Exciton-phonon interaction in quasi-two dimensional layered (PEA)₂(CsPbBr₃)_n-1PbBr₄ perovskite

Two-dimensional (2D) Ruddlesden-Popper perovskites with bulky organic cations have attracted extensive attention in light-emitting devices and photovoltaics due to their robust environment stability, tunable luminescent color, strong exciton binding and promising efficiency. A quantum well (QW) structure is spontaneously formed by sandwiching PbBr4 layers into bulky organic cations. However, some intrinsic excitonic mechanisms in these materials still need to be elucidated. In this study, the exciton-phonon interaction of quasi-2D (PEA)2(CsPbBr3)n-1PbBr4 with different PbBr4 layer numbers (n) was analyzed by temperature-varied photoluminescence (PL), scanning electron microscopy (SEM) and powder X-ray diffraction (PXRD). The mechanism of bandgap shifting with temperature was found to be dominated by the thermal expansion effect in the large-n 2D and bulk perovskite, and gradually switched to exciton-phonon interaction in the n = 1 (PEA)2PbBr4 phase, indicating enhanced exciton-phonon interaction in the thinner quantum well structure. Further analysis showed that the enhanced exciton-phonon interaction originated from the longitudinal optical phonon-exciton Fröhlich interaction rather than acoustic phonon-exciton coupling. We believe that our results will benefit the further optimization of light-emitting devices based on 2D perovskites.