Impact of Wall Slip on Screen Printing of Front-Side Silver Pastes for Silicon Solar Cells

Abstract

Printing of narrow electrodes with higher aspect ratio challenges the formulation of silver paste for front-side metallization of silicon solar cells. Here, we have investigated four pastes differing in solvent composition. The onset of slip, slip velocity on steel and on emulsion over mesh (EOM) have been determined using rotational rheometry. In both cases, v increases linearly with applied stress τ . Its absolute value, the slope v/τ , and the slip layer thickness $\delta _{{{slip}}}$ vary in a wide range, depending on paste composition. Silver deposit, residual silver on the screen, the geometry of the printed electrodes, and the connections between busbar and fingers have been examined using gravimetric methods and optical microscopy. The silver deposit systematically increases, and accordingly, the residual silver on the screen decreases with increasing slip velocity. The busbar/fingers connection area narrows, whereas height and cross-sectional area of the electrodes increase with slip velocity. However, electrode width seems to be related to the pastes’ yield stress. Mass deposit, shape of the busbar/finger connection, and electrode geometry are supposed to have an important impact on cell parameters, e.g., short-circuit current and fill factor. Accordingly, our results suggest that the slip behavior of the paste affects the overall cell efficiency.