Films of PVP (polyvinylpyrrolidone) and LiClO4 have been obtained by dip coating to be used as solid ionic conductors in transparent energy storage systems. The dependence of the ionic conductivity of PVP/LiClO4 films on temperature, lithium salt concentration, and residual solvent content or humidity has been studied. The films were used in a symmetrical supercapacitor (PEDOT/PVP/PEDOT). Whose behaviour with the aging time was analysed as well. It was observed that the experimental differences in the performance of a lithium ion based energy storage devices using these films as solid electrolyte may be due to changes in the residual content of the solvent used in their preparation or the hygroscopic nature of the electrolyte. (C) 2013 Elsevier B.V. All rights reserved.