ABSTRACT
This chapter examines a combined theoretical and experimental effort aimed at providing a better understanding of the role of the sensitizer, particularly of its electronic structure and excited-state properties, in the efficiency of dye-sensitized solar cell devices. Previous theoretical investigations on dye sensitizers were mainly performed by means of semi-empirical and density functional theory (DFT) calculations, and only recently time-dependent DFT investigations on ruthenium (Ru) II sensitizers have appeared in the literature. The photovoltaic properties of the purified N719 and N621 sensitizers have been investigated as a function of the degree of protonation of the anchoring carboxylic groups, considering both diprotonated and monoprotonated dyes. The computed electronic structure changes are consistent with the photovoltaic data for the mono- and diprotonated N719 complexes. The oxidation potential of these complexes is cathodically shifted compared to the N3 sensitizer, which increases the reversibility of Ru III/II couple leading to enhanced stability.
