Recently we have developed aromatic ring-fused, unsymmetrically pi-elongated porphyrins (i.e., naphthalene-fused and quinoxaline-fused porphyrins) that showed broadened, and red-shifted light absorption properties compared to the corresponding porphyrin references, resulting in the power conversion efficiencies of 4.1% and 6.3%, respectively. As demonstrated for other sensitizers in DSSCs, introduction of both electron-donating and electron-withdrawing substituents to a core of pi system would be appealing for the modulation of the light-harvesting properties of sensitizers. In this talk I will present our recent advance in porphyrin-sensitized solar cells.1-10
In particular, I will focus on novel push-pull porphyrins for porphyrin-sensitized solar cells.1-10
For instance, we synthesized for the first time a push-pull porphyrin dye bearing two diarylamino groups and two carboxyphenylethynyl groups as electron-donating and electron-withdrawing anchoring groups, respectively. The absorption spectrum displayed broad and red-shifted absorption, achieving panchromic light-harvesting in visible and NIR regions. Introduction of multiple push-pull groups into meso
-positions is a promising strategy for the rational design of porphyrin sensitizers for light-harvesting applications. The preliminary photovoltaic performance is moderate (3.0%), but the extensive photocurrent generation matches with the excellent light-harvesting ability. Further modulation of the photovoltaic properties of porphyrin DSSCs will be possible by suitable selection of electron-donating and electron-withdrawing groups as well as introduction of the substituents into the porphyrin core.
 H. Imahori, T. Umeyama, and S. Ito, Acc. Chem. Res. 42, 1809 (2009).
 H. Imahori, S. Kang, H. Hayashi, M. Haruta, H. Kurata, S. Isoda, S. E. Canton, Y. Infahsaeng, A. Kathiravan, T. Pascher, P. Chabera, A. P. Yartsev, and V. Sundström, J. Phys. Chem. A, 115, 3679 (2011).
 H. Imahori, H. Iijima, H. Hayashi, Y. Toude, T. Umeyama, Y. Matano, and S. Ito, ChemSusChem, 4, 797 (2011).
 M. Simon, H. Iijima, Y. Toude, T. Umeyama, Y. Matano, S. Ito, N. V. Tkachenko, H. Lemmetyinen, and H. Imahori, J. Phys. Chem. C, 115, 14415 (2011).
 H. Imahori, T. Umeyama, K. Kurotobi, and Y. Takano, Chem. Commun. (Feature Article), 48, 4032 (2012).
 H. Hayashi, A. S. Touchy, Y. Kinjo, Y. Toude, K. Kurotobi, T. Umeyama, Y. Matano, and H. Imahori, ChemSusChem, 6, 508 (2013).
 S. Ye, A. Kathiravan, H. Hayashi, Y. Tong, Y. Infahsaeng, P. Chabera, T. Pascher, A. P. Yartsev, S. Isoda, H. Imahori, and V. Sundström, J. Phys. Chem. C, 117, 6066 (2013).
 K. Kurotobi, K. Kawamoto, Y. Toude, Y. Fujimori, Y. Kinjo, S. Ito, Y. Matano, and H. Imahori, Chem. Lett., 42, 725 (2013).
 K. Kurotobi, Y. Toude, K. Kawamoto, Y. Fujimori, S. Ito, P. Chabera, V. Sundström, and H. Imahori, Chem. Eur. J., 19, 17075 (2013).
 T. Higashino and H. Imahori, Dalton Trans. (Perspective), in press.