INVESTIGATION AND MITIGATION OF LIGHT AND ELEVATED TEMPERATURE INDUCED DEGRADATION IN MULTICRYSTALLINE SILICON SOLAR CELLS.

Abstract

The efficiency of p-type multicrystalline silicon (multi-Si) PERC (passivated emitter and rear cell) solar cells is degraded upon exposure to 1-sun illumination at a temperature of above 50°C. This degradation effect aggravates at elevated temperature and is referred to as “light and elevated temperature induced degradation” (LeTID). LeTID is a serious cause of concern for the photovoltaic industry, as it can result in PERC cell efficiency losses as high as 6-14% (relative). Although several studies have been published on this problem in recent years, LeTID in multi-Si PERC solar cells is not yet well understood. Thus, this thesis studies the characteristics, kinetics and mitigation strategies of LeTID of multi-Si PERC solar cells. First, the characteristics and kinetics of LeTID and regeneration in multi-Si PERC solar cells are investigated. Methods to accelerate and annihilate the LeTID defect in the test environment are identified. Subsequently, mitigation strategies for LeTID in multi-Si PERC solar cells are proposed. Lastly, the impact of metallic impurities and hydrogen in the degradation or regeneration phase of LeTID defect formation in multi-Si wafers PERC cells is studied for the root cause analysis.