N-Type, Ion-Implanted Silicon Solar Cells and Modules

Ion-implanted, screen-printed, high-efficiency, stable, n-base silicon solar cells fabricated from readily available 156-mm pseudosquare Czochralski wafers are described, along with prototype modules assembled from such cells. Two approaches are presented. The first approach, which involves a single phosphorus implant, has been used to produce cells (239 cm²) having a tight distribution of J_sc, V_oc, and fill factor over a wide range of wafer resistivity (factor of 10), with Fraunhofer-certified efficiencies up to 18.5%. In spite of the full screen-printed and alloyed Al back, a method has been developed to solder such cells in a module. The second approach, which involves implanting both phosphorus for back-surface field (BSF) and boron for front emitter, has been used to produce n-base cells having local back contacts and dielectric (SiN_x/SiO₂) surface passivation. Efficiencies up to 19.1%, certified by Fraunhofer, have been realized on 239-cm² cells. A method is also presented to express recombination activity in the cell base as a component of total reverse saturation current density. This allows recombination activity in all three regions of the cell (n⁺ region and its surface, n-base, and p⁺ region and its surface) to be compared as components of the total cell J₀ to aid in maximizing V_oc.