Abstract
Five-membered ring products of cyclometalation reactions are utilized as dyesensitizers for manufacturing very stable dye-sensitized solar cells. Such solar cells have greater stability than standard chelate-type N719 solar cells because the cyclometalated ligands in the five-membered ring products are stronger donors than the thiocyanate groups in the standard type. Solar cells with high overall energy conversion efficiencies are manufactured primarily by using three types of cyclometalated five-membered-ring ruthenium compounds:
1. A solar cell prepared with a phenylpyridine ruthenium compound, e.g., bis(4,4'-dicarboxy- 2,2'-bipyridine) 2-(2,4-difluorophenyl)pyridine ruthenium, shows an overall energy conversion efficiency of 10.1 %.
2. A solar cell with the ruthenium compound with 2,2’-bipyridine bearing two carboxyl ligands and two alkylthienothophene ligands and 2,3’-bipyridine bearing two alkyloxy ligands shows a high overall energy conversion efficiency with 9.4 % with the cobalt electrolyte [Co(phen)3]3+/2+.
3. A solar cell using a clometalated CNN tridentate ruthenium compound bearing an electron-donating substituent of a terminal substituent placed para to the triphenylamine achieves a high overall solar-to-electric energy conversion efficiency of 8.02 %. This result is almost the same as that of N3 under the same conditions.
Keywords: Dye-sensitized solar cells, cyclometalation reactions, five-membered ring, ruthenium, photosensitizers.
Graphical Abstract