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

• Published in: Electrochimica acta Vol. 106; pp. 333 - 341
• Main Authors: Chung, Bo-Mook, Cho, Sung-Bin, Chun, Jung-Woo, Kim, Young-Sik, Okamoto, Kuninori, Huh, Joo-Youl
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2013
• Subjects: Ag ionization; Borosilicate glasses; Contact; Crystalline Si solar cell; Dissolution; Firing ambience; Glass; Ionization; Lead borosilicate glass; Melts; Screen-printed Ag contact; Silver; Solubility; Lead borosilicate glass; Ag ionization; Crystalline Si solar cell; Firing ambience; Screen-printed Ag contact
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2013.05.109

•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. In order to gain further insight into the formation mechanism of fire-through Ag contacts of Si solar cells, the ionization of Ag during the dissolution of Ag powder into a lead borosilicate glass melt was electrochemically investigated at 800°C under various ambient conditions with different oxygen partial pressures (PO2). Voltammetric analyses of the Ag-free and Ag-containing glass melts confirmed that some of the Ag powder dissolved into the molten glass as Ag+ ions through interaction of the powder with oxygen in the ambient atmosphere. The concentration of Ag+ in the molten glass significantly increased with increasing PO2. The dependence of the Ag+ solubility in the molten glass on PO2 was estimated from chronoamperometric measurements for a series of glass melts containing different amounts of Ag powder. The chronoamperometry results clearly demonstrated that the solubility limit of Ag+ in the molten glass at 800°C also increased significantly with increasing PO2. The present results strongly support the mechanism proposed recently for fire-through Ag contact formation in which Ag+ ions dissolved in the molten glass play a crucial role. The present study also suggests that the reaction kinetics during the fire-through Ag contact formation is effectively controlled by adjusting PO2 in the ambient firing conditions as well as by modifying the glass chemistry to alter the solubility of Ag+ ions.