Prediction and control of harmful point defects in thin film photovoltaics: Improving the performance of tin sulfide

Many thin-film photovoltaic materials show promising optical properties, but are limited by low minority-carrier lifetimes. Many factors can lower the carrier lifetime, including structural defects, intrinsic point defects, and extrinsic point defects from impurities. We focus on the case of tin (II) sulfide (SnS), in which point defects in particular may be lifetime-limiting. We model the impact of intrinsic and extrinsic point defects to narrow down the most likely lifetime-limiting defects to the extrinsic iron- and cobalt-on-tin substitutional defects and the sulfur vacancy. We grow material to eliminate these defects and observe over 1 order of magnitude increases in photoluminescence decay time, which is reflective of minority carrier lifetime. We believe that this kind of targeted approach towards point defect management could be applied to new thin film materials.