POCl₃ diffusion with in-situ SiO₂ barrier for selective emitter multicrystalline solar grade silicon solar cells

Abstract

We present an innovative process for the formation of a selective emitter by using an advanced phosphorous glass as a barrier layer against subsequent diffusion. The advanced barrier glass was achieved by the formation of a standard phosphorous glass treated with additional thermal oxidation immediately after deposition in the same process tube. The resistant layer is used as a barrier for the second diffusion after selective opening of the finger contact areas by screen printing of a SiO2 etching paste. The process was applied for multicrystalline Elkem Solar SoG-Si wafers as well as for references from standard EG-Si. The achieved cell parameters were compared with cell results from a homogenous emitter process. While the efficiency was not enhanced so far due to the relatively high shadow loss of the selective emitter solar cells, the open collector voltage could be increased by up to 9 mV and the short wavelength spectral response increased slightly with this selective emitter. The aim of this work was to combine the SiO2 barrier with the shallow POCl3 diffusion in one process step and the optimization of the screenprinting process for selective emitter solar cells.