Synergistic Integration of Dye Molecule and Semiconducting Polymer for Near Infrared Organic Phototransistors

Abstract

Highly sensitive near-infrared (NIR) photodetectors are critical for biomedical applications demanding precision and performance. Organic phototransistors (OPTs) offer superior photo-sensing due to field-effect modulation. Yet, narrow bandgap organic semiconducting polymers (SCPs) are rarely used in high-performance NIR-OPTs because of low mobility and high dark off-current (DOC). Although bulk heterojunction can address these challenges, spin-coating often leads to non-uniform, randomly oriented domains. This study introduces an effective strategy: blending newly synthesized NIR-dye 2-((50-(4-(50-((4,5-bis(hexylthio)-1,3-dithiol-2-ylidene)methyl)-[2,20-bithiophen]-5-yl)-2,5-bis(2-ethylhexyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol-1-yl)-[2,20 bithiophen]-5-yl)methylene)malononitrile (DPPCN) with poly[2,5-bis (3-tetradecylthiophen-2-yl) thieno[3,2-b]thiophene] (PBTTT), a p-type SCP with excellent charge transport properties. Then using a novel Floating Film Transfer Method (FTM) to control molecular self-assembly at the air–liquid interface, the PBTTT/DPPCN system achieves uniaxial molecular orientation (DR ≈3.29) and improved film crystallinity. OPTs made of PBTTT/DPPCN(2%) exhibit remarkable photosensitivity of 2.8 × 103 under NIR and 2.2 × 10⁴ under red light (1 mW cm−2). Optimized devices achieve high photoresponsivity of 4.82 × 103 A W−1 in NIR with EQE reaching ≈1 × 10⁷%, with even greater responsivity to red light. Improved performance is attributed to enhanced charge-transfer interaction between PBTTT and DPPCN, efficient exciton dissociation, and superior charge transport by oriented PBTTT backbones. This approach successfully delivers high-performance OPTs, advancing the potential of organic electronics for biomedical applications and beyond. © 2025 Wiley-VCH GmbH.