A new co-sensitization method employing D–π–A dye with pyridyl group and D–π–Cat dye with catechol unit for dye-sensitized solar cells

• We have developed a convenient co-sensitization method for DSSCs.
• D–π–A dye with pyridyl group and D–π–Cat dye with catechol unit have been used.
• The D–π–A dye is adsorbed at the Lewis acid sites on the TiO2 electrode.
• The D–π–Cat dye is adsorbed at the Brønsted acid site on the TiO2 electrode.
• One-step co-adsorption of two different dyes onto TiO2 electrode has been achieved.

To provide a new co-sensitization approach in dye-sensitized solar cells, we have developed a co-sensitization method employing D–π–A dye sensitizer with pyridyl group and type-II D–π–Cat dye sensitizer with catechol unit. It was found that the D–π–A dye sensitizer with pyridyl group and the type-II D–π–Cat dye sensitizer are adsorbed on the co-adsorbed TiO2 film through the coordinate bonding at the Lewis acid sites and the bidentate linkage at the Brønsted acid site on the TiO2 surface, respectively. This work indicates that a convenient co-sensitization of two different dyes on the TiO2 electrode without the competitive adsorption has been achieved successfully by utilizing the site-selective adsorption behaviour of the D–π–A dye sensitizer with pyridyl group and the type-II D–π–Cat dye sensitizer, resulting in enhancement of dye coverage on the TiO2 electrode.

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