A real-time controllable pressure-driven smart window with Cu²⁺ solution

Thermochromic smart windows represent a groundbreaking advancement in window technology, capable of autonomously adjusting their optical properties in response to fluctuations in ambient temperature. These windows hold significant promise for enhancing building energy efficiency and occupant comfort. However, earlier thermochromic technologies, such as those utilizing VO₂ and hydrogel-based systems, have not achieved widespread adoption due to inherent limitations. These include inadequate solar modulation capabilities (ΔT_sol), low light transmittance (T_lum), and elevated haze levels. To overcome these challenges, we propose a real-time controllable pressure-driven thermally responsive smart window (PD window) utilizing a Cu²⁺ solution. In this innovative design, CuSO₄ solutions are employed to regulate the solar spectrum, achieving a solar modulation capability of 73.6 % and a haze level of less than 1 % with a 20 % weight concentration of CuSO₄. Remarkably, PD windows maintain transparency comparable to traditional double-layer windows in cooler conditions, with a visible light transmittance of 51.4 %. Furthermore, dynamic outdoor chamber experiments have been conducted to assess the energy-saving performance of PD windows. These experiments demonstrate a beneficial impact on reducing indoor temperatures during summer months. The average temperature differences between two chambers, with CuSO₄ concentrations of 1 %, 5 %, 10 %, and 20 %, are 2.23 °C, 1.76 °C, 3.41 °C, and 2.28 °C, respectively.