Preparing and Investigating the Monolithically Stacked Flexible Tandem All-Thin-film Electrochromic Device

A flexible tandem all-thin-film electrochromic device (ATF-ECD) with a device structure of polyethylene terephthalate (PET)/tin doped indium oxide (In2O3:Sn, ITO)/tungsten oxide (WO3)/lithium tantalate (LiTaO3)/ nickel oxide (NiOX)/ITO/NiOX/LiTaO3/WO3/ITO has been fabricated by all magnetron sputtering technologies, in which the bottom ATF-ECD with a superstrate-type structure and the top ATF-ECD with a substrate-type structure are physically and monolithically stacked but electrically connected in parallel. They are systematically investigated for the optical and electrochemical properties through chronoamperometry (CA) and cyclic voltammetry (CV) measurements under different test cases. Both sub-devices work well and the flexible tandem ATF-ECD has achieved a high optical modulation of 59.8% at 600 nm. The numerical simulation is carried out for the tandem ATF-ECD and the single ATF-ECDs with different device structures. The details on transmission spectra are deeply discussed. The flexible tandem ATF-ECD with good electrochromic performances under the low driving voltages provides promising applications in the future smart windows.