E-Thesis 536 views 100 downloads
Understanding the differences in energy levels between CH3NH3PbI3 and (CH3NH3)3Bi2I9 in darkness and under illumination using Kelvin probe measurements / ZUBIN PAREKH
Swansea University Author: ZUBIN PAREKH
Abstract
Deployment of solar energy capacity to rural areas in developing countries requires a cheap and light-weight solar technology. If the solution to this is perovskite solar cells, the use of a lead-free perovskite will avoid toxicity hurdles. In this thesis, two perovskite absorber materials are inves...
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Swansea
2020
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| Institution: | Swansea University |
| Degree level: | Master of Research |
| Degree name: | MSc by Research |
| Supervisor: | Jain, Sagar ; Davies, Matthew; Baikie, Iain |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa59930 |
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| Abstract: |
Deployment of solar energy capacity to rural areas in developing countries requires a cheap and light-weight solar technology. If the solution to this is perovskite solar cells, the use of a lead-free perovskite will avoid toxicity hurdles. In this thesis, two perovskite absorber materials are investigated for their differences in photovoltaic characteristics. Lead-free methylammonium bismuth iodide is analysed alongside methylammonium lead iodide using a range of Kelvin probe techniques. Both perovskite materials are characterised as thin-film photoactive layers deposited on top of fluorine-doped tin oxide glass substrates. Energy level measurement reveals that changing only the metal cation (switching lead with bismuth) completely tunes photo-induced behaviour of the perovskite. Spectroscopic data for surface photovoltage shows the fermi level of (CH3NH3)3Bi2I9 shifts above and below its dark position at different wavelengths of illumination. Under white light pulses, CH3NH3PbI3 performs better with a repeatable surface photovoltage of 250mV. In unique conditions of 500nm light at low intensity, (CH3NH3)3Bi2I9 generates the higher surface photovoltage with 120mV. These surface photovoltages represent the open-circuit voltage contribution from the absorber material. Both perovskites demonstrate that surface photovoltage remains unchanged after over 5 months of storage in a dark ambient environment. Although this is a very positive result, it is speculated that a poorer retention of surface photovoltage would arise if samples were exposed to light during storage. The measured bandgap of (CH3NH3)3Bi2I9 was 1.70eV, and the measured bandgap of CH3NH3PbI3 was 1.598eV. In general, the work provides useful comparative data between two perovskites and shows (CH3NH3)3Bi2I9 could have future applications as a photovoltaic device in monochromatic light conditions or with tandem cells. |
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| Keywords: |
Work function, Kelvin probe, perovskite, solar cells |
| College: |
Faculty of Science and Engineering |