Understanding and Development of Ag Pastes for Silicon Solar Cells with High Sheet-Resistance Emitters

Abstract

The effect of different properties of the inorganic constituents of the Ag paste used for the front metal grid is investigated for high sheet-resistance emitters. Our results show that both glass frit chemistry and Ag particle size are important for achieving good quality ohmic contacts to high sheet-resistance emitters. The melting characteristics of the glass frit determine the firing scheme suitable for low contact resistance and high fill factors (FFs). In addition, small to regular Ag particles were found to help achieve a higher open-circuit voltage (V(oc)) and maintaining a low contact resistance. P self-doping from the paste was not necessary for good contacts to high sheet-resistance emitters for the rapid firing schemes in this paper. High FFs (>0.78) were achieved on untextured FZ Si cells using rapid firing in a lamp-heated belt-furnace with efficiencies of up to 17.4% on a 100 Ω/sq emitter. This corresponds to an efficiency improvement of ~0.3% absolute over the 45 Ω/sq emitter cells.