High-throughput printing of semiconductor precursor layer from microflake particles
Methods and devices are provided for high-throughput printing of semiconductor precursor layer from microflake particles. In one embodiment, the method comprises of transforming non-planar or planar precursor materials in an appropriate vehicle under the appropriate conditions to create dispersions of planar particles with stoichiometric ratios of elements equal to that of the feedstock or precursor materials, even after settling. In particular, planar particles disperse more easily, form much denser coatings (or form coatings with more interparticle contact area), and anneal into fused, dense films at a lower temperature and/or time than their counterparts made from spherical nanoparticles. These planar particles may be microflakes that have a high aspect ratio. The resulting dense film formed from microflakes are particularly useful in forming photovoltaic devices.
1. A method comprising:
formulating an ink of particles wherein about 50% or more of all the particles are microflakes each containing at least one element from group IB, IIIA and/or VIA and having a non-spherical, planar shape with irregular circumferential outline, wherein overall amounts of elements from group IB, IIIA and/or VIA contained in the ink are such that the ink has a desired stoichiometric ratio of the elements;
coating a substrate with the ink to form a precursor layer; and
processing the precursor layer in one or more steps to form a dense film.
2. The method of claim 1 wherein the dense film is used in the formation of a semiconductor absorber for a photovoltaic device.
3. The method of claim 1 wherein substantially all of the particles have a non-spherical, planar shape.
4. The method of claim 1 wherein the particles comprise of microflakes and nanoflakes.
5. The method of claim 1 wherein at least about 75% or more of a total weight of all the particles are microflakes.
6. The method of claim 1 wherein the planar shape of the microflakes creates greater surface area contact between adjacent microflakes that allows the dense film to form at a lower temperature and/or shorter time as compared to a film made from a precursor layer using an ink of spherical nanoparticles wherein the nanoparticles have a substantially similar material composition and the ink is otherwise substantially identical to the ink of claim 1 .
7. The method of claim 1 wherein the planar shape of the microflakes creates greater surface area contact between adjacent microflakes that allows the dense film to form at an annealing temperature at least 50 degrees C. less as compared to a film made from a precursor layer using an ink of spherical nanoparticles that is otherwise substantially identical to the ink of claim 1 .
8. The method of claim 1 wherein the planar shape of the microflakes creates greater surface area contact between adjacent microflakes relative to adjacent spherical nanoparticles and thus promotes increased atomic intermixing as compared to a film made from a precursor layer made from an ink of claim 1 .
9. The method of claim 1 wherein the planar shape of the microflakes creates a higher packing density in the precursor layer that forms the dense film as compared to a film made from a precursor layer made from an ink of spherical nanoparticles of the same composition that is otherwise substantially identical to the ink of claim 1 .
10. The method of claim 1 wherein the planar shape of the microflakes creates a packing density of at least 70% in the precursor layer.
11. The method of claim 1 wherein liquid group IIIA material is included in the ink.
12. The method of claim 1 wherein the microflakes contain sodium.
13. The method of claim 1 wherein the microflakes contain sodium at about 1 at % or less.
14. The method of claim 1 wherein the microflakes contains at least one of the following materials: Cu—Na, In—Na, Ga—Na, Cu—In—Na, Cu—Ga—Na, In—Ga—Na, Na—Se, Cu—Se—Na, In—Se—Na, Ga—Se—Na, Cu—In—Se—Na, Cu—Ga—Se—Na, In—Ga—Se—Na, Cu—In—Ga—Se—Na, Na—S, Cu—S—Na, In—S—Na, Ga—S—Na, Cu—In—S—Na, Cu—Ga—S—Na, In—Ga—S—Na, or Cu—In—Ga—S—Na.
15. The method of claim 1 wherein the film is formed from a precursor layer of the microflakes and a ink containing a sodium compound with an organic counter-ion or a sodium compound with an inorganic counter-ion.
16. The method of claim 1 wherein the film is formed from a precursor layer of the microflakes and a layer of a sodium containing material in contact with the precursor layer and/or microflakes containing at least one of the following materials: Cu—Na, In—Na, Ga—Na, Cu—In—Na, Cu—Ga—Na, In—Ga—Na, Na—Se, Cu—Se—Na, In—Se—Na, Ga—Se—Na, Cu—In—Se—Na, Cu—Ga—Se—Na, In—Ga—Se—Na, Cu—In—Ga—Se—Na, Na—S, Cu—S—Na, In—S—Na, Ga—S—Na, Cu—In—S—Na, Cu—Ga—S—Na, In—Ga—S—Na, or Cu—In—Ga—S—Na; and/or an ink containing the microflakes and a sodium compound with an organic counter-ion or a sodium compound with an inorganic counter-ion.