Solar cell having doped semiconductor heterojunction contacts

1. A solar cell comprising:

a silicon substrate having a front surface and a back surface;

a first doped silicon contact over the back surface of the silicon substrate;

a second doped silicon contact over the first doped silicon contact and in an opening through the first doped silicon contact, the first and second doped silicon contacts having opposite conductivity types; and

a first oxide layer under the first doped silicon contact, under the second doped silicon contact, and in the opening through the first doped silicon contact between the first and second doped silicon contacts.

2. The solar cell of claim 1 , wherein the first doped silicon contact has P-type conductivity and the second doped silicon contact has N-type conductivity.

3. The solar cell of claim 1 , wherein the first and second doped silicon contacts comprise doped amorphous silicon.

4. The solar cell of claim 1 , wherein the first and second doped silicon contacts comprise doped poly crystalline silicon.

5. The solar cell of claim 1 , further comprising:

a second oxide layer between the first and second doped silicon contacts over the back surface of the silicon substrate.

6. The solar cell of claim 1 , wherein the front surface of the silicon substrate is textured.

7. The solar cell of claim 6 , further comprising:

a third oxide layer over the textured front surface of the silicon substrate.

8. The solar cell of claim 1 , further comprising:

a first metal contact that is connected to the first silicon contact; and

a second metal contact that is connected to the second silicon contact.

9. A method of fabricating a solar cell, the method comprising:

providing a silicon substrate;

forming an oxide layer on a surface of the silicon substrate;

forming a first silicon contact of a first conductivity type over the oxide layer;

forming an opening through the first silicon contact;

forming another oxide layer that is continuous with the oxide layer on sidewalls of the opening;

forming a second silicon contact of a second conductivity type that is opposite to the first conductivity type over the first silicon contact and in the opening;

forming a first metal contact that is connected to the first silicon contact; and

forming a second metal contact that is connected to the second silicon contact.

10. The method of claim 9 , wherein the first and second silicon contacts comprise amorphous silicon.

11. The method of claim 9 , wherein the first and second silicon contacts comprise poly crystalline silicon.

12. The method of claim 9 , wherein the surface of the silicon substrate is opposite a light-receiving surface of the silicon substrate.

13. The method of claim 9 , wherein forming the other oxide layer that is continuous with the oxide layer on the sidewalls of the opening comprises:

etching the oxide layer exposed by the opening; and

growing the other oxide layer on the sidewalls of the opening and on an exposed surface of the silicon substrate.

14. The method of claim 9 , wherein the first silicon contact has P-type conductivity and the second silicon contact has N-type conductivity.