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. Sn2SbS2I3is 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.