Sterically demanded unsymmetrical zinc phthalocyanines for dye-sensitized solar cells

Three new sterically demanding unsymmetrical zinc phthalocyanines have been designed and synthesized as sensitizers for dye-sensitized solar cells. All three unsymmetrical phthalocyanines have been completely characterized by elemental analyses, mass spectrometry, FT-IR, 1H NMR, UV-Visible, and fluorescence (steady-state and life-time) spectroscopies as well as electrochemical methods. Photophysical properties (absorption, emission and redox properties) indicate that the LUMO of unsymmetrical phthalocyanines lies above the TiO2 conduction band and HOMO is below the redox electrolyte. The experimental results are supported by DFT/TD-DFT studies. Electrochemical and in-situ spectroelectrochemical studies suggest that the redox reactions belong to the macrocyclic ring-based electron transfer processes. All three unsymmetrical phthalocyanines were tested in DSSC using I-/I3- redox electrolyte system.