Chirality Inducing Polar Photovoltage in a 2D Lead-Free Double Perovskite toward Self-Powered X-ray Detection

Lead-free halide double perovskites (HDPs) have sparked broad interest in developing "green" photodetectors; however, self-powered X-ray detectors in this family remain elusive. Here, by exploiting the chirality-induced polar photovoltaic effect in a chiral-polar 2D HDP, (R-MPA)4AgBiI8 (1, R-MPA = R-β-methylphenethylammonium), we successfully realized self-powered X-ray detection. The significant spontaneous electric polarization in 1 gives it a large polar photovoltage of 0.36 V, which drives the separation and transport of X-ray-generated carriers, thus acquiring the capability of self-powered detection. Consequently, X-ray detectors based on high-quality single crystals of 1 exhibit a high sensitivity of 46.3 μC Gy–1 cm–2 and an ultralow detection limit of 85 nGy s–1 at zero bias. The sensitivity can be further increased to 949.6 μC Gy–1 cm–2 at 50 V bias, outperforming all current 2D HDP detectors. Our work is the first to demonstrate self-powered X-ray detection in single-phase lead-free HDPs, enlightening future design of "green" self-powered radiation detectors.