Iron contamination in silicon solar cell production environments

The fundamental mechanisms of iron impurities in silicon have been thoroughly studied and are well explained in the literature. Of interest to solar cell manufacturers is to understand how these mechanisms manifest in a production environment and, more importantly, how to quickly diagnose and mitigate iron contamination as it occurs. This paper presents examples of iron contamination using p-type CZ wafers processed in production-style environments. The impact of iron on the IV performance of industrial screen printed solar cells is presented, including the time dependence of these effects and how they manifest in the various characterisation techniques that are typically used to diagnose solar cell performance. Examples are given of potential sources of iron contamination and the impact of subsequent processing on the redistribution of those contaminants. The paper demonstrates that iron contamination can occur in a variety of ways, can spread quickly and is severely detrimental to solar cell efficiency. Additionally, it is shown that the fundamental properties of iron in silicon can be used to quickly identify the root cause of contamination in a production environment.