Quantum dot light emitting device with electron auxiliary layer and display device including the same
A light emitting device includes: a first electrode and a second electrode with a surface facing the first electrode; an emission layer disposed between the first electrode and the second electrode and including a quantum dot (e.g., a plurality of quantum dots); and an electron auxiliary layer disposed between the emission layer and the second electrode. The electron auxiliary layer includes a first layer including a first metal oxide, and a second layer disposed on the first layer and including a second metal oxide. A roughness of an interface between the second layer and the second electrode is less than about 10 nm as determined by an electron microscopy analysis. An absolute value of a difference between a conduction band edge energy level of the second layer and a work function of the second electrode may be less than or equal to about 0.5 eV, and a conduction band edge energy level of the first layer may be less than the conduction band edge energy level of the second layer.
1. A light emitting device, comprising:
a first electrode and a second electrode with a surface facing the first electrode;
an emission layer disposed between the first electrode and the second electrode and comprising a quantum dot; and
an electron auxiliary layer disposed between the emission layer and the second electrode,
wherein the electron auxiliary layer comprises a first layer proximate to the emission layer and comprising a plurality of nanoparticles comprising a first metal oxide, and a second layer disposed on the first layer and proximate to the second electrode, the second layer comprising a second metal oxide,
wherein the first metal oxide is represented by Chemical Formula 1:
Zn 1-x M x O Chemical Formula 1
wherein M is Mg, Ca, Zr, W, Li, Ti, Y, Al, or a combination thereof, and
x is greater than 0 and less than or equal to 0.5, and
wherein an amount of carbon in the first layer is greater than an amount of carbon in the second layer,
wherein the amount of carbon in the second layer is less than or equal to 9 mol % and greater than 0.1 mol % based on a total mole amount of elements included in the second layer.
2. The light emitting device of claim 1 , wherein the emission layer does not comprise cadmium, and wherein an interface roughness between the second layer and the surface of the second electrode is less than about 10 nanometers as determined by an electron microscopy analysis.
3. The light emitting device of claim 1 , wherein the amount of the carbon in the second layer with respect to a molar amount of total elements in the second layer is less than or equal to about 8 mol %.
4. The light emitting device of claim 1 , wherein an amount of carbon in the second layer is less than or equal to 7 mol % and greater than 0.3 mol % based on a total mole amount of elements included in the second layer, and wherein the amount of the carbon in the first layer is greater than 8 mole percent based on a total mole amount of elements included in the first layer.
5. The light emitting device of claim 1 , wherein the first metal oxide has a composition different from the second metal oxide.
6. The light emitting device of claim 1 , wherein the first metal oxide and the second metal oxide comprises zinc, and a presence density of zinc in the second layer is greater than a presence density of zinc in the first layer.
7. The light emitting device of claim 1 , wherein the second metal oxide comprises a zinc oxide, a zinc magnesium oxide, a tin oxide, a titanium oxide, or a combination thereof.
8. The light emitting device of claim 1 , wherein the second metal oxide is represented by Chemical Formula 1:
Zn 1-x M x O Chemical Formula 1
wherein M is Mg, Ca, Zr, W, Li, Ti, Y, Al, or a combination thereof, and x is greater than or equal to 0 and less than or equal to 0.5.
9. The light emitting device of claim 1 , wherein the second layer comprises a vapor deposited film of the second metal oxide or wherein the second layer does not include a metal oxide nanoparticle.
10. The light emitting device of claim 9 , wherein an average particle size of the nanoparticles of the first metal oxide is greater than or equal to about 1 nanometer and less than or equal to about 10 nanometers.
11. The light emitting device of claim 1 , wherein a surface of the second layer is disposed directly on a surface of the first layer, and an absolute value of a difference between the conduction band edge energy level of the first layer and the conduction band edge energy level of the second layer is greater than or equal to 0.05 eV and less than or equal to about 1 eV.
12. The light emitting device of claim 11 , wherein an interface roughness between the surface of the second layer and a surface of the first layer is less than or equal to about 12 nanometers as determined by an electron microscopy.
13. The light emitting device of claim 1 , wherein an interface roughness between the second layer and the surface of the second electrode is less than or equal to about 5 nanometers, and a thickness of the second layer is greater than or equal to about 1 nanometer and less than or equal to about 20 nanometers.
14. The light emitting device of claim 1 , wherein an absolute value of a difference between a conduction band edge energy level of the second layer and a work function of the second electrode is less than or equal to about 0.5 electron volts or
wherein a conduction band edge energy level of the first layer is less than the conduction band edge energy level of the second layer and a difference between the conduction band edge energy level of the first layer and the conduction band edge energy level of the second layer is greater than or equal to about 0.05 electron volts.
15. The light emitting device of claim 1 , wherein the light emitting device further comprises a buffer layer disposed on an opposite surface of the second electrode, and the buffer layer comprises an organic metal compound, a metal fluoride, or a combination thereof.
16. The light emitting device of claim 15 , wherein a metal of the organic metal compound or the metal fluoride comprises lithium, aluminum, or a combination thereof; and an organic moiety of the organic metal compound comprises an aromatic cyclic moiety, a heteroaromatic cyclic moiety, or a combination thereof.
17. The light emitting device of claim 1 , wherein the light emitting device further comprises an organic polymer layer disposed on an opposite surface of the second electrode.
18. The light emitting device of claim 17 , wherein the organic polymer layer comprises a polymerization product of a monomer combination comprising a compound having at least one carbon-carbon double bond, and optionally a thiol compound.
19. The light emitting device of claim 1 , wherein the light emitting device emits blue light, and a T50 of the light emitting device may be greater than or equal to about 10 hours.
20. A display device comprising the light emitting device of claim 1 .