Surface passivation of phosphorus-diffused emitters by inline thermal oxidation

We show that inline thermal oxidation is a very promising alternative to the use of conventional batch type quartz tube furnaces for the passivation of industrial phosphorus-diffused emitters. Our results reveal that both inline and batch oxidation allow similar results for oxide layer thickness, sheet resistance and, most important, emitter dark saturation current density J0e even when compressed dry air is used as a cost effective oxygen source. Using a ∼10 nm thin thermal oxide layer and a SiNx antireflection coating of adapted thickness, we achieve J0e values as low as ∼100 fA/cm2 (68 Ω/sq., textured surface). Using a simple inline oxidation process in air ambient, solar cells with a conventional Al-BSF rear side and a thermal SiO2/SiNx passivated front yield average efficiencies of 18.1%, demonstrating 0.3% absolute efficiency gain compared to solely SiNx passivated emitter references.