Vapor phase growth of Cs3Cu2I5/Bi2O2Se heterojunction thin film for fast-response, highly sensitive UV-Vis-NIR broadband photodetectors

Two-dimensional Bi ₂O ₂Se has been extensively investigated for broadband photodetection. However, it suffers from large dark current and relatively slow response speed, limiting its application in low-power consumption and high-speed detection applications. In this work, we successfully fabricated a Cs ₃Cu ₂I ₅/Bi ₂O ₂Se heterojunction for photodetection application via a three-step vapor phase deposition method. A staggered-gap band alignment (type II) at the Cs ₃Cu ₂I ₅/Bi ₂O ₂Se heterojunction is confirmed by pump-probe and photoluminescence quenching measurements. The dark current of the heterojunction photodetector was effectively reduced from 2.35 mA to 19.5 nA after introduction the Cs ₃Cu ₂I ₅ layer. The proposed device displays broad detection range (from 275 to 980 nm), high photoresponsivity (4.24 A/W), large I _light/ I _dark ratio (10 ³). The as-prepared heterojunction photodetector also showed self-powered properties with a high responsivity (0.21 A/W). The remarkable performance of our device for all wavelength can be attributed to the formation of a p-n heterojunction and high crystalline quality of the heterojunction thin film, as well as the good electrical properties of p-Cs ₃Cu ₂I ₅ and n-Bi ₂O ₂Se. This work brings insight into the development of large-scale 2D/perovskite hybrid-based high-performance broadband photodetectors in the future.