Removing the effect of striations in n-type silicon solar cells

Abstract

Several industrial n-type Czochralski silicon ingots were analysed on wafer and cell levels with ECN׳s bifacial n-type solar cell process. In some of the ingots, the solar cell performance in the very top drop of about 1% absolute with respect to cell from the middle part of the ingot. These cells show typical ring shaped pattern. After receiving a post-process anneal treatment at 200°C, the efficiency nearly completly recover. We demonstrated that the improvement is due to bulk lifetime enhancement. The recovery is stable in storage conditions, under illumination and high temperature treatments up to 600°C. The same effect cannot be reproduced in p-type Cz silicon solar cells with similar ring shaped patterns. This indicates that the defects responsible for lifetime and efficiency degradation in wafers affected by ring patterns differ in n-type and p-type.