Screen printable Ag-Al metal pastes for p+ silicon application in solar cells

In this work, we present the development of a new series of screen printable metal contact pastes for p+ doped Si surfaces in solar cells. The p-surface contact metallization is needed for new devices based on n-type wafers and for bifacial cells. The pastes discussed in this paper are lead-free and phthalate-free to address health and environmental concerns. The new series of pastes not only satisfy this expectation but also meet viscosity and printability requirements as well as performance related parameters such as contact resistance. A series of conductive pastes was formulated by varying metal components and glass chemistry. A sequence of analytical experiments was performed to identify the correlation between the paste chemistry and electrical characteristics including bulk resistivity and contact resistance. A cross section SEM study was conducted to identify a potential contact mechanism that reveals a correlation between the metal paste uniform shape spikes and contact resistance.