Conductive paste composition and semiconductor devices made therewith
A conductive paste composition contains a source of an electrically conductive metal, a first oxide component, a second, non-oxide, magnesium-containing component, and an organic vehicle. An article such as a high-efficiency photovoltaic cell is formed by a process of deposition of the paste composition on a semiconductor device substrate (e.g., by screen printing) and firing the paste to remove the organic vehicle and sinter the metal and establish electrical contact between it and the substrate.
1. A paste composition, comprising:
an inorganic solids portion that consists of:
(a) a first oxide component,
(b) a second component that is a magnesium silicide, and
(c) a source of an electrically conductive metal consisting essentially of Ag, Au, Cu, Ni, Pd, Pt, or a mixture or alloy thereof; and
an organic vehicle in which the constituents of the inorganic solids portion are dispersed,
and wherein the first oxide component is a lead-containing oxide.
2. The paste composition of claim 1 , wherein the second component is present in an amount ranging from 0.05% to 7.5%, as measured by weight percentage of the paste composition.
3. The paste composition of claim 1 , wherein the first oxide component is present in an amount ranging from 0.1% to 10% by weight of the paste composition.
4. The paste composition of claim 1 , wherein the source of the electrically conductive metal comprises Ag powder.
5. The paste composition of claim 1 , wherein the electrically conductive metal is substantially Al-free.
6. A process for forming on a substrate an electrically conductive structure comprising at least one electrode, the process comprising:
a) providing a substrate having opposed first and second major surfaces with an insulating layer present on at least the first major surface;
b) applying a paste composition of claim 1 onto a preselected portion of the first major surface; and
c) firing the substrate and the paste composition thereon for a time and at a temperature sufficient to form the electrically conductive structure with electrical contact established between the at least one electrode and the preselected portion.
7. The process of claim 6 , wherein the preselected portion consists essentially of p-type semiconductor material.
8. The process of claim 6 , wherein:
a) the electrically conductive structure comprises electrically separate first and second electrodes;
b) the preselected portion comprises separate first and second subportions that consist essentially of p-type and n-type semiconductor material, respectively;
c) the paste composition is applied onto both the first and second subportions; and
d) the firing forms the electrically conductive structure, with electrical contact established between the first electrode and the first subportion and between the second electrode and the second subportion.
9. The process of claim 6 , wherein:
a) the electrically conductive structure comprises electrically separate first and second electrodes respectively located on the first and second major surfaces;
b) the process further comprises applying the paste composition onto a preselected portion of the second major surface; and
c) the firing forms the electrically conductive structure, with electrical contact established between the first electrode and the preselected portion of the first major surface and between the second electrode and the preselected portion of the second major surface,
and wherein the preselected portion of the first major surface consists essentially of p-type semiconductor material and the preselected portion of the second major surface consists essentially of n-type semiconductor material.
10. An electrically conductive structure comprising an electrode contacting a p-type region of a silicon semiconductor, the electrically conductive structure having been formed by the process of claim 6 .
11. A photovoltaic cell comprising a substrate and an electrically conductive structure thereon, the article having been formed by the process of claim 6 .
12. A photovoltaic cell comprising a substrate and an electrically conductive structure thereon, the article having been formed by the process of claim 8 .
13. A photovoltaic cell comprising a substrate and an electrically conductive structure thereon, the article having been formed by the process of claim 9 .
14. A photovoltaic cell precursor, comprising:
a) a substrate having opposed first and second major surfaces; and
b) a paste composition as recited by 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.
15. The photovoltaic cell precursor of claim 14 , wherein:
a) the preselected portion comprises separate first and second subportions that consist essentially of p-type and n-type semiconductor material, respectively;
b) the paste composition is applied onto the first and second subportions and configured to be formed by the firing operation into the electrically conductive structure comprising electrically separate first and second electrodes in electrical contact with the first and second subportions, respectively.
16. The photovoltaic cell precursor of claim 14 , wherein:
a) the conductive structure comprises electrically separate first and second electrodes respectively located on the first and second major surfaces;
b) the paste composition is further applied onto a preselected portion of the second major surface such that the paste composition is further configured to be formed by the firing operation into a second electrode electrically separated from the first electrode, the first and second electrodes being in electrical contact with the preselected portions of the first and second major surfaces, respectively,
and wherein the preselected portion of the first major surface consists essentially of p-type semiconductor material and the preselected portion of the second major surface consists essentially of n-type semiconductor material.
17. The paste composition of claim 1 , wherein the first oxide component is a lead borate oxide composition in which the lead and boron cations together comprise at least 50% of the total cations.
18. The paste composition of claim 1 , wherein the first oxide component is a lead silicate oxide composition in which the lead and silicon cations together comprise at least 50% of the total cations.
19. The paste composition of claim 1 , wherein the second component is Mg 2 Si.
20. The paste composition of claim 2 , wherein the second component is present in an amount ranging from 0.05% to 3%, as measured by weight percentage of the paste composition.