Method to make electrical contact to a bonded face of a photovoltaic cell
View Patent ↗A photovoltaic cell is formed by bonding a donor body to a receiver element and cleaving a thin lamina from the donor body. Electrical contact is made to the bonded surface of the lamina through vias formed in the lamina. In some embodiments the emitter exists only at the bonded surface or only at the cleaved surface face; the emitter does not wrap through the vias between the surfaces. Wiring contacting each of the two surfaces is formed only at the cleaved face, and one set of wiring contacts the bonded surface through conductive material formed in the vias, insulated from the via sidewalls.
1. A method for forming a photovoltaic assembly, the method comprising:
bonding a first surface of a semiconductor donor body to a receiver element, with zero, one, or more layers intervening;
cleaving a semiconductor lamina from the donor body at a cleave plane, wherein the first surface of the donor body is the first surface of the lamina and remains bonded to the receiver element, and wherein a second surface is created by cleaving, the second surface opposite the first;
after the cleaving step, forming first conductive fingers and second conductive fingers, wherein the lamina is between the first fingers and the receiver element, and between the second fingers and the receiver element; and
forming a photovoltaic cell, wherein the photovoltaic assembly comprises the lamina, the receiver element, and the photovoltaic cell,
wherein, during normal operation of the cell, photocurrent flows from the first fingers to the second fingers or from the second fingers to the first fingers, crossing both the first surface and the second surface of the semiconductor lamina.
2. The method of claim 1 wherein, during normal operation of the cell, photocurrent flows from the first conductive fingers to the first surface, or from the first surface to the first conductive fingers, by way of vias passing through the lamina.
3. The method of claim 1 wherein a thickness of the lamina, between the first surface and the second surface, is between about 0.5 and about 20 microns.
4. The method of claim 1 wherein the first conductive fingers and the second conductive fingers are formed in the same processing steps.
5. The method of claim 1 further comprising, before the bonding step, forming the cleave plane by implanting gas ions through the first surface.
6. The method of claim 1 further comprising, before the bonding step, forming a first heavily doped region at the first surface, the heavily doped region having a first conductivity type.
7. The method of claim 6 wherein the first heavily doped region is the emitter of the cell.
8. The method of claim 6 further comprising forming a second heavily doped region at or adjacent to the second surface, the second conductivity type opposite the first.
9. The method of claim 8 wherein forming the second heavily doped region comprises depositing heavily doped amorphous silicon.
10. The method of claim 1 wherein, in the completed cell, the receiver element serves as a superstrate.
11. A method for forming a photovoltaic assembly, the method comprising:
bonding a first surface of a semiconductor donor body to a receiver element, with zero, one, or more layers intervening;
cleaving a semiconductor lamina from the donor body at a cleave plane, wherein the first surface of the donor body is the first surface of the lamina and remains bonded to the receiver element, and wherein a second surface is created by cleaving, the second surface opposite the first;
after the cleaving step, forming vias through the lamina;
forming first conductive fingers, the lamina between the first conductive fingers and the receiver element, wherein the first conductive fingers are in electrical contact with the first surface by way of conductive material in the vias; and
forming a photovoltaic cell, wherein the photovoltaic cell comprises the lamina.
12. The method of claim 11 wherein a conductive layer intervenes between the receiver element and the lamina, and wherein the conductive material in the vias is in immediate contact with the conductive layer.
13. The method of claim 12 wherein the conductive layer is a transparent conductive oxide.
14. The method of claim 11 wherein the vias have sidewalls, and wherein the conductive material in the vias is electrically isolated from the sidewalls.
15. The method of claim 14 wherein the conductive material in the vias is metal, metal alloy, or metal compound.
16. The method of claim 11 wherein the semiconductor lamina is formed of monocrystalline or multicrystalline silicon.
17. The method of claim 11 wherein a maximum thickness of the lamina between the first surface and the second surface is between about 0.5 microns and about 20 microns.
18. A method for forming a photovoltaic assembly, the method comprising:
bonding a first surface of a semiconductor donor body to a receiver element, with zero, one, or more layers intervening;
cleaving a semiconductor lamina from the donor body at a cleave plane, wherein the first surface of the donor body is the first surface of the lamina and remains bonded to the receiver element, and wherein a second surface is created by cleaving, the second surface opposite the first;
after the cleaving step, forming vias through the lamina, the vias having sidewalls;
forming a conductive material in the vias, the conductive material electrically insulated from the via sidewalls;
forming first conductive fingers, the lamina between the first conductive fingers and the receiver element; and
fabricating a photovoltaic cell, wherein, during normal operation of the completed photovoltaic cell, photocurrent flows from the first fingers to the first surface, or from the first surface to the first fingers, by way of the conductive material in the vias.
19. The method of claim 18 further comprising, before the bonding step, forming a first heavily doped region having a first conductivity type at the first surface.
20. The method of claim 19 wherein the first heavily doped region serves as the emitter of the completed photovoltaic cell.
21. The method of claim 19 wherein the via sidewalls are lightly doped to a second conductivity type opposite the first, or are undoped.
22. The method of claim 18 wherein, following the cleaving step, processing temperature does not exceed about 500 degrees C.
23. The method of claim 18 wherein a maximum thickness of the lamina between the first surface and the second surface is between about 0.5 microns and about 20 microns.