Density Functional Theory Studies of Ruthenium Dye (N3) Adsorbed on a TiO2 Brookite Cluster for Application in Dye Sensitized Solar Cells

Abstract

Titanium dioxide has been a subject of increasing interest due to its application in pigments, photocatalysis and semiconductor materials in dye sensitized solar cells (DSSC). Recent studies suggest that TiO2 brookite exhibits good photocatalytic properties. Efficiency in excess of 11% has been achieved with the use of ruthenium (N3) dyes as DSSC sensitizer. The optical properties, energy level alignment and electronic state energy of the ruthenium (N3) sensitizer to TiO2 cluster were studied to gain insight into the electron injection kinetics and electron injection efficiency of the dye/TiO2 complex. The simulated absorption spectra show absorption peaks at 311, 388 and 480 nm. The HOMO of (N3) lies at −5.03 eV and is centred on the NCS moiety where the donor group is situated, while the LUMO lies at −3.01 eV and is centred on the 4,4-dicarboxy-2,2-bipyridine moiety where the acceptor group is situated. Upon absorption on a brookite cluster, the light absorption maximum red shifted to higher wavelength; this results in the distribution of the LUMO shifting from the dye to the TiO2 cluster. The results suggest favourable electron injection from the dye excited state into TiO2 semiconductor. The results suggest that TiO2 brookite is a promising entrant for DSSC semiconductor.