Branched and linear alkoxy chains-wrapped push-pull porphyrins for developing efficient dye-sensitized solar cells

Abstract

Four alkoxy-wrapped push-pull porphyrin dyes containing the phenothiazine derived donor and the ethynylbenzoic acid acceptor have been designed, synthesized and used as sensitizers for fabricating efficient dye-sensitized solar cells (DSSCs). Branched or linear alkoxy chains were introduced to the ortho-positions of the meso-phenyl moieties to suppress the dye aggregation and charge recombination. The effect of alkoxy chains were investigated in the absence and presence of an additional electron-withdrawing benzothiadiazole unit. In the former cases, almost identical photovoltaic efficiencies of ∼8.3% were achieved for both the branched and the linear alkoxy chains, while in the latter cases, the planar benzothiadiazole unit induces serious dye aggregation and charge recombination, resulting in lower efficiencies of 6.46% and 7.50% for the linear and branched chains, respectively, even though broader absorption was achieved. The relatively higher efficiency achieved for the dyes with branched chains may be related to the better effect of suppressing the dye aggregation and charge recombination. Furthermore, the coadsorption approach was employed, and a highest efficiency of 9.62% was achieved for the dye that features branched chains and the benzothiadiazole unit. These results compose a novel approach for developing efficient DSSCs by combining the coadsorbent with a porphyrin dye containing both the additional benzothiadiazole acceptor and branched alkoxy chains.