Graphene, carbon nanotube and ionic liquid mixtures: towards new quasi-solid state electrolytes for dye sensitised solar cells

Abstract

In this work carbon based nanomaterials in ionic liquids have been studied as potential electrolytes for dye sensitised solar cells (DSSCs). Graphene, single wall carbon nanotubes (SWCNTs) and a mixture of graphene and SWCNTs were incorporated into 1-methyl-3-propylimidazolium iodide (PMII) ionic liquid. The resulting quasi-solid state electrolytes were sandwiched between TiO₂ working electrodes and platinum counter electrodes and subsequent DSSCs were fabricated. Graphene based quasi-solid state electrolytes displayed an increase of light conversion efficiencies in the completed DSSC from 0.16% (for pure PMII) to 2.10%. For SWCNTs, the observed light conversion efficiency increased from 0.16% to 1.43% and for the mixture of graphene and SWCNTs the light conversion efficiency improved from 0.16% to 2.50%. This significant increase occurred because the carbon materials serve simultaneously both as charge transporter in the ionic liquids and as catalyst for the electrochemical reduction of I₃⁻. It is also expected that there is an ionic liquid mediated self-organisation of graphene and SWNT nanomaterials into structured networks, which provide an efficient electron transfer. Thermogravimetric analysis (TGA) studies showed that these electrolytes are stable up to 300 °C.