Preparation And Application Of ZnO-based Transparent Conductive Films

Transparent conductive oxide thin films have the properties of both transparence and conductive, these unique properties make them have wide application prospects in the fields of solar cells、liquid crystal displays、thin-film transistors and so on. Currently, the most widely used transparent conductive film is indium-doped tin oxide (ITO) films, however, In is expensive and toxic, which limit its further application. In contrast, doped zinc oxide thin films have some advantages, such as abundant raw materials、low cost、non-toxic、high stability in hydrogen plasma, which makes it be a promising alternative to ITO.Al-doped ZnO (AZO) thin films were grown by RF magnetron sputtering, and the influences of sputtering power、sputtering pressure、sputtering time and sputtering temperature on the films’properties were studied. After getting the best parameters, we grew the same films on Si for pre-research of its application on crystalline silicon solar cells. At the same time, Al-doped ZnO films were also grown on flexible substrates at room temperature by DC magnetron sputtering, the influences of Ar:O and sputtering pressure on the films’properties were studied. At last, we studied the stability of the films in different conditions, such as in the air、under ultraviolet light and in high temperature. The main results obtained through the study are as follows:1、AZO thin films were prepared on glass substrates by RF magnetron sputtering. We used the Taguchi design method on the optimization of the electrical properties of AZO films, and four influential deposition parameters were studied in this experiment, such as sputtering power、sputtering pressure、sputtering time and sputtering temperature. We can do fewer experiments when using this method, simultaneously we can optimize the experiment parameters and obtain the best parameters in a short time. At the same time, we can conclude how much contribution every parameter making by analysis of variance, the results showed that sputtering temperature and sputtering time made the largest contributions 48.15%and 31.45%in respect. AZO transparent conductive thin films grown at the best parameter has a good crystal property, flat and dense surface. The resistance of the film was 8.16×10-4Ω·cm, its hall mobility and carrier concentration were 12.5cm2/V·s and 6.15×1020cm-3 respectively, visible light transparence of about 90%. These excellent properties show its huge potential applications.2、A new structure of crystalline silicon solar cell was designed:using AZO as both transparent electrode and anti-reflectance layer to replace traditional Ag electrode and Si3N4 thin film. Therefore, we grew AZO transparent conductive thin films on n-Si by RF magnetron sputtering with the best parameters. One of the samples was annealed for contrast because AZO/Si will suffer high temperature when making the back electrode. Then, the surfaces of the films before and after annealing were observed by SEM. The structure and morphology near the interface of AZO film and Si were observed by TEM. Also, the I-V curve of this structure before and after annealing showed good Ohmic contact between AZO film and Si. The results of SIMS indicated that the elements diffused near the interface after annealing, this will reduce the efficiency of the cell, however, we proposed a solution.3^ AZO transparent conductive thin films were prepared on PC flexible substrates at room temperature by DC magnetron sputtering. The influences of Ar:O and sputtering pressure on the films’structure and properties were learned. The result indicated that the films showed the best crystalline quality and surface morphology when Ar:O and sputtering pressure were 100:6 and 0.5Pa. The resistivity and sheet resistance reached 3.83 x l0-4Ωcm and 7.654Ω/sq,when the transmittance was above 80%. This indicated that the properties of AZO films were suited for application in flexible devices. Then, we studied the stability of the films in air, under ultraviolet light and in high temperature, taking into account of its application in flexible devices. The results showed that the electrical properties of the films can be unchanged after being placed in air and ultraviolet light for 6 months and 9 days. When being suffered in high temperature, the surface morphology of the films did not change so much, however, the electrical properties of the films were worse when the transmittance remain unchanged.