Phenothiazine dyes have attracted significant attention as metal-free sensitizers for dye-sensitized solar cells since their introduction in 2007. Since then, over 430 phenothiazine dyes have been prepared and investigated. Despite...

No abstract

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 C6–CDCA, delivering a PCE of 6.84% (8 μm TiO2, 1 mm CDCA, JSC = 8.64 mA cm−2, VOC = 1007 mV, and FF = 0.77).

The geometry of a dye for dye-sensitized solar cells (DSSCs) has a major impact on its optical and electronic properties. The dye structure also dictates the packing properties and how well the dye insulates the metal–oxide surface from oxidants in the electrolyte. The aim of this work is to investigate the effect of planarizing the geometry of the common triarylamine donor, frequently used in dyes for DSSC. Five novel dyes were designed and prepared; two employ conventional triarylamine donors with thiophene and furan π-spacers, two dyes have had their donors planarized through one sulfur bridge (making two distinct phenothiazine motifs), and the final dye has been planarized by forming a double phenoxazine. The synthesis of these model dyes proved to be quite challenging, and each required specially designed total syntheses. We demonstrate that the planarization of the triarylamine donor can have different effects. When planarization was achieved by a 3,7-phenothiazine and double phenoxazine structures, improved absorption properties were noted, and a panchromatic absorption was achieved by the latter. However, an incorrect linking of donor and acceptor moieties has the opposite effect. Further, electrochemical impedance spectroscopy revealed clear differences in charge recombination depending on the structure of the dye. A drawback of planarized dyes in relation to DSSC is their low oxidation potentials. The best photovoltaic performance was achieved by 3,7-phenothazine with furan as a π-spacer, which produces a power conversion efficiency of 5.2% ( J sc = 8.8 mA cm –2 , V oc = 838 mV, FF = 0.70).

The potential of dye-sensitized solar cells (DSSCs) based on synthesized D-A-π-A type dyes with the 9-(p-tolyl)-2,3,4,4a,9,9a-hexahydro-1H-1,4-methanocarbazole building block as a donor fragment was explored. The influence of the structure of...