US-12628496-B2 - Display apparatus having a light-emitting layer

US12628496B2US 12628496 B2US12628496 B2US 12628496B2US-12628496-B2

Abstract

A display apparatus including a light-emitting layer is provided. The light-emitting layer may be disposed between a first electrode and a second electrode. The light-emitting layer may include a first emission stack and a second emission stack on the first emission stack. The first emission stack may include a blue emission material layer. The second emission stack may include an emission buffer layer, a first phosphorescent emission material layer and a second phosphorescent emission material layer, which are sequentially stacked. The emission buffer layer may include a host having an electron transporting properties and a red dopant. The content of the red dopant in the emission buffer layer may decrease as a distance from the first charge generation layer increases. Thus, in the display apparatus, a color change at low-current may be improved.

Inventors

Hui Kun YUN
Wook SONG

Assignees

LG DISPLAY CO., LTD.

Dates

Publication Date: 20260512
Application Date: 20211215
Priority Date: 20201231

Claims (14)

1 . A display apparatus comprising: an anode; a cathode on the anode; a first charge generation layer between the anode and the cathode; a first emission stack between the anode and the first charge generation layer, the first emission stack including a blue emission material layer; and a second emission stack between the first charge generation layer and the cathode, wherein the second emission stack includes an emission buffer layer, a first phosphorescent emission material layer and a second phosphorescent emission material layer, which are sequentially stacked, wherein the emission buffer layer is disposed between the first charge generation layer and the first phosphorescent emission material layer, wherein the emission buffer layer includes a host having an electron transporting properties, wherein the emission buffer layer and the first phosphorescent emission material layer include a red dopant, wherein a content of the red dopant in the emission buffer layer decreases as a distance from the first charge generation layer increases such that a content of the red dopant in a portion of the emission buffer layer disposed close to the first charge generation layer is larger than a content of the red dopant in a portion of the emission buffer layer disposed close to the first phosphorescent emission material layer, and wherein the content of the red dopant in a portion of the emission buffer layer disposed close to the first charge generation layer is larger than a content of the red dopant in the first phosphorescent emission material layer.
2 . The display apparatus according to claim 1 , wherein the first charge generation layer includes a n-type charge generating layer disposed close to the first emission stack and a p-type charge generating layer on the n-type charge generating layer, and wherein the emission buffer layer is in contact with the p-type charge generating layer and the first phosphorescent emission material layer.
3 . The display apparatus according to claim 1 , wherein the red dopant of the emission buffer layer includes a phosphorescent material.
4 . The display apparatus according to claim 3 , wherein the red dopant of the first phosphorescent emission material layer includes a same material as the red dopant of the emission buffer layer.
5 . The display apparatus according to claim 4 , wherein the content of the red dopant in the emission buffer layer decreases such that the content of the red dopant in the emission buffer layer at a surface of the emission buffer layer in contact with the first phosphorescent emission material layer is a same content as a content of the red dopant in the first phosphorescent emission material layer.
6 . The display apparatus according to claim 4 , wherein a host of the first phosphorescent emission material layer includes a same material as the host of the emission buffer layer having the electron transporting properties.
7 . The display apparatus according to claim 1 , the host having the electron transporting properties includes benzo-carbazole.
8 . The display apparatus according to claim 1 , further comprising: a third emission stack between the second emission stack and the cathode; and a second charge generation layer between the second emission stack and the third emission stack, wherein the third emission stack includes a blue emission material layer.
9 . The display apparatus according to claim 8 , wherein the blue emission material layer of the third emission stack includes a same material as the blue emission material layer of the first emission stack.
10 . The display apparatus according to claim 1 , wherein the content of the red dopant in the emission buffer layer decreases such that the content of the red dopant in the emission buffer layer at a surface of the emission buffer layer in contact with the first phosphorescent emission material layer is a same content as a content of the red dopant in the first phosphorescent emission material layer.
11 . The display apparatus according to claim 10 , wherein the emission buffer layer is in direct contact with the p-type charge generating layer of the first charge generation layer and in direct contact with the first phosphorescent emission material layer.
12 . The display apparatus according to claim 1 , wherein the emission buffer layer has a thickness thinner than the first phosphorescent emission material layer.
13 . The display apparatus according to claim 12 , wherein the thickness of the emission buffer layer is 100 Å or less.
14 . The display apparatus according to claim 1 , the emission buffer layer includes: a host having benzo-carbazole; and a dopant having at least one of Ir(Piq)3(Tris(1 phenylisoquinoline)iridium (III)), Ir(piq)2(acac)(Bis(1 phenylisoquinoline)(acetylacetonate)iridiumIII)), Ir(btp)2(acac)(Bis)2 benzo[b]thiophen-2-yl-pyridine)(acetylacetonate)iridiumIII)), and Ir(BT)2(acac) (Bis(2-phenylbenzothazolato)(acetylacetonate)iridiumIII)).

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of Korean Patent Application No. 10-2020-0189744 filed on Dec. 31, 2020, which is hereby incorporated by reference as if fully set forth herein. BACKGROUND Technical Field The present disclosure relates to a display apparatus realizing an image by light emitted from a light-emitting layer. Discussion of the Related Art Generally, an electronic appliance, such as a monitor, a TV, a laptop computer and a digital camera, includes a display apparatus to realize an image. For example, the display apparatus may include at least one light-emitting device. The light-emitting device may emit light displaying a specific color. For example, the light-emitting device may include a light-emitting layer disposed between two electrodes. The light-emitting device may emit the light display a white color. The light-emitting layer may be composed of a plurality of emission material layers (EML). For example, in the display apparatus, the light-emitting layer between a first electrode and a second electrode may include a charge generation layer between a first emission stack and a second emission stack. The first emission stack may include a blue emission material layer. The second emission stack may include a red phosphorescent emission material layer and a green phosphorescent emission material layer, which are sequentially stacked on the charge generation layer. However, since the inflow of holes to the red phosphorescent emission material layer from the charge generation layer is difficult, a driving voltage of the display apparatus may increase. And, when the driving voltage in the display apparatus is reduced by relieving the energy level difference between the charge generation layer and the red phosphorescent emission material layer, it is difficult to adjust the color at low-current due to the rapid movement of the holes. SUMMARY Accordingly, embodiments of the present disclosure are directed to a display apparatus that substantially obviates one or more problems due to limitations and disadvantages of the related art. An aspect of the present disclosure is to provide a display apparatus capable of reducing the driving current and improving the change of the color at the low-current. Additional features and aspects will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the inventive concepts provided herein. Other features and aspects of the inventive concepts may be realized and attained by the structure particularly pointed out in the written description, or derivable therefrom, and the claims hereof as well as the appended drawings. To achieve these and other aspects of the inventive concepts, as embodied and broadly described herein, a display apparatus comprises a first electrode; a second electrode disposed on the first electrode; a first charge generation layer disposed between the first electrode and the second electrode; a first emission stack disposed between the first electrode and the first charge generation layer, the first emission stack including a blue emission material layer; and a second emission stack disposed between the first charge generation layer and the second electrode. The second emission stack includes an emission buffer layer, a first phosphorescent emission material layer and a second phosphorescent emission material layer, which are sequentially stacked. The first phosphorescent emission material layer includes a red dopant. The emission buffer layer includes a host having an electron transporting properties in which a red dopant is doped. The content of the red dopant in the emission buffer layer decreases as a distance from the first charge generation layer increases. The first charge generation layer may include a n-type charge generation layer and a p-type charge generation layer on the n-type charge generation layer. The n-type charge generation layer may be disposed close to the first emission stack. The emission buffer layer may be in contact with the p-type charge generation layer and the first phosphorescent emission material layer. The red dopant of the emission buffer layer may include a phosphorescent material. The red dopant of the emission buffer layer may include one of Ir(Piq)3(Tris(1-phenylisoquinoline)iridium(III)), Ir (piq)2(acac) (Bis(1-phenylisoquinoline) (acetylacetonate) iridiumIII)), Ir(btp)2(acac) (Bis)2-benzo[b]thiophen-2-yl-pyridine)(acetylacetonate)iridiumIII)), Ir(BT)2(acac) (Bis(2-phenylbenzothazolato)(acetylacetonate)iridiumIII)). The red dopant of the first phosphorescent emission material layer may include the same material as the red dopant of the emission buffer layer. The content of the red dopant at a surface of the emission buffer layer being in contact with the first phosphorescent emission material layer may be the same as the content of the red dopant in the first phosphorescent emission mater