Slow Cooling and Efficient Extraction of Hot Carriers in Perovskite Films via Engineering Trap-Mediated Relaxation Channel

Abstract

Long-lived hot carriers (HCs) are highly desired for HC photovoltaics, but achieving slow HC relaxation is challenging because strong electron-phonon interaction typically drives rapid thermalization. Herein, we investigate the influence of excess PbI₂ on HC relaxation in formamidinium lead iodide (FAPbI₃) perovskite films using femtosecond transient absorption spectroscopy. Our results show that excess PbI₂ significantly slows down the HC relaxation at high excitation densities, extending their lifetime to hundreds of picoseconds. This effect arises from intraband trap states (ITS) introduced by excess PbI₂, enabling an ITS-mediated channel that suppress direct HC relaxation under high densities due to hot phonon bottleneck.Owing to the remarkably suppressed HC relaxation, efficient HC extraction was successfully achieved in PbI₂-rich perovskite films by incorporating electron acceptors. Our findings suggest an effective approach to prolong HC lifetime in perovskite films via engineering ITS, offering a valuable guideline for the rational design of high-efficiency HC photovoltaic devices.