Near-infrared organic photodetectors with a soluble Alkoxy-Phthalocyanine derivative

The condition of the bulk-heterojunction (BHJ) is an important factor for photodetectors as it significantly influences the efficiency of exciton dissociation from bound exciton pairs inside the active layer. In this study, we realized near-infrared (NIR) photodetectors with the BHJ system of a soluble donor organic semiconductor, 1,4,8,11,15,18,22,25-octaoctyloxy-phthalocyanine, and phenyl-C61-butyric acid methyl ester. By experimenting with the blend ratio of the organic materials, we observed substantial change of device performance owing to the change in the crystalline condition and morphology of the active layer. Our organic photodiodes with optimized BHJ active layer reached shot noise limited specific detectivity of 2.1 × 1012 Jones and external quantum efficiency of 18% with a bias of −0.5 V at the NIR wavelength of 770 nm. We attributed this improvement to the decrease in grain size inside the BHJ which resulted in an increased exciton dissociation efficiency at the donor–acceptor interface.