Near-infrared photodetectors can be applied to many fields such as optical communication, environmental monitoring, and biomedical imaging. Due to the advantages of organic semiconductor materials, organic photodetectors have the advantages of tunable detection wavelength, low manufacturing cost, light weight, and flexible processing. Typically, devices require an external bias voltage to drive and enhance the photocurrent. Therefore, the development of self-driving photodetectors is important for low-energy optoelectronic devices that can operate independently, wirelessly, and sustainably. At present, in the pursuit of high photocurrent, most photodiode-type photodetectors adopt the method of blending with acceptor materials (BC) to prepare bulk heterojunction (BHJ) structures. In the hybrid film, poor phase separation due to the different surface energies of the donor and acceptor forms, which affects the stability of the device. In addition, unfavorable charge injection due to the simultaneous presence of donor and acceptor components near the anode and cathode interfaces of BHJ devices will result in devices with high dark current density (Jd), low detectability (D *). In order to reduce Jd, many strategies including cleverly adjusting the energy level of the photoactive layer, constructing planar heterojunction (PHJ) structure, vertical phase separation structure, introducing barrier layers, etc., are used to construct high-performance OPDs.

Recently, the team of Prof. Hui Huang from the University of Chinese Academy of Sciences and his collaborators have developed a high-detection rate self-driven organic photodetector (SD device) for near-infrared light detection using an environmentally friendly solvent protection method (ESP), which has been applied In heart rate detection, it has a good application prospect in life and health flexible electronic devices.

ToC figure

Figure 1. Performance parameters of BC and SD devices

In this work, organic photodetectors prepared by an environmentally friendly solvent protection method (ESP) have a good vertical phase separation structure. Based on the noise current at 1 Hz, the D* values of the BC and SD devices are 6.26 × 1010 Jones and 2.55 × 1011 Jones, respectively. According to the noise current at 104 Hz, the D* values of the BC and SD devices are 6.04×1012 Jones and 1.14×1013 Jones, respectively. By adjusting the device structure, the dark current of the SD device is reduced, and the D* value is improved.

Figure 2. Mechanistic study

In the mechanism study, it is pointed out that in a good vertical phase separation structure, the donor is mainly distributed on the side close to the hole transport layer, and the acceptor is mainly distributed on the side close to the electron transport layer, which is beneficial to block the unfavorable charge injection, thereby reducing the The dark current of the device increases the D* value. And in the stability study of photocurrent, it is shown that the donor material with larger surface energy tends to aggregate on the PEDOT:PSS side, indicating that the acceptor material with smaller energy tends to aggregate on the PDINN side, which is different from the vertical phase separation. The structure is consistent, so that the photocurrent of the SD device has better stability.

Figure 3. Properties and applications of flexible devices

 Finally, a flexible SD device was applied to heart rate (HR) detection, in which one of the authors typical systolic and diastolic HR signal peaks with 12 cardiac cycles in 10 s, HR was determined to be 72 beats/min⁻¹, which is consistent with The test results of traditional heart rate detectors are consistent, which proves the application prospect of this research in the field of life and health.

The above research work has been supported by the key research and development plan of the Ministry of Science and Technology, the National Natural Science Foundation of China and the relevant funds of the Academy of Sciences

Paper information:

Self-powered organic photodetectors with high detectivity for near infrared light detection enabled by dark current reduction

Yanan Wei, Hao Chen, Tianhua Liu, Song Wang, Yihang Jiang, Yu Song, Jianqi Zhang, Xin Zhang, Guanghao Lu, Fei Huang, Zhixiang Wei, Hui Huang*

Advanced Functional Materials

DOI: 10.1002/adfm.202106326