Silicon-bridged triphenylamine-based organic dyes for efficient dye-sensitised solar cells

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-à-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.