Effect of thiophene-based π-spacers on N-arylphenothiazine dyes for dye-sensitized solar cells

To study the effect of pi-spacers on dye performance in DSSC, five novel phenothiazine dyes have been prepared where the number of successive thiophenes in the pi-spacer was increased from zero to four. Additionally, a dye bearing thieno[3,2-b]thiophene was synthesized, and compared to its unfused bithiophene analogue. When the number of thiophenes were two or more the light absorption properties was significantly better in the region 400-550 nm compared to the dye without a pi-spacer. DSSC device testing revealed that the reference dye without a pi-spacer gave the best overall performance producing a power conversion efficiency of 5.7% (J(SC) = 10.1 mA cm(-2), V-OC = 0.83 V, FF = 0.68), attributed to the superior V-OC of this dye. The incorporation of one and two thiophenes resulted in a similar performance as the reference, while incorporation of larger oligothiophenes proved to be deleterious to DSSC-performance. Electrochemical impedance spectroscopy indicates that the voltage drops and performance loss associated with these dyes are due to more facile recombination.

Automated summary

In this study, the effect of pi-spacers on dye performance in DSSCs was investigated by synthesizing five novel phenothiazine dyes with varying numbers of thiophenes in the pi-spacer. The light absorption properties of the dye were significantly improved when the number of thiophenes was two or more. However, incorporating larger oligothiophenes proved to be detrimental to DSSC performance, with the reference dye without a pi-spacer demonstrating the best overall performance.