Quantum chemical investigations of electron injection in triphenylamine-dye sensitized TiO2 used in dye sensitized solar cells

Density functional theory (DFT) and time dependent DFT has been applied to shed light on the electronic properties, photophysical properties and electron injection in the photosensitizers 2-cyano-5-(4-(phenyl(4-vinylphenyl)amino)phenyl)penta-2,4-dienoic acid (TC4) and its derivatives. The ground state structures have been optimized by using DFT-B3LYP/6-31G** level of theory. The absorption spectra have been computed by using PCM-TDBHandHLYP/6-311 + G** level of theory. Generally, highest occupied molecular orbitals are delocalized on whole of the dye while lowest unoccupied molecular orbitals are localized on ligand C, conjugated chain and anchoring group. By substituting the vinyl at positions 3,3′ on A- and B-ligands leads toward red shift. The methoxy group as donor is better than the methyl which can improve the electron injection and coupling constant. The light harvesting efficiency of mono-methoxy derivative (11) would be comparable to TC4. The size effect of titanium dioxide (TiO2) (nanoparticles) has been investigated on the electronic structure of the dye. By increasing the size of TiO2 intra-molecular charge transfer from dye to nanoparticles enhanced.