Organic EL element, display device, and light-emitting device
View Patent ↗The present invention aims to provide organic EL elements operating at low voltage to emit light at high intensity. For this aim, each EL element includes an anode, a cathode, a functional layer disposed between the anode and the cathode and including a light-emitting layer composed of organic material, a hole injection layer disposed between the anode and the functional layer, and a bank defining the light-emitting layer. The hole injection layer contains tungsten oxide and exhibits: by UPS measurement, a UPS spectrum having a protrusion appearing near a Fermi surface and within a region corresponding to a binding energy range lower than the top of a valence band; and by XPS measurement, that the tungsten oxide in the hole injection layer satisfies a condition that a ratio in number density of atoms other than tungsten atoms and oxygen atoms to the tungsten atoms is equal to 0.83 or smaller.
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 made of 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 contains a tungsten oxide,
an Ultraviolet Photoelectron Spectroscopy (UPS) spectrum, obtained from a UPS measurement, has a protrusion appearing near a Fermi surface and within a region corresponding to a binding energy range lower than a top of a valence band,
the tungsten oxide contained in the hole injection layer satisfies a condition, determined from an X-ray Photoelectron Spectroscopy (XPS) measurement, that a ratio in a number density of atoms other than tungsten atoms and oxygen atoms to the tungsten atoms does not exceed 0.83,
an inner portion of the hole injection layer is depressed to define a recess,
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,
the UPS measurement includes parameters comprising He I as a light source and a normal line direction to a surface of the substrate as an electron emission angle, and
the XPS measurement includes parameters comprising Al Kα as the light source and the normal line direction to the surface of the substrate as the electron emission angle.
2. The organic EL element according to claim 1 , wherein
in the UPS spectrum, the protrusion appears within the region corresponding to the binding energy range from 1.8 eV to 3.6 eV lower than the top of the valance band.
3. The organic EL element according to claim 1 , wherein
the ratio in the number density of the other atoms to the tungsten atoms does not exceed 0.62.
4. The organic EL element according to claim 1 , wherein
the atoms other than tungsten atoms and oxygen atoms comprise carbon atoms.
5. The organic EL element according to claim 1 , wherein
the hole injection layer is irradiated with ultraviolet light so that
the hole injection layer in the UPS spectrum obtained from the UPS measurement has the protrusion appearing near the Fermi surface and within the region corresponding to the binding energy range lower than the top of a valence band, and
the tungsten oxide contained in the hole injection layer satisfies the condition, as determined by the XPS measurement, that the ratio in the number density of atoms other than tungsten atoms and oxygen atoms to the tungsten atoms does not exceed 0.83.
6. The organic EL element according to claim 1 , wherein
the part of the bank reaches a bottom of the recess of the hole injection layer, and a side surface of the bank slopes upward from the bottom of the recess to a top of the bank.
7. The organic EL element according to claim 1 , wherein
the part of the bank is out of contact with a bottom of the recess.
8. The organic EL element according to claim 1 , wherein
the hole injection layer extends laterally along a bottom surface of the bank.
9. The organic EL element according to claim 1 , wherein
the upper peripheral edge of the recess is a convex portion composed of (i) a part of the upper surface of the hole injection layer in which the recess is not formed and (ii) the inner side surface of the recess.
10. 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 made of 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 contains a tungsten oxide, an Ultraviolet Photoelectron Spectroscopy (UPS) spectrum, obtained from an UPS measurement having:
a protrusion appearing near a Fermi surface and within a region corresponding to a binding energy range lower than a top of a valence band, and
a peak appearing within a another region corresponding to a binding energy range from 4.5 eV to 5.4 eV,
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, and
the UPS measurement includes parameters comprising He I as a light source and a normal line direction to a surface of the substrate as an electron emission angle.
11. The organic EL element according to claim 10 , wherein
in the UPS spectrum, the protrusion appears within the region corresponding to the binding energy range from 1.8 eV to 3.6 eV lower than the top of the valance band.
12. The organic EL element according to claim 10 , wherein the hole injection layer is irradiated with ultraviolet light so that
the hole injection layer, in the UPS spectrum, obtained by the UPS measurement,
has the protrusion appearing near the Fermi surface and within the region corresponding to the binding energy range lower than the top of the valence band, and
the peak appears within the another region corresponding to the binding energy range from 4.5 eV to 5.4 eV.
13. The organic EL element according to claim 10 , wherein
the part of the bank reaches a bottom of the recess of the hole injection layer, and a side surface of the bank slopes upward from the bottom of the recess to a top of the bank.
14. The organic EL element according to claim 10 , wherein
the part of the bank is out of contact with a bottom of the recess.
15. The organic EL element according to claim 10 , wherein
the hole injection layer extends laterally along a bottom surface of the bank.
16. The organic EL element according to claim 10 , wherein
the upper peripheral edge of the recess is a convex portion composed of (i) a part of the upper surface of the hole injection layer in which the recess is not formed and (ii) the inner side surface of the recess.
17. A display apparatus comprising the organic EL element according to claim 1 .
18. A light-emitting apparatus comprising the organic EL element according to claim 1 .
19. The organic EL element according to claim 1 , wherein
a film thickness of a portion of the light-emitting layer above a lower surface that is in contact with the hole injection layer is uniform.
20. The organic EL element according to claim 10 , wherein
a film thickness of a portion of the light-emitting layer above a lower surface that is in contact with the hole injection layer is uniform.