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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