Narrowband absorption far-red organic photodetector for photoplethysmography.

Narrowband absorption organic semiconductors are highly attractive for spectrally selective photodetection applications requiring lightweight and customizable devices. Although narrowband absorption photodetectors have achieved success in the visible range, far-red (650-750 nm) devices are scarce. The far-red wavelength range is relevant for applications in medical diagnostics, such as photoplethysmography for blood oxygen saturation detection. In this study, a non-fullerene bulk heterojunction organic photodetector with a narrowband response in the far-red spectrum is fabricated. The photodetector exhibits a high detectivity of 5.06 × 10 Jones at a bias of -2 V. The full-width at half-maximum of the responsivity peak of the photodetector is 85 nm, which is the smallest spectral width among solution-processed devices. The response speed is 11.56 kHz. The photodetector responds within the microsecond range. The potential of the photodetector for blood oxygen saturation measurement is demonstrated.