Efficient dye-sensitized solar cells based on an iodine-free electrolyte using l-cysteine/l-cystine as a redox couple

Abstract

A new iodine-free electrolyte based on amino acids L-cysteine/L-cystine as a redox couple has been designed and synthesized. DSSCs fabricated with the conventional I⁻/I₃⁻ redox couple gave efficiencies of 8.1% and 6.3% under optimized experimental conditions based on ruthenium dye, N719, and metal-free organic dye, TH202, respectively. Based on the same dyes, the DSSCs employing the new L-cysteine/L-cystine redox couple showed comparable efficiencies of 7.7% and 5.6%, respectively. However, higher incident-photon-to-electron (IPCE) conversion efficiencies and larger J_sc values were found for devices with the L-cysteine/L-cystine redox couple than with I⁻/I₃⁻. From an electrochemical impedance spectroscopic study, we found that the charge recombination between the conduction band electrons in the TiO₂ film and the electrolyte containing the L-cysteine/L-cystine redox couple is restrained.