High-performance organic photodetector with optimized thick bulk-heterojunction for near-infrared sensing

Reducing the dark current density (J_d) of organic photodetectors (OPD) is an effective way to improve some important figures of merits such as on-off ratio and specific detectivity (D*). Many studies have demonstrated that increasing the thickness of the active layer can effectively reduce the J_d of OPD, but at the same time it can cause a sharp decrease in responsivity and external quantum efficiency (EQE). In this work, a preheating spin coating method was used on the thick bulk-heterojunction (BHJ) active layer, which is composed of a polymer donor PBDB-T and a non-fullerene acceptor (NFA) Y6 with near-infrared (NIR) absorption. As a result, the thick BHJ OPD maintains a low J_d while the responsivity and EQE are greatly improved, therefore the optimized devices display a high D* over 10¹² Jones at -0.5 V from 400 nm to 900 nm, indicating its application potential in visible-to-NIR detection. This work provides an effective strategy to enhance the performance of thick BHJ devices.