Studies of a supramolecular photoelectrochemical cell using magnesium tetraphenylporphyrin as photosensitizer

Abstract

Magnesium tetrapyrrole, the natural choice of metal tetrapyrrole in photosynthesis, as a photosensitizer in dye sensitized solar cell applications is performed by constructing solar cells using metal-ligand axial coordination approach on TiO2surface modified with 4-carboxyphenyl imidazole and compared with cells constructed using traditionally used zinc porphyrin as sensitizer. Studies involving optical absorption, steady-state and time-resolved fluorescence, and differential pulse voltammetry, suggested that the employed magnesium tetraphenylporphyrin (MgTPP) to be a better photosentizer compared to zinc tetraphenylporphyrin (ZnTPP) for dye sensitized solar cell applications under the employed self-assembly conditions. Consequently, the constructed solar cells using MgTPP outperformed the cells constructed using ZnTPP in all aspects. That is, the open circuit potential, short circuit current, fill-factor, incident photon-to-current conversion efficiency, and overall efficiency of the solar cell were found to be better for the cells built using MgTPP photosensitizer. In order to further improve the performance of the solar cells, efforts were made to increase the fill-facotor by adding polar acetonitrile to the mediator solvent media made out of dichlorobenzene. Moderate additions of acetonitrile improved the performance of the solar cells. However, the performance of DSSC constructed using pure acetonitrile was poor due to acetonitrile competatively binding to MgTPP instead of imidazolde on the TiO2surface. Electrochemical impedance spectroscopy studies suggested that the significant decrease in the resistance at platinum electrolyte interface facilitating better iodide/iodine mediation and dye regeneration are main contributing factors for this improved cell performance.