Novel Ru(II) complex with 3-(2'-pyridyl)-1,8-naphthalimide derivative for dye-sensitized solar cells

A novel heteroleptic ruthenium(II) complex D1 with a pni (3-(2'-pyridyl)-1,8-naphthalimide) derivative as a heteroleptic donor was designed and theoretical studies were performed of the molar absorptivity of D1 compared to that of the standard N749 dye and [Ru(dcbpy)2(ppy)] (dcbpy = 4,4'-dicarboxy-2,2'-bipyridine, ppy = 2-phenylpyridine). Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to gain an insight into the factors responsible for the photovoltaic properties of the dye sensitizer. The results showed that the absorption spectrum of the D1 dye with the pni derivative was red-shifted compared to N749 and [Ru(dcbpy)2(ppy)], particularly, in the region above 600 nm. The red-shift was attributed to the heteroleptic electron-donating ligands of the D1 dye. According to the molecular orbital analysis, the LUMO of the D1 dye mainly localized on tctpy (4,4',4"-tricarboxy-2-2':6'.2"-terpyridine) moiety. HOMOs of the N749 were localized on the NCS moiety. However, HOMO and HOMO-2 of D1 were localized on the Ru-NCS moiety and the Ru-pni moiety, respectively. Owing to the additional HOMO-2, the D1 dye had a broad absorption spectrum and high photovoltaic efficiency compared to N749.