Ultraflexible Ring‐Shaped Organic Photodetectors for Motion Artifact‐Less Photoplethysmography

Abstract Owing to compact size and affordability, wearable photoplethysmogram sensors provide real‐time physiological parameters that are critical for vital signs monitoring. However, the measurement accuracy, especially during physical activities, is the main obstacle toward clinical practice. Here, ring‐shaped ultraflexible organic photodetectors （OPDs） are proposed that can form conformal contact with the skin fingerprints and monitor pulse wave under faint light source of ≈22 µW cm −2 . The ring‐shape and ultraflexible design, together with optimized donor‐acceptor composition, active layer thickness, and large active area (0.1 cm 2 ) endow the OPDs with low dark current (3.66 × 10 −10 A cm −2 at −1 V), high detectivity (1.5 × 10 13 Jones), and motion artifact‐free when moving at a speed of 5 cm s −1 .