Effectively controlling and balancing the separation, transmission, and recombination of photo-generated carriers is essential for the realization of highly sensitive photodetectors. Traditional organic phototransistors are mostly based on a single layer heterojunction or bulk heterojunction structure. In the former, the donor and acceptor are formed by layered thin film stacking respectively, and in the latter, the donor and acceptor materials are blended to form a photoelectric conversion activity. Floor. Although the above structures provide excellent photodetection performance, they are difficult to take into account both the efficient separation and transmission of photogenerated excitons and the low exciton recombination rate, which severely limits the further improvement of phototransistor photodetection performance.
In order to solve the above problems, researchers from the Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences have proposed a novel composite layered phototransistor structure, which consists of a C8-BTBT channel layer for efficient carrier transmission and an efficient C8- BTBT: PC61BM bulk heterojunction photoactive layer and the ultra-thin MoO3 hole transport layer between them (Figure 1). The excitons generated in the photoactive layer are effectively separated at the body heterojunction, the generated electrons are captured by the acceptor PC61BM (CTE effect), holes are injected into the channel layer, and inorganic MoO3 can further promote the injection of holes and Block electrons, thereby effectively inhibiting electron-hole recombination. Furthermore, the C8-BTBT channel layer with high mobility provides an unimpeded "highway" for hole transport, and holes can be transported freely and at high speed in the channel. Therefore, by ingeniously designing and optimizing all aspects of the generation, separation, transmission, and compound suppression of photogenerated excitons, the photodetection performance of the phototransistor is greatly improved, and the photosensitivity (Ilight / Idark) reaches 2.9′106 The photoresponsivity reached 8.6′103 A / W, the photodetectivity (Detectivity) was 3.4′1014 Jones, and the external quantum efficiency was 3 × 106% under low light irradiation (32μW / cm2).
Not only that, at the device application level, the research team used this novel structure to prepare a flexible photodetector device, and verified the good reliability of the structure in flexible devices through bending experiments (Figure 2a). At the same time, the research team also prepared a phototransistor array structure to verify its excellent potential in photoimaging applications (Figure 2b).
The device structure design ideas proposed in this work have paved a new path to high-performance organic phototransistors. In order to realize high-performance (flexible) photodetectors and optical imaging devices, important design ideas and implementation methods are provided. Not only that, this structure has very excellent universal applicability, and it provides new research for the electronic and optoelectronic principled exploration and device application development of high-performance photodetectors with a wide spectral range from ultraviolet to near infrared and other related organic optoelectronic devices. platform.
The research results were published in "Advanced Materials". The research was supported by Guangdong Science and Technology Plan Project and Shenzhen Science and Technology Plan Project.
Fig.1 (a) Structure diagram of compound layered phototransistor and (b) Energy level distribution diagram
Figure 2 (a) Flexible photodetector and (b) Optical imaging array using a composite layered structure
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