Photonic curing of nanocrystal films for photovoltaics
Methods of making a semiconductor layer from nanocrystals are disclosed. A film of nanocrystals capped with a ligand can be deposited onto a substrate; and the nanocrystals can be irradiated with one or more pulses of light. The pulsed light can be used to substantially remove the ligands from the nanocrystals and leave the nanocrystals unsintered or sintered, thereby providing a semiconductor layer. Layered structures comprising these semiconductor layers with an electrode are also disclosed. Devices comprising such layered structures are also disclosed.
1. A method comprising:
preparing nanocrystals capped with a ligand, wherein the ligand is an organic ligand;
removing the ligand by exchanging the organic ligand with an inorganic ligand;
depositing a film of the nanocrystals onto a substrate; and
irradiating the nanocrystals with one or more pulses of light to sinter the nanocrystals without melting and form the nanocrystals into a semiconductor layer substantially free of the organic ligand, wherein irradiating the nanocrystals with one or more pulses of light includes incorporating the inorganic ligand into the semiconductor layer, and wherein the semiconductor layer is a photovoltaic material.
2. The method of claim 1 , wherein the nanocrystals comprise compounds or alloys of elements in Group I, III, or VI 2 .
3. The method of claim 1 , wherein the nanocrystals are selected from the group consisting of CuInSe 2 , CdTe, Cu(In,Ga)Se 2 (CIGS), Cu(In,Ga)S 2 , Cu 2 ZnSnS 4 , Silicon, and combinations thereof.
4. The method of claim 1 , wherein the ligand is an alkyl, alkenyl, alkynyl, or aryl amine, ester, thioester, ether, or thioether.
5. The method of claim 4 , wherein the ligand is an oleyl amine.
6. The method of claim 1 , wherein the nanocrystals are CuInSe 2 or Cu(In,Ga)Se 2 nanocrystals.
7. The method of claim 1 , wherein the substrate is selected from the group consisting of glass, metal-coated glass, polymer material, metal-coated polymers, metal, metal alloy, quartz, paper, nanowires, and nanotubes.
8. The method of claim 1 , wherein the substrate is selected from the group consisting of Mo-coated glass, Au-coated glass, Ni-coated glass, indium tin oxide-coated glass, Mo-coated polyethylene terephthalate, Au-coated polyethylene terephthalate, Ni-coated polyethylene terephthalate, and indium tin oxide-coated polyethylene terephthalate.
9. The method of claim 1 , wherein the substrate is Mo/MoSe 2 bilayer-coated glass.
10. The method of claim 1 , wherein depositing the nanocrystals onto the substrate is by spray casting, spin coating, gravure, or flexographic printing.
11. The method of claim 1 , wherein a light source of the one or more pulses of light is a flash lamp.
12. The method of claim 1 , wherein a light source of the one or more pulses of light is a broad band light source.
13. The method of claim 1 , wherein a pulse duration is under 1 s.
14. The method of claim 1 , wherein a pulse duration is from about 100 to about 350 μs.
15. The method of claim 1 , wherein a pulse fluence is from about 1.0 to about 7.1 J/cm 2 .
16. The method of claim 1 , wherein irradiating the nanocrystals modifies a conductivity of the film of the nanocrystals, wherein a conductivity of the semiconductor layer is greater than the conductivity of the film of the nanocrystals.
17. The method of claim 1 , wherein the ligand is removed using one or more of thermal removal, chemical removal, optical removal, plasma treatment, solvent washing, or ligand exchange.