High rate direct current magnetron sputtered and texture-etched zinc oxide films for silicon thin film solar cells T. Tohsophon a,b, ⁎ , J. Hüpkes a , H. Siekmann a , B. Rech a , M. Schultheis c , N. Sirikulrat d a Institute of Photovoltaics, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany b Physics Department, Faculty of Science, Srinakharinwirot University,10110 Bangkok, Thailand c Thin Film Materials Division, W.C. Heraeus GmbH, Germany d Physics Department, Faculty of Science, Chiang Mai University, 50200 Chiang Mai, Thailand Available online 14 June 2007 Abstract Aluminum-doped zinc oxide (AZO) films were prepared by in-line direct current (dc) magnetron sputtering on glass substrates. Four types of ceramic targets with 0.5 wt.% or 1 wt.% of aluminum oxide and different preparation methods, namely normal sintered, soft sintered and hot pressed, were employed. The influence of different target manufacturing processes, aluminum concentration and sputtering conditions on AZO films were investigated. Depending on the type of targets and deposition conditions, highly transparent films with low resistivity values in the range of 3.6–11 × 10 − 4 Ω cm were obtained. The etching behaviour in hydrochloric acid and the resulting light scattering properties of the AZO films were strongly influenced by the choice of the target and the deposition conditions. The most favourable films have been successfully applied in thin film solar cells with 1.1-μm microcrystalline silicon absorber layer leading to an initial efficiency of 7.8%. © 2007 Elsevier B.V. All rights reserved. Keywords: Sputtering; Aluminum-doped zinc oxide; Ceramic target; Solar cells 1. Introduction Transparent conducting aluminum-doped zinc oxide (AZO) are used as transparent electrodes for thin film solar cells based on silicon or Cu(In,Ga)(S,Se) 2 (CIGS). The quality of solar cells strongly depends on the quality of AZO films, which have to exhibit high transparency and high electrical conductivity. Additionally for silicon thin film solar cells an adequate surface texture is necessary to introduce light scattering and subsequent light trapping to enhance the current generation [1,2]. Sputter deposition and post deposition wet chemical etching has emerged as an easy method to prepare AZO films for silicon thin film solar cell application. In the past, research was focused on radio frequency (rf) magnetron sputtering from ceramic targets [3–5]. In view of industrial processes, high-quality AZO front contacts have been developed by reactive mid-frequency (mf) magnetron sputtering using metallic targets [6–8]. The properties of reactively sputter deposited films are very sensitive to variations of the working point [7]. Thus, it may be critical to achieve homogeneous film properties on large substrates. Due to this critical issue, high rate sputtering from cost-effective ceramic targets is expected to be simpler for large- scale application. The present work has focused on the investigation of differently prepared targets to perform AZO front contacts for silicon thin film solar cells by direct current (dc) magnetron sputtering. 2. Experimental AZO films were prepared on Corning (1737) glass substrates in an in-line magnetron sputtering system (VISS 300, supplied by von Ardenne Anlagentechnik GmbH, Dresden, Germany) for 30×30 cm 2 substrate size. Four types of 10 × 75 cm 2 ceramic targets with different aluminum concentration of 0.5 wt.% or 1 wt.% were employed. The targets were prepared by three different methods, namely by the standard sintering process at high temperatures (ns), by soft sintering at lower temperature (ss) or by hot pressing (hp). Targets are labeled by the abbreviation of the target preparation process and the Available online at www.sciencedirect.com Thin Solid Films 516 (2008) 4628 – 4632 www.elsevier.com/locate/tsf ⁎ Corresponding author. Physics Department, Faculty of Science, Srinakhar- inwirot University,10110 Bangkok, Thailand. Tel.: +66 2 6641000x8568; fax: +66 2 6641000x8163. E-mail address: thanaporn_ann@yahoo.com (T. Tohsophon). 0040-6090/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.06.061