Staggered Heterojunction and Morphology Modulation Enabling High-Performance NIR Phototransistors

Near-infrared (NIR) organic phototransistors (OPTs) have broad application prospects in night vision, wearable health monitoring, intelligent security, and autonomous driving. This study proposes a material design strategy based on diketopyrrolopyrrole (DPP) donor-acceptor copolymers. Two ultra-narrow bandgap polymers, DPP-BT and DPP-BTT, are synthesized via Stille coupling and blended with DPPT-TT to form the active layer. Both copolymers exhibit narrow bandgaps and extended absorption beyond 1200 nm. The devices demonstrate excellent photoelectric conversion performance under 1300 nm illumination, with responsivity (R) values of 1.4 × 10⁴ A/W for DPP-BT/DPPT-TT and 4.1 × 10⁴ A/W for DPP-BTT/DPPT-TT, and specific detectivity (D*) values of 1.7 × 10¹² and 2.8 × 10¹² Jones, respectively. These results indicate a significant enhancement in photoresponse range and sensitivity. Further tests reveal that both blend systems maintain stable and superior detection performance across a broad spectral range from 500 to 2500 nm. This work provides an effective approach for optimizing the material and device synergy in NIR-OPTs, and lays a foundation for expanding the applications of polymer-based OPTs toward low-cost and large-area fabrication.