Exploring Structural Dynamics and Photophysics in Metal Halide Perovskites and Related Materials
(2025)- Abstract
- Metal halide perovskites and related materials have sparked intense debate in the field of optoelectronic applications, including solar cells, light-emitting diodes, and lasers. Despite significant progress in improving device efficiency and stability, understanding the structure-property relationships remains largely elusive. This thesis presents an in-depth investigation of the structural dynamics and photophysics in lead halide perovskites and lead-free perovskite-inspired materials, utilizing a range of steady-state and time-resolved spectroscopic techniques.
We first observed the orthorhombic-to-tetragonal phase transition in MAPbBr₃ microcrystals at 150 K using temperature-dependent neutron powder diffraction. Different from the... (More) - Metal halide perovskites and related materials have sparked intense debate in the field of optoelectronic applications, including solar cells, light-emitting diodes, and lasers. Despite significant progress in improving device efficiency and stability, understanding the structure-property relationships remains largely elusive. This thesis presents an in-depth investigation of the structural dynamics and photophysics in lead halide perovskites and lead-free perovskite-inspired materials, utilizing a range of steady-state and time-resolved spectroscopic techniques.
We first observed the orthorhombic-to-tetragonal phase transition in MAPbBr₃ microcrystals at 150 K using temperature-dependent neutron powder diffraction. Different from the microcrystals, the transition was absent in nanocrystals due to increased surface energy, strain, and entropy. To address toxicity and stability concerns, we explored lead-free alternatives, focusing on materials with efficient self-trapped exciton (STE) emission. By using the streak camera and femtosecond transient absorption (fs-TA) spectroscopy, we obtained a detailed dynamic picture of STE emission in Cs2ZrCl6 nanocrystals, including a direct visualization of STE formation on a time scale of 400 fs. Next, we investigated nm-scale ODASn2I6 thin film, which exhibits temperature-sensitive STE emission. Temperature-dependent absorption and emission spectra revealed strong thermal quenching of the STE emission above 275 K due to enhanced nonradiative recombination. Using temperature-dependent fs-TA spectroscopy, we uncovered the underlying mechanism: a phonon-assisted nonradiative pathway through a conical intersection between the ground and STE potential energy surfaces. These results will guide designing versatile lead-free perovskite-inspired materials for high-resolution thermography. Finally, we tailored the exciton-phonon coupling strength to design 1D ODASn2I6 and 2D ODASnI4 structures through organic cation modification. ODASn2I6 exhibits stronger exciton-phonon interaction, resulting in STE emission, while ODASnI4 demonstrates free exciton (FE) emission. The fs-TA analysis revealed that STE dynamics are excitation-independent, whereas FE dynamics involve hot carrier cooling and Auger recombination. Most importantly, we observed the room-temperature phonon coherence in ODASn2I6 and identified the phonon mode at 106 cm-1 involving stretching motion in tin iodide oscillates on STE state rather than FE state.
In summary, this thesis provides deep insights into the structural, electronic, and nuclear dynamics of metal halide perovskites and their derivatives. These findings will inspire the development of diverse and multifunctional materials for future optoelectronic applications. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/3e77961e-d493-4b2c-ba32-c7120bf8da49
- author
- He, Yanmei LU
- supervisor
-
- Tönu Pullerits LU
- Kaibo Zheng LU
- Junsheng Chen LU
- opponent
-
- Professor Stranks, Samuel, University of Cambridge
- organization
- publishing date
- 2025
- type
- Thesis
- publication status
- published
- subject
- keywords
- Metal halide perovskites, Perovskite-inspired materials, Ultrafast spectroscopy, Phase transition, Self- trapped Exciton, Excited state dynamics, Phonon coherence
- pages
- 177 pages
- publisher
- Chemical Physics, Lund University
- defense location
- Lecturehall KC:A Join via zoom: https://lu-se.zoom.us/j/63866464226
- defense date
- 2025-01-24 09:15:00
- ISBN
- 978-91-8096-084-7
- 978-91-8096-085-4
- language
- English
- LU publication?
- yes
- id
- 3e77961e-d493-4b2c-ba32-c7120bf8da49
- date added to LUP
- 2024-12-10 14:27:02
- date last changed
- 2024-12-13 11:44:17
@phdthesis{3e77961e-d493-4b2c-ba32-c7120bf8da49,
abstract = {{Metal halide perovskites and related materials have sparked intense debate in the field of optoelectronic applications, including solar cells, light-emitting diodes, and lasers. Despite significant progress in improving device efficiency and stability, understanding the structure-property relationships remains largely elusive. This thesis presents an in-depth investigation of the structural dynamics and photophysics in lead halide perovskites and lead-free perovskite-inspired materials, utilizing a range of steady-state and time-resolved spectroscopic techniques. <br/>We first observed the orthorhombic-to-tetragonal phase transition in MAPbBr₃ microcrystals at 150 K using temperature-dependent neutron powder diffraction. Different from the microcrystals, the transition was absent in nanocrystals due to increased surface energy, strain, and entropy. To address toxicity and stability concerns, we explored lead-free alternatives, focusing on materials with efficient self-trapped exciton (STE) emission. By using the streak camera and femtosecond transient absorption (fs-TA) spectroscopy, we obtained a detailed dynamic picture of STE emission in Cs2ZrCl6 nanocrystals, including a direct visualization of STE formation on a time scale of 400 fs. Next, we investigated nm-scale ODASn2I6 thin film, which exhibits temperature-sensitive STE emission. Temperature-dependent absorption and emission spectra revealed strong thermal quenching of the STE emission above 275 K due to enhanced nonradiative recombination. Using temperature-dependent fs-TA spectroscopy, we uncovered the underlying mechanism: a phonon-assisted nonradiative pathway through a conical intersection between the ground and STE potential energy surfaces. These results will guide designing versatile lead-free perovskite-inspired materials for high-resolution thermography. Finally, we tailored the exciton-phonon coupling strength to design 1D ODASn2I6 and 2D ODASnI4 structures through organic cation modification. ODASn2I6 exhibits stronger exciton-phonon interaction, resulting in STE emission, while ODASnI4 demonstrates free exciton (FE) emission. The fs-TA analysis revealed that STE dynamics are excitation-independent, whereas FE dynamics involve hot carrier cooling and Auger recombination. Most importantly, we observed the room-temperature phonon coherence in ODASn2I6 and identified the phonon mode at 106 cm-1 involving stretching motion in tin iodide oscillates on STE state rather than FE state. <br/>In summary, this thesis provides deep insights into the structural, electronic, and nuclear dynamics of metal halide perovskites and their derivatives. These findings will inspire the development of diverse and multifunctional materials for future optoelectronic applications.}},
author = {{He, Yanmei}},
isbn = {{978-91-8096-084-7}},
keywords = {{Metal halide perovskites; Perovskite-inspired materials; Ultrafast spectroscopy; Phase transition; Self- trapped Exciton; Excited state dynamics; Phonon coherence}},
language = {{eng}},
publisher = {{Chemical Physics, Lund University}},
school = {{Lund University}},
title = {{Exploring Structural Dynamics and Photophysics in Metal Halide Perovskites and Related Materials}},
year = {{2025}},
}