Trench process and structure for backside contact solar cells with polysilicon doped regions
A solar cell includes polysilicon P-type and N-type doped regions on a backside of a substrate, such as a silicon wafer. A trench structure separates the P-type doped region from the N-type doped region. Each of the P-type and N-type doped regions may be formed over a thin dielectric layer. The trench structure may include a textured surface for increased solar radiation collection. Among other advantages, the resulting structure increases efficiency by providing isolation between adjacent P-type and N-type doped regions, thereby preventing recombination in a space charge region where the doped regions would have touched.
1. A solar cell comprising:
a substrate having a front side and a backside;
a thin dielectric layer disposed on the backside of the substrate;
a P-type doped polysilicon region that is disposed on the thin dielectric layer;
an N-type doped polysilicon region that is adjacent to the P-type doped polysilicon region and disposed on the thin dielectric layer;
an isolation region that is disposed between and separates perimeters of the N-type doped polysilicon region and the P-type doped polysilicon region;
a first metal contact finger that contacts the P-type doped polysilicon region; and
a second metal contact finger that contacts the N-type doped polysilicon region.
2. The solar cell of claim 1 , wherein the thin dielectric layer comprises silicon dioxide or silicon nitride.
3. The solar cell of claim 1 , wherein the substrate comprises an N-type doped silicon substrate.
4. The solar cell of claim 1 , further comprising a second dielectric layer disposed between P-type doped polysilicon region and the N-type doped polysilicon region.
5. The solar cell of claim 4 , wherein the second dielectric layer comprises silicon dioxide.
6. The solar cell of claim 1 , wherein the isolation region extends into the substrate.
7. The solar cell of claim 6 , further comprising a second dielectric layer formed in the isolation region.
8. A method of fabricating a solar cell, the method comprising:
forming a first dielectric layer on a substrate;
forming an undoped polysilicon layer on the first dielectric layer;
doping the undoped polysilicon layer into a P-type doped polysilicon region and an N-type doped polysilicon region, wherein the N-type doped polysilicon region is adjacent to the P-type doped polysilicon region; and
forming an isolation region that separates perimeters of the P-type doped polysilicon region and the N-type doped polysilicon region.
9. The method of claim 8 , further comprising:
forming a second dielectric layer on a surface between the P-type doped polysilicon region and the N-type doped polysilicon region.
10. The method of claim 8 , wherein the isolation region is formed after forming the P-type doped polysilicon region and the N-type doped polysilicon region.
11. The method of claim 8 , wherein the isolation region is formed before forming the P-type doped polysilicon region and the N-type doped polysilicon region.
12. The method of claim 8 , further comprising:
forming a passivation region between the isolation region and the substrate.
13. The method of claim 8 , further comprising:
forming a passivation layer on a surface of the isolation region.
14. The method of claim 8 , further comprising:
forming a first metal contact finger that contacts the P-type doped polysilicon region, and
forming a second metal contact finger that contacts the N-type doped polysilicon region.
15. A method of fabricating a solar cell, the method comprising:
forming a first dielectric layer on a substrate;
depositing a pre-doped P-type doped polysilicon region on the first dielectric layer;
depositing a pre-doped N-type doped polysilicon region on the first dielectric layer and adjacent to the pre-doped P-type doped polysilicon region; and
forming an isolation region that separates perimeters of the pre-doped P-type doped polysilicon region and the pre-doped N-type doped polysilicon region.
16. The method of claim 15 , wherein the isolation region is formed after forming the pre-doped P-type doped polysilicon region and the pre-doped N-type doped polysilicon region.
17. The method of claim 15 , wherein the isolation region is formed before forming the pre-doped P-type doped polysilicon region and the pre-doped N-type doped polysilicon region.
18. The method of claim 15 , further comprising:
forming a passivation region between the isolation region and the substrate.
19. The method of claim 15 , further comprising:
forming a passivation layer on a surface of the isolation region.
20. The method of claim 15 , further comprising:
forming a first metal contact finger that contacts the P-type doped polysilicon region, and
forming a second metal contact finger that contacts the N-type doped polysilicon region.