Highly Sensitive UV–Vis‐to‐Near‐Infrared Organic Photodetectors Employing ZnO: Polyethylenimine Ethoxylated Composite as Hole‐Blocking Layer

Significantly suppressed leakage current and reduced shot noise in organic photodetectors (OPDs) are achieved by employing charge blocking layers, which have led to tremendous advances in highly sensitive devices with photoresponse covering from the ultraviolet to near‐infrared regions. However, trap‐assisted charge carrier injection through tunneling can significantly contribute to the sources of leakage current upon the use of charge blocking layers. Herein, it is shown that leakage current in organic photodetectors can be effectively reduced to an intrinsic lower limit by using a composite hole blocking layer (HBL) that consists of zinc oxide (ZnO) blended with different weight concentration of polymer polyethylenimine ethoxylated (PEIE). The best device shows an ultralow dark current density down to 0.18 nA cm−2, which translates to high specific detectivity (D*) over 1 × 1013 Jones in broad response range from 340 to 1100 nm (with peak value of 4.2 × 1013 Jones at 940 nm and 3.5 × 1013 Jones at 1050 nm), approaching to the intrinsic dark current‐limited detectivity value. It is found that the incorporated N atoms fill the deficient site of oxygen in ZnO, thus giving rise to the reduced proportion of emission via defects.