Identifying Carrier Behavior in Ultrathin Indirect-Bandgap CsPbX Nanocrystal Films for Use in UV/Visible-Blind High-Energy Detectors.

High-energy radiation detectors such as X-ray detectors with low light photoresponse characteristics are used for several applications including, space, medical, and military devices. Here, an indirect bandgap inorganic perovskite-based X-ray detector is reported. The indirect bandgap nature of perovskite materials is revealed through optical characterizations, time-resolved photoluminescence (TRPL), and theoretical simulations, demonstrating that the differences in temperature-dependent carrier lifetime related to CsPbX (X = Br, I) perovskite composition are due to the changes in the bandgap structure. TRPL, theoretical analyses, and X-ray radiation measurements reveal that the high response of the UV/visible-blind yellow-phase CsPbI under high-energy X-ray exposure is attributed to the nature of the indirect bandgap structure of CsPbX . The yellow-phase CsPbI -based X-ray detector achieves a relatively high sensitivity of 83.6 μCGy cm (under 1.7 mGy s at an electron field of 0.17 V μm used for medical diagnostics) although the active layer is based solely on an ultrathin (≈6.6 μm) CsPbI nanocrystal film, exceeding the values obtained for commercial X-ray detectors, and further confirming good material quality. This CsPbX X-ray detector is sufficient for cost-effective device miniaturization based on a simple design.