Electron-Phonon Coupling Mediated by Fr\"ohlich Interaction in Rb2SnBr6 Perovskite

Due to their well-suited optoelectronic properties, metal halide perovskites are emerging semiconductor materials with potential applications in solar cells, detectors, and light-emitting diodes. Beyond the traditional 3D perovskites, low-dimensional counterparts have more attractive effects such as excitonic emissions and quantum confinements that are enhanced by the reduced dimensionality, which involve the Electron-Phonon Coupling (EPC). Such phenomenon, which comprehends the interaction between charge carriers and lattice vibrations, usually strongly impacts the photoluminescence (PL) response in low-dimensional frameworks. In this paper, we investigated the intrinsic EPC onto low-temperature PL of the zero-dimensional (0D) Rb2SnBr6 perovskite. Temperature-dependent PL measurements, complemented by various characterization techniques and theoretical calculations, revealed broadband emission with a significant Stokes shift attributed to self-trapped excitons (STEs). The Fr\"ohlich mechanism, mediated by interactions between excitonic charge carriers and longitudinal optical (LO) phonons, primarily accounts for the emission broadening through phonon-assisted radiative recombination. The EPC strength was evaluated through the Huang-Rhys factor S=34, confirming strong correlations between electronic and vibrational properties and supporting the STE emission assumption. The possible mechanism of STE formation was evaluated by the Fr\"ohlich parameter {\alpha} of 1.94 for electrons and 4.73 for holes, which points out a major contribution of the hole-polaron quasi-particle on exciton trapping. Our findings give insights regarding the influence of EPC in 0D perovskites and STE formation, which leads to the assessment of Rb2SnBr6 for light-harvesting applications.