Progress in laser-based foil metallization for industrial PERC solar cells

In this work we present our latest results using aluminium foil as rear side metallization for solar cells with dielectric passivation and laser fired contacts (LFC). Beside the reduction of the material costs compared to screen printed aluminum paste, it is possible to use thinner or even no SiNx capping layer on the rear side Al2O3 passivation, without a decrease in short circuit current density jsc or open circuit voltage VOC. Therefore, the superior reflection of the air gap between passivation and aluminum foil is independent from the passivation layer thickness, as previously announced. Damp-heat-test reveals that a 10 nm thin SiNx capping is sufficient to protect the rear side passivation layer from accelerated aging. With such an optimized passivation and a special front side screen printed metallization scheme without busbars, designed for multi-busbar interconnection, we achieve a cell efficiency of 21.3 % on magnetically cast Cz-Si (156×156 mm2).