Towards 20 solar cell efficiency using silicon from metallurgical process route

摘要

In this work we present high efficient silicon solar cells based on low-cost UMG-Si purified by the metallurgical process route of Elkem Solar with efficiencies close to 20 %. Solar cells were fabricated by two different PERC solar cell process sequences using only processes steps which are already well-known in industry and transferable to mass production. Simultaneously solar cells were fabricated by the state-of-the-art full Al-BSF process as reference. The investigated wafers were cut from a Cz grown crystal based on UMG-Si blended with 40 % poly silicon and were compared to 100 % poly-Si wafers. It is shown that applying PERC processes to the silicon wafers can enhance the cell efficiency by 0.8 % absolute to reach average cell efficiencies of 19.8 % and thus demonstrates the excellent quality of the fabricated c-Si solar cells. Furthermore it is proven that UMG-Si does not show feedstock-related limitations to high efficiency concepts such as the PERC process. To our knowledge these results present the highest obtained cell efficiencies for silicon solar cells based on UMG-Si so far. Studies of light induced degradation of PERC and full Al-BSF solar cells from both kinds of feedstock were conducted to determine the influence of recombination active boron-oxygen complexes on the respective solar cell performance. The obtained results reveal higher losses for PERC solar cells, which can be explained by the higher sensitivity of PERC solar cells to changes of the bulk lifetime. This is also confirmed by PC1D simulations.