Influence of oxygen on Ag ionization in molten lead borosilicate glass during screen-printed Ag contact formation for Si solar cells

•Ag ionization in a glass melt was examined at 800°C under various ambient conditions.•Ag dissolves as Ag+ ions into the molten glass via reaction with ambient oxygen.•Ag+ solubility in the molten glass depends on the oxygen partial pressure.•Reduction potential of Ag+ is much nobler than that of Pb2+ in the molten glass.•Role of Ag+ in the screen-printed Ag contact formation is verified.