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 J 0e 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 /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.