Electro-conductive pastes comprising an oxide additive
In general, the present invention relates to an electro-conductive paste comprising an oxide additive and solar cells obtainable therefrom. More specifically, the present invention relates to electro-conductive pastes, solar cell precursors, processes for preparation of solar cells, solar cells and solar modules. The present invention relates to a conductive paste composition comprising the following paste constituents: a. at least about 70 wt. % Ag particles, based on the paste; b. a vehicle; c. a glass; d. an oxide additive comprising MI, MII, and O; wherein MI and MII are different; wherein MI is selected from the group consisting of: V, Nb, Ta, Cr, Mo, W, Ge, As, Sb, Se, Te, Pb and Bi; wherein MII is selected from the group consisting of: V, Nb, Ta, Cr, Mo, W, Ge, As, Sb, Se, Te, Pb, Bi, Mn, Ce, Zn, Li, Na, K, Rb, Cs, Mg, Ca, Sr and Ba; wherein the oxide additive is crystalline according to electron back scattering diffraction (EBSD) measurement.
1. A conductive paste composition comprising the following paste constituents:
a. at least about 70 wt. % Ag particles, based on the paste;
b. a vehicle;
c. a glass;
d. an oxide additive comprising MI, MII, and O;
wherein MI is selected from the group consisting of: V, Nb, Ta, Cr, Mo, W, Ge, As, Sb, Se, Te, and Pb;
wherein MII is Bi;
wherein the oxide additive is crystalline according to electron back scattering diffraction (EBSD) measurement; and
wherein the content of the glass is at least 1 wt. % based on the paste.
2. The conductive paste composition according to claim 1 , wherein MI is selected from the group consisting of: V, Nb, Ta, Cr, Mo, W, Ge, As, Sb, Se, and Pb.
3. The conductive paste composition according to claim 1 , wherein MI is selected from the group consisting of: V, Nb, Ta, Cr, Mo, W, As, Sb, Se, and Pb.
4. The conductive paste composition according to claim 1 , wherein MI is selected from the group consisting of: V, Nb, Ta, Cr, Mo, W, Ge, Sb, Se, and Pb.
5. The conductive paste composition according to claim 1 , wherein MI is selected from the group consisting of: V, Nb, Ta, Cr, Mo, W, Sb, Se, and Pb.
6. The conductive paste composition according to claim 1 , wherein MI is selected from the group consisting of: V, Nb, Ta, Cr, Mo and W.
7. The conductive paste composition according to claim 1 , wherein MI is selected from the group consisting of: V and Mo.
8. The conductive paste composition according to claim 1 wherein the oxide additive has the general formula MI a MII b O c , wherein a, b and c are positive integers.
9. The conductive paste composition according to claim 8 , wherein the oxide is one or more selected form the group consisting of: Bi 2 (MoO 4 ) 3 , Bi 2 Mo 2 O 9 , BizMoO 6 , Bi 6 MoO 12 , BiVO 4 , Bi 4 V 2 O 11 , Bi 8 V 2 O 17 and Bi 12 V 2 O 23 .
10. The conductive past composition according to claim 1 , wherein the oxide additive further comprises MIII which is selected from the group consisting of: V, Nb, Ta, Cr, Mo, W, Ge, As, Sb, Se, Te, Pb, Bi, Mn, Ce and Zn; wherein MIII is different to both MI and MII.
11. The conductive paste composition according to claim 10 , wherein the oxide additive has the general formula MI d MII e MIII f O g , wherein d, e, f and g are positive integers.
12. The conductive paste composition according to claim 10 , wherein the oxide additive is one or more selected from the group consisting of: BiPbVO 3 , Pb 2 BiV 3 O 11 , BiPb 2 VO 6 , BiPbVO 5 and BiPb 3 V 3 O 12 .
13. The conductive paste composition according to claim 1 , wherein the oxide additive is in the range from about 0.01 to about 5 wt. %.
14. The conductive paste composition according to claim 1 , wherein the glass is in the range from 1 to about 9 wt. %.
15. The conductive paste composition according to claim 1 , wherein the content of the glass is between 1 and 9 wt. % based on the paste.
16. The conductive paste composition according to claim 1 , wherein the content of the glass is between 1.5 and 6 wt. % based on the paste.
17. The conductive paste composition according to claim 1 , wherein the content of the glass is between 2 and 4 wt. % based on the paste.
18. The conductive paste composition according to claim 1 , wherein the glass does not comprise more than about 1 wt. % Pb, based on the weight of Pb atoms and the total weight of the glass.
19. A precursor comprising the following precursor components:
a. a Si wafer having at least one p-type doped region and at least one n-type doped region; and
b. a conductive paste composition according to claim 1 superimposed on the wafer.
20. The precursor according to claim 19 , wherein the paste is superimposed on an n-type doped face.
21. The precursor according to claim 19 , wherein the face on which the paste is applied has a surface dopant concentration less than about 5*10 21 cm −3 .
22. A process for producing a solar cell comprising the following steps:
a. providing a precursor according to claim 19 ;
b. firing the precursor in order to obtain the solar cell.
23. The process according to claim 22 , wherein the temperature of the firing step b. does not exceed 870° C.
24. A solar cell obtainable by a process according to claim 22 .
25. A module comprising at least 2 solar cells, at least one of which is according to claim 24 .