Influence of the auxiliary acceptor and Π-bridge in triarylamine dyes in dye-sensitized solar cells

Four metal-free organic dyes (AFL7–AFL10) based on triarylamine donors and different π-bridges with or without a benzothiadiazole auxiliary acceptor have been synthesized. The dyes’ photophysical and electrochemical properties, theoretical calculations, and dye-sensitized solar cell (DSSC) performances have been investigated. Electrochemical measurement data indicate that varying the π-conjugacy system can tune the HOMO and LUMO energy levels. A high molar extinction coefficient combined with a broad absorption spectrum helps to reinforce the dyes’ light harvesting ability; therefore, it could help to increase the JSC of the DSSCs. Among the four dyes, AFL7 bearing the bithiophene bridge achieves the best photocurrent performance with a JSC value of 16.94 mA cm−2, corresponding to an overall conversion efficiency η of 7.92% under standard AM 1.5 G conditions (that of N719 dye was 8.53% under the same conditions). The results show that the dyes based on the triarylamine donor containing fluorenyl and biphenyl moieties are promising candidates for improving the performance of DSSCs.