Dual-Band, Efficient Self-Powered Organic Photodetectors with Isotype Subphthalocyanine-Based Heterojunctions toward Secure Optical Communications

High-performance heterojunction organic photodetectors (OPDs) are of great significance in optical detecting technology due to their tailorable optoelectronic properties. Herein, we designed and synthesized three n-type subphthalocyanine (SubPc) derivatives PhO-BSubPcF12, CHO-PhO-BSubPcF12, and NO2-PhO-BSubPcF12 via axial nonhalogen substitution on fluorinated SubPc. These SubPc derivatives exhibit improved intramolecular charge transfer, high electron mobilities, optimized energy levels, and good thermal stability. The novel isotype p–n SubPc heterojunctions are evaluated as photosensitive layers in OPDs, which show a UV–visible dual-band response and self-powered effect. The optimal OPD with Br-BSubPc/NO2-PhO-BSubPcF12 presents stable and superior performances with a high responsivity (R) of 0.14 A W–1, a peak external quantum efficiency (EQE) of 30.6%, and an extremely low dark current of 0.92 nA cm–2 under a 570–595 nm illumination without a bias voltage. It has outperformed most of the reported SubPc-based OPDs. The better interfacial contact of p–n SubPc derivatives leads to a large depletion region with decreased trap densities as well as a low carrier recombination rate, which is conducive to the photoinduced carriers’ separation and well-balanced transport, resulting in high device performances. Moreover, a secure communication strategy is successfully demonstrated by dual-band optimal OPD. This work is expected to provide some guidance for molecular engineering and device performance toward multifunctional electronics.