Broadband photomultiplication-type organic photodetectors (PM-OPDs) were fabricated by employing a wide bandgap donor P3HT and narrow bandgap acceptor QxIC as the photoactive layers. The optimal weight ratio of P3HT to QxIC is adjusted as approximately 100:1 to achieve numerous isolated electron traps formed by P3HT/QxIC/P3HT and an efficient hole transport channel in the photoactive layers. The trapped photogenerated electrons in QxIC near the Al electrode will induce interfacial band bending for more efficient hole tunneling injection to obtain a large light current density (J_L), resulting in the external quantum efficiency (EQE) over 100% of the PM-OPDs. The dark current density (J_D) of broadband PM-OPDs can be further suppressed by employing MPA2FPh-BT-BA as an interfacial layer instead of a PEDOT:PSS layer on the ITO electrode. The optimal PM-OPDs display a rather low J_D of 5.7 × 10^-7 A cm^-2 under a -8 V bias, which is lower than 5.3 × 10^-6 A cm^-2 for PM-OPDs with PEDOT:PSS as an interfacial layer under the same bias. Additionally, the J_L of broadband PM-OPDs exhibits a slightly decreased trend by using the MPA2FPh-BT-BA interfacial layer. The signal-to-noise ratio (SNR) of broadband PM-OPDs can be increased from 667 to 3788 by replacing PEDOT:PSS with MPA2FPh-BT-BA as the interfacial layer, benefiting from the markedly decreased J_D and relatively high J_L. The optimal broadband PM-OPDs exhibit EQE values of 8010% at 355 nm and 2170% at 835 nm, as well as specific detectivity values of 9.1 × 10¹² Jones at 355 nm and 5.8 × 10¹² Jones at 835 nm under a -8 V bias.

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