Kazuhito Hashimoto tells Journal of Materials Chemistry about his hot paper.

1. Can you briefly describe what you achieved in this article?
We have synthesized a novel liquid crystalline oligothiophene and an oligothiophene-fullerene dyad and investigated their film morphology. In both films, we observed the spontaneous formation of the fiber-like nanostructures via pi-pi interaction of the oligothiophene groups with the aid of thermal annealing. We have also applied these nanostructures for photovoltaic devices, and the dyad device showed highest external quantum efficiency (EQE) among the dyad based devices.

2. Could you explain the significance of your article to the non-specialist? 
As nanotechnology develops, much research have been done on forming nanostructures suitable for device applications. Organic materials such as supramolecules and block copolymers have drawn considerable attention to form such nanostructures. In this work we have designed and synthesized a novel liquid crystalline oligothiophene and an oligothiophene-fullerene dyad and applied them to organic photovoltaic devices. We achieved quite high external quantum efficiency, indicating efficient charge separation. We also observed spontaneous formation of nanostructures, which could be advantageous for subsequent charge transport.

3. What has motivated you to conduct this work? 
Efficiency of organic photovoltaic devices has been significantly improved since the "bulk-heterojunction" concept was introduced, which is the simple mixture of a donor and an acceptor. In this structure, both the large interface of these two materials and the formation of the charge transport path to the electrode are very important. Currently, this morphology control in the films relies on thermal treatment of the films to induce the crystallization and phase separation of the components. We think that spontaneous formation of nanostructures via self-assembly could provide an easy, reproducible way to achieve the optimum structure for the photovoltaic devices.

4. Where do you see this work developing in the future? 
If we could design the molecules that spontaneously form a suitable size and phase of nanostructure for both the charge separation and transport, it would be a promising strategy to achieve high performance devices. Also, it could be a useful approach to study the mechanism of the opt-electronic process involved in the photovoltaic devices.

5. Are there any particular challenges facing future research in this area? 
Our preliminary results on the photovoltaic device showed improvement in charge separation in the dyad film. However, inefficient charge transport, probably due to the molecular orientation in the film, limited the power conversion efficiency. The orientational control of the molecules in the film is the next challenge to achieve efficient charge transport and thus high performance devices.

Takeshi Nishizawa (left) studied surface chemistry and received his B.S. from Waseda University in 2004. From 2004, he moved to the University of Tokyo to study supramolecular chemistry and received his M.E. from the University of Tokyo in 2006. At present, he is a Ph.D. student at the University of Tokyo and has also been a JSPS research fellow since 2007. His current research interests are supramolecular chemistry and polymer chemistry and their application to opt-electronic devices such as photovoltaic devices.

Keisuke Tajima (centre) received his Ph.D. in Engineering from the University of Tokyo in 2002. After spending two years at Northwestern University in US as a post-doc, he became assistant professor at the University of Tokyo in 2004. His current research interests focus on the polymer chemistry, organic/inorganic hybrid materials, and supramolecular chemistry to construct various nanostructures and their application to opt-electronic devices such as photovoltaic devices.

Kazuhito Hashimoto (right) received his Ph.D. in Chemistry from The University of Tokyo in 1978. At present, he is the Director General of Research Center for Advanced Science and Technology (RCAST) at the University of Tokyo. Also, he is a professor of RCAST and Department of Applied Chemistry at the same University concurrently. He has received several awards for his research excellence from various societies, such as the Japan Lightings Society, the Photochemical Society of Japan, and the Electrochemical Society of Japan. Also, he received the IBM Science Award from IBM Science Foundation in 1997, the Nikkei Environmental Technology Award from Nihon Keizai Shinbun, Inc., in 2004, and the Prime Minister Award from Cabinet Office of Japan in 2004. His current research interests are TiO2 photocatalysis for environmental purifications, photo-functionalized molecular magnets and organic photovoltaic devices.