Method for texturing silicon surface to create black silicon for photovoltaic applications
View Patent ↗The surface of silicon is textured to create black silicon on a nano-micro scale by electrochemical reduction of a silica layer on silicon in molten salts. The silica layer can be a coating, or a layer caused by the oxidation of the silicon.
1. A method of producing a textured silicon surface, comprising:
providing a silicon substrate with a surface layer of silica;
attaching an electrical conductor to the surface layer of silica to provide a silica/electrical conductor interface;
providing an electrolytic cell including a molten salt electrolyte, with the silica/electrical conductor interface forming at least part of one electrode;
applying a potential to the electrical conductor sufficient to reduce the surface layer of silica without depositing a cation from the molten salt electrolyte.
2. A method according to claim 1 , further comprising: forming the surface layer of silica by coating the silicon substrate with silica.
3. A method according to claim 1 , further comprising: forming the surface layer of silica by oxidizing the silicon substrate.
4. A method according to claim 1 in which the electrical conductor is stable in the molten salt electrolyte.
5. A method according to claim 4 , in which the electrical conductor is selected from the group consisting of molybdenum and tungsten.
6. A method according to claim 1 , in which the molten salt electrolyte is at a temperature from 500° C. to 1000° C.
7. A method according to claim 1 , in which the molten salt electrolyte comprises or consists of a halide of calcium, barium, strontium or lithium.
8. A method according to claim 7 , in which the molten salt electrolyte is calcium chloride.
9. A method according to claim 1 , further comprising maintaining the potential applied until a surface morphology with globular structures including single nano-speroids are formed.
10. A method according to claim 9 , in which the surface morphology includes pores, each with a diameter of at least 50 nm.
11. A method according to claim 1 , in which the electrolytic cell further includes a graphite electrode.
12. The method according to claim 9 , in which the surface morphology has a microstructure finer than 1 micron.
13. The method according to claim 12 , in which the surface morphology has a microstructure finer than 100 nm.