Phase-Dependent Large Polaron Formation in Lead Halide Perovskites: A Theoretical Study

Lead halide perovskites (LHPs) have recently garnered significant attention in photovoltaic technology, due to their high energy conversion efficiency, which is attributed to long carrier lifetime and defect tolerance [1]. The formation of large polarons has been proposed as a possible mechanism behind these exceptional photovoltaic properties [2]. Recent femtosecond diffuse X-ray scattering experiments provided clear evidence of large-polaron formation, revealing nanoscale lattice distortions in MAPbBr₃ [3]. Motivated by this observation, using occupation-constrained density functional theory calculations, we investigated the structural deformations resulting from the interaction between excited electrons and phonons, aiming to uncover the mechanism of polaron formation in LHPs APbBr₃ (A = Cs, MA, or FA). Our results reveal a strong phase dependence in large polaron formation, with more pronounced deformation in the tetragonal phase compared to the cubic and orthorhombic phases. Additionally, we observed directional dependence in the deformation and polaronic strain. Our study provides key insights into the polaron formation mechanism in LHPs, highlighting the dependence of large polaron formation on the structural phases in LHPs.