The method is expected to accelerate the proliferation of flexible devices

Professor Toshiki Tajima, from the Department of Applied Chemistry at the Shibaura Institute of Technology, has developed a new method to synthesize an n-type semiconductor in a simple manner (patent pending: 2019-081783). The method eliminates cumbersome synthesis procedures, as it does not require a special catalyst or a leaving group, and it can synthesize colorless transparent membranes of perfluoropolyphenylene (fully fluorine conductive polymer) by electrolytic reduction. The method can also be applied to produce many types of n-type semiconductors. After identifying its scope of application through joint research with companies and other entities, the method can be used to make flexible and light semiconductors for flexible devices. Making the production of n-type semiconductors simpler and cheaper is expected to accelerate research and development in proliferating the use of flexible devices.

Key points:

- It is possible to synthesize perfluoropolyphenylene in a simple manner without a special catalyst or a leaving group by inducing the reductive cleavage of the carbon–fluorine bond through the electrolytic reduction of hexafluorobenzene.
- The method can be applied to make various types of n-type polymer semiconductors.
- The method successfully synthesized colorless transparent membranes.

Research background

Since organic semiconductors are lighter and more flexible than inorganic semiconductors, high expectations are pinned on the use of organic semiconductors for flexible devices. Semiconductor devices are made by combining p-type and n-type semiconductors. While various p-type semiconductors have been developed, the varieties of n-type semiconductor varieties developed so far are extremely limited. The conductive polymer, which was successfully synthesized this time, is useful as an organic semiconductor. Hence, several varieties of p-type semiconductors have been made from the conductive polymer so far. N-type semiconductors can be made by adding fluorine, a strong electron-attracting group, to p-type semiconductors. However, it is difficult to synthesize fully fluorine conductive polymers in a stable manner due to the cumbersome synthesis procedure involved.

Research outline

Professor Tajima succeeded in synthesizing perfluoropolyphenylene gel in a simple manner through the reductive electropolymerization of hexafluorobenzene (see Figure 1). Furthermore, by drying and washing the gel (see Figure 2), he succeeded in making it a colorless transparent membrane. The synthesized membrane is comprised of 60% carbon and 40% fluorine in atomic percentage composition, implying that it is a flexible type of perfluoropolyphenylene with a fewer number of cross-linking. In addition, its element mapping showed that fluorine was uniformly distributed across the entire membrane (see Figure 3).

Figure 1 Before synthesis (left) After synthesis (right)
Figure 2
Perfluoropolyphenylene gel (yellow)
Perfluoropolyphenylene membrane (transparent)
Figure 3
The element mapping of perfluoropolyphenylene membrane (fluorine is indicated in green)

Future prospects

Professor Tajima plans to identify the scope of application of this method through joint research with companies while exploring the utility of perfluoropolyphenylene gel and membrane and the other products produced by this method.


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