Organic electroluminescent device

Abstract

The present disclosure relates to the technical field of display, and specifically relates to an organic electroluminescent device, and in particular, to a highly efficient fluorescence device. An organic electroluminescent device includes a hole transport layer, and a light-emitting layer. The hole transport layer and the light-emitting layer has an interface exciplex formed at an interface therebetween.

Claims

1. An organic electroluminescent device, comprising: a hole transport layer, and a light-emitting layer, wherein the hole transport layer and the light-emitting layer has an interface exciplex formed at an interface therebetween, wherein the light-emitting layer comprises a sensitized material, a first host material, and a fluorescent dye, the sensitized material is a Thermally Activated Delayed Fluorescence material, and a material of the hole transport layer and the first host material of the light-emitting layer form the interface exciplex.

2. The organic electroluminescent device of claim 1, wherein, a triplet level of the interface exciplex is less than a triplet level of the material of the hole transport layer, and the triplet level of the interface exciplex is less than a triplet level of the first host material.

3. The organic electroluminescent device of claim 1, wherein a singlet level of the interface exciplex is greater than a singlet level of the Thermally Activated Delayed Fluorescence material, and a triplet level of the interface exciplex is greater than a triplet level of the Thermally Activated Delayed Fluorescence material.

4. The organic electroluminescent device of claim 1, wherein an energy level gap between a HOMO level of the first host material and a LUMO level of the first host material is greater than 2.5 eV.

5. The organic electroluminescent device of claim 1, wherein a singlet-triplet energy level gap of the TADF material is less than 0.2 eV.

6. The organic electroluminescent device of claim 1, wherein the fluorescent dye accounts for 0.1-20% of a mass of the first host material, and the Thermally Activated Delayed Fluorescence material accounts for 5-80% of the mass of the first host material.

7. The organic electroluminescent device of claim 6, wherein the fluorescent dye accounts for 0.5-10% of the mass of the first host material, and the Thermally Activated Delayed Fluorescence material accounts for 10-40% of the mass of the first host material.

8. The organic electroluminescent device of claim 1, wherein the material of the hole transport layer is a compound having a tertiary aromatic amine or carbazole unit.

9. The organic electroluminescent device of claim 8, wherein the material of the hole transport layer employs one of the following structures: ##STR00059## ##STR00060## ##STR00061## ##STR00062##

10. The organic electroluminescent device of claim 1, wherein the first host material contains one or more units of carbonyl, phosphine oxide, pyrimidine, or pyridine.

11. The organic electroluminescent device of claim 10, wherein the first host material employs one of the following structures: ##STR00063## ##STR00064## ##STR00065##

12. The organic electroluminescent device of claim 1, wherein the Thermally Activated Delayed Fluorescence material has a donor unit and a receptor unit; wherein the donor unit is formed by linking one or more donor groups; and the receptor unit is formed by linking one or more receptor groups.

13. The organic electroluminescent device of claim 12, wherein the donor group is selected from the following groups: ##STR00066## ##STR00067## ##STR00068##

14. The organic electroluminescent device of claim 12, wherein the receptor group is selected from the following groups: ##STR00069##

15. The organic electroluminescent device of claim 1, wherein the Thermally Activated Delayed Fluorescence material employs one of the following structures: ##STR00070## ##STR00071## ##STR00072##

16. The organic electroluminescent device of claim 1, wherein the fluorescent dye employs one of the following structures: ##STR00073## ##STR00074## ##STR00075##

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to illustrate the technical solutions of specific embodiments of the present disclosure or the prior art more clearly, the drawings used in the description of the specific embodiments or the prior art are briefly described below. Apparently, the drawings in the following description are only some embodiments of the present disclosure, and a person of ordinary skill in the art can obtain other drawings according to these drawings without involving any inventive effort.

(2) FIG. 1 is a schematic diagram of energy level transfer of an organic electroluminescent device according to the present disclosure;

(3) FIG. 2 is a schematic structural diagram of an organic electroluminescent device according to Embodiment 1 of the present disclosure;

(4) FIG. 3 is a fluorescence spectrum (emission spectrum) of a hole transport layer material, a first host material, and a mixture thereof according to Embodiment 1 of the present disclosure; and

(5) FIG. 4 is a test spectrum of an organic electroluminescent device of Embodiment 1 and Comparative Embodiment 1 of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

(6) The technical solutions of the present disclosure are clearly and completely described below with reference to the accompanying drawings. It is apparent that the described embodiments are a part of the embodiments of the present disclosure, and not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present disclosure without involving an inventive effort fall within the protection scope of the present disclosure.

(7) The present disclosure may be implemented in different forms, and should not be construed to be limited to the embodiments set forth herein. In contrast, these embodiments are provided such that the present disclosure will be thorough and complete. Moreover, the concept of the present disclosure is thoroughly presented to those skilled in the art. The present disclosure is defined only by the appended claims. In the accompanying drawings, the dimensions and the relative dimensions of layers and regions are exaggerated for clarity. When an element, such as a layer, is “formed on” or “disposed on” another element, the element can be directly disposed on another element, or an intermediate element may be present. In contrast, when an element is “directly formed on” or “directly disposed on” another element, there is no intermediate element.

Embodiment 1

(8) As shown in FIG. 2, this embodiment provides an organic electroluminescent device, including a first electrode 1, a hole transport layer 2, a light-emitting layer 3, an electron transport layer 4, an electron injection layer 5, and a second electrode 6. As an embodiment of the present disclosure, specifically, the structure of the organic electroluminescent device is: ITO/TAPC (50 nm)/TCTA (10 nm)/light-emitting layer (30 nm)/BPBiPA (30 nm)/LiF (0.5 nm)/A1 (150 nm). That is, the material of the first electrode 1 is ITO, the material of the hole transport layer 2 includes TAPC and TCTA, TCTA also has an electron blocking effect, and the material of the electron transport layer 4 is BPBiPA, the material of the electron injection layer 5 is LiF, and the material of the second electrode is A1. The light-emitting layer 3 includes a first host material PhCzTRz, a TADF sensitizer PXZ-DPS, and a fluorescent dye PhtBuPAD. Layer thickness data is shown in the parentheses. The specific structures are as follows:

(9) ##STR00018## ##STR00019##

(10) the triplet level is: TCTA>PhCzTrz>PhtBuPAD.

(11) As shown in FIG. 3, the spectrum of the mixture of the hole transport layer material and the first host material (the mixture of TCTA and PhCzTrz) is significantly red-shifted compared to the emission spectra of the hole transport layer material (TCTA) and the first host material (PhCzTrz), which indicates that an interface exciplex is formed by the hole transport layer material and the first host material. An interface exciplex is formed by the hole transport layer material and the first host material in the light-emitting layer 3. The energy level transfer of an organic electroluminescent device containing the interface exciplex is shown is FIG. 1. On the one hand, as a competitive process, the high RISC rate of the exciplex can inhibit the DET from the exciplex to the fluorescent dye. On the other hand, the enhanced Forster energy transfer from the exciplex to the TADF material can greatly promote the ratio of singlet excitons (>25%) of the TADF material while inhibiting triplet excitons (<75%), which also inhibits the DET from the TADF material to the fluorescent dye. Therefore, the exciton loss of the DET can be greatly reduced in such two paths, which is beneficial to improve the device efficiency.

(12) Moreover, the TADF material and the first host material are adaptively doped in the light-emitting layer, so that the TADF material is diluted to inhibit the quenching effect caused by aggregation, thereby further improving the device efficiency.

Embodiment 2

(13) This embodiment provides an organic electroluminescent device having the same structure as Embodiment 1, except that the first host material is replaced with:

(14) ##STR00020##

Embodiment 3

(15) This embodiment provides an organic electroluminescent device having the same structure as Embodiment 1, except that the TADF material is replaced with:

(16) ##STR00021##

Embodiment 4

(17) This embodiment provides an organic electroluminescent device having the same structure as Embodiment 1, except that the TCTA in the hole transport material is replaced with:

(18) ##STR00022##

Embodiment 5

(19) This embodiment provides an organic electroluminescent device having the same structure as Embodiment 1, except that the first host material is replaced with:

(20) ##STR00023##

Embodiment 6

(21) This embodiment provides an organic electroluminescent device having the same structure as Embodiment 1, except that the first host material is replaced with:

(22) ##STR00024##

Embodiment 7

(23) This embodiment provides an organic electroluminescent device having the same structure as Embodiment 1, except that the hole transport material is replaced with:

(24) ##STR00025##

Embodiment 8

(25) This embodiment provides an organic electroluminescent device having the same structure as Embodiment 1, except that the hole transport material is replaced with:

(26) ##STR00026##

Embodiment 9

(27) This embodiment provides an organic electroluminescent device having the same structure as Embodiment 1, except that the TADF material is replaced with:

(28) ##STR00027##

Embodiment 10

(29) This embodiment provides an organic electroluminescent device having the same structure as Embodiment 1, except that the TADF material is replaced with:

(30) ##STR00028##

(31) In Embodiments 1-10, the fluorescent dye accounts for 0.1-20% of the mass of the first host material, preferably 0.5-10%. The TADF material accounts for 5-80% of the mass of the first host material, preferably 10-40%.

(32) In the foregoing embodiments, the first host material may be selected from the following compounds:

(33) ##STR00029## ##STR00030## ##STR00031##

(34) The hole transport material may be selected from the following compounds:

(35) ##STR00032## ##STR00033## ##STR00034## ##STR00035##

(36) The fluorescent dye may be selected from the following compounds:

(37) ##STR00036## ##STR00037## ##STR00038##

(38) The sensitized material, i.e., the TADF material may be selected from the following compounds:

(39) ##STR00039## ##STR00040## ##STR00041## ##STR00042## ##STR00043## ##STR00044## ##STR00045## ##STR00046## ##STR00047## ##STR00048## ##STR00049## ##STR00050## ##STR00051## ##STR00052## ##STR00053## ##STR00054## ##STR00055## ##STR00056## ##STR00057## ##STR00058##

(40) As transformable embodiments of the present disclosure, the structure of the organic electroluminescent device is not limited thereto. Any organic electroluminescent devices within the scope of the appended claims may achieve the object of the present disclosure and fall within the protection scope of the present disclosure. Reference is made to the prior art for the preparation process, and details are not described in the specification.

Comparative Embodiment 1

(41) This comparative embodiment provides an organic electroluminescent device having the same structure as in Embodiment 1, except that the first host material which forms an exciplex with the hole transport layer is removed from the light-emitting layer, and the TADF sensitizer is separately used as the first host material.

(42) Specifically, the structure of the organic electroluminescent device is: ITO/TAPC (30 nm)/TCTA (10 nm)/light-emitting layer (30 nm)/BPBiPA (30 nm)/LiF (1 nm)/A1 (150 nm).

(43) The light-emitting layer includes a first host material PhCzTRz and a fluorescent dye PhtBuPAD.

Test Example

(44) The characteristics of current, voltage, brightness, and luminescence spectrum, of the device are synchronously tested by a PR 650 spectral scanning brightness meter and a Keithley K 2400 digital source meter system. The organic electroluminescent devices provided in Embodiments 1-4 and Comparative Embodiment 1 are tested. As shown in FIG. 4, the external quantum efficiency of the device provided in Embodiment 1 is greater than that of the device of Comparative Embodiment 1.

(45) TABLE-US-00001 Turn-on Color coordinate Maximum quantum voltage CIE (x, y) efficiency (%) Embodiment 1 2.4 (0.36, 0.58) 24 Embodiment 2 2.5 (0.36, 0.58) 23 Embodiment 3 2.5 (0.36, 0.58) 23 Embodiment 4 2.4 (0.36, 0.58) 24 Comparative 2.9 (0.36, 0.58) 19 Embodiment 1

(46) It is apparent that the foregoing embodiments are merely illustrated for clarity, and are not intended to limit the embodiments. Other variations or modifications of different forms may also be made by a person of ordinary skilled in the art on the basis of the foregoing description. There is no need and no way to exhaust all the embodiments here. Obvious variations or modifications resulting therefrom still fall within the protection scope of the present disclosure.