High-Performance Wearable Organic Photodetectors by Molecular Design and Green Solvent Processing for Pulse Oximetry and Photoplethysmography.

White-light detection from the visible to the near-infrared (NIR) region is central to many applications such as high-speed cameras, autonomous vehicles, and wearable electronics. While organic photodetectors (OPDs) are being developed for such applications, several challenges must be overcome to produce scalable high-detectivity OPDs. This includes issues associated with low responsivity, narrow absorption range, and environmentally friendly device fabrication. Here, we report an OPD system processed from 2-methyltetrahydrofuran (2-MeTHF) sets a record in light detectivity, which is also comparable with commercially available silicon-based photodiodes. The newly designed OPD has been employed in wearable devices to monitor heart rate and blood oxygen saturation. In achieving this, we also develop a framework for a detailed understanding of the structure-processing-property relationship in these OPDs. The BHJ thin films processed from 2-MeTHF were characterized at different length scales with advanced techniques. The BHJ morphology exhibits optimal intermixing and phase separation of donor and acceptor moieties, which facilitates the charge generation and collection process. Benefitting from high charge carrier mobilities and a low shunt leakage current, our newly developed OPD exhibits a specific detectivity of above 10 12  Jones over 400-900 nm, which is higher than those of reference devices processed from chlorobenzene and ortho-xylene. This article is protected by copyright. All rights reserved.