Aluminum-based PVD rear-side metallization for front-junction nPERT silicon solar cells

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Aluminum-based physical vapor deposition metallization for the rear side of front-junction nPERT silicon solar cells is presented. Single-layer Al metallization is compared with Al-Si (1 at% Si) alloy and multi-layer Al-based metallization in terms of Al-spiking, specific contact resistance and back-side reflection. Al-spiking is observed when a single-layer Al metallization is used. Using an Al-Si alloy metallization, Al-spiking is avoided, however, resulting in a strong Si-precipitation. A novel approach consisting of a multi-layer Al-Si/Al stack instead of single-layer Al or Al-Si alloy metallization is developed. Optimizing the thickness of the Al-Si layer in the Al-Si/Al stack significantly decreases Si-precipitation and suppresses the Al-spiking at the same time. In addition, the optimized Al-Si/Al stack showed sufficiently low specific contact resistance and high back-side reflection and this even with a significantly higher thermal stability than the single-layer Al metallization.