Highly sensitive nanocomposite organic photomultiplication photodetectors via enhancing trap-assisted hole injection under reverse bias

Organic photodetectors (OPDs), featuring solution processability and tunable spectral response, show great potential in health monitoring, quality control, and astronomy. However, most of the OPDs relying on the photovoltaic effect suffer from low sensitivity and external quantum efficiency (EQE). Trap-assisted carrier tunneling is a proven strategy to mitigate these limitations. Herein, we fabricated high-sensitivity photomultiplication OPDs (PM-OPDs) based on donor-rich P3HT:PC71BM (100:1) by doping zinc oxide nanoparticles (ZnO NPs) as the active layer, constructing dual electron traps with PC71BM. By increasing the doping ratio of ZnO NPs, active layer extinction, photocurrent density, and device capacitance are enhanced. A higher trap density provides more electron traps to capture photogenerated electrons, causing significant interfacial electron accumulation. This forms a strong Coulomb field that narrows the Schottky barrier, facilitating hole injection from the Al cathode. Capacitance-voltage, bulk trap density, and wavelength-dependent absorption distribution analyses reveal that engineering dual electron traps via ZnO NPs and a minimal amount of PC71BM is crucial. This design effectively enhances hole tunneling injection and thereby contributes to the remarkable improvement in the device’s EQE under reverse bias. Under an applied reverse bias of −8 V, the nanocomposite PM-OPDs exhibit optimal external quantum efficiencies (EQE) of 1.04×105% at 370 nm and 7.56×104% at 600 nm. These values are significantly higher than those of the control device without nanocomposite doping, which only achieves 1.72×104% at 370 nm and 1.41×104% at 600 nm, respectively. Additionally, the responsivity of the optimized nanocomposite PM-OPD reaches 309 A/W at 370 nm and 365 A/W at 600 nm, more than fivefold higher than that of the control device. The nanocomposite PM-OPDs perform stably under the illumination of 375, 505, 660 nm LED light source, and the 20% ZnO NP-doped nanocomposite PM-OPDs have the largest on-off ratio with the response time of 139.5 ms. To avoid the effect of doping ZnO NPs on the dark current, we further insert an ultrathin Al2O3 interfacial modification layer with an atomic-scale thickness of 0.8 nm between the hole transport layer PEDOT:PSS and the dual electron trap active layer P3HT:PCBM:ZnO NPs by the method of atomic layer deposition technology. The results show that the Al2O3 interfacial modification layer can suppress the dark current while largely maintaining the photocurrent of the nanocomposite PM-OPD, greatly improving the on-off current ratio under the applied bias. This work confirms the critical role of dual electron traps and the atomic interfacial layer on enhancing device performance, providing a universal guidance for high-sensitivity PM-OPDs.