反应磁控溅射氧化钨电致变色薄膜结构与性能

Structure and Properties of Tungsten Oxide Electrochromic Films Prepared by Reactive Magnetron Sputtered Method

采用脉冲直流反应磁控溅射镀膜方法在透明导电玻璃FTO（SnO2：F）上制备厚度分别为50、100、150、200、250和300 nm的WO3薄膜。分析了薄膜着色前后晶体结构和表面形貌的变化,对薄膜的循环伏安特性和光学性能进行测试。结果表明：不同厚度氧化钨薄膜均为结晶态,具有单斜晶系结构;随着薄膜厚度增加,薄膜结晶程度逐渐增加;薄膜着色/褪色循环中,不同厚度的WO3薄膜均发生单斜晶系WO2.92与立方晶系WO3的可逆转变,产生晶格应变,并且随厚度增加,薄膜晶格应变先减小后增大,薄膜厚度为250 nm时,变色前后晶格应变最小,厚度增加至300 nm薄膜时,着色产生应变明显增大。在相同驱动电压下,随薄膜厚度增加,光学调制幅度（550 nm）、着色效率先增大后减小,厚度为250 nm时获得最大调制幅度76.01%和着色效率21.04 cm2/C;当厚度进一步增加至300 nm时,薄膜褪色态透过率降低到49.30%后无法继续褪色,着色效率也开始下降。使用XPS分析了薄膜着、褪色状态下W元素的化学态,发现300 nm薄膜褪色后一部分W5＋无法转变成W6＋,导致薄膜仍为蓝色。

Tungsten oxide（WO3）films with thicknesses of 50,100,150,200,250 and 300 nm were fabricated on transparent conductive glass FTO（SnO2：F）via pulsed DC reactive magnetron sputtering.The crystal structure and surface morphology of the films were analyzed.The cyclic voltammetric and optical properties of the films were investigated.The results show that the WO3films with different thicknesses are crystalline and have a monoclinic crystalline structure.The degree of film crystallization increases gradually with the increase of the film thickness.The WO3 films of different thicknesses have a reversible transformation of monoclinic WO2.92 and cubic crystal WO3,resulting in the lattice strain.The lattice strain of the film firstly decreases and then increases with the increase of the film thickness.When the film thickness is 250 nm,the lattice strain is the minimum before and after discoloration,and the thickness further increases to 300 nm.The coloring efficiency and the optical modulation（550 nm）firstly increase and then decrease with the increase of the film thickness at the same driving voltage,and the maximum modulation is76.01%when the thickness is 250 nm,and the coloring efficiency is 21.04 cm2/C.The bleached state of the film decreases to 49.30%,and the coloring efficiency begins to decrease when the thickness further increases to 300 nm.The chemical state of W element in thin film and bleached state was further analyzed by X-ray photoelectron spectroscopy.It is found that part of W5＋ion cannot be transformed into W6＋ion after discoloration of 300 nm film,causing the film to be blue.