First Report of Chenodeoxycholic Acid–Substituted Dyes Improving the Dye Monolayer Quality in Dye-Sensitized Solar Cells

Abstract

Chenodeoxycholic acid (CDCA) is the most used anti-aggregation additive in dye-sensitized solar cells since its introduction to the field in 1993. However, effective suppression of dye aggregation comes at the cost of reduced dye loading, lower open-circuit voltage and limited control of dye/additive distribution when co-sensitizing with free CDCA. To combat this, we report herein a novel dye design concept which employs the covalent attachment of a CDCA moiety to triarylamine sensitizers. The CDCA substituents do not affect the photophysical nor electrochemical properties of the sensitizers, but have a positive effect on the photovoltaic performance with [Cu+/2+(tmby)2](TFSI)1/2 electrolyte. By ensuring a one-to-one ratio of dye and CDCA, paired with isotropic distributions of each component, this approach results in a higher-quality dye monolayer. Compared to the reference system, the novel approach reported here gives higher open-circuit voltage and power-conversion efficiency (PCE). The best device is fabricated with the dye C6-CDCA delivering a PCE of 6.84% (8 µm TiO2, 1 mM CDCA, JSC = 8.64 mA cm-2, VOC = 1007 mV, FF = 0.77).