Impact of metallization techniques on 20% efficient silicon solar cells

The damage to the Si-SiO₂ interface by electron-beam in comparison to thermal (i.e. resistive heating) evaporation of Al and Ti is investigated for oxide thicknesses ranging from 14 to 105 nm. C -V and PCD measurements on MOS test structures fabricated on 1 to 100 Ω-cm p-type FZ-silicon reveal: (1) severe damage to the interface is caused by e-beam, but not by thermal evaporation, (2) in terms of midgap interface state densities and PCD time constants the electron-beam damage is removed by a postmetallization anneal in forming gas for all oxide thicknesses, (3) a photoresist or Al layer of up to 1.6-μm yields no effective shielding. Solar cells with thick passivating oxides (105 nm) gave comparably high efficiencies above 20% for both metallization techniques