Properties of NiOx and its influence upon all-thin-film ITO/NiOx/LiTaO3/WO3/ITO electrochromic devices prepared by magnetron sputtering

• NiOx films sputtered in diverse O2 atmosphere were applied in all-thin-film ECDs.
• Various compositions, microstructures and transmittance of the films were tested.
• ECDs with NiOx prepared in 6% and 4.5% O2 content had higher optical modulation.
• ECD with NiOx prepared in 6% had faster switching responses than that in 4.5%.

Nickel oxides (NiOx) thin films were magnetron sputtered in Ar/O2 mixing gases with the relative O2 concentration varied from 4.5% to 20%. Subsequently, each NiOx film was used to fabricate an all-thin-film glass/ITO/NiOx/LiTaO3/WO3/ITO electrochromic device (ECD). All the ECDs were fabricated monolithically in a same vacuum chamber layer by layer using dc reactive sputtering for NiOx, WO3 and ITO, and radio frequency (rf) sputtering for LiTaO3. Influence of oxygen concentration upon properties of NiOx as well as their corresponding ECDs was focused on and studied through grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible spectrometry. The results show that the as-prepared nickel oxide films can be represented as NiOx with 1.10 ≤ x ≤ 1.21 when O2 concentration in sputtering gas changes. With increasing x, the preferred crystalline orientation (100) of NiOx thin films vanished, and (111) and (220) plane appeared. Owing to the poor crystalline structure in favor of ion transportation in the NiOx layer and less proportion of Ni3+, the device with NiOx film deposited at 6% O2 concentration displayed high transmittance at bleached state and subsequently an excellent transmittance modulation of more than 67%. Coloring and bleaching response time of this device was 85 s and 42 s, respectively. The results confirm that the magnetron-sputtered technical parameters proposed in this work is promising for all-thin-film ECDs with excellent electrochromic performance.