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2010
Conference Paper
Titel
The role of material quality in EWT and standard solar cells on multicrystalline standard and UMG silicon material
Abstract
Industrial multicrystalline silicon solar cells are frequently limited in the conversion efficiency by a moderate electrical material quality. Small carrier diffusion lengths cause losses e.g. in the open circuit voltage. A suitable cell design for high efficient solar cells on such a material is the EWT (Emitter Wrap Through) cell concept where the mean distance for excess carriers to the pn junction is significantly shorter than in typical industrial solar cells. We present experimental results on the material quality at different processing steps and its improvement by optimized high temperature processing. A comparison between standard multicrystalline (mc) silicon and silicon from upgraded metallurgical feedstock (umg-mc) is presented where we focus on the specific impurity contents (by NAA analyses) and differences in the crystal quality. The impact of material quality on the cell performance in both, EWT and standard cell architecture, is addressed by multidimensional numerical simulations. Simulations of cell parameters for the standard cell concept are given together with experimental cell results.
Author(s)