Synthesis of heteroleptic Ru(II) complexes and application for dye-sensitized solar cells

Abstract

Applied with photosynthesis method of plants, dye-sensitized solar cells (DSSCs) is a clean technology converting solar energy into electronic energy. In DSSCs, dyes play a key role in absorbing solar energy, and ruthenium(??) complex [Ru(DCBPY)2(NCS)2][TBA]2 (DCBPY = 4,4'-dicarboxy-2,2'-bipyridine, TBA = tetrabutylammonium), called N719, is used for the most frequently cited dye demonstrating a high efficiency of energy conversion.In this study, novel heteroleptic Ru(II) complexeswere designed and prepared to develop new type of dyes for DSSCs. First of all, as it was expected that the principle of electrochemiluminescence (ECL) of ruthenium(II) complexes possessed a similar tendency to a role of dyes in DSSCs, 1,3-dihydro-1,1,3,3-tetramethyl-7,8-diazacyclopenta[1]phenanthren-2-one (DTDP) that was developed in our lab as an electrochemiluminescent ligand for Ru complex in ECL study was used as a primary ligand. 4,4'-Bis(E-styryl)-2,2'-bipyridine (BSBPY) was also used as another primary ligand because it was expected to be a favorable ligand as well for the absorption of a long wavelength region. In addition to these primary ligands, four types of anchoring ligands, L's, (each L = 4,4'-dicarboxy-2,2'- bipyridine, 4,4'-bis(E-carboxyvinyl)-2,2'-bipyridine, 4,7-dicarboxy-1,10-phenanthroline, 4,7-bis(E-carboxyvinyl)-1,10-phenanthroline) were prepared in good yields. By introducing each primary ligand and anchoring ligand stepwisely followed by salt formation reaction, salt form of four heteroleptic ruthenium(II) complexes [Ru(DTDP)L(NCS)2][TBA] and four [Ru(BSBPY)L(NCS)2][TBA] were synthesized in reasonable yields. To examine the utilization of our synthesized complexes as a photosensitizer in DSSCs, devices loaded with the newly prepared ruthenium(II) complexes were fabricated. Those were exhibited a reasonable power conversion efficiency (PCE) that was comparable to that of N719.