Chalcohalide mixed-anion crystals have seen a rise in interest as “perovskite-inspired materials” with the goal of combining the ambient stability of metal chalcogenides with the exceptional optoelectronic performance of metal halides. Sn2SbS2I3 is a promising candidate, having achieved a photovoltaic power conversion efficiency above 4%. However, there is uncertainty over the crystal structure and physical properties of this crystal family. Using a first-principles cluster expansion approach, we predict a disordered room-temperature structure, comprising both static and dynamic cation disorder on different crystallographic sites. These predictions are confirmed using single-crystal X-ray diffraction. Disorder leads to a lowering of the bandgap from 1.8 eV at low temperature to 1.5 eV at the experimental annealing temperature of 573 K. Cation disorder tailoring the bandgap allows for targeted application or for the use in a graded solar cell, which when combined with material properties associated with defect and disorder tolerance, encourages further investigation into the group IV/V chalcohalide family for optoelectronic applications.
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We thank Stephan Lany and Jacob Cordell for sharing code to analyze IPR from DFT calculations. We thank Alex Ganose for a helpful discussion regarding transport properties. A.N. and S.R.K. acknowledge the EPSRC and SFI Centre for Doctoral Training in Advanced Characterisation of Materials (EP/S023259/1) for funding a Ph.D. studentship. The authors acknowledge the use of the UCL Kathleen and Thomas High Performance Computing Facility. Via membership of the UK’s HEC Materials Chemistry Consortium, which is funded by the EPSRC (EP/L000202, EP/R029431, EP/T022213), this work used the ARCHER2 UK National Supercomputing Service ( www.archer2.ac.uk and the UK Materials and Molecular Modelling (MMM) Hub (Thomas – EP/P020194 and Young – EP/T022213). D.O.S. acknowledges support from the European Research Council, ERC (Grant No. 758345).
© 2023 The Authors. Published by American Chemical Society.