Green Li+- and Er3+-doped poly(epsilon-caprolactone)/siloxane biohybrid electrolytes for smart electrochromic windows

Novel electrolytes composed of a sol-gel derived di-urethane cross-linked poly(epsilon-caprolactone) (d-PCL (530))/siloxane (where 530 is the average molecular weighting mol(-1)) biohybrid network doped with a 50:50 molar mixture of lithium and erbium triflates were prepared in the light of the "mixed cation effect". These environmentally friendly electrolytes, which are multi-wavelength emitters from the UV/VIS to the NIR spectral regions, are attractive candidates for electrochromic devices. Prototype devices based on a glass/ITO/WO3/electrolyte/ITO/glass layered configuration exhibited fast switching speed, high electrochromic reversibility and cyclic stability, along with good coloration efficiency and open circuit memory. The visible average transmittance variation and the optical density change attained were 41.6% and 039, respectively. The combined use of these electrolytes with transparent conducting oxides in the VIS and NIR spectral regions opens exciting new prospects for the fabrication of electrochromic windows exhibiting NIR emission and improved performance in terms of energy efficiency in buildings. In addition, these electrolytes offer new possibilities for the production of dual light emitting and electrochromic windows.