Dual External Electron Injection Barrier Layers Enable High-Performance Near-Infrared Organic Photodetectors Realizing Real-Time Heart Rate Monitoring

Near-infrared organic photodetectors (NIR-OPDs) play important roles in medical monitoring, bio-imaging and night vision, etc. Among them, bulk heterojunction (BHJ)-based photodiode type NIR-OPDs exhibit extraordinary characteristics in photoresponse and photosensitivity. However, their dark current density (Jd) often increases severely as the bias voltage increases, which seriously reduces detection sensitivity for NIR light. Here, a novel structure of dual external electron injection barrier layers (DEBLs) composed of "m-MTDATA/DPEPO:HAT-CN" is proposed to overcome this challenge. For DEBLs, a barrier is established with high injection barrier and long effective injection barrier width to prevent external electrons injection under bias voltage for suppressing Jd (4.22 x 10-8 A cm-2 better than 1.47 x 10-5 A cm-2 of the traditional device at -2 V). More importantly, photo-generated carriers have almost no loss through DEBLs. Therefore, high and stable detectivity (D*) over 1013 Jones are realized under 850 nm from 0 V to nearly -1 V and even far over 1012 Jones at -2 V. More strikingly, the structure of DEBLs is proven to be effective and universal in NIR-OPDs and the device based on it successfully realize the real-time heart rate monitoring of various human states, which exhibits great potential in human health monitoring. The dual external electron injection barrier layers (DEBLs) composed of 'm-MTDATA/DPEPO:HAT-CN' are designed to effectively suppress the dark current caused by directing tunneling under bias voltage, and while maintain excellent photoresponse. Therefore, a universal strategy by utilizing DEBLs to realize high-performance BHJ-based NIR-OPDs and the real-time heart rate monitoring of various human states is obtained. image