Non-Fullerene Acceptor Organic Photodetector for Skin-Conformable Photoplethysmography Applications

Commercial photoplethysmography (PPG) sensors and other biomedical devices that require near-infrared (NIR) light detection are limited by rigid photodetector architectures that cannot interface comfortably with skin. Flexible organic photodetectors could potentially solve this problem; however, organic photodetectors suffer from low NIR sensitivity, largely due to the early absorption cutoffs originating from the use of fullerene acceptors. This work details a new flexible organic photodiode (OPD) based on narrow bandgap non-fullerene-acceptor (NFA) bulk heterojunction (BHJ) incorporating a PTB7-Th and COTIC-4F blend. The photodetector developed for this study reaches an external an external quantum efficiency (EQE) to 60% in the 600–1000 nm range and responsivity (R) as high as ≈0.42 A W^–1. Through the integration of a PEDOT:PSS and PDINO interfacial layers, undesired carrier injection is suppressed, and a detectivity (D*) in the order of ≈10¹³ Jones is achieved. In addition, oxygen saturation and heart rate are successfully measured by integrating the developed photodiode in a PPG sensor.