High Detectivity and Low-Dark Current in Organic Photodetectors by a High-Content Nonfullerene Acceptor-Based Bulk Heterojunction with a Polymer Overlayer.

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 A cm at an applied voltage of -2 V; hence, it achieves the high detectivity of 3.63 × 10 cm Hz W (only considering short noise) and 1.12 × 10 cm Hz W (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.