Incident Light Modulated Bipolar Photocurrent in Self-Powered Photodetectors for Secure Optical Communication

Self-powered photodetectors with bipolar photocurrent characteristics show promising potential for secure optical communication applications. However, ensuring the confidentiality of critical information remains a key challenge when facing potential interception by multiple eavesdroppers. In this study, we developed a self-powered photodetector based on a P3HT:PC₆₁BM (BHJ)/PEDOT:PSS/ZnO architecture that exhibits incident-light-modulated bipolar photocurrent response. This unique bipolar behavior originates from the synergistic effects between the ultraviolet-absorbing ZnO layer and the visible-absorbing BHJ. The photodetector features an n-p-n band structure created by two opposing built-in electric fields at the n-ZnO/p-PEDOT:PSS and p-PEDOT:PSS/n-BHJ interfaces, which drive photocurrents in opposite directions. This distinctive configuration enables the photodetector to generate positive output signals under ultraviolet light irradiation (380 nm) and negative signals under visible light irradiation (620 nm) at 0 V bias, with remarkable responsivities of 14 and 6 mA W^–1, respectively. By utilizing positive ultraviolet signals as valid data carriers and negative visible signals as interference, we successfully established a highly efficient and stable secure optical communication system. This innovative approach demonstrates significant potential for advanced information encryption applications while maintaining simple device architecture.