Creation and Translation of Low-Relieff Texture for a Photovoltaic Cell

• US 20100184248A1
• Filed: 03/30/2010
• Published: 07/22/2010
• Est. Priority Date: 02/05/2008
• Status: Active Grant

• Current Assignee: Neutron Therapeutics Inc.
• Original Assignee: Twin Creeks Technologies, Inc.
• Inventors: Herner, S. Brad, Hilali, Mohamed M.
• Granted Patent: US 8,563,352 B2
• Time in Patent Office: Days
• US Class Current: 438/71
• CPC Class Codes: H01L 31/0236 Special surface textures
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy

Abstract

Low-relief texture can be created by applying and firing frit paste on a silicon surface. Where frit contacts the surface at high temperature, it etches silicon, dissolving silicon in the softened glass frit. The result is a series of small, randomly located pits, which produce a near-Lambertian surface, suitable for use in a photovoltaic cell. This texturing method consumes little silicon, and is advantageously used in a photovoltaic cell in which a thin silicon lamina comprises the base region of the cell. When the lamina is formed by implanting ions in a donor wafer to form a cleave plane and cleaving the lamina from the donor wafer at the cleave plane, the ion implantation step will serve to translate texture formed at a first surface to the cleave plane, and thus to the second, opposing surface following cleaving. Low-relief texture formed by other methods can be translated from the first surface to the second surface in this way as well.

Claims

1. A method to form texture at a surface of a photovoltaic cell, the method comprising the steps of:

applying a mixture containing glass frit to a first surface of a silicon body;

firing the glass frit mixture, causing selective etching of silicon at the first surface;

removing all of the fired glass frit, leaving the first surface textured; and

fabricating the photovoltaic cell, wherein the photovoltaic cell comprises the textured first surface.

2. The method of claim 1 wherein the glass frit is one or more of lead oxide glass, bismuth oxide glass, zinc oxide glass, aluminum oxide glass, cadmium oxide glass, magnesium oxide glass, borosilicate glass, calcium borosilicate glass, palladium oxide glass, barium borosilicate glass, or zirconium oxide glass.

3. The method of claim 1 wherein the textured first surface has an average peak-to-valley height between about 50 nm and about 1 micron.

4. The method of claim 1 wherein, at the textured first surface, the average pitch of the textured first surface is between about 0.5 microns and about 5 microns.

5. The method of claim 1 wherein the silicon body is monocrystalline silicon.

6. The method of claim 1 wherein, in the completed photovoltaic cell, the first surface is a surface of a silicon lamina having a thickness between about 1 microns and about 10 microns.

7. The method of claim 6 further comprising, following the step of removing all of the fired glass frit, providing a receiver element adhered to the first surface with zero, one, or more layers intervening.

8. The method of claim 6 further comprising, before the application of glass frit mixture, cleaving the silicon lamina from a silicon wafer, wherein the first surface is created during the cleaving step.

9. The method of claim 1 wherein the silicon body is a lamina having a thickness less than about ten microns.

10. The method of claim 1 wherein the step of applying a mixture of glass frit comprises applying the mixture of glass frit to at least 70 percent of the area of the first surface

11. A method to texture opposing surfaces of a lamina, the method comprising the steps of:

creating a first texture at a first surface of a donor body, wherein, for at least 50 percent of the area of the first surface, average peak-to-valley height is between about 100 nm and about 1500 nm, and average peak-to-peak distance is between about 140 nm and about 2100 nm;

implanting ions through the textured first surface, thereby defining a cleave plane within the donor body; and

cleaving the lamina from the donor body at the cleave plane,

wherein the first surface of the donor body is a first surface of the lamina, and

wherein a second surface of the lamina, the second surface opposite the first surface, is created by cleaving, and

wherein, immediately following the cleaving step, the second surface has a second texture, wherein for at least 50 percent of the area of the second surface, average peak-to-valley height is between about 100 nm and about 1500 nm, and average peak-to-peak distance is between about 140 nm and about 2100 nm.

12. The method of claim 11 wherein the step of creating texture at a first surface comprises applying a mixture containing glass frit to the first surface.

13. The method of claim 11 wherein lamina thickness is between about 1 micron and about 10 microns.

14. The method of claim 11 wherein, for at least 80 percent of the area of the first surface, average peak-to-valley height is between about 100 nm and about 1000 nm and average peak-to-peak distance is between about 140 nm and about 1400 nm.

15. The method of claim 14 wherein the step of creating the first texture at the first surface comprises etching at the first surface with a selective etchant, wherein the selective etchant etches the (100) plane at a higher etch rate than the (111) plane.

16. The method of claim 11 further comprising fabricating a photovoltaic cell, the photovoltaic cell comprising the lamina.

17. The method of claim 16 wherein the lamina comprises a base of the photovoltaic cell.

18. The method of claim 16 further comprising, between the implanting step and the cleaving step, providing a receiver element adhered to the first surface of the donor body with zero, one, or more layers intervening.

19. The method of claim 18 wherein the step of providing a receiver element adhered to the first surface of the donor body with zero, one, or more layers intervening comprises applying a material or stack of materials to the first surface, or to a layer on or above the first surface, wherein the receiver element is formed from the material or stack of materials.

20. The method of claim 19 wherein the receiver element has a final thickness of at least 50 microns.

21. The method of claim 11 wherein, for at least 50 percent of the area of the first surface, average peak-to-valley height is between about 300 nm and about 1000 nm.