Low-temperature Fabrication of Highly-Efficient, Optically-Transparent (FTO-free) Graphene Cathode for Co-Mediated Dye-Sensitized Solar Cells with Acetonitrile-free Electrolyte Solution

Propionitrile electrolyte solutions mixed with sulfolane or with 1-ethyl 3-methyl imidazolium tetracyanoborate (ionic liquid) are optimized for Co(bpy)33+/Co(bpy)32+-mediated DSCs working at low illumination intensity. Highly-active cathode catalysts based on graphene oxide, either pure or mixed with graphene nanoplatelets or with stacked graphene fibers, can be prepared at temperatures ≤200 °C. The catalytic layers are well adhering to the substrates, i.e. to FTO or to stainless-steel surfaces, both the flat steel sheet and the steel wires in woven fabric consisting of transparent polyester (PEN) fibers in warp and stainless steel wires in weft (Sefar B23). The dye-sensitized solar cells with various cathodes, fabricated either from Pt or from optimized graphene-based catalysts, and supported by either FTO or by stainless-steel/PEN fabric, show similar solar conversion efficiencies between 6.9 and 7.9% at 0.25 sun illumination.