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1066-A06-01

Polycrystalline Silicon Thin-film Solar Cells on ZnO:Al Coated Glass Christiane Becker, Pinar Dogan, Benjamin Gorka, Florian Ruske, Tobias Hänel, Jan Behrends, Frank Fenske, Klaus Lips, Stefan Gall, and Bernd Rech Dep. Silicon Photovoltaics, Helmholtz-Zentrum Berlin für Materialien und Energie (formerly Hahn-Meitner-Institut Berlin), Kekulestr. 5, Berlin, 12489, Germany ABSTRACT Thin film solar cells based on polycrystalline silicon are an appealing option combining the advantages of thin film technologies, namely low cost, and the superior electrical properties of crystalline silicon. The specific structure aimed at in this work uses the relatively simple contacting scheme used in amorphous silicon thin film solar cells which relies on a front contact consisting of a transparent conducting oxide (TCO). Electron-beam evaporation is applied as preparation method for the silicon films with high deposition rate. Solid phase crystallization (SPC) is used to crystallize the silicon films after deposition. In this work the properties of as-deposited and crystallized silicon films produced by e-beam evaporation are investigated as a function of deposition temperature. It is shown that the largest crystallites are obtained for deposition around 300°C and subsequent treatment at 600°C, while deposition at higher temperatures leads to small crystal grains which are not changed significantly during SPC. Solar cells have been prepared on TCO-coated glass and were studied by measurements of the external quantum efficiency.

INTRODUCTION Thin film solar cells based on silicon usually use amorphous and/or microcrystalline silicon layers as absorbers. Tandem solar cells consisting of two stacked thin film solar cells currently reach stabilized efficiencies of about 10 %. An appealing alternative is the use of thin crystalline films as absorbers as, unlike amorphous silicon, they do not suffer from light-induced degradation. The main challenge is the formation of high quality films with a thickness of a few micrometers on a low cost substrate at high deposition rate and low temperatures. The desired substrate for this type of solar cells is glass, which limits the feasible process temperatures to around 600°C. At these temperatures, films of amorphous silicon are transformed into polycrystalline silicon by solid phase crystallization (SPC). This concept has already been used over ten years ago by Sanyo to produce a single junction solar cell with a conversion efficiency of almost 10% [1]. CSG Solar has recently shown mini-modules of 10 x 10 cm2 with an efficiency of 10.4% [2]. A key technological challenge is the formation of suitable contacts to the device. While CSG uses a sophisticated scheme of point contacts, thin film technology based on amorphous silicon uses a simple design, which is based on a TCO (transparent conductive oxide) front contact and laser scribing for integrated series connection of solar cells. This work aims at the formation of poly-Si thin film solar cells on TCO-coated glass substrates by SPC i