Glass beads coating process
A method of texturing a substrate or superstrate support material is provided, in which a thin textured film ( 32 ) is applied to the surface of the support material such as glass sheet ( 11 ). The dipping process is performed by loading a sheet ( 50 ) of the support material ( 11 ) into a frame ( 51 ) which provides a small number of small area contact points ( 52, 53 ) at which the sheet ( 50 ) is supported and lowering the frame ( 51 ) into texturing solution ( 59 ) comprising a mixture ( 59 ) of Sol-Gel ( 61 ) and texturing particles ( 62 ) comprising SiO 2 monospheres. The sheet is then withdrawn from the texturing solution and the resultant film allowed to dry. The film is then sintered and the resulting film provides a textured surface suitable for the formation of a photovoltaic device.
1. A method of manufacturing a thin film photovoltaic device on a transparent sheet of substrate or superstrate support material, the method comprising the steps of
a) dipping the support material in a container of film material in liquid form comprising a mixture of texturing particles in a predetermined concentration in an SiO 2 sol-gel,
b) removing the support material to deposit the texturing particles on exposed surfaces in a single layer, and wherein particle separation within the single layer is controlled by adjusting the concentration of particles in the sol-gel and speed of withdrawal of the support material from the solution;
c) hardening the liquid film material to form a textured film on the support material, whereby the texturing film, after hardening, comprises the texturing particles bound in an SiO 2 matrix;
d) forming a thin film of semiconductor material on the textured film; and
e) forming a photovoltaic device into the thin film of semiconductor material.
2. The method of claim 1 , wherein the textured film is an SiO 2 layer which includes monospheric SiO 2 particles located in a smooth SiO 2 film.
3. The method of claim 2 , wherein the monospherical particles are in the range of 0.1-2 μm in diameter, after hardening.
4. The method of claim 2 , wherein the monospherical particles are in the range of 0.5-9 μm in diameter, after hardening.
5. The method of claim 2 , wherein the monospherical particles are in the range of 0.65-0.75 μm in diameter, after hardening.
6. The method of claim 5 , wherein the smooth SiO 2 film has a thickness in the range of 0.2-0.8 times the diameter of the monospheric particles, after hardening.
7. The method of claim 6 , wherein the SiO 2 film is in the range of 0.35-0.5 times the particle diameter, after hardening.
8. The method of claim 6 , wherein the SiO 2 film is in the range of 0.25-0.35 μm, after hardening.
9. The method of claim 8 , wherein the hardening step comprises sintering the textured film at a temperature in the range of 300° C.-600° C.
10. The method of claim 9 , wherein a separate anti-reflection layer is located between the textured film and the semiconductor film to act as a barrier layer.
11. The method of claim 10 , wherein the semiconductor film is silicon, the separate anti-reflection layer is silicon nitride, and the silicon nitride layer thickness is 70 nm±20%.
12. The method of claim 1 , wherein the textured film is applied to the surface support material by mixing crushed quartz into a glass sol, applying the mixture to the surface substrate of the support material and heating to sinter the glass sol to form a dielectric layer.
13. The method of claim 12 , wherein the crushed quartz has particle dimensions in the order of 0.5-3 μm.
14. The method of claim 12 , wherein the crushed quartz has particle dimensions in the order of 1-2 μm.
15. The method of claim 1 , wherein the sol-gel texturing solution has a low viscosity which is adjusted to allow the desired film thickness to be attained for the particular application.
16. The method of claim 15 , wherein the film thickness of the SiO 2 layer is determined by the speed at which the substrate material is pulled from the texturing solution.
17. The method of claim 1 , wherein the SiO 2 particles deposited on the substrate are deposited with each particle being separated from surrounding particles by distances in the range of from 0 to 5 times the particle diameter.
18. The method of claim 17 , wherein each particle is separated from surrounding particles by distances in the range of 0 to 3 times the particle diameter.
19. The method of claim 18 , wherein particle separation is controlled by the humidity of air in which the film is dried.
20. The method of claim 1 , wherein the dipping of the support material is achieved by placing a sheet of support material on a support frame such that the sheet is supported at a plurality of points, lowering the frame and supported sheet into a vessel of the texturing solution deep enough to allow the sheet of support material to be submerged, and retrieving the sheet from the vessel.
21. The method of claim 20 , wherein the sheet is supported at only 4 points.
22. The method of claim 1 , wherein the thin film photovoltaic device is a crystalline silicon thin film solar cell.
23. The method as claimed of claim 1 , wherein the thin film photovoltaic device is an amorphous silicon thin film solar cell.
24. The method of claim 23 , wherein a transparent conducting layer is formed over the textured film and a thin silicon film is formed over the transparent conducting layer.
25. The method of claim 23 , wherein the texturing film containing the texturing particles is a transparent conducting layer.
26. The method of claim 22 , wherein the scale of textured surface features is in the range of 0.01-10 μm.
27. The method of claim 26 , wherein the lower limit of the feature size is in the order of a wavelength of light in crystalline silicon.
28. The method of claim 26 , wherein the lower limit of the feature size is in the order of 0.03 μm.
29. The method of claim 28 , wherein the texturing includes large scale features which have dimensions greater than the thickness of the silicon film.
30. The method of claim 29 , wherein the texturing layer includes surface features having a scale in a range from 0.5-0.2 times the thickness of the silicon film.
31. The method of claim 22 , wherein the thickness of the silicon film is less than 5 μm.
32. The method of claim 31 , wherein the thickness of the solution film is 2 μm or less.
33. The method of claim 32 , wherein the thickness of the silicon film is at least 0.05 μm or greater.
34. The method of claim 33 , wherein the thickness of the silicon film is greater than 1 μm.
35. The method of claim 22 , wherein the surface of the silicon film remote from the support material has a reflective material formed over it.
36. The method of claim 35 , wherein the reflective material is a metallisation structure used to contact active regions of the cell.
37. The method of claim 36 , wherein the metallisation structure is separated from a majority of a back surface of the silicon by an insulating layer.