Identifying Carrier Behavior in Ultrathin Indirect-Bandgap CsPbX3 Nanocrystal Films for Use in UV/Visible-Blind High-Energy Detectors

Abstract

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 CsPbX₃ (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 CsPbI₃ under high-energy X-ray exposure is attributed to the nature of the indirect bandgap structure of CsPbX₃ . The yellow-phase CsPbI₃ -based X-ray detector achieves a relatively high sensitivity of 83.6 μCGy_air^-1 cm^-2 (under 1.7 mGy_air s^-1 at an electron field of 0.17 V μm^-1 used for medical diagnostics) although the active layer is based solely on an ultrathin (≈6.6 μm) CsPbI₃ nanocrystal film, exceeding the values obtained for commercial X-ray detectors, and further confirming good material quality. This CsPbX₃ X-ray detector is sufficient for cost-effective device miniaturization based on a simple design.

Keywords: UV-vis blind devices; X-ray detectors; ab-initio electronic structure calculations; indirect bandgap perovskites; time-resolved spectroscopy (TRPL).