Density functional theory study on ruthenium dyes and dye@TiO2 assemblies for dye sensitized solar cell applications

Cyclometalated ruthenium dyes improve significantly the performance of dye sensitized solar cells (DSSCs) based on conventional ruthenium dyes. Here, this study examined four thiocyanate-free cyclometalated ruthenium dyes using the density functional theory (DFT). The geometrical, electronic structural, and photophysical propertiesof the dyes and the dyes tethered to a TiO2 surface were examined in both the presence and absence of an acetonitrile solvent. The Kohn-Sham eigenvalues of the molecular orbitals of the dyes were destabilized by ca. 2 eV in the presence of the solvent. The absorption peaks did not change significantly in position but hyper chromic shifts of more than two-fold occurred. When adsorbed on a TiO2 surface, the dyes showed redshifted absorption of approximately 20 nm. To the best of our knowledge, a systematic and comprehensive first-principles investigation on cyclometalated ruthenium dyes in vacuum, solvent, and tethered to TiO2 has been carried out for the first time.