Aluminum pastes and use thereof in the production of silicon solar cells

1. An aluminum paste comprising particulate aluminum and an organic vehicle comprising organic solvent(s), wherein the particulate aluminum comprises 50 to 90 wt. % of spherical-shaped aluminum powder and 10 to 50 wt. % of nodular-shaped aluminum powder, the wt. % being based on the sum of the spherical-shaped aluminum powder and the nodular-shaped aluminum powder, wherein both the spherical-shaped aluminum powder and the nodular-shaped aluminum powder have a D50 particle size of 4 μm to 12 μm.

2. The aluminum paste of claim 1 , wherein the particulate aluminum comprises 50 to 75 wt. % of spherical-shaped aluminum powder and 25 to 50 wt. % of nodular-shaped aluminum powder, the wt. % being based on the sum of the spherical-shaped aluminum powder and the nodular-shaped aluminum powder.

3. The aluminum paste of claim 2 , wherein the particulate aluminum comprises 60 to 70 wt. % of spherical-shaped aluminum powder and 30 to 40 wt. % of nodular-shaped aluminum powder, the wt. % being based on the sum of the spherical-shaped aluminum powder and the nodular-shaped aluminum powder.

4. The aluminum paste of claim 1 , wherein the sum of spherical-shaped plus nodular-shaped aluminum powder accounts for more than 90 wt. % of the particulate aluminum.

5. The aluminum paste of claim 1 , wherein the sum of spherical-shaped plus nodular-shaped aluminum powder accounts for 100 wt. % of the particulate aluminum.

6. The aluminum paste of claim 1 , wherein the particulate aluminum is present in a proportion of 50 to 80 wt. %, based on total aluminum paste composition.

7. The aluminum paste of claim 1 additionally comprising one or more glass frits in a total proportion of 0.01 to 5 wt. %, based on total aluminum paste composition.

8. The aluminum paste of claim 1 , wherein the organic vehicle further comprises organic polymer(s) and/or organic additive(s).

9. A process of forming a silicon solar cell comprising the steps:

(i) applying an aluminum paste of claim 1 on the back-side of a silicon wafer having a p-type region, an n-type region and a p-n junction, and

(ii) firing the surface provided with the aluminum paste, whereby the wafer reaches a peak temperature of 700 to 900° C.

10. The process of claim 9 , wherein the application of the aluminum paste is performed by printing.

11. The process of claim 9 , wherein firing is performed as cofiring together with other front-side and/or back-side metal pastes that have been applied to the silicon wafer to form front-side and/or back-side electrodes thereon during firing.

12. A silicon solar cell comprising an aluminum back electrode wherein the aluminum back electrode is produced making use of an aluminum paste of claim 1 .

13. The silicon solar cell of claim 12 , further comprising a silicon wafer.