Large area deposition of Al-doped ZnO for Si-based thin film solar cells by magnetron sputtering

V. Sittinger, W. Dewald, B. Szyszka

With the demand of a low cost and high quality TCO layer in thin film solar cell applications the need of a production process for ZnO:Al films suited for large area coatings in industry became apparent. Throughout the last years strong efforts have been made in order to use Al-doped ZnO films on glass as substrates for amorphous or amorphous/microcrystalline silicon solar cells. The material promises better properties compared to the conventionally used SnO2:F films due to the possibility of a tailored surface texture for optimized light trapping. With the rise of production capacities the first sputtering coaters for large area deposition of ZnO:Al are now being set up.

On lab scale, best optical and electrical properties and etch morphologies are achieved by RF sputtering of ceramic targets. With reactive magnetron sputtering it is possible to produce high quality films on large area at low target cost, while increased demands on process control of the reactive process limit process yield and reproducibility up to now. In order to fully exploit the potential of the reactive sputtering process, the optimum operation point has to be stabilized during deposition and adjusted throughout the lifetime of the targets. Nowadays even cost efficient sintered ceramic ZnO:Al2O3 targets with high conductivity can be sputtered by using DC power and thus offer an interesting alternative to the reactive process. At slightly higher costs they offer an advantage in reliability, yield and process stability. Both deposition methods will be compared and discussed with regard to silicon based thin film solar cell technologies.

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The Authors

	Dr. Volker Sittinger Fraunhofer IST Volker Sittinger studied physics at the University of Karlsruhe. From 1996 to 2001 he worked as a scientific assistant at the Institute of Solar Energy Research GmbH (ISFH) at the branch office Hannov... Read more
	Dr. Bernd Szyszka Head of Department Large Area Coating Fraunhofer IST Read more