Color-stable organic light emitting diode stack
The present invention relates to OLED devices and stacks for OLED devices that include a symmetric emissive-layer architecture. In one embodiment, the present invention relates to an emissive stack having three layers, wherein the top and bottom layers emit light in the same or similar color region while the middle layer emits light in a different color region than the other two layers. In such an embodiment, the three layers are in contact with each other with no other layers in between. The symmetric emissive-layer architecture of the present invention can be used to improve the color stability of OLED devices.
1. An organic light emitting device, comprising:
an anode, and a hole-transport layer;
a hybrid blue emissive stack that includes a fluorescent blue dopant and a phosphorescent blue dopant, the hybrid blue emissive stack disposed over the hole-transport layer, and the hole-transport layer positioned between the anode and the hybrid blue emissive stack;
a charge-generation layer disposed over the hybrid blue emissive stack;
an emissive stack disposed over the charge-generation layer, the emissive stack includes N emissive layers, and N is an integer of at least 3, wherein at least one middle emissive layer in the emissive stack other than the first and the Nth emissive layers emits light in a different color region than the first and the Nth emissive layers, and the difference between the emission peak of the first emissive layer and the emission peak of the Nth emissive layer in the emissive stack is less than about 10 nm;
wherein at least one of the middle emissive layers has a thickness that is ten times a thickness of the first emissive layer; and
wherein the different color region is represented by a peak emission greater than about 10 nm;
an electron-transport layer disposed over the emissive stack; and
a cathode disposed over the electron-transport layer.
2. The device of claim 1 , wherein the first and the Nth emissive layers are red emissive layers, and at least one emissive layer in the emissive stack other than the first and the Nth emissive layers is a green emissive layer.
3. The device of claim 1 , wherein each emissive dopant in each emissive layer in the N-layer emissive stack is a phosphorescent emissive dopant.
4. The device of claim 3 , wherein at least one emissive layer in the N-layer emissive stack comprises a red phosphorescent dopant, and at least one emissive layer in the N-layer emissive stack comprises a green phosphorescent dopant.
5. The device of claim 1 , wherein N is 4.
6. The device of claim 5 , wherein at least two emissive layers in the N-layer emissive stack other than the first and Nth emissive layers emits light in a different color region than the first and Nth emissive layers.
7. The device of claim 1 , wherein a change in each 1931 CIE (x, y) color coordinate of light emitted from the N-layer emissive stack is 0.02 or less for any change in current density within the range of about 2 mA/cm 2 to 80 mA/cm 2 .
8. The device of claim 7 , wherein a Duv value of light emitted from the N-layer emissive stack is less than 0.02 when the device is aged to 70% of its initial luminance (LT70).
9. The device of claim 1 , wherein a change in each 1931 CIE (x, y) color coordinate of light emitted from the N-layer emissive stack is 0.02 or less for any change in luminance within the range of about 800 cd/m 2 to 30,000 cd/m 2 .
10. A product comprising the device of claim 1 , wherein the product is selected from the group consisting of: a touchscreen, a flat panel display, a computer monitor, a medical monitor, a television, a billboard, a general illumination device, a signal, a heads up display, a fully transparent display, a flexible display, a laser printer, a telephone, a cell phone, a personal digital assistant (PDA), a laptop computer, a digital camera, a camcorder, a viewfinder, a microdisplay, a vehicle, a large area wall, a theater, a stadium screen, and a sign.
11. The device of claim 1 , wherein the first and the Nth emissive layers are green emissive layers and at least one emissive layer in the first emissive stack other than the first and the Nth emissive layers is a red emissive layer.
12. The device of claim 1 , wherein the N emissive layers in the emissive stack consist of top-middle-bottom layers having a configuration of colors selected from the group consisting of red-green-red or green-red-green.
13. The device of claim 1 , wherein the N emissive layers in the emissive stack consist of top-middle-bottom layers having a configuration of colors selected from the group consisting of green-yellow-green or yellow-green-yellow.
14. The device of claim 1 , wherein the N emissive layers in the emissive stack consist of top-middle-bottom layers having a configuration of colors selected from the group consisting of yellow-red-yellow, and red-yellow-red.
15. The device of claim 1 , wherein the N emissive layers in the emissive stack consist of top-middle-bottom layers having a configuration of colors selected from the group consisting of yellow-blue-yellow, and blue-yellow-blue.
16. The device of claim 3 , wherein N is 4.
17. The device of claim 16 , wherein a change in each 1931 CIE (x, y) color coordinate of light emitted from the N-layer emissive stack is 0.02 or less for any change in current density within the range of about 2 mA/cm 2 to 80 mA/cm 2 , and for any change in luminance within the range of about 800 cd/m 2 to 30,000 cd/m 2 .
18. The device of claim 1 , wherein the N emissive layers are in direct contact with one another.
19. The device of claim 1 , wherein each of the N emissive layers comprises at least one host material and at least one emissive dopant.
20. The device of claim 19 , wherein the composition of the at least one emissive dopant in the first emissive layer is the same as that of at least one emissive dopant in the Nth emissive layer.