−40 °C–60 °C useable transparent hydrogel electrolyte for flexible and tailorable electrochromic devices with excellent performance

Abstract

Self-powered electrochromic devices (defined as SECDs) driven by metal electrodes have attracted wide attention due to their low voltage, low energy consumption characteristics, and getting rid of the limitation of external power supplies. However, the applicability in extreme temperature environments is severely hampered by the inadequate choice of electrochromic electrolytes. Herein, we adopt the ethylene glycol-assisted salty PVA-type hydrogel electrolyte with a minimum freezing point as low as −50 °C. Based on the hybrid Zn2+ and Al3+, the ion conductivity of hydrogel electrolyte at room temperature is 1.56 mS cm−1, and the fracture strain can exceed 300%. The hydrogel electrolyte can maintain average transmittance of 95% within a wide temperature range of −40 °C–60 °C. After freezing at −30 °C, the breaking elongation can reach 352%, and the tensile strength is up to 4.45 MPa. Based on the W18O49 films and the hydrogel electrolyte, the modulation of the SECDs can reach 63%, and the cycle life is more than 1000 times. After building the flexible device, the modulation of the flexible SECDs based on the PEN/ITO substrate is 51% at 25 °C and 43% at −40 °C. What's more, the flexible SECDs can be tailored and worked normally without packaging, which can promote the development of the cryogenic and tailorable application of the flexible SECDs.