Lead-free metal-halide perovskites have attracted considerable attention in X-ray detection due to their high atomic numbers, solution processability, and environmental benignity. Among them, all-inorganic bismuth-based halide perovskites are regarded as promising candidates because of their low toxicity, tunable halide composition, and excellent environmental stability. However, spray-coated thick films often suffer from insufficient interfacial adhesion to substrates and film cracking, which severely deteriorate film quality and device performance. In this work, polyvinylpyrrolidone (PVP) is introduced into the precursor solution as an additive to regulate the film formation process and enhance the interfacial adhesion of spray-coated thick films.
The results demonstrate that the PVP effectively suppresses interfacial delamination and crack formation, leading to the formation of compact and continuous thick films. Compared with the film without PVP, the PVP-modified film exhibits significantly improved crystallinity, with the diffraction intensity increased by 1.9 times, longer photoluminescence lifetime of 9.20 ns, and a high resistivity of 4.55×10¹¹ Ω·cm, indicating suppressed leakage current. Based on the optimized thick film, the fabricated direct X-ray detector exhibits a low dark current of 0.03 nA at 4 V, a large mobility-lifetime product (μτ = 7.62×10^-5 cm² V^-1), and a low detection limit of 30 nGy_air S^-1 and a sensitivity of 1250 μC Gy_air^-1 cm^-2. In addition, the introduction of PVP improves the environmental stability of the device, and retained 93% of the initial sensitivity under the atmospheric environment after 90 days. These results demonstrate that PVP additive engineering is an effective approach for improving the microstructure, interfacial adhesion, and optoelectronic properties of spray-coated Cs₃Bi₂I_xBr_9-x thick films, thereby enhancing the performance and long-term stability of direct X-ray detectors. This work provides a practical strategy for developing high-performance, low-toxicity, and stable thick-film X-ray detection materials.