Slow cooling and efficient extraction of hot carriers in perovskite films via engineering trap-mediated relaxation...

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 (ITSs) introduced by excess PbI₂, enabling an ITS-mediated channel that suppresses direct HC relaxation under high densities due to a 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 the HC lifetime in perovskite films via engineering ITSs, offering valuable guidance for the rational design of high-efficiency HC photovoltaic devices.