Lattice dynamics and self-trapped excitons in the Cs₂SnBr₆ double perovskites

Abstract

We performed a comprehensive study on the electrical characteristics, lattice dynamics, and structural stability of Cs2SnBr6 double perovskites. The origin and symmetry of the four phonon modes active in Raman scattering are clearly identified by combining mirco-Raman spectroscopy and first-principle calculations, that is, one external translational mode of the Cs+ lattice with T2g symmetry and three internal modes of the octahedral with A1g, Eg, and T2g symmetries. Our results show a significant correlation with first-principles calculations, validating using a band-structured electronic approach to understanding the behavior of charge carriers, and electron-phonon interactions in Cs2SnBr6. The formation of Self-trap excitons is a direct consequence of the enhancement of electron-vibration couplings, which in turn causes large Stokes shifts (0.508 eV) and the broadband emission spanning 430 to 715 nm. A fundamental understanding of the dynamics of Self-trapped excitons is of vital for their optoelectronic applications.