Controlling Electron/Hole Recombination in Near-Infrared Polymer Phototransistors through an Insulation Medium: A Pathway to Ultrahigh Photosensitivity

In near-infrared (NIR) polymer phototransistors, the photoresponse is proportional to the turn-on voltage shift (Δ V th ). Due to the narrow band gap of NIR polymers, the Δ V th value is usually small. However, the use of a single bulk heterojunction (BHJ) layer has a minimal effect on increasing the value of Δ V th . This is because doping with high concentrations of acceptors results in strong current traps and accelerates electron/hole recombination. In this work, a new strategy is proposed to control the recombination of electrons/holes. By doping an insulating medium made of polystyrene (PS) into BHJs, PC 61 BM:PS:PDPP3T-based ternary NIR phototransistors with high acceptor concentrations were prepared by using a one-step film transfer method (FTM). Compared with a PC 61 BM:PDPP3T-based binary device (1:1), a ternary device (1:1:1) exhibited a significant performance improvement. The Δ V th value (∼29.5 ± 1.0 V) increased by approximately 4-fold, the I ph / I dark (∼4.4 × 10 6 ) increased by a factor of 3000 to 4000-fold, and the dark current decreased by 2–3 orders of magnitude (@ V g = 0 V). Additionally, the ternary devices demonstrated excellent performance across a wide ternary ratio range (1:1:1 to 4:2:1).