Theoretical study of Ru (II) complexes by using the conjugated-donor antenna moiety for DSSCs

Abstract

In this study, a novel heteroleptic ruthenium complex of [Ru(dcbpy)(L)(NCS)2] (CQ), where dcbpy = 4,4′-dicarboxy-2,2′-bipyridine and L = a coumarin derivative, was designed and studied theoretically for its photoelectrochemical properties for use in dye-sensitized solar cells(DSSCs). We compared the well-known [Ru(dcbpy)2(NCS)2] (N3) and CQ. To gain insight into the structural, electronic, and optical properties of the heteroleptic ruthenium complex, we performed density functional theory (DFT)/time-dependent DFT (TDDFT) calculations on the complexes of the heteroleptic ruthenium complex. A molecular orbital analysis confirmed that the highest occupied molecular orbitals (HOMOs) of complexes were localized above the ruthenium center, the NCS ligand, and the coumarin moiety. The lowest unoccupied molecular orbital (LUMO) was essentially localized above the dcbpy. The TDDFT results showed that the CQ with a chromophore ligand had broader, stronger absorption spectra in the region above 400 nm compared to the N3 dye. From these results, we were able to determine how substituted antenna moiety influenced the electronic and the optical properties. We expect the ruthenium complex to perform better than the N3 dye in terms of conversion efficiency in DSSCs.