Development of a Self-Powered Bidirectional Transient Organic Photodetector for Ultrafast Secure Aerial and Underwater Optical Communication

Secure optical communication requires photodetectors that are fast, broadband, bidirectional, and stable. Traditional devices often face issues like narrow spectral response, unidirectional operation, and poor durability. We present a bidirectional transient organic photodetector (T-OPD) for aerial and underwater self-powered applications, structured as ITO/PEDOT:PSS/Active layer/Ionic liquid gel (IL)/ITO. Both the top (ITO/IL) and the bottom electrodes (ITO/PEDOT:PSS) exhibited an average transparency of 80–85% across the entire UV–vis-NIR spectrum (400–940 nm), allowing the devices to operate bidirectionally. Using a blend of polymer donor PM6 and nonfullerene acceptor Y6, it detects broadband from UV to NIR (940 nm). The ultrathin layer of IL gel provides water resistance and also induces a nanoscale interfacial electric double layer (EDL), which enhances charge separation and sensitivity without external bias, maintaining stability during 168 h of unencapsulated self-powered operation underwater immersion. The device has fast response times (30 and 47 μs) and a high cutoff frequency (∼187 kHz). Exploiting these features, we demonstrate a self-powered secure aerial and underwater bidirectional communication system, where one wavelength channel transmits the primary data and another provides encryption. Stable optical signal transmission through a water channel and clear waveform recovery highlight the device’s robustness as a promising technology for secure communication, with applications in naval operations, diver-to-surface communication, aircraft-to-sea transmissions, and marine IoT networks.