Hydroxypropyl cellulose-based gel electrolyte for electrochromic devices

Hydroxypropyl cellulose-based polymer (HPC) electrolytes were prepared and characterized. A gel electrolyte was tested in electrochromic devices. The membranes were obtained by casting method from dichloromethane solution. The best samples displayed ionic conductivity values of 3.5 × 10^-5 and 1.1 × 10^-4 S cm^-1 at 25 and 50 °C, respectively. The DSC analyses evidenced glass transition temperature of -37 °C and the TGA showed three stages degradation of the sample starting at 130 °C. The 3.5 V electrochemical stability of the samples using SnO₂:Sb/glass (ATO) electrodes was determined by cyclic voltammetry in the -2 to 1.5 V interval. Moreover, the samples displayed transparency and excellent adhesion to different surfaces. Small electrochromic devices were assembled with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as primary and polyaniline or Prussian blue (PB) as complementary electrochromic layer. Performance of the devices was analysed by cyclic voltammetry at different scan rating. UV-vis transmittance results revealed 35% of colour change at 650 nm for electrochromic device (ECD) with glass/ITO/PB/HPC/PEDOT:PSS/ITO/glass configuration. Twenty repetitive colour/bleaching cycles showed absorbance value change of about 0.22. The obtained results confirmed that HPC-based electrolytes are good candidates to be applied in ECDs with conducting polymers as primary and secondary electrochromic coatings.