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

TL;DR

This study reveals a phonon avalanche phenomenon in highly photoexcited hybrid perovskite crystals, showing how collective phonon emissions influence carrier dynamics and could impact optoelectronic device performance.

Contribution

It provides the first direct observation of a phonon avalanche in hybrid perovskites, linking ultrafast electron-lattice interactions to carrier confinement and transport.

Findings

Detection of a hot-phonon bottleneck effect.

Identification of a regenerative phonon avalanche mechanism.

Correlation between phonon emission and carrier confinement.

Abstract

In hybrid lead halide perovskites, the coupling between photogenerated charges and the ionic degrees of freedom plays a crucial role in defining the intrinsic limit of carrier mobility and lifetime. However, direct investigation of this fundamental interaction remains challenging because its relevant dynamics occur on ultrashort spatial and ultrafast temporal scales. Here, we unveil the coupled electron-lattice dynamics of a CH3NH3PbI3 single crystal upon intense photoexcitation through a unique combination of ultrafast electron diffraction, time-resolved photoelectron spectroscopy, and time-dependent ab initio calculations. We observe the structural signature of a hot-phonon bottleneck effect that prevents rapid carrier relaxation, and we uncover a phonon avalanche mechanism responsible for breaking the bottleneck. The avalanche involves a collective emission of low-energy phonons - mainly associated with the organic sub-lattice - that proceeds in a regenerative manner and correlates with the accumulation and confinement of photocarriers at the crystal surface. Our results indicate that in hybrid perovskites carrier transport and spatial confinement are key to controlling the electron-phonon interaction and their rational engineering is relevant for future applications in optoelectronic devices.