Efficient Solar Cells Based on Porphyrin and Concerted Companion Dyes Featuring Benzo 12-Crown-4 for Suppressing...

In recent years, various porphyrin dyes have been designed to develop efficient dye-sensitized solar cells (DSSCs). Based on our previously reported porphyrin dye XW43, which contains a phenothiazine donor with two diethylene glycol (DEG)-derived substituents, we herein report a porphyrin dye XW89 by introducing a benzo 12-crown-4 (BCE) unit onto the N atom of the phenothiazine donor. On this basis, XW90 and XW91 have been synthesized by replacing a DEG chain in XW89 with two DEG chains and a 12-crown-4 unit, respectively. For iodine electrolyte-based DSSCs, dyes XW89-XW91 exhibit V_OC values of 765-779 mV, higher than that of XW43 (755 mV), which may be related to the strong capability of the BCE group in binding Li⁺ and thus suppressing the downward shift of the TiO₂ conduction band and interfacial charge recombination. Moreover, the smaller size of 12-crown-4 than the DEG unit enables higher adsorption amounts of the dyes than XW43, contributing to an enhanced J_SC value. Due to the presence of two BCE units, dye XW91 exhibits the highest dye loading amount and J_SC of 1.86 × 10^-7 mol cm^-2 and 19.79 mA cm^-2, respectively, affording a high PCE of 11.1%. To further enhance the light-harvesting ability, a concerted companion (CC) dye XW92 has been constructed by linking the two subdye units corresponding to the porphyrin dye XW91 and an organic dye. As a result, XW92 affords an enhanced J_SC and efficiency. Further coadsorption of XW92 with chenodeoxycholic acid achieved the highest efficiency of 12.1%. This work provides an effective approach for fabricating efficient DSSCs sensitized by porphyrin and CC dyes based on the introduction of crown ether units with smaller sizes and stronger Li⁺ affinities.