β-In2S3 for photovoltaic devices: investigation of the native point defects with ab initio first-principle calculations

Herein, we report a theoretical investigation based on DFT calculations devoted to the nature of charge carriers in the β-In2S3 material used as buffer in chalcopyrite thin-film solar cells. Our simulations led to unambiguous results concerning the incapability for this material to be a p-type semiconductor. Furthermore, it is demonstrated that the insertion of indium into a Td interstitial site seems to be the driving force leading to a natural n-type conductivity. Our calculations took into account different atmospheres in order to be directly comparable with experimental data. In particular, the competitive InS structure was considered. It is shown that the S-poor condition strongly lesser the defect formation energy and should be privileged to achieve high free electron concentrations for potential applications.