Organic Sensitizers with Extended Conjugation Frameworks as Cosensitizers of Porphyrins for Developing Efficient Dye-Sensitized Solar Cells.

Relatively high efficiencies have been achieved for porphyrin-based DSSCs. For the purpose of designing efficient co-sensitizers, we herein report systematically optimized dyes XC1-XC5 employing a triphenylamine donor, a benzothi-adiazole moiety as the auxiliary acceptor, and a benzoic acid acceptor. One hexyl and four hexyloxy groups were intro-duced, and an ethynylene moiety was introduced between the donor and the auxiliary acceptor to afford XC1. To fur-ther extend the absorption wavelength, a second ethynylene moiety was introduced between the acceptor and the aux-iliary acceptor to afford XC2. XC3 and XC4 were designed by introducing one and two methyl substituents, respectively, into the meta-positions of the anchoring carboxyl group. XC5 was further synthesized by inserting a cyano substituent into one of the ortho-positions of the carboxyl group with the purpose to strengthen the intramolecular charge trans-fer (ICT) effect and thus broaden the absorption wavelength. As expected, compared with the Jsc (14.29 mA·cm-2) of XC1, the corresponding Jsc values for XC2-XC5 were enhanced to 16.50, 16.95, 16.73, 17.74 mA·cm-2, respectively. Moreover, XC4 exhibits the highest Voc of 770 mV owing to the presence of a maximum of seven chains, which can effectively suppress dye aggregation. As a result, compared with XC1, XC2-XC5 exhibit improved efficiencies of 8.67, 9.05, 8.78 and 9.30%, respectively. In addition, the efficiencies of XC3 and XC5 were further enhanced by cosensitizing them with our previously reported porphyrin dye XW28 under various conditions. Finally, a remarkable efficiency of 10.50% was achieved for the cells cosensitized with XC5 and XW28. These results indicate that the combination of good planarity of extended D--A framework with multiple alkoxy/alkyl chains may compose an effective optimizing strategy for de-signing and synthesizing excellent cosensitizers for porphyrins.