Aluminum grid as backside conductor on epitaxial silicon thin film solar cells
One embodiment of the present invention provides a solar cell. The solar cell includes a substrate, a first heavily doped crystalline-Si (c-Si) layer situated above the substrate, a lightly doped c-Si layer situated above the first heavily doped crystalline-Si layer, a second heavily doped c-Si layer situated above the lightly doped c-Si layer, a front side electrode grid situated above the second heavily doped c-Si layer, and a backside electrode grid situated on the backside of the substrate.
1. A solar cell, comprising:
a metallurgical-grade silicon substrate;
a first doped crystalline-silicon layer that is epitaxially formed on the metallurgical-grade silicon substrate;
a lightly doped crystalline-silicon base layer epitaxially formed on the first doped crystalline-silicon layer, wherein a doping concentration of the first doped crystalline-silicon layer is greater than that of the lightly doped crystalline-silicon base layer;
a second doped crystalline-silicon layer which is formed on the lightly doped crystalline-silicon base layer and has a doping concentration greater than that of the lightly doped crystalline-silicon base layer;
a first metal electrode grid; and
a second metal electrode grid;
wherein the lightly doped crystalline-silicon base layer, first doped crystalline-silicon layer, second doped crystalline-silicon layer, and second electrode grid are positioned on a first side of the metallurgical-grade silicon substrate;
wherein the lightly doped crystalline-silicon base layer is between the first doped crystalline-silicon layer and second doped crystalline-silicon layer;
wherein the second metal electrode grid is electrically coupled to the second doped crystalline-silicon layer; and
wherein the first metal electrode grid is positioned on a second side of the metallurgical-grade silicon substrate.
2. The solar cell of claim 1 , wherein the second metal electrode grid comprises a number of finger strips and at least one busbar.
3. The solar cell of claim 1 , further comprising a dielectric passivation layer between the second doped crystalline-silicon layer and the second metal electrode grid, wherein the dielectric passivation layer is in direct contact with the second doped crystalline-silicon layer.
4. The solar cell of claim 1 , wherein the first doped crystalline-silicon layer is in direct contact with the metallurgical-grade silicon substrate.
5. The solar cell of claim 1 , wherein the first and second doped crystalline-silicon layers are in direct contact with the lightly doped crystalline-silicon base layer.
6. The solar cell of claim 1 , wherein the lightly doped crystalline-silicon base layer is n-type doped.
7. The solar cell of claim 1 , wherein the first doped crystalline-silicon layer is p-type doped.
8. The solar cell of claim 1 , wherein the second doped crystalline-silicon layer is n-type doped.
9. The solar cell of claim 1 , wherein the first and second metal electrode grids comprise Al.
10. The solar cell of claim 9 , wherein the first and second metal electrode grids further comprise one or more of the following materials:
frit;
Ag;
Pd;
Cr;
Zn; and
Sn.
11. The solar cell of claim 1 , further comprising an anti-reflection layer between the second doped crystalline-silicon layer and the second metal electrode grid.