Laminated WO3-NiO Electrochromic Glass:From Starting Material to Device Assembling
WO3-NiO-based electrochromic devices(ECDs),which can actively regulate visible and infrared(IR)light and offer outstanding energy-efficient performance,have been extensively investigated owing to their potential application in smart windows for energy-efficient buildings and light-modulated skylight glass for electric vehicles.However,the high cost and low production efficiency of ECDs severely restrict their large-scale application.Compared with the conventional ECD fabrication process,which involves stacking multiple films on a single glass substrate,the lamination process for assembling a WO3-NiO ECD by laminating the individual components of glass/TCO/WO3 and glass/TCO/NiO with a transparent adhesive electrolyte interlayer is gradually becoming mainstream for realizing low-cost,commercially viable,large-area ECDs.However,for the practical production and new application of large-area laminated devices,one must perform a systematic survey from the starting material to device assembly,including high-quality EC oxide targets for large-area sputtering deposition;sputtered EC films with a regulated composition,microstructure,high performance,and color;achieve large transparent adhesive electrolyte foils with high room-temperature ionic conductivity,temperature stability,and high adhesive strength;perform a large-area ECD lamination process in the existing commercialized facilities;realize curved-device fabrication;and achieve an energy-efficient device with neutral color in both tinted and bleached states.Hence,researchers have conducted a series of studies,and the progress is presented in this review.First,the requirements and preparation methods of WO3 and NiO ceramic targets for large-scale production are presented.An appropriate level of electrical conductivity is required to satisfy middle-frequency sputtering,which is the most commonly used sputtering mode in commercialized films.The EC performance and W/O stoichiometric ratio of a WO3 film sputtered using a ceramic target can be effectively adjusted by changing the sputtering power and gas pressure under pure Ar atmosphere.In this study,the deposition rate increases from 6.9 to 20.8 nm as the sputtering power increases from 100 to 250 W.Additionally,an 18-nm-thick amorphous tin-zinc-oxide film is used to shield the sputtered WO3 film so that a room-temperature-deposited film with excellent cyclic stability can be achieved.A high content of niobium(Nb/(Nb+W)=54.1 at.%)is introduced into the WO3 matrix to realize a neutral-tinted color and a relatively lower IR absorption in the tinted state.In the NiO film,Li/Si co-doping followed by rapid thermal annealing can enhance the transmittance near the short-wavelength zone in the bleached state,the charge capacity,and the cyclic stability.Additionally,W/Zn co-doping enables a NiO EC film with superior performance to be achieved after tempering at 640 ℃.For the transparent adhesive electrolyte interlayer,a new strategy for significantly improving the ionic conductivity of polyvinyl-butyral(PVB)via a cross-linking reaction with 3-glycidoxypropyltrimethoxysilane(KH560)is established.The cross-linked PVB solid polymer electrolyte(SPE)with 10 wt.%KH560 exhibits a high room-temperature ionic conductivity(1.51 × 10-4 S·cm-1).Additionally,the prepared PVB-SPE exhibits comprehensive optical,mechanical,and thermal performances,including high visible transmittance(>91%),relatively high adhesive strength(2.13 MPa),and superior thermal stability(up to 150 ℃).The WO3-NiO ECDs with sizes of 5 cm × 5 cm to 30 cm × 30 cm can be assembled in a commercialized autoclave to realize perfect lamination using the PVB-SPE foil.The device can be operated stably at temperatures ranging from-20 ℃ to 80 ℃,thus underscoring the potential of the PVB-SPE for realizing commercially viable large-area ECDs.Additionally,an ECD is assembled using the WO3 system with a high Nb doping content.The ECD has a neutral color(a*=0.6;b*=-2.7)and presents a high energy efficiency in reducing the interior-space air temperature by approximately 4.3 ℃ in its fully tinted state.