Method of making thin silicon sheets for solar cells
A thin layer of single-crystal silicon is produced by forming first trenches in a silicon substrate having (111) orientation; forming narrower second trenches at the bases of the trenches; anisotropically etching lateral channels ( 4 ) from the second trenches, until adjacent etch fronts ( 16 ) substantially meet; and detaching said layer from the substrate. The trenches may be arranged so that the resultant layer has rows of slots, whit the slots in adjacent rows being mutually offset. Solar cells may be formed on strips ( 5 ) between the trenches, having lengths of more than 50 mm, widths of up to 5 mm, and thicknesses of less than 100 microns, and having two electrical contacts on the same face ( 6 ) of each strip ( 5 ).
1. A process for producing a layer of single-crystal silicon, said process comprising the steps of forming parallel, first trenches in a silicon substrate of substantially (111) orientation; applying an etch-resistant layer to the surface of said first trenches; forming a series of narrower second trenches inside said first trenches; contacting said second trenches with an etchant to which {111} planes of silicon are substantially resistant, and etching lateral channels from said second trenches until adjacent and opposing etch fronts at least substantially meet, thereby defining said layer of single-crystal silicon; and detaching said layer from said substrate.
2. A process according to claim 1 wherein said first and second trenches extend continuously from one edge of said silicon substrate to an opposite edge of said silicon substrate.
3. A process according to claim 1 wherein said first and second trenches do not extend as far as at least one edge of said silicon substrate.
4. A process according to claim 3 where said first and second trenches do not extend to any edge of said silicon substrate.
5. A process according to claim 1 wherein said adjacent and opposing etch fronts meet.
6. A process according to claim 1 wherein said layer of single-crystal silicon comprises a plurality of strips of silicon.
7. A process according to claim 6 where said strips are attached to said layer at least at one end of said strips, said process further comprising the step of separating said strips from said layer of silicon.
8. A process according to claim 6 or claim 7 further comprising the steps of forming a plurality of solar cells from said plurality of strips before or after said strips are separated.
9. A solar cell prepared by the process of claim 8 .