Device including quantum dots and method for making same

Patent metadata

Field	Value
Publication number	US-9520573-B2
Application number	US-201213422683-A
Country	US
Kind code	B2
Filing date	Mar 16, 2012
Priority date	May 16, 2011
Publication date	Dec 13, 2016
Grant date	Dec 13, 2016

Abstract

A device comprises an anode; a cathode; a layer therebetween comprising quantum dots; and a first layer comprising a material capable of transporting and injecting electrons in, or forming, contact with the cathode, the material comprising nanoparticles of an inorganic semiconductor material. In one embodiment of the device, quantum dots comprise a core comprising a first semiconductor material that confines holes better than electrons in the core and an outer shell comprising a second semiconductor material that is permeable to electrons. In another embodiment of the device, the nanoparticles comprise n-doped inorganic semiconductor material, and a second layer comprising a material capable of transporting electrons is disposed between the layer including quantum dots and the first layer, wherein the second layer has a lower electron conductivity than the first. In a further embodiment of the device, the first layer is UV treated. A method and other embodiments are also disclosed.

First claim

What is claimed is:

1. A light emitting device comprising:
a pair of electrodes comprising an anode and a cathode;
an emissive layer comprising electroluminescent quantum dots disposed between the electrodes, wherein the quantum dots comprise a core comprising a first semiconductor material and an outer shell surrounding the core, the outer shell comprising a second semiconductor material;
a first layer comprising an electron injection and transport material comprising nanoparticles of an n-doped inorganic semiconductor, the first layer being in contact with the cathode and positioned between the emissive layer and the cathode, wherein the n-doped inorganic semiconductor comprises zinc oxide, titanium oxide, or a mixture including at least one of the foregoing that is n-doped, and
a second layer comprising an electron transport material comprising nanoparticles of an inorganic semiconductor, the second layer being disposed between the emissive layer and the first layer, wherein the second layer has a lower electron conductivity than the first layer, and
wherein the device has a peak external quantum efficiency of at least 14% when measured over the voltage range of 1 V to 10 V.

2. A light emitting device in accordance with claim 1 wherein the absolute value of the difference between E conduction band edge of the inorganic semiconductor material included in the second layer and E LUMO of the quantum dots is no greater than 0.5 eV measured relative to vacuum level with an energy level=0 eV.

3. A light emitting device in accordance with claim 1 wherein the first layer is UV (ultraviolet light) treated.

4. A light emitting device in accordance with claim 1 wherein the first semiconductor material confines holes better than electrons in the core and the second semiconductor material is permeable to electrons.

5. A light emitting device in accordance with claim 1 wherein the absolute value of the difference between E conduction band edge of the first semiconductor material included in the quantum dot core and E conduction band edge of the second semiconductor material included in the outer shell of the quantum dot is less than the absolute value of the difference between E valence band edge of the first semiconductor material and E valence band edge of the second semiconductor material, wherein the differences are calculated based on the E conduction band edge and E valence band edge values for bulk forms of the first and second semiconductor materials measured relative to vacuum level with an energy level=0 eV.

6. A light emitting device in accordance with claim 1 wherein the device has a peak external quantum efficiency in a range from 14% to 19.1% when measured over the voltage range of 1 V to 10 V.

7. A light emitting device in accordance with claim 1 wherein the first layer and the cathode form an ohmic contact during operation of the device.

8. A light emitting device in accordance with claim 1 further including a layer comprising a material capable of transporting holes disposed between the layer comprising quantum dots and the anode.

9. A light emitting device in accordance with claim 1 further including hole injection layer between the layer comprising quantum dots and the anode.

10. A light emitting device in accordance with claim 1 wherein at least a portion of the quantum dots comprise a core comprising a first semiconductor material, a first shell surrounding the core comprising a second semiconductor material, and a second shell comprising a third semiconductor material, the second shell surrounding the first shell.

11. A light emitting device in accordance with claim 1 wherein the device is encapsulated.

12. A light emitting device in accordance with claim 1 wherein the device has a peak internal quantum efficiency of the device of at least about 80%.

13. A light emitting device in accordance with claim 1 wherein the nanoparticles of an n-doped inorganic semiconductor have an average particle size less than 20 nm.

14. A light emitting device in accordance with claim 1 wherein the nanoparticles of an n-doped inorganic semiconductor have an average particle size less than 10 nm.

15. A light emitting device in accordance with claim 1 wherein the nanoparticles of an n-doped inorganic semiconductor have an average particle in a range from about 2 to about 6 nm.

16. A light emitting device in accordance with claim 1 wherein the n-dopant comprises indium, aluminum, or gallium.

17. A light emitting device in accordance with claim 4 wherein the absolute value of the difference between E conduction band edge of the first semiconductor material included in the quantum dot core and E conduction band edge of the second semiconductor material included in the outer shell of the quantum dot is less than the absolute value of the difference between E valence band edge of the first semiconductor material and E valence band edge of the second semiconductor material, wherein the differences are calculated based on the E conduction band edge and E valence band edge values for bulk forms of the first and second semiconductor materials measured relative to vacuum level with an energy level=0 eV.

18. A light emitting device in accordance with claim 4 wherein the first semiconductor material comprises CdSe and the second semiconductor material comprises CdS.

19. A light emitting device in accordance with claim 4 having a peak EQE of at least 18% when measured over a voltage range from 1 Volt to 10 Volts.

20. A light emitting device in accordance with claim 4 having a light turn-on voltage less than 2 Volts.

21. A light emitting device in accordance with claim 4 having a light turn-on voltage less than 1.5 Volts.

22. A light emitting device in accordance with claim 5 wherein the first semiconductor material comprises CdSe and the second semiconductor material comprises CdS.

23. A light emitting device in accordance with claim 5 wherein the absolute value of the difference between E conduction band edge of the first semiconductor material included in the quantum dot core and E conduction band edge of the second semiconductor material included in the outer shell of the quantum dot is less than the absolute value of the difference between E valence band edge of the first semiconductor material and E valence band edge of the second semiconductor material, wherein the differences are calculated based on the E conduction band edge and E valence band edge values for bulk forms of the first and second semiconductor materials measured relative to vacuum level with an energy level=0 eV.

24. A light emitting device in accordance with claim 10 wherein the first semiconductor material comprises CdSe, the second semiconductor material comprises CdS, and the third semiconductor material comprises ZnS.

25. A light emitting device including an emissive layer comprising electroluminescent quantum dots disposed between an anode and a cathode,
a first layer comprising an electron injection and transport material comprising nanoparticles of a first inorganic semiconductor material, the first layer being disposed between the layer comprising quantum dots and the cathode, wherein the first layer and the cathode form an ohmic contact during operation of the device,
wherein the first inorganic semiconductor material includes at least one of zinc oxide, a titanium oxide, a niobium oxide, an indium tin oxide, copper oxide, nicke

Assignees

• Zhou Zhaoqun
• Kazlas Peter T
• Mashford Benjamin S
• Qd Vision Inc

Inventors

• Zhou Zhaoqun
• Kazlas Peter T
• Mashford Benjamin S

Classifications

• H10K30/50

  Photovoltaic [PV] devices · CPC title

• H10K50/115

  comprising active inorganic nanostructures, e.g. luminescent quantum dots · CPC title

• C09K11/025 Primary

  non-luminescent particle coatings or suspension media · CPC title

• H10H20/812

  within the light-emitting regions, e.g. having quantum confinement structures · CPC title

• H01L51/4233 Primary

  Electricity · mapped topic