KCS

Narrow bandgap organic semiconductors are relevant as key materials components for the fabrication of near-infrared (NIR) organic solar cells (OSCs) and organic photodetectors (OPDs). Much of the interest arises due to the tunability of their energy levels and absorption properties through designing the molecular architecture. However, the benefits of NIR organic semiconductors remain comparatively unexplored in the context of OSCs and OPDs. A critical challenge arises as one decreases optical bandgaps (Egopt) with respect to the counterbalance between the driving force for charge separation and voltage loss in the solar cell devices. We thus designed and synthesized narrow bandgap nonfullerene acceptors (NFAs), which exhibit thin film absorbances that span from 600 nm to 1100 nm. As a preliminary assessment of NIR light sensing as a practical application, we carried out a simple photoplethysmography (PPG) test using our OPDs. The present OPDs could achieve a high maximum responsivity over 0.5 A W‑1 in the NIR region beyond 900 nm, marking one of the highest responsivity achieved by organic photodiodes in the NIR spectrum.