Direct X-Ray Detectors Based on an Organic Zinc Bromide Hybrid

Direct X-ray detectors, which convert X-ray radiation to electrical charge and then digital images, are used in various areas, including medical diagnostics, security screening, and industrial inspection. The most commonly used materials for the fabrication of direct X-ray detectors are inorganic semiconductors, such as silicon and selenium, which often suffer from limitations in performance, versatility, and cost-effectiveness. Searching for new-generation materials for direct X-ray detectors has been continually pursued to address these issues, among which metal halide perovskites have recently received great attention for their efficient X-ray absorption, high carrier transport properties, as well as facile synthesis. However, the lead toxicity, environmental instability, and high dark current due to ion migration have limited the potential of perovskite-based direct X-ray detectors for real-life applications. Zero-dimensional (0D) organic metal halide hybrids (OMHHs), containing metal halide polyhedral anions fully isolated and surrounded by organic cations, exhibit significantly better stability and lower current drift as compared to conventional metal halide perovskites. In this talk, I will introduce our recent efforts in the development of direct X-ray detectors based on 0D OMHHs. More specifically, I will discuss the use of a semiconducting 0D OMHH, (TPA-P)₂ZnBr₄, for the fabrication of highly sensitive and stable direct X-ray detectors. With molecular sensitization, wherein metal halide species (ZnBr₄^2-) act as X-ray absorber and organic semiconducting components (TPA-P⁺, 4-(4-(diphenylamino)phenyl)-1-propylpyridin-1-ium) as charge transporters, 0D (TPA-P)₂ZnBr₄-based X-ray detectors are found to exhibit an impressive sensitivity of 1,984 μC Gy_air^-1cm^-2 at 20 V reverse bias and a low detection limit of 0.88 μGy_airs^-1. Electronic characterizations have revealed a low trap density of 3.84x10⁹ cm^-3 and a high mobility lifetime product of 5.67x10^-4cm².V^-1 at 20 V for solution-grown 0D (TPA-P)₂ZnBr₄single crystals. The high resistivity of 5.05×10¹⁰Ω.cm of 0D (TPA-P)₂ZnBr₄ plays a crucial role in realizing a very low and stable dark current of around 13.4 pA under 24 hours of operation. The combination of low-cost facile preparation, high detection sensitivity, low detection limit, and superior stability make semiconducting 0D OMHHs highly promising active materials for direct X-ray detectors.