High-performance solution-processed TIIG-based polymer photodetector with detectivity across scalable SWIR applications

Abstract

Developing cost-efficient, flexible, and Restriction of Hazardous Substances (RoHS)-compliant short-wave infrared (SWIR) photodetectors compatible with roll-to-roll processing remains a significant challenge. Here we present a simplified organic ‘metal–semiconductor–metal’ (MSM) photodetector featuring a single solution-processed bulk heterojunction of a newly synthesized thienoisoindigo-based ultralow-bandgap polymer, TIIG-Se-DFT, blended with the nonfullerene acceptor (NFA) Y6. The TIIG-Se-DFT polymer, incorporating selenophene and fluorinated thiophene units, combines a narrow bandgap of 0.96 eV with strong absorption across 700–1600 nm and forms films with local molecular order, enabling broadband light harvesting without multistep layer stacking. Device simplicity is achieved using an interdigitated Au electrode and a single solution-processed active layer, minimizing vacuum deposition and eliminating interlayer damage due to solvent exposure. The resulting photodetector reaches a specific detectivity (D*) of ≈2 × 10¹¹ Jones at 1150 nm, retains >0.13 × 10¹⁰ Jones at the eye-safe 1550 nm telecom band, and delivers 86/36 µs rise/fall times at 1 V_bias. Dark current is held to 4.6 × 10⁻⁸ A cm⁻², and encapsulated devices preserve >95% responsivity after 800 hours of ambient aging. The simplified, high-sensitivity processing advances TIIG-Se-DFT:Y6 SWIR photodetectors toward industrial scale suitable for wearables, light detection and ranging (LiDAR), and optical communications.