Emergent Molecular Function Research Group

Principal Investigator

PI Name Kazuo Takimiya
Degree D.Eng.
Title Group Director


Our Team engages in the development and application of new functional organic molecules. Organic molecules can be designed and synthesized as they should have appropriate molecular and electronic structures for certain functionalities, and such functional molecules are utilized in fabricating optoelectronic devices such as organic field-effect transistors (OFETs) and organic solar cells (organic photovoltaics, OPVs). Recent our achievements are 1) development of high-performance molecular semiconductors applicable to OFETs with the highest mobilities, and 2) development of versatile semiconducting polymers that can be utilized to high performance solution-processed OTFTs and OPVs.

Research Fields

Chemistry, Engineering, Materials Sciences


Our group has developed several new building blocks for constructing semiconducting polymers and has recently been working with a particular type of polymer called PNNT-DT, consisting of naphthodithiophene- (NDT) and naphthobisthiadiazole- (NTz) building blocks, both of which were developed in our group. Although PNNT-DT can afford OPVs showing moderate power conversion efficiency (~5.5%), its low solubility decreases its processability. Thus, we recently attached additional alkyl groups to the polymer and found that not only the solubility of the polymer was enhanced, but also significantly improved the power-conversion efficiencies of solar cells made with these polymers. In these solar cells, the new alkylated polymers were arranged so that the polymer chains lay flat in stacks on the surface rather than aligned perpendicular to it. This causes the charge carriers, electrons and holes, to move perpendicular to the surface rather than parallel, improving the power-conversion efficiency. This drastic change in orientation produced solar cells with an efficiency of up to 8.2%, which is among the highest for OPVs with these newly developed semiconducting polymers.


Drastic change in polymer orientation and improved solar cell performances by alkylation.
Adapted from “J. Am. Chem. Soc. 2013, 135, 8834–8837.” with permission (© 2013 American Chemical Society).



Kazuo Takimiya

Group Director takimiya[at]riken.jp R

Kohsuke Kawabata

Research Scientist

Masahiro Nakano

Special Postdoctoral Researcher

Hiroyoshi Sugino

Postdoctoral Researcher

Chengyuan Wang

Postdoctoral Researcher

Takuya Ogaki

Postdoctoral Researcher

Morten Jensen

Postdoctoral Researcher

Nobuhiko Ohtsuka

Junior Research Associate

Johan Jean-Claude Maurice Hamonnet


Shunichi Tanaka




2-1 Hirosawa, Wako, Saitama 351-0198 Japan