Electroluminescent device, production method thereof, and display device including the same
An electroluminescent device including an anode; a cathode; a light emitting layer disposed between the anode and the cathode; and an electron transport layer disposed between the light emitting layer and the cathode, wherein the light emitting layer includes a plurality of semiconductor nanoparticles, the electron transport layer includes zinc oxide nanoparticles including a Group IIA metal and an acid salt of an alkali metal that has an oxycarbonyl moiety, and the zinc oxide nanoparticles have an average size of less than or equal to about 20 nanometers (nm).
1. An electroluminescent device, comprising:
an anode;
a cathode;
a light emitting layer disposed between the anode and the cathode; and
an electron transport layer disposed between the light emitting layer and the cathode,
wherein the light emitting layer comprises a plurality of semiconductor nanoparticles,
wherein the electron transport layer comprises zinc oxide nanoparticles comprising a Group IIA metal; and an acid salt of an alkali metal that has an oxycarbonyl moiety, and
wherein the zinc oxide nanoparticles have an average size of less than or equal to about 20 nanometers.
2. The electroluminescent device of claim 1 , wherein
the electroluminescent device is configured to emit blue light, green light, or red light.
3. The electroluminescent device of claim 1 , wherein
the plurality of semiconductor nanoparticles do not comprise cadmium, lead, mercury, or a combination thereof.
4. The electroluminescent device of claim 1 , wherein
the alkali metal comprises potassium, rubidium, cesium, or a combination thereof, and
the Group IIA metal comprises magnesium,
optionally wherein the zinc oxide nanoparticles further comprise Zr, W, Li, Ti, Y, Al, gallium, indium, tin (Sn), cobalt (Co), vanadium (V), or a combination thereof.
5. The electroluminescent device of claim 1 , wherein
the average size of the zinc oxide nanoparticles is greater than or equal to about 1 nanometers and less than or equal to about 8 nanometers.
6. The electroluminescent device of claim 1 , wherein
in the electron transport layer,
a mole ratio of carbon to the Group IIA metal is greater than or equal to about 4.1:1 and less than or equal to about 8:1, and
a mole ratio of oxygen to the Group IIA metal is greater than or equal to about 13:1 and less than or equal to about 25:1.
7. The electroluminescent device of claim 1 ,
wherein in the electron transport layer, a mole ratio of alkali metal to zinc is greater than or equal to about 0.08:1 and less than or equal to about 0.5:1, or
wherein in the electron transport layer, a mole ratio of alkali metal to the Group IIA metal is greater than or equal to about 0.8:1 and less than or equal to about 2:1.
8. The electroluminescent device of claim 1 , wherein
the carboxylic acid salt of the alkali metal is represented by ACOOM 1 , wherein A is hydrogen, a substituted or unsubstituted C 1-10 hydrocarbon group, or a combination thereof, and M 1 is sodium, potassium, rubidium, cesium, or a combination thereof.
9. The electroluminescent device of claim 1 , wherein
the acid salt of the alkali metal comprises a formate, an acetate, a propionate, a butyrate, a valerate, a caproate, or a combination thereof.
10. The electroluminescent device of claim 1 , wherein
the electron transport layer has a first surface facing the light emitting layer and a second surface opposite the first surface, and
an amount of the alkali metal in a portion adjacent to the first surface of the electron transport layer is greater than an amount of the alkali metal in a portion adjacent to the second surface of the electron transport layer.
11. The electroluminescent device of claim 1 , wherein
the electron transport layer comprises a first layer and a second layer disposed on the first layer,
wherein the first layer faces the light emitting layer, and
an amount of the acid salt of the alkali metal in the first layer is greater than an amount of the acid salt of alkali metal in the second layer.
12. The electroluminescent device of claim 11 ,
Wherein the second layer does not comprise alkali metal, or
wherein an amount of the alkali metal in the first layer is about 1.5 times or greater and about 100 times or less than an amount of the alkali metal in the second layer.
13. The electroluminescent device of claim 1 , wherein
the electron transport layer has a thickness of greater than or equal to about 5 nanometers and less than about 60 nanometers.
14. The electroluminescent device of claim 1 , wherein the electroluminescent device exhibits a maximum external quantum efficiency of greater than or equal to about 13% and optionally a maximum luminance of greater than or equal to about 72000 nit.
15. A method of producing the electroluminescent device of claim 1 , comprising:
forming the light emitting layer on the first electrode;
forming an electron transport layer on the light emitting layer; and
forming a second electrode on the electron transport layer,
wherein the forming of the electron transport layer comprises,
dispersing the zinc oxide nanoparticles, and the acid salt of the alkali metal in a first organic solvent to prepare a first mixture;
applying the first mixture on the light emitting layer to form a film; and
optionally thermally treating the film to a temperature of less than or equal to about 160° C.
16. The method of claim 15 , wherein
the acid salt of the alkali metal comprises a formate, an acetate, a propionate, a butyrate, valerate, a caproate, or a combination thereof.
17. The method of claim 15 , wherein
the forming of the electron transport layer further comprises:
preparing a second mixture by dispersing zinc oxide nanoparticles comprising the Group IIA metal in a second organic solvent; and
applying the second mixture on the film and optionally conducting an additional heat-treatment on it.
18. The method of claim 15 , wherein
after forming the second electrode, the method further comprises maintaining the device at a temperature of about 60° C. to about 100° C.
19. A display device comprising the electroluminescent device of claim 1 .
20. The display device of claim 19 , wherein
the display device comprises a portable terminal device, a monitor, a notebook computer, a television, an electric sign board, a camera, or an electronic component.