"Conjugated polymers," which are composed of linked π-conjugated molecules, can absorb visible light and have efficient luminescence properties, and are used in organic electronics materials such as OLEDs and polymer solar cells.  Since photophysical processes based on excitons generated by photoabsorption proceed on a time scale of femtoseconds (10−15 s) to microseconds (10−6 s), we have been studying photophysical and photochemical phenomena on a molecular time scale by using time-resolved spectroscopy with ultrashort laser pulses.  Our laboratory uses time-resolved spectroscopy with ultrashort laser pulses to elucidate the mechanisms of photophysical and photochemical phenomena on the molecular time scale.

Blending multiple conjugated molecular materials can create new functions.  For example, by blending an electron-donating polymer (D) with an electron-accepting polymer (A), charge carriers are generated by electron transfer from the D material to the A material.  Since the physical properties of these charge carriers are governed by the phase-separated structure on the nanometer scale, we observe and control the phase-separated structure on the molecular spatial scale and study the relationship between the structure and the optolectronic properties and functions.

We are developing polymer solar cells, which are expected to be the next generation of solar cells, using conjugated polymer blend films.  We aim to improve power conversion efficiency by developing new materials and devising new charge generation principles, and by making full use of time-resolved spectroscopy to answer questions such as "How is photocurrent generated?" and "How are charge carriers transported?"  On the basis on such molecular-level analysis, we are working on improvements to realize highly efficient polymer solar cells.