Effects of Central Metal Ions in Porphyrin-sensitized Solar Cells with Halogen Redox Mediators

Abstract

Effects of central metal ions in porphyrin-sensitized solar cells were investigated by using 5-(4-carboxyphenyl)-10,15,20-tris(2,4,6-trimethylphenyl)porphyrins as sensitizers and I⁻/I₃⁻ or Br⁻/Br₃⁻ as redox mediators. Zn(II), Cu(II), Pd(II), and free-base porphyrins were synthesized, and the properties of them and the photovoltaic performances of the dye-sensitized solar cells (DSSCs) using them are compared. The electron injection processes from the dyes into TiO₂ were investigated by changing Li⁺ concentration in the electrolytes. The regeneration processes of the dyes were examined by comparing the electrolytes with different redox potentials (I⁻/I₃⁻ or Br⁻/Br₃⁻). With the Br⁻/Br₃⁻ redox mediator, palladium porphyrin yielded both higher short-circuit current density (J_sc) and open-circuit voltage (V_oc) than that with the I⁻/I₃⁻ mediator and achieved the highest power conversion efficiency among all combinations in this study.