Spray Deposited Nanostructured CuO Thin Films: Influence of Substrate Temperature and Annealing Process

In this study, CuO thin films were deposited on glass substrates at a wide range of temperatures from 450ºC to 550ºC with steps of 25ºC by chemical spray pyrolysis technique. Aiming to investigate the effect of annealing process, one of the resulting films was annealed at 450ºC for 3 hours under ambient air. Based on X-ray diffraction, all the resulting films are monoclinic with two prominent peaks at ~36º and ~39º. The crystallite size of the CuO film deposited at 450ºC was found to be the largest in comparison with the others. As the substrate temperature increased, a gradual change was observed for the CuO thin film surface morphology and in the case of annealed film, the grains and their boundaries became indistinguishable. The resistivity of the films was reduced by virtue of increasing the substrate temperature and also, both the mobility and carrier concentration of the annealed film were improved drastically after annealing. As expected, the CuO thin films absorption was considerable in the visible region and gradually declined after 800nm. The estimated band gap value of the CuO film deposited at 450ºC were fairly close to the optimum band gap for solar applications.

本研究采用化学喷雾热解（chemical spray pyrolysis）技术，在450℃至550℃、以25℃为温度步长的宽温度区间内，于玻璃衬底上沉积氧化铜（CuO）薄膜。为探究退火工艺的影响，对其中一块所制得的薄膜在空气氛围下以450℃退火3小时。经X射线衍射（X-ray diffraction）分析，所有所制得的薄膜均为单斜晶系，在约36°与约39°处存在两个显著特征衍射峰。相较于其余薄膜，在450℃下沉积的氧化铜薄膜晶粒尺寸最大。随着衬底温度升高，氧化铜薄膜的表面形貌逐渐发生演变；经退火处理的薄膜，其晶粒与晶界变得难以分辨。随着衬底温度升高，薄膜的电阻率逐渐降低；此外，经退火处理后，该薄膜的迁移率与载流子浓度均得到显著提升。正如预期，氧化铜薄膜在可见光区域具有可观的光吸收性能，并在波长超过800nm后吸收能力逐渐下降。在450℃下沉积的氧化铜薄膜的估算带隙值，与太阳能应用的最优带隙值较为接近。