Efficient dye-sensitized solar cells based on concerted companion dyes: Systematic optimization of thiophene units in the organic dye components

To develop efficient concerted companion (CC) dyes for fabricating high-performance DSSCs, three organic dyes XL1-XL3 have been designed by varying the position and number of the β-hexylthiophene (HT) bridges, and these organic dye units are covalently linked with our previously reported porphyrin dye XW10 to construct the corresponding CC dyes XW74-XW76. Among the organic dyes, XL3 contains two β-hexylthiophene units at both the donor and acceptor parts and thus possesses stronger light-harvesting capability in the green light region. Because of the most complementary absorption between XL3 and XW10 as well as the excellent photovoltaic behavior of the individual XL3 dye, the corresponding CC dye XW76 affords the best PCE (10.78%) among all the CC dyes. Upon coadsorption with CDCA, XW76 affords a highest PCE of 11.35%, which outperforms the previous cosensitization system of XW10+WS-5. This work provides an approach for developing efficient DSSCs based on CC dyes composed of an organic dye unit with suitable π spacers inserted at appropriate positions.