Multikristallines n-Typ-Silizium : Materialcharakterisierung und Solarzellenprozessierung

Abstract

This thesis contains the characterisation of block cast multicrystalline silicon (mc-Si) and the development of a solar cell process based on this material. Metallic impurities occuring commonly in mc-Si create recombination centers that have much lower capture cross section for holes than for electrons. This means that the lifetimes of the minority charge carrier in n-type Si should be higher compared to p-type Si containing the same concentration of impurities. The lifetime measurements presented in this work confirm this. This opens the opportunity to produce mc n-type Si solar cells with higher efficiencies than with the industrially used mc p-type Si.BBr3-Diffusion is optimised for emitter-diffusion on n-type mc-Si, showing a gettering effect of this process step, which leads to an increase of the lifetime of the minority charge carriers. In addition, the surface passivation of the emitter by thermal SiO2, SiNx and - as a new method - with SiCx is investigated. The best results are achieved with thermal SiO2, but also the results obtained with SiCx are promissing. With the new developped process a record efficiency of 15.2% is obtained on n-type mc-Si with a back-surface-field concept. Simulations show, that the very good electronic quality should lead to significantly higher efficiencies in the future.