High-Sensitivity Organic Upconversion Photodetectors for Near-Infrared Photoplethysmography

Abstract

Near-infrared photoplethysmography (PPG) plays a critical role in noninvasive monitoring of arterial pulse and cardiovascular function. However, conventional organic near-infrared photodetectors are intrinsically limited by insufficient photodetection capability and noise suppression capability, making it highly challenging to simultaneously achieve high sensitivity, low noise, and high signal readability under low-light conditions. Here, we propose and demonstrate an organic electrically driven upconversion (UPC) strategy, in which weak near-infrared optical signals are upconverted into visible light and subsequently reabsorbed within the device, enabling signal amplification and high-fidelity readout at the device level. Under an applied bias of 10 V, the UPC device exhibits an external quantum efficiency of 134% at 835 nm, a responsivity of 0.90 A/W at 840 nm, and a specific detectivity of 3.7 × 10¹² Jones. Benefiting from these outstanding optoelectronic properties, the PPG system based on this UPC device can clearly resolve arterial pulse waveforms, including systolic peaks, diastolic valleys, and distinct dicrotic notches. These results demonstrate the device’s high sensitivity to biological pulse signals and provide a new physical pathway and engineering paradigm for the design of high-performance organic photodetectors in biomedical monitoring applications.