Impact of the Crystal Structure on Solar Cell Parameters of Ribbon Growth on Substrate (RGS) Solar Cells

Abstract

Ribbon Growth on Substrate (RGS) is a cost-effective method to produce silicon wafers directly from molten silicon without material losses due to wire sawing. This technique decouples crystallization and pulling direction of the silicon wafers which results in good wafer quality at a very high production speed of about one wafer per second. The multicrystalline wafers have typical grain sizes between 0.1 mm and 0.5 mm so that spatially resolved investigations of the effect of the crystal structure on cell performance are expected to improve wafer production and cell processing. One processed RGS solar cell was measured with Light Beam Induced Current (LBIC) and Lock-In Thermography (LIT) and the data was correlated with dislocation densities and electron microscopy investigations. In regions where the as grown wafer is thinner compared to the average wafer thickness, the internal quantum efficiency shows a tendency towards lower values. This can be traced back to high defect densities introduced by mechanical stresses during casting. An Energy Dispersive X-ray (EDX) analysis revealed carbon and oxygen impurities and possible precipitates. Also metal impurities in some of the defect-rich regions were found which may affect their electronic properties.