Solar cell having Ti- or Ta-containing thermal and diffusion barrier layer for foil-based metallization
Methods of fabricating solar cells using a metal-containing thermal and diffusion barrier layer in foil-based metallization approaches, and the resulting solar cells, are described. For example, a method of fabricating a solar cell includes forming a plurality of semiconductor regions in or above a substrate. The method also includes forming a metal-containing thermal and diffusion barrier layer above the plurality of semiconductor regions. The method also includes forming a metal seed layer on the metal-containing thermal and diffusion barrier layer. The method also includes forming a metal conductor layer on the metal seed layer. The method also includes laser welding the metal conductor layer to the metal seed layer. The metal-containing thermal and diffusion barrier layer protects the plurality of semiconductor regions during the laser welding.
1. A solar cell, comprising:
a substrate;
a plurality of doped semiconductor regions in or above the substrate;
a metal-containing layer disposed above the doped semiconductor regions, wherein the metal-containing layer is a layer selected from the group consisting of a layer of titanium nitride (TiN), a layer of titanium tungsten (TiW), and a layer of tantalum nitride (TaN);
a conductive seed layer disposed on the metal-containing layer, wherein the conductive seed layer comprises a metal species not included in the metal-containing layer, wherein the conductive seed layer has a thickness in the range of 0.05 to 20 microns and comprises the metal species in an amount greater than 90 atomic %; and
conductive foil portions disposed on and spot-welded to the conductive seed layer, the conductive foil portions comprising the metal species.
2. The solar cell of claim 1 , further comprising:
a conductive layer disposed on the doped semiconductor regions, wherein the metal-containing layer is disposed on the conductive layer, and
wherein the conductive layer comprises the metal species.
3. The solar cell of claim 2 , wherein the conductive layer has a thickness in the range of 20-100 nanometers.
4. The solar cell of claim 1 , further comprising:
a trench disposed between each of the doped semiconductor regions and extending partially into the substrate.
5. The solar cell of claim 1 , wherein the metal-containing layer is a layer of titanium nitride (TiN).
6. The solar cell of claim 1 , wherein the metal-containing layer is a layer of titanium tungsten (TiW).
7. The solar cell of claim 1 , wherein the metal-containing layer is a layer of tantalum nitride (TaN).
8. A solar cell, comprising:
a single crystalline silicon substrate;
a plurality of alternating N-type and P-type polycrystalline silicon regions disposed on a thin dielectric layer disposed on the single crystalline silicon substrate;
a non-aluminum metal-containing layer disposed above the alternating N-type and P-type polycrystalline silicon regions, wherein the non-aluminum metal-containing layer is a layer selected from the group consisting of a layer of titanium nitride (TiN), a layer of titanium tungsten (TiW), and a layer of tantalum nitride (TaN);
an aluminum seed layer disposed on the non-aluminum metal-containing layer, wherein the aluminum seed layer has a thickness in the range of 0.05 to 20 microns and comprises aluminum in an amount greater than 90 atomic %; and
aluminum foil portions disposed on and spot-welded to the aluminum seed layer.
9. The solar cell of claim 8 , further comprising:
an aluminum layer disposed on the alternating N-type and P-type polycrystalline silicon regions, wherein the non-aluminum metal-containing layer is disposed on the aluminum layer.
10. The solar cell of claim 9 , wherein the aluminum layer has an amount of aluminum less than required to form a eutectic mixture with the plurality of alternating N-type and P-type polycrystalline silicon regions.
11. The solar cell of claim 9 , wherein the aluminum layer is a layer of aluminum having a thickness in the range of 20-100 nanometers.
12. The solar cell of claim 8 , further comprising:
a trench disposed between each of the alternating N-type and P-type polycrystalline silicon regions and extending partially into the single crystalline silicon substrate.
13. The solar cell of claim 8 , wherein the non-aluminum metal-containing layer is a layer of titanium nitride (TiN).
14. The solar cell of claim 8 , wherein the non-aluminum metal-containing layer is a layer of titanium tungsten (TiW).
15. The solar cell of claim 8 , wherein the non-aluminum metal-containing layer is a layer of tantalum nitride (TaN).
16. A solar cell, comprising:
a single crystalline silicon substrate;
a plurality of alternating N-type and P-type doped regions disposed in the single crystalline silicon substrate;
a non-aluminum metal-containing layer disposed above the alternating N-type and P-type doped regions, wherein the non-aluminum metal-containing layer is a layer selected from the group consisting of a layer of titanium nitride (TiN), a layer of titanium tungsten (TiW), and a layer of tantalum nitride (TaN);
an aluminum seed layer disposed on the non-aluminum metal-containing layer, wherein the aluminum seed layer has a thickness in the range of 0.05 to 20 microns and comprises aluminum in an amount greater than 90 atomic %; and
metal foil portions disposed on and spot-welded to the aluminum seed layer.
17. The solar cell of claim 16 , wherein the metal foil are aluminum foil portions.
18. The solar cell of claim 16 , further comprising:
an aluminum layer disposed on the alternating N-type and P-type doped regions, wherein the non-aluminum metal-containing layer is disposed on the aluminum layer.
19. The solar cell of claim 18 , wherein the aluminum layer has an amount of aluminum less than required to form a eutectic mixture with the plurality of alternating N-type and P-type doped regions.
20. The solar cell of claim 18 , wherein the aluminum layer is a layer of aluminum having a thickness in the range of 20-100 nanometers.