Engineering Random Copolymers With Medium- and Narrow-Bandgap Segments for Shortwave Infrared Organic Photodetectors Featuring Low Dark Current and Enhanced Detectivity

Organic photodetectors (OPDs) hold great promise for shortwave infrared (SWIR) applications. However, their path toward commercialization remains dependent on breakthroughs in material innovation. A key challenge lies in a general trade-off observed across previous studies: extending the spectral response toward longer wavelengths often results in elevated dark current density (J_dark) and reduced external quantum efficiency (EQE), which are inherently conflicting performance metrics, thereby limiting detectivity (D*). To overcome this, a novel strategy based on random copolymerization by introducing a medium-bandgap segment into the narrow-bandgap polymer backbone is proposed. This design preserves SWIR absorption while suppressing leakage current, enabling the simultaneous retention of EQE and reduction of J_dark. By systematically tuning the composition ratio between medium- and narrow-bandgap segments, the optoelectronic properties to break the traditional trade-off and significantly improve D* is optimized. The optimized device achieved a D* of 1.07 × 10¹¹ Jones at 1300 nm, with an EQE of 17.6% and a J_dark of 9.3 × 10⁻⁶ A/cm². To the best of this knowledge, this represents one of the best results to date, underscoring the potential of this copolymer design as a highly effective strategy for advancing SWIR OPD technology.