Improving the electronic devices' performance and reducing the manufacturing costs

Hanyang University announced on November 11 that Professor Jang Jae-young's team from Hanyang University's Department of Energy Engineering recently developed the principle of molecular doping reaction of organic semiconductors and technology to control them.

The technology is expected to reduce manufacturing costs by improving the performance of various electronic devices such as energy harvesting devices, organic light emitting diodes (OLEDs), and organic transistors and thus simplifying the manufacturing process.

Organic semiconductors composed of carbon-based molecules have been studied as key materials for organic electronic devices such as OLED since they can be bent or stretched. In particular, the "molecular doping", mixing molecular additives to control the electrical and optical properties of organic semiconductors, is drawing a lot of attention from scientists.

Among the various additives, recent research is focusing on the substance "tris (pentafluorophenyl) borane (hereinafter BCF)." This results in two different forms of doping reaction by using the properties of Lewis acids and Brønsted acids that appear when reacted with water.

For example, boron (B) in a BCF molecule causes a Lewis acid-base reaction with an unshared electron pair of atoms, such as nitrogen (N) and oxygen (O), which make up an organic semiconductor, called Lewis acid doping. On the other hand, BCF that reacts with water causes a reaction of transferring protons (H+) to organic semiconductors, which is called Brønsted acid doping.

Such unique and complex reactions of BCF are influenced by various factors, such as external environment and the structure of organic semiconductors. However, there has yet to be much progress in research to control these complex reactions.

Professor Jang's team analyzed the BCF doping reaction by using two organic semiconductors that have similar chemical structures but different Lewis bases, which are applied to thermoelement. As a result, they found out that Lewis acid doping suppressed Brønsted acid doping and greatly hindered charge transfer in semiconductors by bending the flat framework of organic semiconductors and breaking down the crystal structure.

The research team suggested a technology that can selectively cause only doping of Brønsted by heat-treating an organic semiconductor film doped with BCF at a temperature of 120 degrees Celsius, based on the difference in the binding strength of the two doping reactions caused by the properties of Lewis acids and Bronsted acids.

This study is significant in that regulating molecular doping not only improves the performance of organic thermoelement but also is applicable to other electronic devices. Especially, this technology is expected to improve the low performance of wearable electronic devices.

Professor Jang said, "When molecular doping is properly controlled with this study, the charge transfer properties of organic semiconductors can be maximized. In particular, it can be used as a key technology to improve the low performance of wearable electronic devices ."

The research which was conducted with the support of the National Research Foundation of Korea with funding from Ministry of Science and ICT (Mid-sized Research Support Project, Leading Research Center Support Project, and Nano and Material Technology Development Project), was published on the November 10 of “Advanced Functional Materials”, a world-renowned material science journal, and was selected as a cover paper.