KR102026462B1 - Organic light emitting diode comprising phosphorescence green host materials having thermally activated delayed fluorescence properties - Google Patents

Abstract

The present invention relates to an organic light emitting device comprising a delayed fluorescent first compound and a green phosphorescent second compound. According to the present invention, provided is an organic light emitting device having improved theoretical quantum efficiency by utilizing excitons of triplets of dopants.

Description

ORGANIC LIGHT EMITTING DIODE COMPRISING PHOSPHORESCENCE GREEN HOST MATERIALS HAVING THERMALLY ACTIVATED DELAYED FLUORESCENCE PROPERTIES}

The present invention relates to an organic light emitting device comprising a delayed fluorescent first compound and a green phosphorescent second compound.

OLED technology is steadily making efforts in Europe, the United States, Japan, and Korea to apply to the lighting field as well as displays. In particular, many studies are being conducted to improve the efficiency and lifespan of OLED devices.

The excitons generated in the light emitting layer of the OLED device are formed in the singlet and triplet states at 25% and 75%, respectively, but the external quantum efficiency cannot be emitted because most triplet excitons cannot be emitted. (EQE) is low

Therefore, development of a fluorescent material for an organic light emitting device excellent in efficiency and lifespan is required.

Korean Patent Publication No. 10-2018-0073238 (published Jul 02, 2018)

An object of the present invention is to provide an organic light emitting device including a host compound of a novel structure in which a delayed fluorescent concept is introduced.

Another object of the present invention is to provide a highly efficient long-life organic light emitting device capable of stably transferring energy from a host to a dopant by designing molecules such that energy difference between triplet and singlet is small.

It is still another object of the present invention to provide an organic light emitting device having high efficiency which can improve theoretical quantum efficiency by utilizing excitons of triplets of dopants.

An object of the present invention includes a first electrode, a second electrode and a light emitting layer positioned between the first electrode and the second electrode, the light emitting layer is a delayed fluorescent first compound and a green phosphorescent light-emitting agent represented by the following formula (1) It is achieved by an organic light emitting element containing two compounds.

[Formula 1]

In formula 1, X _1, X ₂ and X ₃ is a carbon or nitrogen hydrogen a substituted independently, at least one is nitrogen, R ₁ to R ₃ are each other the same or different and each is hydrogen, deuterium, a halogen group, -CN, substituted or unsubstituted C1 to C40 straight or branched alkyl group, substituted or unsubstituted C2 to C40 straight or branched alkenyl group, substituted or unsubstituted C2 to C40 straight or branched chain Alkynyl group, substituted or unsubstituted C3 to C40 monocyclic or polycyclic cycloalkyl group, substituted or unsubstituted C2 to C40 monocyclic or polycyclic heterocycloalkyl group, substituted or unsubstituted C6 to C60 monocyclic or polycyclic aryl A group, a substituted or unsubstituted C2 to C40 monocyclic or polycyclic heteroaryl group, R ₁ and R ₂ form a condensed ring with a ring containing at least one of X ₁ , X ₂ and X ₃ Do There.

R ₃ may be selected from a substituted or unsubstituted C1 to C30 alkyl group and the following compounds,

R ₅ may be omitted, or may be selected from substituted or unsubstituted C1 to C30 alkyl groups and the following compounds.

R ₄ may be omitted or selected from substituted or unsubstituted C 1 to C 30 alkyl groups and the following compounds.

The second compound may be selected from the following compounds.

According to the present invention, there is provided an organic light emitting device including a host compound having a novel structure in which the concept of delayed fluorescence is introduced.

According to the present invention, a high efficiency long life organic light emitting device capable of stably transferring energy from a host to a dopant by designing a molecule such that the energy difference between triplet and singlet is small is provided.

According to the present invention, an organic light emitting device having improved theoretical quantum efficiency is provided by utilizing excitons of triplets of dopants.

1 is a cross-sectional view of an organic light emitting diode according to an embodiment of the present invention.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims.

The size and thickness of each component shown in the drawings are shown for convenience of description, and the present invention is not necessarily limited to the size and thickness of the illustrated configuration.

Each of the features of the various embodiments of the present invention may be combined or combined with each other, partly or wholly, and various technically interlocking and driving are possible as one skilled in the art can fully understand, and each of the embodiments may be independently implemented with respect to each other. It may be possible to do it together in an association.

1 is a cross-sectional view of an organic light emitting diode according to an embodiment of the present invention.

Referring to FIG. 1, an organic light emitting diode 1 according to an exemplary embodiment of the present invention may include a hole injection disposed between a first electrode 110, a second electrode 120, and a first electrode 110 and a second electrode 120. The layer 211, the hole transport layer 212, the light emitting layer 213, and the electron transport layer 214 are included. The emission layer 213 includes a delayed fluorescent first compound and a green phosphorescent second compound represented by Chemical Formula 1 below.

[Formula 1]

In Formula 1, X ₁ , X ₂ and X ₃ are independently hydrogen or substituted carbon or nitrogen, at least one is nitrogen, R ₁ to R ₃ are the same as or different from each other, and each hydrogen, deuterium, halogen, -CN, substituted or unsubstituted C1 to C40 straight or branched alkyl group, substituted or unsubstituted C2 to C40 straight or branched alkenyl group, substituted or unsubstituted C2 to C40 straight or branched chain Alkynyl group, substituted or unsubstituted C3 to C40 monocyclic or polycyclic cycloalkyl group, substituted or unsubstituted C2 to C40 monocyclic or polycyclic heterocycloalkyl group, substituted or unsubstituted C6 to C60 monocyclic or polycyclic aryl forming the ring and condensed rings containing group, a substituted or unsubstituted C2 to is selected from monocyclic or polycyclic heteroaryl group the group consisting of C40, R ₁ and R ₂ is X _1, X ₂ and X _3, at least one of a Do There.

R ₃ may be selected from a substituted or unsubstituted C1 to C30 alkyl group and the following compounds.

R ₄ or R ₅ may be selected from substituted or unsubstituted C1 to C30 alkyl groups and the following compounds.

The compound according to the present invention can be selected from among the compounds shown below.

The second compound may be selected from the following compounds, and any compound having green phosphorescence properties is not limited to the following compounds.

Hereinafter, a first compound of the organic light emitting diode according to the present invention will be described with reference to FIGS. 2 and 3.

In order to implement a high efficiency organic light emitting device, a host material having an appropriate band gap and energy level must be developed. Materials with appropriate energy levels facilitate efficiency of energy transfer to dopants, which increases efficiency, lowers drive voltages, and increases lifetime. In addition, the organic materials used are thermally stable by having a high glass transition temperature (T _g ) and decomposition temperature (T _d ), thereby enabling continuous and stable operation of the device.

2 and 3 show the distribution of the molecular orbital function of the compound 1-1 of the compound represented by the formula (1) according to the present invention, compound 1-1 can be represented by the following scheme.

The first compound according to the invention comprises a core comprising at least one nitrogen. These cores have an electron-receiving property to act as acceptors, and the non-covalent electron pairs of nitrogen form planes through hydrogen bonds with two phenyl groups.

In addition, conjugation is appropriately disconnected by connecting a carbazole, which easily gives an electron, and acts as a donor, and a core containing at least one nitrogen with a phenyl group and meta.

On the other hand, as the phenyl group is substituted at position 1 of carbazole, steric hindrance occurs, so that the carbazole is almost perpendicular to the plane of the core containing at least one nitrogen. Accordingly, as shown in FIGS. 2 and 3, the molecular orbital distributions of the LUMO at the triazine position and the HOMO at the carbazole position are spatially separated, respectively, and the phenyleromo (LUMO) which becomes the linker. ) And the homogeneous distribution of the molecular orbital function of HOMO.

The first compound according to the present invention is a host having a characteristic of thermally activated delayed fluorescence, which has a smaller band gap between singlet and triplet, and energy of two bandgap compared to a conventional host. Has a level similar to a triplet. Therefore, when applied to the organic light emitting device has a low driving voltage effect.

In addition, due to the small band gap difference of the first compound according to the present invention having a delayed fluorescent characteristic, the reverse intersystem crossing in which the excitons of the triplet move to the singlet term: RISC) will occur.

orster resonance energy transfer: FRET)란, 쌍극자-쌍극자 상호작용에 의해 하나의 들뜬 분자에서 다른 분자로 비복사 과정을 통해 에너지가 전이되는 현상을 말한다.The excitons moved to the singlet are the singlet and triplet of the green phosphorescent dopant, the second compound having green phosphorescence through Foster energy transfer (FRET). Will quickly move to). Foster Energy Transfer (F

orster resonance energy transfer (FRET) refers to a phenomenon in which energy is transferred through non-radiative processes from one excited molecule to another by dipole-dipole interaction.

This fast transition rate of RISC and FRET effectively prevents exciton-polaron annihilation and the like, thereby increasing the operational lifetime of the organic light emitting device.

Meanwhile, the excitons moved to the singlet of the second compound dopant are transferred to the triplet through intersystem crossing (ISC), and the excitons are triplets. Is moved from the ground state to the ground state and finally glows in the green phosphorescence dopant.

At this time, the conventional fluorescence compound is one exciton of the singlet (25%) falls directly to the ground state (efficiency 25%), while the second phosphor of the green phosphorescent compound according to the present invention is a singlet (singlet) Since one exciton of is moved to the triplet and the total of four excitons fall to the ground state (25% each efficiency, 100% total efficiency), the quantum efficiency increases significantly Development of organic light emitting device is possible.

Therefore, the organic light emitting device including the first compound and the second compound according to the present invention has a low driving voltage due to the small energy difference between the single and triple terms of the delayed fluorescent first compound which is a host, and the conversion speed of FRET and RISC is low. Faster lifespan is increased, and quantum efficiency is greatly improved by triplet excitons of the green phosphorescent second compound as a dopant.

The glass transition temperature of the first compound according to the present invention is 140 ℃ or more, the melting temperature may be 270 ℃ or more. As a result, it is possible to implement an organic light emitting device having high efficiency and excellent thermal stability.

Hereinafter, Preparation Examples of Compounds 1-1 and 1-19, Examples 1 and 2, and Comparative Examples 1 and 2 of the organic light emitting diode will be described. However, the preparation examples and examples described below are merely for illustrating or explaining the present invention in detail, and should not be construed as limiting the present invention by the examples described below.

1. Compound 1-1

(1) Preparation of Intermediate 1-phenyl-9H-carbazole

1-bromo-9H-carbazole (24.6g, 100mmol) and phenanthren-9-ylboronic acid (15.9g, 130mmol), tetrakis (triphenylphosphine) palladium (0) (5.8g, 5mmol), Potassium carbonate (55.3g, 400mmol) Was added to 300 mL of toluene, 150 mL of ethanol and 150 mL of water, and the mixture was stirred under reflux for about 24 hours. After cooling to room temperature, an organic solvent layer was separated, silica gel was added, and concentrated in a concentrator to prepare a solid column. 19.5 g (yield 80%) of 1-phenyl-9H-carbazole was obtained after removing impurities through column separation (eluent: 10% dichloromethane + 90% hexane).

(2) Preparation of Compound 1-1

9,9 '-(5- (4,6-diphenyl-1,3,5-triazin-2-yl) -1,3-phenylene) bis (1-phenyl-9H-carbazole) represented by compound 1-1 Was prepared using the following reactions.

2- (3,5-dibromophenyl) -4,6-diphenyl-1,3,5-triazine (16.5g, 35mmol) and 1-phenyl-9H-carbazole (19.5g, 80mmol), CuI (4.6, 0.24mmol ), Potassium carbonate (33.2 g, 240 mmol) was added to 120 mL of DMF and stirred under reflux for about 7 days. After cooling to room temperature, the reaction solution was added to 1.2L of water to precipitate, and the resulting solid was filtered. The resultant was washed three times with water and two times with methanol, followed by drying. 9,9 '-(5- (4,6-diphenyl-1,3,5-triazin-) after removing impurities through column separation (100% of eluent hexane → 30% dichloromethane in hexane 70%) 11.1 g (yield 40%) of 2-yl) -1,3-phenylene) bis (1-phenyl-9H-carbazole) was obtained.

2. Compound 1-19

(1) Preparation of Intermediate 1-([1,1'-biphenyl] -4-yl) -9H-carbazole

1-bromo-9H-carbazole (24.6g, 100mmol) and [1,1'-biphenyl] -4-ylboronic acid (25.7g, 130mmol), tetrakis (triphenylphosphine) palladium (0) (5.8g, 5mmol), Potassium Carbonate (55.3 g, 400 mmol) was added to 300 mL of toluene, 150 mL of ethanol, and 150 mL of water, followed by stirring under reflux for about 24 hours. After cooling to room temperature, an organic solvent layer with a solid is separated, silica gel is added, and concentrated in a concentrator to prepare a solid column. After removing impurities through column separation (eluent: 10% dichloromethane + 90% hexane), 23.0g of 1-([1,1'-biphenyl] -4-yl) -9H-carbazole (yield 72 %) Was obtained.

(2) Preparation of Compound 1-19

9,9 '-(5- (4,6-diphenyl-1,3,5-triazin-2-yl) -1,3-phenylene) bis (1-phenyl-9H-carbazole) represented by compound 1-19 Was prepared using the following reactions.

2- (3,5-dibromophenyl) -4,6-diphenyl-1,3,5-triazine (16.5g, 35mmol) and 1-phenyl-9H-carbazole (23g, 72mmol), CuI (4.6g, 0.24mmol ), Potassium carbonate (33.2 g, 240 mmol) was added to 120 mL of DMF and stirred under reflux for about 7 days. After cooling to room temperature, the reaction solution was added to 1.2L of water to precipitate, and the resulting solid was filtered. The resultant was washed three times with water and two times with methanol, followed by drying. Impurities are removed through column separation (100% of hexane to 100% dichloromethane in 70% of hexane), followed by five or more recrystallizations to obtain 9,9 '-(5- (4,6-diphenyl-1, 9.0 g (yield 26%) of 3,5-triazin-2-yl) -1,3-phenylene) bis (1-([1,1'-biphenyl] -4-yl) -9H-carbazole)) Got it.

NMR data of the synthesized compounds are as follows.

compound 1 H NMR (CDCl ₃₎ MS

Compound 1-1

1H δ
1 H NMR (500 MHz, CDCll 3) δ 8.70 (4H, d), 8.24 (4H, d), 8.03 (2H, s), 7.64-7.61 (2H, m), 7.58-7.55 (4H, m), 7.51- 7.46 (3H, m), 7.44-7.34 (8H, m), 7.15 (4H, broad s), 6.77-6.69 (6H, m) 792.3 Compound 1-19

1H δ
1 H NMR (500 MHz, CDCll 3) δ 8.70 (4H, d), 8.24 (4H, d), 8.03 (2H, s), 7.64-7.61 (2H, m), 7.58-7.55 (4H, m), 7.51- 7.46 (3H, m), 7.44-7.34 (8H, m), 7.15 (4H, broad s), 6.77-6.69 (6H, m) 792.3

Hereinafter, an organic light emitting device was manufactured using GH-1, GH-2, the compound 1-1 and 1-19 of the present invention, and GD-1 as the second compound, respectively. .

[Production of Organic Light Emitting Device]

1. Comparative Example 1

After the ITO substrate was patterned so that the light emitting area was 2 mm × 2 mm in size, washing was performed with isopropyl alcohol and UV ozone, respectively. Thereafter, the ITO substrate was mounted on the substrate holder of the vacuum deposition apparatus and pressure was applied such that the vacuum degree was 1 × 10 ⁻⁷ torr. Thereafter, plasma treatment was performed for 3 minutes under N ₂ atmosphere.

First, a HAT-CN compound was vacuum deposited to form a 5 nm thick. This compound acts as a hole injection layer. An NPB material was formed on the first hole transport layer to a thickness of 50 nm. Subsequently, a HT-1 material was formed to a thickness of 10 nm as a second hole transport layer.

Thereafter, the GH-1 material was co-deposited at a thickness of 30 nm such that the GD-1 material was doped with a dopant to about 10% by mass to form a green light emitting layer.

An electron transport layer was formed on the light emitting layer with an ET-1 compound having a thickness of 35 nm. Then, LiF material was deposited to form an electron injection layer having a thickness of 1 nm. Thereafter, Al was deposited to a thickness of 100 nm to form a cathode to fabricate an organic EL device.

2. Comparative Example 2

The organic light emitting device was manufactured in the same manner as in Comparative Example 1, except that only the host material of the emission layer was changed to the GH-2 material.

3. Example 1

An organic light emitting device was manufactured in the same manner as in Comparative Example 1, except that only the host material of the emission layer was changed to Compound 1-1.

4. Example 2

An organic light emitting device was manufactured in the same manner as in Comparative Example 1, except that only the host material of the emission layer was changed to Compound 1-19.

The luminescence properties of the organic light emitting diodes prepared by Comparative Example 1, Comparative Example 2, Example 1, and Example 2 of the present invention were added to a constant current of 10 mA / cm ² , and the light emission characteristics of the organic light emitting diodes were measured by PR-670, a photoresearch company. .

The current density, driving voltage, current efficiency, and external quantum efficiency of the organic light emitting diodes of Examples 1 and 2 and Comparative Examples 1 and 2 were measured and shown in Table 2 below.

matter Drive current J (mA / cm ² ) Drive Voltage Current efficiency (cd / A) EQE (%) Comparative Example 1 GH-1 10 5.2 10.1 3.3 Comparative Example 2 GH-2 10 4.4 47.7 15.0 Example 1 1-1 10 4.4 51.2 16.7 Example 2 1-19 10 4.4 49.0 15.6

As shown in Table 2, Examples 1 and 2 show the current efficiency (cd / A), and the external quantum efficiency at the same driving voltage (V) which affects the organic light emitting element as compared with Comparative Examples 1 and 2. It can be seen that QE is improved in size. Therefore, it can be seen that the organic light emitting device including the phosphorescent green host material according to the present invention has improved lifespan and improved efficiency as compared with the related art.

The present invention is not necessarily limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

Claims (5)

A first electrode;
Second electrode; And
A light emitting layer disposed between the first electrode and the second electrode,
The light emitting layer includes an organic light emitting device comprising a first compound of delayed fluorescent and a green phosphorescent second compound selected from the compounds shown below.

delete delete delete The method of claim 1,
The second compound,
An organic light emitting device, characterized in that selected from the following compounds.

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