In the relentless pursuit of developing high-performance, stable and environmentally friendly materials for X-ray detection, we present a new class of Bi-based hybrid organic-inorganic perovskites. An X-ray detector based on a new zero-dimensional (0D) triiodide-induced lead-free hybrid perovskite, (DPA)2BiI9 (DPA = C5H16N22+), has been developed demonstrating outstanding detection performance, including high X-ray sensitivity (20 570 μC Gyair-1 cm-2), low detectable dose rate (0.98 nGyair s-1), fast response time (154/162 ns) and excellent long-term stability.