The Effect of Intrinsic Defects in Grain Boundaries on Non-Radiative Recombination in CsPbI3 and CsPbBr3

Abstract

The photoluminescence (PL) response of halide perovskite (HP) photovoltaic absorbers near grain boundaries (GBs) remains poorly understood. Spatially resolved PL measurements reveal pronounced variations in emission intensity around GBs, underscoring their importance in charge carrier dynamics within polycrystalline HP films. However, the microscopic origins of these variations remain unclear and are likely influenced by the interplay between intrinsic point defects and the extended structural environment of GBs. In this study, the relationship between defects in GBs and non-radiative recombination is investigated by performing first-principles calculations in γ-CsPbBr3 and γ-CsPbI3 across three geometries: bulk, Σ3(111)(0,0), and Σ3(112)(0,0) GB. Defect formation is found to be energetically more favorable at GBs than in the bulk, establishing GBs as thermodynamic sinks for intrinsic defects. We find pronounced stabilization of halide interstitials, halide vacancies, Pb interstitial, and PbBr antisite at GBs. Pb-related defects show the largest reduction in formation energy, directly linked to the enhanced free volume at the GB plane. This prediction is corroborated by elemental analysis of CsPbBr3 crystals, which reveals Pb-enriched regions at the GBs. Despite this thermodynamic preference, the corresponding charge transition levels remain largely unchanged relative to bulk. These results indicate that the reduced PL observed at GBs is dominated by the high concentration of Pb-related defects and supplemented by halide interstitials, providing new insight into the defect-microstructure interplay that limits HP photovoltaic performance.