Study On Properties Of WO₃ Electrochromic Films And Devices Prepared By DC Magnetron Sputtering

The electrochromic materials are developed as new functional materials in broad application prospects and demonstrate huge industrial value,especially in the field of building energy conservation thanks to their unique optical control capabilities.The WO₃ films are often used as cathode inorganic electrochromic materials because they possess some unique advantages such as large reserves,environmental friendliness and excellent performance.They have attracted widespread attention in the scientific and industrial circles since they are expected to be applied as"smart windows"in the future.In this study,we focused on improving the insufficient response speed and stability of WO₃ thin films through adjusting their microstructure during the preparation process.After that,the crystal structure of the film was further optimized by in-situ heating or subsequent annealing treatments.The influence of crystal structure on the electrochromic properties was investigated.In addition,the characteristics of the electrode layer Ni O_x were also studied.Based on the above studies,the WO₃ and Ni O_x thin films were assembled into WO₃//Ni O_x:Li complementary type electrochromic devices.The specific research content and results of the thesis are as follows:Direct current magnetron sputtering technique was used to prepare WO₃ film.The influence of sputtering power,gas pressure as well as oxygen-argon flow ratio on the film structure and electrochromic performance was systematically investigated.The results showed that the prepared WO₃ thin films exhibited the best electrochromic performance as the sputtering power was 270 W with a sputtering gas pressure of 2.5 Pa and the flow rate between oxygen and argon of 1:1.The average modulation amplitude in the visible wavelength range was as high as 70.1%.The fading response time was 5.6 s and the coloring time was 7.9 s.The WO₃ thin films also exhibited excellent cycle stability in the Li⁺electrolyte.The investigated WO₃films with different crystal structures were obtained by in-situ heating or by the further annealing treatments.The influence of crystal structure on the electrochromic properties was investigated.The mechanism of high-temperature degradation of the film was studied by subsequent annealing treatment.The research results showed that the amorphous WO₃ film had a larger light modulation range,faster response speed and higher coloring efficiency compared to those with cystal structure.In contrast,the crystalline WO₃film had better cycle stability.When the substrate temperature was 300℃,the prepared WO₃film presented a loose amorphous-nanocrystalline mixed state structure.Micro voids were observed to distribute homgeneously on their surface.However,their electrochromic performance is best.The light modulation range was 73.1%,and the coloring/fading time was10.5 s/4.4 s.The coloring efficiency was as high as 60.3 cm²/C.After the high temperature annealing,the amorphous structure of the film was destroyed,causing the degradation of its electrochromic performance.Ni O_x:Li thin films were also prepared as a counter electrode for electrochromic devices.The results showed that Ni O_x films doped with a certain amount of Li could increase the vacancy concentration,improve the crystallization degree and optimize the orientation of the deposited thin films as Li⁺ions entered Ni²⁺vacancies in Ni O_x films.When the substrate temperature was 300℃,the Ni O_x:Li thin film demonstrated good crystallinity and excellent performance.On the other hand,the assembled WO₃//Ni O_x:Li complementary type electrochromic device showed a light modulation range of about 60%and possessed relatively good cyclic voltammetry characteristics.