Electronic Structure of AgBi2I7 Perovskite: Substitution Effects and Structural Stability
Axel Erbing a, Hua Wu b d, Huimin Zhu b, Malin B. Johansson b, Gabriel J. Man c, Soham Mukherjee c, Håkan Rensmo c, Erik M. J. Johansson b, Michael Odelius a
a Department of Physics, Albanova University Center, Stockholm University, 106 91 Stockholm, Sweden
b Physical Chemistry, Department of Chemistry-Ångström Laboratory, Uppsala University, Box 523, 751 20, Uppsala, Sweden
c Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Box 516, SE 75120 Uppsala, Sweden
d State Key Laboratory on Integrated Optoelectronics and College of Electronic Science and Engineering, Jilin University, Changchun, China
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, Axel Erbing, 257
Publication date: 11th February 2019

During the last decade, perovskite-based solar cells have become a topic of intense research in the field of photovoltaics, with the hope of developing a material for economically viable use. The current most popular perovskite photovoltaics rely on organic-inorganic lead-based materials [1, 2], which pose environmental and health hazards due to the toxicity of lead. To significantly reduce this risk, the substitution of lead with other metals, such as the much less toxic bismuth, have been attempted [3].
The electronic structure of perovskite materials can be modeled using periodic density functional theory (DFT). The Kohn-Sham orbitals are used to interpret the photoelectron spectra and the orbital energies are associated with the electron binding energies. Hence, it is possible to extract both the band structure and the projected density of states (PDOS) from the calculations which are important to understand a materials photovoltaic properties.

In this work, cubic phase AgBi2I7 is studied theoretically with DFT. In particular, the effects on the electronic structure due to gradual antimony and bromine substitutions in the crystal are investigated, with the aim of understanding how these changes affect the cell efficiency. The structural stability of the system and how it relates to the relative distribution of Ag and vacancies is also studied. Using Monte Carlo sampling, trends in the total energy of the system as a function of the atom distribution within crystal sites are examined to understand why certain configurations are more stable under geometry optimization than others. The theoretical work is carried out in close collaboration experiments and is supported by X-ray photoelectron spectroscopy, UV-Vis spectra, and X-ray diffraction measurements.

This work was supported by the Swedish Energy Agency (STEM 2017-006797),
and the Swedish Research Council (2015-03956 and 2016-04590).

The theoretical modeling was made possible through generous allocations of computer time provided by the Swedish National Infrastructure for Computing (SNIC)
at the Swedish National Supercomputer Center (NSC) and the High Performance Computer Center North (HPC2N) and
Chalmers Centre for Computational Science and Engineering (C3SE), Sweden.

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