Short-Wave Infrared Organic Photodetectors With Ultralow Dark Current Density Under Biased Operating Conditions

Commercial photodetectors integrated on readout circuits typically operate under bias voltage, necessitating low dark current density (J_d) to achieve high detectivity. However, suppressing J_d remains a critical challenge for organic photodetectors (OPDs), particularly those operating in the short-wave infrared (SWIR) region. Herein, we report SWIR-OPDs that achieve ultralow J_d under high bias voltage by developing a narrow bandgap p-type polymer as the SWIR absorber, thereby establishing an alternative material platform for high-performance SWIR-OPDs. The new polymer PDCBT-DTO2F adopts a push-pull architecture comprising quaterthiophene donor units and 5,6-dicyano-2,1,3-benzothiadiazole acceptor moieties. Substituting the alkyl chains on quaterthiophene units with alkoxy chains significantly enhanced the intramolecular charge transfer effect and backbone coplanarity. This modification simultaneously yielded intense SWIR absorption, high crystallinity, reduced trap density, and low energetic disorder. Through extensive device optimization, the SWIR-OPD based on PDCBT-DTO2F exhibited J_d as low as 15.6 nA cm^{- 2} under -2 V and 58.1 nA cm^-2 even under -5 V. Consequently, a detectivity of 1.04 × 10¹² Jones was realized at 1100 nm under -2 V bias, ranking among the best performance for SWIR-OPDs operating under reverse bias.