Trench process and structure for backside contact solar cells with polysilicon doped regions
View Patent ↗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 method of fabricating a solar cell, the method comprising:
forming a first dielectric layer on a solar cell substrate;
forming a P-type doped region and an N-type doped region on a backside of a solar cell substrate, the P-type and N-type doped regions being over the first dielectric layer, the backside being opposite a front side of the solar cell that faces the sun during normal operation, the substrate comprising an N-type silicon wafer;
forming a trench separating the P-type doped region and the N-type doped region; and
depositing a second dielectric layer in the trench;
wherein the P-type doped region comprises polysilicon that is pre-doped with a P-type dopant prior to formation over the first dielectric layer and the N-type doped region comprises polysilicon that is pre-doped with an N-type dopant prior to formation over the first dielectric layer.
2. The method of claim 1 wherein the trench is formed before the P-type and N-type doped regions.
3. The method of claim 1 wherein the second dielectric layer comprises silicon nitride.
4. The method of claim 1 further comprising:
electrically coupling a first metal contact finger to the P-type doped region on the backside of the substrate; and
electrically coupling a second metal contact finger to the N-type doped region on the backside of the substrate.
5. The method of claim 1 further comprising:
randomly texturing a surface of the trench.
6. The method of claim 1 further comprising:
forming a passivation layer on a surface of the trench.
7. A method of fabricating a solar cell, the method comprising:
diffusing dopants from a first dopant source to form a P-type doped region on a solar cell substrate;
diffusing dopants from a second dopant source to form an N-type doped region on the solar cell substrate, the P-type doped region and the N-type doped region being external to the solar cell substrate; and
forming a trench between the P-type doped region and the N-type doped region, the trench dividing a first dielectric layer under the P-type doped region and the N-type doped region.
8. The method of claim 7 wherein the trench is formed after the formation of the P-type doped region and N-type doped region.
9. The method of claim 7 wherein the trench is formed before the formation of the P-type doped region and the N-type doped region.
10. The method of claim 7 wherein the P-typed doped region and the N-type doped region are formed in polysilicon.
11. The method of claim 7 further comprising:
forming a passivation region in the substrate under the trench.
12. The method of claim 7 further comprising:
forming a passivation layer on a surface of the trench.
13. A method of fabricating a solar cell, the method comprising:
forming a P-type doped region and an N-type doped region on a backside of a solar cell substrate, the P-type and N-type doped regions being over a dielectric layer; and
forming a trench between the P-type doped region and the N-type doped region, the dielectric layer being divided by the trench.
14. The method of claim 13 wherein the trench is formed before the P-type and N-type doped regions.
15. The method of claim 13 further comprising:
depositing another dielectric layer in the trench.
16. The method of claim 13 further comprising:
electrically coupling a first metal contact finger to the P-type doped region on the backside of the substrate; and
electrically coupling a second metal contact finger to the N-type doped region on the backside of the substrate.
17. The method of claim 13 wherein the P-type doped region comprises polysilicon that is pre-doped with a P-type dopant prior to deposition over the dielectric layer and the N-type doped region comprises polysilicon that is pre-doped with an N-type dopant prior to formation over the dielectric layer.
18. The method of claim 13 further comprising:
randomly texturing a surface of the trench.
19. The method of claim 13 further comprising:
forming a passivation region in the solar cell substrate under the trench.
20. The method of claim 13 further comprising:
forming a passivation layer on a surface of the trench.
21. A method of fabricating a solar cell, the method comprising:
forming a first dielectric layer on a solar cell substrate;
forming a passivation region in the solar cell substrate;
forming a P-type doped region and an N-type doped region on a backside of a solar cell substrate, the P-type and N-type doped regions being over the first dielectric layer, the backside being opposite a front side of the solar cell that faces the sun during normal operation, the substrate comprising an N-type silicon wafer;
forming a trench separating the P-type doped region and the N-type doped region, the passivation region being under the trench; and
depositing a second dielectric layer in the trench.