Solar cells with tunnel dielectrics

1. A solar cell, comprising:

a first dielectric formed over a first portion of the silicon substrate;

a second dielectric formed over second portion of the silicon substrate, wherein the first dielectric is a different type of dielectric than the second dielectric;

a doped semiconductor formed over the first and second dielectric;

a positive-type metal contact formed over the doped semiconductor and the first dielectric; and

a negative-type metal contact formed over the doped semiconductor and over the second dielectric.

2. The solar cell of claim 1 , wherein the first dielectric comprises at least an oxide monolayer in contact with the silicon substrate.

3. The solar cell of claim 1 , wherein the second dielectric comprises a plurality of oxide monolayers.

4. The solar cell of claim 1 , wherein the first dielectric comprises silicon nitride.

5. The solar cell of claim 1 , wherein the second dielectric comprises silicon dioxide.

6. The solar cell of claim 1 , wherein the doped semiconductor comprises doped polysilicon.

7. The solar cell of claim 1 , wherein the doped semiconductor comprises a P-type doped polysilicon and an N-type doped polysilicon.

8. The solar cell of claim 7 , wherein the P-type doped polysilicon is formed over the first dielectric and the N-type doped polysilicon is formed over the second dielectric.

9. The solar cell of claim 8 , wherein the silicon substrate comprises a first doped region under the first dielectric and a second doped region under the second dielectric.

10. The solar cell of claim 9 , wherein a dopant concentration ratio between the P-type doped polysilicon and the first doped region is at least 10.

11. The solar cell of claim 1 , wherein the doped semiconductor comprises doped amorphous silicon.

12. A solar cell, comprising:

a first dielectric formed over a first doped region of a silicon substrate;

a second dielectric formed over a second doped region of the silicon substrate, wherein the first dielectric is a different type of dielectric than the second dielectric;

a first doped polysilicon formed over the first dielectric;

a second doped polysilicon formed over the second dielectric;

a positive-type metal contact formed over the first doped polysilicon; and

a negative-type metal contact formed over the second doped polysilicon.

13. The solar cell of claim 12 , wherein the first dielectric comprises at least an oxide monolayer in contact with the silicon substrate.

14. The solar cell of claim 12 , wherein the second dielectric comprises a plurality of oxide monolayers.

15. The solar cell of claim 12 , wherein the first dielectric comprises silicon nitride.

16. The solar cell of claim 12 , wherein the second dielectric comprises silicon dioxide.

17. The solar cell of claim 12 , wherein a dopant concentration ratio between the first doped polysilicon and the first doped region is at least 10.

18. A solar cell, comprising:

silicon nitride formed over a P-type doped region of the silicon substrate;

silicon dioxide formed over an N-type doped region of the silicon substrate;

P-type doped polysilicon formed on the silicon nitride;

N-type doped polysilicon formed on the silicon dioxide;

a positive-type metal contact formed on the P-type doped polysilicon region; and

a negative-type metal contact formed on the N-type doped polysilicon region.

19. The solar cell of claim 18 , wherein a dopant concentration ratio between the P-type doped polysilicon and the P-type doped region is at least 10.

20. The solar cell of claim 18 , wherein the silicon nitride comprises at least an oxide monolayer in contact with the silicon substrate.