Micrometer-Scale Cs₃Cu₂I₅ Thick Film Directly Grown on n-Si to Construct Planar Heterojunction for UV Detection

Integrating wide band gap semiconductor materials with silicon (Si) to create heterojunctions is an effective strategy for enhancing the ultraviolet (UV) sensitivity of optoelectronic devices. However, epitaxially growing high-quality wide band gap films on Si substrates at low temperatures without compromising the properties of Si remains challenging. In this study, we introduce a low-cost mist chemical vapor deposition (CVD) technique to deposit Cs 3 Cu 2 I 5 perovskite films and fabricate a simple-structured Cs 3 Cu 2 I 5 /n-Si planar heterojunction. This technique enables an orderly deposition and rapid crystallization process, distinct from traditional solution-based methods. Herein, we report for the first time a compact, thick Cs 3 Cu 2 I 5 film with an average grain size of 5.27 μm and a thickness of approximately 2.8 μm exhibiting orientated growth along the (303) plane. Furthermore, the simply constructed Cs 3 Cu 2 I 5 /n-Si photodiode exhibited a maximum photoresponsivity of 186 mA W –1 and a specific detectivity of 2.5 × 10 12 Jones under 278 nm illumination. The on–off cycling tests demonstrated excellent operational stability, with unpackaged devices retaining 90% of their initial photocurrent after two months of storage under ambient conditions.