Study On The Properties Of Wo₃ And Ni O_x Thin Films And All-solid-state Electrochromic Devices Prepared By Magnetron Sputtering

Electrochromic"smart windows"are capable of selectively absorbing or transmitting sunlight and thermal radiation,which can significantly reduce energy consumption in buildings and alleviate the problem of resource scarcity.Currently prepared all-solid electrochromic devices are still unable to meet the requirements of practical applications.This thesis addresses the issues of how to improve the optical modulation amplitude and cycle life of the electrochromic films and devices,and shorten the response time of coloring and bleaching,etc.The WO₃ and NiO_x electrochromic films are prepared by magnetron sputtering,and the electrochromic properties of the films are improved by regulating the deposition process parameters and Cu doping.An all-solid-state electrochromic device ITO/WO₃/Li PON/NiO_x/ITO was constructed and the performance of the device was analysed and discussed.The main studies and results are as follows:(1)The WO₃ electrochromic films were prepared by the medium frequency magnetron sputtering method,and the microscopic morphological characteristics of the WO₃ films at different sputtering pressures and their relationship with the electrochromic properties were investigated.The results show that the best electrochromic performance is achieved at a sputtering pressure of 4 Pa,when the WO₃ films are amorphous and the surface particles are coarse and the layer is moderately sparse.The optical modulation amplitude of the films is81.0%at 550 nm,and the response times for coloring and bleaching are 7.8 s and 5.85 s respectively.Furthermore,the current density only decreases by approximately 6.3%after1500 cycles,providing excellent cycling performance.(2)The NiO_x electrochromic films were prepared by DC magnetron sputtering,and the effect of sputtering pressure on the electrochromic properties of the films was investigated.The optical modulation amplitude of NiO_x film mainly depends on the variation of coloration state transmission rate.Within a certain range,as the sputtering pressure increases,the surface particles become coarser and the pores increase,which is conducive to the insertion and extraction of Li⁺and e^-,thus enhancing the electrochemical properties of NiO_x films.When the sputtering pressure is 2.4 Pa,the optical modulation amplitude of the NiO_x film is 54.49%,and the coloring takes only 2.2 s,and the bleaching time is 1.4 s.(3)By modulating the doping amount by varying the sputtering power of Cu,a critical value was found to exist to optimise the electrochromic performance of the films.At a doping power of 40 W,the optical modulation amplitude of the film increases to 60.29%.Cu doping distorts the NiO_x lattice and forms a channel structure with large pores inside the crystal,which is more conducive to Li⁺transport;it also allows more Ni atoms to participate in the electrochromic process,further enhancing the performance of the NiO_x film.In addition,Cu doping increases the electrical conductivity of the film by a factor of about three,enhances the carrying capacity of the current,reduces the degree of attenuation and improves the cycling performance of the NiO_x film.(4)The ITO/WO₃/Li PON/NiO_x/ITO all-solid-state complementary electrochromic device was built.Due to the superposition effect,the electrochromic performance of the device is enhanced,with an optical modulation amplitude of 67.99%and coloring and bleaching times of 6.05 s and 7.4 s,respectively,which is better than the ITO/WO₃/Li PON/ITO device.In addition,too low a voltage applied to the device will lead to less insertion of ions and electrons during the electrochromic reaction,and too high a voltage will make the electrochromic reaction incomplete.5 V was found to be the suitable voltage for the device,and the electrochromic performance does not decrease and the response time is accelerated in high temperature environment,indicating that the constructed electrochromic device has certain environmental adaptability.