Optical Phonon Assisted Carrier Dynamics in APbBr₃ Single Crystals

The low-frequency phonon modes in lead halide perovskites (LHPs), responsible for intrinsic strong carrier-phonon coupling, has led to the observation of peculiar properties like long carrier-lifetime, long carrier diffusion length, moderate carrier mobility, etc. As the phonon population strongly governs the carrier dynamics, the fundamental understanding of the role of carrier-phonon coupling on carrier dynamics is crucial for the potential application of LHPs in optoelectronics. Herein, using steady-state photoluminescence (PL) and time-resolved spectroscopy, we demonstrate temperature-dependent carrier dynamics in APbBr₃ (A= MA/Cs) single crystals. Strikingly, moving from cryogenic to room temperature, we observe an unusual blue-shift of PL and long carrier-lifetime on the order of ns. The PL blue-shift with temperature is in stark contrast to the red-shift observed in conventional semiconductors and is attributed to thermal expansion in the lattice. Whereas, the long carrier-lifetime at room temperature is ascribed to the dominance of optical phonon mediated polaron formation. The long-lived carrier at room temperature promotes the candidature of LHPs in photovoltaics.