White organic light emitting device
A white organic light emitting device which has high color temperature characteristics and no change in color coordinates according to luminance change, includes a first electrode and a second electrode opposite to each other on a substrate, a charge generation layer formed between the first electrode and the second electrode, a second stack including a second light emitting layer formed between the charge generation layer and the second electrode, and a first stack including a first light emitting layer formed between the first electrode and the charge generation layer, wherein the first emitting layer has low singlet-triplet exchange energy to change triplet excitons into a singlet state by triplet-triplet annihilation and a dopant concentration of the first light emitting layer is adjusted according to a luminance change curve of the second stack.
1. A white organic light emitting layer comprising:
a first electrode and a second electrode opposite to each other on a substrate;
a charge generation layer between the first electrode and the second electrode;
a first stack including a first light emitting layer between the first electrode and the charge generation layer, wherein the first light emitting layer includes a fluorescent dopant; and
a second stack including a second light emitting layer between the charge generation layer and the second electrode;
wherein the fluorescent dopant has a concentration at which concentration quenching occurs in the first light emitting layer and at which a slope of a first luminous efficiency change curve of the first light emitting layer including the fluorescent dopant is fit to a slope of a second luminous efficiency change curve of the second light emitting layer at luminance values of 5000 Cd/cm2 or less,
wherein the fluorescent dopant has the concentration at which the slope of the first luminous efficiency change curve of the first light emitting layer including the fluorescent dopant is the same as the slope of the second luminous efficiency change curve of the second light emitting layer; and
wherein the first and second luminance efficiency change curves are according to luminance.
2. The white organic light emitting layer according to claim 1 , wherein the first stack further comprises a first hole injection layer, a first hole transport layer, a second hole transport layer, and a first electron transport layer on the first light emitting layer.
3. The white organic light emitting layer according to claim 2 , wherein the second stack further comprises a second hole injection layer, a third hole transport layer, and a second electron transport layer on the second light emitting layer.
4. The white organic light emitting layer according to claim 1 , wherein the first light emitting layer is a light emitting layer comprising a blue fluorescent dopant in at least one host, and the second light emitting layer is a single light emitting layer formed by doping at least one host with both a red phosphorescent dopant and a green phosphorescent dopant.
5. The white organic light emitting layer according to claim 1 , wherein the first light emitting layer is a light emitting layer comprising a blue fluorescent dopant in at least one host, and the second light emitting layer is a single light emitting layer formed by doping at least one host with a yellow-green phosphorescent dopant or doping one host with a green phosphorescent dopant.
6. The white organic light emitting layer according to claim 2 , wherein the first electron transport layer includes at least two electron transport layers, one of the at least two electron transport layers is formed of a material minimizing diffusion of a metal from the first light emitting layer, and the other of the at least two electron transport layers is formed of an organic material enabling electron injection through doping with a metal.
7. The white organic light emitting layer according to claim 6 , wherein one of the at least two electron transport layers adjacent to the first light emitting layer has a higher triplet energy level than a triplet energy level of the first light emitting layer.
8. The white organic light emitting layer according to claim 2 , wherein the first hole transport layer has a higher triplet energy level than a triplet energy level of the first light emitting layer.
9. The white organic light emitting layer according to claim 3 , wherein the second electron transport layer and the third hole transport layer have a higher triplet energy level than a triplet energy level of the second light emitting layer.
10. The white organic light emitting layer according to claim 1 , wherein
the fluorescent dopant is from 4 wt % to 10 wt % of the first light emitting layer; and the second light emitting layer includes a phosphorescent dopant and excludes the fluorescent dopant.
11. The white organic light emitting layer according to claim 1 , wherein
the first light emitting layer has a singlet-triplet exchange energy that is less than 0.6 eV and 0.1 eV or more.
12. The white organic light emitting layer according to claim 2 , wherein
the triplet energy of the first electron transport layer is higher than the triplet energy of the host of the first light emitting layer.
13. The white organic light emitting layer according to claim 1 , wherein the concentration quenching occurs in the first light emitting layer such that carriers collide with each other within dopant particles to thereby cause degradation of luminous efficiency.
14. A method of making a white organic light emitting layer, comprising:
providing a first electrode and a second electrode opposite to each other on a substrate;
forming a charge generation layer between the first electrode and the second electrode;
forming a first stack including a first light emitting layer between the first electrode and the charge generation layer;
forming a second stack including a second light emitting layer between the charge generation layer and the second electrode;
determining a slope of a first luminous efficiency change curve of the first light emitting layer and a slope of a second luminous efficiency change curve of the second light emitting layer;
including a fluorescent dopant in the first light emitting layer, wherein the including the fluorescent dopant includes
adjusting the concentration of the fluorescent dopant to have a concentration at which concentration quenching occurs in the first light emitting layer and at which the slope of the first luminous efficiency change curve is adjusted to be closer to the slope of the second luminous efficiency change curve,
whereby a slope of the first luminous efficiency change curve of the first light emitting layer including the fluorescent dopant is fit to the slope of the second luminous efficiency change curve of the second light emitting layer at luminance values of 5000 Cd/cm2 or less.
15. The method of claim 14 , wherein the concentration quenching occurs in the first light emitting layer such that carriers collide with each other within dopant particles to thereby cause degradation of luminous efficiency.