Self-supported film and silicon wafer obtained by sintering
A silicon wafer for a photovoltaic cell is produced by a debinding step of a self-supported film formed of at least one main thin layer comprising at least 50% volume of silicon particles, devoid of silicon oxide and encapsulated in a polymer matrix protecting them against oxidation, followed by a sintering step to form the silicon wafer.
1. A self-supported film including at least a main thin layer comprising at least 50% volume of silicon particles encapsulated in a polymer matrix protecting the silicon particles against oxidation, the silicon particles being devoid of silicon oxide and the polymer matrix comprising at least one oxygen-free polymer protecting against oxidation.
2. The film according to claim 1 , wherein the main thin layer comprises between 70% and 85% volume of silicon particles.
3. The film according to claim 1 , wherein the oxygen-free polymer is formed from at least an alkene monomer.
4. The film according to claim 3 , wherein the oxygen-free polymer is selected from the group consisting of polyethylene and polypropylene.
5. The film according to claim 1 , wherein at least a part of the silicon particles has a mean diameter comprised between 10 μm and 100 μm.
6. The film according to claim 1 , wherein at least a part of the silicon particles has a mean diameter comprised between 10 nm and 100 nm.
7. The film according to claim 1 , wherein the main thin layer comprises n-type or p-type doping elements.
8. The film according to claim 1 , wherein it comprises at least two superposed main thin layers each comprising respectively n-doped and p-doped silicon particles.
9. The film according to claim 1 , wherein it comprises two protective layers each comprising at least the polymer matrix and between which at least the main thin layer is arranged.
10. A method for producing a silicon wafer for a photovoltaic cell, comprising:
providing a self-supported film including at least a main thin layer comprising at least 50% volume of silicon particles encapsulated in a polymer matrix protecting the silicon particles against oxidation, the silicon particles being devoid of silicon oxide and the polymer matrix comprising at least one oxygen-free polymer protecting against oxidation,
debinding the self-supported film so as to remove the polymer matrix, and
sintering the self-supported film so as to form the silicon wafer.
11. The method according to claim 10 , wherein debinding the self-supported film is preceded by forming the self supported film, forming the self-supported film comprising at least production of the main thin layer by extrusion of a mixture comprising at least the silicon particles devoid of silicon oxide and granules of at least one oxygen-free polymer protecting against oxidation or of at least one precursor of said oxygen-free polymer.
12. The method according to claim 11 , wherein the mixture comprises a dispersing agent configured to prevent silicon particles from agglomerating in the polymer matrix.
13. The method according to claim 10 , wherein the mixture comprises mineral particles absorbing water and oxygen.
14. The method according to claim 13 , wherein the mineral particles are selected from the group consisting of clays and carbon nanotubes.
15. The method according to claim 10 , wherein the surface of the silicon particles is cleaned with hydrofluoric acid before the main thin layer is formed.
16. The method according to claim 10 , wherein debinding the self-supported film comprises heating the self-supported film at a temperature comprised between about 300° C. and about 500° C.
17. The method according to claim 10 , wherein sintering the self-supported film comprises heating the self-supported film at a temperature comprised between about 1000° C. and about 1300° C.
18. The method according to claim 10 , wherein sintering the self-supported film is performed in a hydrogen atmosphere.