Diminished Trap-Induced Leakage Current at the Organic/Electrode Interface for High-Performance Organic Photodetectors

The influence of the absence of a π-conjugated polymer-based charge-blocking layer (CBL) or interlayer between the photoactive layer/electrode interface in organic photodetectors (OPDs) is investigated. As compared to devices with a charge-blocking layer, OPDs with a metal/photoactive layer/metal sandwich structure exhibit similar external quantum efficiency but lower dark current density hence a higher specific detectivity (D*). The decrease in dark current density in devices without a CBL can be attributed to the elimination of additional trap states in the CBL, provided that a large charge injection barrier is maintained at the metal/active layer interface. In a device with the CBL, a clear dependence between the density of trap states (tDOS) and the magnitude of dark current density is verified. As such, suppressing undesired injection and trap-induced leakage current may cancel each other out in the device with a CBL. By evaluating the trap-induced leakage of current, we proposed that the key to obtain high specific detectivity in OPDs is to use a charge-blocking layer with low trap density or to use a CBL-free device structure.