Impact of Halide Substitution in the Inorganic Framework on the Optical Activity of Chiral Metal-Halide Perovskites

Abstract

The combination of chiroptical and semiconducting properties makes chiral hybrid metal-halide perovskites a promising class of materials for optoelectronic and optospintronic devices. Still, the detailed connection between the material composition and optical activity remains to be fully understood. Here, we study the effect of halogen substitution on optical activity in the chiral hybrid perovskite (R,S,rac)-3BrMBA₂PbI_4(1–x)Br_4x. We find that an unusual sign-flip occurs in the circular dichroism (CD) spectrum as the optical gap blue-shifts with increasing bromide content. We explain this observation by shifts in the energy level alignment caused by the halide substitution. We also observed an inverse relationship between the CD intensity and the microstrain induced in the lattice for mixed-halide compositions, which we attribute to inhomogeneity in chirality transfer across the inorganic framework. Last but not least, transient Faraday rotation measurements reveal that the (R/S)-3BrMBA₂PbBr₄ system exhibits a significant spin lifetime even at room temperature, underscoring its potential for spintronic applications.