Semiconductor-nanocrystal/conjugated polymer thin films
View Patent ↗The invention described herein provides for thin films and methods of making comprising inorganic semiconductor-nanocrystals dispersed in semiconducting-polymers in high loading amounts. The invention also describes photovoltaic devices incorporating the thin films.
1. A method of producing a photovoltaic device, comprising:
introducing a population of elongated semiconductor nanocrystals into a semiconducting polymer in a binary solvent to form a nanocrystal-polymer composite, the population of elongated nanocrystals having aspect ratios greater than about 2;
depositing a photoactive film comprising the nanocrystal-polymer composite onto a first planar electrode;
heating the photoactive film until the binary solvent is substantially removed from the photoactive film;
aligning at least a portion of the nanocrystals predominantly normal to a plane of the photoactive film such that between about 10 and 99% of the nanocrystals have a long axis which is aligned not more than 20 degrees from a normal to the plane of the photoactive film; and
depositing a second electrode onto the photoactive film opposite the first electrode.
2. The method of claim 1 , wherein the nanocrystals comprise rods.
3. The method of claim 1 , further comprising providing a hole injecting layer between the photoactive film and the first planar electrode.
4. The method of claim 1 , wherein at least the portion of the nanocrystals comprise branched nanocrystals.
5. The method of claim 4 , wherein at least a portion of the branched nanocrystals have four arms and have a tetrahedral symmetry.
6. The method of claim 1 , wherein the photoactive film has a thickness of between about 100 nm and 350 nm.
7. The method of claim 1 , wherein the polymer is a conjugated polymer, and wherein the photoactive film comprises the conjugated polymer having the nanocrystals embedded therein.
8. The method of claim 7 , wherein the conjugated polymer is selected from the group consisting of (poly(2-methoxy-5-(2′-ethylhexyloxy)p-phenylenevinylene) (MEH-PPV) and poly(3-hexylthiophene) (P3HT).
9. The method of claim 1 , wherein the nanocrystals comprise rods having lengths of between about 20 nm and 200 nm.
10. The method of claim 1 , wherein the nanocrystals are selected from the group consisting of CdSe, InP and CdTe.
11. The method of claim 1 , wherein said aligning comprises using an electric field to align the portion of the nanocrystals.
12. The method of claim 1 , wherein said aligning comprises using a magnetic field to align the portion of the nanocrystals.
13. The method of claim 1 , wherein said aligning comprises using stretch alignment to align the portion of the nanocrystals.
14. The method of claim 1 , wherein the nanocrystals comprise tetrapods which orient themselves naturally in the photoactive film.
15. The method of claim 1 , wherein said depositing the photoactive film on the first planar electrode comprises spin casting a solution of the film onto the first electrode.
16. The method of claim 15 wherein aligning comprises using a magnetic field to align at least the portion of the nanocrystals.
17. The method of claim 16 wherein the nanocrystals comprise InP.
18. The method of claim 4 , wherein at least a portion of the branched nanocrystals have at least one arm with an aspect ratio greater than about 1.
19. The method of claim 4 , wherein at least a portion of the branched nanocrystals have at least one arm with an aspect ratio greater than about 2.
20. The method of claim 4 , wherein at least a portion of the branched nanocrystals have at least one arm with an aspect ratio greater than about 5.
21. The method of claim 1 , wherein at least a portion of the nanocrystals have aspect ratios greater than about 20.
22. The method of claim 1 , wherein at least a portion of the nanocrystals have aspect ratios of about 50.
23. The method of claim 1 , wherein at least a portion of the nanocrystals have aspect ratios of between about 2 and 10.
24. The method of claim 1 , wherein at least a portion of the nanocrystals have aspect ratios greater than 5.
25. The method of claim 1 , wherein at least a portion of the nanocrystals have aspect ratios of about 10.
26. The method of claim 1 , wherein at least a portion of the nanocrystals comprise a core and a shell.
27. The method of claim 1 , wherein at least a portion of the nanocrystals have lengths similar to the thickness of the photoactive film.
28. The method of claim 1 , wherein the population of nanocrystals spans a substantial portion of the thickness of the photoactive film.
29. The method of claim 1 , wherein at least a portion of the nanocrystals individually span a substantial portion of the thickness of the photoactive film.
30. The method of claim 1 , wherein at least a portion of the nanocrystals are self-aligning.