Preparation And Electrochromic Property Of Mesoporous WO₃ Thin Films

WO₃ exhibits electrochromic characteristics,but the compact WO₃ films have some drawbacks,such as long response time and low co-efficiency,since low specific surface area prevents them from contacting fully with the electrolyte and producing color reaction.To solve this problem,mesoporous WO₃ films are fabricated and the electrochromic property of mesoporous WO₃ films was carried out in this paper.The research idea of this paper is that mesoporous WO₃ thin films were prepared by means of anodic oxidation and thermal annealing of the tungsten films,then the electrochromic property of the annealed WO₃ thin films was studied as well.The specific contents are as follows.Firstly,the tungsten thin films were prepared on glass substrates by magnetron sputtering at different sputtering current and substrate temperature,then the samples were annealed,and the microstructure,surface morphology and transmittance of the obtained tungsten films were characterized by XRD,SEM and UV-Vis spectrophotometer.The optimum technology para-meters of tungsten thin films are as follows:the sputtering current is 0.14A,substrate tempera-ture is room temperature.Then tungsten thin films were prepared on ITO glass substrate under the optimized parameters.Metastableβ-W is obtained,its crystallization is better,the grain is clearly visible,the surface is smooth and the whole structure tends to be complete.Secondly,the tungsten thin films prepared on ITO glass substrate were anodic oxidized.Oxidation time and anodic voltage have obvious effect on the pore size and microstructure of mesoporous WO₃ films.A uniform and clear mesoporous structure can be obtained at anodic voltage of 20V,room temperature,oxidation time of 50min.The obtained mesoporous WO₃ films are amorphous,the holes are uniform and well arranged,but the transmittance of films is low.Annealing treatment helps to form the crystallization of WO₃ and mesoporous structure with higher porosity.After annealing process of 400 degrees heat preservation for 3 hours and5 hours in air,optical transmittance of the mesoporous WO₃ thin films is obviously improved.The mesoporous WO₃ films annealed for 5 hours exhibit a higher optical transmittance.Finally,electrochromic experiments were carried out on mesoporous WO₃ films annealied at 400 degrees for 3 and 5 hours,the electrochromic properties of mesoporous WO₃ films were also studied by analyzing their optical modulation amplitude,response time and memory storage capacity.Research shows that:the average optical modulation amplitude of mesoporous WO₃ thin films annealed at 400 degrees for 5 hours is about 71%in the visible light area,the WO₃ thin films annealed for 3 hours is only 35%.The mesoporous WO₃ thinfilms annealed for 5 hours have better optical modulation function,shorter optical response time,and stronger memory storage capacity.This is due to their higher specific surface area and more inner holes.