Organic phototransistors are a class of photodetectors based on organic semiconductor materials that are controlled by gate voltage and can convert captured optical signals into electrical signals. On the one hand, because it can regulate and amplify the photoresponse current generated in the material layer through the third terminal electrode, it has a high detection rate and responsivity, and is widely used in the fields of imaging, optical communication, biomedical sensing, and weak light detection. It has broad application prospects; on the other hand, because organic materials have the characteristics of solution processing, low cost, light weight, flexibility, etc., they also show unique advantages in the field of wearable and flexible electronics in the future.

   In the research of many organic phototransistors, there is a steady-state photoconductivity phenomenon, that is, the photocurrent generated by the device changes from a high-resistance state to a low-resistance state when illuminated. The phenomenon of maintaining a low resistance state for a period. Since additional gate voltage needs to be applied to cancel the steady state photoconductivity of the device, the response speed and operating frequency of the phototransistor device are reduced. On the other hand, the existence of steady-state photoconductivity has provided a new idea for the development of optical memory functional devices. The memory effect of phototransistors on light can be used to construct memory image sensing devices and photo synapses that simulate the human eye. visual perception system. At present, the principle and generation mechanism of steady-state photoconductivity in organic phototransistors are still unclear. Therefore, it is very important to understand the generation mechanism of steady-state photoconductivity for device regulation and application.

The research group of Prof. Xiujuan Zhang and Prof. Jiansheng Jie of the Institute of Functional Nano and Soft Materials of Soochow University revealed a new mechanism for the source of the steady-state photoconductivity phenomenon widely existing in organic phototransistors. They found that oxygen molecules adsorbed on organic small molecule semiconductors will A new deep level state is generated inside it, and the trapping effect of this level state on electrons is an important reason for the steady-state photoconductivity phenomenon in the phototransistor. This study reveals the generation mechanism of steady-state photoconductivity in phototransistors, and provides new ideas for the subsequent performance regulation of phototransistor devices and the application of new devices.

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