Synthesis, photophysical characterization, and photoelectrochemical evaluation of a palladium porphyrin sensitizer for TiO2-based dye-sensitized solar cells

Abstract

An unsymmetrical (A3B) palladium porphyrin bearing a cyanoacrylic acid at one meso position has been synthesized for evaluation as a photosensitizer in dye-sensitized solar cells based on titanium dioxide ( TiO 2) as a comparison to other metalloporphyrins and as a proxy for other potential triplet-state photosensitizer compounds. The synthesis of this palladium porphyrin has provided new insight into the mechanism and product distribution of decarboxylative hydrolysis of malonic acid when attached at the porphyrin meso position. A crystal structure determination for a meso-formyl palladium porphyrin has been determined, showing saddle-distortion of the porphyrin core. The photophysical behavior of the palladium porphyrin sensitizer and its performance in photoelectrochemical cells are described and interpreted in the context of bimolecular excited state quenching pathways including oxygen sensitization, triplet–triplet annihilation and electron transfer events. Palladium porphyrins are proposed as a sensitizer class with potential for high efficiency dye-sensitized solar cells, but with the caveat that some overpotential for electron injection is necessary to compete against the multiple decay pathways that are specially available to triplet state photosensitizers.