Hydrogenation of Cast-Mono Silicon Solar Cells

Abstract

Cast-mono silicon is a potential alternative to monocrystalline silicon solar cells as it produces mono-like silicon wafers using the cost effective process used for multicrystalline silicon wafers. This material has shown to have flaws in the ingot growth process which are mainly the propagation of dislocations during the casting of ingots. The crystallographic properties of these dislocations have been studied and their influence on solar cells produced from this material has been observed. In this thesis different regions of cast-mono silicon ingots (from mono-like to heavily dislocated areas) are studied using lifetime test structures and solar cells manufactured from these regions. The fundamental limitations are identified and presented using standard photovoltaic characterization methods. Hydrogenation has been introduced and implemented in this work as a method of overcoming the limiting defects caused by dislocations in cast-mono silicon. The efficacy of various hydrogenation methods is presented. Changes in the limitations identified in the previous section were observed and analyzed. The maximum benefit of hydrogenation in dislocated areas is shown in this work. Cells and lifetime test structures that were not hydrogenated and hydrogenated were light soaked at elevated temperatures to test their stability in regards to the improvement that was obtained in the dislocated regions. It was shown how stable cast-mono solar cells are before and after hydrogenation and if the benefits of hydrogenation remain after a long duration of light soaking. It was concluded that dislocations are a dominant and problematic defect in cast-mono solar cells with severe losses in the silicon bulk. Hydrogenation can be an effective method for mitigating these effects and improving the performance of cast-mono solar cells. Cast-mono solar cells degrade similar to their multicrystalline counterparts grown using the casting ingot growth method. Hydrogenation can be used to both mitigate and slow down degradation but the dislocations degrade regardless and do not recover after degradation