Preparation And Properties Of NiO Electrochromic Films By DC Megnetron Sputtering Method

Electrochromic refers to a change in the optical properties of a material that is reversible and maintainable during electrochemical processes.Nickel oxide(NiO)thin film is an excellent anodic discoloration material,its cost is relatively low,and the optical density difference between colored and bleached states is large,and it is a thin film material with great research and application prospects.In this paper,DC reactive magnetron sputtering was used to fabricate multiple NiO thin films under different conditions using FTO glass as the substrate.The influences of deposition time,oxygen-to-argon flow ratio,sputtering power,deposition pressure,and substrate temperature on the structure and electrochromic properties of NiO thin films(KOH as electrolyte)were systematically investigated,and NiO-based electrochromic device was fabricated.The results of the study are as follows:(1)The deposited NiO thin films are all of cubic structure NiO.As the sputtering time increases,the intensity of the(200)diffraction peak gradually increases and the crystallinity of the film becomes better and better.The increase in film thickness will increase the charge capacity of the film,but the bleach state and initial state transmittance will decrease,and the response time will increase.The transmittance modulation of the sample with a thickness of 80 nm is 50%,and the bleaching transmittance is 71%.The thinner NiO film has better electrochromic properties.(2)The increase of oxygen-to-argon flow ratio will decrease the deposition rate and the initial state transmittance of the film.When the oxygen-to-argon flow ratio is low,it is mainly(111)and(200)preferred orientation,when the oxygen-to-argon flow ratio rises to 0.2 The crystallinity of the film deteriorates,but the XRD pattern shows a weak(220)diffraction peak.The samples with oxygen-to-argon flow ratio of 0.05had the highest bleaching transmittance(44%)and transmittance modulation(36%)at a film thickness of 280 nm,and the samples with an oxygen-to-argon flow ratio of0.02 had the highest coloration efficiency.It reaches 30 cm~2/C.Nickel oxide films deposited under low oxygen-to-argon flow ratio have better electrochromic properties.(3)With the increase of sputtering power(100~200 W),the intensity of the(200)diffraction peak is gradually strengthened,and the crystallinity of the film is improved.However,when the power is increased to 250 W,the intensity of the diffraction peak decreases and the crystallinity of the film deteriorates.The NiO film deposited at 250 W has the largest transmittance modulation,reaching 27%,and the fastest response time,coloring time is 7.25 s,bleaching time is 3.71 s.However,the sputtering power has no obvious effect on other electrochromic performance indexes.(4)The film deposited at 0.7 Pa is mainly(200)preferred,and the(111)preferred orientation occurs after the pressure is increased.As the deposition pressure increases,the charge storage of NiO thin film tends to decrease,but it has no obvious effect on other electrochromic performance indexes.(5)With the increase of substrate temperature(10~150°C),the diffraction peak intensity of(111)plane and(200)plane of NiO thin film increases slightly,and the activation time of the film increase gradually,when the substrate temperature is150°C.NiO thin films have little electrochromic activity.The electrochromic properties of the NiO thin films deposited at 10°C were the best,the bleaching transmittance was 69%,and the transmittance modulation was 53%.The film deposited at 50°C has a faster response time,1.44 s for coloring and 0.91 s for bleaching.Substrate temperature can not be too high,control at 10~50°C can get better electrochromic performance of the film.(6)After optimizing the deposition parameters,the NiO film has a colorization efficiency of 71 cm~2/C after 1000 cycles,and the response time is faster(coloring time is 1.21 s,bleaching time is 0.41 s).The FTO/NiO/KOH/FTO electrochromic device was fabricated using the film as an electrochromic layer.The device exhibited a bleaching transmittance of 61%and transimittance modulation of 25%at 550nm.