Study On Texture Mechanism And The Surface Texture Uniformity Of AZO Film

Al-doped zinc oxide (AZO) transparent conductive film has low resistivity and high visible light transmittance, and textured structure can effectively reduce light reflection, increase the absorption of light and improve the conversion efficiency of solar cells,So it is widely applied to former electrode of thin film solar cells. It is extremely important to prepare the textured AZO thin film which has good photoelectric properties, higher haze and more uniform surface morphology for being applied to thin film solar cells, reducing the solar cell production costs and achieving large-scale industrialization production.For the time bing, the AZO thin film prepared by magnetron sputtering technique was etched by the 0.5% dilute HCl and could obtain excellent surface texture; but it is generally much difficult to gain the textured AZO thin film which has higher haze and more uniform textured structure in large area. So,it has very important significance to solve the problem for its application widely.In this paper, AZO thin film was etched by the mixed etching solution made by adding a certain amount of acetic acid into the dilute HCl. The affects on photoelectric properties, surface texture uniformity and reaction mechanism of AZO thin film was investigated after adding acetic acid, expecting to have certain directive significance for the uniformity of textured structure in large area.In this paper,the transparent conductive AZO thin films were deposited on glass substrate by DC-magnetron sputtering from ZnO/Al2O3 ceramic target doped 2wt.% Al2O3, and the textured AZO films were prepared by wet etching method.The affect of deposition parameters and etchant solution on electrical and optical properties of the textured AZO films was investigated systematically by four point probe, HMS-3000 Hall effect measurement system,UV-VIS-IR spectrophotometry and scanning electron microscopy(SEM),respectively.The results indicate:(1) Optimize the preparation technological parameters of AZO thin film.The results showed that the AZO thin films which had good photoelectric properties were prepared when O2 and Ar gas flow ratio was 0.007:1,air pressure was 0.5～0.6Pa,reaction temperture was 397～400℃, sputtering power was 225W and deposition time was 40min.the resistivity of he AZO thin films was up 5～9×10-4Ω·cm and the visible light transmittance was about 83%.(2) AZO thin films were etched by three etching solutions. The results showed that the textured AZO thin films having the best surface morphology and more uniform textured structure were gained when AZO thin films were etched by the mixed etching solution made by adding a certain amount of acetic acid into the 0.5% dilute HCl.(3) AZO thin films were etched by the mixed etching solution made by adding different volume of acetic acid into the dilute HCl.The results showed that the textured AZO thin films having higher haze were gained when the volume ratio of added acetic acid to 0.5% dilute HCl was 0.5:1.(4) AZO thin films were etched with different textured time by the mixed etching solution when the volume ratio of added acetic acid to 0.5% dilute HCl was 0.5:1.The results showed that AZO thin films can obtain uniform 'crater' shape textured structure when etching time is 5s; the size of the crater becone bigger when AZO thin films were etched longer time and textured structure become more non-uniform when when etching time is 55s.(5)AZO thin films were etched with same textured time at different air pressure.The results showed that AZO thin films have good density and can gain good surface topography after textured when air pressure is lower,and the film adhesion is pooer and has more point defect at higher air pressure,so textured structure is non-uniform.(6) AZO thin films were etched by 0.5% dilute HCl and by the mixed etching solution made by adding a certain volume of acetic acid into the0.5%,0.4%,0.3% dilute HCl,respectively.The results showed that the textured AZO thin films having higher haze were gained when the volume ratio of added acetic acid to 0.5% dilute HCl was 0.5:1,and etching time is 45s.(7) AZO thin films were etched 15s or 35s by the mixed etching solution made by adding different volume of acetic acid into the dilute HCl,respectively. Testing film thickness, and then calculating the corrosion rate. The results showed that the corrosion rate become smaller in gradually with the increase of acetic volume, and the corrosion rate was minimum when the volume ratio of added acetic acid to 0.5% dilute HCl was 0.5:1;but the corrosion rate begun to get bigger when we continued to increase the volume of acetic acid. The acetic acid molecules associated with hydrogen for ring of double molecules,and its strric hindrance made reaction rate slower adding a little acetic acid.But continuing to add acetic acid,the concentration of H+ also increased along with the increase of acetic acid and accelerated the reaction rate significantly.