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Time-resolved spectroscopy of charge-carrier dynamics in metal halide perovskites and other semiconductors for photovoltaics
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Butler-Caddle, Edward (2023) Time-resolved spectroscopy of charge-carrier dynamics in metal halide perovskites and other semiconductors for photovoltaics. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3973314
Abstract
This thesis reports optical measurements and analysis of the charge-carrier dynamics in semiconductor materials and structures that are used in photovoltaic cells. Observing the carrier dynamics in these devices is crucial for understanding the properties that are limiting efficiency, so that improvements can be achieved more quickly through design, rather than trial and error.
In perovskite solar cells, the charge transport layers (CTLs) on either side of the perovskite layer provide the asymmetry required to generate a photovoltage and photocurrent. In this work, the charge-carrier transfer and recombination behaviour at each individual interface is studied by measuring the carrier dynamics when only one interface is present i.e. a bilayer of a perovskite and either an electron transport layer (ETL) or a hole transport layer (HTL). In addition to using optical techniques that are more commonly employed in the literature, optical pump terahertz probe spectroscopy (OPTP) was used to measure the carrier density accurately in the first few nanoseconds, which revealed very different behaviour for fullerene based ETLs and the commonly used HTL, Spiro-OMeTAD. These measurements were then compared to two mathematical models of differing complexity, which provided greater understanding of the measured dynamics. The different behaviours observed at different interfaces have important implications for solar cell design.
A limitation of using OPTP to study semiconductors used in photovoltaics is that the carrier lifetimes are often much longer than the time range of the technique. An electronically delayed OPTP technique (E-OPTP) was developed, that has virtually unlimited time range whilst maintaining sub-nanosecond resolution. An efficient method to sample photoconductance decays longer than the laser repetition period was proposed, and was used to study the impact of surface passivation on the carrier dynamics in silicon. This technique was compared to inductively-coupled photoconductance measurements, which highlighted the superior spatial and temporal resolution of E-OPTP that allows in-plane and out-of-plane diffusion to be studied. The diffusion was modelled using analytical solutions of the ambipolar continuity equation. Overall, this work demonstrates the suitability of this technique for studying semiconductors with long carrier lifetimes.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QC Physics | ||||
Library of Congress Subject Headings (LCSH): | Photovoltaic cells, Charge carrier processes, Perovskite materials, Solar cells, Electron transport, Terahertz spectroscopy | ||||
Official Date: | April 2023 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Lloyd-Hughes, James | ||||
Sponsors: | Engineering and Physical Sciences Research Council | ||||
Format of File: | |||||
Extent: | xiv, 196 pages : illustrations | ||||
Language: | eng |
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