Li+- and Eu3+-Doped Poly(epsilon-caprolactone)/Siloxane Biohybrid Electrolytes for Electrochromic Devices

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The sol–gel process has been successfully combined with the “mixed cation” effect to produce novel luminescent and ion conducting biohybrids composed of a diurethane cross-linked poly(ε-caprolactone) (PCL530)/siloxane hybrid network (PCL stands for the poly(ε-caprolactone) biopolymer and 530 is the average molecular weight in gmol–1) doped with a wide range of concentrations of lithium and europium triflates (LiCF3SO3and Eu(CF3SO3)3, respectively) (molar ratio of ca. 50:50). The hybrid samples are all semicrystalline: whereas atn= 52.6 and 27.0 (n, composition, corresponds to the number of (C(═O)(CH2)5O) repeat units of PCL(530) per mixture of Li+and Eu3+ions) a minor proportion of crystalline PCL(530) chains is present, atn= 6.1, a new crystalline phase emerges. The latter electrolyte is thermally stable up to 220 °C and exhibits the highest conductivity over the entire range of temperatures studied (3.7 × 10–7and 1.71 × 10–4S cm–1at 20 and 102 °C, respectively). According to infrared spectroscopic data, major modifications occur in terms of hydrogen bonding interactions at this composition. The electrochemical stability domain of the biohybrid sample withn= 27 spans more than 7 V versus Li/Li+. This sample is a room temperature white light emitter. Its emission color can be easily tuned across the Commission Internationale d’Éclairage (CIE) chromaticity diagram upon simply changing the excitation wavelength. Preliminary tests performed with a prototype electrochromic device (ECD) comprising the sample withn= 6.1 as electrolyte and WO3as cathodically coloring layer are extremely encouraging. The device exhibits switching time around 50 s, an optical density change of 0.15, good open circuit memory under atmospheric conditions (ca. 1 month) and high coloration efficiency (577 cm2C–1in the second cycle).
Original languageUnknown
Pages (from-to)2953-2965
JournalAcs Applied Materials & Interfaces
Issue number8
Publication statusPublished - 1 Jan 2011

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