Suppression of Photo-Mediated Traps in Integrated Organic Photovoltaic–Photodetector Devices via N-Type Self-Assembly-Driven Interfacial Engineering

Integrated organic photodetector-photovoltaics (OPD-OPVs) combine energy harvesting and photodetection, facilitating the development of self-sustaining sensors. The electron transport layers (ETLs) of these devices are critical for regulating the charge-transport dynamics across both functions. ZnO, a conventional ETL material offering efficient charge extraction, suffers critical instability issues (photocatalytic degradation of organics), leading to increased defect-mediated leakages, severely limiting its commercialization. To address the scarcity of alternatives to ZnO ETLs, a molecularly engineered, n-type, self-assembled monolayer (SAM)-based ETL, ((3-(1,3-dioxoisoindolin-2-yl)propyl)phosphonic acid) (3-PAPh), is developed. 3-PAPh chemisorbs onto the electrode, a process that templates a structurally ordered morphology, wherein the resulting 3-PAPh reduces the interfacial trap density and establishes a high activation energy barrier, fundamentally suppressing the parasitic leakage currents. A PM6:Y6-based device employing this synergistic ETL yielded a record-low noise current (7.65 fA at V → 0 V) and high measured specific detectivity (1.03 × 10¹³ cm Hz^0.5 W⁻¹ at 808 nm and bandwidth = 1 Hz) in self-powered OPD mode, while affording efficient indoor power generation (output power density = 74.4 µW cm⁻² under LED 1000 lx (2700 K)) in OPV mode. The chemically inert interface prevented trap formation during operation, maintaining >87% power-conversion efficiency after maximum power-point tracking for 500 min.