Light-emitting nanocomposite particles

• US 8,361,823 B2
• Filed: 06/29/2007
• Issued: 01/29/2013
• Est. Priority Date: 06/29/2007
• Status: Expired due to Fees

• Current Assignee: Nanoco Technologies Limited (Nanoco Group Plc)
• Original Assignee: Eastman Kodak Company
• Inventors: Kahen, Keith B.
• Primary Examiner(s): Maldonado, Julio J
• Assistant Examiner(s): MCCALL SHEPARD, SONYA D
• Application Number:
  US11/770,833
• Publication Number:
  US 20090001349A1
• Time in Patent Office: 2,041 Days
• Field of Search: 977/773, 977/774, 977949-952, 977/954, 977/882, 977890-892, 977778-787, 257 9- 39, 257 79-103, 257/E33.003, 257/E21.352, 257 33001- 33077, 438 22- 47, 438 64- 73
• US Class Current: 438/47
• CPC Class Codes: H05B 33/145 Arrangements of the electroluminescent material

Abstract

A method of making an inorganic light emitting layer includes combining a solvent for semiconductor nanoparticle growth, a solution of core/shell quantum dots, and semiconductor nanoparticle precursor(s); growing semiconductor nanoparticles to form a crude solution of core/shell quantum dots, semiconductor nanoparticles, and semiconductor nanoparticles that are connected to the core/shell quantum dots; forming a single colloidal dispersion of core/shell quantum dots, semiconductor nanoparticles, and semiconductor nanoparticles that are connected to the core/shell quantum dots; depositing the colloidal dispersion to form a film; and annealing the film to form the inorganic light emitting layer.

Claims

1. A method of making an inorganic light emitting layer comprising:

(a) combining a solvent for conductive semiconductor nanoparticle growth, a solution of core/shell semiconductor quantum dots, and semiconductor nanoparticle precursor(s), selected to provide a conductive path for electrons and holes through the conductive semiconductor nanoparticles and into the core/shell quantum dots;

(b) growing conductive semiconductor nanoparticles to form a crude solution of core/shell semiconductor quantum dots, conductive semiconductor nanoparticles, and conductive semiconductor nanoparticles that are connected to the core/shell semiconductor quantum dots;

(c) forming a single colloidal dispersion of core/shell semiconductor quantum dots, conductive semiconductor nanoparticles, and conductive semiconductor nanoparticles that are connected to the core/shell semiconductor quantum dots;

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

(e) annealing the film to form the inorganic light emitting layer that provides a conductive path for electrons and holes from the edges of the inorganic light emitting layer, through the conductive semiconductor nanoparticles and into the core/shell quantum dots.

2. The method of claim 1 wherein the solvent for semiconductor nanoparticle growth is a coordinating solvent.

3. The method of claim 1 wherein step (a) comprises combining the solvent for semiconductor nanoparticle growth with the core/shell semiconductor quantum dots and a first precursor, heating to a temperature of 100°

C. or greater, and adding a second semiconductor precursor.

4. The method of claim 1 wherein the growing step includes heating, subjecting the mixture to elevated pressures, or providing microwave energy to the mixture, or combinations thereof.

5. The method of claim 1 further including performing a ligand exchange to cover the surface of the core/shell semiconductor quantum dots, conductive semiconductor nanoparticles, and conductive semiconductor nanoparticles that are connected to the core/shell semiconductor quantum dots with organic ligands whose boiling point is below 200°

C.

6. The method of claim 1 wherein the cores of the core/shell semiconductor quantum dots comprise a type IV, III-V, IV-VI, or II-VI semiconductor material.

7. The method of claim 1 wherein the conductive semiconductor nanoparticles connected to core/shell semiconductor quantum dots comprise a first semiconductor material and the shells of the core/shell semiconductor quantum dots comprise a second semiconductor material and wherein the bandgap energy levels of the first semiconductor material are within 0.2 eV of the bandgap energy levels of the second semiconductor material.

8. The method of claim 1 wherein the shells of the core/shell semiconductor quantum dots comprise type IV, III-V, IV-VI, or II-VI semiconductor material.

9. The method of claim 1 wherein the core/shell semiconductor quantum dots include cores containing Cd_xZn_1-xSe, where x is between 0 and 1, and shells containing elements selected from the group consisting of Zn, S, and Se or combinations thereof.

10. The method of claim 1 wherein the core/shell semiconductor quantum dots include a shell of sufficient thickness so as to confine a conduction band electron or valence band hole to the core region and wherein, when so confined, the wave function of the electron or hole does not extend to the surface of the core/shell semiconductor quantum dot.

11. The method of claim 1 wherein the conductive semiconductor nanoparticles connected to core/shell semiconductor quantum dots comprise type IV, III-V, IV-VI, or II-VI semiconductor material.

12. The method of claim 1 wherein the conductive semiconductor nanoparticles connected to core/shell semiconductor quantum dots comprise conductive nanowires wherein the conductive nanowires have an average diameter of less than 20 nm and an aspect ratio greater than 10.

13. The method of claim 12 wherein the conductive nanowires have an average diameter of less than 5 nm and an aspect ratio greater than 30.

14. The method of claim 1 further including the step of adding a second colloidal dispersion comprising semiconductor nanowires to the single colloidal dispersion.

15. The method of claim 1 wherein the annealing step includes a first annealing step at a temperature between 120°

C. and 220°

C. for a time up to 60 minutes and a second annealing step at a temperature between 250°

C. and 400°

C. for a time up to 60 minutes.