Array of small contacts for solar cell fabrication
View Patent ↗Fabrication of a solar cell using a printed contact mask. The contact mask may include dots formed by inkjet printing. The dots may be formed in openings between dielectric layers (e.g., polyimide). Intersections of overlapping dots may form gaps that define contact regions. The spacing of the gaps may be dictated by the alignment of nozzles that dispense the dots. Using the dots as a contact mask, an underlying dielectric layer may be etched to form the contact regions through the underlying dielectric layer. Metal contact fingers may be formed over the wafer to form electrical connections to corresponding diffusion regions through the contact regions.
1. A method of fabricating a solar cell, the method comprising:
forming a first dielectric layer over a wafer to be processed into a solar cell;
forming a plurality of second dielectric layers over the first dielectric layer; and
inkjet printing a plurality of dots at least in openings between the second dielectric layers to form a plurality of gaps formed by intersections of the dots, the spacing of the gaps being dictated by an alignment of inkjet printer nozzles that dispense the dots.
2. The method of claim 1 wherein the second dielectric layers comprise polyimide screen printed over the wafer.
3. The method of claim 1 further comprising:
forming contact regions through the first dielectric layer using the plurality of dots as a mask;
removing the plurality of dots from the wafer; and
forming metal contact fingers over the first dielectric layer to create electrical connections through the contact regions to diffusion regions under the first dielectric layer.
4. The method of claim 3 wherein the at least some of the metal contact fingers comprise N-type metal contact fingers formed to create electrical connections to corresponding N-type diffusion regions through at least some of the contact regions and P-type metal contact fingers formed to create electrical connections to corresponding P-type diffusion regions through at least some of the contact regions, the P-type and N-type diffusion regions being formed on a backside of the wafer, which is opposite a front side of the wafer facing the sun during normal operation.
5. The method of claim 4 wherein the N-type metal contact fingers but not the P-type metal contact fingers are formed over the second dielectric layers.
6. The method of claim 1 wherein the first dielectric layer comprises silicon dioxide and the second dielectric layers comprise polyimide.
7. The method of claim 1 wherein the dots are printed in one pass of a printhead including the nozzles in one direction over the wafer.
8. The method of claim 7 further comprising:
passing the printhead over the wafer at least in another pass to print another dot covering a gap in the plurality of gaps.
9. A method of fabricating a solar cell, the method comprising:
forming a first dielectric layer over a solar cell wafer;
forming a plurality of second dielectric layers over the first dielectric layer;
printing a plurality of dots at least in an opening between two of the second dielectric layers, the plurality of dots forming a contact mask that forms a plurality of gaps, each of the gaps being defined by intersections of overlapping dots in the plurality of dots; and
etching portions of the first dielectric layer exposed through the gaps to form a plurality of contact regions exposing a plurality of diffusion regions of the solar cell.
10. The method of claim 9 further comprising:
removing the plurality of dots from the wafer; and
forming metal contact fingers in the plurality of contact regions to electrically connect to corresponding ones in the plurality of diffusion regions.
11. The method of claim 10 wherein some of the metal contact fingers comprise N-type metal contact fingers electrically connected to N-type diffusion regions in the plurality of diffusion regions on a backside of the solar cell and some of the metal contact fingers comprise P-type metal contact fingers electrically connected to P-type diffusion regions in the plurality of diffusion regions on the backside of the solar cell.
12. The method of claim 9 wherein the plurality of second dielectric layers is screen printed on the first dielectric layer.
13. The method of claim 9 wherein the plurality of dots are printed using an inkjet printer.
14. The method of claim 9 wherein the plurality of second dielectric layers comprise polyimide.
15. The method of claim 9 wherein the first dielectric layer comprises silicon dioxide.
16. A method of fabricating a solar cell, the method comprising:
printing a plurality of dots over a solar cell wafer in an opening between two dielectric layers, the plurality of dots defining gaps with each gap being formed by intersections of overlapping dots in the plurality of dots, the spacing between the gaps being defined by a physical alignment of nozzles that dispense the plurality of dots such that the plurality of dots is not critically aligned to a feature of a solar cell wafer over which the plurality of dots is printed;
etching another layer under the plurality of dots using the plurality of dots as an etch mask to form contact regions to an underlying diffusion region, the contact regions being defined by the gaps; and
forming metal contact fingers over the other layer, the metal contact fingers being formed to electrically connect to the underlying diffusion region through the contact regions.
17. The method of claim 16 wherein the other layer comprises silicon dioxide.
18. The method of claim 16 wherein the two dielectric layers comprise polyimide.
19. The method of claim 16 wherein the metal contact fingers comprise N-type metal contact fingers and the underlying diffusion region comprises an N-type diffusion region.
20. The method of claim 16 wherein plurality of dots is printed in one pass of an inkjet printer over the wafer in one direction.