Investigations of RGS silicon solar cells

Abstract

The German government organization “Bundesanstalt für Geowissenschaften und Rohstoffe” (federal agency for geological sciences and resources) assembled a study in 2009 about the availability of the mainly used resources for energy production like coal, gas, oil and uranium. Estimating the available quantities and consumption, the study comes to the conclusion that a stable supply is only given within a range of decades. With the strong dependence of energy to industry and human civilization itself (e.g. fuel for agricultural machines) the so-called renewable energies are gaining in importance. Most of these technologies like wind power, bio-mass energy or solar thermal energy depend at least indirectly of sun radiation. Among these, photovoltaics is maybe the most elegant technology since it produces electric energy directly out of the incident sun light.For a further development of photovoltaics as a relevant energy source world-wide the competitiveness on the market has to increase. Basically, this means an enhancement of the efficiency of solar cells and a reduction of the production costs. Several approaches in ribbon silicon technologies try to prevent or lower these costs. One of these techniques is the Ribbon Growth on Substrate (RGS) process. In this approach the silicon wafers are directly casted out of the melt onto reusable substrates. Very high production rates in the order of one wafer per second can be achieved. However, the resulting material quality suffers from various crystal defects which affect the conversion efficiency.The focus of this work lies on the influence of crystal defects on the performance of RGS solar cells. Studying RGS material is not necessarily only self-sufficient. Similar defects can be found in other silicon materials, too. Investigations in the RGS crystal structure the application of modern solar cell processes may serve as example for other materials.