Banded Spherulite Formation in Chiral Halide Perovskites

Halide perovskites containing chiral organic moieties have been recognized recently for their remarkable chirality induced spin selectivity properties. Notably, the compounds exhibit chirality transfer from the chiral organic to the inorganic metal halide components. Here, we investigate the growth of the chiral halide perovskites as textured thin films containing banded spherulite structures. The compound, (S-NPB)2PbBr4 in particular, exhibits robust banded spherulite formation when the processing conditions are optimized. These banded spherulites containing extrinsic chirality of helical twists in them leading to their mesoscopic structure. We show the temperature control over these structures during the growth and characterize the pitch and growth of the helical twists within these films. The results presented here have implications for the chirality induced spin selectivity of these materials, as the compound contains meta chirality, not only in the crystallographic structure, but also in the mesoscale banded spherulites formed.