E-Spray-Deposited CsPbBr ₃ /Cs ₂ AgBiBr ₆ Type-II Heterojunction Enabling High-Sensitivity Self-Powered X-ray Detection

Perovskite-based Type-II heterojunctions offer a promising route for self-powered X-ray detection by leveraging built-in electric fields for carrier separation. However, solution deposition of a thick Type-II heterojunction, especially the heterojunction with a sharp interface, remains a challenge. Here, we demonstrate a thick-film CsPbBr 3 /Cs 2 AgBiBr 6 Type-II heterojunction fabricated via electrostatic spray (E-spray) deposition with a solvent-compatible layer sequence. By depositing CsPbBr 3 from a DMSO-based precursor first, followed by Cs 2 AgBiBr 6 from a DMF-based precursor, we achieve a sharp interface with minimized intermixing, as evidenced by cross-sectional SEM and ToF-SIMS. UPS-derived band alignment, time-resolved photophysical characterization, and polarity-dependent electrical/X-ray response collectively support heterojunction-assisted carrier separation and collection. The device exhibits self-powered X-ray detection with a sensitivity of 226.82 μC Gy air –1 cm –2 at 0 V, a low detection limit of 0.028 μGy air s –1, and stable operation under repeated X-ray irradiation. This work provides a scalable strategy for high-sensitivity, low-power direct X-ray detectors, advancing perovskite-based imaging applications.