High-sensitivity Visible-blind Near-infrared Narrowband Organic Photodetectors Realized by Controlling Trap Distribution

Narrowband photodetectors, which only respond to the spectral bands of interest but not to other spectral ranges, are widely used in biological sensors, medical monitoring, intelligent communication and other fields. Recent developments in artificial intelligence and wearable electronic devices have fostered a growing demand for visible-blind near-infrared (NIR) narrowband photodetectors. Herein, a novel hierarchical device structure based on the exciton dissociation narrowing (EDN) mechanism is proposed to realize NIR narrowband organic photodetectors (OPDs) with a response peak at 940 nm. Compared with traditional EDN type narrowband OPDs, the new device has a significantly higher peak external quantum efficiency (EQE) at 940 nm. The transient photocurrent measurement results show that the differences in device performance arise from diversity in the dynamics of the carrier trapping and de-trapping processes. Impedance analysis shows that the central trap energy levels of the two devices are located at different trap depths. Deep Gaussian trap density of states distributions cause unfavorable space-charge effects, counteract the internal electric field, and increase the recombination loss, resulting in a significant difference in the EQE of the two devices. The visible-blind NIR OPD with optimized device structure can effectively resist the interference of ambient light, in addition, the sensitivity of the narrowband OPD in the NIR window at 940 nm has been enhanced by trap density of states distribution control. Therefore, it has a strong detection ability for weak infrared radiation. We also fabricated a flexible photodetector based on the optimized device structure with a sensitive area of 1.152 cm(2). The device was attached to the surface of human skin, and the noninvasive real-time monitoring of human heart-rate was successfully realized by the reflective PPG technology with a flexible narrowband photodetector for the first time, demonstrating the superiority of this new structure in making high performances narrowband NIR OPDs for practical application. [GRAPHICS] .