Vapour-deposited hybrid metal-halide perovskite thin films for photovoltaic applications
<p>Hybrid metal-halide perovskite semiconductors have recently shown to be excellent photoabsorbers for photovoltaic devices. There are a variety of techniques that can be used to fabricate hybrid metal-halide thin films, from facile low temperature solution processing methods to vapour depo...
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| Format: | Thesis |
| Language: | English |
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2018
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| _version_ | 1797078579831373824 |
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| author | Patel, J |
| author2 | Herz, L |
| author_facet | Herz, L Patel, J |
| author_sort | Patel, J |
| collection | OXFORD |
| description | <p>Hybrid metal-halide perovskite semiconductors have recently shown to be excellent photoabsorbers for photovoltaic devices. There are a variety of techniques that can be used to fabricate hybrid metal-halide thin films, from facile low temperature solution processing methods to vapour deposition methods. Physical vapour deposition, in particular thermal evaporation, is one such technique, which is easily up-scalable and widely used in industry. Additionally, vapour deposition is a solvent-free technique that yields smooth, uniform and pin-hole free thin films. </p> <p>This thesis reports an investigation of hybrid metal-halide perovskite, CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> (MAPbI<sub>3</sub>) thin films, and their subsequent implementation in photovoltaic devices. The initial investigation follows the formation dynamics of the MAPbI<sub>3</sub> thin films from sequentially depositing the precursors, PbI<sub>2</sub> and CH<sub>3</sub>NH<sub>3</sub>I (MAI), whilst keeping the substrates at 273 K. Upon heating the substrates to room temperature, the MAI diffused into the PbI<sub>2</sub>. The diffusion is tracked using Fourier transform infrared spectroscopy (FTIR) and x-ray crystal diffraction analysis. The results show that exposing the films to moist air facilitates the diffusion and aids in creating a crystalline perovskite thin film.</p> <p>Dual-source vapour deposition is a technique whereupon both the precursors are evaporated at the same time, yielding a perovskite thin film immediately. An investigation on how different substrates influence the perovskite thin film, was carried out. It is found that perovskite growth on TiO<sub>2</sub> induces regions of amorphous perovskite at the interface. The presence of amorphous perovskite explains why photovoltaic devices which have a TiO<sub>2</sub>/MAPbI<sub>3</sub> interface show current-voltage hysteresis. However, incorporating a layer of continuous fullerene thin film on the substrate leads to the formation of crystalline perovskite at the interface, and the corresponding photovoltaic devices show no hysteresis.</p> <p>MAPbI<sub>3</sub> photovoltaic devices were carefully investigated at low-temperatures (15 K – 350 K) using Fourier transform photocurrent spectroscopy (FTPS). The photocurrent spectra of MAPbI3 devices showed that the excess PbI2 usually found in MAPbI<sub>3</sub> thin films contributes to the photocurrent. Furthermore, a lower limit of the exciton binding energy of 9.1 meV was extracted for MAPbI<sub>3</sub> by comparing the low temperature absorption spectra with the photocurrent spectra.</p> <p>Finally, organic bulk heterojunction photovoltaic devices were investigated. The effect of UV light on the devices for 18 hours was carefully tracked using FTPS. Initially, the results show a decrease in external quantum efficiency (EQE) at high photon energies. A closer look at the EQE spectra reveal a change in the sub-band gap absorption, indicative of a change in the micromorphology of the bulk heterojunction. These findings indicate the need to find non-fullerene acceptors.</p> |
| first_indexed | 2024-03-07T00:33:56Z |
| format | Thesis |
| id | oxford-uuid:80bf1295-9554-47d2-9778-96ccb93fd126 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T00:33:56Z |
| publishDate | 2018 |
| record_format | dspace |
| spelling | oxford-uuid:80bf1295-9554-47d2-9778-96ccb93fd1262022-03-26T21:25:30ZVapour-deposited hybrid metal-halide perovskite thin films for photovoltaic applicationsThesishttp://purl.org/coar/resource_type/c_db06uuid:80bf1295-9554-47d2-9778-96ccb93fd126Solar energy--ResearchFourier transform infrared spectroscopyThin-film FabricationEnglishORA Deposit2018Patel, JHerz, L<p>Hybrid metal-halide perovskite semiconductors have recently shown to be excellent photoabsorbers for photovoltaic devices. There are a variety of techniques that can be used to fabricate hybrid metal-halide thin films, from facile low temperature solution processing methods to vapour deposition methods. Physical vapour deposition, in particular thermal evaporation, is one such technique, which is easily up-scalable and widely used in industry. Additionally, vapour deposition is a solvent-free technique that yields smooth, uniform and pin-hole free thin films. </p> <p>This thesis reports an investigation of hybrid metal-halide perovskite, CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> (MAPbI<sub>3</sub>) thin films, and their subsequent implementation in photovoltaic devices. The initial investigation follows the formation dynamics of the MAPbI<sub>3</sub> thin films from sequentially depositing the precursors, PbI<sub>2</sub> and CH<sub>3</sub>NH<sub>3</sub>I (MAI), whilst keeping the substrates at 273 K. Upon heating the substrates to room temperature, the MAI diffused into the PbI<sub>2</sub>. The diffusion is tracked using Fourier transform infrared spectroscopy (FTIR) and x-ray crystal diffraction analysis. The results show that exposing the films to moist air facilitates the diffusion and aids in creating a crystalline perovskite thin film.</p> <p>Dual-source vapour deposition is a technique whereupon both the precursors are evaporated at the same time, yielding a perovskite thin film immediately. An investigation on how different substrates influence the perovskite thin film, was carried out. It is found that perovskite growth on TiO<sub>2</sub> induces regions of amorphous perovskite at the interface. The presence of amorphous perovskite explains why photovoltaic devices which have a TiO<sub>2</sub>/MAPbI<sub>3</sub> interface show current-voltage hysteresis. However, incorporating a layer of continuous fullerene thin film on the substrate leads to the formation of crystalline perovskite at the interface, and the corresponding photovoltaic devices show no hysteresis.</p> <p>MAPbI<sub>3</sub> photovoltaic devices were carefully investigated at low-temperatures (15 K – 350 K) using Fourier transform photocurrent spectroscopy (FTPS). The photocurrent spectra of MAPbI3 devices showed that the excess PbI2 usually found in MAPbI<sub>3</sub> thin films contributes to the photocurrent. Furthermore, a lower limit of the exciton binding energy of 9.1 meV was extracted for MAPbI<sub>3</sub> by comparing the low temperature absorption spectra with the photocurrent spectra.</p> <p>Finally, organic bulk heterojunction photovoltaic devices were investigated. The effect of UV light on the devices for 18 hours was carefully tracked using FTPS. Initially, the results show a decrease in external quantum efficiency (EQE) at high photon energies. A closer look at the EQE spectra reveal a change in the sub-band gap absorption, indicative of a change in the micromorphology of the bulk heterojunction. These findings indicate the need to find non-fullerene acceptors.</p> |
| spellingShingle | Solar energy--Research Fourier transform infrared spectroscopy Thin-film Fabrication Patel, J Vapour-deposited hybrid metal-halide perovskite thin films for photovoltaic applications |
| title | Vapour-deposited hybrid metal-halide perovskite thin films for photovoltaic applications |
| title_full | Vapour-deposited hybrid metal-halide perovskite thin films for photovoltaic applications |
| title_fullStr | Vapour-deposited hybrid metal-halide perovskite thin films for photovoltaic applications |
| title_full_unstemmed | Vapour-deposited hybrid metal-halide perovskite thin films for photovoltaic applications |
| title_short | Vapour-deposited hybrid metal-halide perovskite thin films for photovoltaic applications |
| title_sort | vapour deposited hybrid metal halide perovskite thin films for photovoltaic applications |
| topic | Solar energy--Research Fourier transform infrared spectroscopy Thin-film Fabrication |
| work_keys_str_mv | AT patelj vapourdepositedhybridmetalhalideperovskitethinfilmsforphotovoltaicapplications |