Field-induced anodization for silicon solar cell passivation

Anodic aluminium oxide formed on silicon wafers can passivate phosphorus-doped silicon surfaces. We describe here a new method for forming these layers which involves forward-biasing a solar cell such that the n-type surface becomes anodic. Aluminium, deposited on the n-type silicon surface over a thin tunnel oxide, can be anodized to form a porous layer. However, unlike anodization processes where the aluminium is physically contacted, increases in effective minority carrier lifetime were only observed after a subsequent anneal at 400 °C in an industrial belt furnance. Anodic aluminium oxide layers formed over n-type silicon surfaces may find applications as rear surface passivation layers for n-type cells. Furthermore, the process can be adapted to the anodization of silicon and thus provide a low temperature method of forming thin silicon dioxide layers which are commonly-used in conjunction with other passivation layers.