Screen printing metallization of boron emitters

This paper analyzes the influence of the composition of screen printing metal pastes on contacting boron emitters for crystalline silicon solar cells, optimized on the basis of commercial Ag-paste Ferro 3347 by adding silicon and aluminum. Aluminum provides a lower contact resistance, while silicon prevents the spiking and alloying of aluminum with the silicon of the Substrate. The best pastes have turned out to be high Si-concentrated, which have provided a final specific contact resistance of 3-4 m Omega cm(2) on screen printed boron emitters diffused at 1000 degrees C for 8 min, with shunt conductance lower than 0.6 mS/cm(2). The final fill factors have been better than 77.5% and open circuit voltages have exceeded 605 mV on Czochralski (Cz) n type 0.7 Omega cm solar cells. These results have proven the feasibility of our screen printing process for P(+)nn(+) structures. Copyright (C) 2009 John Wiley & Sons, Ltd.