Smart windows prepared from Bombyx mori silk

We introduce a bioinspired strategy for the synthesis of green polymer electrolytes (PEs) that relies on the use of silk fibroin (SF). The two series of PEs prepared, doped with lithium bis(trifluoromethanesulfonyl)imide or lithium tetrafluoroborate and incorporating glycerol, exhibited outstanding filmogenic properties, very high transparency, and suitable adhesion to glass substrates. Despite their poor ionic conductivity, the SF-based films were employed in the construction of glass/ITO/WO3/PE/CeO2–TiO2/ITO/glass electrochromic devices displaying an optical modulation up to 5.5 % at λ=633 nm, a switching speed of about 15 s, stability up to 5160 cycles, and coloration efficiency up to −53.1 m2 C−1. This work, in which we provide the proof-of-concept, paves the way for new design approaches for silk-based materials, which would enlarge the range of applications of SF to the energy field.