Understanding process-related efficiency variations in mc-Si PERC cells

摘要

This paper introduces and explains a simulation-assisted approach for determining and ranking the most influential causes of variations in experimentally obtained solar cell efficiencies, using the example of an industrially feasible multicrystalline silicon (mc-Si) passivated emitter and rear cell (PERC) process. With the objectives of being independent of material variations and of analysing process-related impacts only, 51 neighbouring high-performance mc-Si wafers are distributed in an experiment in which more than 800 mc-Si PERC cells in total are processed, and this sub-group is comprehensively characterized. The elevated data serve as input for modelling the resulting distribution of cell efficiencies on the basis of numerical 3D simulations, metamodelling and Monte Carlo runs. In order to understand the most detrimental impacts responsible for a widening of this distribution, a variance-based sensitivity analysis is conducted, where the parameters are ranked according to their impact on the total variance of cell efficiencies. In this case, it is possible to explain over 80% of the measured total variance; moreover, the rear-side passivation and a wrap-around during the emitter etch-back process can be identified as responsible for 80% of the variance. The approach presented is especially helpful for ramping up PERC production; however, since it is basically transferable to any solar cell concept, it can also be applied to optimize established production lines.