Quantum dot light emitting layer

• US 20070057263A1
• Filed: 09/14/2005
• Published: 03/15/2007
• Est. Priority Date: 09/14/2005
• Status: Active Grant

• Current Assignee: Nanoco Technologies Limited (Nanoco Group Plc)
• Original Assignee: Eastman Kodak Company
• Inventors: Kahen, Keith
• Granted Patent: US 7,615,800 B2
• Time in Patent Office: Days
• US Class Current: 257/79
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C09K 11/02 Use of particular materials as binders, particle coatings or suspension media therefor
• CPC Class Codes: C09K 11/565 with zinc cadmium
• CPC Class Codes: C09K 11/883 with zinc or cadmium
• CPC Class Codes: H01L 33/08 with a plurality of light emitting regions, e.g. laterally discontinuous light emitting layer or photoluminescent region integrated within the semiconductor body H01L27/15 takes precedence
• CPC Class Codes: H05B 33/14 characterised by the chemical or physical composition or the arrangement of the electroluminescent material , or by the simultaneous addition of the electroluminescent material in or onto the light source
• CPC Class Codes: Y10S 977/95 Electromagnetic energy

Abstract

An inorganic light emitting layer having a plurality of light emitting cores, each core having a semiconductor material that emits light in response to recombination of holes and electrons, each such light emitting core defining a first bandgap; a plurality of semiconductor shells formed respectively about the light emitting cores to form core/shell quantum dots, each such semiconductor shell having a second bandgap wider than the first bandgap; and a semiconductor matrix connected to the semiconductor shells to provide a conductive path through the semiconductor matrix and to each such semiconductor shell and its corresponding light emitting core so as to permit the recombination of holes and electrons.

Claims

1. An inorganic light emitting layer comprising:

(a) a plurality of light emitting cores, each core having a semiconductor material that emits light in response to recombination of holes and electrons, each such light emitting core defining a first bandgap;

(b) a plurality of semiconductor shells formed respectively about the light emitting cores to form core/shell quantum dots, each such semiconductor shell having a second bandgap wider than the first bandgap; and

(c) a semiconductor matrix connected to the semiconductor shells to provide a conductive path through the semiconductor matrix and to each such semiconductor shell and its corresponding light emitting core so as to permit the recombination of holes and electrons.

2. The inorganic light emitting layer of claim 1 wherein each light emitting core includes a Type IV, III-V, or II-VI semiconductor material.

3. The inorganic light emitting layer of claim 2 wherein each light emitting core includes CdSe.

4. The inorganic light emitting layer of claim 1 wherein each semiconductor shell includes a Type II-VI semiconductor material.

5. The inorganic light emitting layer of claim 4 wherein each semiconductor shell includes ZnS.

6. The inorganic light emitting layer of claim 2 wherein each semiconductor shell includes a Type II-VI semiconductor material.

7. The inorganic light emitting layer of claim 1 wherein the semiconductor matrix is formed from inorganic nanoparticles that includes Type IV, III-V, or II-VI semiconductor material.

8. The inorganic light emitting layer of claim 7 wherein the bandgap of the semiconductor matrix material is within 0.2 eV of the bandgap of the semiconductor shell material.

9. A method of making the inorganic light emitting layer of claim 1 comprising:

(a) providing a colloidal dispersion of the core/shell quantum dots and semiconductor matrix nanoparticles;

(b) depositing the colloidal dispersion to form a film; and

(c) annealing the film to form the inorganic light emitting layer.

10. The inorganic light emitting layer of claim 9 wherein the layer thickness is 10 to 100 nm.

11. The inorganic light emitting layer of claim 9 wherein the deposited film is annealed at a temperature between 250 and 300 C for up to 60 minutes.

12. An inorganic light emitting device comprising:

(a) spaced anode and cathode electrodes; and

(b) an inorganic light emitting layer according to claim 1 disposed between the anode and cathode electrodes.

13. The inorganic light emitting device of claim 12 including a p-type transport layer disposed between the anode and inorganic light-emitting layer.

14. The inorganic light emitting device of claim 13 wherein the p-type transport layer includes p-type ZnSe, ZnS, or ZnTe.

15. The inorganic light emitting device of claim 13 wherein the conductivity of the p-type transport layer is enhanced by a dopant including nitrogen or lithium or both.

16. The inorganic light emitting device of claim 12 including a n-type transport layer disposed between the cathode and inorganic light-emitting layer.

17. The inorganic light emitting device of claim 16 wherein the n-type transport layer includes n-type ZnSe or ZnS.

18. The inorganic light emitting device of claim 16 wherein the conductivity of the n-type transport layer is enhanced by a Type III dopant including Al, In, or Ga.

19. The inorganic light emitting device of claim 13 including a n-type transport layer disposed between the cathode and inorganic light-emitting layer.

20. The inorganic light emitting device of claim 19 wherein the n-type transport layer includes n-type ZnSe, or ZnS.

21. The inorganic light emitting device of claim 19 wherein the conductivity of the n-type transport layer is enhanced by a Type III dopant including Al, In, or Ga.

22. An inorganic light emitting device comprising:

(a) a substrate;

(a) an anode formed on the substrate and a cathode spaced from the anode; and

(b) an inorganic light emitting layer according to claim 1 disposed between the anode and cathode.

23. The inorganic light emitting device of claim 22 wherein the substrate includes p-type semiconductor material.

24. The inorganic light emitting device of claim 23 wherein the light emitting layer is formed on one side of the substrate and the anode is formed on the other side of the substrate.

25. The inorganic light emitting device of claim 22 wherein the substrate is formed of glass, metal foil, or plastic and the anode is formed on the substrate.