Solar cells and method of manufacturing thereof
A photovoltaic cell, the cell comprising: a silicon substrate of bulk silicon material having front and rear surfaces; an emitter layer on the rear surface of said substrate; elongate channels through the emitter layer; elongate contacts to the bulk of the silicon substrate within at least some of the elongate channels, wherein the contacts are narrower than the channels; and gaps in the emitter between at least some of the elongate contacts and the emitter layer on the sides of the contacts.
1. A photovoltaic cell, the cell comprising:
a silicon substrate of bulk silicon material having front and rear surfaces;
an emitter layer on the rear surface of said substrate;
laser ablated elongate substantially rectangular channels through the emitter layer;
elongate contacts to the bulk of the silicon substrate within at least some of the elongate channels, wherein the contacts are narrower than the channels; and
air-gaps in the emitter between at least some of the elongate contacts and the emitter layer on the sides of the contacts, wherein said air-gaps have two substantially parallel walls, wherein a distance between said parallel walls is between 2-10 μm.
2. A cell according to claim 1 , wherein the emitter layer comprises a doped layer with opposite polarity to the silicon substrate.
3. A cell according to claim 1 , wherein the emitter comprises an induced emitter created by a passivation layer provided on the rear surface of the substrate, and wherein the laser ablated elongate channels comprise channels through the passivation layer.
4. A cell according to claim 1 , wherein the cell further comprises a passivation layer produced on the emitter layer at the rear surface of the substrate, and wherein the laser ablated elongate channels comprise channels through the passivation and emitter layer.
5. A cell according to claim 1 , wherein the elongate contacts have a width of between 10 μm-100 μm.
6. A cell according to claim 1 , wherein the elongate contacts have a thickness of between 10 μm-100 μm.
7. A cell according to claim 1 , wherein the ratio of the height to width of the elongate contacts is between about 0.3 and 3.
8. A cell according to claim 1 , wherein the contacts are formed of a conducting material that is substantially homogeneous over its thickness.
9. A cell according to claim 1 , wherein a heavily doped layer is created at least between the contacts to the bulk material and the substrate.
10. A cell according to claim 9 , wherein the gaps separate between the heavily doped layer and the emitter layer.
11. A cell according to claim 1 , wherein the cell further comprises additional elongate channels through the passivation layer on the rear surface of the substrate and additional elongate contacts to said emitter layer within said channels through the passivation layer.
12. A cell according to claim 1 , wherein the cell further comprises an emitter layer at the front surface of the substrate and a passivation layer on the emitter layer at the front surface of the substrate, and the cell further includes contacts to the emitter layer at the front surface of the substrate.
13. A cell according to claim 11 , wherein the elongate contacts to the emitter layer have a width of between 10 μm-100 μm.
14. A cell according to claim 11 , wherein the elongate contacts to the emitter layer have a thickness of between 10 μm-100 μm.
15. A cell according to claim 11 , wherein the ratio of the height to width of the elongate contacts to the emitter layer is between about 0.1 and 1.
16. A cell according to claim 1 , wherein said cell includes an additional passivation layer at its rear surface.
17. A cell according to claim 16 wherein said additional passivation layer is present only in said gaps.
18. A cell according to claim 1 , further comprising:
a reflective layer at the rear surface of the cell.
19. A cell according to claim 18 , wherein the reflective layer is a thin metal layer.
20. A cell according to claim 18 , wherein the reflective layer is a dielectric layer.
21. A method of producing a contact to a silicon substrate through an emitter, the method comprising:
creating a rectangular channel opening in the emitter layer at a surface of said substrate by laser ablation; and
depositing conducting material in said opening, the conducting material being smaller in size than the opening such that air-gaps are left between the conducting material and the sidewalls of the opening, wherein said air-gaps have two substantially parallel walls and wherein a distance between said parallel walls is between 2-10 μm.
22. A method according to claim 21 , wherein producing a contact to a silicon substrate through an emitter layer comprises producing a contact to a silicon substrate having a passivation layer over the emitter layer and wherein creating an opening comprises creating an opening through the passivation layer and through at least part of the emitter layer.
23. A method according to claim 21 , wherein the method further comprises:
heavily doping at least the point of connection of the deposited conducting material with the substrate.
24. A method according to claim 22 , wherein the method further comprises:
creating an additional opening in the passivation layer at said surface; and
depositing conducting material in the additonal opening thereby creating a contact to the emitter layer.
25. A method according to claim 24 , wherein the method further comprises:
producing a first busbar for connecting between the contacts to the bulk of the substrate; and
producing a second busbar for connecting between the contacts to the emitter layer.
26. A method according to claim 25 , wherein producing a first and second busbar comprises producing first and second busbars such that there is no connection between the first and second busbars.
27. A method according to claim 21 , further comprising:
etching the gaps in the opening; and
passivating at least the etched gaps.
28. A method according to claim 27 , wherein etching the gaps comprises etching with TMAH.
29. A method according to claim 27 , wherein etching the gaps comprises etching with KOH.
30. A method according to claim 27 , wherein the method further comprises:
passivating the etched gaps.
31. A method according to claim 30 , wherein passivating the etched gaps comprises passivating an entire surface of the substrate.
32. A method according to claim 30 , wherein passivating the etched gaps comprises passivating substantially only the silicon in the etched gaps.
33. A method according to claim 21 , wherein the method further comprises:
creating an opening in a passivation layer at an opposite surface to said surface; and
depositing conducting material in the opening at the opposite surface, thereby creating a contact to an emitter layer at said opposite surface.
34. A method according to claim 33 , wherein depositing conducting material in the opening thereby creating a contact to the emitter layer comprises depositing conducting material having a width of between 10 μm-100 μm.
35. A method according to claim 33 , wherein depositing conducting material in the opening thereby creating a contact to the emitter layer comprises depositing conducting material having a thickness of between 10 μm-100 μm.
36. A method according to claim 33 , wherein depositing conducting material in the opening thereby creating a contact to the emitter layer comprises depositing conducting material having a ratio of the height to width between about 0.1 and 1.
37. A method according to claim 21 , wherein depositing conducting material in said opening comprises depositing by laser.
38. A method of producing a contact to a silicon substrate through an emitter, the method comprising:
creating an opening in the emitter layer at a surface of said substrate by laser ablation; and
depositing, by laser, conducting material in said opening, the conducting material being smaller in size than the opening such that air-gaps are left between the conducting material and the sidewalls of the opening, wherein said air-gaps have a width of between 2-10 μm.