| WO3 has the advantages of low working voltage,non-toxic,low cost,excellent cycling performance,good color memory performance,etc.What's more,all solid state inorganic electrochromic devices(ECD)based on WO3 exhibits excellent performance in terms of low cost and stable electrochromic properties,and can be fabricated by magnetron sputtering technology for large area devices.Hence,all solid state inorganic electrochromic devices based on WO3 possess great potential for industrialization.However,there remain many problems in the uniformly preparation of large size WO3 films and devices and in the improvements of their electrochromic performance,which hinder the practical application and marketization of the electrochromic devices.In this thesis,the effects of oxygen content and working pressure on the structure,morphology,and electrochromic properties of WO3 films,fabricated by using the middle frequency twin reaction magnetron sputtering technology,are systematically investigated.Based on the as-prepared WO3 films,all solid state inorganic electrochromic devices with the structure of Glass/ITO/WO3/LixWOy/NiWOz/ITO were successfully prepared.Moreover,large size devices are also explored.The main contents are as follows:(1)Effects of the oxygen content and the working pressure during the fabrication on the morphology and the crystallinity of the WO3 films with a size of 370×470mm2 prepared are investigated.It is found that the sputtering rate and the relative crystallinity tend to decrease with increasing oxygen content and working pressure,meanwhile,the surface morphology also changes obviously.The thickness uniformity of WO3 films under different oxygen content and working pressure is less than ±5.1%.WO3 film has a monoclinic structure with(002)preferred orientation and all have a certain degree of crystallinity.(2)The electrochromic properties of the as-prepared WO3 films and the related mechanism are studied.WO3 films prepared with different oxygen contents can all be optically modulated by a large content during the charge insertion/extraction process.Meanwhile,the differences in the crystallinity and the morphology caused by the different oxygen content affect the injection and extraction processes of Li+,whereas it has little effect on the cycle life of the film.With increasing the working pressure during the fabrication process of WO3 films,the optical modulation ability of the WO3 films during the charge insertion/extraction process decreases,and the extraction of Li+ from WO3 film is more difficult.As a result,the film hysteresis is heavy.Meanwhile,the excessively high working pressure goes against the cycle stability of the film.With the optimum sputtering parameters,i.e.,the oxygen content of 51%and the working pressure of 4.7mTorr,the optical modulation at wavelength(550nm)with an extent of 63.49%is achieved.Moreover,the colored state can completely block the infrared region of light,and there was no current density degradation after 100 CA cycles.(3)With the as-prepared optimized WO3 films,all solid inorganic electrochromic devices were fabricated and the properties were investigated.Furthermore,the devices with large size were also prepared.Under an applied DC voltage of ±2.5V,the device with a size of 135×60 mm2 exhibits outstanding electrochromic properties:The optical modulation at wavelength(550nm)of the device can amount to 57.25%,the average transmittance in the ultraviolet and infrared regions can be dynamically adjusted from 1.5%to 10%and 0.7%to 52%,respectively.Moreover,the colored and bleached time of the device were 22s and 24s respectively,and the electrochromic efficiency was 85.63cm3/C.What's more exciting thing is that ECD still had good cyclic stability after 5500 cycles.At last,we obtained uniform discoloration of ECD with a maximum scale of 370×470mm2,and we also found that the response time of the device extended with increasing the device size due to the change of the ECD's surface resistance. |
PDF Full Text Request