Patent ID: 8227292

Claim:
A process for the production of a MWT silicon solar cell comprising the steps: (1) providing a p-type silicon wafer with (i) holes forming vias between the front-side and the back-side of the wafer and (ii) an n-type emitter extending over the entire front-side and the inside of the holes, (2) applying a conductive metal paste to the holes of the silicon wafer to provide at least the inside of the holes with a metallization, (3) drying the applied conductive metal paste, and (4) firing the dried conductive metal paste, whereby the wafer reaches a peak temperature of 700 to 900° C., wherein the conductive metal paste has no or only poor fire-through capability and comprises (a) at least one particulate electrically conductive metal selected from the group consisting of silver, copper and nickel and (b) an organic vehicle, wherein the conductive metal paste comprises as component (c) at least one glass frit selected from the group consisting of (i) lead-free glass frits with a softening point temperature in the range of 550 to 611° C. and containing 11 to 33 wt. % of SiO 2 , >0 to 7 wt. % of Al 2 O 3 and 2 to 10 wt. % of B 2 O 3 and (ii) lead-containing glass frits with a softening point temperature in the range of 571 to 636° C. and containing 53 to 57 wt. % of PbO, 25 to 29 wt. % of SiO 2 , 2 to 6 wt. % of Al 2 O 3 and 6 to 9 wt. % of B 2 O 3 .