KR100292830B1 - Organic light-emitting device having improved luminous efficiency - Google Patents

Abstract

The present invention provides an organic electroluminescent device including an organic layer including an organic light emitting layer and an electron injection electrode, wherein the organic layer further includes a hole transport layer and / or an electron transport layer, and the hole transport layer is 1.10 eV or more and less than 1.90 eV. An organic electroluminescent device comprising a polyimide formed from a carboxylic dianhydride compound having an electron affinity and / or the electron transport layer comprising a polyimide formed from a diamine compound having an ionization potential of 6.80 eV to 7.70 eV The organic electroluminescent device of the present invention can be driven at a low voltage, and the luminous efficiency is greatly improved.

Description

Organic electroluminescent device with improved luminous efficiency {ORGANIC LIGHT-EMITTING DEVICE HAVING IMPROVED LUMINOUS EFFICIENCY}

The present invention relates to an organic electroluminescent device having greatly improved uniformity, internal density, and luminous efficiency of a thin film.

The general structure of the organic light emitting device is composed of a transparent electrode, an organic layer including an organic light emitting layer and an electrode. In the above structure, the electrode may be divided into a positive electrode and a negative electrode in the case of a direct current drive, and is independent of the pole in the case of an alternating current. In the case of DC driving, the organic layer may further include a hole transport layer between the anode and the organic light emitting layer and / or an electron transport layer between the organic light emitting layer and the cathode in order to increase efficiency. Also, depending on the functions of the organic thin film layer used in the hole transport layer, the light emitting layer, and the electron transport layer, the single layer (when the organic thin film layer has hole and electron transport characteristics and has light emission characteristics), and the second layer (the thin film layer on the anode side has hole transport characteristics). The organic light emitting layer of the cathode may have a light emitting and electron transporting property, and an organic material thin film having three layers (each organic thin film layer comprises a hole transporting layer, a light emitting layer, and an electron transporting layer). In addition, a layer having one function may have a multi-layered structure, or materials having different functions may be present in one layer. The positive electrode is mainly manufactured by coating ITO (indium tinoxide) on a glass substrate. As the negative electrode, magnesium, aluminum, indium, silver-magnesium alloy, or the like can be used. The device having such a structure has been conventionally manufactured by a wet process such as vacuum deposition or spin coating of a material forming each layer.

The conventionally developed method for developing an organic light emitting device having high efficiency is a p-n junction double layer structure using a p-type organic semiconductor and an n-type organic semiconductor, that is, a hole transport layer / light emitting electron transport layer structure. In such a structure, by controlling the electronic structures of the p-type organic semiconductor and the n-type organic semiconductor, electrons and holes injected from the electrode are confined to the pn junction to minimize leakage current, thereby minimizing leakage current. The light emitting device can be developed. In particular, in order to increase the uniformity and stability of the thin film of the p-type organic semiconductor, the hole transport material guest is dispersed in the polyimide host to effectively impart hole transport characteristics.

The polyimide may be formed from a polyimide precursor obtained by polymerizing a soluble polyetherimide or carboxylic dianhydride compound with a diamine compound. Generally, pyromellitic dianhydride (PMDA) and 4,4'-diaminodi Polyimides made from phenylether (ODA, 4,4'-diaminodiphenylether) are known to have high stability. However, the polyimide prepared from PMDA-ODA has a problem that the efficiency of closing electrons injected into the hole transport layer is relatively low by using PMDA having a relatively high electron affinity.

Accordingly, an object of the present invention is to solve the above problems and to provide an organic electroluminescent device having high luminous efficiency, excellent thickness uniformity and apparent density.

1 shows the structure of an organic electroluminescent device according to an embodiment of the present invention,

2 shows the structure of a device that can be used in the manufacture of the organic electroluminescent device of the present invention,

3 is a graph showing the current, light emission intensity-voltage (Fig. 3a) and luminous efficiency-current (Fig. 3b) characteristics of the organic electroluminescent device according to Example 1 of the present invention,

4 is a graph showing the current, light emission intensity-voltage (FIG. 4A) and luminous efficiency-current (FIG. 4B) characteristics of the organic EL device according to Example 2 of the present invention.

5 is a graph showing the current, light emission intensity-voltage (FIG. 5A) and luminous efficiency-current (FIG. 5B) characteristics of the organic EL device according to Comparative Example 1. FIG.

<Explanation of symbols for the main parts of the drawings>

1: flat glass 2: ITO transparent anode

3: hole transport layer 4: light emitting and electron transport layer

5: electrode 6: suture

7: glass 10, 20, 30, 40: crucible

50: exhaust line 60: shutter

70 thickness gauge 80 substrate

In the present invention to achieve the above object, in the organic electroluminescent device comprising an anode transparent electrode, an organic layer including an organic light emitting layer and an electron injection electrode, the organic layer further comprises a hole transport layer and / or an electron transport layer, The hole transport layer comprises a polyimide formed from a carboxylic dianhydride compound having an electron affinity of at least 1.10 eV and less than 1.90 eV, and / or the electron transport layer comprises a polyimide formed from a diamine compound having an ionization potential of 6.80 eV to 7.70 eV. It provides an organic electroluminescent device comprising a.

Hereinafter, the present invention will be described in detail.

The organic layer included in the organic electroluminescent device of the present invention has a p-n junction structure of a hole transport layer / light emitting electron transport layer or a hole transport / light emitting layer / electron transport layer. In the organic layer, a host-guest structure using a polymer as a host is used to increase stability.

As the host material, a polyimide having a repeating unit of formula (I) having thermal and structural stability may be used.

(I)

Wherein A and B are residues derived from carboxylic dianhydride and diamine compound, respectively, and n is an integer of 2 or more.

In the preparation of the organic layer including the polyimide, either wet or vapor deposition may be used. For example, when polyimide is used as the host material of the hole transport layer, the hole transport layer can be produced by vacuum deposition polymerization. The vacuum deposition polymerization method is a method of producing a desired polymer thin film by reacting with each other on the surface of a substrate by depositing two or more single molecules which are highly reactive with each other, and may improve thickness uniformity and internal density of the deposited film.

Carboxylic acid dianhydride compounds that can be used in the present invention are compounds having an electron affinity of 1.10 eV or more and less than 1.90 eV, and specific examples thereof include 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride (BTDA, 3,3', 4,4'-benzophenonetetracarboxylic dianhydride), 3,4,3 ', 4'-biphenyltetracarboxylic dianhydride (3,4,3', 4'-biphenyltetracarboxylic dianhydride), 4,4'-oxydiphthalic anhydride ( ODPA, 4,4'-oxydiphthalic anhydride), terphenyltetracarboxylic dianhydride (TPDA), 4,4 '-(hexafluoropropylidene) diphthalic dianhydride (6FDA, 4,4'-(hexafluoropropylidene) diphthalic anhydride), 1,1'-bis (3,4-dicarboxylic acid phenyl anhydride) -1-phenyl-2,2,2-trifluoroethane (3FDA, 1,1'-bis (3,4- dicarboxylicphenyl anhydride) -1-phenyl-2,2,2-trifluoroethane). Structural formula and electron affinity of the compound are shown in Table 1.

Diamine compounds that can be used in the present invention are compounds having an ionization potential of 6.80 eV to 7.70 eV, and specific examples thereof include 4,4'-diaminodiphenyl ether (ODA), 4,4-phenylene diamine (PDA), 2 , 2-bis (4-aminophenyl) hexafluoropropane (6FDAM), 1,1-bis (4-aminophenyl) -1-phenyl-2,2,2-trifluoroethane (3FDAM), benzidine, 1,3-bis (3-aminophenoxy) benzene (APB), 4,4'-diaminodiphenylether (4,4'-DDE), 3,3'-diaminodiphenylmethane, 3,4 '-Diaminodiphenylmethane, 4,4'-diaminodiphenylmethane (DDM), 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone (DDS), 2,2 -Bis [4- (4-aminophenoxy) phenyl] propane, α, α'-bis (4-aminophenyl) -1,4-diisopropylbenzene, 2,2-bis [4- (4-amino Phenoxy) phenyl] hexafluoropropane, 2,2-bis (3-aminophenyl) hexafluoropropane, 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane, 4,4 Bis (aminocyclo Sil) methane, 4,4'-bis (2-chloroanilino) methane, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 4,4'-diaminobibenzyl, 2 , 2-bis (3-amino-4-methylphenyl) hexafluoropropane, 2,2-bis (4-aminophenyl) hexafluoropropane, 1,4-bis (4-aminophenoxy) benzene, 1, 3-bis (m-aminophenoxy) benzene, 4,4'-methylene-bis-o-toluidine, 3,3'-diamino-4,4'-dihydroxybiphenyl, 4,4'-dia Minooctafluorophenyl and the like, the structural formula and ionization potential of some of these are shown in Table 2.

Examples of the hole transport material include N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-diphenyl-4,4'-diamine (TPD) and poly (N) -Vinylcarbazole) (PVK), 4,4 ', 4 "-tri (N-carbazolyl) triphenylamine (TCTA), 4,4', 4" -tris (3-methylphenylamino) triphenylamine ( m-MTDATA). The hole transport layer preferably has a thickness of 200 to 600 kPa. The hole transport material is dispersed in the polyimide in a weight ratio of 2:98 to 95: 5.

Examples of the organic light emitting material used in the present invention include tris (8-hydroxyquinolinolato) aluminum (Alq ₃ ) and 4- (dicyanomethylene) -2-methyl-6- (4-dimethylamino Styryl) -4H-pyran (DCM), 1,4-distyrylbenzene, anthracene, tetracene, pentrasene, coronene, perylene, pyrene, bis (8-quinolinolato) zinc (II), 9 , 10-diphenylanthracene, tris (4,4,4-trifluoro-1- (2-thienyl) -1,3-butanediono) -1,10-phenathroline europium (III) ( Eu (TTFA) 3Phen), Tris (2,4-pentadiono) -1,10-phenathroline terbium (III) (Tb (ACAC) 3Phen), Tris (4,4,4-trifluoro- 1- (2-thienyl) -1,3-butanediono) -1,10-phenathroline disprosium (III) (Dy (TTFA) 3Phen) and the like. The organic light emitting material can be deposited by a conventional method, the thickness is preferably 100 to 400Å.

Examples of electron transfer materials that can be used in the present invention are 2- (4-biphenyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole (butyl-PBD), oxadiazole Derivatives (OXD) and the like.

In the case of vacuum mixed deposition of a polyimide layer formed from a carboxylic acid dianhydride having a low electric affinity as the hole transport layer of the present invention, the carboxylic acid dianhydride compound, the diamine compound and the hole transporting material may be prepared in the range of 49: 49: 2 to 2.5: 2.5: 95. It can be used by weight ratio. At this time, in the case of carboxylic dianhydride, the temperature of 170 to 300 ℃, the deposition rate of 0.05 kPa / sec to 5 kPa / sec, the vacuum degree of 5x10 ^-5 to 5x10 ^-7 torr (torr), the temperature of 150 to 200 ℃ in diamine, A deposition rate of 0.05 kPa / sec to 5 kPa / sec and a vacuum of 5x10 ^-5 to 5x10 ^-7 Torr, a temperature of 200 to 400 ° C for hole transport materials, a deposition rate of 0.1 kPa / sec to 5 kPa / sec and a 5x10 ^-5 to Deposited under conditions of vacuum degree of 5 × 10 ⁻⁷ Torr. The polyimide precursor is then converted to polyimide by heat treatment at a temperature of 100 to 600 ° C. for 1 to 10 hours.

The organic light emitting and electron transport material is vacuum-deposited on the hole transport layer to prepare an electron transport and light emitting layer.

Alternatively, after preparing the hole transporting and emitting layer by a conventional method, when vacuum mixing and depositing a polyimide layer formed from a diamine having a high ionization potential as an electron transporting layer, the carboxylic dianhydride compound, the diamine compound and the electron transporting material may be used. It can be used in the weight ratio of 49: 2 to 2.5: 2.5: 95. The deposition conditions of the carboxylic dianhydride compound and the diamine compound are the same as those of the above-mentioned hole transport layer preparation by vacuum mixed deposition, and the electron transport material has a deposition rate of 0.1 kV / sec to 5 kV / sec at a temperature of 200 to 400 ° C. and 5 × 10 ^−5. Deposited under conditions of vacuum degree of from 5 × 10 ⁻⁷ Torr. The polyimide precursor is then converted to polyimide by heat treatment at a temperature of 100 to 600 ° C. for 1 to 10 hours.

The electrode is manufactured by depositing a metal such as aluminum on the prepared organic layer. The device may then be encapsulated in a conventional manner.

The present invention will be described in more detail with reference to the following examples. However, the scope of the present invention is not limited only to the following examples.

Example 1

The substrate coated with the patterned ITO layer in the desired shape was cleaned and mounted (80) in a sample holder in the chamber as shown in FIG.

4,4'-oxydiphthalic dianhydride (OPDA), 4,4'-diaminodiphenylether (ODA), N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1, 0.01 g of 1'-diphenyl-4,4'-diamine (TPD) and tris (8-hydroxyquinolinolato) aluminum (Alq ₃ ) were added to the crucibles 10 to 40 in the chamber, respectively. .

A rotary pump and an oil diffusion pump were used to bring the reference pressure in the chamber to 2 x 10 ^-6 torr.

The temperatures of crucibles 10, 20 and 30 containing ODPA, ODA and TPD were raised to 180 ° C, 160 ° C and 220 ° C, respectively.

The shutters of the crucibles 10, 20, and 30 were opened to start deposition to produce a hole transport layer thin film of 180 Å, and then the shutter was closed. Subsequently, the temperature was raised to 180 ° C. at a rate of 2 ° C./min, followed by heat treatment for 1 hour to convert to polyimide. At this time, the ratio of the hole transport material: polyimide in the final thin film was 1: 1.

Subsequently, Alq ₃ was deposited to a thickness of 200 kPa on the thin film, and aluminum was then deposited to 3000 to 4000 kPa using a vacuum coating system for metal.

The device of the thin film process was encapsulated using a sealant and a glass plate to complete the device of the present invention.

The light emission characteristics of the fabricated device are shown in FIGS. 3A and B. In Fig. 3A, curve ① represents the current density according to the applied voltage, and curve ② represents the brightness according to the applied voltage. The emission characteristics are shown in Table 3.

Example 2

The device of the present invention was completed by repeating the procedure of Example 1 except that the thickness of the hole transport layer was 150 kPa.

The light emission characteristics of the fabricated device are shown in FIGS. 4A and 4B. In Fig. 4A, curve ① represents the current density according to the applied voltage, and curve ② represents the brightness according to the applied voltage. The emission characteristics are shown in Table 3.

Comparative Example 1

The procedure of Example 1 was repeated except that PMDA-ODA was used instead of ODPA-ODA as the polyimide precursor used in the hole transport layer to complete the device.

Light emission characteristics of the fabricated device are shown in FIGS. 5A and 5B. In Fig. 5A, curve ① shows the current density according to the applied voltage, and curve ② shows the brightness according to the applied voltage. The emission characteristics are shown in Table 3.

Maximum emission wavelength (nm) ON voltage (V) Working voltage (V) Luminous Efficiency (Applied Voltage) (lm / W) Example 1 516 5 9 13 Example 2 516 4 8 23 Comparative Example 1 516 6 10 8 (10 V)

From the above results, the luminous efficiencies of Examples 1 and 2 were 13 and 23 lm / W, respectively, while the luminous efficiency of the comparative example was 8 lm / W, which indicates that the luminous efficiency of the device of the present invention was improved.

As described above, in the present invention, the hole transporting and / or electron transporting layer is manufactured by using a carboxylic acid dianhydride having a low electron affinity and a high ionization potential to increase the hole and electron injection efficiency during driving to greatly increase the luminous efficiency of the device. Can be improved.

In addition, the organic light emitting layer of the present invention can be used in a variety of optoelectronic devices, it is essentially used when high efficiency and thickness accuracy is required, such as a laser diode (laser diode).

Claims (6)

An organic electroluminescent device comprising an anode transparent electrode, an organic layer including an organic light emitting layer, and an electron injection electrode, wherein the organic layer further includes a hole transport layer and / or an electron transport layer, wherein the hole transport layer is 1.10 eV or more and less than 1.90 eV An organic electroluminescent device comprising a polyimide formed from a carboxylic dianhydride compound having an electron affinity of and / or the electron transport layer comprises a polyimide formed from a diamine compound having an ionization potential of 6.80 to 7.70 eV. . The method of claim 1, The carboxylic dianhydride compound is 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,4,3', 4'-biphenyltetracarboxylic dianhydride (BPDA), 4,4 ' -Oxydiphthalic anhydride (OPDA), terphenyl tetracarboxylic dianhydride (TPDA), 4,4 '-(hexafluoropropylidene) diphthalic anhydride (6FDA) and 1,1'-bis (3,4-di Carboxylic acid phenyl anhydride) -1-phenyl-2,2,2-trifluoroethane (3FDA). The method of claim 1, The diamine compound is 4,4'-diaminodiphenyl ether (ODA), 4,4-phenylene diamine (PDA), 2,2-bis (4-aminophenyl) hexafluoropropane (6FDAM), 1, 1-bis (4-aminophenyl) -1-phenyl-2,2,2-trifluoroethane (3FDAM), benzidine, 1,3-bis (3-aminophenoxy) benzene (APB), 4,4 '-Diaminodiphenylether (4,4'-DDE), 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane (DDM ), 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone (DDS), 2,2-bis [4- (4-aminophenoxy) phenyl] propane, α, α ' -Bis (4-aminophenyl) -1,4-diisopropylbenzene, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, 2,2-bis (3-aminophenyl ) Hexafluoropropane, 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane, 4,4-bis (aminocyclohexyl) methane, 4,4'-bis (2-chloroanyl Lino) methane, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone , 4,4'-diaminobibenzyl, 2,2-bis (3-amino-4-methylphenyl) hexafluoropropane, 2,2-bis (4-aminophenyl) hexafluoropropane, 1,4- Bis (4-aminophenoxy) benzene, 1,3-bis (m-aminophenoxy) benzene, 4,4'-methylene-bis-o-toluidine, 3,3'-diamino-4,4'- An organic electroluminescent device, characterized in that it is selected from the group consisting of dihydroxybiphenyl and 4,4'-diaminooctafluorophenyl. The method of claim 1, The hole transport layer is a carboxylic acid dianhydride: diamine: hole transporting material in a weight ratio of 49: 49: 2 to 2.5: 2.5: 95, in the case of the carboxylic acid dianhydride, the temperature of 170 to 300 ℃, 0.05 Pa / sec to 5 Pa / sec and the deposition rate and degree of vacuum of 5x10 ^-5 to 5x10 ^-7 Torr of diamine is temperature, 0.05Å / sec to 5Å / sec and a deposition rate of between 150 and 5x10 200 ℃ for ^- a vacuum degree of 5 to 5x10 ^-7 torr, a hole In the case of the transport material, the vacuum deposition polymerization was carried out under the conditions of 200 to 400 ° C., deposition rate of 0.1 kV / sec to 5 kV / sec and vacuum degree of ⁵ × 10 ⁻⁵ to 5 × 10 ⁻⁷ Torr, and then at 100 to 600 ° C. An organic electroluminescent device, characterized in that it is prepared by heat treatment for 1 to 10 hours. The method of claim 1, The electron transporting layer uses a carboxylic acid dianhydride: diamine: electron transport material in a weight ratio of 49: 49: 2 to 2.5: 2.5: 95, and in the case of the carboxylic acid dianhydride, a temperature of 170 to 300 ° C., 0.05 Pa / sec to 5 Pa / Seconds deposition rate and 5x10 ^-5 to 5x10 ^-7 Torr vacuum, temperature of 150 to 200 ° C for diamine, deposition rates of 0.05 kV / sec to 5 kV / sec and 5x10 ^-5 to 5x10 ^-7 Torr vacuum, electron transport In the case of the material, vacuum deposition polymerization was carried out under conditions of a temperature of 200 to 400 ° C., a deposition rate of 0.1 μs / sec to 5 μs / sec and a vacuum degree of ⁵ × 10 ⁻⁵ to 5 × 10 ⁻⁷ Torr, followed by 1 at a temperature of 100 to 600 ° C. Organic electroluminescent device, characterized in that it is prepared by heat treatment for 10 hours. The method of claim 1, And said hole transporting layer comprises polyimide formed from 4,4'- oxydiphthalic anhydride and 4,4'-diaminodiphenyl ether.