Thermally activated delayed fluorescence material and application thereof in organic electroluminescence device

Abstract

The present invention discloses a thermally activated delayed fluorescence material and application thereof in an organic electroluminescence device. The thermally activated delayed fluorescence material is a compound having the general structure of Formula I or Formula II: ##STR00001## In Formula I and Formula II, R.sub.1 is a cyano, p is 1, 2 or 3, q is 1, 2 or 3, m is 1 or 2, n is 1 or 2, Ar.sub.1 is a phenyl substituted with one or more groups selected from C.sub.1-6 alkyl, methoxy, ethoxy, or phenyl, Ar.sub.2 and Ar.sub.3 are selected from the following groups: ##STR00002## ##STR00003## ##STR00004## ##STR00005##
and X is bromine or iodine. The present invention further discloses application of the thermally activated delayed fluorescence material as a host material or a luminescent dye of a luminescent layer of an organic electroluminescence device.

Claims

1. A thermally activated delayed fluorescence material, wherein the thermally activated delayed fluorescence material is a compound having a structure shown in formulas 1-2 to 1-5: ##STR00038## ##STR00039##

2. An organic electroluminescence device, comprising a luminescent layer, wherein the luminescent layer comprises a host material and a luminescent dye doped in the host material, and one of the host material and the luminescent dye is the thermally activated delayed fluorescence material according to claim 1.

3. The organic electroluminescence device according to claim 2, wherein the luminescent dye is the thermally activated delayed fluorescence material, the luminescent dye accounts for 0.5 wt %-10 wt % of the luminescent layer.

4. The organic electroluminescence device according to claim 2, wherein the luminescent dye is the thermally activated delayed fluorescence material, the luminescent dye accounts for 5 wt % of the luminescent layer.

5. The organic electroluminescence device according to claim 2, wherein the luminescent dye is the thermally activated delayed fluorescence material, the organic electroluminescence device comprises an anode, a hole transport layer, a luminescent layer, an electron transport layer, and a cathode, which are successively deposited on a substrate and are laminated.

6. The organic electroluminescence device according to claim 5, wherein the anode and the hole transport layer has a hole injection layer disposed therebetween.

7. The organic electroluminescence device according to claim 2, wherein the host material is the thermally activated delayed fluorescence material, the luminescent dye accounts for 1 wt %-10 wt % of the luminescent layer.

8. The organic electroluminescence device according to claim 2, wherein the luminescent dye is the thermally activated delayed fluorescence material according to claim 1.

9. An application of the thermally activated delayed fluorescence material according to claim 1, wherein the thermally activated delayed fluorescence material is used as a host material or a luminescent dye of a luminescent layer of an organic electroluminescence device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is the schematic diagram of the structure of an organic electroluminescence device of the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

(2) The present invention will be further illustrated below by referring to the drawings and the special examples, to enable a person skilled in the art to better understand and implement the present invention, but the examples are not taken as limiting the present invention.

(3) A thermally activated delayed fluorescence material provided in the invention is a compound having the general structure of Formula I or Formula II:

(4) ##STR00015##

(5) In Formula I and Formula II, R.sub.1 is a cyano, p is 1, 2 or 3, q is 1, 2 or 3, m is 1 or 2, n is 1 or 2,

(6) Ar.sub.1 is a phenyl substituted with one or more groups selected from C.sub.1-6 alkyl, methoxy, ethoxy, or phenyl,

(7) Ar.sub.2 and Ar.sub.3 are selected from the following groups:

(8) ##STR00016## ##STR00017## ##STR00018## ##STR00019##
and X is bromine or iodine.

(9) According to the thermally activated delayed fluorescence material, by introducing heavy atoms such as bromine or iodine into original TADF molecules, reverse intersystem crossing and intersystem crossing of the TADF material can be increased through the heavy atom effect, so that the lifetime of triplet excitons can be reduced, and ultimately the lifetime of a device can be increased.

(10) Specifically, the thermally activated delayed fluorescence material of the present invention is compounds having the following structures, and properties and preparation methods of the compounds are as follows:

(11) ##STR00020##
Preparation Method:

(12) Synthesis of the compound having the structure represented by Formula (1-1): in the nitrogen range, 3-bromocarbazole (5 mmol) is dissolved in 2 mL of anhydrous THF, then sodium hydride (5 mmol) is added, and the mixture is stirred at room temperature for 30 minutes; subsequently, 1,2-dicyano-4,5-difluorobenzene (1 mmol) is added to a reaction flask and stirring is continued for 1 hour; finally, 2 mL of cold water is added to the mixture to quench the reaction. After the mixture is cooled to room temperature, a product of Formula (1-1) is purified by vacuum filtration followed by column chromatography, and the product is dried in vacuum. Yield: 75%.

(13) Molecular weight obtained through mass spectrometry: 615.97.

(14) Relative molecular mass percentage of each element obtained through elemental analysis: C: 62.36; H: 2.62; N: 9.09; Br: 25.93.

(15) ##STR00021##
Preparation Method:

(16) Synthesis of the compound having the structure represented by Formula (1-2): in the nitrogen range, 3-bromophenothiazine (10 mmol) is dissolved in 4 mL of anhydrous THF, then sodium hydride (10 mmol) is added, and the mixture is stirred at room temperature for 30 minutes; subsequently, 2,3,5,6-tetrafluoro nitrile benzene (1 mmol) is added to a reaction flask and stirring is continued for 1 hour; finally, 2 mL of cold water is added to the mixture to quench the reaction. After the mixture is cooled to room temperature, a product of Formula (1-2) is purified by vacuum filtration followed by column chromatography, and the product is dried in vacuum. Yield: 62%.

(17) Molecular weight obtained through mass spectrometry: 1206.80.

(18) Relative molecular mass percentage of each element obtained through elemental analysis: C: 54.70; H: 2.42; N: 5.80; S: 10.62; Br: 26.46.

(19) ##STR00022##
Preparation Method:

(20) Synthesis of the compound having the structure represented by Formula (1-3): the reactant 3-bromophenothiazine is replaced with 3-bromophenoxazine, the compound having the structure represented by Formula (1-3) is obtained by a synthesis method which is the same as that of Formula (1-2), and yield is 59%.

(21) Molecular weight obtained through mass spectrometry: 1142.89.

(22) Relative molecular mass percentage of each element obtained through elemental analysis: C: 57.77; H: 2.56; N: 6.12; O: 5.60; Br: 27.95.

(23) ##STR00023##
Preparation Method:

(24) Synthesis of the compound having the structure represented by Formula (1-4): the reactant 3-bromophenothiazine is replaced with 9-p-iodobenzene phenazine, the compound having the structure represented by Formula (1-4) is obtained by a synthesis method which is the same as that of Formula (1-2), and yield is 55%.

(25) Molecular weight obtained through mass spectrometry: 1631.03.

(26) Relative molecular mass percentage of each element obtained through elemental analysis: C: 58.14; H: 3.03; N: 7.72; I: 31.11.

(27) ##STR00024##
Preparation Method:

(28) Synthesis of the compound having the structure represented by Formula (1-5): in the nitrogen range, (1,1-p-dibromobenzene) p-aminobenzene (15 mmol) is dissolved in 6 mL of anhydrous THF, then sodium hydride (15 mmol) is added, and the mixture is stirred at room temperature for 30 minutes; subsequently, 2,4,6-tetrafluoro-1,3,5-tricyanobenzene (1 mmol) is added to a reaction flask and stirring is continued for 1 hour; finally, 2 mL of cold water is added to the mixture to quench the reaction. After the mixture is cooled to room temperature, a product of Formula (1-5) is purified by vacuum filtration followed by column chromatography, and the product is dried in vacuum. Yield: 31%.

(29) Molecular weight obtained through mass spectrometry: 1355.80.

(30) Relative molecular mass percentage of each element obtained through elemental analysis: C: 55.78; H: 2.68; N: 6.20; Br: 35.34.

(31) ##STR00025##
Preparation Method:

(32) Synthesis of the compound having the structure represented by Formula (2-1): in the nitrogen range, 3,6-dibromocarbazolylbenzene (10 mmol) is dissolved in 4 mL of anhydrous THF, then sodium hydride (15 mmol) is added, and the mixture is stirred at room temperature for 30 minutes; subsequently, 1-phenyl-1,3,5-triazine (1 mmol) is added to a reaction flask and stirring is continued for 1 hour; finally, 2 mL of cold water is added to the mixture to quench the reaction. After the mixture is cooled to room temperature, a product of Formula (2-1) is purified by vacuum filtration followed by column chromatography, and the product is dried in vacuum. Yield: 49%.

(33) Molecular weight obtained through mass spectrometry: 955.33.

(34) Relative molecular mass percentage of each element obtained through elemental analysis: C: 56.58; H: 2.64; N: 7.33; Br: 33.46.

(35) ##STR00026##
Preparation Method:

(36) Synthesis of the compound having the structure represented by Formula (2-2): in the nitrogen range, p-bromobenzene (5 mmol) is dissolved in 4 mL of anhydrous THF, then sodium hydride (5 mmol) is added, and the mixture is stirred at room temperature for 30 minutes; subsequently, 2,4-bis(3-bicarbazole)-6-fluoro-1,3,5-triazine (1 mmol) is added to a reaction flask and stirring is continued for 1 hour; finally, 2 mL of cold water is added to the mixture to quench the reaction. After the mixture is cooled to room temperature, a product of Formula (2-2) is purified by vacuum filtration followed by column chromatography, and the product is dried in vacuum. Yield: 53%.

(37) Molecular weight obtained through mass spectrometry: 895.21.

(38) Relative molecular mass percentage of each element obtained through elemental analysis: C: 76.34; H: 3.82; N: 10.93; Br: 8.91.

(39) ##STR00027##
Preparation Method:

(40) Synthesis of the compound having the structure represented by Formula (2-3): in the nitrogen range, p-iodobenzene (10 mmol) is dissolved in 4 mL of anhydrous THF, then sodium hydride (10 mmol) is added, and the mixture is stirred at room temperature for 30 minutes; subsequently, 2,4-bis(3-bicarbazole)-1,3,5-triazine (1 mmol) is added to a reaction flask and stirring is continued for 1 hour; finally, 2 mL of cold water is added to the mixture to quench the reaction. After the mixture is cooled to room temperature, a product of Formula (2-3) is purified by vacuum filtration followed by column chromatography, and the product is dried in vacuum. Yield: 53%.

(41) Molecular weight obtained through mass spectrometry: 891.04.

(42) Relative molecular mass percentage of each element obtained through elemental analysis: C: 60.62; H: 3.05; N: 7.86; I: 28.47.

(43) ##STR00028##
Preparation Method:

(44) Synthesis of the compound having the structure represented by Formula (2-4): in the nitrogen range, p-diiodobenzene-4,4-diaminobenzenes (5 mmol) is dissolved in 4 mL of anhydrous THF, then sodium hydride (5 mmol) is added, and the mixture is stirred at room temperature for 30 minutes; subsequently, 4-fluoro-2,6-phenyl-1,3,5-triazine (1 mmol) is added to a reaction flask and stirring is continued for 1 hour; finally, 2 mL of cold water is added to the mixture to quench the reaction. After the mixture is cooled to room temperature, a product of Formula (2-4) is purified by vacuum filtration followed by column chromatography, and the product is dried in vacuum. Yield: 40%.

(45) Molecular weight obtained through mass spectrometry: 1313.93.

(46) Relative molecular mass percentage of each element obtained through elemental analysis: C: 52.08; H: 2.91; N: 6.39; I: 38.61.

(47) ##STR00029##
Preparation Method:

(48) Synthesis of the compound having the structure represented by Formula (2-5): the reactant 3,6-dibromocarbazolylbenzene is replaced with 3,7-dibromophenoxazinebenzene, the compound having the structure represented by Formula (2-5) is obtained by a synthesis method which is the same as that of Formula (2-1), and yield is 61%.

(49) Molecular weight obtained through mass spectrometry: 986.87.

(50) Relative molecular mass percentage of each element obtained through elemental analysis: C: 54.74; H: 2.55; N: 7.09; O: 3.24; Br: 32.37.

(51) ##STR00030##
Preparation Method:

(52) Synthesis of the compound having the structure represented by Formula (2-6): the reactant 3,6-dibromocarbazolylbenzene is replaced with 3,7-dibromophenoxazine-m-benzene, the compound having the structure represented by Formula (2-6) is obtained by a synthesis method which is the same as that of Formula (2-1), and yield is 61%.

(53) Molecular weight obtained through mass spectrometry: 1174.82.

(54) Relative molecular mass percentage of each element obtained through elemental analysis: C: 45.99; H: 2.14; N: 5.96; O: 2.72; I: 43.19.

(55) ##STR00031##
Preparation Method:

(56) Synthesis of the compound having the structure represented by Formula (2-7): in the nitrogen range, dibromo-benzene (10 mmol) is dissolved in 4 mL of anhydrous THF, then sodium hydride (10 mmol) is added, and the mixture is stirred at room temperature for 30 minutes; subsequently, 2,4-difluoro-6-(11-phenyl-11,12-dihydroindolo[3,2b]carbazolyl)-2,6-phenyl-1,3,5-triazine (1 mmol) is added to a reaction flask and stirring is continued for 1 hour; finally, 2 mL of cold water is added to the mixture to quench the reaction. After the mixture is cooled to room temperature, a product of Formula (2-7) is purified by vacuum filtration followed by column chromatography, and the product is dried in vacuum. Yield: 34%.

(57) Molecular weight obtained through mass spectrometry: 721.03.

(58) Relative molecular mass percentage of each element obtained through elemental analysis: C: 64.93; H: 3.21; N: 9.71; Br: 22.15.

(59) ##STR00032##
Preparation Method:

(60) Synthesis of the compound having the structure represented by Formula (2-8): in the nitrogen range, 6-phenyl-2,9-diiodo-indolo[2,3a]carbazole (10 mmol) is dissolved in 4 mL of anhydrous THF, then sodium hydride (10 mmol) is added, and the mixture is stirred at room temperature for 30 minutes; subsequently, 6-fluoro-2,4-diphenyl-1,3,5-triazine (1 mmol) is added to a reaction flask and stirring is continued for 1 hour; finally, 2 mL of cold water is added to the mixture to quench the reaction. After the mixture is cooled to room temperature, a product of Formula (2-8) is purified by vacuum filtration followed by column chromatography, and the product is dried in vacuum. Yield: 31%.

(61) Molecular weight obtained through mass spectrometry: 815.44.

(62) Relative molecular mass percentage of each element obtained through elemental analysis: C: 57.44; H: 2.84; N: 8.59; I: 31.13.

(63) ##STR00033##
Preparation Method:

(64) Synthesis of the compound having the structure represented by Formula (2-9): in the nitrogen range, 11-p-bromophenyl-indolo[2,3a]carbazole (7 mmol) is dissolved in 4 mL of anhydrous THF, then sodium hydride (10 mmol) is added, and the mixture is stirred at room temperature for 30 minutes; subsequently, 6-fluoro-2,4-p-dibromophenyl-1,3,5-triazine (1 mmol) is added to a reaction flask and stirring is continued for 1 hour; finally, 2 mL of cold water is added to the mixture to quench the reaction. After the mixture is cooled to room temperature, a product of Formula (2-9) is purified by vacuum filtration followed by column chromatography, and the product is dried in vacuum. Yield: 36%.

(65) Molecular weight obtained through mass spectrometry: 800.34.

(66) Relative molecular mass percentage of each element obtained through elemental analysis: C: 58.53; H: 2.77; N: 8.75; Br: 29.95.

(67) The thermally activated delayed fluorescence material of the present invention can be used as a luminescent dye for a luminescent layer of an organic electroluminescence device.

(68) As shown by FIG. 1, the organic electroluminescence device of the present invention comprises an anode 02, a hole injection layer 04, a hole transport layer 05, a luminescent layer 06, an electron transport layer 07 and a cathode 03, which are successively deposited on a substrate 01 and are laminated.

(69) The material of the luminescent layer 06 comprises a host material and a luminescent dye doped in the host material, and

(70) the luminescent material is a compound having the structure of Formula I or Formula II.

(71) The embodiments of the organic luminescence display device of the present invention: the anode 02 may employ an inorganic material or an organic conductive polymer. The inorganic material may generally employ metal oxides such as indium tin oxide (ITO), zinc oxide (ZnO), and indium zinc oxide (IZO) or metals of high work functions such as gold, copper and silver, preferably ITO. The organic conductive polymer is preferably one of polythiophene/polyvinyl sodium benzenesulfonate (hereafter referred to as simply PEDOT/PSS) and polyaniline (hereafter referred to as simply PANI).

(72) The cathode 03 generally employs metals of low work function such as lithium, magnesium, calcium, strontium, aluminum and indium or their alloys with copper, gold or silver, or an electrode layer that is formed by the alternating of a metal and a metal fluoride. In the present invention the cathode is preferably laminated LiF layer and Al layer (the LiF layer is on the outer side).

(73) The material of the hole transport layer 05 may be selected from lower molecular weight materials of the arylamine type and the branched polymer type, preferably NPB.

(74) The material of the electron transport layer 07 may employ an organic metal complex (such as Alq.sub.3, Gaq.sub.3, BAlq or Ga (Saph-q)) or other materials that are commonly used for electron transport layer, such as aromatic condensed ring type (such as pentacene and perylene) or o-phenanthroline type (such as Bphen and BCP) compounds.

(75) The organic electroluminescence device of the present invention may also be provided with the hole injection layer 04 between the anode 02 and the hole transport layer 05. The material of the hole injection layer 04 may employ, for example, 4,4,4-tris(3-methylphenylaniline)triphenylamine doped F4TCNQ or copper phthalocyanine (CuPc), or may be a metal oxide, such as molybdenum oxide and rhenium oxide.

(76) The thicknesses of the layers may employ the conventional thicknesses of the layers in the art.

(77) The present invention further provides a preparation method of the organic electroluminescence device, which comprises successively depositing on the substrate 01 the anode 02, the hole injection layer 04, the hole transport layer 05, the luminescent layer 06, the electron transport layer 07 and the cathode 03, which are laminated, and packaging.

(78) The substrate may be glass or a flexible base sheet. The flexible base sheet may employ a polyester type or polyimide type compound material or a thin sheet metal. The laminating and the packaging may employ any suitable method that is known by a person skilled in the art.

Comparative Example 1

(79) This comparative example uses ITO (indium tin oxide) as the anode; NPB as the hole injection layer; TCTA as the hole transport layer; the luminescent layer uses CBP as the host material and DSA-Ph as the luminescent dye, and the mass percentage of the luminescent dye doped in the luminescent layer is 5 wt %; Bphen as the electron transport layer; LiF (5 nm)/Al as the cathode. The structures are as follows:

(80) ITO/NPB (40 nm)/TCTA (10 nm)/CBP: 5 wt % DSA-Ph (30 nm)/Bphen (40 nm)/LiF (5 nm)/Al

(81) ##STR00034##

Comparative Example 2

(82) The structure of this Comparative Example differs from that of Comparative Example 1 only in that the luminescent dye used in the luminescent layer is 2CzPN:

(83) ITO/NPB (40 nm)/TCTA (10 nm)/CBP: 5 wt % 2CzPN (30 nm)/Bphen (40 nm)/LiF (5 nm)/Al

(84) ##STR00035##

Embodiment 1

(85) The structure of this embodiment differs from that of Comparative Example 1 only in that the luminescent dye used in the luminescent layer is compound 1-1 of the present invention:

(86) ##STR00036##
ITO/NPB (40 nm)/TCTA (10 nm)/CBP: 5 wt % compound 1-1 (30 nm)/Bphen (40 nm)/LiF (5 nm)/Al

(87) TABLE-US-00001 Current Lumen Serial Luminance efficiency efficiency number cd/m.sup.2 Voltage V cd/A lm/W x (V) y (V) T.sub.95 h Comparative 1000 6.7 10.2 4.8 0.16 0.35 51 Example 1 Comparative 1000 4.5 11.38 6.25 0.12 0.32 24 Example 2 Embodiment 1 1000 4.3 12.20 7.23 0.14 0.29 78

(88) According to the TADF material in Embodiment 1, due to the introduction of the heavy atoms, reverse intersystem crossing and intersystem crossing of the TADF material are increased through the heavy atom effect, so that the lifetime of triplet excitons is reduced, and ultimately the lifetime of the device is increased.

Embodiments 2-5

(89) The structures of Embodiments 2-5 differ from that of Embodiment 1 only in that the doping concentration of the luminescent dye compound 1-1 in the luminescent layer is different: ITO/NPB (40 nm)/TCTA (10 nm)/CBP: 0.5-10 wt % compound 1-1 (30 nm)/Bphen (40 nm)/LiF (5 nm)/Al

(90) Embodiments with Different Doping Concentrations

(91) TABLE-US-00002 Doping Current Lumen Serial concentration Luminance efficiency efficiency number of dye wt % cd/m.sup.2 Voltage V cd/A lm/W x (V) y (V) T.sub.95 h Embodiments 1 5 1000 4.3 12.20 7.23 0.14 0.29 78 Embodiments 2 0.5 1000 3.2 10.35 6.02 0.14 0.29 55 Embodiments 3 1 1000 4.0 10.56 5.98 0.14 0.29 61 Embodiments 4 3 1000 4.2 11.32 6.99 0.14 0.29 69 Embodiments 5 10 1000 4.4 10.79 6.89 0.14 0.29 79

(92) From the above table, it can be seen that the increase of the concentration of the luminescent dye causes the current efficiency of the device to increase first and then decrease. When the doping concentration is 5 wt %, the current efficiency of the device is the highest, and the voltage of the device basically does not change, but the lifetime of the device is increased as the doping concentration of the luminescent dye increases.

Embodiment 6

(93) The OLED structure in this embodiment differs from Embodiment 1 only in that the luminescent layer is doped with a different compound having the structure of Formula I or Formula II as the luminescent dye:

(94) ITO/NPB (40 nm)/TCTA (10 nm)/CBP: 5 wt % (compound having the structure of Formula I or Formula II) (30 nm)/Bphen (40 nm)/LiF (5 nm)/Al

(95) TABLE-US-00003 TADF material used in Current Lumen Serial luminescent Luminance efficiency efficiency number layer cd/m.sup.2 Voltage V cd/A lm/W x (V) y (V) T.sub.95 h OLED1 1-2 1000 5.4 13.26 8.98 0.13 0.22 59 OLED2 1-3 1000 4.9 11.38 6.57 0.15 0.22 62 OLED3 1-4 1000 5.0 29.32 19.25 0.56 0.50 132 OLED4 1-5 1000 4.8 30.21 20.36 0.50, 0.48 111 OLED5 2-1 1000 4.9 31.15 22.89 0.51, 0.49 110 OLED6 2-2 1000 4.5 38.56 24.25 0.49, 0.45 75 OLED7 2-3 1000 5.0 28.78 20.45 0.55, 0.50 121 OLED8 2-4 1000 5.5 6.00 5.21 0.20, 0.35 59 OLED9 2-5 1000 4.8 18.26 15.23 0.22 0.40 78 OLED10 2-6 1000 5.5 8.75 17.41 0.20 0.41 62 OLED11 2-7 1000 5.4 16.62 16.66 0.16 0.21 41 OLED12 2-8 1000 5.3 17.12 15.91 0.17 0.21 50 OLED13 2-9 1000 5.2 18.22 15.02 0.17, 0.22 52

(96) From the above table, it can be seen that the lifetime of the thermally activated delayed fluorescence material containing the heavy atoms of bromine or iodine, as well as the lifetime of the device protected by the invention are both increased, the reason is that reverse intersystem crossing and intersystem crossing of the TADF material are increased through the heavy atom effect, so that the lifetime of triplet excitons is reduced, and ultimately the lifetime of the device is increased.

Embodiments 7-9

(97) The difference between the OLED structure in the embodiments and Embodiment 1 lies in that the host material in the luminescent layer is compound 2-2, and the luminescent dye is Ir(ppy).sub.3. The doping concentration (weight percentage in the luminescent layer) of Ir(ppy).sub.3 is 1-10 wt %. ITO/NPB (40 nm)/TCTA (10 nm)/compound 2-2: 1-10 wt % Ir(ppy).sub.3 (30 nm)/Bphen (40 nm)/LiF (5 nm)/Al

Comparative Example 3

(98) The difference between the structure of this Comparative Example and Embodiments 7-9 is only that the host material used for the luminescent layer is CBP:

(99) ITO/NPB (40 nm)/TCTA (10 nm)/CBP: 5 wt % Ir(ppy).sub.3 (30 nm)/Bphen (40 nm)/LiF (5 nm)/A1

Comparative Example 4

(100) The difference between the structure of this Comparative Example and Embodiments 7-9 is only that the host material used for the luminescent layer is CC2TA:

(101) ##STR00037##

(102) TABLE-US-00004 Doping concentration Current Lumen T.sub.95 h Serial of dye Luminance efficiency efficiency (at number wt % cd/m.sup.2 Voltage V cd/A lm/W x (V) y (V) 10000 cd/m.sup.2) Embodiments 7 5 wt % 1000 3.4 67 91 0.27 0.63 274 Embodiments 8 1 wt % 1000 3.0 60 86 0.26 0.63 260 Embodiments 9 10 wt % 1000 4.2 59 82 0.27 0.64 280 Comparative 5 wt % 1000 5.4 45 62 0.26 0.63 242 Example 3 Comparative 5 wt % 1000 3.9 62 90 0.26 0.62 266 Example 4

(103) From the above table, it can be seen by comparing Embodiment 7, Embodiment 8 and Embodiment 9 with different doping concentrations that the electrical property of the device increases first and then decreases with an increase in the doping concentration of the luminescent dye, and is optimize at the doping concentration of 5 wt %, but the lifetime of the device increases as the doping concentration of the dye increases. In addition, the lifetime of the device protected by the present invention with the thermally activated delayed fluorescence material containing the heavy bromine atoms serving as the host is longer than that of a conventional device with CBP as a host (Comparative Example 3), and comparing with a device with a thermally activated sensitized fluorescent material of the same structure but without heavy atoms serving as a host (Comparative Example 4), the electrical property does not change much, but the lifetime of the device of Example 7 is longer than that of the device of Comparative Example 4, because the reverse intersystem crossing coefficient of the TADF material is increased through the heavy atom effect, so that the lifetime of triplet excitons is reduced, and ultimately the lifetime of the device is increased.

(104) The above-described embodiments are merely preferred embodiments for fully explaining the present invention, and the scope of protection of the present invention is not limited thereto. The equivalent substitutions or alternations that are made by a person skilled in the art on the basis of the present invention all fall within the protection scope of the present invention. The protection scope of the present invention is limited by the claims.