Sensitive detection of near-infrared (NIR) light enables many important applications in both research and industry. Current organic photodetectors suffer from low NIR sensitivity typically due to early absorption cutoff, low responsivity and/or large dark/noise current under bias. Herein, organic photodetectors based on a novel ultranarrow bandgap non-fullerene acceptor, CO1-4Cl, are presented, showcasing a remarkable responsivity over 0.5 A W-1 in the NIR spectral region (920-960 nm), which is the highest amongst organic photodiodes. By effectively delaying the onset of the space charge limited current and suppressing the shunt leakage current, the optimized devices show a large specific detectivity around 10 12 Jones for NIR spectral region up to 1010 nm, close to that of a commercial Si photodiode. The presented photodetectors can also be integrated in photoplethysmography for real-time heart rate monitoring, suggesting its potential for practical applications. Near-infrared (NIR) light usually corresponds to the region of electromagnetic radiation with wavelength spanning from about 750 nm to 1400 nm. [1] Despite being invisible to human visual perception, NIR sensing finds applications in a variety of technologies, including medical monitoring, [2] quality inspection, [3] machine vision, [4] and bio-imaging. [5] NIR sensing has been conventionally realized with detectors based on single-crystal inorganic semiconductor materials (e.g. Si, Ge, GaInAs), which typically have drawbacks including costly processing, mechanical inflexibility, and sensitivity to temperature. [6-8] Owing to the low cost, solution processing, material tunability, unique structure-property relationships and good mechanical flexibility, organic semiconductors emerged as an exciting candidate for integrated electronics, lighting, solar cells and photodetection. Particularly, photodetectors based on organic semiconductors have witnessed increasing research endeavor, Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff))
