Dye-sensitized nanocrystalline TiO2 solar cells (DSSCs) have attracted considerable interest because of their high conversion of sunlight to electricity and easy fabrication. To overcome the prohibitive cost of ruthenium metal complexes, several groups have developed metal free sensitizers and obtained efficiency in the range of 9~10%. However, a major issue for the low photoconversion efficiency of many organic dyes in dye-sensitized solar cell is due to the formation of dye aggregates on the semiconductor surface. Therefore, for obtaining efficient photoconversion based on organic dyes, aggregation needs to be avoided through the CD (cyclodextrin). The optimal sensitizers, which combine broad visible light absorption with an excited-state directionality for favorable electron-transfer dynamics, is a key issue in the development of DSSC. So, we used a two type concept. First is the novel cosensitization based on the controlled construction of the film architecture in which a primary monolayer of dye is spatially separated from a secondary monolayer of another dye suing a layer of Al2O3, resulting in the configuration TiO2 / Dye1 / Al2O3 / Dye2. Second concept, a tandem-structured dye sensitized solar cell composed of a front and a back sub-cells was assembled by using spectrally complementary organic dye combinations. Other issue is the organic solar cells (OPV). Solution processed organic solar cells based on bulk-heterojunction (BHJ) materials comprising of small molecule chromophores and fullerene derivatives have offered special opportunities showing their promising power-conversion efficiencies above 4% as attractive alternatives to p-conjugated (semiconducting) polymers. Although the BHJ devices fabricated by small molecule chromophore present lower efficiency than ~7% of that by polymer, these approaches by small molecule seem to fascinate more than polymer from the viewpoint of mass production for commercial application due to their low reproducibility for characteristics such as average molecular weight (Mw) and polydispersity index (PDI) as well as difficulty in purification. We have also focused on the development of new chromophores for small molecule BHJ solar cell.
1. H. Choi, S. Kim, S. O. Kang, J. Ko, M-. S. Kang, J. N. Clifford, A. Forneli, E. Palomares, M. K. Nazeeruddin, M. Gr?tzel. Angew. Chem. Int. Ed. 2008, 47, 8259.
2. H. Choi, S. O. Kang, J. Ko, G. Gao, H. S. Kang, M-. S. Kang, M. K. Nazeeruddin, M. Gr?tzel. . Angew. Chem. Int. Ed. 2009, 48, 5938.
3. H.Choi, S. Paek, J. Song, C. Kim, N. Cho and J. Ko, Chem. Commun., 2011, 47, 5509.
4. H-. M. Ko, H. Choi, S. Paek, K. Kim, K. Song, J-. K. Lee and J. Ko, J. Mater. Chem., 2011, 21, 7248.