Discovering the intermediate of dye regeneration in dye-sensitized solar cells: Theoretical investigations on the interaction between organic dye with different donors and X−/X3− (X = I, Br)

• Intermediate forms of dye regeneration for four D-A dyes were obtained.
• Br−/Br3− is appropriate alternative based on the matched redox potential.
• Triphenylamine group can balance regeneration and recombination better.

Dye regeneration was a key process to influence lifetime and open-circuit voltage of dye-sensitized solar cells. In order to explore the mechanism of dye regeneration, the intermediate forms of this reaction were searched by first principle calculations in this study. The possible intermediat forms were obtained by analyzing the reactivity of four organic dyes with different donors and two electrolyte ions (I− and Br−). Then comparing their structures, interaction energy and reaction free energy, most appropriate intermediate forms were screened out. Throughout the comparison between I− and Br−, we found that Br−/Br3- could be a good redox couple if the redox potential matched with the energy gap of dye. In particular, steric-hindrance was likely the most influential factor in determining the intermediate forms. It is suggested that triphenylamine homologues as donor groups may both interact with electrolyte easily and accordingly keep off the electrolyte from semiconductor effectively.

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