Bright Circularly-Polarized Photoluminescence in 2D Chiral Lead-Halide Perovskites

Chiral 2D hybrid halide perovskites, which combine the advantages of chirality and exceptional optoelectronic properties, are promising materials for chiroptical and opto-spintronics applications. However, hybrid perovskites with strong chirality from highly distorted crystal structures have shown low luminescence efficiencies so far. Here, we report chiral 2D (R/S/Rac)-3BrMBA₂PbI₄ perovskite single crystals and thin films with external photoluminescence quantum efficiency as high as 39% and circularly polarized photoluminescence up to 52%, at room temperature. We use single-crystal x-ray diffraction and density-functional theory to elucidate the chirality transfer from chiral crystal structures to spin orbit split band structures. Using time-resolved chiroptical spectroscopy, we find very fast radiative recombination rates, which outcompete loss channels and rationalize the excellent photoluminescence yields. We further find polarized excitons with depolarization times exceeding the radiative decay times, which underpin the highly polarized luminescence. We assign the superior optoelectronic properties of our layered hybrid perovskites to their unique crystal structures controlled by cation engineering. Our report paves the way for high-performance hybrid perovskite photonic devices for chiroptical and spin-orbit logic applications.