KR100799223B1 - Hole injecting material and organic electroluminescent device comprising same - Google Patents

Abstract

The present invention relates to a compound of formula 1 and an organic electroluminescent device comprising the same as a hole injection layer material, the compound of formula 1 according to the invention is included in the organic electroluminescent device as a hole injection layer electrical stability and luminous efficiency It is possible to improve red light emission and to realize high luminance and high color purity.

Where

R ₁ is hydrogen, halogen, or substituted or unsubstituted C _1-6 alkyl or C _6-18 aryl.

Description

Hole injecting layer material and organic electroluminescent device comprising same {HOLE INJECTING MATERIAL AND ORGANIC ELECTROLUMINESCENT DEVICE COMPRISING SAME}

1 is a schematic structural cross-sectional view of an organic electroluminescent device according to the present invention,

Figure 2 is a schematic structural cross-sectional view of the organic electroluminescent device manufactured in Examples 1 to 5 of the present invention,

3 is a graph showing the correlation between the driving voltage and the brightness of the organic electroluminescent devices manufactured in Examples 1 to 5 and Comparative Examples of the present invention,

4 is a graph showing a correlation between driving voltage and luminous efficiency of organic electroluminescent devices manufactured in Examples 1 to 5 and Comparative Examples of the present invention.

5 is a graph showing a luminance change over time of the organic electroluminescent devices manufactured in Examples 1 to 5 and Comparative Examples of the present invention.

The present invention relates to a hole injection layer material having a low driving voltage characteristics and an organic electroluminescent device comprising the same.

The flat panel display plays a very important role in supporting a highly visual information society, centered on the internet, which is rapidly growing in recent years. In particular, organic electroluminescent devices (organic EL devices) capable of low voltage driving with self-luminous type have superior viewing angles and contrast ratios compared to liquid crystal displays (LCDs), which are mainstream flat panel displays, and require no backlight. Light weight and thinness are possible, and it has an advantage in terms of power consumption. In addition, the fast response speed and wide color reproduction range have attracted attention as a next generation display device.

In general, an organic EL device is formed on a glass substrate in order of an anode made of a transparent electrode, an organic thin film including a light emitting region, and a metal electrode. In this case, the organic thin film may include a hole injection layer (HIL), a hole transport layer (HTL), an electron transport layer (ETL), or an electron injection layer (electron injection) in addition to the emitting layer (EML). layer, EIL), and may further include an electron blocking layer (EBL) or a hole blocking layer (HBL) due to light emission characteristics of the light emitting layer.

When an electric field is applied to the organic EL device having such a structure, holes are injected from the anode and electrons are injected from the cathode, and the injected holes and electrons are recombined in the emission layer through the hole transport layer and the electron transport layer, respectively, and emit excitons. To form. The formed light exciton emits light as it transitions to ground states, in which a light emitting layer (guest) is doped into the light emitting layer (host) to increase the efficiency and stability of the light emitting state.

In order to utilize the organic electroluminescent device in various display media, the life of the device is important, and various studies are currently being conducted to increase the life of the organic electroluminescent device. In particular, various studies have been conducted on organic materials inserted into a hole injection layer or a buffer layer inserted between the anode and the hole transport layer for excellent life characteristics of the organic light emitting device (SA Van Slyke et al. , Appl. Phys. Lett. , 69, 2160, 1996) .As a result, there is a demand for a hole injection layer material having high uniformity and low crystallinity when forming a thin film after deposition while providing high hole injection characteristics from an anode to an organic layer. (Youngkyoo Kim et al. , Appl. Phys. Lett. , 82, 2200, 2003).

In addition, by delaying the diffusion of the metal oxide into the organic layer from the anode electrode (ITO), which is one of the causes of shortening the life of the organic electroluminescent device (CO Poon et al. , Appl. Phys. Lett. , 82, 155, 2003), There is a need for the development of a hole injection layer material having stable characteristics, that is, a high glass transition temperature, for Joule heating generated during device driving (Shizuo Tokito, Appl. Phys. Lett. , 70 ( 15 ), 1929). , 1997).

However, the luminous efficiency and device lifetime characteristics in terms of hole injection ability of the hole injection layer material studied so far have problems, and thus there are many difficulties in developing a long-life device.

Accordingly, it is an object of the present invention to provide a hole injection layer material having a low driving voltage characteristic and an organic electroluminescent device comprising the same.

In accordance with the above object, the present invention provides a compound of the formula:

Formula 1

Where

R ₁ is hydrogen, halogen, or substituted or unsubstituted C _1-6 alkyl or C _6-18 aryl.

Hereinafter, the present invention will be described in detail.

Compound of Formula 1 of the present invention is a compound of Formula 1 wherein R ₁ is hydrogen; halogen; Alkyl selected from -CH ₃ , -CH ₂ CH ₃ , -CH (CH ₃ ) ₂ , -C (CH ₃ ) ₃ and -CH ₂ (CH ₂ ) ₂ CH ₃ ; Or aryl selected from phenyl, 4-alkylated phenyl, 1-naphthyl, 2-naphthyl and anthracenyl.

Preferred examples of the compound of formula 1 of the present invention are shown in the following formulas 1a to 1e.

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Compounds of the present invention, as shown in Scheme 1 below, are described in Krzysztof Danel, Chem. Mater. , 14, 3860-3865, 2002].

That is, after stirring the N, N-phenyl-1,4-phenylene diamine compound and the bromoaromatic compound under sodium t -butoxide and anhydrous xylene catalyst, tri- t -butylphosphine (P ( ^t Bu) ₃ ) and palladium acetate (Pd (OAc) ₂ ) were added to reflux for 2 to 24 hours in the range of 25 ° C. to 150 ° C., and the obtained compound was again reacted with 1,4-dibromodiphenyl compound and sodium t -butoxide. After stirring under a side (NaO ^t Bu, 20 mol) and anhydrous xylene catalyst, tri- t -butylphosphine (P ( ^t Bu) ₃ ) and palladium acetate (Pd (OAc) ₂ ) were added to 25 ° C. to 150 ° C. The compound of formula 1 of the present invention may be prepared by refluxing for 2 to 24 hours in a range.

In addition, the present invention provides an organic electroluminescent device comprising the compound as a hole injection layer material.

In general, an organic electroluminescent device has a single layer type including a light emitting layer between an anode, a cathode, and two electrodes as one structural unit, or a multilayer structure in which an anode, a light emitting layer, and a cathode are sequentially stacked together with a charge transport layer.

At this time, the multilayered device in which the light emitting layer and the charge transporting layer are combined is superior to the single-layered device consisting of only one light emitting layer, which is a combination of the light emitting material and the charge transporting material. This is because the charge transport layer binds the holes or electrons injected from the electrode to the light emitting layer region so that the number density of the injected holes and electrons is balanced. In particular, in the case of a phosphorescent light emitting device, since the emission duration of the phosphorescent material is long, in order to increase efficiency, it is necessary to trap holes in the light emitting layer so that the holes remain in the light emitting layer for a long time to show excellent phosphorescence properties. More preferred.

A schematic cross-sectional view of an organic electroluminescent device according to the present invention is shown in FIG. 1. As shown in FIG. 1, the basic organic electroluminescent device of the present invention has a structure in which a transparent electrode (anode), a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and a metal electrode (cathode) are sequentially stacked. In order to improve luminous efficiency, a hole blocking layer may be included between the light emitting layer and the electron transporting layer, or a hole blocking layer and an electron blocking layer may be further included between the light emitting layer and the electron transporting layer and between the light emitting layer and the hole transporting layer, respectively. .

In the organic electroluminescent device according to the present invention, the transparent electrode (anode) and the metal electrode (cathode) are conventional electrode materials, for example, the transparent electrode is indium tin oxide (ITO) or SnO ₂ , and the metal electrode It may be formed of a metal such as Li, Mg, Ca, Ag, Al and In or an alloy thereof, and in the case of a metal electrode may have a single layer or a multilayer structure of two or more layers.

The hole injection layer may include one selected from the compounds of Formula 1 of the present invention, and may be formed to have a thickness of 10 to 60 nm.

The hole transport layer may be a conventional hole transport material, for example, 4,4-bis [N- (1-naphthyl) -N-phenyl-amine] biphenyl (α-NPD) of Formula 2 and N of Formula 3 , N-diphenyl-N, N-bis (3-methylphenyl) -1,1-biphenyl-4,4-diamine (TPD) and the like may be included alone or in combination of two or more, and as separate layers It is also possible to laminate two or more layers. The hole transport layer can be formed to a thickness in the range of 5 to 30 nm.

The light emitting layer and the electron transporting layer may include a conventional green light emitting material, for example, tris (8-quinolinolato) aluminum (Alq ₃ ) of Formula 4 below. The light emitting layer and the electron transporting layer may each be formed to a thickness in the range of 30 to 40 nm.

In addition, as the electron injection layer material inserted between the cathode and the electron transport layer, LiF may be used, and may be formed to a thickness in the range of 0.5 to 1.5 nm.

The anode, cathode, light emitting layer, injection layer, and transport layer may be formed by a conventional deposition method.

The compound of Formula 1 of the present invention exhibits high hole injection ability with low driving voltage characteristics, and thus is included in the organic electroluminescent device to exhibit excellent chemical and electrical stability and luminous efficiency. It can be useful.

Hereinafter, the present invention will be described in detail by way of examples.

However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited to the following examples.

Preparation Example 1 Preparation of Compound of Formula 1a

N, N-phenyl-1,4-phenylene diamine 26 g (0.1 mol), 7.02 g (0.045 mol) bromobenzene, 4.8 g (0.05 mol) sodium t- butoxide and anhydrous styrene 200 After putting mL into the flask and stirring for 10 minutes, 0.1 mL (0.001 mol) of tri- t- butylphosphine and 0.22 g (0.001 mol) of palladium acetate were added thereto, and the mixture was refluxed at 70 ° C. for 5 hours. This was extracted with methylene chloride (CH ₂ Cl ₂ , MC) and recrystallized with MC / MeOH mixture, and then 16.8 g (0.05 mol) of the obtained reaction product, 31.2 g (0.1 mol) of 1,4-dibromodiphenyl, sodium t -butoxide, 9.6 g (0.1 mol) and anhydrous Xi into the alkylene 200 ㎖ to the flask and stirred for 10 minutes. 0.1 ml (0.001 mol) of tri-t-butylphosphine and 0.22 g (0.001 mol) of palladium acetate were added thereto, followed by refluxing at 70 ° C. for 5 hours, followed by extraction with methylene chloride and recrystallization with MC / MeOH mixture. To prepare a compound of formula 1a according to the present invention.

¹ H-NMR (300 MHz, CDCl ₃ ) 7.25 (d, 4H, J = 4.5 Hz, 4H), 7.18 (m, 12H), 6.54 (m, 22H), 6.18 (m, 8H)

¹³ C-NMR (300 MHz, CDCl ₃ ), 142.5, 141.6, 140.4, 136.8, 136.2, 131.0, 129.8, 129.1, 128.3, 122.9, 122.4, 122.1, 121.8, 121.7, 121.2, 120.8

FAB-MS: calculated MW 822.37, m / e = 822.20

Preparation Example 2 Preparation of Compound of Formula 1b

A compound of Chemical Formula 1b of the present invention was prepared in the same manner as in Preparation Example 1, except that 7.7 g (0.045 mol) of 4-Bromotoluene was used instead of 7.02 g (0.045 mol) of bromobenzene. It was.

¹ H-NMR (300 MHz, CDCl ₃ ) 7.23 (d, 4H, J = 4.2 Hz, 4H), 7.05 (m, 10H), 6.54 (m, 12H), 6.2 (m, 18H). 2.43 (s, 6H)

¹³ C-NMR (300 MHz, CDCl ₃ ), 141.9, 141.3, 138.2, 136.4, 136.0, 131.5, 131.8, 131,2, 129.4, 128.0, 128.7, 124.0, 123.08, 122.90, 122,75, 122.62, 122.33, 122.51 , 122.32, 121.08, 21.

FAB-MS: calculated MW 850.40, m / e = 850.67

Preparation Example 3 Preparation of Compound of Formula 1c

A compound of Chemical Formula 1c of the present invention was prepared in the same manner as in Preparation Example 1, except that 9.6 g (0.045 mol) of 1-bromo-4 -t- butylbenzene was used instead of 7.02 g (0.045 mol) of bromobenzene. Prepared.

¹ H-NMR (300 MHz, CDCl ₃ ) 7.42 (d, J = 5.8 Hz, 4H), 7.26 (m, 12H), 6.40 (m, 12H), 6.02 (m, 16H). 1.45 (s, 18 H)

¹³ C-NMR (300 MHz, CDCl ₃ ), 142.42, 141.35, 137.3, 136.4, 136.08, 131.45, 131.31, 131,15, 129.40, 129.02, 128.34, 124.07, 123.80, 123.22, 122,65, 122.52, 122.13, 122.01 , 121.82, 121.08, 35.02, 34.87.

FAB-MS: calculated MW 934.50, m / e = 934.23

Preparation Example 4 Preparation of Compound of Formula 1d

A compound of Chemical Formula 1d of the present invention was prepared by the same method as Preparation Example 1, except that 10.5 g (0.045 mol) of 1-bromo-4-phenylbenzene was used instead of 7.02 g (0.045 mol) of bromobenzene. .

¹ H-NMR (300 MHz, CDCl ₃ ) 7.51 (d, J = 4.6 Hz, 4H), 7.33 (m, 12H), 6.72 (m, 18H), 6.24 (m, 20H).

¹³ C-NMR (300 MHz, CDCl ₃ ), 142.27, 141.15, 140.42, 137.3, 136.82, 136.50, 136.12, 131.75, 131.41, 131,15, 130.21, 129.54, 129.29, 128.74, 124.17, 123.88, 123.21, 122,75 , 122.57, 122.31, 122.01, 121.72, 121.18, 120.57

FAB-MS: calculated MW 974.43, m / e = 974.03

Preparation Example 5 Preparation of Compound of Formula 1e

A compound of Chemical Formula 1e was prepared in the same manner as in Preparation Example 1, except that 11.1 g (0.045 mol) of parabromophenyltoluene was used instead of 7.02 g (0.045 mol) of bromobenzene.

¹ H-NMR (300 MHz, CDCl ₃ ) 7.42 (d, J = 5.8 Hz, 4H), 7.11 (m, 18H), 6.67 (m, 18H), 6.00 (m, 14H). 2.45 (s, 6H)

¹³ C-NMR (300 MHz, CDCl ₃ ), 142.62, 142.05, 141.55, 137.37, 136.24, 136.08, 135.04, 131.65, 131.20, 131,32, 130.05, 129.44, 129.10, 128.14, 127.82, 124.17, 123.84, 123.84, 123.84 , 61, 122.42, 122.11, 122.03, 121.72, 121.28, 21.02

FAB-MS: calculated MW 1003.28, m / e = 1002.23

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Examples 1 to 5: Preparation of an organic electroluminescent device using the compound of formula 1a to 1e

Water-based detergent, ultrapure water, isopropyl alcohol and methanol were used sequentially to A glass substrate (Asahi Glass Co., Sheet Resistance 8 Ω / cm ² ) coated with indium tin oxide (ITO) was ultrasonically cleaned to prepare a transparent electrode (anode). Compounds of formulas 1a to 1e were vacuum-deposited on the transparent electrodes, respectively, to form a hole injection layer having a thickness of 60 nm, and then a 4,4-bis [N- (1-naphthyl) -N-phenyl-amine] ratio thereon. Phenyl (α-NPD) was deposited to form a 20 nm hole transport layer, followed by tris (8-quinolinolato) aluminum (Alq ₃ ) to form a 60 nm light emitting / electron transport layer, and LiF It was deposited to form an electron injection layer of 1 nm. By depositing Al on the electron injection layer to form a cathode of 150 nm, the organic electroluminescent devices of Examples 1 to 5 according to the present invention were prepared, respectively.

As shown in FIG. 2, the organic electroluminescent devices of Examples 1 to 5 manufactured are [ITO transparent electrode (150 nm) / hole injection layer (60 nm) / α-NPD hole of one of the compounds of Formulas 1a to 1e. Transport layer (20 nm) / Alq ₃ light emission / electron transport layer (60 nm) / LiF electron injection layer (1 nm) / Al electrode (100 nm)] are laminated in order from the bottom.

Comparative Example: Fabrication of Organic Electroluminescent Device Using α-NPD as Hole Injection Layer

Same method as in Examples 1 to 5, except that 4,4-bis [N- (1-naphthyl) -N-phenyl-amine] biphenyl (α-NPD) was used as the hole injection layer material. An organic electroluminescent device was prepared.

Similarly, as shown in FIG. 2, the organic electroluminescent device of Comparative Example prepared was [ITO transparent electrode (150 nm) / α-NPD hole injection layer (40 nm) / α-NPD hole transport layer (40 nm) / Alq ₃ light emission. / Electron transporting layer (60 nm) / LiF electron injection layer (1 nm) / Al electrode (100 nm)] has a structure laminated in order from the bottom.

Electroluminescence Characterization

By applying a forward bias DC voltage to the organic electroluminescent devices of Examples 1 to 5 and Comparative Examples thus prepared, electroluminescence (EL) characteristics were measured by a PR-650 manufactured by photo research, and the measurement results were driven. The relationship between voltage and luminance (FIGS. 3 and 1) and driving voltage and luminous efficiency (FIGS. 4 and 1) is shown.

As a result, as shown in Figure 3, 4 and Table 1, all of the organic electroluminescent device of Examples 1 to 5 according to the present invention showed better voltage characteristics, that is, lower driving voltage characteristics than the device of the comparative example, The luminous efficiency was about 2 to 3 times higher.

Life characteristic evaluation

For the devices of Examples 1 to 5 and Comparative Examples, in order to protect the organic electroluminescent device by applying an ultraviolet curing agent to the side of the organic substrate, the glass cover with a dehydrating agent (BaO) film is attached to the device through ultraviolet curing The encapsulation process was performed, and it was driven by DC current to measure the luminance decrease with time from 1000 cd / m 2.

As a result, as shown in Table 2 and Figure 5, all of the organic electroluminescent device of Examples 1 to 5 exhibited excellent life characteristics compared to the organic electroluminescent device of the comparative example.

As described above, the hole injection layer material according to the present invention exhibits high hole injection capability with low driving voltage characteristics, and thus is included in the organic electroluminescent device to exhibit excellent chemical and electrical stability and luminous efficiency, and particularly in terms of device life. Since it shows an excellent effect, it can be usefully used as a hole injection layer material of the organic electroluminescent device.

Claims (4)

An organic electroluminescent device comprising a compound of formula 1 as a hole injection layer material: Formula 1

Where R ₁ is hydrogen, halogen, or substituted or unsubstituted C _1-6 alkyl or C _6-18 aryl. The method of claim 1, In formula 1, R ₁ is hydrogen, halogen, —CH ₃ , —CH ₂ CH ₃ , —CH (CH ₃ ) ₂ , —C (CH ₃ ) ₃ , —CH ₂ (CH ₂ ) ₂ CH ₃ , phenyl, An organic electroluminescent device, characterized in that a group selected from 4-alkylated phenyl, 1-naphthyl, 2-naphthyl and anthracenyl. The method of claim 1, An organic electroluminescent device according to claim 1, wherein the compound of Formula 1 is selected from the compounds of Formulas 1a to 1e. Formula 1a

Formula 1b

Formula 1c

Formula 1d

Formula 1e

The method of claim 1, An organic electroluminescent device comprising a multilayer structure in which transparent electrodes (anodes), hole injection layers, hole transport layers, light emitting layers, electron transport layers, electron injection layers and metal electrodes (cathodes) are sequentially stacked.

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