Novel Interface Resonance‐Enhanced Organic Photodetectors with High Stability and Detectivity for Health Monitoring

Wearable organic photodetectors (OPDs) operating in the near‐infrared (NIR) are pivotal for non‐invasive photoplethysmography (PPG)‐based health diagnostics. Yet, their practical deployment is impeded by excessive dark current density ( J d ) and poor stability. Here, it is demonstrated that strategic interfacial engineering—inserting an ultrathin Au interlayer atop the alcohol‐soluble polyelectrolyte (PFN‐Br)—simultaneously suppresses J d and fortifies device stability. The new interfacial layer with lower defect density reduces non‐radiative recombination and elevates the electron‐injection barrier, suppressing J d to 1.12 × 10 −10 A cm −2 (at 0.1 V) and affording a record specific detectivity ( D * ) of 8.76 × 10 13 Jones at 860 nm. Concurrently, the ITO/PFN‐Br/Au stack cooperates with the MoO 3 /Ag top mirror to establish an optical microcavity that red‐shifts the spectral response by ≈50 to 860 nm, perfectly matching the hemoglobin isosbestic point for oxygen saturation level (SpO 2 ) monitoring. Integrating the optimized OPD into a lightweight convolutional‐neural‐network (DESNet) platform yields accurate, cuff‐less blood‐pressure estimation ( R 2 = 0.81 for diastolic pressure) and SpO 2 readings that agree within ±2% of clinical gold standards. This work provides a universal design paradigm for high‐ D * , stable OPDs and validates their translational potential in wearable multi‐parameter health surveillance.