Conductive paste composition and semiconductor devices made therewith
The present invention provides a thick-film paste composition for printing the front side of a solar cell device having one or more insulating layers. The thick-film paste comprises an electrically conductive metal and an oxide composition dispersed in an organic medium that includes an organopolysiloxane and a fluorine-containing degradation agent.
1. A paste composition comprising:
an organic solids portion that comprises:
(a) a source of electrically conductive metal, and
(b) an inorganic oxide-based component, and a vehicle in which the constituents of the inorganic solids portion are dispersed, the vehicle comprising:
(c) an organopolysiloxane, wherein the organopolysiloxane comprises a copolymer having a structure represented by Formula (III):
in which each of the R 1 , R 2 , R 3 , and R 4 groups is independently selected from C1-C8 alkyl, C2-C8 alkenyl, C2-C8 alkynyl, or C6-C10 aryl groups optionally comprising one or more substituents selected from alkoxy, hydroxy, carbonyl, carboxyl, amino, epoxy, methacrylic, glycidoxy, ureido, sulfide, methacryloxy, sulfhydryl, and halogen groups, and with the proviso that the R 1 and R 4 groups are different and m and n are integers, each of which may range independently from 50 to 100,000;
(d) a fluorine-containing degradation agent; and
(e) a solvent.
2. The paste composition of claim 1 , wherein the fluorine-containing degradation agent comprises a substance having formula [M k+ ] [X − ] k , wherein M k+ is a cation with positive charge k and X − is F − or (HF 2 ) − .
3. The paste composition of claim 2 , wherein the fluorine-containing degradation agent comprises a substance having the formula M + X − , wherein M k+ is a monovalent cation and X − is F − or (HF 2 ).
4. The paste composition of claim 3 , wherein M + has the formula R 1 R 2 R 3 R 4 N + , wherein N is nitrogen and each of R 1 to R 4 is independently H or any alkyl or aryl group having 1 to 15 carbons.
5. The paste composition of claim 4 , wherein the fluorine-containing degradation agent comprises tetrabutylammonium fluoride.
6. The paste composition of claim 1 , wherein the organopolysiloxane has a number average molecular weight M n ranging from 5 to 1,000 kDa.
7. The paste composition of claim 1 , wherein the electrically conductive metal comprises silver.
8. The paste composition of claim 1 , wherein the source of the electrically conductive metal comprises 85 to 99.75% by weight of the solids.
9. The paste composition of claim 1 , wherein the oxide-based component comprises 0.25 to 15% by weight of the solids.
10. The paste composition of claim 1 , wherein the inorganic oxide-based component comprises a lead tellurium oxide glass frit that optionally comprises at least one of 0.25 to 5 wt% B 2 O 3 or 0.1 to 5 wt% Li 2 O.
11. A process comprising:
(a) providing a semiconductor substrate having opposing first and second major surfaces and comprising an insulating layer situated on the first major surface of the semiconductor substrate;
(b) applying a paste composition as recited by claim 1 onto at least a portion of the first major surface; and
(c) firing the semiconductor substrate and the paste composition under conditions sufficient for the paste composition to penetrate the insulating layer and form an electrode in electrical contact with the semiconductor substrate.
12. A photovoltaic cell precursor, comprising:
(a) a semiconductor substrate having opposing first and second major surfaces; and
(b) a paste compositions as recited in claim 1 , the paste composition being applied onto a preselected portion of the first major surface and configured to be formed by a firing operation into an electrically conductive structure comprising an electrode in electrical contact with the substrate.