Low-cost multi-junction 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 doped metallurgical grade silicon 99.9%-99.999% doped as one of a p-type or n-type and having an upper side and an underside, the upper side for facing the sun;
a first thin-film structure comprising an intrinsic silicon layer formed directly on and in direct contact with the upper side of the substrate and a first doped layer of opposite polarity as that of the substrate and formed directly on and in direct contact with the intrinsic layer, to thereby form a first p-i-n structure with the substrate;
a second thin-film structure formed over the first thin film structure;
a top conductive contact formed above the second 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 first intrinsic layer and the first doped layer comprises an amorphous silicon layer.
3. The solar cell of claim 2 , wherein at least one of the first intrinsic layer and the first doped 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 the same polarity as the substrate formed on the underside of the substrate and a metal layer formed over the doped conductive layer.
5. The solar cell of claim 4 , wherein the top conductive contact comprises a transparent conductor formed over the first doped 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 on the underside of the substrate such that it is positioned between the underside of the substrate and the doped conductive layer.
8. The solar cell of claim 1 , wherein the second thin-film structure comprises a first doped thin-film formed over the first thin-film structure, an intrinsic thin-film formed over the first doped thin-film, and a second doped thin-film formed over the intrinsic thin-film, thereby forming a second thin-film p-i-n structure over the first p-i-n structure.
9. The solar cell of claim 1 , wherein the first doped layer is an n-type layer formed over and in contact with the intrinsic layer, and wherein the second thin-film structure comprises a p-type layer formed over and in contact with the first n-type layer, a second intrinsic layer formed over the p-type layer and having a higher thickness than the first intrinsic layer, and a second n-type layer.
10. The solar cell of claim 9 , further comprising a diffusion layer formed in the metallurgical grade substrate, the diffusion layer being one of an n-type or p-type.
11. The solar cell of claim 1 , wherein the substrate consists essentially of a p-type metallurgical grade silicon of resistivity of about 1.0 Ωcm.
12. The solar cell of claim 1 , wherein the upper side comprises a textured surface.
13. The solar cell of claim 1 , wherein the bottom conductive contact comprises a p-type layer formed directly over and in contact with the underside of the substrate, and an aluminum layer formed over the p-type layer.