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In hybrid lead halide perovskites, the coupling between photogeneratedcharges and the ionic degrees of freedom plays a crucial role in defining theintrinsic limit of carrier mobility and lifetime. However, direct investigationof this fundamental interaction remains challenging because its relevantdynamics occur on ultrashort spatial and ultrafast temporal scales. Here, weunveil the coupled electron-lattice dynamics of a CH3NH3PbI3 single crystalupon intense photoexcitation through a unique combination of ultrafast electrondiffraction, time-resolved photoelectron spectroscopy, and time-dependent abinitio calculations. We observe the structural signature of a hot-phononbottleneck effect that prevents rapid carrier relaxation, and we uncover aphonon avalanche mechanism responsible for breaking the bottleneck. Theavalanche involves a collective emission of low-energy phonons - mainlyassociated with the organic sub-lattice - that proceeds in a regenerativemanner and correlates with the accumulation and confinement of photocarriers atthe crystal surface. Our results indicate that in hybrid perovskites carriertransport and spatial confinement are key to controlling the electron-phononinteraction and their rational engineering is relevant for future applicationsin optoelectronic devices.

Observation of a phonon avalanche in highly photoexcited hybrid perovskite single crystals