(a) Comparision of Roman spectra before and after transferring graphene on ion–gel; (b) transmittance versus wavelength of grapheme/ion–gel/ITO/glass composite structure, with inset showing SEM image of ion–gel film on glass substrate; (c) ion–gel film without graphene; (d) ion–gel film with transferred graphene; molecular formula of (e) [EMIM]TF2N, and (f) PVDF.