Effect of pi-linkers on phenothiazine sensitizers for dye-sensitized solar cells

Eleven new dyes have been synthesized in order to investigate the effect of five different pi-spacers and two different auxiliary donors in phenothiazine-based sensitizers for dye-sensitized solar cells. The target molecules were synthesized in 5-7 steps from 10H-phenothiazine. Evaluation of the photovoltaic performance revealed that introducing a pi-spacer does not necessarily increase the power conversion efficiency. Still, dyes with a furan pi-spacer were found to be slightly more efficient compared to their thiophene counterparts, and more efficient than no spacer. Dyes with phenyl based pi-spacers resulted in less efficient solar cells, and especially so when incorporating two fluorine atoms. Surprisingly, introducing an additional electron donating group in the auxiliary donor had no pronounced effect on the photovoltaic performance of the dyes.