Ruske, F.; Schönau, S.; Ring, S.; Neubert, S.; Stannowski, B.; Sittinger, V.; Götzendörfer, S.; Rech, B.: Material properties of high-mobility TCOs and application to solar cells. In: Ferechteh H. Teherani ... [Ed.] : Oxide-based Materials and Devices V : 2 - 5 February 2014, San Francisco, California, United States . SPIE, 2014 (Proceedings of SPIE ; 8987). - ISBN 978-0-8194-9900-4, p. 898723/1-9
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The benefit of achieving high electron mobilities in transparent conducting oxides (TCOs) is twofold: they first exhibit superior optical properties, especially in the NIR spectral range, and secondly their low resistivity enables the usage of thinner films. Remarkably high mobilities can be obtained in Al-doped zinc oxide by post-deposition annealing under a protective layer. The procedure has not only shown to increase mobility, but also strongly reduces sub-bandgap absorption. Extensive optical, electrical and structural characterization is carried out in the films in order to clarify the microscopic origins of the changes in material properties. While the annealing of defect states, most likely deep acceptors, seems clear, earlier results also suggest some influence of grain boundaries. Tailing, on the contrary, seems to be linked to extended defects. In application to a-Si:H/µc-Si:H thin film solar cells the films have already shown to increase spectral response. When reducing the film thickness, the main challenge is to provide a suitable light trapping scheme. Normally this is achieved by a wet chemical etching step in diluted HCl, which provides a surface structure with suitable light scattering properties. Therefore a TCO-independent light scattering approach using textures glass was applied in conjunction with the high mobility zinc oxide. The substrate enables the use of very thin TCO layers with a strongly reduced parasitic absorption.