Interfacial Defect Passivation and Leakage Suppression for Enhanced Detectivity in Organic Photodetectors via...

Inverted organic photodetectors (OPDs) have attracted significant attention due to their facilitated interfacial optimization at the bottom electrode and compatibility with diverse solution processes. However, high dark current originating from the electron transport layer (ETL) remains a major factor limiting device performance. In particular, interfacial defects and leakage currents in ITO/ZnO-based inverted OPDs lead to degradation of detectivity $\left(D_{\mathrm{shot}}^{*}\right)$ and signal-to-noise ratio (SNR). In this study, inverted OPDs incorporating an octadecylphosphonic acid (ODPA) self-assembled monolayer (SAM) on an indium tin oxide (ITO) electrode were fabricated, and the effects of interfacial modulation were systematically investigated. The device architecture consisted of ITO/ODPA/ZnO nanoparticles (NPs)/P3HT:PCBM/MoO₃/Ag. Compared to reference devices without SAM treatment, the ODPA-modified OPDs exhibited a reduction in dark current by a factor of approximately 13, decreasing from 8.55 × 10^-4 to 6.36 × 10^-5 A cm^-2 at -2 V, while maintaining stable photoresponse characteristics. This pronounced suppression of dark current is attributed to effective modulation of the electronic properties at the ITO/ZnO interface by the ODPA SAM, which suppresses interfacial leakage pathways. These results demonstrate that phosphonic acid-based SAMs provide an effective interfacial engineering strategy for achieving low-noise characteristics in inverted OPDs and offer a viable approach for the design of high-performance organic photodetectors.