Double-Pattern Textured ZnO:Ga Thin Films Fabricated by an APPJ and an DC Sputtering

Abstract

Transparent conductive oxides (TCO) are essential for superstrate solar cells due to its outstanding optical and electrical properties. 1 In ordertoimprovetheefficiencyofsolarcells,itisimportanttofabricate high-quality TCO substrates. Recently, zinc oxide (ZnO) based TCO have attracted significant attention because of high abundance, low cost and non-toxicity. Moreover, ZnO films doped with group III elements are more stable than tin-doped indium oxides (ITO) and fluorine-doped tin oxides (FTO) in the hydrogen and silan (SiH4) plasma discharge. 2,3 Hence, they are very suitable for the process of microcrystalline silicon (μc-Si) and amorphous silicon (a-Si) solar cells. For silicon based thin film solar cells, textured ZnO electrodes are necessary to increase light absorption in μc-Si absorbers and to reduce the degradation in a-Si absorbers. This is because that textured ZnO films can scatter the incident light efficiently and enhance the light trapping effect. To date, many efforts have been made to achieve superior textured ZnO films. Post wet etching by diluted acids for aluminum-doped zinc oxides (AZO) and gallium-doped zinc oxides (GZO) is the well-known method. 4,5 However, this process creates a lot of waste in ZnO and is not fit for large-scale production. Recently, pyramid-like textured zinc oxides doped with boron (BZO) have been successfully fabricated by a low pressure chemical vapor deposition (LPCVD) or a metal organic chemical vapor deposition (MOCVD) without any post treatments. 6,7 Nevertheless, disadvantages of these techniques are expensive equipments and the usage of toxic precursors. Here, we developed a novel, safe, and low-cost technique to produce textured GZO films. A bi-layer structure of organosilicon/ GZO was conducted to fabricate double-pattern textured GZO films on glass substrates. This bi-layer structure was achieved by an atmospheric pressure plasma jet (APPJ) and a dc magnetron sputtering. The surface morphology, optical characteristics and conductivity of double-pattern textured GZO films can be effectively controlled by the haze of organosilicon underlayers. After a post-annealing treatment in high vacuum, double-pattern textured GZO films can reveal the excellent optical transmittance and electrical conductivity.