Ambient‐Stable Near‐Infrared Organic Photodetectors with Ultrahigh Detectivity and Ultrafast Response for Biometric Monitoring

PM6:Y6 is adopted as the active layer to prepare highly efficient organic photodetectors (OPDs), which is applied to realize a biometric sensor for real-time heart-rate monitoring. Here, the effects of the device structure, thickness, deposition process, and solvent on the subsequent performance of the OPDs are examined. Through judicious choice of the fabrication conditions, an OPD is obtained displaying a dark current density of less than 8.77 x 10(-10) A cm(-2), a responsivity of greater than 0.516 A W-1, and a high detectivity of 3.1 x 10(13) Jones, measured at bias of -2 V (870 nm). This OPD featured a wide linear dynamic range (LDR, 530 nm) of 104 dB at -2 V, an ultrahigh cutoff frequency (750 kHz) and rise/fall times of less than 220 ns under a reverse bias of -2 V. This sub-microsecond response and high detectivity is comparable with, and in some cases better than, those of the state-of-the-art perovskite-PDs and Si-PDs. The OPD displays consistent responses, good repeatability, and stability [ambient: 50% humidity, 25 degrees C)]. The air-stable and portable OPD-based photoplethysmogram system provides clear signal resolution, potentially benefitting its applicability to blood pressure monitoring.