Control of Hot Carrier Cooling in Lead Halide Perovskites by Point Defects.

Abstract

Hot carriers (HCs) in lead halide perovskites are prone to rapidly relax at the band edge and waste plentiful photon energy, severely limiting their conversion efficiency as HC photovoltaic devices. Here, the HC cooling dynamics of MAPbI3 perovskite with common vacancy point defects (e.g., MAv+ and Iv-) and an interstitial point defect (e.g., Ii-) is elucidated, and the underlying physics is explicated using ab initio nonadiabatic molecular dynamics. Contrary to vacancy point defects, the interstitial point defect reduces the band degeneracy, decreases the HC -phonon interaction, weakens the nonadiabatic coupling, and ultimately slows down hot electron cooling by a factor of 1.5-2. Furthermore, the band-by-band relaxation pathway and direct relaxation pathway are uncovered for hot electron cooling and hot hole cooling, respectively, explaining why hot electrons can store more energy than hot holes during the cooling process. Besides, oxygen molecules interacting with Ii- sharply accelerate the hot electron cooling, making it even faster than that of the pristine system and revealing the detrimental effect of oxygen on HC cooling. This work provides significant insights into the defect-dependent HC cooling dynamics and suggests a new strategy to design high-efficiency HC photovoltaic devices.