Application of Triphenylamine-Based Sensitizers with Two Carboxylic Acid Groups to Dye-Sensitized Solar Cells

Two triphenylamine-based dyes (TPAR3 and TPAR6) containing two carboxylic acid groups with different conjugated lengths were synthesized and characterized with regard to their photophysical and photoelectrochemical properties. Experimental results showed that the λ_max of TPAR6 either in methanol solution or on TiO₂ film was red-shifted and broadened by extending the π-conjugated bridge. However, the performance of TPAR3-based dye-sensitized solar cell (DSC) was superior to that of TPAR6. This reason was due to the serious self-quenching of the electronically excited state in TPAR6 molecule, resulting from its cis-trans isomerization. The effects of addition of guanidinium thiocyanate (GT) in the electrolyte on the performance of DSCs based on TPAR3 were also investigated, revealing a maximum energy conversion efficiency of 4.02% at 0.100 mol·L⁻¹ GT.