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 × 10 3 under NIR and 2.2 × 10⁴ under red light (1 mW cm − 2 ). Optimized devices achieve high photoresponsivity of 4.82 × 10 3 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.