Low-cost solar cells and methods for their production
Methods for fabricating solar cells without the need to perform gasification of metallurgical-grade silicon are disclosed. Consequently, the costs and health and environmental hazards involved in fabricating the solar or silicon grade silicon are being avoided. A solar cell structure comprises a metallurgical grade doped silicon substrate and a thin-film structure formed over the substrate to form a p-i-n junction with the substrate. The substrate may be doped p-type, and the thin film structure may be an intrinsic amorphous layer formed over the substrate and an n-type amorphous layer formed over the intrinsic layer.
1. A solar cell comprising:
a multi-crystalline substrate consisting essentially of a metallurgical grade silicon of 99.9%-99.999% purity doped as one of a p-type or n-type, the substrate having an upper side for facing light and an underside;
a thin-film structure formed directly on and in direct contact with the upper side of the substrate, thereby forming a p-i-n junction with the substrate; wherein the thin-film structure comprises an intrinsic layer formed directly on and in direct contact with the upper side of the substrate and a doped thin layer of opposite polarity of the substrate formed directly on and in direct contact with the intrinsic layer;
a top conductive contact formed above the thin-film structure;
a bottom conductive contact formed on the underside of the substrate.
2. The solar cell of claim 1 , wherein at least one of the intrinsic layer and the doped thin layer comprises an amorphous silicon layer.
3. The solar cell of claim 2 , wherein at least one of the intrinsic layer and the doped thin layer comprises hydrogen atoms dispersed within a silicon layer.
4. The solar cell of claim 3 , wherein the bottom conductive contact comprises a doped conductive layer of same polarity as the substrate formed over the underside of the substrate and a metal layer formed over the doped conductive layer.
5. The solar cell of claim 3 , wherein the top conductive contact comprises a transparent conductor formed over the doped thin layer.
6. The solar cell of claim 5 , further comprising at least one of a protective layer and an anti-reflective layer formed over the transparent conductor.
7. The solar cell of claim 4 , further comprising an amorphous intrinsic layer formed between the underside of the substrate and the doped conductive layer.
8. A solar cell comprising:
a multi-crystalline substrate consisting essentially of a p-type boron-doped metallurgical grade silicon of 99.9%-99.999% purity and having a front surface facing light and a back surface;
an intrinsic amorphous silicon layer formed directly on and in direct contact with the front surface of the substrate;
an n-type amorphous silicon layer formed directly on and in direct contact with the intrinsic amorphous silicon layer;
a transparent conductive layer formed over and in contact with the n-type amorphous silicon layer;
contacts formed over the transparent conductive layer; and,
a bottom conductive contact formed over the back surface of the substrate.
9. The solar cell of claim 8 , wherein the substrate comprises a texturized front surface.
10. The solar cell of claim 8 , wherein the transparent conductive layer comprises indium tin oxide.
11. The solar cell of claim 8 , wherein the bottom conductive contact comprises sputtered aluminum.
12. The solar cell of claim 8 , wherein the bottom conductive contact comprises a p-type layer formed directly over and in contact with the back surface of the substrate, and a sputtered aluminum layer formed over the p-type layer.
13. A solar cell comprising:
a polycrystalline substrate consisting essentially of a p-type metallurgical grade silicon of 99.9%-99.999% purity and a resistivity of about 1.0 Ωcm and having a front surface for facing the sun and a back surface;
an intrinsic amorphous silicon layer formed directly on and in direct contact with the front surface of the substrate;
an n-type amorphous silicon layer formed directly on and in direct contact with the intrinsic amorphous silicon layer;
a transparent conductive layer formed over and in contact with the n-type amorphous silicon layer.
14. The solar cell of claim 13 , further comprising:
contacts formed over the transparent conductive layer; and,
a bottom conductive contact formed over the back surface of the substrate.
15. The solar cell of claim 14 , wherein the bottom conductive contact comprises:
a p-type layer formed directly over and in contact with the back surface of the substrate, and an aluminum layer formed over the p-type layer.
16. The solar cell of claim 13 , wherein the front surface comprises a textured surface.
17. The solar cell of claim 13 , wherein the intrinsic amorphous silicon layer is of thickness below 100 Å.
18. The solar cell of claim 13 , wherein the polycrystalline substrate has a thickness of 250-500 um.