Ultrasensitive organic phototransistors based on novel hybrid-layered architecture

(Nanowerk News) Organic phototransistors (OPTs) are widely used in environmental/health monitoring, quantum communication, chemical/biomedical sensing, remote control, surveillance and image sensors, with the merits of low-cost, light-weight, high efficiency and good environmental friendliness.
The interfacial charge effect is very crucial for high-sensitivity OPTs. Conventional layered and hybrid OPTs suffer from the trade-off in well balancing the separation, transport, and recombination of photogenerated charges.
Prof. Jia Li and Yuanhong Gao from the Shenzhen Institutes of Advanced Technology (SIAT) of the Chinese Academy of Sciences and their collaborators developed a novel hybrid-layered architecture to improve the overall photodetection performance of organic phototransistor by simultaneously taking advantages of charge-trapping effect and efficient carrier transport.
Their findings were published in Advanced Materials ("A Novel Hybrid-Layered Organic Phototransistor Enables Efficient Intermolecular Charge Transfer and Carrier Transport for Ultrasensitive Photodetection").
The structure of a hybrid-layered phototransistor
Fig1. The structure of the hybrid-layered phototransistor (Image: Prof. Jia Li) (click on image to enlarge)
The structure of the novel hybrid-layered phototransistor (HL-OPT) consists of a high mobility organic semiconductor channel layer for fast carrier transport, an organic bulk heterojunction (BHJ) photoactive layer, and an ultrathin inorganic interlayer sandwiched in between.
Excitons generated in the photoactive layer, dissociated into electrons and holes at the donor/acceptor BHJ. The generated electrons are readily trapped by the acceptors nearby and holes are injected into the channel layer to increase the carrier concentration.
An inorganic interlayer is chosen to further enhance hole injection and block electrons, subsequently suppressing electron-hole recombination. As a result, by combining the virtues of charge-trapping effect and fast carrier transport, significant enhancement in the overall photodetection performance is achieved from the HL-OPT.
To evaluate potential applications of the high-performance HL-OPT, the researchers fabricated the devices on flexible substrates and confirmed their excellent flexibility. Meanwhile, the devices were also integrated into a one-dimensional array and demonstrated the reliability of the HL-OPT in photosensitive imaging system. "These successful trials make the HL-OPT particularly appealing for the applications in flexible and wearable optoelectronic devices." said Prof. Li.
Ultrasensitive organic phototransistor
Fig2. Ultrasensitive organic phototransistors based on the novel Hybrid-Layered Architecture. (Image: Prof. Jia Li)
This work provides new insights into the design and optimization of high-performance photodetectors, spanning the ultraviolet and near infrared range, and suggested the fundamental issues pertaining to electronic and photonic properties of the devices.
"Another exciting point is that this organic photodetector can be potentially fabricated by using printing techniques, which would further reduce the process cost," said Li. "I hope this work can provide the market with a promising solution for photodetectors by combining both high performance and low cost."
Source: Chinese Academy of Sciences
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