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

Abstract

ABSTRACT 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 Al 3+ intercalation and coloring the device without an applied voltage. The large‐area (100 cm 2 ) 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 CO 2 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.