Aluminum-tin paste and its use in manufacturing solderable electrical conductors
View Patent ↗The present invention is directed to a paste composition comprising Al and Sn dispersed in an organic medium and to paste compositions that provide a solderable electrode. The present invention is further directed to an electrode formed from the paste composition and a semiconductor device and, in particular, a solar cell comprising such an electrode. The paste compositions that provide a solderable electrode are particularly useful for forming a solar cell back side solderable electrode.
1. A paste composition consisting of:
(a) 10-70 wt % aluminum powder having aluminum particles of particle size in the range of 0.5-10 μm;
(b) 5-85 wt % tin powder having tin particles of particle size in the range of 1-200 μm; and
(c) organic medium with 0.1-5 wt % polymer binder;
wherein said aluminum powder and said tin powder are dispersed in the organic medium and wherein the wt % are based on the total weight of said paste composition.
2. The paste composition of claim 1 , said paste composition consisting of:
(a) 15-50 wt % aluminum powder having aluminum particles of particle size in the range of 0.5-10 μm;
(b) 35-80 wt % tin powder having tin particles of particle size in the range of 10-200 μm; and
(c) organic medium with 0.1-5 wt % polymer binder;
wherein said aluminum powder and said tin powder are dispersed in said organic medium and wherein the wt % are based on the total weight of said paste composition.
3. The paste composition of claim 2 , said tin powder having tin particles of particle size in the range of 10-150 μm.
4. The paste composition of claim 1 , said paste composition consisting of:
(a) 10-25 wt % aluminum powder having aluminum particles of particle size in the range of 0.5-10μm;
(b) 65-85 wt % tin powder having tin particles of particle size in the range of 1-10 μm; and
(c) organic medium with 0.1-5 wt % polymer binder;
wherein said aluminum powder and said tin powder are dispersed in said organic medium and wherein the wt % are based on the total weight of said paste composition.
5. The paste composition of claim 4 , said tin powder having tin particles of particle size in the range of 3-10 μm.
6. A solar cell comprising:
(a) a non-solderable aluminum back side electrode containing gaps between areas of the non-solderable aluminum back side electrode; and
(b) a solderable aluminum-tin back side electrode obtained by firing a solderable aluminum-tin back side paste deposited as tabbing bus bars in the gaps between areas of the non-solderable aluminum back side electrode, said solderable aluminum-tin back side paste consisting of:
(1) 10-70 wt % aluminum powder having aluminum particles of particle size in the range of 0.5-10 μm;
(2) 5-85 wt % tin powder having tin particles of particle size in the range of 1-200 μm; and
(3) organic medium with 0.1-5 wt % polymer binder;
wherein the aluminum powder and the tin powder are dispersed in the organic medium and wherein the wt % are based on the total weight of the paste composition.
7. The solar cell of claim 6 , said tin powder having tin particles of particle size in the range of 10-150 μm.
8. A solar cell containing a front surface and a back surface, said solar cell comprising:
a solderable aluminum-tin back side electrode obtained by firing a solderable aluminum-tin back side paste covering the entire back side surface of said solar cell, said solderable aluminum-tin back side paste consisting of:
(1) 10-70 wt % aluminum powder having aluminum particles of particle size in the range of 0.5-10 μm;
(2) 5-85 wt % tin powder having tin particles of particle size in the range of 1-200 μm; and
(3) organic medium with 0.1-5 wt % polymer binder;
wherein the aluminum powder and the tin powder are dispersed in the organic medium and wherein the wt % are based on the total weight of the paste composition.
9. A solar cell containing a front surface and a back surface, said solar cell comprising:
(a) non-solderable aluminum back side electrode covering the entire back side surface; and
(b) a solderable aluminum-tin back side electrode obtained by firing a solderable aluminum-tin back side paste deposited on portions of the non-solderable aluminum back side electrode, said solderable aluminum-tin back side paste consisting of:
(1) 10-25 wt % aluminum powder having aluminum particles of particle size in the range of 0.5-10 μm;
(2) 65-85 wt % tin powder having tin particles of particle size in the range of 1-10 μm; and
(3) organic medium with 0.1-5 wt % polymer binder; wherein the aluminum powder and the tin powder are dispersed in the organic medium and wherein the wt % are based on the total weight of the paste composition.
10. The solar cell of claim 9 , said tin powder having tin particles of particle size in the range of 3-10 μm.