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 solar cell substrate having a front side configured to face the sun during normal operation and a backside opposite the front side;
an oxide layer over the backside of the solar cell;
a P-type doped region and an N-type doped region of the solar cell over the oxide layer, wherein the P-type doped region and the N-type doped region comprise polysilicon;
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
a passivation region in the solar cell substrate and directly under the trench.
2. The solar cell of claim 1 , wherein the solar cell substrate comprises an N-type silicon wafer.
3. The solar cell of claim 2 , wherein the passivation region comprises N-type dopants.
4. The solar cell of claim 1 , wherein the trench extends into a textured backside surface of the solar cell substrate.
5. 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.
6. The solar cell of claim 5 , further comprising:
a dielectric layer formed in the trench.
7. The solar cell of claim 6 , 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.
8. The solar cell of claim 7 , wherein the dielectric layer comprises silicon nitride.
9. A method of fabricating a solar cell, the method comprising:
providing a solar cell substrate having a front side configured to face the sun during normal operation and a backside opposite the front side;
forming an oxide layer over the backside of the solar cell;
forming a P-type doped region and an N-type doped region of the solar cell over the oxide layer, wherein the P-type doped region and the N-type doped region comprise polysilicon;
forming 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
forming a passivation region in the solar cell substrate and directly under the trench.
10. The method of claim 9 , wherein the solar cell substrate comprises an N-type silicon wafer.
11. The method of claim 10 , wherein forming the passivation region comprises:
diffusing N-type dopants into the N-type silicon wafer.
12. The method of claim 1 , further comprising:
forming a first metal contact finger that is electrically connected to the P-type doped region; and
forming a second metal contact finger that is electrically connected to the N-type doped region.
13. The method of claim 12 , further comprising:
forming a dielectric layer formed in the trench.
14. The method of claim 13 , 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.
15. The method of claim 14 , wherein the dielectric layer comprises silicon nitride.
16. A solar cell comprising:
a solar cell substrate having a front side configured to face the sun during normal operation and a backside opposite the front side, wherein the solar cell substrate comprises an N-type silicon wafer;
an oxide layer over the backside of the backside of the solar cell substrate;
a P-type doped region and an N-type doped region of the solar cell over the oxide layer, wherein the P-type doped region and the N-type doped region comprise polysilicon;
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
a passivation region in the solar cell substrate and directly under the trench, the passivation region comprising N-type dopants.
17. The solar cell of claim 16 , wherein the trench extends into a textured backside surface of the solar cell substrate.
18. The solar cell of claim 16 , 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.
19. The solar cell of claim 18 , further comprising:
a dielectric layer formed in the trench.
20. The solar cell of claim 19 , 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.