Symmetrical Al sub(2)O sub(3)-based passivation layers for p- and n-type silicon

The Al[sub 2]O[sub 3] nanolayers, as currently used in the solar industry, provide excellent passivation over the entire injection level range for p-type Si. A high concentration of negative fixed charges guarantees excellent field effect passivation. However, on n-type Si, those fixed charges create an inversion layer at the surface, which opens an additional near-surface recombination channel. This results in a reduced minority carrier lifetime at low injection levels, which is the operation condition of solar cells. In this work, a passivation layer stack is presented, showing excellent performance within the complete injection level range symmetrically for both p- and n-type Si. This layer stack consists of 20 nm Al[sub 2]O[sub 3] combined with a thin Hf)[sub 2] or SiO[sub 2] interface. The comparison of both passivation stacks shows that the introduction of an ultrathin HfO[sub 2] interface is the most promising approach to achieve a symmetrical passivation layer for p- and n-type Si.