Eradicating impurities in zero-dimensional metal lead halide perovskite films for stable, low dark current X-ray detectors

Zero-dimensional cesium lead halide (Cs4PbI6) perovskite shows great potential in direct X-ray detection with a low dark current and high stability, but impurity phases including cesium iodide (CsI) and CsPbI3 can easily form in polycrystalline Cs4PbI6 films. Herein, we explore the growth kinetics of Cs4PbI6 polycrystal thick films via spray-coating method by optimizing their structure, composi-tion, and optical properties. Combined experimental and computa-tional studies disclose that under high-temperature annealing, Cs4PbI6 crystals decompose and form impurities, which could be eliminated by controlling the annealing temperature. The optimized thick film enables a high on/off ratio and a super-low dark current (3 nA cm -2) X-ray detector device of an FTO/Cs4PbI6/carbon sandwich with a decent sensitivity of 245 mCGy- 1 air cm -2 under 30 keV X-ray irradiation at an applied electric field of 55 V mm -1. The device re-mains stable after continuous operation for a total accumulated dose of 8.17 3 106 mGyair, equivalent to 4 million chest X-ray scans.