Charge Carrier Trapping at Surface Defects of Perovskite Solar Cell Absorbers: A First-Principles Study.

The trapping of charge carriers at defects on surfaces or grain boundaries is detrimental for the performance of perovskite solar cells (PSCs). For example, it is the main limiting factor for carrier lifetime. Moreover, it causes hysteresis in the current-voltage curves, which is considered to be a serious issue for PSCs' operation. In this work, types of surface defects responsible for carrier trapping are clarified by a comprehensive first-principles investigation into surface defects of tetragonal CHNHPbI (MAPbI). Considering defect formation energetics, it is proposed that a Pb-rich condition is preferred to an I-rich one; however, a moderate condition might possibly be the best choice. Our result paves the way for improving the performance of PSCs through a rational strategy of suppressing carrier trapping at surface defects.