Photo-Induced Electrochromism: Toward a Self-Coloring Smart Window

Smart windows that dynamically regulate solar radiation are crucial for reducing building energy consumption. Electrochromic (EC) smart windows offer high-performance optical modulation but require an external power supply, whereas photochromic (PC) smart windows are self-powered but suffer from low modulation and poor bistability. To bridge this gap, we introduce a novel photo-induced electrochromism (PIEC) mechanism in a proof-of-concept smart window operating with both light and electricity as stimuli. The PIEC device utilizes a sub-stoichiometric WO_3-x cathode and a tailored ethylene glycol-based electrolyte, in which photogenerated holes are consumed by the electrolyte, driving Al³⁺ intercalation and coloring the device without an applied voltage. The large-area (100 cm²) PIEC device achieves tri-band regulation with solar, luminous, and infrared transmittances of 11.2%, 17.9%, and 2.81%, respectively, completely blocking longer-wavelength IR radiation. The performance is further enhanced in the electrically induced coloring state. In a simulated house model, the device reduced indoor temperatures by 7°C-10°C, and simulations confirmed substantial energy savings of 44% and a reduction in CO₂ emissions by 88.5 kg. m^-2. This dual-mode, tri-band (Vis-NIR-IR) PIEC device defines a new class of smart windows that combine self-powering with user-controlled, high-performance dynamic tinting.