A method of manufacturing a graphene-containing electrolyte includes, in the order recited: (a) deoxidizing graphene oxide to form graphene; (b) dissolving the graphene in a carbonate solvent to provide a graphene-containing solution; and (c) adding an oxidation-reduction agent composed of 1-butyl-2,3-dimethylimidazolium iodide (BDI) and optionally iodine (I2) into the graphene-containing solution to provide the graphene-containing electrolyte. Deoxidizing the graphene oxide may be accomplished by dissolving the graphene oxide in an aqueous solvent that is a mixture of water and an alkyl imidazole-based iodine to form a solution; and centrifuging the solution to obtain the graphene. A dye-sensitized solar cell may include the graphene-containing electrolyte to fill a space defined between first and second electrodes.