Addressing separation and edge passivation challenges for high efficiency shingle heterojunction solar cells

We are reporting the fabrication of high efficiency Silicon heterojunction shingle solar cells with very limited performance losses related to the cell separation. A clean and innovative separation process was elaborated and optimized, based on 45° rotated silicon brick and wafers fabrication, allowing the alignment of the preferential cleavage plan (110) with the solar cells bus bars. Hence, a simple but efficient mechanical crack propagation was sufficient to insure a proper shingles cell cut. The smooth resulting solar cell edges were found to be sensitive to surface passivation technologies. Aluminum oxide layers fabricated by atomic layer deposition were specifically developed so that their activation process is fully compatible with heterojunction low temperature constraints (typically less than 220°C). Interestingly, we showed that the annealing temperature alone was not sufficient to activate such layers; alternative forming gas annealing and/or light soaking treatments were thus successfully applied instead with very high passivation values measured on bare samples. Such layers were then deposited and activated on 45° wafer based cleaved heterojunction solar cells edges. Applied for example on heterojunction shingle cell configuration, we managed to recover up to 80% of the initial efficiency loss due to the separation, limiting the overall efficiency losses to less than 0.2% absolute.