Chirality\nInducing Polar Photovoltage in a 2D Lead-Free\nDouble Perovskite toward Self-Powered X‑ray Detection

Lead-free halide double perovskites (HDPs) have sparked\nbroad interest\nin developing “green” photodetectors; however, self-powered\nX-ray detectors in this family remain elusive. Here, by exploiting\nthe chirality-induced polar photovoltaic effect in a chiral-polar\n2D HDP, (<i>R</i>-MPA)₄AgBiI₈ (<b>1</b>, <i>R</i>-MPA = <i>R</i>-β-methylphenethylammonium),\nwe successfully realized self-powered X-ray detection. The significant\nspontaneous electric polarization in <b>1</b> gives it a large\npolar photovoltage of 0.36 V, which drives the separation and transport\nof X-ray-generated carriers, thus acquiring the capability of self-powered\ndetection. Consequently, X-ray detectors based on high-quality single\ncrystals of <b>1</b> exhibit a high sensitivity of 46.3 μC\nGy^–1 cm^–2 and an ultralow detection\nlimit of 85 nGy s^–1 at zero bias. The sensitivity\ncan be further increased to 949.6 μC Gy^–1 cm^–2 at 50 V bias, outperforming all current 2D HDP detectors.\nOur work is the first to demonstrate self-powered X-ray detection\nin single-phase lead-free HDPs, enlightening future design of “green”\nself-powered radiation detectors.