Impact of Screen-Printed Pure Copper Pastes on Silicon Heterojunction Solar Cells

Abstract

Screen-printing of pure copper pastes is an attractive method to totally substitute silver in silicon heterojunction (SHJ) solar cells, in order to reduce their manufacturing costs and dependence to scarce raw materials. However, copper is known to be a fast diffuser in crystalline silicon and create recombination active defects, while few knowledges are available on its behavior in SHJ structure without barrier layer. Here, we investigate the impact of two commercial pure copper screen-printing pastes, deposited on the amorphous silicon doped layers, either on the front (n-side) or on the rear side (p-side) of SHJ precursors and annealed at 200 °C. Compared to precursors with silver paste reference or silver-coated copper paste that degrade through time because of a-Si ageing in air, the tested pure copper pastes induce a strongly side-dependent degradation measured by PCD carrier lifetime and photoluminescence (PL), with a larger degradation for a p-side deposition. Furthermore, the degraded area and the strength of the impact depends on the paste used. The strong difference of impact between the two deposition sides was shown to be due to the formation of 100-200 nm large copper oxide particles at the surface of a-Si(p) layers for p-side printed cells. This work helps better understanding copper behavior in SHJ stack and highlights a reduced contamination risk with pure copper pastes deposited on the n-side of SHJ cells without barrier layer.