KR19990086810A - High melting point complex and organic light emitting device comprising the same - Google Patents

Abstract

The present invention relates to a high melting point complex and an organic light emitting device comprising the same.

Formula 1

The layer containing the high melting point complex compound represented by the general formula (1) is interposed between the anode and the cathode for injecting electrons to form an organic light emitting device, thereby lowering the driving voltage and functioning as an electron transporting layer for emitting light at the same time.

Description

High melting point complex and organic light emitting device comprising the same

The present invention relates to a high melting point complex and an organic light emitting device including the same.

BACKGROUND ART Electroluminescent devices using light emitting materials are widely used in office automation equipment, household appliances, automobiles and aircrafts as display devices such as indicators, indicators, and scales, and are also used in flat panel displays using thin film inorganic light emitters. Recently, a method of emitting light at low voltage using organic materials has also been proposed (C. W. Tang and S. A. Vanslyke: Appl. Phys. Lett. 51 913 (1987)).

In general, the organic light emitting device is stacked in the order of the anode layer, the hole transport layer, the electron transport layer having a light emitting property and the cathode layer. The hole transporting layer receives holes from the anode and delivers holes to the electron transporting layer. In the electron transporting layer, electrons injected from the cathode layer and holes transferred from the hole transporting layer are recombined and converted into low energy levels to emit light. It consists of

The organic light emitting device may be manufactured in various forms, and examples of the structure and a method of manufacturing the organic light emitting device are well known as follows. A thin layer of indium tin oxide, a transparent electrode, was deposited on a glass substrate as an anode, and a material for transferring holes was formed to a thickness of several tens of nanometers by thermal vacuum deposition. Representative hole transport materials include aryl amine molecules. In this case, in order to strengthen the interface between the anode and the hole transport material, a material such as phthalocyanine copper may be formed in a thin film using a thermal evaporation method to increase the life of the device. In addition, a plastic substrate may be used instead of a glass substrate, and a conductive polymer or a conductive material having a high work function may be used instead of indium tin oxide. Also, on the hole transport material, an aluminum complex of 8-hydroxy quinoline is widely used to form a thin film as a material for transporting electrons. The conditions to be equipped with such an electron transporting material should be well received electrons from the cathode and high light emission efficiency generated from the combination of holes and electrons. In order to increase the luminous efficiency, the electron transport material may be doped with a fluorescent material having high quantum efficiency, or an electron injection material may be used between the cathode and the electron transport layer to facilitate electron injection into the electron transport material. On the electron injecting layer or the electron transporting layer, a metal cathode is again deposited several hundred nanometers thick. In order to facilitate the injection of electrons, metals having low ionization levels or their alloys are used.

In general, the melting point of a material is known to be closely related to the glass transition temperature of the material. Since the thermal stability of the organic light emitting device is directly affected by the glass transition temperature of the material constituting the thin film, organic light emission It is important that the materials used in the device have a high melting point (K. Naito and A. Miura: J. Phys. Chem. 97, 6240 (1993)).

N, N'-diphenyl-N, N'-bis (3methylphenyl)-[1, 1'-biphenyl] -4, 4'-diamine (hereinafter abbreviated as TPD) Due to the low thermal stability of only 167 ℃ melting point there is a problem that the performance of the light emitting device is rapidly degraded at high temperatures. To compensate for this, various derivatives have been synthesized and applied to devices. Representative examples include 4,4 ', 4'-tris (3-methylphenylphenylamine) triphenylamine (4,4', 4'-tris (3-methylphenyl-

phenylamine), such as triphenylamine), has been developed with high molecular weight and melting point of 203 ° C (Appl. Phys. Lett. 65. 807, 1994). However, this material has a high melting point but only a glass transition temperature of 75 ° C. More recently, hole transport materials have been developed that have thermal stability with glass transition temperatures approaching 150 ° C. (Appl. Phys. Lett. 70. 1929, 1997). The thermal stability improvement of this hole transport material is close to the glass transition temperature of 175 ° C. of the aluminum complex of 8-hydroxyquinoline, which is a representative electron transport material that is conventionally thermally stable. As an anode material used in an organic light emitting device, an electrode using aluminum and lithium as an alloy having better electron injection ability than an electrode made by depositing a magnesium and silver in a ratio of 10: 1, or lithium flow An electrode formed by depositing aluminum on a thin film of LiF (LiF), or an electrode deposited by depositing aluminum on a lithium oxide (Li ₂ O) ultra thin film instead of the lithium fluoride may be used. These new electrodes have the effect of lowering the operating voltage and increasing the efficiency of the organic light emitting device to improve the performance of the entire device. The development of materials for such organic light emitting devices is geared toward the development of high performance multicolor displays and the reliability of the products.

One of the most problematic problems in the current material sector is the development of blue emitters with electron transport capabilities. To operate at high brightness, thermal stability must be high and the band gap must correspond to blue. In addition, to operate at low voltages, the material must have the ability to transport carriers (especially electrons). In addition, when the electron injection layer is not used separately, the conduction band of the blue light emitter should be low in order to facilitate electron injection, and the blue light emitter should have excellent adhesion with the cathode in order to extend the life of the device. Examples of the electron transport layer having a blue band gap include bis (2-methyl-8-quinolinolato) (para-phenylphenolato) aluminum (III) (bis (2-methyl-8) described in US Pat. No. 5,150,006. There is a complex compound called -quinolinolato) (para-phenylphenolato) aluminum (III)) (hereinafter abbreviated as B-Alq). The material has a blue band gap and doping a small amount of blue phosphor, such as perylene, results in longer device life and control of color purity. For low voltage driving of the device, an aluminum complex of 8-hydroxy quinoline having a green band gap must be inserted between the cathode and B-Alq to facilitate the injection of electrons. B-Alq also has a melting point of 230 ℃ can cause problems in heat resistance. In addition, the blue emitter composed of the organic material described in US Pat. No. 5,516,577 is used by inserting the 8-hydroxy quinoline aluminum complex between the cathode and the blue emitter for low voltage driving. There are two main reasons for inserting a material that facilitates injection of electrons between the blue emitter and the cathode. The first is because the energy level of the conduction band of the blue light emitter is generally too high compared to the work function of the cathode. For this reason, injection of electrons into the electron transport layer is not smooth, resulting in an increase in driving voltage. Therefore, it is desirable to insert a material having a relatively low energy in the conduction band between the cathode and the cathode. Second is stability at the interface with the cathode. In general, aluminum complexes of 8-hydroxyquinoline having a high melting point are known to form a relatively stable interface with the cathode. However, if the aluminum complex compound of 8-hydroxy quinoline also contains moisture, crystallization occurs, which also shortens the life of the device.

The advantages of the multilayer structure composed of the above-mentioned hole transport layer, electron transport layer, electron injection layer, etc. are also effective for fabricating an organic light emitting device using a polymer. PPV [poly (phenylenevinylene)] with green band gap is (2- (4-biphenyl) -5- (4-tert-butylphenyl) -1,3,4- oxadiazole)) (abbreviated as PBD) as a thin film between the cathode and PPV increases the device efficiency (Appl. Phys. Lett. 61, 2793, 1992). This phenomenon is because the PBD layer serving as the electron injection and transport has a larger band gap than the light emitting PPV, thus limiting the excitons formed by the pair of holes and electrons to the PPV layer, thereby preventing the loss of the excitons by the electrodes. Will increase. As another example, CN-PPV may be used instead of PBD. In the latter case, since the band gap of the CN-PPV is smaller than the PPV, light emission occurs in the CN-PPV rather than the PPV (Nature 365. 628, 1993). However, in the case of CN-PPV, the energy level of the conduction band is lower than that of PPV, which facilitates the injection of electrons, thereby driving the device at low voltage. For the practical use of the device, the material of each layer in the multilayer structure should be selected to improve the efficiency of the organic light emitting device and to extend the life of the device.

Known electron injecting, transporting and luminescent materials include 8-hydroxy quinoline aluminum complexes with green band gaps, 10-hydroxybenzo [h] quinoline beryllium complexes (US Pat. No. 5,529,853), 2- (2'-hydroxy-5'-methylphenyl-benzo-triazole beryllium complex (US Pat. No. 5,486,406), etc. is known as a representative material, and the material corresponding to the blue band gap is B-Alq (US Pat. No. 5,150,006). ), 4, 4'-bis (2, 2'-diphenylvinyl) biphenyl (abbreviated as DPVBi) (US Pat. No. 5,516,577), 2- (O-hydroxyphenyl) benzoxazole zinc complex and 2- (O-hydroxyphenyl) -benzothiazole zinc complex (European Patent 0 652 273 A1) etc. are known, etc. The materials used in the prior art are structurally different from the complex compounds of the present invention. The electron injection layer is not smooth because electron injection from the cathode such as B-Alq or DPVBi is not smooth. In general, in order to facilitate the injection of electrons from the cathode, the conduction band energy of the material forming the electron injection layer must be low, and the green band gap is the most widely known and used aluminum complex of 8-hydroxyquinoline. to be.

The problem caused in this case is that when the exciton is formed in a material having a blue band gap, green light emission may be observed when the thickness of the material is not thick enough or its formation is close to the electron injection layer. That is, in the fabrication of devices for blue light emission, green light emission may occur together, which may cause problems in color purity. Therefore, it is important that the electron injection layer has a wide band gap and low conduction band energy.

Another important factor in practical device fabrication is the formation of stable interfaces with the electrodes. When the material having the structure of the organic or complex forms an interface with the metallic cathode, if the stability of the interface is reduced, the lifetime and the lifetime of the device are reduced. This problem is often observed even when the melting point of the material interfacing with the metal is low, which creates a discontinuous interface when the material is crystallized by heat generated during storage of the device at high temperatures or during operation of the device, thus preventing electron injection. Thereby forming a trap that increases the driving voltage or decreases the luminous efficiency. Therefore, it is very important to select a material that has a high melting point that can suppress crystallization even at high temperatures and forms a stable interface with the metal. Materials known to play this role so far are aluminum complexes of 8-hydroxyquinoline, although they have a green band gap.

The present invention uses a complex different from the chemical structure of a conventionally developed electron transport material as described above as an electron transport layer, and has a structure having a high melting point and various band gaps such as blue and green depending on the chemical structure. Its purpose is to provide the application of materials to organic light emitting devices.

1 is a view showing a photoluminescence spectrum obtained from an organic light emitting device prepared by doping the high melting point complex of the present invention.

According to the present invention, a compound having the general structural formula of the following general formula (1) is provided.

<Formula 1>

Wherein at least one of Y ₁ to Y ₈ represents a nitrogen atom and the other represents CR _i , ie a carbon atom containing a substituent, wherein the substituent CR _i represents the corresponding Y _i (i is 1 to 8) R _i may again represent a hydrogen atom, an alkoxy group, a carbonyl group, an aromatic group, a lower hydrocarbon group having 1 to 5 carbon atoms, a nitrile group, and may form a ring of elements between adjacent substituents. Represents an S or O atom, wherein M is a divalent or trivalent metal, for example Be ⁺² , Zn ⁺² , Mg ⁺² , Ca ⁺² , Al ⁺³ , where n represents 2 or 3 .

In addition, according to the present invention, an organic light emitting device comprising an anode layer, a hole transporting layer, a light emitting layer, an electron injection layer and a cathode layer in an order, wherein the electron injection layer or the light emitting layer comprises the general formula (1) Is provided.

Hereinafter, the present invention will be described in more detail.

Specific examples of the complex compound represented by the general formula 1 used in the present invention are as follows.

<Formula 1>

<Formula 2>

<Formula 3>

<Formula 4>

<Formula 5>

<Formula 6>

<Formula 7>

<Formula 8>

<Formula 9>

<Formula 10>

<Formula 11>

<Formula 12>

In the present invention, as illustrated above, the aromatic group of the molecule constituting the ligand contains a nitrogen atom in its resonance structure. As a result, the compounds constituting the organic light emitting device of the present invention showed a high melting point. In general, in order to increase the melting point, a molecular weight or a polar group should be introduced into the molecule. Commonly used approaches to increase the molecular weight of complexes include the use of ligands in which two or more metals are included in one complex or several aromatic groups are fused.

The structure of the complex compound used in the present invention has a new structure that is not used in the prior art, and their melting point shows a high melting point of 300 ° C. or higher depending on the structure, and the compound represented by Formula 1 has a melting point of 425 ° C. To reach. The complexes exemplified above form a thin film of good quality that does not crystallize for a long time when deposited in a thin film form on a glass substrate.

According to the photoluminescence spectrum, the complexes exemplified above exhibit emission bands ranging from blue to yellow depending on the structure of the ligand and the type of metal. This property indicates that the complex compound can be used to fabricate a device ranging from blue to red by the selection of a suitable device structure and doping of a highly efficient fluorescent dye to the band gap of the compound. As known in the prior art, doping of a suitable concentration of fluorescent dye has the effect of improving the efficiency of the organic light emitting device and at the same time extending the life (US Pat. No. 5,150,006). To achieve this effect, a fluorescent dye similar to the band gap of the electron transport layer containing the fluorescent dye should be used.

The complex compound of the present invention may be used as an electron injection material in addition to the property of forming a light emitting layer by doping a fluorescent dye as described above. In order to be used as a material forming the electron injection layer, electron injection from the cathode must be smoothly formed, and a strong interface must be formed with the metallic material forming the cathode. As shown in the following examples, some of the complexes used in the present invention lower the drive voltage of the device and at the same time constitute a device that is stable at high temperatures.

<Synthesis Example 1 (Formula 1)>

Formula 13 Formula 1

After dissolving 5 ml of water and 40 mg of beryllium chloride (BeCl ₂ ) in a 100 ml flask, 0.23 g of a ligand having the structure of Formula 13 and 40 mg of sodium hydroxide (NaOH) were mixed with 60 ml of a mixture solution of ethyl alcohol and water (5: 1). Dissolve in and add to the above aqueous beryllium chloride solution. The mixed solution was filtered after reaction at 60 ° C. for 3 hours to obtain 0.22 g of a pale yellow solid product (95% yield).

The melting point of the thermal analysis was 426 ℃ and the chemical composition by elemental analysis is as follows.

Theoretical value; C: 62.1%, H: 3.0%, N: 12.0%, Be: 1.9%

Experimental value; C: 62.1%, H: 3.0%, N: 11.0%, Be: 1.6%

<Synthesis Example 2 (Formula 2)>

Formula 13 Formula 2

In a 100 ml flask, 0.23 g of a ligand having the structure of Formula 13 was dissolved in 50 ml of ethanol, and then 110 mg of zinc acetate [Zn (OAc) ₂ H ₂ O] was added. The mixed solution was filtered after reaction at 60 ° C. for 3 hours to obtain 0.21 g of a pale yellow solid product (80% yield).

As a result of the thermal analysis, the melting point is 384 ° C and the chemical composition by elemental analysis is as follows.

Theoretical value; C: 55.4%, H: 2.7%, N: 10.7%, Zn: 12.6%

Experimental value; C: 55.4%, H: 2.5%, N: 10.5%, Zn: 12.1%

<Synthesis Example 3 (Formula 4)>

Formula 14 Formula 4

After dissolving 5 ml of water and 40 mg of beryllium chloride (BeCl ₂ ) in a 100 ml flask, 0.21 g of a ligand having the structure of Formula 14 and 40 mg of sodium hydroxide (NaOH) were mixed with 60 ml of ethyl alcohol and water (5: 1). Dissolve in and add to the above aqueous beryllium chloride solution. The mixed solution was filtered after reaction at 60 ° C. for 3 hours to obtain 0.2 g of a white solid product (98% yield).

As a result of thermal analysis, the melting point is 331 ° C. and the chemical composition by elemental analysis is as follows.

Theoretical value; C: 66.8%, H: 3.3%, N: 12.9%, Be: 2.1%

Experimental value; C: 66.7%, H: 3.1%, N: 12.7%, Be: 2.0%

<Synthesis Example 4 (Formula 6)>

Formula 15 Formula 6

In a 50 ml flask, 0.24 g of a ligand having the structure of Formula 15 is dissolved in 20 ml of ethanol, and then 0.125 g of zinc acetate [Zn (OAc) _2. 2H ₂ O] is added. The mixed solution was filtered after reaction at 60 ° C. for 6 hours to obtain 0.21 g of a pale yellow solid product (79% yield).

The thermal analysis showed that the melting point was 391 ° C.

Example 1

A glass substrate coated with a thin film of indium tin oxide (General Vacuum) is cleaned with methyl alcohol, isopropyl alcohol, and acetone for 5 minutes using an ultrasonic cleaner, and then treated with a strong oxidant. The substrate is vacuum-deposited to a thickness of 60 nm at a rate of 0.1 ~ 0.3 nm / sec NPD, a hole transporting material after the transfer to the vacuum deposition equipment. Alq 3 serving as a light emitting layer is deposited on the hole transport layer at a thickness of 30 nm at a rate of 0.1 to 0.3 nm / sec. Then, an electron injection layer having the structure of Formula 1 is deposited on the Alq3 layer at a thickness of 30 nm at a rate of 0.1 to 0.3 nm / sec. After placing a mask for forming an electrode on the electron injection layer, a lithium fluoride having a thickness of 0.5 nm and aluminum having a thickness of 200 nm are sequentially deposited to form a cathode.

When the forward voltage was applied to the organic light emitting device, green light emission was observed at a luminance of 500 cd / m ² at 4.1 V.

Comparative Example 1

A light emitting device was manufactured in the same manner as in Example 1. However, instead of the electron injection layer used in Example 1, the layer thickness of Alq3 was 60 nm. As a result, the total thickness of the organic material present between the two electrodes is equal to 120 nm, and Alq3 serves as a light emitting layer and an electron injection layer simultaneously.

When the forward voltage was applied to the organic light emitting device, green light emission was observed at a luminance of 500 cd / m ² at 5.7 V.

Example 2

In order to confirm the role of the electron transport layer in addition to the electron injection layer of the compound having the structure of formula (1), the material having the structure of formula (1) was doped with rubrene (rubrene) to manufacture the following device.

A glass substrate coated with a thin film of indium tin oxide (General Vacuum) is cleaned with methyl alcohol, isopropyl alcohol, and acetone for 5 minutes using an ultrasonic cleaner, and then treated with a strong oxidant. The substrate is vacuum-deposited to a thickness of 60 nm at a rate of 0.1 ~ 0.3 nm / sec NPD, a hole transporting material after the transfer to the vacuum deposition equipment. The compound having Formula 1 is deposited on the hole transport layer at a thickness of 60 nm at a rate of 1 nm / sec. At this time, the fluorescent dye, rubrene is deposited simultaneously at a concentration of 5%. After placing a mask for forming an electrode on the electron injection layer, a lithium fluoride having a thickness of 0.5 nm and aluminum having a thickness of 200 nm are sequentially deposited to form a cathode.

When the forward voltage was applied to the organic light emitting device, yellow light emission due to rubrene was observed, and the electroluminescence spectrum at this time was as shown in FIG. 1.

The layer containing the high melting point complex compound of the present invention is interposed between the cathode and the light emitting layer to lower the driving voltage and simultaneously function as an electron transport layer for emitting light.

Claims (7)

High melting point complex represented by the following general formula (1): Formula 1 From here, At least one of Y ₁ to Y ₈ represents a nitrogen atom and the rest are carbon atoms containing a substituent, X represents an S or O atom, M is a divalent or trivalent metal, n is 2 or 3. The method of claim 1, A high melting point complex compound wherein the substituent is a hydrogen atom, an alkoxy group, a carbonyl group, an aromatic group, a lower hydrocarbon group having 1 to 5 carbon atoms or a nitrile group. The method of claim 2, A high melting point complex compound wherein the substituent is a substituent capable of forming an elementary ring between adjacent substituents. a) an anode; b) a cathode for injecting electrons; And c) a layer interposed between the positive electrode and the negative electrode and comprising a high melting point complex compound represented by the following general formula (1) Formula 1 An organic light emitting device comprising a. The method of claim 4, wherein An organic light emitting device comprising a glass or plastic substrate under the anode. The method of claim 4, wherein The organic light emitting device of the anode comprises a conductive polymer or a conductive metal oxide. The method of claim 4, wherein An organic light emitting device in which a hole transport layer is interposed between the anode and a layer containing a high melting point complex compound represented by Formula 1.