Aprotic Polar Electrolyte Facilitates Indoor Dynamic Optical-Thermal Management in Silver-Based Electro-Reflective Smart Windows

The electrochromic devices explored in this study show tremendous promise for energy conservation, enabling active, adaptive control of solar heat and lighting in buildings. However, a majority of existing devices fail to perform optimally in areas with significant temperature fluctuations. Addressing this challenge, we introduce a new aprotic polar electrolyte (APE) for use in a reversible silver deposition electrochromic device. This novel device boasts an impressive ability to switch from a highly transparent state (with light transmittance at 650 nm being equal to or greater than 80%) to a reflective mirror-like state (with light transmittance at 650 nm being equal to or less than 1%) across an extensive temperature range spanning from −40 to 40 °C. The device's switching threshold decreases with lower temperatures, moving from −1.97 V at 40 °C to −2.37 V at −40 °C. The coloration process completes in as swift as 3.5 s at 40 °C and in 13.6 s at −40 °C, while the bleaching process requires 16.3 s at 40 °C and extends to 71.0 s at −40 °C. Achieving high optical contrast (with a ΔT = 80% at 650 nm) at varied temperatures, the device also demonstrates exceptional durability across numerous cycles.