Degradation of multicrystalline silicon solar cells and modules after illumination at elevated temperature

Abstract In this work the performance stability of rear side passivated multicrystalline silicon solar cells and modules under carrier injection at different temperatures is investigated. Compared to most other tests the degradation procedure were extended to significantly longer time periods and include relevant module temperatures in field. Severe power degradation levels of above 10% can be detected after several hundred to thousand hours (corresponding ~5–20 years depending on the location) which cannot be explained by B–O complex formation or FeB pair dissociation. After detection of this light induced degradation at temperatures above 50°C the common abbreviation LID was renamed and state more precisely Light and elevated Temperature Induced Degradation (LeTID). A high number of cells and modules degraded in laboratory and outdoor using material from different wafer suppliers confirm the relevance of this effect. LeTID is a multicrystalline silicon bulk phenomenon leading to a highly injection dependent lifetime characteristic after degradation and features a regeneration phase after degradation. 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 and 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.