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

Abstract

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.