Dual‐Band Perovskite Bulk Heterojunction Self‐Powered Photodetector for Encrypted Communication and Imaging

Abstract Self‐powered, dual‐band photodetection of electromagnetic signals promises wide photoelectric applications in imaging, communication, environmental monitoring, and rescue. However, most reported dual‐band photodetectors (PDs) based on various heterojunctions are realized by complex fabrication processes, which may introduce defects in the depletion layer. Here, first, a self‐powered dual‐band PD based on lead‐free perovskite bulk heterojunction (Cs₃Bi₂Br₉/Cs₃BiBr₆) fabricated by a one‐step spatial confinement method is demonstrated. Its two peaks of self‐powered responsivities are 59.4 mA W⁻¹ at 360 nm and 3.09 mA W⁻¹ at 450 nm. A high on/off ratio (18881), fast response speed (rise time 200 ns; decay time 1.09 µs), high detectivity (1.2 × 10¹² Jones), and cycle stability are realized under UV band, which exceeds most reported state‐of‐the‐art lead‐free halide perovskite PDs. The dual‐band PD is suitable for encrypted communication and image sensing. This research represents a new frontier in the search for novel dual‐band high‐performance PDs based on lead‐free perovskite bulk heterojunction fabricated by low‐cost and simple fabrication methods.