An ITO free All Tungsten-Based Electrochromic Energy Storage Device as Smart Window.

Excessive electricity usage in buildings, notably for heating and cooling, accounts for over 30% of energy consumption, creating a pressing need for energy-saving solutions. Electrochromic Smart Windows (ECSW) aims to reduce energy use while maintaining comfort but faces high costs due to materials like tin-doped indium oxide (ITO) and thick electrochromic films. Moreover, achieving full opacity in the colored state of ECSW is a bottleneck for the industry to overcome privacy concerns. Herein, efforts are directed toward finding cost-efficient alternatives, with all-tungsten-based mesh networks showing promise due to enhanced stability. This newly developed ITO-free, all-tungsten ECSW displays minimal transmittance (≈3%) in the colored state using only 260 nm thick sub-stoichiometric tungsten oxide (WO 3-x ) film within a lithium-ion-based electrolyte. The ECSW device of size (25 cm 2 ) also demonstrates areal capacitance of ≈13 mF cm -2 to power a liquid crystal display (LCD) for ≈25 min, showcasing its energy storage capabilities. Additionally, to confirm scalability and cost-effectiveness, a larger 15 × 15 cm 2 ECSW utilized a single hybrid electrode, highlighting the potential for reducing costs when scaling up production processes. This advancement represents a significant stride toward accessible and energy-efficient smart window technology, offering broader applicability within modern architectural practices.