Picowatt-Sensitive and Air-Stable Heterojunction UV Photodetectors Enabled by Large-Grained CsCu2I3 Film via Microgap Thermal Sublimation

Large-grained perovskite films are critical for mitigating carrier recombination and ensuring device robustness. Here, we report a microgap thermal sublimation (MGTS) method for fabricating high-quality, large-grained CsCu₂I₃ films designed for air-stable UV photodetection. By engineering a submillimeter sublimation zone under low-vacuum conditions, our approach enables self-regulated deposition that yields densely packed, highly crystalline films with preferential (221) orientation on both crystalline GaN and amorphous glass substrates. Kinetic gas theory analysis suggests that our microgap configuration maintains a vapor collision probability below 40%, facilitating efficient precursor transport and uniform film growth with grain sizes exceeding 20 μm. The resulting CsCu₂I₃/GaN heterojunction UV photodetectors, operating in self-powered mode, achieve a responsivity of 106.34 mA/W, a detectivity of 9.24 × 10¹¹ Jones, and rise/fall times of 4.12 μs/2.12 ms. Notably, the devices demonstrate picowatt-level detection limits and imaging capability. This work establishes MGTS as a scalable, cost-effective platform for developing air-stable, wide-bandgap copper halide perovskites for next-generation UV optoelectronics.