at frequencies of 1, 2, 5, 10, and
20 kHz. The sample temperature was controlled using a Quantum Design Physical
Property Measurement System (PPMS) Dynacool. The dielectric measurements were
taken using an Andeen-Hagerling 2700A 50 Hz-20 kHz Ultra-Precision Capacitance
Bridge.
4.3 Results and Discussion
4.3.1 Structural Characterization
The synthesis of each material yielded similar small, tabular, yellow crystallites;
though, the crystallization can be altered to produce larger single crystals. All three
materials crystallize in the Pbca space group as shown in Figure 4.1. The refinement
data for (1-MQ)PbI3 and (1-MQ)(1-NA)Pb2I6 can be found in Tables 4.1 and 4.2.
The inorganic portion of each 1D material consists of similar face-sharing lead iodide
octahedra. In (1-MQ)PbI3 and (1-NA)PbI3, the inorganic chains are parallel to the
b-axis while in (1-MQ)(1-NA)Pb2I6 the chains are parallel to the a-axis. Each of the
60

4.3. Results and Discussion
Figure 4.1: Crystal structures of (1-NA)PbI3, (1-MQ)(1-NA)Pb2I6, and (1-
MQ)PbI3. The lead octahedra in (1-MQ)(1-NA)Pb2I6 are colored differently to visualize the three lead sites.
end member hybrids has one unique lead site whereas the mixed hybrid crystallizes
with three.
When comparing just (1-MQ)PbI3 and (1-NA)PbI3, there are very minor differences aside from the different cations. A small distortion in the octahedral bond
angles in (1-MQ)PbI3 is seen due to the difference in location of the cationic charge
center compared to (1-NA)PbI3. In (1-NA)PbI3, the inorganic octahedra have very
symmetric bond lengths and angles. In (1-MQ)PbI3, the angles in the octahedra are
distorted further away from 90◦ and 180◦
to bring the iodine atoms closer to the
nitrogen atoms in the quinolinium rings. This translates to a shorter distance of
4.09 Å between the quinolinium nitrogen and the iodine atoms in (1-MQ)PbI3 when
compared to the 4.23 Å distance between the equivalent carbon atom in 1-NA and
the iodine atoms of (1-NA)PbI3. By comparing the interatomic distances between
the ammonium nitrogens and the nearest iodine atoms to the interatomic distances
between the methyl carbons and the nearest iodine atoms in (1-NA)PbI3 and (1-
MQ)PbI3, respectively, it was concluded that hydrogen bonding plays a significant
role in the (1-NA)PbI3 whereas other electrostatic interactions are the driving force
in (1-MQ)PbI3. The shortest ammonium nitrogen to iodine distance in (1-NA)PbI3
61

4.3. Results and Discussion
is 3.53 Å, which is on the longer end of the scale for hydrogen bonds. The shortest
distance between a quinolinium nitrogen and iodine in (1-MQ)PbI3 is 4.09 Å, which
is on the scale of other electrostatic interactions. While hydrogen bonding is not
possible in (1-MQ)PbI3, hydrogen bonding does play a role in the cationic packing of
1-NA in (1-NA)PbI3.
Refinement of the single crystal data for the mixed hybrid revealed a doubling of
the c-axis, resulting in an approximate unit cell volume doubling. Since the carbon
and nitrogen atoms in the 1-MQ and 1-NA cations are indistinguishable by X-ray
methods, the atomic position of those atoms could not be differentiated during the
refinement. Despite not being able to definitively assign the carbon and nitrogen
atom positions, the X-ray data indicate that the mixed hybrid does incorporate both
cations and is not a solid solution, as seen in Figure 4.1.
Additionally, the lead iodide octahedra are either canted (green) or slightly distorted (grey) from fully symmetric depending on the lead site, indicating a mixing
of the organic cations in (1-MQ)(1-NA)Pb2I6 (Figure 4.1). The green octahedra tilt
slightly in (00l) planes where the cations appear to be pointing in opposite directions
in relation to the methyl or ammonium groups. In the (00l) planes where the cations
are facing more in the same direction, the grey octahedra instead distort to bring the
iodide atoms closer to the nitrogen atoms. The cations pack in a more symmetrical
way around the canted octahedra, leading to the whole unit shifting rather than distorting as it does at the grey lead site where the cations do not pack symmetrically
around the octahedra.
Looking at the cationic packing around the octrahedral rods, the canted octahedra
are surrounded by four 1-NA cations and two 1-MQ cations, and vice versa for the
distorted octahedra. Since the 1-NA cations exhibit hydrogen bonding interactions
with the iodine atoms, it is more polarizable than the 1-MQ cations. Consequently,
62

4.3. Results and Discussion
it is reasonable to infer that the grey octahedra, which are surrounded by a greater
number of the more rigid 1-MQ cations, would exhibit more significant distortion. In
contrast, the green octahedra, surrounded by the softer and more polarizable 1-NA
cations, exhibit canting rather than distortion.
Figure 4.2: 1H spin echo solid-state NMR spectra of (a) (1-NA)PbI3, (b) (1-
MQ)PbI3, and (c) (1-MQ)(1-NA)Pb2I6. (d) 1H{14N} dipolar heteronuclear multiple quantum correlation (D-HMQC) 112 solid-state NMR spectrum of (1-MQ)(1-
NA)Pb2I6. All NMR spectra were acquired with a 9.4 T magnetic field and a 50 kHz
magic angle spinning (MAS) frequency.
In order to confirm the ordering and arrangement of the 1-NA and 1-MQ cations in
the crystal structure of (1-MQ)(1-NA)Pb2I6, our collaborators—Sujeewa N. S. Lamahewage and Prof .Aaron J. Rossini—performed a variety of solid-state NMR experiments. Figures 4.2 a-c show 1H spin echo solid-state NMR spectra of (1-NA)PbI3, (1-
MQ)PbI3, and (1-MQ)(1-NA)Pb2I6.
1H longitudinal relaxation time constants (T1)
were measured with saturation recovery experiments and gave values of ca. 3.3 s,
19.3 s, and 6.9 s for (1-NA)PbI3, (1-MQ)PbI3, and (1-MQ)(1-NA)Pb2I6, respectively.
The observation of an intermediate 1H T1 for (1-MQ)(1-NA)Pb2I6 is consistent with
mixing of cations in the same crystalline lattice. The 1H solid-state NMR spectra
63

4.3. Results and Discussion
of all compounds shows two main sets of 1H NMR signals, with the lower-frequency
signals having maximum intensity around 5.5 ppm, and the second higher-frequency
signals having maximum intensity around 8.5 ppm. For (1-MQ)PbI3 and (1-MQ)(1-
NA)Pb2I6, the low-frequency 1H NMR signal is assigned to methyl groups of 1-MQ.
For all compounds, the high-frequency 1H NMR signals primarily arise from aromatic
hydrogen atoms.
Figure 4.3: 1H{14N} D-HMQC solid-state NMR spectra for (1-NA)PbI3, (1-
MQ)PbI3, and (1-MQ)(1-NA)Pb2I6.
1H{14N} D-HMQC112 solid-state NMR spectra
for (a) (1-NA)PbI3, (b) (1-MQ)PbI3, and (c) (1-MQ)(1-NA)Pb2I6. The spectra were
acquired in a 9.4 T magnetic field with a 50 kHz MAS frequency. The optimum total
dipolar recoupling time used for all experiments was 1.28 ms.
1H{14N} dipolar heteronuclear multiple quantum correlation (D-HMQC)1
experiments were performed on all three compounds. The 1H{14N} D-HMQC spectra
show that the ammonium hydrogen atoms of 1-NA resonate at ca. 9 ppm, while
the methyl protons of 1-MQ (which are adjacent to the quinoline nitrogen atom)
resonate at 5.5 ppm (Figure 4.2d and Figure 4.3). As expected, the indirect 14N
dimension clearly shows two distinct 14N NMR signals. These NMR signals are centered at −280 ppm and −107 ppm and are assigned the ammonium nitrogen of 1-NA
and the quinolinium nitrogen of 1-MQ, respectively. These assignments are obvious
when comparing the 1H{14N} D-HMQC spectra of each compound and considering
64

4.3. Results and Discussion
the observed 1H correlations (Figure 4.3). Both 14N NMR signals have a single welldefined discontinuity, consistent with the presence of only one of each nitrogen atom
in the asymmetric unit of the crystal structure of (1-MQ)(1-NA)Pb2I6.
Figure 4.4: 207Pb spin echo solid-state NMR spectra of (a) (1-NA)PbI3, (b) (1-
MQ)PbI3, and (c) (1-MQ)(1-NA)Pb2I6. All NMR spectra were acquired with a 9.4 T
magnetic field and a 50 kHz magic angle spinning (MAS) frequency.
Figures 4.4a–c show 207Pb solid-state NMR spectra of (1-NA)PbI3, (1-MQ)PbI3,
and (1-MQ)(1-NA)Pb2I6, respectively. Peak fitting was used to determine the
isotropic chemical shifts (δiso) of each 207Pb solid-state NMR spectra shown in Figure
4.4. The δiso for 207Pb solid-state NMR spectra of each (1-NA)PbI3 and (1-MQ)PbI3
hybrid systems are 952 ppm and 891 ppm, respectively. The mixed-cation (1-MQ)(1-
NA)Pb2I6 shows a 207Pb spectrum with a peak that is similar in breadth to that of (1-
NA)PbI3, which is somewhat surprising given that there are three distinct Pb atoms
in the asymmetric unit of the crystal structure of (1-MQ)(1-NA)Pb2I6. However, it
65

4.3. Results and Discussion
is well known that lead and tin iodide perovskites often give rise to homogeneously
broadened 119Sn and 207Pb NMR signals.113–117 The homogeneous broadening arises
from the strong scalar and dipolar couplings between 207Pb and 127I (a 100% abundant I = 5/2 nucleus) and dynamic exchange of iodide atoms or fast 127I relaxation
that is caused by sizeable quadrupolar interactions. 115,116 Due to the homogeneous
broadening of the 207Pb solid-state NMR spectra, it is difficult to observe distinct
207Pb NMR signals for (1-MQ)(1-NA)Pb2I6.
Figure 4.5: 1H{207Pb} TONE D-HMQC118 solid-state NMR spectra for (a) (1-
NA)PbI3, (b) (1-MQ)PbI3, and (c) (1-MQ)(1-NA)Pb2I6. The spectra were acquired
in a 9.4 T magnetic field with a 50 kHz magic angle spinning (MAS) frequency. The
optimum total dipolar recoupling time used for all experiments was 1.2 ms. (d) The
comparison of 207Pb spin echo solid-state NMR spectrum of (1-MQ)(1-NA)Pb2I6 with
the extracted columns corresponding to two different 1H chemical shifts in (c).
66

4.3. Results and Discussion
1H{207Pb} t1-noise eliminated (TONE) D-HMQC118 were performed on all three
compounds (Figure 4.5). These experiments show correlations between the 207Pb
NMR signals and 1H NMR signals of both cations, confirming that the cations are
within a 5 Å distance of the Pb atoms in all systems. Interestingly, extracting 207Pb
NMR spectra at different 1H chemical shifts (columns) from the 2D 1H{207Pb} TONE
D-HMQC spectrum of (1-MQ)(1-NA)Pb2I6 results in partial resolution of distinct
207Pb NMR signals, consistent with the presence of multiple Pb sites in the asymmetric unit of this compound (Figure 4.5).
We also performed plane wave density functional theory gauge-including projector augmented wave (GIPAW) 119 calculations on all compounds. These calculations
predict 207Pb isotropic chemical shielding (δiso) are 6906 ppm and 6860 ppm for
(1-NA)PbI3 and (1-MQ)PbI3 hybrid systems, respectively. In contrast, for the (1-
MQ)(1-NA)Pb2I6, three different 207Pb sites were predicted with δiso = 6604 ppm,
6796 ppm, and 6898 ppm (Figure 4.4c).
The 1H→13C cross polarization (CP) solid-state NMR spectra of (1-MQ)(1-
NA)Pb2I6 provide additional evidence for ordering of the cation positions in (1-
MQ)(1-NA)Pb2I6. Similar full widths at half height (FWHH) of ca. 152 Hz and
ca. 169 Hz are observed for the methyl 13C NMR signals of (1-MQ)PbI3 and (1-
MQ)(1-NA)Pb2I6, respectively (Figure 4.6).
Finally, we prepared a sample of (1-MQ)(1-NA)Pb2I6 where the ammonium hydrogen atoms were replaced with deuteron atoms in order to enable 2H solid-state NMR
experiments. As discussed below, the 2H-labelling enabled us to perform 1H-2H dipolar coupling measurements that can probe the distance between methyl and ammonium protons of 1-MQ and 1-NA.
Figure 4.7a shows the 2H spin echo solid-state NMR spectrum (black) acquired
at B0 = 9.4 T magnetic field with 20 kHz MAS frequency, and the simulation is
67

4.3. Results and Discussion
Figure 4.6: 1H→13C CP solid-state NMR spectra for (a) (1-NA)PbI3, (b) (1-
MQ)PbI3, and (c) (1-MQ)(1-NA)Pb2I6. The spectra were acquired in a 9.4 T magnetic field with a 50 kHz MAS frequency.
shown in cyan. The 2H isotropic chemical shift (δiso), quadrupolar coupling constant
(CQ), and asymmetry parameter (η) were obtained by fitting the peak intensities of
the side band manifold. The simulation gives the 2H δiso, CQ, η which are 7.1 ppm,
164 kHz, and 0.12, respectively. The measured CQ values suggest there is relatively
slow reorientation of the ND3 groups on the 2H NMR time scale.
Figure 4.7b shows 1H{2H} DE-RESPDOR100,120 dephased spectrum (red, S)
recorded with 2H saturation pulses and the control spectrum (black, S0) recorded
without saturation pulses. The difference spectrum (S0-S, green) is illustrated below.
A plot of 1– S/S0 as a function of the recoupling duration yields the dephasing curve
(Figure 4.8). Here, all experimental data points correspond to the dephasing observed
at the methyl protons of the 1-MQ; although, due to the limited resolution of the 1H
68

4.3. Results and Discussion
Figure 4.7: (a) 2H spin echo solid-state NMR spectrum (black) of (1-MQ)(1-
NA)Pb2I6 hybrid system in a 9.4 T magnetic field with a 20 kHz MAS frequency.
The peak fitting is shown in cyan solid line. (b) 1H{2H} DE-RESPDOR spectra
recorded (red) with or (black) without 30 µs
2H saturation pulses. The difference
spectrum (green) is shown below. Both spectra were acquired in a 9.4 T magnetic
field with a 50 kHz MAS frequency.
NMR spectra, the dephasing from the aromatic 1H spins will also contribute. With
knowledge of the 2H, CQ, and η, the 1H{2H} DE-RESPDOR dephasing curve for the
deuterated (1-MQ)(1-NA)Pb2I6 can be modeled.
Multispin 1H-2H (n = 3) numerical SIMPSON simulations were performed to
model the dephasing curve. In order to simplify the analysis, we assume that the
dipolar couplings are the same for all 1H-2H spin pairs. Although the crystal structure of (1-MQ)(1-NA)Pb2I6 suggests unique 1H-2H distances for each hydrogen and
deuterium atom, it is important to keep in mind that the methyl groups are likely
rotating with frequencies on the order of a MHz, which will result in averaging of
the distances (and slight averaging of the dipolar coupling constant). A root mean
square deviation (RMSD) calculation was utilized to idenfity the best fit 1H-2H distance. This analysis suggested that the average 1H-2H distance is 3.8 Å between the
methyl protons of 1-MQ and the 2H of the 1-NA molecule (Figure 4.9).
Figure 4.8b shows part of the crystal structure of (1-MQ)(1-NA)Pb2I6, illustrating
the distances between the methyl group of 1-MQ and the nearest ammonium groups
69

4.3. Results and Discussion
Figure 4.8: (a) 1H{2H} DE-RESPDOR dephasing curves for the (1-MQ)(1-NAd3)Pb2I6: red circles correspond to the experimental data points. The solid lines
correspond to numerical SIMPSON simulation for 1H–2H distances of 3.70, 3.75,
3.80, 3.85, 3.90, 3.95, and 4.00 Å, respectively. All simulations were performed with
a multispin 1H-2H3 system to mimic coupling between a methyl hydrogen and three
ammonium deuterons. (b) Representation of orientation of molecules and the distance
between ammonium hydrogen atoms of 1-NA and methyl hydrogen atoms of 1-MQ
in the plane wave DFT optimized crystal structure.
of 1-NA. Note, plane wave DFT was used to optimize the hydrogen atom positions
in this structure. The distances for the methyl hydrogen (H atom q) to the three
nearest ammonium hydrogen atoms (H atoms a, b, and c) is 3.95 Å. For all of the
methyl protons, the average distance to the nearest three ammonium protons is 4.45 Å
(Table S1). While our measured value of 3.8 Å is shorter than this average value, it is
important to keep in mind that there are additional nearby ammonium groups in the
Figure 4.9: RMSD curve as a function of 1H-2H distances.
70

4.3. Results and Discussion
lattice that will also contribute to the dephasing in the 1H{2H} RESPDOR experiments, explaining why the measured distance is shorter than the average distance
seen in the DFT optimized crystal structure. In summary, the 1H{2H} RESPDOR
experiments are consistent with the proposed crystal structure of (1-MQ)(1-NA)Pb2I6
that shows ordering of the 1-NA and 1-MQ positions in the lattice that results in the
hydrogen atoms of the methyl and ammonium groups separated by 4.45 Å on average.
Figure 4.10: Crystal structures of (1-NA)PbI3, (1-MQ)(1-NA)Pb2I6, and (1-
MQ)PbI3, with dipole vectors projected.
Solid-state NMR confirmed that the 1-NA and 1-MQ cations are indeed packed
within the same crystal structure and are ordered. However, this method does not
confirm the specific positions of the 1-NA and 1-MQ cations. In order to rationalize
the final packing configuration shown in Figure 4.1, we projected the dipole moments
of 1-NA and 1-MQ onto the structures, as shown in Figure 4.10. The dipole strengths
of 1-NA and 1-MQ are 7.98 D and 2.47 D, respectively. Due to the significantly larger
dipole moment of 1-NA, it is reasonable to assign 1-NA to cationic positions where
their dipoles would cancel out in short proximity. In contrast, the 1-MQ cations, with
weaker dipole moments, are assigned to positions where there is a net dipole moment
within the (00l) planes.
71

4.3. Results and Discussion
The octahedral distortion in (1-MQ)(1-NA)Pb2I6 is also nicely contrasted to that
of the octahedral distortion in (1-MQ)PbI3. As illustrated in Figure 4.10, there is a
stronger net dipole moment within the (00l) plane in (1-MQ)PbI3, resulting in a larger
octahedral distortion compared to (1-MQ)(1-NA)Pb2I6. As for (1-NA)PbI3, we can
observe that the dipole moment of 1-NA cations are cancelled out immediately with
its neighboring cations. The tendency of 1-NA cations to have dipole cancellation
in close proximity, compared to 1-MQ cations, as illustrated with the end-member
hybrids (1-MQ)PbI3 and (1-NA)PbI3, further supports our designation of the 1-MQ
and 1-NA cations in (1-MQ)(1-NA)Pb2I6.
Figure 4.11: Band structures and DOSs of (a) (1-NA)PbI3, (b) (1-MQ)(1-NA)Pb2I6,
and (c) (1-MQ)PbI3.
72

4.3. Results and Discussion
4.3.2 Optoelectronic Properties
Based on the DOS and band diagram data, it is evident that (1-MQ)(1-NA)Pb2I6 and
(1-MQ)PbI3 have similar conduction band characteristics, as shown in Figures 4.11b
and c. Both materials display an isolated band with organic character, contrasting
with the continuous nature of the bands seen in (1-NA)PbI3, as illustrated in Figure
4.11a. These isolated bands correspond to the LUMO energy of the 1-MQ cation. Due
to the higher LUMO energy of 1-NA cation, it does not contribute to the conduction
band minimum (CBM) of (1-NA)PbI3. Additionally, the bands in all three systems
are quite flat and do not display much dispersion.
Figure 4.12: Charge density projections of (1-NA)PbI3, (1-MQ)(1-NA)Pb2I6, and
(1-MQ)PbI3 at the VBM and CBM.
Charge density projections visualized using VESTA clearly delineate the electronic differences at the band edge between the materials. Figure 4.12 shows the
projected charge densities for (1-NA)PbI3, (1-MQ)(1-NA)Pb2I6, and (1-MQ)PbI3 at
73

4.3. Results and Discussion
their respective CBM and valence band maximum (VBM). For (1-NA)PbI3, the charge
density is localized around the inorganic portion of the system at the band edges. In
contrast, for (1-MQ)PbI3, the charge density shifts from the inorganic octahedra at
the VBM to the π-orbitals of the 1-MQ cations at the CBM. The (1-MQ)(1-NA)Pb2I6
system exhibits electronic properties very similar to (1-MQ)PbI3. The VBM displays
inorganic character around all octahedra and the CBM displays organic character
Figure 4.13: Pawley fits of (a) (1-NA)PbI3, (b) (1-MQ)PbI3, and (c) (1-MQ)(1-
NA)Pb2I6 powder XRD patterns, with Rwp values of 3.7%, 2.8% and 4.6%, respectively. (d) Powder XRD pattern of (1-MQ)(1-NA)Pb2I6 with fast-cooling synthesis.
74

4.3. Results and Discussion
localized around the 1-MQ cations. This phenomenon aligns with the lower LUMO
energy of the 1-MQ cation compared to the 1-NA cation.
(1-NA)PbI3, (1-MQ)(1-NA)Pb2I6, and (1-MQ)PbI3 were synthesized in powder
form to further characterize the properties of the hybrid systems. Powder XRD was
performed on all three hybrids to assess the phase purity of each material. Pawley
Figure 4.14: XRD of (a) (1-NA)PbI3, (b) (1-MQ)(1-NA)Pb2I6, and (c) (1-MQ)PbI3
films.
75

4.3. Results and Discussion
fittings of the powder XRD patterns for (1-NA)PbI3, (1-MQ)PbI3, and (1-MQ)(1-
NA)Pb2I6 (Figure 4.13), indicate that the bulk products are pure single-phase materials. However, (1-MQ)(1-NA)Pb2I6 can only be synthesized in small amounts as
slow crystallization is required to ensure phase purity. It was found in previous (1-
MQ)(1-NA)Pb2I6 powder synthesis that fast cooling results in phase segregation into
(1-MQ)(1-NA)Pb2I6 and (1-MQ)PbI3, as shown in Figure 4.13d. This phase segregation is particularly evident at approximately 7.5◦and 11◦
, where three distinct XRD
reflections are observed.
Spin-coated films were also fabricated to investigate the optoelectronic properties
of the hybrid materials. XRD patterns of (1-NA)PbI3 and (1-MQ)PbI3 indicate phase
purity, whereas the XRD pattern of the (1-MQ)(1-NA)Pb2I6 system reveals phase
segregation. The presence of both (1-MQ)(1-NA)Pb2I6 and (1-MQ)PbI3 in the film
is clearly observed due to the three distinct XRD peaks around 11◦
, as illustrated in
Figure 4.14b. This is likely due to using the fast-cooled (1-MQ)(1-NA)Pb2I6 powder in
making the precursor solution. Due to the limited amounts of phase-pure (1-MQ)(1-
NA)Pb2I6, we were unable to fully characterize the material, as we will demonstrate
for the end members in the subsequent sections.
Figure 4.15: Absorption of (1-NA)PbI3 and (1-MQ)PbI3 films, normalized at their
respective excitonic absorption peak.
76

4.3. Results and Discussion
UV-vis absorption data for (1-NA)PbI3 and (1-MQ)PbI3 films, shown in Figure 4.15, reveal higher excitonic absorption energy of (1-NA)PbI3 (383 nm/3.24 eV)
compared to (1-MQ)PbI3(405 nm/3.06 eV). This observation aligns with the relative
band gap energies calculated (Figure 4.11), where (1-NA)PbI3 has a larger band gap
compared to (1-MQ)PbI3.
Figure 4.16: Temperature-dependent emission of (a) (1-NA)PbI3 and (b) (1-
MQ)PbI3 films. The films were excited at 365 nm.
The different electronic behaviors of (1-NA)PbI3, (1-MQ)(1-NA)Pb2I6, and (1-
MQ)PbI3 observed in the computational data are reflected in their temperaturedependent emission properties. For the (1-NA)PbI3 film (Figure 4.16a), we observe
an increase of emission intensity as the temperature decreases. Below 40 K, the broad
emission peak begins to red-shift, accompanied by an emergence of a triplet emission.
This results in a final broad emission centered around 640 nm, and a more intense
triplet emission at approximately 500 nm. As shown in Figure 4.17a, the triplet
emission starts emerging at higher temperatures for the powder emission data (taken
by Dr. Megan Cassingham). It is also more pronounced at 3 K compared to the
film emission data, likely due to the larger amount of material probed in the powder
emission experiment.
77

4.3. Results and Discussion
In contrast, the (1-MQ)PbI3 system does not exhibit triplet emission. Instead, it
shows a broad emission centered around 606 nm, with minor energy shifts across the
temperature range studied, as illustrated in Figure 4.16b. Additionally, the emission
intensity of the (1-MQ)PbI3 film peaks at 65 K and decreases as the temperature
continues to drop. In comparison, the powder emission data taken by Dr. Megan
Cassingham (Figure 4.17c), peaks at a slightly lower temperature of 60 K, and exhibits
more energy shifting. This slight discrepancy could be due to the different sample
setups between the powder and film emission experiments.
Figure 4.17: Temperature-dependent powder emission of (a) (1-NA)PbI3, (b) (1-
MQ)(1-NA)Pb2I6, and (c) (1-MQ)PbI3. The powders were excited at 365 nm.
78

4.3. Results and Discussion
The temperature-dependent powder emission of (1-MQ)(1-NA)Pb2I6 reveals a
unique combination of emission profiles observed in (1-NA)PbI3 and (1-MQ)PbI3.
The 508 nm emission feature starts emerging at 50 K and continues to increase in
intensity as the temperature decreases. This is reminiscent of the triplet emission feature observed in (1-NA)PbI3, albeit emerging at a lower temperature and not vibronic
in nature. The more prominent broad emission feature is centered around 612 nm,
and red-shifts to a wavelength of 625 nm at higher temperatures. Moreover, the
emission intensity peaks at 5 K before decreasing at higher temperatures. The broad
emission energy and temperature-dependent behavior resemble that of (1-MQ)PbI3.
Figure 4.18: Integrated intensities of (a) (1-NA)PbI3, (b) (1-MQ)(1-NA)Pb2I6, and
(c) (1-MQ)PbI3 emission spectra as a function of temperature.
79

4.3. Results and Discussion
In Figure 4.18, the emission spectra of each hybrid is integrated and plotted as
a function of temperature to better visualize the temperature-dependent emission
behaviors of the hybrids. From 3.6 to 50 K, the integrated intensity of (1-MQ)(1-
NA)Pb2I6 peaks at 5 K before dropping as the temperature increases, resulting in a
curve similar to that of (1-MQ)PbI3. At temperatures higher than 50 K, the integrated intensity of (1-MQ)(1-NA)Pb2I6 decreases with increasing temperature before
plateauing, similar to the behavior observed for (1-NA)PbI3. These plots illustrates
that the temperature-dependent emission behavior of (1-MQ)(1-NA)Pb2I6 is a combination of its end members.
Figure 4.19: Emission and excitation spectra of (a) (1-NA)I and (b) (1-MQ)I in
2-methylTHF at 77 K.
To better understand the differences in emission properties of the hybrids, the
organic salts were also investigated. Figure 4.19 shows the emission and excitation
spectra of the (1-NA)I and the (1-MQ)I salts in 2-methylTHF at 77 K. Both (1-
NA)I and (1-MQ)I salts show triplet emission centered around 510 nm. The triplet
emission of (1-NA)I aligns with the triplet emission observed in (1-NA)PbI3, confirming that the triplet emission originates from the organic cation 1-NA. Interestingly,
despite observing triplet emission in (1-MQ)I, this triplet emission is absent in the
(1-MQ)PbI3 system.
80

4.3. Results and Discussion
Figure 4.20: Dielectric measurements of (a) (1-NA)PbI3 and (b) (1-MQ)PbI3 pellets, collected from 2 to 300 K.
Figure 4.21: Dielectric measurements of (a) (1-NA)PbI3 and (b) (1-MQ)PbI3 pellets, collected from 300 to 2 K.
The temperature-dependent emission behavior of (1-NA)PbI3 and (1-MQ)PbI3
can be correlated to the capacitance and dielectric loss data (Figures 4.20 and 4.21).
Unfortunately, we were unable to conduct dielectric measurements on (1-MQ)(1-
NA)Pb2I6 due to the limited amounts available. (1-NA)PbI3 shows a frequencydependent dielectric loss feature at 95 K, indicating a rigidity change in the organic
81

4.3. Results and Discussion
cation. This corresponds to the onset of the triplet emission at 100 K observed in the
(1-NA)PbI3 powder emission data (Figure 4.17a).
On the other hand, the capacitance and dielectric loss of (1-MQ)PbI3 exhibit a
feature-less frequency dependence characteristic of a dielectric material, which can be
attributed to thermal contraction during cooling. Additionally, (1-MQ)PbI3 shows
a higher overall dielectric loss compared to (1-NA)PbI3, likely due to the smaller
bandgap. Both the cooling and warming traces are effectively identical, with random
fluctuations between points reflecting vibrations of the sample holder and wires.
The difference in the emission properties of the two end-member hybrids is likely
attributed to the differing LUMO energies of the two organic cation species. For (1-
NA)PbI3, the LUMO of 1-NA is higher than the CBM. At room temperature, while
there is a possibility for electrons to excite to the triplet states, they quickly relax
down to the CBM before radiatively decaying to the ground state. As the hybrid
system cools, the pathways for non-radiative decay decrease due to the reduction of
molecular and phonon vibrations, leading to an increase of emission intensity. At
temperatures below 100 K, the energy to depopulate the triplet states decreases,
resulting in the onset of triplet emission.
In the case of (1-MQ)PbI3, the LUMO of 1-MQ is isolated and lower in energy
than the rest of the conduction band. At room temperature, the electrons excite from
the VBM into the LUMO of 1-MQ. As the (1-MQ)PbI3 system cools, the reduction
in molecular and phonon vibrations leads to an increase of emission intensity. At
temperatures below than 65 K, we hypothesize that the LUMO of 1-MQ acts as a
trap state, reducing the radiative decay of the hybrid.
82

4.4. Summary
4.4 Summary
In summary, we have decisively demonstrated that the organic cations in (1-MQ)(1-
NA)Pb2I6 pack in an ordered fashion, as evidenced by both single crystal X-ray and
solid-state NMR techniques. The large difference in the dipoles of the 1-NA and 1-MQ
cations gives rise to minor variations in the lead sites, and is likely contributing to
the ability to overcome entropy and avoid random packing. This material is the first
of its kind, showcasing the potential to further explore this space and target stronger
donor–acceptor pairs to create more interesting charge transfer characteristics.
Additionally, the optical properties of these materials highlight the significant role
that the organic cation plays in contributing to the electronic structure. Despite 1-
NA and 1-MQ being very structurally similar, the differences in their dipole energies
and their LUMO energies greatly impact the emission profile of each hybrid material.
The charge density at the CBM dictates the emission state of the systems.
83

4.5. Supplemental Information
4.5 Supplemental Information
4.5.1 Material Characterization
1H NMR of 1-methylquinolinium iodide (1-MQ)I salt
1H NMR (400 MHz, DMSO-d6) δ 9.49 (ddt, J = 5.8, 1.6, 0.8 Hz, 1H), 9.27 (m,
1H), 8.48 (m, 2H), 8.28 (ddd, J = 8.8, 7.0, 1.5 Hz, 1H), 8.16 (dd, J = 8.4, 5.8 Hz,
1H), 8.05 (ddd, J = 8.1, 7.0 1.0 Hz, 1H), 4.63 (d, J = 0.6 Hz, 3H)
84

4.5. Supplemental Information
Table 4.1: Crystallographic data for single crystal structure determination of (1-
MQ)PbI3.
Parameter (1-MQ)PbI3
Chemical formula C10H10NPbI3
Formula weight 732.08
Temperature (K) 100
Crystal system orthorhombic
Space Group P bca
a 14.7847 (2)
b 8.03690 (10)
c 25.4893 (4)
Volume 3028.72(7)
Z 8
CA (0.57490, 0.95400, 0.33850)
HA (0.55799, 1.01727, 0.36738)
CB (0.55740, 0.79600, 0.43750)
HB (0.59751, 0.88419, 0.44748)
HC (0.54993, 0.72062, 0.46649)
HD (0.49975, 0.84121, 0.42790)
CC (0.66150, 0.52200, 0.30690)
HE (0.68410, 0.46336, 0.27821)
C5 (0.62930, 0.69700, 0.29920)
N6 (0.59660, 0.70380, 0.39190)
C9 (0.62570, 0.55200, 0.39560)
H9 (0.62526, 0.50645, 0.42911)
C10 (0.65870, 0.44500, 0.35440)
H10 (0.67609, 0.33488, 0.35983)
C11 (0.63070, 0.76300, 0.24980)
H11 (0.65031, 0.70249, 0.22093)
C12 (0.60060, 0.93000, 0.24540)
H12 (0.59730, 0.98071, 0.21269)
C14 (0.57580, 1.01600, 0.29080)
H14 (0.55860, 1.12682, 0.28690)
C24 (0.60170, 0.78000, 0.34400)
I2 (0.31778, 0.80615, 0.51178)
I3 (0.42038, 0.31652, 0.41206)
I4 (0.34122, 0.80822, 0.33879)
Pb1 (0.24977, 0.56038, 0.4207)
Rint 0.064
85

4.5. Supplemental Information
Table 4.2: Crystallographic data for single crystal structure determination of (1-
MQ)(1-NA)Pb2I6.
Parameter (1-MQ)(1-NA)Pb2I6
Chemical formula C20H18N2Pb2I6
Formula weight 732.08
Temperature (K) 100
Crystal system orthorhombic
Space Group P bca
a 7.87499(18)
b 24.7657(7)
c 31.1618(9)
Volume 6077.5(3)
Z 13
Pb1 (0.86504, 0.37992, 0.25032)
I2 (0.61947, 0.29268, 0.20825)
Pb3 (0.50000, 0.50000, 0.00000)
Pb4 (0.00000, 0.50000, 0.00000)
I5 (0.61385, 0.47081, 0.21116)
I6 (1.10809, 0.37399, 0.16862)
I7 (0.25089, 0.41721, 0.04706)
I8 (0.75227, 0.51410, 0.08092)
I9 (0.25052, 0.59232, 0.03370)
C15 (0.60810, 0.31040, 0.09250)
N10 (0.63530, 0.36650, 0.10310)
H15A (0.66455, 0.38657, 0.07703)
H15B (0.72831, 0.36941, 0.12385)
86

4.5. Supplemental Information
Table 4.2 – continued from previous page
Parameter (1-MQ)(1-NA)Pb2I6
H15C (0.53137, 0.38152, 0.11562)
C20 (0.46600, 0.28370, 0.10090)
H20 (0.37689, 0.30407, 0.11380)
C11 (1.01200, 0.27880, 0.04360)
H11 (1.11576, 0.29622, 0.03661)
C13 (0.85250, 0.19590, 0.04380)
H13 (0.84333, 0.15830, 0.03814)
C1 (0.89010, 0.30750, 0.06220)
H1 (0.90383, 0.34501, 0.06771)
C21 (0.73900, 0.28000, 0.07340)
C23 (0.56500, 0.20020, 0.07400)
H23 (0.55093, 0.16280, 0.06843)
C26 (0.71660, 0.22620, 0.06360)
C36 (0.43100, 0.23030, 0.09320)
H36 (0.32502, 0.21441, 0.10013)
C18 (0.99400, 0.22450, 0.03380)
H18 (1.08455, 0.20655, 0.01953)
N9 (0.19000, 0.55750, 0.16330)
C7 (0.26890, 0.51420, 0.13830)
H9A (0.31024, 0.52792, 0.11333)
H9B (0.19019, 0.48837, 0.13246)
H9C (0.35546, 0.49945, 0.15373)
C3 (0.28660, 0.60530, 0.16740)
C2 (0.45040, 0.61420, 0.15080)
87

4.5. Supplemental Information
Table 4.2 – continued from previous page
Parameter (1-MQ)(1-NA)Pb2I6
H2 (0.50755, 0.58677, 0.13511)
C6 (0.03920, 0.54900, 0.17990)
H6 (-0.01624, 0.51534, 0.17597)
C8 (0.52600, 0.66360, 0.15770)
H8 (0.63690, 0.67005, 0.14684)
C12 (0.28990, 0.69530, 0.19560)
H12 (0.23494, 0.72385, 0.21047)
C4 (0.44470, 0.70370, 0.18000)
H4 (0.49894, 0.73756, 0.18428)
C5 (-0.04100, 0.59110, 0.20410)
H5 (-0.14941, 0.58543, 0.21666)
C16 (0.03810, 0.63810, 0.20890)
H16 (-0.01625, 0.66642, 0.22421)
C17 (0.20570, 0.64670, 0.19110)
Rint 0.0495
88

4.5. Supplemental Information
4.5.2 Solid State NMR
Table 4.3: Information on the distance between methyl hydrogen and ammonium
hydrogen atoms in 1-NA and 1-MQ in the optimized crystal structure.
Label Distance (Å) Label Distance (Å)
pa 5.27 pd 4.53
pb 3.93 pe 5.85
pc 4.78 pf 5.08
qa 4.38 qd 6.22
qb 3.51 qe 7.60
qc 3.96 qf 6.73
ra 5.05 rd 5.71
rb 4.08 re 7.05
rc 5.10 rf 6.58
Averages 4.45 6.15
89

4.5. Supplemental Information
Table 4.4: Experimental solid-state NMR parameters.
Figure NMR
B0(T) MAS
τ rec.delay # of scans X. sat X RF field Dip. recpl. Expt.
expt. (kHz) (s) scans pulse (
µs) (kHz) t/(ms) t (h)
4.2a
1H Spin echo 9.4 50 4.23 64 - - - 0.08
4.2b
1H Spin echo 9.4 50 25.1 64 - - - 0.45
4.2c
1H Spin echo 9.4 50 8.97 64 - - - 0.16
4.2d 207Pb Spin echo 9.4 50 0.5 20480 - - - 2.8
4.4a 207Pb Spin echo 9.4 50 0.5 20480 - - - 2.8
4.4b 207Pb Spin echo 9.4 50 0.5 61440 - - - 8.5
4.4c
1H14N DHMQC 9.4 50 9.23 - 20 62.1 1.28 5.3
4.7a
2H Spin echo 9.4 20 0.1 112640 - - - 3.1
4.7b
1H2H DE-RESPDOR 9.4 50 9.23 64 30 107.5 2.4 0.33
4.8a
1H2H DE-RESPDOR 9.4 50 9.23 64 30 107.5 variable 2.6
90

Chapter 5
Multipurpose Electrical Probe and Optical Probe
Designs for the PPMS
5.1 Introduction
The Quantum Design Physical Properties Measurement System (PPMS) Dynacool
is an open-architecture, variable temperature–field system capable of performing a
variety of automated measurements. Our particular model features a 14 T magnet and
a closed-loop helium (He) compressor, which eliminates the need of liquid cryogens
and recycles the He used to cool down the system to sub-zero Kelvin temperatures,
significantly reducing He consumption. The PPMS offers continuous low-temperature
control (below 4.2 K) and precise field and temperature sweep modes. Importantly,
this system can be easily adapted to custom user experiments, making it ideal for the
work presented in this thesis.
Dielectric and photophysical measurements are a throughline across the chapters
of this thesis, as the combination of these measurements elucidates the optoelectronic
properties of the hybrid metal halide materials studied. This chapter presents the
work done in designing and testing two custom-built probes: a multipurpose electrical
probe and an optical probe.
The multipurpose electrical probe was designed for electrical measurements such
as dielectric and Hall effect measurements on various sample types. The first half of
this chapter outlines the three iterations of the electrical probe design and the tests
performed to validate each design.
91

5.2. Multipurpose Electrical Probe
The latter half of this chapter focuses on the two optical probe designs in which I
was involved in designing and testing. While previous optical probe designs were made
by former graduate students, this work presents the most up-to-date design for the
optical probe. This optical probe was designed to measure emission and excited state
lifetimes of various materials in a film structure. This section details the improvements made over the two iterations of optical probe design and the photophysical
measurements conducted on several materials to validate these designs.
5.2 Multipurpose Electrical Probe
The multipurpose electrical probe is designed for various electrical measurements with
different sample setups. It was used for all the dielectric measurements presented in
this thesis. Additionally, the probe can be perform Hall effect measurements on
various sample types. This work is done in close collaboration with Prof. Brent
Melot.
5.2.1 Design of Multipurpose Electrical Probe
The customized probe for electrical measurements is shown in Figure 5.1. The top
of the probe features four female SMA connectors, each attached to a stainless steel
coxial cable (LakeShore). These cables run along a plastic rod, ending in a Cu cage
that houses the customized sample stage holders. The stainless steel coxial cables help
to prevent electrical signal interference and cross-talk, which is crucial for obtaining
high quality signals in sensitive measurements such as dielectric measurements. The
plastic rod is chosen to minimize thermal conductivity, allowing the chamber and
sample to reach sub-zero Kelvin temperatures.
92

5.2. Multipurpose Electrical Probe
Figure 5.1: Electrical probe used for dielectric and Hall effect measurements in the
PPMS. (a) Whole probe, showing four stainless steel coaxial cables running down the
plastic rod. (b) Top of the probe with four female SMA connectors. (c) Bottom of
the probe, featuring a Cu cage with a CNC-milled printed circuit board (PCB).
5.2.2 Sample Stage Designs for Dielectric Measurements
Parallel plate capacitors made of the material of interest are used to carry out dielectric measurements. Measurements were taken from 2 or 10 to 300 K at frequencies of
1, 2, 5, 10, and 20 kHz. The sample temperature was controlled by using a Quantum
Design PPMS Dynacool. The dielectric measurements were taken using an AndeenHagerling 2700A 50 Hz–20 kHz Ultra-Precision Capacitance Bridge.
The capacitance, C of a parallel plate capacitor with area A and electrode plate
separation d is defined as:
C = ε0εr
A
d
where ε0 is the permittivity of vacuum, 8.5 × 10−12 F/m, and εr is the relative
permittivity or dielectric constant of the material.
For all dielectric sample stage designs, the materials probed for their dielectric
properties were pressed into pellets. In our first iteration of the dielectric sample
stage design (Figure 5.2a), we applied Ag epoxy (Electron Microscopy Sciences) to
93

5.2. Multipurpose Electrical Probe
Figure 5.2: The first sample stage setup for dielectric measurements. (a) Whole
dielectric sample stage setup. Each face of the capacitor is connected to a stainless
steel coaxial cable by soldering the insulated Cu wire to the PCB. (b) Capacitor
sample with insulated Cu attached to both faces of the pellet using Ag epoxy.
both sides of a pressed pellet. The Ag epoxy served as the electrode plates for the
capacitor and was used to attach an enameled Cu wire on either side of the capacitor,
as illustrated in 5.2b. The other end of the Cu wire was then soldered onto a connector
pin that is connected to a coaxial cable. This sample setup was used for the dielectric
measurements collected for (MDA)Pb2I6 and (MDA)Pb2Br6, as shown in Figure 6.6.
In this design, the Ag epoxy was found to occasionally react with the hybrid
material, introducing impurities to the pellet and making the data collected unreliable. There were also large random fluctuations between data points, which are
attributed to the vibrations of the sample holder and wires. Subsequent sample stage
setup were designed to address these issues.
In the second setup, two single-sided Cu printed circuit boards (PCBs) were CNCmilled, with pogo pins and probe pins soldered on, creating a sandwich setup as shown
in Figure 5.3. Approximately 200 nm of Al was vapor deposited on both faces of the
pressed pellet using vacuum thermal evaporation (VTE), serving as the electrode
plates of the capacitor. EPDM gaskets were used to center the pellet and ensure even
94

5.2. Multipurpose Electrical Probe
Figure 5.3: (a) The second sample stage setup for dielectric measurements, comprising top and bottom CNC-milled copper PCBs. Each PCB has a soldered pogo pin
acting as an electrical contact to the Al-coated faces of the pellet, shown in the right
figure. The pellet is centered with an EPDM gasket. (b) The assembled dielectric
setup, shown with (left) and without (right) the EPDM gasket.
pressure distribution when the setup was sandwiched together. Pogo pins were used
as electrical contacts to the coaxial cables, maintaining a closed circuit throughout
the temperature range probed.
This design circumvents the reactivity issues caused by the Ag epoxy. However,
due to the lack of stability and the narrow pogo pins, electrical contact is often lost
during measurement. This occurred because the pogo pins scratched off the deposited
Al on the pellet or the pellet broke due to excessive pressure.
A Ni disk was placed in between the pogo pin and the pellet to alleviate some
of the pressure, and the data collected with this setup is shown in Figure 5.4. This
improved the electrical connection throughout the temperature range measured, but
random fluctuations between data points persisted, potentially masking capacitance
or dielectric loss features. Additionally, the pellet frequently broke with this setup,
making it difficult to repeat dielectric measurements to ensure data consistency. Note
95

5.2. Multipurpose Electrical Probe
Figure 5.4: Dielectric measurements of (1-MQ)(1-NA)Pb2I6 pellets using the second
sample stage setup. (a) Collected on warming, from 10 to 300 K. (b) Collected on
cooling, from 300 to 10 K.
that the (1-MQ)(1-NA)Pb2I6 hybrid pellet used in Figure 5.4 was determined to be
not phase pure. This data set is shown purely to demonstrate the effectiveness of this
dielectric sample stage setup.
Figure 5.5: The third sample stage setup for dielectric measurements. Two copper
plungers serve as electrodes for the sample, with a compresssion spring ensuring
electrical contact across the temperature range. The sample stage is connected to the
probe by soldering the coaxial cables to the copper plungers.
96

5.2. Multipurpose Electrical Probe
For the final iteration of the dielectric sample stage setup, a sample holder made
of PEEK plastic was CNC-milled to house the hybrid pellet, as illustrated in Figure
5.5. Approximately 200 nm Al was vapor deposited on both faces of the pellet to act
as electrode plates, similar to the second dielectric setup. CNC-milled Cu plungers
was used as electrical contacts instead of pogo pins. The Cu plungers had a larger
contact surface area to the pellet, improving electrical contact and preventing the
pellet breaking easily under pressure. A coaxial cable was soldered to the other
end of the Cu plunger. The top Cu plunger consists of two separate pieces with a
compression spring in between them, which maintains electrical contact throughout
the temperature range as the materials expand/contract during warming/cooling.
Figure 5.6: Dielectric measurements of (1-MQ)(1-NA)Pb2I6 pellets using the third
sample stage setup. (a) Collected on warming, from 2 to 300 K. (b) Collected on
cooling, from 300 to 2 K.
For comparison, the dielectric data collected for the (1-MQ)(1-NA)Pb2I6 pellet
using this third setup is presented in Figure 5.6. The data shows markedly reduced
fluctuations, with clear capacitance and dielectric loss features. Note that this (1-
MQ)(1-NA)Pb2I6 pellet was also not phase pure, and the data set is presented solely
to demonstrate the improvements made with this third dielectric sample stage setup.
97

5.2. Multipurpose Electrical Probe
However, the random fluctuations persists in other data sets (Figure 4.20 and 4.21).
Thus, further improvements to this dielectric setup to reduce vibrations from the
setup are still necessary.
One improvement that has been implemented, but not presented in this thesis, is
the connection between the coaxial cable and the Cu plunger. This connection is now
made by threading the wire onto the plunger. The Cu plungers are threaded, and a
ring terminal is crimped onto the ends of the coaxial cable. The two are connected by
screwing on a hex nut, ensuring cleaner data collection due to the absence of solder.
5.2.3 Design of Chip for Four-Point Hall Measurements
The Hall effect was used to characterize the electronic transport properties of materials, such as resistivity, carrier mobility, and carrier density. The sample stage setups
were designed for a van der Pauw sample geometry, with the samples being either
a pellet or film. The electronic transport properties were measured using Keithley instruments: 7001 Switch System, 6517B Electrometer/High Resistance Meter,
2182A Nanovoltmeter, and 6220 Precision Current Source.
For the first Hall effect sample stage setup, Cu wires were attached to the four
corners of the sample using Ag conductive adhesive (478SS, Electron Microscopy
Sciences). The other end of the Cu wire was soldered to the four probe pins on
a CNC-milled PCB, as shown in Figure 5.7b. Each probe pin was connected to a
stainless steel coaxial cable, which was then connected to the Keithley instruments.
A similar reactivity issue arose with the Ag conductive adhesive, where it was
sometimes found to react with the hybrid metal halide samples. This reactivity was
exacerbated when a film sample is used instead of a pellet. If the Ag adhesive reacts
with the hybrid material, an electrical connection could not be established due to
the degradation of the sample around the Ag adhesive. Moreover, the Cu wires often
98

5.2. Multipurpose Electrical Probe
Figure 5.7: The first sample stage setup for Hall effect measurements. (a) Whole
Hall effect sample stage setup. The sample stage is connected via probe connector
pins soldered onto the PCB. (b) Close-up of Hall effect sample stage setup. Cu wires
are attached to four points of the hybrid pellet using an Ag adhesive. The Cu wires
are then soldered to the four pins.
broke off due to the fragile connection of the Ag adhesive. The next iteration moved
away from using Ag adhesive as a connection to overcome these issues.
In the second Hall effect sample stage setup, pogo pins were used to establish the
four electrical contacts required for a van der Pauw sample geometry. A sandwich
configuration consisting of two CNC-milled PCBs and eight pogo pins was designed, as
illustrated in Figure 5.8. The pogo pins and the Cu traces on the PCBs established a
connection from the four corners of the sample to the four coaxial cables on the probe.
Pogo pins were chosen to maintain a closed circuit throughout the temperature range
measured, accommodating the thermal contraction and expansion of the materials.
However, due to the narrow pogo pins used, the pellet samples often broke, or
the film sample were scratched by the pins, causing an open circuit. Additionally,
the hybrid materials investigated in this thesis were too insulating, resulting in poor
electrical signal from both Hall effect sample stage setups. Further improvements on
this Hall effect sample stage setup should be pursued using more conductive samples.
99

5.3. Optical Probe
Figure 5.8: The second sample stage setup for Hall effect measurements. (a) Assembled Hall effect sample stage setup with a hybrid pellet. (b) Projection and crosssectional view of the sample stage setup.
5.3 Optical Probe
The optical probe was developed through a collaboration between the labs of Prof.
Mark Thompson and Prof. Brent Melot. Our objective was to design a probe capable
of collecting emission and lifetime measurements in the PPMS.
Conducting photophysical measurements in the PPMS offers several advantages.
Its cooling system, a closed-loop He compressor, consumes significantly less liquid He
compared to the cryostat setup previously used in the lab. This system efficiently
100

5.3. Optical Probe
cools the chamber to sub-zero Kelvin temperatures. Additionally, the PPMS chamber features a superior and reliable temperature control system, ensuring that the
sample temperature is accurately equilibrated to the reported readout. Moreover,
the PPMS chamber offers the opportunity to probe emission and lifetime behavior as
a function of magnetic field, enabling a more comprehensive characterization of the
photophysical properties of a material.
5.3.1 Design of Optical Probe for Emission and Lifetime
Measurements
As aforementioned, this optical probe is the result of a collaboration between the labs
of Prof. Mark Thompson and Prof. Brent Melot. Numerous iterations of the optical
probe designs have been tested by previous graduate students, including Dr. JoAnna
Milam-Guerrero and Dr. Rasha Hamze.
The first design and experiments were conducted in close collaboration with Dr.
Savannah Kapper.121 This initial design laid the groundwork for subsequent improvements. The second design, along with the accompanying experiments, were conducted
independently, building on the foundation established by previous iterations.
One major issue with previous designs was that the light collection was insufficient
for the spectrometer to pick up a signal. This problem was significantly improved
by installing 2 mm diameter, 7-fiber optic bundles (Thorlabs, BF20LSMA01 and
BF20HSMA01). The larger diameter of the fiber bundles increased the amount of
light traveling from the LED light source to the spectrometer.
An illustration of the optical probe setup for emission collection is depicted in
Figure 5.9. A 375 nm LED light source (Thorlabs, M375F2) is connected via SMA
connections to two fiber optic bundles (Thorlabs, BF20HSMA01, High OH) that
run from the outside of the probe top to the Cu cage at the bottom of the probe.
101

5.3. Optical Probe
Figure 5.9: Schematic of the optical probe setup for emission collection.
The intensity of the LED light source is controlled using a LED driver (Thorlabs,
LEDD1B). The excitation light is then directed to the film sample with a polished
stainless steel mirror.
The light emitted by the film sample is collected from the edge of the substrate
using two fiber optic bundles (Thorlabs, BF20LSMA01, Low OH), which run from
the substrate to the outside of the probe top. The light is then passed through a
395 nm filter and finally to a spectrometer (Ocean Optics, OCEAN-HDX-UV-VIS).
102

5.3. Optical Probe
Figure 5.10: (a) Optical probe for emission and lifetime measurements in the PPMS.
(b) Close-up of the Cu cage with a film inserted. The image below shows 2 wt% facIr(ppy)3 in PS film under 375 nm excitation.
Excited state lifetimes were determined by the time-correlated single-photon counting
method (TCSPC) using an IBH Fluorocube instrument.
Figure 5.10a shows the optical probe used for emission and lifetime measurements.
A close-up of the sample holder within the Cu cage is depicted in Figure 5.10b. The
image below shows 2 wt% fac-Ir(ppy)3 in polystyrene (PS) film emitting bright green
light, demonstrating sufficient excitation light traveling through the fiber bundles to
excite the sample. In the first probe design, the material of interest was doped at
2 wt% in PS films, which were drop-casted onto quartz substrates.
103

5.3. Optical Probe
Figure 5.11: (a) Temperature-dependent emission of 2 wt% MAC–Au–Cz in PS
film. (b) Integrated intensities of MAC–Au–Cz emission spectra as a function of
temperature. The inset shows the chemical structure of MAC–Au–Cz (dipp = 2,6-
diisopropylphenyl).
5.3.2 Photophysical Measurements with First Probe Design
MAC–Au–Cz was selected as one of the compounds to test using the new optical probe
setup, as previous studies on this compound were done using the old cryostat. 122
Temperature-dependent emission of 2 wt% MAC–Au–Cz in PS film using this setup
is presented in Figure 5.11a. The integrated intensities of MAC–Au–Cz emission are
plotted as a function of temperature in Figure 5.11b, revealing a significant drop in
emission intensity at 280 K. This drop is attributed to the PS film peeling off the
substrate due to the differential thermal contraction between the film and substrate.
The emission remained broad and featureless across the temperature range, with a
slight blue shift as the temperature decreased. This phenomenon is consistent with
hindered molecular rotation in the rigid matrix at lower temperatures. However,
the optical probe could only stabilize at temperatures as low as 40 K for emission
collection.
Another compound tested with the optical probe was fac-Ir(ppy)3. Figure 5.12a
illustrates the temperature-dependent emission of 2 wt% fac-Ir(ppy)3 in PS film.
104

5.3. Optical Probe
Figure 5.12: (a) Temperature-dependent emission of 2 wt% fac-Ir(ppy)3 in PS film.
(b) Integrated intensities of fac-Ir(ppy)3 emission spectra as a function of temperature.
The inset shows chemical structure of fac-Ir(ppy)3.
Similar to MAC–Au–Cz, a significant drop in emission intensity occurs at 260 K,
indicating that the PS film peeled off from the substrate. The emission profile becomes
more vibronic as the temperature decreases. Unfortunately, the optical probe could
not stabilize at temperatures below 25 K.
Figure 5.13: (a) Temperature-dependent lifetime of 2 wt% MAC–Au–Cz in PS film
taken using the PPMS (red dots) and cryostat (black squares). 122 (b) Temperaturedependent lifetime of 2 wt% MAC–Au–Cz in PS film taken using the PPMS with
two- and three-level fits.
105

5.3. Optical Probe
The temperature-dependent lifetime of 2 wt% MAC–Au–Cz in PS film was collected from 5 to 330 K and compared to the lifetime data collected using the old
cryostat,122 as shown in Figure 5.13a. At temperatures of 180 K and above, the
lifetime data collected using the PPMS align well with the cryostat data. However,
below 180 K, the PPMS lifetime data start to deviate, showing significantly longer
lifetimes. This deviation suggests that the previously tested sample was not effectively
cooled by the old cryostat, causing the actual sample temperature to be higher than
the cryostat readout. This temperature discrepancy would explain the significantly
shorter lifetimes reported using the old cryostat.
Dr. Savannah Kapper also fitted the PPMS lifetime trace with both a two- and
a three-level Boltzmann model (Figure 5.13). While the two-level model does not
fit the low-temperature lifetime data, the three-level model fits well across the entire
temperature range. Parameters such as the singlet–triplet energy gap can be derived
from the fit and are detailed in Dr. Savannah Kapper’s thesis. 121 These parameters
were found to be more reasonable than the previously reported data, further validating
the use of the optical probe in the PPMS for photophysical measurements.
5.3.3 Photophysical Measurements with Current Probe
Design
The major flaw in the previous optical probe design was its inability to stabilize at low
temperatures. This issue was traced to the use of aluminum as the material for the
probe, which is an excellent heat conductor. As a result, heat from the outside of the
PPMS chamber was conducted through the probe into the chamber, making it nearly
impossible to stabilize at temperatures below 25 K. This problem was remedied by
replacing the aluminum with stainless steel.
106

5.3. Optical Probe
Another improvement was the replacement of the quartz substrate with two sapphire substrates. Sapphire is a better heat conductor, ensuring that the film sample
cools down effectively. Thinner sapphire substrates were used so that they could
be sandwiched together, preventing the polymer-based films from peeling off the
substrate during cooling. For measurements with organometallic compounds, the
compound was doped at 2 wt% in PS films, which were drop-casted onto sapphire
substrates. In the case of hybrid lead halide films, they were spin-coated directly
onto the sapphire substrates. Additionally, the polished stainless steel mirror was
replaced with a UV-enhanced-aluminum-coated right-angle prism mirror (Thorlabs,
MRA10-F01) to improve the reflection of excitation light onto the film sample.
Figure 5.14: Temperature-dependent lifetime studies of fac-Ir(ppy)3 film. The lifetime data measured in the PPMS (gray and black triangles) are compared to lifetime
data measured in the new cryostat (pink diamond and red circle) and reported lifetime data by Yersin et al.
123 Both films for the PPMS and cryostat studies were made
using PS, while the film by Yersin et al. was made using PMMA.
107

5.3. Optical Probe
Temperature-dependent lifetime data of 2 wt% fac-Ir(ppy)3 in PS film was collected from 2 to 50 K using the updated optical probe and the PPMS. This PPMS
lifetime data is compared to the lifetime data collected using the new cryostat by Dr.
Anton Razgoniaev and Dr. Jonas Schaab, as well as the lifetime data published by
Yersin et al.,
123 presented in Figure 5.14. Notably, with the updated optical probe,
we were able to collect lifetime data at a lower temperature of 2 K, compared to the
previous lowest temperature of 5 K with the older design.
Compared to the lifetime data collected using the new cryostat, the PPMS lifetime data exhibits longer lifetimes at temperatures of 12 K and lower. Additionally,
the lifetime traces collected during the cooling down and warming up of the PPMS
chamber overlap perfectly, with no observable hysteresis. These behaviors highlight
the reliability of the PPMS temperature control system. The lifetime data reported
by Yersin et al.123 is longer compared to both the PPMS and cryostat data. This
discrepancy could be due to the different polymer matrix used in making the film
sample, as Yersin et al. used polymethyl methacrylate (PMMA) instead of PS, which
is used in our studies.
Figure 5.15: (a) Temperature sweep studies from 3 to 300 K at set magnetic fields
of -14, 0, and 14 T on 2 wt% fac-Ir(ppy)3 in PS film. (b) Magnetic field sweep study
on 2 wt% fac-Ir(ppy)3 in PS film at 3 K.
108

5.3. Optical Probe
With the updated optical probe, the system is now able to stabilize at temperatures as low as 3 K. Several magnetic field-dependent photophysical studies on 2 wt%
fac-Ir(ppy)3 in PS film were carried out with this updated probe.
While holding the magnetic field at -14 T, 0 T, and 14 T, the lifetime data of
2 wt% fac-Ir(ppy)3 in PS film were collected from 3 to 300 K. As shown in Figure
5.15a, the lifetime data in the presence of a magnetic field begin to deviate from the
lifetime data without a magnetic field at temperatures below 100 K. The strong 14 T
magnetic field significantly shortens the lifetimes of fac-Ir(ppy)3 at low temperatures.
At 3 K, the lifetime decreases from 127 µs at 0 T to 32 µs at ±14 T.
To further investigate the effect of magnetic field on the lifetime of fac-Ir(ppy)3,
the magnetic field was swept from 0 to 14 T in 1 T increments while the temperature is
held at 3 K. As shown in Figure 5.15b, the lifetimes decrease with increasing magnetic
field, exhibiting a sinusoidal behavior. This phenomenon indicates that the magnetic
field is altering the energy levels of the excited states, resulting in changes in lifetimes.
Figure 5.16: Magnetic field-dependent emission of 2 wt% fac-Ir(ppy)3 in PS film at
3 K.
The 3 K emission profile of 2 wt% fac-Ir(ppy)3 in PS film was collected at magnetic fields ranging from -14 to 14 T in 1 T increments, as shown in Figure 5.16.
109

5.3. Optical Probe
The emission intensities remain largely consistent across the different magnetic fields.
However, the emission profile changes slightly with the magnetic field, with the higher
energy feature at 515 nm becoming more prominent at higher magnetic fields.
The magnetic field clearly affects both the excited states lifetime and emission
profile of fac-Ir(ppy)3. While further analysis is needed to fully understand these
phenomena, these studies demonstrate the utility of using the PPMS to study the
photophysical properties of materials.
Figure 5.17: Temperature-dependent emission of (1-NA)PbI3 film from 10 to 40 K.
Figure 5.17 depicts the temperature-dependent emission of (1-NA)PbI3 film. The
broad emission feature centered around 685 nm increases in intensity as the temperature lowers, and at temperatures of 12 K and below, a triplet emission centered
around 500 nm is observed. The emission profile agrees well with the film and powder
data collected on the new cryostat (Figures 4.16 and 4.17). However, the emission
features are not as well resolved due to the low signal-to-noise ratio of the PPMS
110

5.3. Optical Probe
emission data. Moreover, the emission at temperatures above 40 K was too weak
to measure with the spectrometer, whereas the cryostat setup was able to measure
emission until 300 K.
Figure 5.18: (a) Temperature-dependent emission of (2-AEP)2PbI4 film from 10 to
50 K. (b) Detector sensitivity comparison by measuring the emission of (2-AEP)2PbI4
film at 4 K using the new cryostat setup.
Temperature-dependent emission of (2-AEP)2PbI4 films were also studied using
the updated optical probe setup and the PPMS, as shown in Figure 5.18a. The higher
energy emission centered around 550 nm exhibits vibronic character, with the intensity ratio between the two peaks reversing as the temperature lowers. Additionally,
a lower energy emission feature centered around 580 nm emerges as the temperature
decreases. This emission profile differs from the room temperature emission, which
is a broad emission peak at 554 nm (Figure 3.5). Similar to the (1-NA)PbI3 film,
the emission of (2-AEP)2PbI4 film was too weak to detect with the spectrometer at
temperatures above 50 K.
This is mainly due to the sensitivity difference between the detectors in the Ocean
Optics spectrometer and the Photon Technology International (PTI) QuantaMaster
spectrofluorometer. To test this difference, the emission of (2-AEP)2PbI4 film was
taken at 4 K using the new cryostat with both the Ocean Optics spectrometer and
111

5.4. Summary
the PTI spectrofluorometer (Figure 5.18b). The PTI detector collected an emission
intensity ten times higher than that of the Ocean Optics detector. Hence, due to the
difference in detector sensitivity, the PPMS emission data inherently have a lower
signal-to-noise ratio.
5.4 Summary
We successfully built two custom probe designs—a multipurpose electrical probe and
an optical probe—to perform various measurements in the PPMS. These probes were
instrumental in elucidating the optoelectronic properties of hybrid metal halide materials studied in this thesis. Additionally, the work done in designing these probes
expands the types of measurements that can be conducted in the versatile PPMS.
112

Chapter 6
Polarizable Anionic Sublattices Can Screen
Molecular Dipoles in Non-Centrosymmetric
Inorganic–Organic Hybrid
6.1 Introduction
To target materials for Objective 2, Dr. Megan Cassingham synthesized two 1D
hybrid lead halides containing 4,4-methylenedianiline (MDA), specifically in their
iodide and bromide analogs. Both phases crystallize in the non-centrosymmetric
space group Fdd2, where the MDA adopts a chevron-like configuration, creating a
macroscopic dipole running throughout the material. This configuration gives rise
to second harmonic generation (SHG) when excited at 1064 nm, with the bromide
analog exhibiting a stronger phase-matching response than the iodide analog. A
similar pattern is observed in the temperature-dependent emission of these materials,
where the bromide analog shows stronger emission than the iodide analog.
To better understand the polar nature of the materials and rationalize the observed
optical behavior, dielectric measurements were taken. There is a strong correlation
between the evolution of luminescence in the two phases and the features in the
dielectric loss. The dielectric loss features are attributed to the freezing of rotational
of degrees of freedom in the ammonium portion of the MDA cations, which leads to
an increase in emission intensity. The absence of structural transition features in the
dielectric data is unexpected, given the highly coherent alignment of molecular dipoles
113

6.2. Experimental
within the structure. We postulate that the polarizability of the halide sublattice acts
to screen the internal electric field created by the molecular dipoles.
This work and the corresponding publication124 were mainly carried out by Dr.
Megan Cassingham, with the dielectric measurements performed by myself. It showcases the unique combination of photophysical and dielectric measurements, providing
complementary insights into the optoelectronic properties of new hybrid materials.
This approach demonstrated its utility in characterizing new hybrid materials and
has been adopted for the other chapters in this thesis.
6.2 Experimental
6.2.1 Synthesis
The organic precursors, MDA·2HI and MDA·2HBr, were first prepared by dissolving
0.1 g (0.50 mmol) of MDA in 5 mL of acetone. 0.5 mL of 57 wt% (7.57 M) HI or
48 wt% (8.89 M) HBr was then added and stirred to combine. This solution was then
transferred to a glass Petri dish and placed on a warm hot plate to evaporate the
solvent.
Crystals of (MDA)Pb2I6 were grown following the procedure reported by Lemmerer and Billings.125 0.1 g (0.22 mmol) of lead (II) iodide (PbI2, 99.9985%, metals basis, Alfa Aesar) and 0.055 g (0.28 mmol) 4,4’-methylenedianiline (MDA, 97%,
Sigma Aldrich) were dissolved separately in 3 mL and 5 mL of hydroiodic acid (HI,
57 wt%, stabilized, Sigma Alrdich) in 2 dram and 8 dram scintillation vials, respectively. Each solution was stirred continuously while heating to 110 °C in an aluminum
bead bath placed atop a hot plate.
Once the solids were fully dissolved, the solution of lead iodide was added to that
of the MDA and stirred while continuing to heat. The solution was allowed to cool
114

6.2. Experimental
naturally to room temperature within the bead bath to encourage crystallization.
The resulting crystals were subsequently collected via vacuum filtration and rinsed
thoroughly with diethyl ether (≥98%, stabilized, VWR). To prevent any degradation
due to exposure to the atmosphere, samples were either stored in a dessicator or
Ar-filled glove box to minimize degradation due to atmospheric exposure.
The synthesis of (MDA)Pb2Br6 was adapted from the iodide with substituion of
lead (II) bromide (PbBr2, 99.998%, metals basis, Alfa Aesar) and hydrobromic acid
(HBr, 48 wt%, VWR). In contrast to the iodide, cooling to room temperature did not
result in crystallization, so diethyl ether was layered on top at room temperature and
allowed to sit for at least 24 hours. Attempts to make the chloride analog did not
yield an isostructural product and instead resulted in a slightly different polymorph,
which is further discussed in Dr. Megan Cassingham’s thesis. 95
6.2.2 Structure Determination
X-ray powder diffraction (XRD) was used to confirm the purity and composition of
(MDA)Pb2I6 and (MDA)Pb2Br6. Samples were ground using an agate mortar and
pestle and characterized with a Bruker D8 Advance powder diffractometer equipped
with a Cu-Kα source and LynxEye XE–T detector. Data was collected from 5 to 70◦
2θ angles with 0.02◦
step size and 1 s per step. High resolution synchrotron XRD
data was collected using the mail-in program at the 11-BM beamline at the Advanced
Photon Source (APS), Argonne National Laboratory. Discrete detectors covering an
angular range from -6 to 16◦ 2θ were scanned over a 34◦ 2θ range, with data points
collected every 0.001◦ 2θ and scan speed of 0.01◦ per s. The resulting patterns were
evaluated using the method of Rietveld refinement as implemented in the TOPASAcademic (v6)107 and GSAS-II software packages. 126 Figure 6.1 shows the results of
115

6.2. Experimental
the refinements as well as the Rwp values. Single crystal data for (MDA)Pb2Br6 was
collected using a Bruker APEX diffractometer with a CCD area detector.
6.2.3 DFT Calculations
Periodic DFT calculations were performed using the Vienna Ab initio Simulation
Package (VASP), 76–79 using the projector augmented wave method to describe the
interaction between core and valence electrons. 80 Density of states and band diagram
plots were visualized using sumo. 81 Pb 5d electrons were included in the valence, and
all pseudopotentials were scalar-relativistic. Due to the size of the unit cells, the functional of Perdew, Burke and Ernzerhof adapted for solids (PBEsol) 82 was used for
geometrical relaxation, while the Heyd, Scuseria and Ernzerhof (HSE06) 109,127 functional, with the explicit inclusion of spin-orbit coupling (HSE06+SOC), was used for
electronic structure calculations, including density of states and electronic band structure, performed using the PBEsol-relaxed structures. PBEsol and HSE06+SOC have
been previously demonstrated to be highly accurate in the prediction of structural
and electronic properties respectively of hybrid inorganic-organic materials. 128–130 The
total energy of both bromide and iodide compounds was found to be converged to
within 1 meV per atom using a plane wave energy cutoff of 400 eV, and a Γ-centred
k-point mesh of 4×4×4. Geometry optimization was considered converged when the
forces on each atom fell below 0.01 eV Å
−1
, and the planewave cutoff was increased
to 560 eV during relaxation to avoid Pulay stresses.
6.2.4 Photophysical Properties Measurements
Diffuse reflectance data was collected from 800–250 nm using a PerkinElmer
Lambda 950 UV-Vis-NIR spectrophotometer equipped with a 150 mm integrating
116

6.2. Experimental
sphere to determine the onset of absorption in powders diluted to 3 wt% in MgO and
to approximate the optical band gap using the Kubelka-Munk transform. 131
Approximately 2 g of both (MDA)Pb2I6 and (MDA)Pb2Br6 were ground and
sieved into distinct particle size ranges (<20, 20–45, 45–63, 63–75, 75–90, 90–125 µm)
for the phase matching experiment. The respective powders were transferred to individual quartz tubes and sealed for measurement. Relevant comparisons with known
SHG-active materials were made by grinding and sieving crystalline α-SiO2 and potassium dihydrogenphosphate (KDP) into the same particle size ranges. The samples
were excited using a Nd-YAG laser source with 1064 nm output. Any light emitted
at 532 nm was amplified via a photomultiplier tube and collected at a detector. No
index matching fluid was used in the experiment.
Photoluminesence spectra of (MDA)Pb2Br6 and (MDA)Pb2I6 were collected using
neat solid samples in a cryostat system as described below. Each sample was sandwiched between two 1 mm thick sapphire disks and excited at 365 nm LED source.
Steady state emission spectra were collected from 4–290 K using a Photon Technology International QuantaMaster model C-60SE spectrofluorimeter in tandem with a
Janis model SHI-4-2 optical He cryostat equipped with a Lakeshore model 335 temperature controller. Excited state lifetimes were evaluated from 4–150 K and were
determined by the time-correlated single-photon counting method (TCSPC) using
an IBH Fluorocube instrument using a 372 nm pulsed diode for the (MDA)Pb2Br6
sample; whereas, the (MDA)Pb2I6 was not bright enough to evaluate the lifetime at
any temperature.
6.2.5 Dielectric Properties Measurements
Parallel plate capacitor method was used to measure the dielectric properties of
(MDA)Pb2I6 and (MDA)Pb2Br6. Each material was ground using an agate mortar
117

6.3. Results and Discussion
and pestle and pressed into a 10 mm diameter, 2.02 mm thickness pellet. To adhere
electrical contacts on either faces of the pellets, conductive silver epoxy was used.
The silver epoxy also acts as the electrodes of the parallel plate capacitor. Dielectric
measurements were taken from 2 to 400 K at frequencies of 1, 2, 5, 10, and 20 kHz.
The sample temperature was achieved by using a Quantum Design Physical Properties Measurement System (PPMS) Dynacool. The dielectric measurements were
taken using an Andeen-Hagerling 2700A 50 Hz-20 kHz Ultra-Precision Capacitance
Bridge.
6.3 Results and Discussion
The preparation described above yielded small, yellow (iodide) or white (bromide)
needle-like crystals, which differs slightly from the report of Lemmerer and Billing for
(MDA)Pb2I6 who note their crystals adopted a plate-like habit. 125 Rietveld refinement132 against synchrotron XRD scattering from ground crystals, shown in Figure
6.1a and b, shows the bulk of the product is a highly pure single phase with tables of
the refined parameters given in Table 6.2 and 6.3.
The structure of the hybrid crystallizes in the non-centrosymmetric space group
F dd2 (#43) and is illustrated from two different perspectives in the insets of Figure
6.1a and b. The fully inorganic regions consists of edge-sharing chains of lead-centered
octahedra running along the c-axis with the MDA cations positioned in between and
held in place through hydrogen bonding between the ammonium group and iodide
ions. Interestingly, the molecules adopt a chevron-like configuration with the methylene bridge of each pointing in a coherent fashion along the c-axis, parallel to the
inorganic chains, which creates an obvious macroscopic dipole running throughout
118

6.3. Results and Discussion
Figure 6.1: Results of the Rietveld refinement of the (a) (MDA)Pb2I6 and (b)
(MDA)Pb2Br6 structures against synchrotron X-ray diffraction data collected on the
11-BM beamline at Argonne National Laboratory.
the material. Such an ordered dipole within a polar space group should be expected
to give rise to non-linear optical signals, which will be revisited in detail later.
The calculated densities of state (DOS) for (MDA)Pb2Br6 and (MDA)Pb2I6,
shown in Fig 6.2, reveals a contribution from the lead halide octahedra to both the
conduction and valence band edges. The MDA cations have a greater energy contribution to the valence band maximum in (MDA)Pb2Br6 compared to (MDA)Pb2I6.
As would be expected, the band gap energy for the bromide hybrid increases relative to the iodide hybrid with a direct band gap of 3.54 eV in (MDA)Pb2Br6 and a
direct band gap of 2.69 eV in (MDA)Pb2I6. The lead 6s and the bromine 4p/iodine
5p orbitals in both materials are at the top of the valence band, but the carbon 2p
orbital is much closer to the band edge in (MDA)Pb2Br6. The lead 6p orbital sits
at the conduction band minimum with the carbon 2p orbital very close to the band
edge in both hybrids.
119

6.3. Results and Discussion
Figure 6.2: Density of states and band diagrams for (a) (MDA)Pb2I6 and (b)
(MDA)Pb2Br6.
Figure 6.3: Kubelka–Munk transform of (a) (MDA)Pb2I6 and (b) (MDA)Pb2Br6
with photos of powder inset.
120

6.3. Results and Discussion
Diffuse reflectance spectra in the UV-visible range were collected from powders
of (MDA)Pb2I6, (MDA)Pb2Br6, PbI2, PbBr2, MDA·2HI, and MDA·2HBr to examine
the optical properties. A Kubelka–Munk transformation was applied to each data
set to estimate the optical band gap of each sample. Transforms for PbI2, PbBr2,
MDA·2HI, and MDA·2HBr can be found in Figure 6.7. Figure 6.3 shows the Kubelka–
Munk transform for (MDA)Pb2I6 and (MDA)Pb2Br6 along with insets of the bulk
powder for each sample. The band gaps for (MDA)Pb2I6 and (MDA)Pb2Br6 are
2.65 eV and 2.90 eV, respectively, as determined by a linear fit to the onset of absorption. The absorption onsets for both PbI2 and MDA·2HI were red shifted compared
to (MDA)Pb2I6. Whereas, the absorption onset for PbBr2 and MDA·2HBr were blue
shifted compared to (MDA)Pb2Br6.
(MDA)Pb2Br6 emits weakly at 595 nm at 290 K and strongly at 630 nm when
cooled to 4 K (Figure 6.4b) while (MDA)Pb2I6 emits only very weakly at temperatures
below 80 K (Figure 6.4a). In addition to the overall peak shapes, the temperature
dependence of the principal emission band for bromide and iodide compounds show
similar behavior. (MDA)Pb2I6 has an emission maximum of 620 nm at 4 K with a
red shift to 628 nm at 75 K. . At temperatures up to 40 K, there is a clear peak at
450 nm that can be attributed to free exciton emission in (MDA)Pb2Br6. The small
feature at 690 nm corresponds to the frequency doubling of the light source.
The lifetime data for (MDA)Pb2Br6 show that at low temperatures, the material
is frozen into a state with a markedly longer lifetime as seen in the inset of Figure
6.4b. The integrated intensities of the emission bands (replotted onto a cm−1 axis)
are constant in the 10–90 K range (Table 6.1). It is unlikely that the radiative and
nonradiative rates would have the same temperature dependence, so the changes
in lifetime in this temperature regime are due to a drop in the radiative rate at
lower temperatures. Fitting of the lifetime data to an Arrhenius model (Figure 6.4b
121

6.3. Results and Discussion
Figure 6.4: Emission of (a) (MDA)Pb2I6 and (b) (MDA)Pb2Br6 from 4 K to 290 K
(λex = 365 nm). The inset shows (MDA)Pb2Br6 lifetime curve and fit from 10–90K.
Data were fit using a two-level model.
inset) gives an activation energy between the long and short lived states of 23 meV.
Unfortunately, luminescence from (MDA)Pb2I6 is too weak to give accurate lifetime
data, even at the lowest temperatures. Above 100 K, nonradiative decay process(es)
begins to compete with the radiative decay of the excited state, and the luminance
efficiency drops continuously to a photoluminescence quantum yield < 1% at room
temperature for both compounds.
The polar nature of the space group encouraged us to investigate the non-linear
optical properties, which revealed SHG activity for both halides. as illustrated in
Figure 6.5. Compared to α-SiO2, the SHG intensity of (MDA)Pb2I6 is approximately
half as strong in the <20 µm range. In contrast, (MDA)Pb2Br6 shows a slightly larger
response in the 95–125 µm size range. Additionally, (MDA)Pb2I6 exhibits non-phasematching behavior, while (MDA)Pb2Br6 demonstrates phase-matching behavior. A
comparison of the phase-matching performance of (MDA)Pb2Br6 with KDP is also
shown in Figure 6.5. It is curious, however, that despite what appears to be a substantial well-aligned molecular dipole, neither (MDA)Pb2I6 nor (MDA)Pb2Br6 displays a
strong SHG intensity.
122

6.3. Results and Discussion
Figure 6.5: SHG phase matching curves of (a) (MDA)Pb2I6 and (b) (MDA)Pb2Br6
relative to α-SiO2 and KDP.
To better understand the polar nature of the material, temperature-dependent
capacitance measurements were performed and are shown in Figure 6.6. The real
part of the capacitance for both samples follows the typical dependence expected for
a simple thermal contraction of the lattice on cooling, and it is notable that there are
no peaks or significant changes in slope, which rules out any ferroelectric transitions
below room temperature. More interestingly, there appears to be a strong correlation
between the evolution of luminescence in the two phases and features in the dielectric
loss. We attribute this observation to a freezing of the rotation degrees of freedom
on the ammonium portion of the MDA cations as previously described by Fabini
et al,
133,134 which would suppress a source of non-radiative quenching of the excited
state and allow the observation of luminescence.
Aside from the weak SHG, there are no signatures in the dielectric properties to
suggest that the ordered dipole on the MDA molecules introduces any novel functionality, which is somewhat surprising given the highly coherent alignment within
the structure. We, therefore, postulate that the polarizability of the halide sublattice
123

6.3. Results and Discussion
acts to screen the internal electric field created by these dipoles. 135 A recent report
from Shen et al. offers deeper insight on this. Their report on a non-centrosymmetric
morpholinium lead chloride and bromide systems show phase-matching SHG effects
of 0.70 and 0.81 times KDP, respectively, which would seem to contradict what is seen
in the MDA hybrids.136 Yet, in contrast to the materials we report, the dipole in their
hybrids is primarily arises from the acentric coordination environment of the metal
halide octahedra. So while we believe the local electric field on the MDA molecules
serves to polarize the charge cloud of the inorganic sublattice to produce a screening
effect, the dipole of the morpholinium compounds is actually expected to increase
in more polarizable lattices as this allows for greater displacement of lead from the
center of its octahedra, in good agreement with their observations.
Figure 6.6: Capacitance and dielectric loss measurements on (a) (MDA)Pb2I6 and
(b) (MDA)Pb2Br6.
While the dielectric constant was difficult to evaluate at room temperature due to
very high dielectric loss resulting from non-negligible electrical conductivity through
the pellet, data collected at 2 K and 20 kHz indicates a value of 11.0 and 8.3 respectively for (MDA)Pb2Br6 and (MDA)Pb2I6. This supports the idea that the reduced
polarizability of the (MDA)Pb2Br6 inhibits its ability to screen the internal electric
124

6.4. Summary
field and allows it to exhibit a stronger SHG response. 137,138 This finding provides a
powerful materials design principle to guide the development of hybrids with polar or
non-linear optical properties and points towards chloride and fluoride based hybrids to
ensure low electrical conductivity and small screening of any resulting electric fields.
6.4 Summary
In summary, we have demonstrated that (MDA)Pb2I6 and (MDA)Pb2Br6 both adopt
non-centrosymmetric structures and consequently, exhibit weak SHG activity. Counterintuitively, the iodide exhibits a weaker dielectric constant than the bromide and
as a result shows a similarly weaker SHG response. This behavior suggests that
the increased polarizability of the iodide screens the ordered dipole on the MDA
molecules. While neither material exhibits a ferroelectric transitions, this trend in
SHG activity may suggest that the design of polar hybrids should focus on chloridebased phases to maximize the attainable dipole moment.
125

6.5. Supplemental Information
6.5 Supplemental Information
6.5.1 Expanded Photophysics and Optical Measurements
Figure 6.7: Kubelka Munk transforms of (a) MDA·2HBr (b) MDA·2HI (c) PbBr2
(d) PbI2 from diffuse reflectance data; x-intercept of red fit lines corresponds to the
band gap of each material.
126

6.5. Supplemental Information
Table 6.1: Integrated intensities of (MDA)Pb2Br6 emission spectra from 10–90 K.
Temperature (K) Area (x105
)
10 3.26
12 3.26
14 3.25
16 3.24
18 3.25
20 3.25
25 3.31
30 3.33
35 3.34
40 3.34
45 3.44
50 3.41
60 3.47
70 3.55
80 3.76
90 3.85
127

6.5. Supplemental Information
6.5.2 Material Characterization
Table 6.2: Results of the Rietveld refinement of (MDA)Pb2I6 and (MDA)Pb2Br6
against the synchrotron powder diffraction data.
Parameter (MDA)Pb2I6 (MDA)Pb2Br6
Space Group F dd2 F dd2
a 25.35484 (11) 23.892617
b 43.13847 (21) 41.678311
c 4.537309 (21) 4.370651
C1 (0.7712, 0.17342, 0.9399) (0.5, 0.5, 1.411)
C2 (0.7208, 0.18129, 0.8439) (0.4903, 0.52876, 1.2094)
H2 (0.691, 0.1703, 0.9175)
C3 (0.71397, 0.20524, 0.6404) (0.4365, 0.53759, 1.116)
H3 (0.6795, 0.2106, 0.5748) (0.4051, 0.5266, 1.1983)
C4 (0.75756, 0.22134, 0.5328) (0.4278, 0.5621, 0.9061)
H4 (0.3911, 0.5672, 0.8389)
C5 (0.80796, 0.21347, 0.6288) (0.4737, 0.57884, 0.796)
H5 (0.8377, 0.2245, 0.5552)
C6 (0.81478, 0.18952, 0.8323) (0.5279, 0.57204, 0.8907)
H6 (0.8492, 0.1841, 0.8979) (0.5588, 0.5841, 0.8163)
C7 (0.75, 0.25, 0.344) (0.5356, 0.54676, 1.1004)
H7 (0.5723, 0.5418, 1.1693)
H7A (0.7812, 0.2529, 0.2152)
H7B (0.7188, 0.2471, 0.2152)
N1 (0.7793, 0.1495, 1.163) (0.4637, 0.60461, 0.571)
H1A (0.8144, 0.1476, 1.2025) (0.467, 0.4964, 1.5432)
H1B (0.7666, 0.131, 1.0957) (0.533, 0.5036, 1.5432)
H1C (0.7619, 0.1549, 1.3323)
H1N (0.433, 0.6189, 0.652)
H2N (0.447, 0.596, 0.376)
H3N (0.5, 0.6159, 0.53)
I1/ Br1 (0.671777, -0.01021, 0.6956) (0.42612, 0.73777, 0.5526)
I2/ Br2 (0.845551, 0.099621, 0.67675) (0.55268, 0.66626, -0.4321)
I3/ Br3 (0.693605, 0.082704, 0.17638) (0.40478, 0.65269, 0.066)
Pb1 (0.762971, 0.048165, 0.69027) (0.48763, 0.7013, 0.05691)
Rwp 8.447 2.908
128

6.5. Supplemental Information
Table 6.3: Crystallographic data for single crystal structure determination of
(MDA)Pb2Br6
Parameter (MDA)Pb2Br6
Chemical formula C13H16N2Pb2Br6
Formula weight 1094.12
Temperature (K) 100
Crystal system orthorhombic
Space Group F dd2
a 23.895 (5)
b 41.682 (9)
c 4.3708 (10)
Volume 4353.3(17)
Z 8
C1 (0.50000, 0.50000, 1.41100)
H1A (0.46701, 0.49635, 1.54323)
H1B (0.53299, 0.50365, 1.54323)
C2 (0.49030, 0.52876, 1.20940)
C3 (0.43650, 0.53759, 1.11600)
H3 (0.40513, 0.52657, 1.19828)
C4 (0.42780, 0.56210, 0.90610)
H4 (0.39106, 0.56722, 0.83891)
C5 (0.47370, 0.57884, 0.79600)
C6 (0.52790, 0.57204, 0.89070)
H6 (0.55877, 0.58406, 0.81626)
C7 (0.53560, 0.54676, 1.10040)
H7 (0.57234, 0.54182, 1.16931)
N1 (0.46370, 0.60461, 0.57100)
H1N (0.43300, 0.61890, 0.65200)
H2N (0.44700, 0.59600, 0.37600)
H3N (0.50000, 0.61590, 0.53000)
Br1 (0.42612, 0.73777, 0.55260)
Br2 (0.55268, 0.66626, -0.43210)
Br3 (0.40478, 0.65269, 0.06600)
Pb1 (0.48763, 0.70130, 0.05691)
Rint 0.035
129

References
References
[1] Rose, G. De Novis Quibusdam Fossilibus Quae In Montibus Uraliis Inveniuntur;
Typis A.G. Schadii, 1839.
[2] Goldschmidt, V. M. Naturwissenschaften 1926, 14, 477–485.
[3] Bartel, C. J.; Sutton, C.; Goldsmith, B. R.; Ouyang, R.; Musgrave, C. B.;
Ghiringhelli, L. M.; Scheffler, M. Science Advances 2019, 5, eaav0693.
[4] Wells, H. L. Zeitschrift für Anorganische Chemie 1893, 3, 195–210.
[5] NREL Best Research-Cell Efficiency Chart. 2024; https://www.nrel.gov/pv/
cell-efficiency.html.
[6] Weber, D. Zeitschrift für Naturforschung 1978, 33b, 1443–1445.
[7] Weber, D. Zeitschrift für Naturforschung 1978, 33b, 862–865.
[8] Wasylishen, R. E.; Knop, O.; Macdonald, J. B. Solid State Communications
1985, 56, 581–582.
[9] Poglitsch, A.; Weber, D. The Journal of Chemical Physics 1987, 87, 6373–6378.
[10] Onoda-Yamamuro, N.; Matsuo, T.; Suga, H. Journal of Physics and Chemistry
of Solids 1990, 51, 1383–1395.
[11] Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. Journal of the American
Chemical Society 2009, 131, 6050–6051.
[12] Kim, H. S.; Lee, C. R.; Im, J. H.; Lee, K. B.; Moehl, T.; Marchioro, A.;
Moon, S. J.; Humphry-Baker, R.; Yum, J. H.; Moser, J. E.; Grätzel, M.;
Park, N. G. Scientific Reports 2012, 2, 1–7.
[13] Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J. Science
2012, 338, 643–647.
130

References
[14] Heo, J. H.; Im, S. H.; Noh, J. H.; Mandal, T. N.; Lim, C. S.; Chang, J. A.;
Lee, Y. H.; Kim, H. J.; Sarkar, A.; Nazeeruddin, M. K.; Grätzel, M.; Seok, S. I.
Nature Photonics 2013, 7, 486–491.
[15] Knutson, J. L.; Martin, J. D.; Mitzi, D. B. Inorganic Chemistry 2005, 44,
4699–4705.
[16] Eperon, G. E.; Stranks, S. D.; Menelaou, C.; Johnston, M. B.; Herz, L. M.;
Snaith, H. J. Energy and Environmental Science 2014, 7, 982–988.
[17] De Wolf, S.; Holovsky, J.; Moon, S. J.; Löper, P.; Niesen, B.; Ledinsky, M.;
Haug, F. J.; Yum, J. H.; Ballif, C. Journal of Physical Chemistry Letters 2014,
5, 1035–1039.
[18] Herz, L. M. ACS Energy Letters 2017, 2, 1539–1548.
[19] Kim, J.; Lee, S. H.; Lee, J. H.; Hong, K. H. Journal of Physical Chemistry
Letters 2014, 5, 1312–1317.
[20] Yin, W. J.; Shi, T.; Yan, Y. Applied Physics Letters 2014, 104 .
[21] Alcocer, M. J. P.; Leijtens, T.; Herz, L. M.; Petrozza, A.; Snaith, H. J. Science
2013, 342, 341–344.
[22] Dunlap-Shohl, W. A.; Zhou, Y.; Padture, N. P.; Mitzi, D. B. Chemical Reviews
2019, 119, 3193–3295.
[23] Kagan, C. R.; Mitzi, D. B.; Dimitrakopoulos, C. D. Science 1999, 286, 945–947.
[24] Mitzi, D. B.; Dimitrakopoulos, C. D.; Kosbar, L. L. Chemistry of Materials
2001, 13, 3728–3740.
[25] Mitzi, D. B.; Dimitrakopoulos, C. D.; Rosner, J.; Medeiros, D. R.; Xu, Z.
Advanced Materials 2002, 14, 1772–1776.
[26] Era, M.; Morimoto, S.; Tsutsui, T.; Saito, S. Applied Physics Letters 1994, 65,
676–678.
[27] Chondroudis, K.; Mitzi, D. B. Chemistry of Materials 1999, 11, 3028–3030.
[28] Tan, Z. K.; Moghaddam, R. S.; Lai, M. L.; Docampo, P.; Higler, R.; Deschler, F.;
Price, M.; Sadhanala, A.; Pazos, L. M.; Credgington, D.; Hanusch, F.; Bein, T.;
Snaith, H. J.; Friend, R. H. Nature Nanotechnology 2014, 9, 687–692.
[29] Dou, L.; Yang, Y. M.; You, J.; Hong, Z.; Chang, W. H.; Li, G.; Yang, Y. Nature
Communications 2014, 5, 5404.
131

References
[30] Xing, G.; Mathews, N.; Lim, S. S.; Yantara, N.; Liu, X.; Sabba, D.; Grätzel, M.;
Mhaisalkar, S.; Sum, T. C. Nature Materials 2014, 13, 476–480.
[31] Meng, L.; You, J.; Yang, Y. Nature Communications 2018, 9, 5265.
[32] Grancini, G.; Roldán-Carmona, C.; Zimmermann, I.; Mosconi, E.; Lee, X.;
Martineau, D.; Narbey, S.; Oswald, F.; De Angelis, F.; Graetzel, M.; Nazeeruddin, M. K. Nature Communications 2017, 8, 15684.
[33] Niu, G.; Guo, X.; Wang, L. Journal of Materials Chemistry A 2015, 3, 8970–
8980.
[34] Li, N.; Niu, X.; Chen, Q.; Zhou, H. Chemical Society Reviews 2020, 49, 8235–
8286.
[35] Rong, Y.; Hu, Y.; Mei, A.; Tan, H.; Saidaminov, M. I.; Seok, S. I.; McGehee, M. D.; Sargent, E. H.; Han, H. Science 2018, 361 .
[36] Boyd, C. C.; Cheacharoen, R.; Leijtens, T.; McGehee, M. D. Chemical Reviews
2019, 119, 3418–3451.
[37] Kundu, S.; Kelly, T. L. EcoMat 2020, 2, 1–22.
[38] Shannon, R. D. Acta Crystallographica Section A: Crystal Physics, Diffraction,
Theoretical and General Crystallography 1976, 32, 751–767.
[39] Mitzi, D. B. Journal of the Chemical Society, Dalton Transactions 2001, 1–12.
[40] Zhao, Y.; Zhu, K. Chemical Society Reviews 2016, 45, 655–689.
[41] Fan, Z.; Sun, K.; Wang, J. Journal of Materials Chemistry A 2015, 3, 18809–
18828.
[42] Walsh, A. Journal of Physical Chemistry C 2015, 119, 5755–5760.
[43] Gao, W.; Gao, X.; Abtew, T. A.; Sun, Y.-Y.; Zhang, S.; Zhang, P. Physical
Review B 2016, 93, 085202.
[44] Smith, I. C.; Hoke, E. T.; Solis-Ibarra, D.; McGehee, M. D.; Karunadasa, H. I.
Angewandte Chemie - International Edition 2014, 53, 11232–11235.
[45] Tsai, H. et al. Nature 2016, 536, 312–317.
[46] Zhang, X.; Wu, G.; Yang, S.; Fu, W.; Zhang, Z.; Chen, C.; Liu, W.; Yan, J.;
Yang, W.; Chen, H. Small 2017, 13, 1–8.
132

References
[47] Wu, G.; Li, X.; Zhou, J.; Zhang, J.; Zhang, X.; Leng, X.; Wang, P.; Chen, M.;
Zhang, D.; Zhao, K.; Liu, S.; Zhou, H.; Zhang, Y. Advanced Materials 2019,
31, 1–11.
[48] Liu, C.; Huhn, W.; Du, K. Z.; Vazquez-Mayagoitia, A.; Dirkes, D.; You, W.;
Kanai, Y.; Mitzi, D. B.; Blum, V. Physical Review Letters 2018, 121, 146401.
[49] Tremblay, M. H.; Boyington, A.; Rigin, S.; Jiang, J.; Bacsa, J.; Al Kurdi, K.;
Khrustalev, V. N.; Pachter, R.; Timofeeva, T. V.; Jui, N.; Barlow, S.;
Marder, S. R. Chemistry of Materials 2022, 34, 935–946.
[50] Manser, J. S.; Saidaminov, M. I.; Christians, J. A.; Bakr, O. M.; Kamat, P. V.
Accounts of Chemical Research 2016, 49, 330–338.
[51] Rahimnejad, S.; Kovalenko, A.; Forés, S. M.; Aranda, C.; Guerrero, A.
ChemPhysChem 2016, 17, 2795–2798.
[52] Burrows, P. E.; Forrest, S. R.; Sapochak, L. S.; Schwartz, J.; Fenter, P.;
Buma, T.; Ban, V. S.; Forrest, J. L. Journal of Crystal Growth 1995, 156,
91–98.
[53] Baldo, M. A.; Kozlov, V. G.; Burrows, P. E.; Forrest, S. R.; Ban, V. S.;
Koene, B.; Thompson, M. E. Materials Research Society Symposium - Proceedings 1997, 488, 587–592.
[54] Yang, F.; Shtein, M.; Forrest, S. R. Nature Materials 2005, 4, 37–41.
[55] Shtein, M.; Mapel, J.; Benziger, J. B.; Forrest, S. R. Applied Physics Letters
2002, 81, 268–270.
[56] Forrest, S. R.; Burrows, P. E.; Stroustrup, A.; Strickland, D.; Ban, V. S. Applied
Physics Letters 1996, 68, 1326–1328.
[57] Navarro, F. F. Fabrication and Study of Organic and Inorganic Optoelectronics
Using a Vapor Phase Deposition (VPD). Ph.D. thesis, University of Southern
California, 2016.
[58] Du, K. Z.; Tu, Q.; Zhang, X.; Han, Q.; Liu, J.; Zauscher, S.; Mitzi, D. B.
Inorganic Chemistry 2017, 56, 9291–9302.
[59] Momma, K.; Izumi, F. Journal of Applied Crystallography 2008, 41, 653–658.
[60] Chen, P.; Bai, Y.; Wang, S.; Lyu, M.; Yun, J. H.; Wang, L. Advanced Functional
Materials 2018, 28, 1–10.
133

References
[61] Straus, D. B.; Hurtado Parra, S.; Iotov, N.; Gebhardt, J.; Rappe, A. M.; Subotnik, J. E.; Kikkawa, J. M.; Kagan, C. R. Journal of the American Chemical
Society 2016, 138, 13798–13801.
[62] Febriansyah, B.; Lekina, Y.; Ghosh, B.; Harikesh, P. C.; Koh, T. M.; Li, Y.;
Shen, Z.; Mathews, N.; England, J. ChemSusChem 2020, 13, 2693–2701.
[63] Boeije, Y. et al. J. Am. Chem. Soc 2023, 145, 21330–21343.
[64] Passarelli, J. V.; Fairfield, D. J.; Sather, N. A.; Hendricks, M. P.; Sai, H.;
Stern, C. L.; Stupp, S. I. Journal of the American Chemical Society 2018, 140,
7313–7323.
[65] Nussbaum, S.; Socie, E.; Yao, L.; Yum, J. H.; Moser, J. E.; Sivula, K. Chemistry
of Materials 2022, 34, 3798–3805.
[66] Ghosh, D.; Marjit, K.; Ghosh, G.; Ghosh, S.; Patra, A. Journal of Physical
Chemistry C 2022, 126, 1490–14597.
[67] Gélvez-Rueda, M. C.; Van Gompel, W. T.; Herckens, R.; Lutsen, L.; Vanderzande, D.; Grozema, F. C. Journal of Physical Chemistry Letters 2020, 11,
824–830.
[68] Feng, Z. et al. Advanced Optical Materials 2023, 11, 1–8.
[69] Van Landeghem, M.; Van Gompel, W.; Herckens, R.; Lutsen, L.; Vanderzande, D.; Van Doorslaer, S.; Goovaerts, E. Journal of Physical Chemistry
C 2021, 125, 18317–18327.
[70] Gao, Y. et al. Nature Chemistry 2019, 11, 1151–1157.
[71] Li, X.; Hoffman, J. M.; Kanatzidis, M. G. Chemical Reviews 2021, 121, 2230–
2291.
[72] Li, W.; Feng, X.; Guo, K.; Pan, W.; Li, M.; Liu, L.; Song, J.; He, Y.; Wei, H.
Advanced Materials 2023, 35, 1–10.
[73] Li, Y.; Cheng, H.; Zhao, K.; Wang, Z. S. ACS Applied Materials and Interfaces
2019, 11, 37804–37811.
[74] Li, X.; Ke, W.; Traoré, B.; Guo, P.; Hadar, I.; Kepenekian, M.; Even, J.;
Katan, C.; Stoumpos, C. C.; Schaller, R. D.; Kanatzidis, M. G. Journal of the
American Chemical Society 2019, 141, 12880–12890.
[75] Goh, Y. G.; Cassingham, M. A.; Zavalij, P. Y.; Djurovich, P. I.; Thompson, M. E.; Melot, B. C. Inorganic Chemistry 2024, 63, 10160–10166.
134

References
[76] Kresse, G.; Hafner, J. Physical Review B 1993, 47, 558.
[77] Kresse, G.; Hafner, J. Physical Review B 1994, 49, 14251.
[78] Kresse, G.; Furthmüller, J. Physical Review B 1996, 54, 11169–11186.
[79] Kresse, G.; Furthmüller, J. Computational Materials Science 1996, 6, 15–50.
[80] Blochl, P. Physical Review B 1994, 50, 17953–17979.
[81] Ganose, A. M.; Jackson, A. J.; Scanlon, D. O. Journal of Open Source Software
2018, 3, 717.
[82] Perdew, J. P.; Ruzsinszky, A.; Csonka, G. I.; Vydrov, O. A.; Scuseria, G. E.;
Constantin, L. A.; Zhou, X.; Burke, K. Physical Review Letters 2008, 100,
136406.
[83] Li, G.; Song, J.; Wu, J.; Song, Z.; Wang, X.; Sun, W.; Fan, L.; Lin, J.;
Huang, M.; Lan, Z.; Gao, P. ACS Energy Letters 2021, 6, 3614–3623.
[84] Baur, W. H. Acta Crystallographica Section B 1974, 30, 1195–1215.
[85] Robinson, K.; Gibbs, G. V.; Ribbe, P. H. Science 1971, 172, 567–570.
[86] Mitzi, D. B. Inorganic Chemistry 2000, 39, 6107–6113.
[87] Jana, M. K.; Janke, S. M.; Dirkes, D. J.; Dovletgeldi, S.; Liu, C.; Qin, X.; Gundogdu, K.; You, W.; Blum, V.; Mitzi, D. B. Journal of the American Chemical
Society 2019, 141, 7955–7964.
[88] Xu, Z.; Mitzi, D. B. Chemistry of Materials 2003, 15, 3632–3637.
[89] Soe, C. M. M.; Stoumpos, C. C.; Kepenekian, M.; Traoré, B.; Tsai, H.; Nie, W.;
Wang, B.; Katan, C.; Seshadri, R.; Mohite, A. D.; Even, J.; Marks, T. J.;
Kanatzidis, M. G. Journal of the American Chemical Society 2017, 139, 16297–
16309.
[90] Wei, Q.; Ren, H.; Liu, J.; Liu, Q.; Wang, C.; Lau, T. W.; Zhou, L.; Bian, T.;
Zhou, Y.; Wang, P.; Lei, Q.; Mohammed, O. F.; Li, M.; Yin, J. ACS Energy
Letters 2023, 8, 4315–4322.
[91] Zhuang, Q.; Li, H.; Zhang, C.; Gong, C.; Yang, H.; Chen, J.; Zang, Z. Advanced
Materials 2023, 35, 1–9.
[92] Yan, L.; Jana, M. K.; Sercel, P. C.; Mitzi, D. B.; You, W. Journal of the
American Chemical Society 2021, 143, 18114–18120.
135

References
[93] Sheikh, T.; Shinde, A.; Mahamuni, S.; Nag, A. ACS Energy Letters 2018, 3,
2940–2946.
[94] Sheikh, T.; Shinde, A.; Mahamuni, S.; Nag, A. Materials Research Express
2019, 6, 124002.
[95] Cassingham, M. Effects of Cationic Species on the Structure and Properties
of Hybrid Organic-Inorganic Materials. Ph.D. thesis, University of Southern
California, 2024.
[96] Sheldrick, G. M. Acta Crystallographica Section A: Foundations of Crystallography 2008, 64, 112–122.
[97] Lemmerer, A.; Billing, D. G. Acta Crystallographica Section E 2006, 62, m904–
m906.
[98] Mitrofanov, A.; Berencén, Y.; Sadrollahi, E.; Boldt, R.; Bodesheim, D.;
Weiske, H.; Paulus, F.; Geck, J.; Cuniberti, G.; Kuc, A.; Voit, B. Journal
of Materials Chemistry C 2023, 11, 5024–5031.
[99] Harris, R. K.; Becker, E. D.; Cabral de Menenzes, S. M.; Goodfellow, R.;
Granger, P. Proceedings of the 5th European Conference on Antennas and Propagation, EUCAP 2011 2001, 73, 1795–1818.
[100] Brinkmann, A.; Kentgens, A. P. Journal of the American Chemical Society
2006, 128, 14758–14759.
[101] Oas, T. G.; Griffin, R. G.; Levitt, M. H. The Journal of Chemical Physics 1988,
89, 692–695.
[102] Hu, B.; Trébosc, J.; Amoureux, J. P. Journal of Magnetic Resonance 2008,
192, 112–122.
[103] Cavadini, S.; Abraham, A.; Bodenhausen, G. Chemical Physics Letters 2007,
445, 1–5.
[104] Tošner, Z.; Vosegaard, T.; Kehlet, C.; Khaneja, N.; Glaser, S. J.; Nielsen, N. C.
Journal of Magnetic Resonance 2009, 197, 120–134.
[105] Bak, M.; Rasmussen, J. T.; Nielsen, N. C. Journal of Magnetic Resonance 2000,
147, 296–330.
[106] Tošner, Z.; Andersen, R.; Stevensson, B.; Edén, M.; Nielsen, N. C.;
Vosegaard, T. Journal of Magnetic Resonance 2014, 246, 79–93.
[107] Coelho, A. A. Journal of Applied Crystallography 2018, 51, 210–218.
136

References
[108] Perdew, J. P.; Burke, K.; Ernzerhof, M. Physical Review Letters 1996, 77,
3865–3868.
[109] Heyd, J.; Scuseria, G. E.; Ernzerhof, M. The Journal of Chemical Physics 2003,
118, 8207.
[110] Heyd, J.; Scuseria, G. E.; Ernzerhof, M. The Journal of Chemical Physics 2006,
124, 219906.
[111] Ong, S. P.; Richards, W. D.; Jain, A.; Hautier, G.; Kocher, M.; Cholia, S.;
Gunter, D.; Chevrier, V. L.; Persson, K. A.; Ceder, G. Computational Materials
Science 2013, 68, 314–319.
[112] Mueller, L. Journal of the American Chemical Society 1979, 101, 4481–4484.
[113] Hanrahan, M. P.; Men, L.; Rosales, B. A.; Vela, J.; Rossini, A. J. Chemistry of
Materials 2018, 30, 7005–7015.
[114] Karmakar, A.; Askar, A. M.; Bernard, G. M.; Terskikh, V. V.; Ha, M.; Patel, S.;
Shankar, K.; Michaelis, V. K. Chemistry of Materials 2018, 30, 2309–2321.
[115] Kubicki, D. J.; Prochowicz, D.; Salager, E.; Rakhmatullin, A.; Grey, C. P.;
Emsley, L.; Stranks, S. D. Journal of the American Chemical Society 2020,
142, 7813–7826.
[116] Shmyreva, A. A.; Safdari, M.; Furó, I.; Dvinskikh, S. V. Journal of Chemical
Physics 2016, 144 .
[117] Rosales, B. A.; Men, L.; Cady, S. D.; Hanrahan, M. P.; Rossini, A. J.; Vela, J.
Chemistry of Materials 2016, 28, 6848–6859.
[118] Venkatesh, A.; Luan, X.; Perras, F. A.; Hung, I.; Huang, W.; Rossini, A. J.
Physical Chemistry Chemical Physics 2020, 22, 20815–20828.
[119] Pickard, C. J.; Mauri, F. Physical Review B - Condensed Matter and Materials
Physics 2001, 63, 2451011–2451013.
[120] Atterberry, B. A.; Carnahan, S. L.; Chen, Y.; Venkatesh, A.; Rossini, A. J.
Journal of Magnetic Resonance 2022, 336, 107147.
[121] Kapper, S. C. Photophysical Properties of Luminescent Iridium and Coinage
Metal Complexes. Ph.D. thesis, University of Southern California, 2021.
[122] Hamze, R.; Shi, S.; Kapper, S. C.; Ravinson, D. S. M.; Estergreen, L.;
Jung, M. C.; Tadle, A. C.; Haiges, R.; Djurovich, P. I.; Peltier, J. L.; Jazzar, R.; Bertrand, G.; Bradforth, S. E.; Thompson, M. E. Journal of the American Chemical Society 2019, 141, 8616–8626.
137

References
[123] Hofbeck, T.; Yersin, H. Inorganic Chemistry 2010, 49, 9290–9299.
[124] Cassingham, M. A.; Goh, Y. G.; McClure, E. T.; Hodgkins, T. L.; Zhang, W.;
Liang, M.; Dawlaty, J. M.; Djurovich, P. I.; Haiges, R.; Halasyamani, P. S.;
Savory, C. N.; Thompson, M. E.; Melot, B. C. ACS Applied Materials and
Interfaces 2023, 15, 18006–18011.
[125] Lemmerer, A.; Billing, D. G. CrystEngComm 2012, 14, 1954–1966.
[126] Toby, B. H.; Von Dreele, R. B. J. Appl. Crystallogr. 2013, 46, 544–549.
[127] Krukau, A. V.; Vydrov, O. A.; Izmaylov, A. F.; Scuseria, G. E. The Journal of
Chemical Physics 2006, 125, 224106.
[128] Yin, W.; Yang, J.; Kang, J.; Yan, Y.; Wei, S. Journal of Materials Chemistry
A 2015, 3, 8926–8942.
[129] Bass, K. K.; Estergreen, L.; Savory, C. N.; Buckeridge, J.; Scanlon, D. O.;
Djurovich, P. I.; Bradforth, S. E.; Thompson, M. E.; Melot, B. C. Inorganic
Chemistry 2016, 56, 42–45.
[130] Fabian, D. M.; Ganose, A. M.; Ziller, J. W.; Scanlon, D. O.; Beard, M. C.;
Ardo, S. ACS Applied Energy Materials 2019, 2, 1579–1587.
[131] Kubelka, P.; Munk, F. Zeitschrift für Physik 1931, 12, 593–601.
[132] Rietveld, H. M. Applied Crystallography 1969, 2, 65–71.
[133] Fabini, D. H.; Hogan, T.; Evans, H. A.; Stoumpos, C. C.; Kanatzidis, M. G.;
Seshadri, R. Journal of Physical Chemistry Letters 2016, 7, 376–381.
[134] Fabini, D. H.; Siaw, T. A.; Stoumpos, C. C.; Laurita, G.; Olds, D.; Page, K.;
Hu, J. G.; Kanatzidis, M. G.; Han, S.; Seshadri, R. Journal of the American
Chemical Society 2017, 139, 16875–16884.
[135] Wilson, J. N.; Frost, J. M.; Wallace, S. K.; Walsh, A. APL Materials 2019, 7,
010901.
[136] Shen, C.; Sun, D.; Dang, Y.; Wu, K.; Xu, T.; Hou, R.; Chen, H.; Wang, J.;
Wang, D. Inorganic Chemistry 2022, 61, 16936–16943.
[137] Kirkwood, J. G. The Journal of Chemical Physics 2004, 4, 592.
[138] Rumble, J. R. CRC Handbook of Chemistry and Physics: 102nd Edition. 2021–
2022.
138

Abstract (if available)

Abstract This collection of works presents the knowledge we have gained on the deposition and optoelectronic properties of low-dimensional hybrid lead halides. Our studies aimed to understand how integrating larger organic molecules with desired functionalities can alter the optoelectronic properties of the resulting hybrid systems. A key focus was on fabricating phase-pure hybrid films, a crucial factor for determining the feasibility of new materials in optoelectronic devices.

Linked assets

University of Southern California Dissertations and Theses

Conceptually similar

PDF

Effects of cationic species on the structure and properties of hybrid organic-inorganic materials

PDF

Two-dimensional metal dithiolene metal-organic frameworks as conductive materials for solar energy conversion

PDF

Optical properties of lead and bismuth halide perovskites for photovoltaic applications

PDF

Understanding the relationship between crystal chemistry and physical properties in magnetic garnets

PDF

Navigating the future of teacher professional development: Three essays on teacher learning in informal and digital context

PDF

Thermoelectric and transport studies of low dimensional materials & hot electron-driven photocatalysis on plasmon-resonant grating nanostructures

PDF

Controlling structure and photophysical properties of bi triple perovskite through substitutional series Cs₃Bi₂Br₍₉₋ₓ₎Iₓ

PDF

Low-dimensional material based devices for neuromorphic computing and other applications

PDF

Hot electron driven photocatalysis and plasmonic sensing using metallic gratings

PDF

The existence of absolutely continuous invariant measures for piecewise expanding operators and random maps

PDF

Impurity gas detection for spent nuclear fuel (SNF) canisters using ultrasonic sensing and deep learning

PDF

The effects of crystal structure and composition on the magnetism of garnets & phyllosilicates

PDF

Understanding the structure-property relationship in electrode materials for electrochemical energy storage

PDF

Controlled heteroatom functionalization of carbon-carbon bonds by aerobic oxidation

PDF

Aggregation and the structure of value

PDF

Semiconductor devices for vacuum electronics, electrochemical reactions, and ultra-low power in-sensor computing

PDF

Efficient control optimization in subsurface flow systems with machine learning surrogate models

PDF

Dimensional analysis: essays on the metaphysics and epistemology of quantities

PDF

Inorganic/organic hybrid materials and grafted coatings via vapor phase deposition processes

PDF

The mechanism of parenchymal cell proliferation in adult male mouse submandibular gland (SMG)

Asset Metadata

Creator Goh, Yang "Gemma" (author)

Core Title Film deposition and optoelectronic properties of low-dimensional hybrid lead halides

School College of Letters, Arts and Sciences

Degree Doctor of Philosophy

Degree Program Chemistry

Degree Conferral Date 2024-08

Publication Date 08/30/2024

Defense Date 07/26/2024

Publisher Los Angeles, California (original), University of Southern California (original), University of Southern California. Libraries (digital)

Tag low-dimensional hybrid metal halides,OAI-PMH Harvest

Format theses (aat)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Melot, Brent (committee chair), Ravichandran, Jayakanth (committee member), Thompson, Mark (committee member)

Creator Email gemgoh@gmail.com,yanggoh@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-oUC113999ZI6

Unique identifier UC113999ZI6

Identifier etd-GohYangGem-13452.pdf (filename)

Legacy Identifier etd-GohYangGem-13452

Document Type Dissertation

Format theses (aat)

Rights Goh, Yang "Gemma"

Internet Media Type application/pdf

Type texts

Source 20240830-usctheses-batch-1204 (batch), University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the author, as the original true and official version of the work, but does not grant the reader permission to use the work if the desired use is covered by copyright. It is the author, as rights holder, who must provide use permission if such use is covered by copyright.

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus MC 2810, 3434 South Grand Avenue, 2nd Floor, Los Angeles, California 90089-2810, USA

Repository Email cisadmin@lib.usc.edu