Enhanced electrochromism in short wavelengths for NiO:(Li, Mg) films in full inorganic device ITO/NiO:(Li, Mg)/Ta2O5/WO3/ITO
Résumé
Great interest has been drawn to the electrochromism demonstrated by inorganic materials, leading to various applications including smart windows and displays. NiO, as a cheap material, shows anodic electrochromism and is highly suitable for device applications in conjunction with WO3, but its strong optical absorbance has been largely overlooked. Herein, improved electrochromic properties in particular in short wavelengths was achieved by co-doping of Mg and Li in NiO:(Li, Mg) thin films grown using RF sputtering. Secondary Ion Mass Spectroscopy technique in combination with X-ray Photoelectron Spectroscopy characterization provides direct evidence of the introduction of Mg as well as Li in the film. Whatever the Li and Mg content, X-Ray Diffraction and Raman spectroscopy studies only bring out the NiO face-centered cubic rock salt structure. Electrochemical cycling shows pronounced anodic electrochromism for NiO:(Li, Mg) thin films. Inorganic all-solid-state monolithic multilayered devices are traditionally composed of a pair of electrodes with NiO and WO3 separated by Li containing electrolyte such as LiTaO3 or LiNbO3 sputtered from expensive but low efficient ceramic targets. Based on optimal NiO:(Li, Mg) films, large switchable electrochromism both in visible (∼58%) and ultraviolet band (∼50%) is reconciled in electrochromic device Glass/ITO/NiO:(Li, Mg)/Ta2O5/WO3/ITO. The co-doping of NiO with Mg and Li is capable of simultaneously widening the gap and avoiding the use of Li containing electrolyte, through NiO pre-lithiation. We believe the new, low-cost approach would provide references with respect to practical applications desired for their successful commercial mass production.
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