Why Mixed Halides\nin 2D Chiral Perovskites Weaken\nChirality-Induced Spin Selectivity

2D Ruddlesden–Popper (RP) perovskites, upon inclusion\nof\na chiral amine, exhibit chirality-induced spin selectivity (CISS).\nAlthough alloying at the halogen site in MBA-based RPs (MBA: methylbenzylammonium)\nis one of the suitable routes to tune the CISS effect, the mixed-halide\nRP perovskites exhibited complete suppression of chirality when probed\nthrough circular dichroism (CD). Here, we present the CISS effect\nin a series of mixed-halide RP perovskites. We show that photoinduced\nhalide segregation is the origin for the apparent chirality suppression.\nThe spin-dependent charge transport was evidenced through magnetic-conducting\natomic force microscopy (mc-AFM) studies and magnetoresistance (MR)\nmeasurements. The mc-AFM results show that in (<i>R</i>/<i>S</i>-MBA)<sub>2</sub>PbI<sub>4(1–<i>x</i>)</sub>Br<sub>4<i>x</i></sub>, the CISS effect decreases with\nbromide inclusion, nonmonotonically; the microstrain developed in\nthe lattice and the spin-polarized charge transport are found to be\ncorrelated. Such a behavior has been explained through an inhomogeneity\nin the strength of the hydrogen bond between the organic moieties\nand halogens in the inorganic framework of the compounds. Our results\nfurther inferred that the hydrogen-bond-induced coupling transfers\nthe chirality from the amine to the inorganic sublattice. The work\nexplains the weakened CISS effect in mixed-halide chiral RP perovskites\nand provides a strategy to tune the spin-polarized charge transport\nas well.