Halogen-Dependent\nCircular Dichroism and Magneto-Photoluminescence\nEffects in Chiral 2D Lead Halide Perovskites

Chiral lead halide perovskites (chiral LHPs) have emerged\nas one\nof the best candidates for opto-spintronics due to their large spin–orbit\ncoupling (SOC) and unique chirality-induced spin selectivity (CISS)\neven in the absence of a magnetic field. Here, we report the impact\nof halide composition on circular dichroism (CD) and magneto-photoluminescence\n(PL) effects of chiral 2D LHPs (<i>R</i>/<i>S</i>-MBA)<sub>2</sub>PbBr<sub><i>x</i></sub>I<sub>4–<i>x</i></sub> (MBA = C<sub>6</sub>H<sub>5</sub>CH<sub>2</sub>(CH<sub>3</sub>)NH<sub>3</sub>). By tuning the mixing ratio of Br/I halide\nanions, we find that (<i>R</i>/<i>S</i>-MBA)<sub>2</sub>PbBr<sub><i>x</i></sub>I<sub>4–<i>x</i></sub> thin films exhibit tunable and wide wavelength range CD signals.\nSimultaneously, the main CD signals near the exciton absorption band\ngradually blue shift until they disappear. Moreover, the halogen-dependent\nnegative magneto-PL effects of (<i>R</i>/<i>S</i>-MBA)<sub>2</sub>PbBr<sub><i>x</i></sub>I<sub>4–<i>x</i></sub> thin films excited by left/right circularly polarized\nlight can be detected at room temperature. We demonstrated that the\nhalide composition can effectively modulate exciton splitting and\nchirality transfer in (<i>R</i>/<i>S</i>-MBA)<sub>2</sub>PbBr<sub><i>x</i></sub>I<sub>4–<i>x</i></sub> owing to the chirality-induced SOC and crystalline structure\ntransition, which lead to the adjustable CD signals. The interplay\nof Rashba-type band spin splitting and spin mixing among bright triplet\nexciton states is responsible for the halogen-dependent magneto-PL\neffect of chiral 2D LHPs. This study enables chiral 2D LHPs with CISS\nto be a new class of promising opto-spintronics materials for exploring\nhigh-performance spin-light-emitting diodes by halide engineering.