【作者】 王颖；

【导师】 柴卫平；

【作者基本信息】 大连交通大学 ， 材料加工工程， 2012， 博士

【摘要】 ZnO:Al (AZO)透明导电薄膜具有优良的光电性能,在氢等离子体中具有较高的稳定性,源材料丰富且廉价,这使得其做为透明前电极在硅基薄膜太阳能电池中获得了广泛的研究和应用。而具有凹凸不平表面形貌的绒面AZO薄膜,更可以实现有效的陷光效应,增加太阳能电池吸收层对光的吸收,从而提高电池的转换效率。因此,研究具有较好陷光能力、高透过率、低电阻率绒面AZO薄膜的制备及特性具有重要意义。目前,绒面AZO薄膜大多采用先溅射沉积后稀HCl溶液腐蚀的方法制备,然而稀HCl溶液较快的腐蚀速度使得腐蚀过程和绒面形貌难以控制。因此本论文采用碱性NaOH溶液对磁控溅射技术制备的平面AZO薄膜进行腐蚀,从而获得具有陷光能力的绒面AZO透明导电薄膜,以期实现对腐蚀过程和绒面形貌的控制。论文系统地研究了平面和绒面AZO薄膜的结构、表面形貌、光电特性和陷光能力,并探索了腐蚀后再沉积法制备绒面AZO薄膜对陷光能力的影响。主要研究内容如下：以ZnO:Al2O3(98wt.%:2wt.%)陶瓷靶为溅射靶材,利用直流脉冲磁控溅射技术制备平面AZO薄膜,系统地研究了衬底温度、Ar流量、工作气压、退火温度和薄膜厚度对平面AZO薄膜特性的影响。溅射法制备的AZO薄膜均为六方纤锌矿结构,具有(002)择优取向。所有的AZO薄膜在可见光波段均具有90%以上的平均透过率,溅射沉积条件对AZO薄膜的透射光谱吸收边和导电性能均具有影响。通过研究结果得到制备优良光电特性的AZO薄膜的最佳沉积条件：衬底温度为270℃、工作气压为0.8Pa、Ar流量为50sccm、溅射功率为350W。此时AZO薄膜的可见光平均透过率在90%以上,电阻率为1.3×10-3Ω.cm。采用碱性NaOH溶液腐蚀平面AZO薄膜,成功地获得了具有较好绒面形貌和陷光能力的绒面AZO薄膜,薄膜表面呈现分布均匀的尺寸为0.5-1μm的理想“弹坑”状绒面结构,此时绒面AZO薄膜电阻率为3.2×10-3Ω.cm,且具有高透过率和体现较好陷光能力的高绒度值。系统地研究了以NaOH溶液为腐蚀液时,不同沉积条件和腐蚀条件下制备的绒面AZO薄膜的特性。所有绒面AZO薄膜均具有较好的透光性,可见光平均总透过率均达到90%以上。当衬底温度高于270℃以后,随着衬底温度的升高,绒面结构的弹坑尺寸逐渐变小,且绒度值逐渐减小。Ar流量的增加使得腐蚀后的AZO薄膜表面形貌从“蜂窝”状转变为“弹坑”状结构,绒度值逐渐增大。较高的工作气压不利于有效绒面结构的形成。腐蚀时间或腐蚀浓度的增加使得薄膜表面的弹坑尺寸逐渐增大而弹坑密度减小,从而增加绒面AZO薄膜的陷光能力。腐蚀温度的升高并不能促进有效绒面结构的形成。研究了AZO薄膜绒面结构的形成机理,探讨了绒面形貌控制、陷光能力改善和制备条件之间的关系,并且对修正的Thornton模型进行了补充。采用腐蚀后再沉积法制备绒面AZO薄膜,即在经过溅射沉积和NaOH溶液腐蚀后,再次进行溅射沉积,研究了腐蚀前后的两次溅射沉积条件对绒面AZO薄膜陷光能力的影响。当两次溅射沉积条件不同时,在保证可见光高透过率的同时,绒面AZO薄膜的陷光能力得到明显改善。更多还原

【Abstract】 As standard front contacts, ZnO:Al (AZO) films have received great interest in the applications of silicon-based thin film solar cells, owing to their good optoelectronic properties, as well as their low cost, abundant resource and stability under hydrogen plasma environment. Moreover, AZO film with rough surface can realize light trapping effect and increase the absorption of light in the absortion layer, which can achieve a high efficiency in thin film solar cells. Therefore, it is very important to study the preparation and properties of textured AZO films with high transparency in the visible wavelength range, low resistivity and good light trapping ability.At present, surface textured AZO films were prepared by wet chemical etching after sputtering deposition, and HCl solution was used in most research. However, it is difficult for HCl solution to control the etching process and surface morphology of AZO films because of the high etching rate of HCl solution. In this thesis, through the wet chemical etching process after sputtering deposition, surface textured AZO films with light trapping ability were obtained in NaOH solution in order to control the etching process and surface morphology. The structural, optoelectronic properties, surface morphology and light trapping ability of smooth and textured AZO films were investigated in detail. And light trapping ability of textured AZO films deposited by re-deposition after etching was studied. The main research contents are as follows:The smooth AZO films were prepared by direct current pulse magnetron sputtering from a ceramic ZnO:Al2O3(98wt.%:2wt.%) target. The influence of substrate temperature, Ar flow rate, working pressure, annealing temperature and film thickness on the smooth AZO films was studied. All the sputtering AZO films had a hexagonal wurtzite structure with (002) preferred orientation. And all the AZO films had an average transmittance of above90%throughout the visible wavelength range. The deposition conditions had important effects on the absorption edge of the transmittance spectra and the electrical properies of AZO films. From the research results, the optimum deposition conditions for AZO films with good optoelectronic properties were obtained:substrate temperature (270℃), working pressure (0.8Pa), Ar flow rate (50sccm) and sputtering power (350W). AZO films deposited under this condition had an average transmittance of above90%throughout the visible wavelength range, and the resistivity was1.3×10-3Ω·cm.NaOH solution was used to etch the smooth AZO films, and effective surface textured structures were obtained successfully. The surface of AZO film was almost uniformly covered by the craters with diameters ranging from0.5to1μm, which is an effective feature for light trapping. Moreover, the resistivity of the textured AZO film is3.2×10-3Ω·cm, and the high transparency and light trapping ablity were also obtained. The influence of deposition and etching conditions on the properties of textured AZO films etched with NaOH solution was studied. All the AZO films had high transparency throughout the visible wavelength range, and the average transmittance reached above90%. When substrate temperature was higher than270℃, the crater size and haze became smaller with the increasing substrate temperature. With the increasing of Ar flow rate, different surface features ranging from honey-comb-like to crater-like structures were observed and the haze was increased. The higher working pressure was not fit for the formation of textured structure. With the increasing etching time and concentration, the crater size was increased while the crater density was decreased, which improved the light trapping ability of textued AZO films. But textured structure was not obtained by increasing the etching temperature. The formation mechanism of textured structure of AZO films was investigated, and the relation between the textured morphology control, light trapping ability improving and preparation condition was discussed. Furthermore, modified Thornton model was supplemented.Textured AZO films were prepared by re-deposition after etching. During the deposition+etching (NaOH solution)+deposition process, the influence of sputtering deposition conditions before and after etching on the light trapping prperties of textured AZO films was studied. When the deposition and the re-deposition condition are different, light trapping ability of textured AZO films with high transparency throughout the visible wavelength range was improved obviously.更多还原