Three dyes based on a triphenylamine (TPA) moiety using a silicon bridge have been synthesised, namely CL-1D, CL-OMe and CL-SiMe. Structural benefits of long alkyl chains and electron donor group on photo conversion efficiency (PCE) of dye sensitized solar cells is discussed. A previously synthesised dye, denoted CL-1, which contained long alkyl chains and exhibited an efficiency of 6.90%, was compared with CL-SiMe, which contained shorter alkyl chains and showed and efficiency of 3.41%. A large drop in J(sc) and V-oc was found to be the reason for the appreciable decline in efficiency for CL-SiMe vis-a-vis CL-1. Electron donor group studies were performed using CL-1D and CL-OMe. CL-1D, which contained bulky aniline electron donor groups, showed an efficiency of 4.20%, whilst CL-OMe, featuring smaller methoxy donor groups had an efficiency of 5.50%. Theoretical UV-Vis absorption spectra were obtained for the CL-1D dye by time-dependent density functional theory (TD-DFT); the experimental and calculated values of the energy for maximum absorbance were in good agreement with experimental data.

A chromophore containing a coplanar dihexyl-substituted dithienosilole (CL1) synthesised for use in dye-sensitised solar cells displayed an energy conversion efficiency of 6.90% under AM 1.5 sunlight irradiation. The new sensitiser showed a similar fill factor and open-circuit voltage when compared with N719. Impedance measurements showed that, in the dark, the charge-transfer resistance of a cell using CL1 in the intermediate-frequency region was higher compared to N719 (69.8 versus 41.3 Ω). Under illumination at AM 1.5G-simulated conditions, the charge-transfer resistances were comparable, indicative of similar recombination rates by the oxidised form of the redox couple. The dye showed instability in ethanol solution, but excellent stability when attached to TiO 2 . Classical molecular dynamics indicated that interactions between ethanol and the dye are likely to reduce the stability of CL1 in solution form. Time-dependent density functional theory studies were performed to ascertain the absorption spectrum of the dye and assess the contribution of various transitions to optical excitation, which showed good agreement with experimental results.