Lebensdauerspektroskopie metallischer Defekte in Silicium und Analyse monokristalliner Materialalternativen

Abstract

This work was motivated by the large impact of the electrical material quality on the performance of crystalline silicon solar cells. The material quality is determined by electrically active defects in silicon. A main objective of this work was developing and improving analysing methods based on lifetime spectroscopy to increase and further complete the knowledge of electrically active metallic defects in silicon. In particular, the temperature and injection-dependent charge carrier lifetime has been investigated to determine the characteristics of metallic point defects. The spectroscopic potential of this method has been investigated and compared to other analysing methods. Additional studies were performed in correlation with the metastable boron-oxygen defect complex in boron doped monocrystalline silicon crystals. The large photovoltaic market share of Czochralski-silicon causes the economic importance of the light-induced degradation losses due to this defect. Against this background investigations were performed within the present work regarding monocrystalline silicon material alternatives to avoid light-induced degradation losses. Cell efficiency degradation could be avoided by the use of gallium doping. Nevertheless, although optimised high temperature process steps were used the oxygen contamination of the silicon played a key role regarding the achieved efficiencies. In addition float-zone silicon crystals with a small amount of oxygen contamination were investigated. This material was crystallised with a special process which is potentially suitable to significantly reduce the float-zone material price. In summary, application of the investigated materials for cell processing is a very promising alternative to increase the cell efficiency which is stable under illumination.