Visible-Blind Narrowband Near-Infrared Photodetector for Precise Real-Time Photoplethysmography Measurement.

The visible-blind narrowband photodetector (NPD) with spectral selective sensitivity to near-infrared (NIR) light is an important technology in the field of cardiovascular health assessment. However, the biological information carried by NIR light constantly changes signals with small amplitude and fast speed, which puts high requirements on the performance of detectors. Herein, visible-blind NIR NPDs were constructed by integrating solution-processable films of perovskite, CuSCN, and organic semiconductors. The NIR response was provided by the organic bulk heterojunction (OBHJ) film with a narrow band gap. A thick perovskite layer was applied to screen the incident visible light and suppress the leakage current in the dark state. CuSCN with a high LUMO level blocked the extraction of the visible-light-induced free electrons. The width of the response window was restricted by adjusting the band gap of the perovskite and the donor/acceptor ratio of the OBHJ film. The optimized NIR NPD exhibits a comprehensive performance including visible-blind response, a tunable response spectrum, a high responsivity/detectivity, and a short response time. In practical photoplethysmography measurements, the detector can record the human heart rate in real time through a noninvasive technique and precisely monitor the whole cardiac cycle, which provides an effective method for early detection of cardiovascular symptoms for timely diagnosis and treatment.