To achieve high detectivity in organic photodetectors, the suppression of the dark current density and the improvement of responsivity are necessary at the same time. In this work, we introduce a polymer donor overlayer on top of the high-acceptor-content bulk heterojunction film to minimize the randomness of charge pathways in the mixed phase of donor/acceptor blends. This design strategy of the active layer successfully suppresses the dark current density to 2.91 × 10-10 A cm-2 at an applied voltage of -2 V; hence, it achieves the high detectivity of 3.63 × 1013 cm Hz1/2 W-1 (only considering short noise) and 1.12 × 1010 cm Hz1/2 W-1 (including by thermal and flicker noise) with enhancing responsivity under near-infrared illumination after introducing the polymer overlayer. Further, the reduction of the donor/acceptor interface in bulk heterojunctions enables our photodetector to maintain over 98% of its initial detectivity after 1000 h under 85 °C thermal stress. This study demonstrates a simple yet effective way to establish a unipolar charge pathway for high detectivity organic photodetectors by designing the photoactive layer.
Kim et al. (Fri,) studied this question.