A New Light Induced Volume Degradation Effect of mc-Si Solar Cells and Modules

In this work the performance stability of rear side passivated mc-Si solar cells and modules under carrier injection at different temperatures is investigated. Severe degradation levels of above 10% can be detected which cannot be explained by B-O complex formation or FeB pair dissociation. A high statistic of cells and modules degraded in lab and outdoor using material from different suppliers confirm the relevance of this new effect. LeTID (Light and elevated Temperature Induced Degradation) is a mc-Si bulk phenomena leading to a highly injection dependent degradation and features a regeneration phase after degradation. Characteristics of LeTID as a function of temperature and injection level are presented and a comparison between laboratory and outdoor tests is drawn. The time constant of this degradation mechanism accelerates with increasing temperature, however, the time span for degradation and regeneration of thousands of hours at relevant temperatures between 60-85°C demands for a solution on wafer material or processing side. LeTID can be significantly reduced by adapting the cell process and processing sequence.