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 solar cell comprising:
an N-type solar cell substrate having a front side configured to face the sun during normal operation and a backside opposite the front side;
a P-type doped region and an N-type doped region of the backside of the solar cell;
a trench between the P-type doped region and the N-type doped region, the trench physically separating the P-type doped region from the N-type doped region and extending into the solar cell substrate; and
a dielectric layer formed in the trench, the dielectric layer having a positive fixed charge density and formed on a surface of the solar cell substrate exposed in the trench.
2. The solar cell of claim 1 , wherein the dielectric is formed on a textured surface of the solar cell substrate exposed in the trench.
3. The solar cell of claim 1 , wherein the P-type doped region and the N-type doped region comprise polysilicon.
4. The solar cell of claim 1 , wherein the solar cell substrate comprises silicon.
5. The solar cell of claim 1 , wherein further comprising an oxide layer between the solar cell substrate and the P-type and N-type doped regions.
6. The solar cell of claim 1 , wherein the dielectric layer comprises silicon nitride.
7. The solar cell of claim 1 , further comprising:
a first metal contact finger that is electrically connected to the P-type doped region; and
a second metal contact finger that is electrically connected to the N-type doped region.
8. The solar cell of claim 7 , wherein the first metal contact finger and the second metal contact finger are interdigitated.
9. The solar cell of claim 7 , wherein the first metal contact finger is electrically connected to the P-type doped region through the dielectric layer and the second metal contact finger is electrically connected to the N-type doped region through the dielectric layer.
10. A solar cell comprising:
a P-type doped polysilicon region and an N-type doped polysilicon region on a backside surface of an N-type silicon substrate;
a trench between the P-type doped polysilicon region and the N-type doped polysilicon region, the trench physically separating the P-type doped polysilicon region from the N-type doped polysilicon region;
a silicon nitride layer formed in the trench, the silicon nitride layer having a positive fixed charge density and formed on a textured surface of the N-type silicon substrate exposed in the trench;
a first metal contact finger that is electrically connected to the P-type doped polysilicon region; and
a second metal contact finger that is electrically connected to the N-type doped polysilicon region.
11. The solar cell of claim 10 , wherein the first metal contact finger is interdigitated with the second metal contact finger.
12. The solar cell of claim 10 , further comprising:
an oxide layer between the N-type silicon substrate and the P-type and N-type doped polysilicon regions.
13. The solar cell of claim 12 , wherein the first metal contact finger is electrically connected to the P-type doped polysilicon region through the silicon nitride layer and the second metal contact is electrically connected to the N-type doped polysilicon region through the silicon nitride layer.
14. A solar cell comprising:
an N-type solar cell substrate having a front side configured to face the sun during normal operation and a backside opposite the front side;
a P-type doped region and an N-type doped region of the solar cell over the backside of the solar cell substrate;
a trench between the P-type doped region and the N-type doped region, the trench physically separating the P-type doped region from the N-type doped region and extending into the solar cell substrate;
a dielectric layer over the trench, the dielectric layer having a positive fixed charge density;
a first metal contact finger that is electrically connected to the P-type doped region through the dielectric layer; and
a second metal contact finger that is electrically connected to the N-type doped region through the dielectric layer.
15. The solar cell of claim 14 , wherein the solar cell substrate is a silicon substrate.
16. The solar cell of claim 14 , wherein the dielectric layer is formed on a textured surface of the solar cell substrate exposed in the trench.
17. The solar cell of claim 14 , wherein the P-type doped region and the N-type doped region comprise polysilicon.
18. The solar cell of claim 14 , wherein the first metal contact finger and the second metal contact finger are interdigitated.
19. The solar cell of claim 14 , further comprising:
another dielectric layer between the solar cell substrate and the P-type and N-type doped regions.
20. The solar cell of claim 19 , wherein the other dielectric layer between the solar cell substrate and the P-type and N-type doped regions comprises an oxide.