Low resistance TiO_2-passivated calcium contacts to for crystalline silicon solar cells

摘要

It has recently been shown that low resistance Ohmic contact to lightly doped n-type crystalline silicon (c-Si) is possible by direct metallization via a thin layer of the low work function metal calcium (? ~2.9 eV) and an overlying aluminium capping layer. Using this approach upper limit contact resistivities of < 2 mΩcm~2 can be realised on undiffused n-type surfaces. However, recombination at the Ca / Si interface limits the application of the Ca contact to very low contact fractions which leads to non-negligible resistive losses and an increase in device fabrication complexity. Here we show that the low resistance Ohmic contact of the Ca / Al structure is retained after the addition of a TiO_2 interlayer, leading the way to the development of a passivated contact device utilizing TiO_2 and Ca.