Reactive Sputter Deposition of WO3/Ag/WO3 Film for Indium Tin Oxide (ITO)-Free Electrochromic Devices

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• 作者：Yi Yin ; Changyong Lan ; Huayang Guo ; Chun Li
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2016
• 出版时间：February 17, 2016
• 年：2016
• 卷：8
• 期：6
• 页码：3861-3867
• 全文大小：417K
• ISSN：1944-8252

文摘

Functioning both as electrochromic (EC) and transparent-conductive (TC) coatings, WO₃/Ag/WO₃ (WAW) trilayer film shows promising potential application for ITO-free electrochromic devices. Reports on thermal-evaporated WAW films revealed that these bifunctional WAW films have distinct EC characteristics; however, their poor adhesive property leads to rapid degradation of coloring-bleaching cycling. Here, we show that WAW film with improved EC durability can be prepared by reactive sputtering using metal targets. We find that, by introducing an ultrathin tungsten (W) sacrificial layer before the deposition of external WO₃, the oxidation of silver, which leads to film insulation and apparent optical haze, can be effectively avoided. We also find that the luminous transmittance and sheet resistance were sensitive to the thicknesses of tungsten and silver layers. The optimized structure for TC coating was obtained to be WO₃ (45 nm)/Ag (10 nm)/W (2 nm)/WO₃ (45 nm) with a sheet resistance of 16.3 Ω/□ and a luminous transmittance of 73.7%. Such film exhibits compelling EC performance with decent luminous transmittance modulation ΔT_lum of 29.5%, fast switching time (6.6 s for coloring and 15.9 s for bleaching time), and long-term cycling stability (2000 cycles) with an applied potential of ±1.2 V. Thicker external WO₃ layer (45/10/2/100 nm) leads to larger modulation with maximum ΔT_lum of 46.4%, but at the cost of significantly increasing the sheet resistance. The strategy of introducing ultrathin metal sacrificial layer to avoid silver oxidation could be extended to fabricating other oxide–Ag–oxide transparent electrodes via low-cost reactive sputtering.