Ž . Thin Solid Films 392 2001 327333 Upscaling of texture-etched zinc oxide substrates for silicon thin film solar cells J. Muller a,  , G. Schope a , O. Kluth a , B. Rech a , M. Ruske b , J. Trube c , B. Szyszka d , ¨ ¨ X. Jiang d , G. Brauer d ¨ a ( ) Institute of Photo oltaics IPV , Research Center Julich GmbH, D-52425 Julich, Germany ¨ ¨ b Applied Films GmbH and Co. KG, Research and De  elopment, Siemensstr. 100, D-63755 Alzenau, Germany 1 c ( ) Balzers Process Systems GmbH BPS , Siemensstr. 100, D-63755 Alzenau, Germany d ( ) Fraunhofer Institute for Surface Engineering and Thin Films IST , Bienroder Weg 54 E, D-38108 Braunschweig, Germany Abstract Ž 2 . Large area 320 400 mm glassZnO-films were prepared by high-rate d.c. magnetron sputtering from ceramic targets and compared to lab-type r.f.- and m.f.-sputtered ZnO. The very uniform and initially smooth films exhibit excellent electrical and Ž 4 . optical properties resistivity 5 10  cm, transmission 80% for visible light and 1500-nm thick films . Upon etching in Ž . diluted hydrochloric acid they develop a surface texture. Independent of sputter technique d.c. or r.f. and substrate size, higher substrate temperatures and lower sputter gas pressures have a similar influence on the film structure and lead to more robust and etch-resistant films. Showing excellent light scattering properties, amorphous silicon pin solar cells prepared on these large area glassZnO samples exhibit initial efficiencies up to 9.2%, proving the viability of sputtered and texture-etched ZnO as TCO-substrate for industrial solar module production.  2001 Elsevier Science B.V. All rights reserved. Keywords: Silicon; Solar cells; Sputtering; Zinc oxide 1. Introduction Ž . Transparent conductive oxides TCOs are an inte- gral part of silicon thin film solar cells. In the pin- Ž . superstrate structure the TCO used as a front contact material has to combine low series resistance, high transparency and an adequate surface texture. The latter property is essential both to minimize reflection losses at the front side and to enhance the optical path length within the solar cell by scattering and subse- quent trapping of the incident light. While on labora- tory-scale high-quality glassSnO :F-substrates with 2 excellent light-scattering properties are available, large-area module manufacturing so far has to rely on Ž . fluorine-doped SnO -substrates SnO :F possessing 2 2  Corresponding author. Ž . E-mail address: joa.mueller@fz-juelich.de J. Muller . ¨ 1 Ž . Formerly Balzers Process Systems GmbH BPS . BPS used throughout text. less favorable light trapping properties and hence limit- ing the cell performance. The availability of a high- quality, low-cost and large area TCO-substrate would lead to a significant improvement in module efficiency. Ž . In recent years, doped zinc oxide ZnO films have emerged as an alternative to SnO :F on laboratory 2 scales. As substrates for solar cell applications, rough boron doped ZnO:B films have been prepared for example by low pressure chemical vapor deposition Ž .   LPCVD 1,2 . Another method is r.f.- or d.c.-mag- netron sputtering from mostly aluminum doped cer- Ž . Ž . amic ZnO:Al O or metallic Zn:Al targets. The 2 3 sputtering process leads to smooth ZnO films, which can be easily textured by a post-deposition chemical  etching step 3 . Sputtered and texture-etched ZnOAl combines low resistivity and high optical transmittance with excellent light trapping properties for long wave- lengths. Solar cells on these substrates yield high  stabilized efficiencies 4 . The next step towards an industrial mass production of Si thin film solar cells on 0040-609001$ - see front matter  2001 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 4 0 - 6 0 9 0 01 01052-5