X-ray detectors play a vital role in medical diagnostics, industrial inspection, and security screening. However, widely used commercial direct-conversion detectors based on amorphous Si or Se typically offer sensitivities below 100 μC Gy⁻¹ cm⁻² and demand high fabrication costs, limiting performance in applications that require extremely low radiation doses. Hybrid organic–inorganic perovskite halides (HOIPs) have recently emerged as attractive alternatives due to their strong X-ray attenuation, large mobility–lifetime product, and compatibility with scalable solution processing. While single-crystal perovskites can deliver exceptional sensitivity, their growth and device fabrication remain complex. In contrast, spin-coated polycrystalline perovskites provide a rapid and low-cost route, yet film thickness—and thus sensitivity—is inherently restricted by conventional processing. [1]

Here, we overcome these limitations using a hot spin-coating strategy to deposit thick formamidinium lead halide (FAPbBr₂I) layers for lateral X-ray detectors based on interdigitated electrodes. The resulting films exhibit substantially improved attenuation and sensitivity. Importantly, we also evaluate the commonly overlooked contribution of air ionization surrounding the device, which can significantly inflate measured sensitivity and has seldom been rigorously addressed in prior studies. [2], [3] We find that this effect becomes especially pronounced in our ultra-small active-area devices (0.0002 cm²), where the ionized air volume is comparable to the device’s own active region. As a result, air ionization contributes 79% of the collected charge, inflating the apparent sensitivity by a factor of 4.8. However, our detectors still demonstrate an apparent sensitivity of 988.7 ± 16.9 μC Gy⁻¹ cm⁻² when the air contribution is included, whereas the corrected intrinsic sensitivity is 206.7 ± 5.5 μC Gy⁻¹ cm⁻². This real sensitivity surpasses most previously reported spin-coated perovskite devices and exceeds that of commercial amorphous semiconductor detectors, confirming the suitability of our approach for low-dose medical imaging and industrial non-destructive evaluation.

Furthermore, this work demonstrates the substantial measurement error introduced by atmospheric ionization, emphasizing that its removal is essential for accurate characterization of direct-conversion X-ray detectors. We apply a reference-device methodology to decouple true device response from air contributions,[4] providing a reliable framework for future studies of small-area spin-coated perovskite X-ray detectors.