Theoretical study of novel xanthene-linked L-(D-π-a)2-type double-anchored dyes for dye-sensitized solar cells: Effects of π bridge length and TiO2 adsorption pattern

To investigate the effects of varying π bridge lengths on the structural and electronic properties, two _L-(D-π-A)₂-type dye molecules were simulated using density functional theory (DFT). In this study, KS-19 employed thiophene as the π bridge, while KS-21 incorporated 2,2′-bithiophene. The optimized geometry revealed that the presence of 2,2′-bithiophene in the KS-21 molecule enhances its degree of conjugation, thereby exhibiting superior molecular stability. The additional thiophene unit in KS-21 was found to facilitate a red shift in the absorption spectra based on optical property analysis. Furthermore, 2,2′-bithiophene within the KS-21 molecule proved more effective for achieving dye regeneration and complete electron injection. Additionally, we simulated their adsorption behavior on titanium dioxide clusters and calculated their adsorption energies. Our investigation demonstrated that the KS-21 dye with a 2,2′-bithiophene π spacer exhibited enhanced photovoltaic performance. Consequently, double-anchored dyes incorporating extended π conjugated structures show significant promise across various applications in dye-sensitized solar cells.