Novel heteroleptic ruthenium (II) complex with DPBPZ derivative for dye-sensitized solar cells

Herein, as Ru(II) complex for the dye-sensitized solar cells (DSSCs), we designed and investigated a novel heteroleptic ruthenium complex [Ru(dcbpy)(dpbpz)(NCS)2] with dpbpz derivative to enhance photovoltaic performance. The density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to gain insight into the factors responsible for photovoltaic properties as dye sensitizer. Molecular orbitals analysis confirmed that HOMO of [Ru(dcbpy)2(NCS)2] and [Ru(dcbpy)(dpbpz)(NCS)2] are delocalized over the ruthenium t2g character with sizable contribution from the NCS ligand orbitals. The LUMO of [Ru(dcbpy)2(NCS)2] is localized over the dcbpy moiety. However, LUMO of [Ru(dcbpy)(dpbpz)(NCS)2] is localized over the dpbpz moiety and LUMO + 1 is localized the dcbpy moiety. Overall, the absorption spectrum of the present Ru complex was more broad than that of [Ru(dcbpy)2(NCS)2] known as N3 dye. Especially, absorption band in the region between 500 nm and 600 nm was red-shifted. Moreover, the distance between the HOMO of [Ru(dcbpy)(dpbpz)(NCS)2] and the anchoring moiety is longer than that of [Ru(dcbpy)2(NCS)2]. This means that [Ru(dcbpy)(dpbpz)(NCS)2] have longer charge-separated lifetime than [Ru(dcbpy)2(NCS)2. These results are attributed to the extended pi-conjugation of dpbpz moiety. Therefore, we suggest that newly designed [Ru(dcbpy)(dpbpz)(NCS)2] heteroleptic ruthenium complex would be a good candidate as a dye sensitizer of DSSCs, comparable to [Ru(dcbpy)2(NCS)2].