Sn/Cl Co-Doped ZnO Cathode Interfacial Layer for High-Performance Organic Photodetectors.

Organic photodetectors (OPDs) hold significant promise for applications spanning medical monitoring, bioimaging and night vision due to their unique advantages, such as flexibility, light weight, and potential for large-area fabrication. Nevertheless, the dark current density (Jd) of OPDs exhibits a pronounced increase under applied reverse bias, which consequently degrades the specific detectivity (D*). To tackle this challenge, this work proposes an interface engineering strategy based on Sn/Cl co-doped ZnO (SCZO). The doping effectively reduces oxygen defects in ZnO, causing the valence band maximum (VBM) to shift downward, thereby suppressing hole injection under bias and reducing Jd. Experiments show that the SCZO-based device exhibits a Jd of 4.05 × 10-11 A cm-2 at -0.1 V, nearly one order of magnitude lower than that of the control device (4.07 × 10-10 A cm-2). Notably, the SCZO-based OPD enables real-time and accurate monitoring of human heart rate, demonstrating its considerable potential for health-monitoring applications. Furthermore, OPDs incorporating the SCZO interface exhibit excellent imaging performance under 820 nm illumination. These findings underscore the significant potential of SCZO-based OPDs for flexible, wearable health monitoring and near-infrared imaging applications.