Multi-pulse time-resolved terahertz spectroscopy of metal halide perovskite
File(s)
Author(s)
Zheng, Xijia
Type
Thesis
Abstract
Processibility is becoming an increasingly attractive property for optoelectronics that require mass deployment such as solar cells and LEDs. Processible optoelectronics can be fabricated using solution-based processes, such as ink-jet printing and still achieve remarkable performances. For instance, among single-junction processible solar cells, halide perovskite solar cells (PSC) show the highest efficiency. However, the photophysical properties of processible optoelectronics, including PSCs, are significantly more complex than those of traditional semiconductors.
Photoexcitation upon PSC generates populations of electron quasiparticles, such as excitons and polarons. Their kinetics and interaction with each other govern the fundamental physical properties of the PSCs. When a PSC is excited with photon energy well above its bandgap, which is a realistic situation concerning the solar spectrum, “hot” excitons with large excess energy are generated, and evolve into hot carriers populated deep into the conduction band. If hot carriers are not extracted before they relax to band edge, all excess energy is lost to heat. Therefore, it is crucial to understand hot carrier dynamics to enable rational design of PSCs.
This thesis employs time-resolved terahertz spectroscopy (TRTS) to study the underlying hot carrier photophysics of PSCs. Studies of perovskites utilising TRTS in the past decade are reviewed in detail, and their limitations are identified. The commonly used optical-pump-terahertz-probe (OPTP) scheme is found to be insufficient for studying hot carrier dynamics, and an improved TRTS scheme is proposed. The new scheme adds an infrared excitation pulse (push) well below bandgap, forming a pump-push-probe scheme (PPP-THz), which allows manipulation of carrier temperature without altering the carrier population.
Finally, non-parametric, model-less data analysis methods for high-dimensional time-resolved spectroscopy data are proposed and implemented, including rank estimation, matrix factorisation, eigendecomposition-based time-series analysis, and dimensionality reduction. Those methods are bundled into a GUI software which also features automatic data post-processing, visualisation and navigation of high-dimension datasets.
Photoexcitation upon PSC generates populations of electron quasiparticles, such as excitons and polarons. Their kinetics and interaction with each other govern the fundamental physical properties of the PSCs. When a PSC is excited with photon energy well above its bandgap, which is a realistic situation concerning the solar spectrum, “hot” excitons with large excess energy are generated, and evolve into hot carriers populated deep into the conduction band. If hot carriers are not extracted before they relax to band edge, all excess energy is lost to heat. Therefore, it is crucial to understand hot carrier dynamics to enable rational design of PSCs.
This thesis employs time-resolved terahertz spectroscopy (TRTS) to study the underlying hot carrier photophysics of PSCs. Studies of perovskites utilising TRTS in the past decade are reviewed in detail, and their limitations are identified. The commonly used optical-pump-terahertz-probe (OPTP) scheme is found to be insufficient for studying hot carrier dynamics, and an improved TRTS scheme is proposed. The new scheme adds an infrared excitation pulse (push) well below bandgap, forming a pump-push-probe scheme (PPP-THz), which allows manipulation of carrier temperature without altering the carrier population.
Finally, non-parametric, model-less data analysis methods for high-dimensional time-resolved spectroscopy data are proposed and implemented, including rank estimation, matrix factorisation, eigendecomposition-based time-series analysis, and dimensionality reduction. Those methods are bundled into a GUI software which also features automatic data post-processing, visualisation and navigation of high-dimension datasets.
Version
Open Access
Date Issued
2023-08
Date Awarded
2024-01
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Bakulin, Artem
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)