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Abstract

The combination of chiroptical and semiconducting properties makes chiral hybrid metal-halide perovskites a promising class of materials for optoelectronic and opto-spintronic devices. Still, the detailed connection between 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)- 3BrMBA2PbI4(1-x)Br4x. We find that an unusual sign-flip occurs in the circular dichroism (CD) spectrum as the optical gap blueshifts 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 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.