Band Alignment and Polaron Formation in 2D/3D Perovskites and Mixed Pb/Sn 3D Perovskites
Arup Mahata b, Daniele Meggiolaro b, Filippo De Angelis b
a Computational Laboratory for Hybrid/Organic Photovoltaic (CLHYO), Istituto CNR di Scienze e Tecnologie Molecolari (ISTM-CNR), Via Elce di Sotto 8, 06123 Perugia, Italy
b CompuNet, Istituto Italiano di Tecnologia, Genova, Italy, Via Morego, 30, Genova, Italy
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
Oral, Arup Mahata, presentation 157
Publication date: 11th February 2019

Lead halide perovskites are outstanding materials for photovoltaics due to their high efficiencies in solar cells devices. The origin of the long carrier-lifetime in this class of materials is still under debate and, among different hypothesis, the formation of large polarons preventing the recombination of charge couples is one of the most fascinating. In this work, we report a systematic study of the polaron formation process in metal halides perovskites focusing on the influence of the chemical composition of the perovskite on the polaron stabilization energy. We have investigated i) the role of the halide through the analysis of the polarons in iodide and bromide perovskites; ii) the effects of the Sn-doping in mixed and pure metal phases and iii) the indirect effects associated with the cation size and cation’s orientation in the lattice. Our study reveals that polaron formation is promoted by the bond asymmetry, with larger stabilization energies in bromide and low concentration Sn-doped perovskites compared to pure lead / tin iodide perovskites. Other factors like octahedral tilting, the size of organic cations (MA vs. FA) and their orientation in the space, i.e. dipoles, seem to play only a limited role in the process.

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