DFT and TDDFT study on organic dye sensitizers D5, DST and DSS for solar cells

The geometries, electronic structures, polarizabilities and hyperpolarizabilities, and UV-vis spectra of organic dye sensitizers D5, DST and DSS were studied by using density functional theory (DFT) and time-dependent DFT. The calculated geometries indicate that the strong conjugated effects are formed in the dyes. The polarizabilities depend on the length of conjugate bridge of the dye. The features of UV-vis spectra were assigned to π→π∗ transitions according to the qualitative agreement between experiment and the TDDFT calculations. The absorption in visible region are all photoinduced electron transfer processes, the diphenylaniline group in D5 and the aniline group in DST and DSS are main chromophore that contributed to the sensitization, the interfacial electron transfer is due to an electron injection processes from excited dyes to semiconductor conduction band. The role of different conjugate bridge in geometries, electronic structures and spectra properties were analyzed in a comparative study of the dyes.