Strong Coupling of Self-Trapped Excitons to Acoustic Phonons in Bismuth Perovskite ${\text{Cs}}_3{\text{Bi}}_2{\text{I}}_9$

Abstract

To assess the potential optoelectronic applications of metal-halide perovskites, it is critical to have a detailed understanding of the nature, strength, and dynamics of the interactions between carriers and the polar lattices. Here, we report the electronic and structural dynamics of bismuth-based perovskite ${\text{Cs}}_3{\text{Bi}}_2{\text{I}}_9$ revealed by transient reflectivity and ultrafast electron diffraction. A cross-examination of these experimental results combined with theoretical analyses allows the identification of the major carrier-phonon coupling mechanism and the associated time scales. It is found that carriers photoinjected into ${\text{Cs}}_3{\text{Bi}}_2{\text{I}}_9$ form self-trapped excitons on an ultrafast time scale. However, they retain most of their energy and their coupling to Fröhlich-type optical phonons is limited at early times. Instead, the long-lived excitons exert an electronic stress via deformation potential and develop a prominent, sustaining strain field as coherent acoustic phonons in 10 ps. From sub-ps to ns and beyond, a similar extent of the atomic displacements is found throughout the different stages of structural distortions, from limited local modulations to a coherent strain field to the Debye-Waller random atomic motions on longer times. The current results suggest the potential use of bismuth-based perovskites for applications other than photovoltaics to take advantage of carriers' stronger self-trapping and long lifetime.

21 pages, 4 figures for the main text

References in corpus (4)

• Visualization of Dynamic Polaronic Strain Fields in Hybrid Lead Halide Perovskites
• Unconventional light-induced states visualized by ultrafast electron diffraction and microscopy
• Ultrafast carrier-coupled interlayer contraction, coherent intralayer motions, and phonon thermalization dynamics of black phosphorus
• Phase Coexistence in Cs3Bi2I9 Ferroelastics: Optical, Dilatation and Ultrasonic Velocity Studies

Cited by in corpus (2)

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• Direct Observation of Energy Transport Dynamics and High Thermal Conductance across Single Solid-Molecule Junctions