Analysis and Reduction of Lifetime-limiting Defects in Multicrystalline Silicon

Abstract

Block-cast multicrystalline silicon is the working horse for photovoltaic devices. Multicrystalline silicon solar cells can be produced on a lower budget compared to those processed from monocrystalline material, but efficiencies are limited to a lower level by defects as impurities, grain boundaries or dislocations.The impact of different defect types is characterized in this work. Phosphorous gettering and hydrogenation are known to reduce some of these effects, but most of the underlying physical mechanisms are unknown.In this work, among other mechanisms, especially the interaction between hydrogen diffusing into the multicrystalline silicon bulk and interstitial iron is illuminated and a model explaining the observed effect is suggested.Another possibility of improving multicrystalline silicon material quality is to avoid the introduction of impurities into the crystal by using high-purity materials for the crystallization process. Therefore the quality of multicrystalline silicon grown in high-purity crucibles coated with high-purity silicon nitride is evaluated in this work.