Laser polishing of a solar cell substrate
View Patent ↗Provided herein are methods of polishing and texturing surfaces thin-film photovoltaic cell substrates. The methods involve laser irradiation of a surface having a high frequency roughness in an area of 5-200 microns to form a shallow and rapidly expanding melt pool, followed by rapid cooling of the material surface. The minimization of surface tension causes the surface to re-solidify in a locally smooth surface. the high frequency roughness drops over the surface with a lower frequency bump or texture pattern remaining from the re-solidification.
1. A method for smoothing a front surface of substrate for thin-film photovoltaic stacks, the method comprising:
irradiating the front surface with laser energy to heat the surface in localized areas of between 5 to 200 microns and form a plurality of shallow, rapidly expanding melt pools;
after forming the melt pools, cooling the front surface to form a smoothed surface and further comprising maintaining the temperature of a back surface of the substrate at a constant temperature, said constant temperature being between about 0 and 100° C.
2. The method of claim 1 wherein the irradiating the front surface with laser energy comprises exposing the front surface to laser beams at a rate of about 10-1000 kHz.
3. The method of claim 1 wherein the smoothed surface comprises interconnected surface features.
4. The method of claim 3 wherein the interconnected surface features have a maximum aspect ratio of no more than 1:1.
5. The method of claim 1 wherein irradiating the front surface with laser energy comprises rastering a laser beam over the surface at frequency of at least about 100 kHz.
6. The method of claim 5 where the irradiating the front surface with laser energy comprises rastering multiple laser beams over the surface.
7. The method of claim 1 wherein the substrate is a metallic material.
8. The method of claim 7 wherein the substrate comprises steel, aluminum or titanium.
9. The method of claim 7 wherein the substrate is a stainless steel substrate.
10. The method of claim 1 wherein the substrate is a polymer material.
11. The method of claim 1 wherein the substrate is oriented at an angle of no more than 10° from vertical during the irradiation.
12. The method of claim 1 further comprising depositing a photovoltaic stack comprising a light absorbing layer on the smoothed surface.
13. The method of claim 1 wherein cooling the melt pools forms a patterned surface, said patterned surface characterized by substantially uniformly arrayed raised features separated by a distance of between about 5 and 200 microns.
14. The method of claim 13 wherein the average aspect ratio of the raised features of the patterned surface is less than 1:1.
15. A method of texturing a front surface a layer for thin-film deposition, comprising:
providing a substrate having front and back surfaces, said front surface having raised surface features having an aspect ratio of at least 1:1;
rastering a laser beam over the front surface to irradiate localized areas of the front surface, thereby forming partially overlapping melt pools in the substrate;
solidifying the melt pools to thereby retexture the surface, wherein the features of the retextured surface have aspect ratios no greater than about 0.5:1.
16. A method of texturing a front surface a layer for thin-film deposition, comprising:
providing a substrate having front and back surfaces, said front surface having raised surface features having a length scale of less than about 10 microns;
rastering a laser beam over the front surface to irradiate localized areas of the front surface, thereby forming partially overlapping melt pools in the substrate;
solidifying the melt pools to thereby retexture the surface, wherein the retextured surface has raised surface features having a length scale between about 10 microns and 1 mm.
17. The method of claim 15 , wherein the substrate is a metallic material.
18. The method of claim 15 , wherein the substrate is a polymer material.
19. The method of claim 16 , wherein the substrate is a metallic material.
20. The method of claim 16 , wherein the substrate is a polymer material.