Dyad powers solar cells

04-14-2009: The highest recorded power conversion efficiency for dyad-based solar cells has been achieved by Japanese scientists.

Keisuke Tajima, Kazuhito Hashimoto and co-workers at the University of Tokyo and the Japan Science and Technology Agency have developed new dyad materials with highly crystalline donor groups and applied these to solar cells. The dyad materials showed a significant increase in power conversion efficiencies over past dyad systems, with the best efficiency so far being reported as 0.37%. However, Tajima and Hashimoto have recorded efficiencies of up to 1.28% for their new dyad materials.

Tajima explains that previous attempts by the group to improve efficiencies of these dyad-based solar cells were limited due to insufficient charge transport and therefore resulting in charge recombination. In this system, a new oligo(p-phenylenevinylene) (OPV)-fullerene dyad is made. The OPV acts as a donor group which gives rise to strong π-π intramolecular interactions within the system, and thus improved the crystallinity of the material. The increase in power efficiency, clearly indicates the importance of crystallinity for improvement in carrier transport in the dyad-based solar cell.

‘If we further optimize molecular design of dyads, for example introduction of a low band gap donor or self-organization ability, further improved photocurrent or charge carrier transport is expected,’ says Tajima. ‘Dyads could be a useful material for studying the mechanism of the opto-electronic process involved in organic solar cells.’

‘To reach the efficiency achieved in state-of-the-art polymer:fullerene mixture bulk heterojunction systems, we believe that it is of great importance for a dyad system to achieve a highly ordered and oriented nanostructure,’ explains Tajima. ‘Therefore, the next challenge would be designing molecules which achieve such a nanostructure, possibly through self-organization of the molecules.’

Original article: Takeshi Nishizawa, et al. Chem. Commun., 2009