PERC Solar Cell Performance Predictions from Multicrystalline Silicon Ingot Metrology Data

Abstract

The influence of the as-grown material quality on the performance of multicrystalline silicon PERC solar cells is investigated using recently developed spectral photoluminescence imaging techniques on ingot level, i.e. on bricks, and is examined in conjunction with photoluminescence measurements on as-cut wafers. The effect of material parameters, including bulk lifetime, dislocation density and resistivity, are studied with regard to their effect on cell output across a sample set of three directionally solidified production bricks of widely varying bulk lifetime and dislocation density. The data is analyzed statistically using a linear mixed model. Bulk lifetime is found a highly significant predictor of the cell performance across the studied sample set confirming the predictions of computer simulations. The prediction accuracy is found greatest for material with low dislocation density where a linear correlation between cell performance and as-grown bulk lifetime is found. The dislocation densities measured on as-cut wafers remain a more accurate predictor for medium to highly dislocated material, but predictions are improved by adding bulk lifetime as an additional predictor in the model. Dislocation density measurements taken on the side facets of silicon bricks were identified as not being significant predictors for this data set. However, the detection may enable the classification of bricks into broad dislocation defect classes, which is expected to further improve the overall prediction accuracy for models using the predictor lifetime only in comparison to a non-differentiating global prediction models explored in this study. With increasing cell efficiencies and an ongoing trend of reducing the dislocation density in industrial multicrystalline wafers our findings suggest that the bulk lifetime, measurable on bricks, i.e. directly after ingot growth, becomes an increasingly relevant parameter.