Paper-based lead-free thin film X-ray detectors with high sensitivity and superior environmental stability

Low-dimensional, lead-free halide perovskites are promising candidates for next-generation radiation detectors due to their favorable optoelectronic properties and environmental safety. Among them, Cs₃Bi₂Br₉ has thus attracted significant attention for its layered structure and intrinsic stability. Although Cs₃Bi₂Br₉ has already been explored for X-ray detection, simple and scalable fabrication routes for its thin films on flexible low-cost substrates remain underdeveloped. Here, we demonstrate a sustainable, all-dry abrasion method to directly deposit Cs₃Bi₂Br₉ thin films onto biodegradable office-grade printing paper at room temperature, enabling the fabrication of flexible, lead-free X-ray detectors. The resulting devices exhibit a resistivity of 6.9 × 10⁹ Ω cm and a mobility-lifetime (μτ) product of 9.07 × 10-⁴ cm² V⁻¹, yielding X-ray detection sensitivities of 660-860 μC Gy_air⁻¹ cm⁻². Reducing the electrode spacing to 50 μm further enhances sensitivity to ~28,000 μC Gy_air ^-1 cm^-2 which is one of the largest values that reported for thin film-based X-ray detectors, indicating strong potential for miniaturized applications. In addition to high sensitivity, the devices deliver effective imaging performance with a spatial resolution of 1.0 lp/mm (with 28 cm between X-ray source and detectors) and retain stable operation after more than 30 days of air exposure. This work introduces a green and scalable platform for developing high-performance, lead-free, and environmentally sustainable X-ray detectors.