Interplay of Static and Dynamic Disorder in the Mixed-Metal Chalcohalide Sn₂SbS₂I₃

Chalcohalide mixed-anion crystals have seen a rise ininterestas "perovskite-inspired materials" with the goal ofcombining the ambient stability of metal chalcogenides with the exceptionaloptoelectronic performance of metal halides. Sn2SbS2I3 is a promising candidate, having achieved aphotovoltaic power conversion efficiency above 4%. However, thereis uncertainty over the crystal structure and physical propertiesof this crystal family. Using a first-principles cluster expansionapproach, we predict a disordered room-temperature structure, comprisingboth static and dynamic cation disorder on different crystallographicsites. These predictions are confirmed using single-crystal X-raydiffraction. Disorder leads to a lowering of the bandgap from 1.8eV at low temperature to 1.5 eV at the experimental annealing temperatureof 573 K. Cation disorder tailoring the bandgap allows for targetedapplication or for the use in a graded solar cell, which when combinedwith material properties associated with defect and disorder tolerance,encourages further investigation into the group IV/V chalcohalidefamily for optoelectronic applications.