Fabrication and analysis of dye-sensitized solar cells (DSSCs) using porphyrin dyes with catechol anchoring groups

Herein we report the preparation and application of 4 different zinc(II) tetrakis(dihydroxyphenyl) porphyrins (ZnTDHPP) as the sensitizing dyes in dye-sensitized solar cells (DSSCs). The experimental results include solution and solid state UV-Vis data, steady state current-voltage characteristics, and our theoretical analysis comprised of density functional theory (DFT) and Langmuir isotherm adsorption formalism. The results show that the Zn tetrakis(2,3-dihydroxyphenyl) porphyrin (Zn2,3TDHPP) and Zn tetrakis(3,4-dihydroxyphenyl) porphyrin (Zn3,4TDHPP) with adjacent hydroxyl groups attaches to a TiO2 surface much more strongly than carboxylate. The catechol anchoring group showed high stability of the dye on the TiO2 surface. The cells prepared from these porphyrins showed no significant desorption of dye from the TiO2 surface after several days. The DSSCs based on Zn2,3TDHPP showed the best photovoltaic performance under AM 1.5 irradiation comparable to the conventional Zn tetrakis(p-carboxyphenyl) porphyrin (ZnTCPP), despite lower dye loading on the TiO2 surface. However, non-cooperative OH bonding to TiO2 for Zn2,4TDHPP and Zn2,5TDHPP shows weak attachment to the TiO2 surface and lower efficiencies. DFT calculations showed that the Zn2,3TDHPP structure is more non-planar than the others, which may suppress dye aggregation. The adopted adsorption modeling is fitted to the experimental data to study the kinetics of dye loading. The study can herald development of a new class of porphyrin sensitizer for DSSC applications