Understanding the differences between MABiI3 and MAPbI3 under an advanced Kelvin Probe system
Zubin Parekh a, Conor Davidson b, Matthew Davies a, Iain Baikie b, Sagar Jain a
a SPECIFIC, College of Engineering, Swansea University, Bay Campus, Swansea, SA1 8EN, UK
b KP Technology, Burn Street, Wick, Caithness, KW1 5EH, UK
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Poster, Zubin Parekh, 259
Publication date: 11th February 2019


The future of perovskite solar cells is bright. It could be even brighter with a serious lead-free competitor to methylammonium lead iodide (MAPbI3). Methylammonium bismuth iodide (MABiI3) is one of those perovskites that has potential to provide benefits over MAPbI3; it is less toxic and atmospherically more stable [1][2][3][4].  


This purpose of this study was to measure differences in semiconductor properties such as fermi level response to light, HOMO level and band gap. Comparing these characteristics highlights why MAPbI3 has the superior PCE; a smaller band gap, and larger open circuit voltage under illumination was measured for MAPbI3.


The work function response of MAPbI3 is 150mV larger than the response of MABiI3 – this is a representative of a greater open circuit voltage achievable. Hence, MAPbI3 PCE values are commonly >15% [5][6] [7] whilst MABiI3 PCE values are around 3% [8]. 


Surface photovoltage spectroscopy has revealed that MABiI3 experienced a work function decrease under low energy light (650-850nm) and a work function increase under high energy light (400-600nm). MABiI3 has complex activity under illumination. An understanding of the immediate light response is required to be able to explore ways of increasing the open circuit voltage of MABiI3 solar cells. This study shares ideas of why MABiI3 responds inversely to different wavelengths of light.


Author Z. Parekh is thankful to Materials and Manufactruing Academy (M2A) and KP Technology for funding. In addition, thank you to KP Technology for the experimental support provided and use of their facility. Authors are grateful to European Union's Horizon 2020 research and innovation program. 


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