NIR‐emitting Electrochromic Windows for Cold Climate Region Buildings

Abstract Electrochromic devices (ECDs) comprising visible/near‐infrared (NIR) transparent amorphous indium zinc oxide (a‐IZO) outermost layers and novel NIR‐emitting electrolytes are proposed for smart windows of buildings in cold climate regions. The electrolytes are composed of a di‐urethane cross‐linked poly(oxyethylene)(POE)/siloxane hybrid matrix (d‐Ut(600), 600 is the average molecular weight of the POE chains in gmol −1 ), 1‐butyl‐3‐methylimidazolium chloride ionic liquid, and the Er(tta) 3 (H 2 O) 2 complex (tta − is 2‐thenoyltrifluoracetonate). The electrolytes, synthesized by sol‐gel route, were obtained as transparent, flexible, and hydrophilic monoliths with nanoscale surface roughness, exhibiting emission in the NIR wavelength region. The first electro‐optical tests, performed in 2019, with an archetypal ECD including amorphous tungsten oxide and crystalline nickel oxide as EC layers, a‐IZO as outermost layers, and d‐Ut(600) 400 Er(tta) 3 (H 2 O) 2 [Bmim]Cl (400 is the molar ratio of oxyethylene units/Er 3+ ion) as the electrolyte, demonstrated rather low coloration efficiency (CE in /CE out ) values of −4/+6 cm 2 C −1 at 555 nm. After 3 years of storage at rest in the dark and at room temperature, the same device demonstrates a huge performance enhancement, leading to CE in /CE out values about two orders of magnitude higher, apart from higher optical density, and improved cycling stability. In addition, this device offers a bright hot, and semi‐bright warm dual modulation operation suitable for smart windows of skylights, roof lights, upper windows, inclined glazing, and privacy glazing of buildings located in cold climate regions.