Methods of making quantum dot films
Optical and optoelectronic devices and methods of making same. Under one aspect, an optical device includes an integrated circuit an array of conductive regions; and an optically sensitive material over at least a portion of the integrated circuit and in electrical communication with at least one conductive region of the array of conductive regions. Under another aspect, a method of forming a nanocrystalline film includes fabricating a plurality of nanocrystals having a plurality of first ligands attached to their outer surfaces; exchanging the first ligands for second ligands of different chemical composition than the first ligands; forming a film of the ligand-exchanged nanocrystals; removing the second ligands; and fusing the cores of adjacent nanocrystals in the film to form an electrical network of fused nanocrystals. Under another aspect, a film includes a network of fused nanocrystals, the nanocrystals having a core and an outer surface, wherein the core of at least a portion of the fused nanocrystals is in direct physical contact and electrical communication with the core of at least one adjacent fused nanocrystal, and wherein the film has substantially no defect states in the regions where the cores of the nanocrystals are fused.
1. A method of forming a nanocrystalline film, the method comprising:
(a) fabricating a plurality of nanocrystals, the nanocrystals having a core and an outer surface, a plurality of first ligands having a first length being attached to the outer surface;
(b) exchanging the plurality of first ligands attached to the outer surface of the nanocrystals for a plurality of second ligands having a second length and having a different chemical composition than the plurality of first ligands;
(c) forming a film of ligand-exchanged nanocrystals, wherein at least a portion of the ligand-exchanged nanocrystals are adjacent at least one other ligand-exchanged nanocrystal;
(d) removing the second ligands attached to the outer surfaces of the nanocrystals of the film of ligand-exchanged nanocrystals so as to bring the outer surfaces of adjacent nanocrystals into closer proximity; and
(e) fusing the cores of adjacent nanocrystals so as to form an electrical network of fused nanocrystals, wherein removing the second ligands comprises volatilizing the second ligands during fusing the cores of adjacent nanocrystals.
2. The method of claim 1 , wherein volatilizing the second ligands causes a relatively small change in the volume of the film of ligand-exchanged nanocrystals.
3. The method of claim 1 , wherein fusing the cores of adjacent nanocrystals comprises annealing the film of ligand-exchanged nanocrystals.
4. The method of claim 1 , further comprising modifying the outer surfaces of the fused nanocrystals.
5. The method of claim 4 , wherein modifying the outer surfaces comprises depositing a semiconductor shell on the fused nanocrystals.
6. A method of forming a device, the method comprising:
(a) forming a film of nanocrystals, the nanocrystals having a core and an outer surface, a plurality of ligands being attached to the outer surface, at least a portion of the nanocrystals being in physical contact with at least one adjacent nanocrystals;
(b) removing the ligands from at least a portion of the nanocrystals;
(c) annealing the film of nanocrystals so as to fuse the cores of the nanocrystals to the cores at least one adjacent nanocrystal and thus form an electrical network of fused nanocrystals; and
(d) providing first and second electrodes in spaced relation and in electrical communication with first and second portions of the electrical network of fused nanocrystals, wherein providing the first and second electrodes in spaced relation and in electrical communication with the electrical network of fused nanocrystals comprises forming the first electrode on the substrate, subsequently performing steps (a)-(c), and subsequently providing the second electrode over the electrical network of fused nanocrystals.
7. The method of claim 6 , wherein the second electrode comprises at least one of aluminum, gold, platinum, silver, magnesium, copper, indium tin oxide (ITO), tin oxide, tungsten oxide, and combinations and layer structures thereof.
8. The method of claim 6 , wherein the second electrode is at least partially optically transparent.
9. The method of claim 6 , wherein the second electrode comprises at least one of a bandpass filter and a bandblock filter.
10. A method of forming a nanocrystalline film from a plurality of nanocrystals, the nanocrystals having a core and an outer surface, a plurality of ligands being attached to the outer surface, the method comprising:
(a) forming a film of ligand-attached nanocrystals, wherein at least a portion of the ligand-attached nanocrystals are adjacent at least one other ligand-attached nanocrystal;
(b) removing the ligands attached to the outer surfaces of the nanocrystals of the film of ligand-exchanged nanocrystals; and
(c) fusing the cores of adjacent nanocrystals so as to form an electrical network of fused nanocrystals, wherein removing the ligands comprises volatilizing the ligands during of fusing the cores of adjacent nanocrystals.
11. The method of claim 10 , wherein fusing the cores of adjacent nanocrystals comprises annealing the film of ligand-attached nanocrystals.
12. The method of claim 10 , further comprising modifying the outer surfaces of the fused nanocrystals.
13. The method of claim 12 , wherein modifying the outer surfaces comprises depositing a semiconductor shell on the fused nanocrystals.