Role of the ambient oxygen on the silver thick-film contact formation for crystalline silicon solar cells

In order to understand the mechanism of Ag crystallite formation at the paste/Si interface, the interfacial reactions between a Ag paste containing PbO-based glass frit and an n-type (100) Si wafer during firing at 800 °C were examined by varying the oxygen partial pressure (Po₂) in the firing ambience. The formation of inverted pyramidal Ag crystallites at the glass/Si interface was attributed to the redox reaction between the Ag⁺ ions dissolved in the fluidized glass and the Si wafer. Without any oxygen in the firing ambience, no Ag crystallite was formed. The Po₂ in the firing ambience strongly affected the size and distribution of the Ag crystallites, as well as the sintering behavior of Ag powder, via its influence on the reaction forming the Ag⁺ ions. The present study results demonstrated that the ambient oxygen plays a crucial role in the formation of thick-film Ag contacts for crystalline Si solar cells.