New paper on the oxygen content of CuGa thin films
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Impurities in the CIGS layer lower the efficiency of the solar cell. Although a small proportion of oxygen is present in all sputtering targets, the actual quantity varies depending on the manufacturing process. The oxygen content is lower in cast targets than in targets manufactured using powder metallurgical techniques which, however, possess a significantly improved microstructure. "Our investigations were driven by the question whether the higher oxygen content in powder metallurgical targets also has an impact on the sputtered layers, or not." explains Christian Linke, R&D project manager at Plansee. A sputtering test using a cast target showed that the oxygen content of the film was 200 times greater than that of the target. In the case of powder metallurgical targets, the level of impurities increased by a factor of 2, with the result that the oxygen content in the sputtered films was practically identical for the two manufacturing methods (approximately 0.4 atomic percent). The oxygen content is therefore determined mainly by the residual gas in the sputtering chamber. The higher oxygen content of powder-metallurgical CuGa targets is therefore not critical for the production of CuGa precursor films.
As a result, customers can take full advantage of powder metallurgical targets compared to cast targets: An extremely fine-grained microstructure which leads to a more homogeneous gallium distribution in the film. This significantly improves process stability – which has been confirmed by a comparative study in a pilot production system.
Would you like all the details? The detailed research results can be found in the Proceedings of the 28th EU-PVSEC 2013 published under the title “Chemical purity of copper-gallium thin films deposited from different sputtering targets”.