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

Chenodeoxycholic acid (CDCA) is the most used antiaggregation 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, a lower open-circuit voltage, and limited control of dye/additive distribution when cosensitizing with free CDCA. To combat this, herein, a novel dye design concept that uses the covalent attachment of a CDCA moiety to triarylamine sensitizers is reported. The CDCA substituents do not affect the photophysical or electrochemical properties of the sensitizers but have a positive effect on the photovoltaic performance with [Cu+/2+(tmby)(2)](TFSI)(1/2) electrolyte (tmby = 4,4 ',6,6 '-tetramethyl-2,2 '-bipyridine, TFSI = bis(trifluoromethanesulfonyl)imide). 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 with the reference system, the novel approach reported herein gives a higher open-circuit voltage and power conversion efficiency (PCE). The best device is fabricated with the dye C-6-CDCA, delivering a PCE of 6.84% (8 mu m TiO2, 1 mm CDCA, J(SC) = 8.64 mA cm(-2), V-OC = 1007 mV, and FF = 0.77)