Dye-Sensitized Solar Cell (DSSC) Materials

　　Grätzel et al. first developed a dye-sensitized solar cell (DSSC) in 1991.¹⁾ The DSSC is a liquid-type device that involves nanoporous titanium oxide (TiO₂) as a semiconducting electrode, organic dye-sensitizer and electrolyte solution containing a redox component. This is expected to be a low cost solar cell, because there is a simpler device structure compared with the other solar cells.²⁾ The DSSC is usable under conditions with weak light. Thus, it is expected that the DSSC may be installed in a room. A ruthenium complex with a bipyridine ligand is one of popular organic dyes for the solar cell.³⁾ In the polypyridine ligand of the ruthenium complex, we can introduce some carboxyl or phosphonic acid groups forming a linkage with TiO₂. In addition, metal-free organic dyes (eg. D-102, D-131 and D-358) were also developed, because they do not contain any expensive ruthenium atoms.^4,5) Several examples of DSSC with all solid systems are reported as well.⁶⁾