Blocking Layer Induced Bi-Directional Biased Photomultiplication-Type Near-Infrared Flexible Organic Photodetectors

Photomultiplication-type organic photodetectors (PM-OPDs) effectively amplify photogenerated signals, eliminating the need for external amplifiers and simplifying detection systems. Current designs require high bias voltages, leading to significant power consumption. This study introduces PM-OPDs with reduced bias voltage by incorporating a hole-blocking layer (HBL) between the active layer and electrode. Deep HOMO level and thin HBL facilitate hole accumulation and energy level bending, lowering bias voltage and enhancing electron injection. The elevated LUMO level of the HBL minimizes non-radiative recombination and prolongs the lifetime of accumulated holes, resulting in greater photogains. Four HBLs-BCP, PFN-Br, BPhen, and C60-are explored with ZnO serving as an electron transporting layer (ETL). By applying a bi-directional bias of +/- 0.5 V, PM-OPDs are enabled to operate with an EQE of 19560% and a detectivity of 2.8 x 1013 Jones. The versatility of this mechanism is validated across three active layer combinations. Compared to commercial silicon photodetector, the flexible PM-OPDs achieved a 139.3-fold increase in photocurrent in photoplethysmography under faint light conditions. This work presents a promising strategy for developing bi-directional biased PM-OPDs with reduced power consumption while maintaining high gains for various practical applications. Photomultiplication-type organic photodetectors with reduced bi-directional bias are realized, employing four different hole-blocking layers to manipulate non-radiative recombination and tunneling injection. Under -2 V reverse bias, these devices achieve an external quantum efficiency 113 700% and a specific detectivity of 5 x 1013 Jones. Flexible devices for PPG applications produce a photocurrent 139.3 times higher than a silicon photodetector image