Bidirectional and Dual‐Mode Organic Photodetector Enables Secure Ultraviolet Communication

Abstract Traditional optical communication mode with single‐band photodetector depicts terrible confidentiality and it depends on sophisticated cryptography schemes to obtain a secure communication process. Dual‐band photodetectors have potential to realize a secure optical communication with a straightforward optical encryption strategy. However, previous reports of dual‐band organic photodetectors (OPD) relied on the multi‐stacked photosensitive layers thus there remain challenges in spectral matching and interfaces contacting. Here, a structurally simple bidirectional and UV–vis dual‐band OPD is proposed, with single photosensitive layer sitting between electrodes. By elaborately regulating the optical field distribution and vertical phase segregation of the bulk heterojunction (BHJ), this OPD presents completely distinct spectral response ranges under bidirectional illuminations. Finally, this OPD outputs outstanding self‐powered UV and vis dual‐band responsivities (up to 30 and 50 mA W −1 ) as the light illuminates from forward and backward direction, respectively. In addition, a stable and reliable optical communication system is realized based on this OPD where the UV response conveys valid information and further superimposes vis response for encryption. This design concept offers a simple alternative for achieving varied response windows and opens up a novel optical encryption method, which has potential be applied in a close‐range private communication process.