Stacked PECVD backside dielectrics : an option for a firing stable passivation of industrial type screen-printed silicon solar cells

Abstract

On the way to higher efficiencies and reduced costs material quality has to increase while wafer thickness decreases. With industrial screen-printed Cz solar cells reaching above 19% efficiency [1] the wellestablished Al-BSF is a limiting factor for further improvement. Simple and cost effective to deposit dielectrics with good characteristics for backside passivation have to be found. Our approach is a multilayer stack-system consisting of amorphous silicon carbide (SiCx), silicon oxide (SiO2) and silicon nitride (SiNx). This system enables us to achieve a low surface recombination velocity of 7.6 cm/s although a transparent SiCx layer with high carbon content (CH4/SiH4 flow rate of 8) is used. SiCx passivates n- and p-doped silicon at high deposition rates and low deposition temperatures. The cross compatibility of the used dielectrics enables us to deposit the stack system within one deposition step.