Tunnel Oxides Formed by Field-induced Anodization for Silicon Solar Cell Passivation

Abstract

High-quality tunnel oxide layers play a key role as an interfacial layer in a number of high-efficiency silicon solar cell designs. They need to be sufficiently thin to allow carriers to tunnel through and be homogenous and stoichiometric across the silicon wafer surface to ensure low recombination velocities if high efficiencies are to be achieved. This paper reports on the formation of ultra-thin silicon oxide layers by field-induced anodization (FIA), a process which intrinsically ensures uniform oxide thickness as the film is grown by passing a current perpendicularly through the silicon wafer to the surface that is anodised. The FIA oxides contain a lower fraction of Si-rich sub-oxides compared to wet-chemical oxides, resulting in lower interface recombination velocities. The broader energetic distribution of interface trap states and reduced capture cross section as a result of forming gas annealing is able to further reduce recombination at the siliconoxide interface. Due to its low-temperature requirements, FIA has the potential to be used to form low-cost tunnel oxide layers for a range of silicon solar cell designs.