From organic photodetectors to monolithic skin-conformal photoplethysmography systems

Photoplethysmography (PPG) is widely used for wearable cardiovascular monitoring, yet reliable skin-conformal operation remains limited by unstable optical coupling, motion artifacts, rigid peripheral components, power demands, and insufficient system-level integration. Organic optoelectronics offer a compelling route to address these limitations by enabling ultrathin light emitters, photodetectors, transistors, photovoltaics, and displays with mechanical compliance, spectral tunability, and low-temperature processability. In this Review, we discuss skin-conformal organic PPG not as an isolated photodetection technology, but as an integrated epidermal optoelectronic system. We summarize the materials, device architectures, optical geometries, and wavelength-dependent physiological responses underlying organic PPG sensing, and examine how monolithic integration expands PPG from pulse detection to oxygen-saturation sensing, pulse-timing analysis, signal amplification, artifact suppression, self-powered operation, and real-time visualization. Finally, we highlight challenges in process compatibility, crosstalk, breathable encapsulation, long-term stability, and clinical validation toward continuous personalized cardiovascular monitoring.