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

Abstract

In near-infrared (NIR) polymer phototransistors, the photoresponse is proportional to the turn-on voltage shift (ΔVth). Due to the narrow band gap of NIR polymers, the ΔVth value is usually small. However, the use of a single bulk heterojunction (BHJ) layer has a minimal effect on increasing the value of ΔVth. 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, PC61BM:PS:PDPP3T-based ternary NIR phototransistors with high acceptor concentrations were prepared by using a one-step film transfer method (FTM). Compared with a PC61BM:PDPP3T-based binary device (1:1), a ternary device (1:1:1) exhibited a significant performance improvement. The ΔVth value (∼29.5 ± 1.0 V) increased by approximately 4-fold, the Iph/Idark (∼4.4 × 106) increased by a factor of 3000 to 4000-fold, and the dark current decreased by 2-3 orders of magnitude (@ Vg = 0 V). Additionally, the ternary devices demonstrated excellent performance across a wide ternary ratio range (1:1:1 to 4:2:1).