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  Angermann, H.: Conditioning of solar cell substrates by wet-chemical oxides: Surface morphology and electronic interface properties. In: 7th solid state surfaces and interfaces (7th SSSI), November 22-25, 2010. Smolenice Castle, Slovak Republic, 2010, p. 9-13

Abstract:
Crucial pre-conditions for the development of economically attractive solar cells are the fur-ther improvements of the energy conversion efficiency, the reduction of material consumption and the saving of manufacturing costs. Therefore the suitability and cost-effectiveness of wet-chemical cleaning and passivation methods has to be taken carefully into consideration. Presently, close to 90% of the worldwide solar cell production is based on crystalline silicon (c-Si) wafers; in the remaining market share, thin film amorphous (a-Si), micro-and nano-crystalline Si is dominating. A priceless advantage is the nearly boundless availability, the environ-mental sustainability, and the knowledge about Si, which has been accumulated in recent years in microelectronic device manufacturing. Thermally prepared Si oxide (SiO2) layers are characterized by high chemical and electrical stability and provide excellent surface passiva-tion. In Si thin film structures, which are necessary for solar cell applications, interfaces takes up a major part of the device and recombination losses due to interface defects. Moreover, on textured surfaces, which are utilized in high efficiency solar cells to enhance anti-reflection properties, the interface area and the crystallographic irregularities are increased and conse-quently surface defects become more critical to the electronic device properties of subse-quently prepared thin and ultra-thin oxide layers. It is well known from investigations of MOS devices that the quality of thin thermal oxide films strongly depends on interface micro-roughness and oxide density and that interfacial defects give rise to interface elec-tronic charges such as interface-trapped charges and fixed oxide charge . Therefore, successful applications of ultra-thin silicon oxide films in solar cells manufacturing require alternative smoothing and oxidation methods to achieve Si/SiO2 interfaces with low micro-roughness (<dr>) and low interface state density (Dit). We established correlations be-tween surface morphology, interface charge, interface defects and interface recombination losses at polished, saw damage etched and textured substrates. The effect of electronic inter-face properties on the solar cells performance is discussed for ultra-thin, differently deposited SiO2 layers and for well-directed prepared wet-chemical oxides. Also the influences of native oxides, which are unintentionally formed during wet-chemical processes, rinsing and storage in air, were investigated.