Three‐Mode Modulation Electrochromic Device with High Energy Efficiency for Windows of Buildings Located in Continental Climatic Regions

Abstract

A sustainable use of energy in buildings demands energy‐efficient windows. A new design concept for electrochromic (EC) smart windows, easy to implement at the industrial level, is introduced here. It enables simultaneous control of visible and near‐infrared (NIR) solar radiation, thus contributing to reduce heating and cooling loads especially in buildings located in areas experiencing wide daily temperature ranges. The EC device comprises amorphous indium zinc oxide, a conducting oxide transparent in the visible and NIR spectral regions, as nonactive layer, and a sol–gel protonic ionic liquid‐doped di‐ureasil electrolyte displaying high transparency and proton conductivity. The device offers three voltage‐operated modes: bright hot (+3.0 V: transmittances of 70/83% at 555/1000 nm), semi‐bright warm (−2.0 V: transmittances of 37/35% at 555/1000 nm), and dark cold (−2.5 V: transmittances of 6/4% at 555/1000 nm). Its main figures of merit are: high switching efficiency (transmittance variations of 64/79% at 555/1000 nm), high optical density modulation (1.1/1.3 at 555/1000 nm), high optical contrast ratio in the visible region (lightness variation of ≈43), good cycling stability, and unprecedented coloration efficiency (−12538/−14818 cm2 C−1 and +2901/+3428 cm2 C−1 at 555/1000 nm), outstanding optical memory (transmittance variation loss of only 24% more than 4 months after coloration), and self‐healing ability following mechanical stress.

Electrochromic Device Composed of a Di-Urethanesil Electrolyte Incorporating Lithium Triflate and 1-Butyl-3-Methylimidazolium Chloride

“…Accordingly, the device became progressively darker (L * = 70.0, a * = −1.50, and b * = 7.90; L * = 50.6, a * = −5.66, and b * = 2.60 (Figure 5d); L * = 37.3, a * = −6.13, and b * = −0.32; and L * = 35.4, a * = −1.52, and b * = 3.33 (Figure 5e), respectively (Table 1). The maximum electrochromic and optical contrast values achieved upon application of −2.5 V [ T = 70% (Table 2) and L * = 48.1 (Table 1), respectively] are of the same order of magnitude as those reported for the PIL-doped d-U(2000) (Cardoso et al, 2019; Table 2).…”

“…The response times of the ECDs were 1-2 s for coloring and 50 s for bleaching. It is noteworthy that the time to color was thus much faster than that reported for the ECD including the di-ureasil d-U(2000) incorporating long POE chains and doped with a protonic IL (PIL) (Cardoso et al, 2019). The as-prepared ECD1 exhibited a T value of 73% at 555 nm.…”

“…The combination of an active electrode layer of vanadium-modified titanium oxide with a nanocrystalline WO 3 layer resulted in an ECD switchable across four distinct optical modes (fully transparent, visible blocked, NIR blocked, and visible plus NIR blocked) upon application of low voltages (Barawi et al, 2018). Recently we proposed the use of NIR-transparent TCOs enabling simultaneous modulation of light and heat (Fernandes et al, 2018;Cardoso et al, 2019;Nunes et al, 2019).…”

“…It must exhibit high transparency to visible light, good adhesion to the electrodes, appropriate mechanical properties, high thermal stability, high ionic conductivity, and high electrochemical stability within the switching voltage range. With this goal in mind, we devoted significant efforts to the synthesis of sol-gel derived electrolytes (henceforth designated as ormolytes -organically modified silicate electrolytes) based on di-urea cross-linked poly(oxyethylene) (POE)/silica (diureasil) and di-urethane cross-linked poly(epsilon-caprolactone) PCL(530)/silica host hybrid matrices doped with alkaline metal salts (Nunes et al, 2007;Fernandes et al, 2011bFernandes et al, , 2017Pereira et al, 2016), transition metal salts (Alves et al, 2013), lanthanide metal salts (Leones et al, 2014;Alves et al, 2018;Nunes et al, 2019), mixtures of alkaline and lanthanide metal salts (Fernandes et al, 2011a(Fernandes et al, , 2014a, mixtures of an alkaline metal triflate salt and a lanthanide complex (Fernandes et al, 2014b), mixtures of an alkaline metal salt and an ionic liquid (IL) (Fernandes et al, 2015), or solely an IL (Neto et al, 2015;Cardoso et al, 2019). In the last decade we also focused our attention on the synthesis of polymer electrolytes based on natural host polymers, such as polysaccharides [chitosan (Alves et al, 2018), kappa-carrageenan (Nunes et al, 2017(Nunes et al, , 2019, gelatin (Alves et al, 2013), and gellam gum (Neto et al, 2015)] and proteins [deoxyribonucleic acid (DNA) (Leones et al, 2014) and silk fibroin (Pereira et al, 2016)].…”

Luminescent Electrochromic Devices for Smart Windows of Energy-Efficient Buildings

“…Following previous recent works of our group focused on the development of novel ECDs with improved features to meet the requirements of the next generation of smart windows for future zero-energy buildings [24,38], we introduce here, for the first time, a new ECD concept that relies on the combination of NIR transparent TCO and NIR-emitting electrolyte. The TCO chosen was IMO.…”