Polycrystalline Lead Halide Perovskites: Synthesis and Application As X-Ray Detectors

X-ray inspection is an essential tool for ensuring security. X-ray inspection systems are used to detect contraband in passenger vehicles, trains, and cargo containers. High penetration depths of the x-rays, combined with the large detector area required for these subjects, requires extensive detector masses for sufficient detection. US government directives aim for more thorough screening at ports of entry, resulting in a demand for x-ray inspection systems. The detector materials used in the present inspection systems are a significant contributor to the system's cost, creating a need for alternative detector materials with adequate performance and low gravimetric cost. In this dissertation, we present research performed on the synthesis of polycrystalline lead halide perovskites and their characterization as x-ray detectors. We optimized a solid-state reaction to produce CsPbCl3:Yb powder with high light output and measured its intrinsic scintillator characteristics. While the luminescence decay time of CsPbCl3:Yb was deemed insufficient for a dynamic x-ray inspection system, we evaluated its imaging properties in a static radiography setting and found it suitable for general imaging. To address the potential use of polycrystalline perovskites in x-ray inspection, we compacted CsPbX3 perovskites into wafers capable of x-ray detection by direct conversion. The performance of similar polycrystalline detectors is hindered by ion migration that occurs under bias, causing high dark current and hysteresis. We implemented an ionic liquid passivation strategy and layered compositionally altered powders to form a heterojunction to address the ion migration. Both strategies were shown to improve the electrical properties of the detectors, and the sensitivity, limit of detection, and charge transport of the detectors were characterized. We regard the compacted polycrystalline perovskite wafers used as direct radiation detectors as the format with the most potential for use in an x-ray inspection environment of the research completed here.