Lattice Energy Reservoir in Metal Halide Perovskites
Metal halide perovskite-based technologies have been rapidly developed during the last decade. However, to date, the fundamental question, why are halide perovskites superior to conventional semiconductors? has remained elusive. Here, we propose a new theory of lattice energy reservoir (LER) in halide perovskites and elucidate that LER can comprehensively impact charge carrier dynamics and thus enhance device performance, from hot carrier cooling, carrier recombination, anomalous upconversion fluorescence, illumination induced fluorescence enhancement (photobrightening), to high efficiency solar cells and light-emitting diodes. An LER is a dynamic nanodomain in halide perovskites with suppressed thermal transport that can accumulate energy from phonon coupling and then feedback to subgap carriers and result in subgap carrier upconversion. The LER directly results in slowed cooling of hot carriers and significantly prolonged carrier recombination, anomalous upconversion fluorescence, as usually termed as defect tolerance, as well as the anomalous ultraslow phenomena including persistent polarization, memory effect, and photobrightening. The LER theory rationalizes the superior optoelectronic properties and device performance and provides a novel physical understanding for anomalous phenomena observed uniquely in halide perovskites.