Organic EL element and production method for same

• US 8,927,976 B2
• Filed: 01/14/2013
• Issued: 01/06/2015
• Est. Priority Date: 08/06/2010
• Status: Active Grant

• Current Assignee: JDI Design and Development GK
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Nishiyama, Seiji, Ohuchi, Satoru, Komatsu, Takahiro, Tsukamoto, Yoshiaki, Fujimura, Shinya, Fujita, Hirofumi
• Primary Examiner(s): Such, Matthew W
• Assistant Examiner(s): Kilpatrick, Warren H
• Application Number:
  US13/740,348
• Publication Number:
  US 20130126843A1
• Time in Patent Office: 722 Days
• Field of Search: 257/40, 438/46
• US Class Current: 257/40
• CPC Class Codes: H10K 2102/331 Nanoparticles used in non-emissive layers, e.g. in packaging layer
• CPC Class Codes: H10K 50/17 Carrier injection layers
• CPC Class Codes: H10K 50/813 characterised by their shape
• CPC Class Codes: H10K 50/818 Reflective anodes, e.g. ITO combined with thick metallic layers
• CPC Class Codes: H10K 71/00 Manufacture or treatment specially adapted for the organic devices covered by this subclass

Abstract

An organic EL element includes a hole injection layer yielding excellent hole conduction efficiency, and comprises: an anode; a cathode; a functional layer disposed between the anode and the cathode, and including a light-emitting layer containing organic material; the hole injection layer disposed between the anode and the functional layer; and a bank defining an area in which the light-emitting layer is to be formed, wherein the hole injection layer includes tungsten oxide, tungsten atoms constituting the tungsten oxide include both tungsten atoms with a valence of six and tungsten atoms with a valence less than six, the hole injection layer includes a crystal of the tungsten oxide, a particle diameter of the crystal being on an order of nanometers, an inner portion of the hole injection layer is depressed to define a recess, and an upper peripheral edge of the recess is covered with a part of the bank.

Claims

1. An organic electroluminescent (EL) element, comprising:

an anode;

a cathode;

a functional layer disposed between the anode and the cathode, and including a light-emitting layer containing an organic material;

a hole injection layer disposed between the anode and the functional layer; and

a bank that defines an area in which the light-emitting layer is to be formed, wherein

the hole injection layer includes a tungsten oxide,

tungsten atoms constituting the tungsten oxide include both tungsten atoms with a valence of six and tungsten atoms with a valence less than six,

the hole injection layer includes a crystal of the tungsten oxide, a particle diameter of the crystal being on an order of nanometers,

an inner portion of the hole injection layer is depressed to define a recess, and

an upper peripheral edge of the recess is covered with a part of the bank, the upper peripheral edge of the recess comprising at least a portion of an inner side surface of the recess.

2. The organic EL element of claim 1, wherein

the tungsten atoms with the valence less than six are tungsten atoms with a valence of five.

3. The organic EL element of claim 2, wherein

a ratio W⁵⁺/W⁶⁺ of the number of the tungsten atoms with a valence of five to the number of the tungsten atoms with a valence of six is at least 3.2%.

4. The organic EL element of claim 3, wherein

the ratio W⁵⁺/W⁶⁺ is at least 3.2% and at most 7.4%.

5. The organic EL element of claim 1, wherein

a hard X-ray photoelectron spectroscopy spectrum of a surface of the hole injection layer exhibits a first peak and a second peak, the first peak corresponding to a 4f_7/2 energy level of the tungsten atoms with a valence of six, and the second peak being in a region lower than the first peak in terms of binding energy.

6. The organic EL element of claim 5, wherein

the second peak is in a region between 0.3 electron volts and 1.8 electron volts lower, in terms of binding energy, than the first peak.

7. The organic EL element of claim 5, wherein

an area intensity of the second peak is between 3.2% and 7.4% of an area intensity of the first peak.

8. The organic EL element of claim 1, wherein

tungsten atoms with a valence less than six cause a band structure of the hole injection layer to have an occupied energy level in a range between 1.8 electron volts and 3.6 electron volts lower than a lowest energy level of a valence band in terms of binding energy.

9. The organic EL element of claim 1, wherein

the hole injection layer includes a plurality of crystals of the tungsten oxide, each of the crystals having a particle diameter of between 3 nm and 10 nm.

10. The organic EL element of claim 1, wherein

regular linear structures at intervals of between 1.85 angstroms and 5.55 angstroms appear in a lattice image by transmission electron microscopy observation of the hole injection layer.

11. The organic EL element of claim 10, wherein

in a 2D Fourier transform image of the lattice image, a pattern of concentric circles centering on a center point of the 2D Fourier transform image appears.

12. The organic EL element of claim 11, wherein

in a plot of distance from the center point versus normalized luminance, the normalized luminance being a normalized value of the luminance of the 2D Fourier transform image at the corresponding distance, at least one peak of the normalized luminance appears.

13. The organic EL element of claim 12, wherein

with a peak width being a difference between the distance corresponding to a position of a peak of the normalized luminance appearing closest to the center point in the plot and the distance corresponding to a position at which the peak of the normalized luminance begins to rise, the peak width is less than 22 when a difference between the distance corresponding to the center point and the distance corresponding to the peak of the normalized luminance appearing closest to the center point is 100.

14. The organic EL element of claim 1, wherein

the functional layer includes amine-containing material.

15. The organic EL element of claim 1, wherein

the functional layer further includes one of a hole transfer layer that transfers holes, and a buffer layer that one of adjusts optical characteristics and blocks electrons.

16. The organic EL element of claim 1, wherein

the part of the bank reaches an inner bottom surface of the recess of the hole injection layer, and a side surface of the bank slopes upward from the inner bottom surface of the recess to a top surface of the bank.

17. The organic EL element of claim 1, wherein

the part of the bank is out of contact with an inner bottom surface of the recess.

18. The organic EL element of claim 1, wherein

the hole injection layer extends laterally along a bottom surface of the bank.

19. The organic EL element of claim 1, wherein

the upper peripheral edge of the recess is a convex portion composed of a part of the upper surface of the hole injection layer in which the recess is not formed and the portion of the inner side surface of the recess.

20. The organic EL element of claim 1, wherein

the bank is liquid-repellent and the hole injection layer is liquid-philic.

21. An organic EL panel comprising the organic EL element of claim 1.

22. An organic EL light-emitting apparatus comprising the organic EL element of claim 1.

23. An organic EL display apparatus comprising the organic EL element of claim 1.

24. A method of manufacturing an organic EL element, comprising:

preparing an anode;

forming a tungsten oxide layer on the anode using a sputtering gas including argon gas and oxygen gas and using tungsten as a sputtering target, under film forming conditions such that a total pressure of the sputtering gas is at least 2.3 Pa and at most 7.0 Pa, a partial pressure of the oxygen gas in the sputtering gas is at least 50% and at most 70%, an input power density per unit area of the sputtering target is at least 1.5 W/cm² and at most 6.0 W/cm², and a value yielded by dividing the total pressure of the sputtering gas by the input power density is larger than 0.7 Pa·

cm²/W;

forming a bank material layer containing material constituting a bank above the tungsten oxide layer;

forming a recess by removing a portion of the bank material layer so that the tungsten oxide layer is partially exposed and an upper surface of the tungsten oxide layer in the recess is closer to the anode than an upper peripheral edge of the recess, the recess having an inner bottom surface and an inner side surface that is continuous with the inner bottom surface;

heat-treating a remaining portion of the bank material layer, the remaining portion of the bank material layer being made fluid so that the bank material layer extends to cover the upper peripheral edge of the recess, the upper peripheral edge of the recess comprising at least a portion of the inner side surface of the recess;

forming functional layer including a light-emitting layer above an exposed surface of the tungsten oxide layer after the heat treatment; and

forming a cathode above the functional layer.

25. The method of manufacturing an organic EL element of claim 24, wherein

the tungsten oxide layer is formed so that tungsten atoms constituting the tungsten oxide layer include both tungsten atoms with a maximum valence thereof and tungsten atoms with a valence less than the maximum valence, and so as to include a tungsten oxide crystal having a particle diameter on an order of nanometers.

26. The method of manufacturing an organic EL element of claim 24, wherein

when forming the tungsten oxide layer, the value yielded by dividing the total pressure of the sputtering gas by the input power density is less than 3.2 Pa·

cm2/W.