Tandem OLEDs having low drive voltage

• US 7,075,231 B1
• Filed: 01/03/2005
• Issued: 07/11/2006
• Est. Priority Date: 01/03/2005
• Status: Active Grant

• Current Assignee: Global OLED Technology LLC (LG Display Co., Ltd.)
• Original Assignee: Eastman Kodak Company
• Inventors: Hatwar, Tukaram K., Liao, Liang-Sheng, Klubek, Kevin P., Vargas, J. Ramon, Comfort, Dustin L.
• Primary Examiner(s): Williams, Joseph
• Assistant Examiner(s): Won, Bumsuk
• Application Number:
  US11/028,033
• Publication Number:
  US 20060145604A1
• Time in Patent Office: 554 Days
• Field of Search: 313/506, 313/503, 313/504, 313/509
• US Class Current: 313/506
• CPC Class Codes: C09K 2211/1029 containing one nitrogen atom as the heteroatom
• CPC Class Codes: C09K 2211/1037 with sulfur
• CPC Class Codes: H10K 2102/351 Thickness
• CPC Class Codes: H10K 50/155 comprising dopants
• CPC Class Codes: H10K 50/165 comprising dopants
• CPC Class Codes: H10K 50/19 Tandem OLEDs
• CPC Class Codes: H10K 71/30 Doping active layers, e.g. electron transporting layers
• CPC Class Codes: H10K 85/324 comprising aluminium, e.g. Alq3
• CPC Class Codes: H10K 85/631 Amine compounds having at least two aryl rest on at least one amine-nitrogen atom, e.g. triphenylamine
• CPC Class Codes: H10K 85/6574 comprising only oxygen in the heteroaromatic polycondensed ring system, e.g. cumarine dyes

Abstract

A tandem OLED includes an anode, a cathode, and at least two electroluminescent units disposed between the anode and the cathode, wherein each of the electroluminescent units includes at least one hole-injecting layer, one hole-transporting layer, one organic light-emitting layer, one electron-transporting layer, and one electron-injecting layer. The OLED also includes at least one intermediate connector, wherein each of the intermediate connectors includes at least one layer, and wherein each of the intermediate connectors is disposed between electroluminescent units, wherein the thickness of each layer in each of the electroluminescent units and the intermediate connectors is selected to satisfy the test condition that the voltage drop from the anode to the cathode is less than 4.0 V×N (the number of electroluminescent units) at 20 mA/cm².

Claims

1. A tandem OLED comprising:

a) an anode;

b) a cathode;

c) at least two electroluminescent units disposed between the anode and the cathode, wherein each of the electroluminescent units includes at least one hole-injecting layer, one hole-transporting layer, one organic light-emitting layer, one electron-transporting layer, and one electron-injecting layer;

d) at least one intermediate connector, wherein each of the intermediate connectors includes at least one layer, and wherein each of the intermediate connectors is disposed between electroluminescent units; and

e) wherein the thickness of each layer in each of the electroluminescent units and the intermediate connectors is selected to provide high luminous efficiency using optical out-coupling while satisfying the test condition that the voltage drop from the anode to the cathode is less than 4.0 V×

N (the number of electroluminescent units) at 20 mA/cm².

2. The tandem OLED of claim 1 wherein there are three electroluminescent units disposed between the anode and the cathode, wherein each of the electroluminescent units includes at least one hole-injecting layer, one hole-transporting layer, one organic light-emitting layer, one electron-transporting layer, and one electron-injecting layer and two intermediate connectors, wherein each of the intermediate connectors includes at least one layer, and wherein each of the intermediate connectors is disposed between electroluminescent units, and the thickness of each layer in each of the electroluminescent units and the intermediate connectors is selected to provide high luminous efficiency using optical out-coupling while satisfying the test condition that the voltage drop from the anode to the cathode is less than 12 V at 20 mA/cm².

3. The tandem OLED of claim 1 wherein the hole-transporting layer in contact with the organic light-emitting layer in each of the electroluminescent units has a thickness of less than or equal to 10 nm, wherein the organic light-emitting layer in each of the electroluminescent units has a thickness of less than or equal to 20 nm, wherein the electron-transporting layer in contact with the organic light-emitting layer in each of the electroluminescent units has a thickness of less than or equal to 10 nm, and wherein each of the layers in each of the intermediate connectors has a thickness of less than or equal to 5 nm.

4. The tandem OLED of claim 1 wherein the hole-transporting layer in contact with the organic light-emitting layer in each of the electroluminescent units has a thickness of less than or equal to 5 nm, wherein the organic light-emitting layer in each of the electroluminescent units has a thickness of less than or equal to 15 nm, wherein the electron-transporting layer in contact with the organic light-emitting layer in each of the electroluminescent units has a thickness of less than or equal to 5 nm, and wherein each of the layers in each of the intermediate connectors has a thickness of less than or equal to 3 nm.

9. The tandem OLED of claim 1 wherein the hole-injecting layer in each of the electroluminescent units is a p-type doped layer containing at least one hole-transporting material and at least one p-type dopant.

10. The tandem OLED of claim 9 wherein the hole-transporting material includes N,N′

-di(naphthalene-1-yl)-N,N′

-diphenyl-benzidine (NPB), N,N′

-diphenyl-N,N′

-bis(3-methylphenyl)-1,1-biphenyl-4,4′

-diamine (TPD), N,N,N′

,N′

-tetranaphthyl-benzidine (TNB), 4,4′

,4″

-tris(N-3-metylphenyl-N-phenyl-amino)-triphenylamine (m-MTDATA), 4,4′

,4″

-tris(N,N-diphenyl-amino)-triphenylamine (TDATA), dihydrophenazine compounds, or hexaazatriphenylene compounds, or combinations thereof.

11. The tandem OLED of claim 9 wherein the p-type dopant includes oxidizing agents capable of forming a charge transfer complex with the host material.

12. The tandem OLED of claim 9 wherein the p-type dopant includes iodine, FeCl₃, FeF₃, SbCl₅, MoO₃, WO₃, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄-TCNQ), other derivatives of 7,7,8,8-tetra-cyanoquinodimethane (TCNQ), or hexaazatriphenylene compounds, or combinations thereof.

13. The tandem OLED of claim 1 wherein the organic light-emitting layer in each of the electroluminescent units individually emits red, green, blue, or white color, or combinations thereof.

14. The tandem OLED of claim 1 wherein the electron-injecting layer in each of the electroluminescent units is an n-type doped layer containing at least one electron-transporting material and at least one n-type dopant.

15. The tandem OLED of claim 14 wherein the electron-transporting material includes tris(8-hydroxyquinoline)aluminum (Alq), 4,7-diphenyl-1,10-phenanthroline (Bphen), 2,9-dimethyl-4,7-diphenyl-1,10 -phenanthroline (BCP), other phenanthroline derivatives, or 2,2′

-[1,1′

-biphenyl]-4,4′

-diylbis[4,6-(p-tolyl)-1,3,5-triazine] (TRAZ), or combinations thereof.

16. The tandem OLED of claim 14 wherein the n-type dopant includes Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, La, Ce, Nd, Sm, Eu, Tb, Dy, or Yb, or combinations thereof.

17. The tandem OLED of claim 1 wherein each layer in each of the intermediate connectors includes organic material, metal compound, or high work function metal, or combinations thereof.

18. The tandem OLED of claim 1 wherein each layer in each of the intermediate connectors is a doped layer or a non-doped layer.

19. The tandem OLED of claim 1 wherein each of the intermediate connectors includes a layer of MoO₃, NiMoO₄, CuMoO₄, WO₃, ZnTe, Al₄C₃, AlF₃, B₂S₃, CuS, GaP, InP, or SnTe, or combination thereof.

20. The tandem OLED of claim 1 wherein each of the intermediate connectors includes the layer of Ti, Zr, Ti, Nb, Ta, Cr, Mo, W, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Al, In, or Sn, or combinations thereof.

5. A tandem OLED comprising:

a) an anode;

b) a cathode;

c) at least two electroluminescent units disposed between the anode and the cathode, wherein each of the electroluminescent units includes at least one hole-injecting layer, one hole-transporting layer, one organic light-emitting layer, one electron-transporting layer, and one electron-injecting layer;

d) at least one intermediate connector, wherein each of the intermediate connectors includes at least one layer, and wherein each of the intermediate connectors is disposed between electroluminescent units; and

e) wherein the thickness of each layer in each of the electroluminescent units and the intermediate connectors is selected to provide high luminous efficiency using optical out-coupling while satisfying the test condition that the voltage drop from the anode to the cathode is less than 3.5 V×

N at 1000 cd/m².

6. The tandem OLED of claim 5 wherein there are three electroluminescent units disposed between the anode and the cathode, wherein each of the electroluminescent units includes at least one hole-injecting layer, one hole-transporting layer, one organic light-emitting layer, one electron-transporting layer, and one electron-injecting layer and two intermediate connectors, wherein each of the intermediate connectors includes at least one layer, and wherein each of the intermediate connectors is disposed between electroluminescent units, and the thickness of each layer in each of the electroluminescent units and the intermediate connectors is selected to provide high luminous efficiency using optical out-coupling while satisfying the test condition that the voltage drop from the anode to the cathode is less than 10.5 V at 1000 cd/m².

7. The tandem OLED of claim 5 wherein the hole-transporting layer in contact with the organic light-emitting layer in each of the electroluminescent units has a thickness of less than or equal to 10 nm, wherein the organic light-emitting layer in each of the electroluminescent units has a thickness of less than or equal to 20 nm, wherein the electron-transporting layer in contact with the organic light-emitting layer in each of the electroluminescent units has a thickness of less than or equal to 10 nm, and wherein each of the layers in each of the intermediate connectors has a thickness of less than or equal to 5 nm.

8. The tandem OLED of claim 5 wherein the hole-transporting layer in contact with the organic light-emitting layer in each of the electroluminescent units has a thickness of less than or equal to 5 nm, wherein the organic light-emitting layer in each of the electroluminescent units has a thickness of less than or equal to 15 nm, wherein the electron-transporting layer in contact with the organic light-emitting layer in each of the electroluminescent units has a thickness of less than or equal to 5 nm, and wherein each of the layers in each of the intermediate connectors has a thickness of less than or equal to 3 nm.