A DFT study of the regeneration process of zinc porphyrin analogues in dye-sensitized solar cells

Abstract

The regeneration reaction of sensitizers in dye-sensitized solar cells is one of the critical steps in photonic chemical circuits. In this report, the two-step regeneration reaction of a series of zinc porphyrin sensitizers with a variety of substituent groups, i.e., CN–, F–, Cl–, H–, PhCH₃–, OH– and NH₂– groups, has been studied using density functional theory (DFT). The effects of the substituent groups on the structures of zinc porphyrin sensitizers, the regeneration intermediates and the reaction thermodynamics and kinetics have been explored. It is found that substituent groups at meso-position of zinc porphyrins strongly influenced the mode of two-step regeneration. For Por-CN, Por-F and Por-Cl, the formation of DyeI_Zn and DyeI_Zn-I intermediates are dominant, whereas for Por-H, Por-PhCH₃ and Por-OH, the formation of DyeI_Py and DyeI_Py-I intermediates predominate. Due to the stronger electron-withdrawing effect of CN– and F–, the corresponding Por-CN and Por-F have no energy barrier in reaction. This suggests that their regeneration should be faster than the others. Besides two-step regeneration, alternative regenerations including one-step regeneration and reductive quenching reaction of excited dye and the influences of substituent groups on the electron injection efficiency are also estimated. These results provide valuable information for the design of novel zinc porphyrin analogues for DSCs.