Preparation And Properties Of Novel MoO₃ Electrochromic Films

Electrochromic devices（ECDs） can be wildly used in smart windows, displays, militaries and other fields. The basic structure of ECDs have five layers, including transparent conducting layer I, electrochromic layer, electrolyte layer, ion storage layer, and transparent conducting layer II. At present, Indium tin oxide（ITO） film is the most commonly used transparent conducting layer because of its low resistance and high transmittance. But the rare of Indium element cause that ITO film is expensive and high-cost. On the other hand, its brittleness limits the development and applications of flexible ECDs. Dielectric-metal-dielectric（DMD） structure film is considered a more ideal transparent conducting layer, which exhibits high transmittance, low resistance, good flexibility and low cost. Our previous study found that by employing high performance electrochromic material as a dielectric layer, we can integrate the transparent conducting layer and electrochromic layer bi-functionality in one DMD film, which can simplify achieve the high performance of the rigid ECDs. In view of the important significances and challenges of flexible ECDs and in order to obtain high performance flexible ECDs, based on the previous work, we choose the classic MoO₃ as the dielectric layer and Ag as the metal layer, and set up a MoO₃/Ag/MoO₃（MAM） thin film which combine the function of the transparent conducting layer and the electrochromic layer. Through systematic study the relationship between the composition, structure and properties of MAM film, we could obtain high-performance flexible and rigid ECDs with rapid response time, high optical contrast, high efficiency and good stability.The main research contents are as follows:1. We prepared MAM films on glass substrates by electron beam evaporation technique. By using a method of the combination of the numerical simulationand the experimental validation and optimizing the film thickness, we obtained high performance MAM（30/11/50 nm） film, which reveals excellent conductivity and high transmittance. Its surface resistance is only 9.3 Ω â–¡-1 and average transmission in visible light range（400 800 nm） is 59.4%. Additionally, the MAM film shows excellent electrochromic properties. Compared with MoO₃（50 nm） film on ITO transparent conductor layer, MAM（30/11/50 nm） films have higher electrochromic colored efficiency（40.5 vs. 23.6 cm2 C–1）, higher optical contrast（30.9 vs. 20.4%,528 nm） and better cyclic stability. These results laid the foundation down for further high performance flexible ECDs study.2. We further prepared MAM films on flexible polythylene terephthalate（PET） substrates by electron beam evaporation technique. The optimized flexible MAM film has achieved excellent electrochemical and mechanical durability. After 2000 times bending test, the resistance of the flexible MAM（30/11/50 nm） film changed slightly from 12.5 Ω â–¡-1 to 26.7 Ω â–¡-1. In contrast, the resistance of the PET/ITO/MoO₃（50 nm）significantly increased from 30.5 Ω â–¡-1 increases to 1134 Ω â–¡-1. In addition, the electrochromic property of the flexible MAM film is also significantly better than that of PET/ITO/MoO₃ film. The electrochromic colored efficiency of the flexible MAM is 34.9 cm2 C–1, the optical contrast is 27.7%, the cyclic stability is more than 200 times, and the bending property is more than 2000 times. All researches above would provide a new approach for the preparation of high performance flexible ECDs.