Identification of lead vacancy defects in lead halide perovskites

Abstract

Perovskite photovoltaics advance rapidly, but questions remain regarding point defects: while experiments have detected the presence of electrically active defects no experimentally confirmed microscopic identifications have been reported. Here we identify lead monovacancy (V_Pb) defects in MAPbI₃ (MA = CH₃NH₃⁺) using positron annihilation lifetime spectroscopy with the aid of density functional theory. Experiments on thin film and single crystal samples all exhibited dominant positron trapping to lead vacancy defects, and a minimum defect density of ~3 × 10¹⁵ cm^-3 was determined. There was also evidence of trapping at the vacancy complex [Formula: see text] in a minority of samples, but no trapping to MA-ion vacancies was observed. Our experimental results support the predictions of other first-principles studies that deep level, hole trapping, [Formula: see text], point defects are one of the most stable defects in MAPbI₃. This direct detection and identification of a deep level native defect in a halide perovskite, at technologically relevant concentrations, will enable further investigation of defect driven mechanisms.