Polymer electrolytes for electrochromic devices through solvent casting and sol-gel routes

Abstract

Ionically conductive membranes of gelatin and d-PCL(530)/siloxane doped with cyano-based ionic liquids (ILs) were prepared through solvent casting and sol-gel methods, respectively. The membranes were characterized in terms of ionic conductivity, thermal behavior, morphology, and structure. All samples, except the d-PCL(530)/siloxane matrix, exhibited a predominantly amorphous morphology. The samples prepared through solvent casting and sol-gel displayed a minimum thermal stability of 170 and 230°C, respectively. The ionic conductivity varied according with the type, quantity, and length of the alkyl chain of the cation of the ILs. The sample with the highest ionic conductivity was gelatin0.5[C2mim][N(CN)2] with 2.40×10−3Scm−1 at 25°C and 1.68×10−2Scm−1 at 95°C. The good results of ionic conductivity encouraged the assembly and characterization of prototypes of electrochromic devices (ECDs). The best results were obtained with glass/ITO/WO3/gelatin1[C2mim][SCN]/CeO2-TiO2/ITO/glass configuration that showed a fast color switching time (~15s) and a good open circuit memory (~4h). The ECD changed its color from pale blue to transparent, and its charge density decreased from −17.53 to −2.71mCcm−2 during 640 color/bleaching cycles.