Near‐Infrared Organic Photodetectors toward Skin‐Integrated Photoplethysmography‐Electrocardiography Multimodal Sensing System

Abstract In the fast‐evolving landscape of decentralized and personalized healthcare, the need for multimodal biosensing systems that integrate seamlessly with the human body is growing rapidly. This presents a significant challenge in devising ultraflexible configurations that can accommodate multiple sensors and designing high‐performance sensing components that remain stable over long periods. To overcome these challenges, ultraflexible organic photodetectors (OPDs) that exhibit exceptional performance under near‐infrared illumination while maintaining long‐term stability are developed. These ultraflexible OPDs demonstrate a photoresponsivity of 0.53 A W −1 under 940 nm, shot‐noise‐limited specific detectivity of 3.4 × 10 13 Jones, and cut‐off response frequency beyond 1 MHz at −3 dB. As a result, the flexible photoplethysmography sensor boasts a high signal‐to‐noise ratio and stable peak‐to‐peak amplitude under hypoxic and hypoperfusion conditions, outperforming commercial finger pulse oximeters. This ensures precise extraction of blood oxygen saturation in dynamic working conditions. Ultraflexible OPDs are further integrated with conductive polymer electrodes on an ultrathin hydrogel substrate, allowing for direct interface with soft and dynamic skin. This skin‐integrated sensing platform provides accurate measurement of photoelectric and biopotential signals in a time‐synchronized manner, reproducing the functionality of conventional technologies without their inherent limitations.