KR20010035597A - Organic electroluminescent device having improved color purity - Google Patents

Abstract

PURPOSE: An organic electroluminescent device having high colorimetric purity is provided to improve the color purity by forming an adjustable organic electroluminescent layer. CONSTITUTION: The organic electroluminescent device having high colorimetric purity comprises a transparent substrate, an electroluminescent layer, a metallic electrode layer, a hole transport layer, and an electron transport layer. The electroluminescent layer has blue electroluminescent material and doping material whose band gap is over the 2.65 eV. An indium tin oxide(ITO) is coated on a glass substrate to form the transparent substrate. The hole transport agents include N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1, 1'-diphenyl-4,4'-diamine(TPD).

Description

Organic electroluminescent device with improved color purity {ORGANIC ELECTROLUMINESCENT DEVICE HAVING IMPROVED COLOR PURITY}

The present invention relates to an organic electroluminescent device having improved color purity.

Conventional blue light emitting organic electroluminescent devices have a broad emission spectrum and light blue of a wavelength biased toward a longer wavelength. 1 is an absorbance (solid line) and electroluminescence (dashed line) spectrum of 4,4'-bis (2,2'-diphenylvinyl) biphenyl, which is typically used as a blue light emitting material in the prior art. It can be seen that the maximum wavelength is about 475 to 490 nm, which is wider than the actual blue color (wavelength: 460 nm).

Such a conventional blue light emitting layer does not have a big problem when used in a single blue light emitting device, but when applied to an organic electroluminescent device in which the light emitting layer is composed of red, green, and blue and emits all colors, full white light is obtained. It was difficult to implement various colors.

Therefore, there has been a need to provide a light emitting layer that can be precisely adjusted to express complete white light and various colors.

It is an object of the present invention to provide an organic electroluminescent device comprising a light emitting layer which can be precisely adjusted so that color purity can be improved to express complete white light and various colors.

1 is an electroluminescence spectrum of 4,4'-bis (2,2'-diphenylvinyl) biphenyl,

FIG. 2A is an absorbance (●) and photoluminescence (○) spectrum of 2- (2-hydroxyphenyl) benzoxazolato lithium (LiPBO) thin film,

2B is an electroluminescence spectrum when the light emitting layer includes only 2- (2-hydroxyphenyl) benzoxazolato lithium (LiPBO),

FIG. 3A shows absorption and photoluminescence (?) Of a thin film comprising 2- (2-hydroxyphenyl) benzoxazolato lithium (LiPBO) and a dopant 1,4-bis (2-methylstyryl) benzene. ) Spectrum,

3B is an electroluminescence spectrum when the light emitting layer includes 2- (2-hydroxyphenyl) benzoxazolato lithium (LiPBO) and a dopant 1,4-bis (2-methylstyryl) benzene.

In the present invention to achieve the above object in the organic electroluminescent device comprising a transparent electrode, an organic light emitting layer and a metal electrode sequentially formed on a transparent substrate, the organic light emitting layer is a blue organic light emitting material and the blue organic light emitting material Provided is an organic electroluminescent device characterized by comprising an organic doping material having a smaller electron affinity and a band gap of 2.65 eV or more.

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

The organic electroluminescent device of the present invention has a structure including a transparent electrode, an organic light emitting layer, and a metal electrode, and may include a hole transport layer and / or an electron transport layer in order to increase electron transfer efficiency.

Indium Tin Oxide (ITO) -glass is etched into an appropriate shape as the cathode transparent electrode substrate.

Conventional monomolecular and polymeric hole transport materials may be used for the hole transport layer of the present invention. Alternatively, in the case of using a polyimide containing a functional group capable of playing a hole transport role, the polyimide alone may be a hole transport layer. Examples of specific monomolecular transport materials include poly (N-vinylcarbazole) (PVCz, PVK), N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-diphenyl- 4,4'-diamine (TPD), and the like.

When the polyimide alone becomes a hole transport layer, for example, pyromellitic dianhydride (PMDA) of the general formula (1) and diamine having a hole transport characteristic of the following general formula (2) are N, N'-diphenyl- N, N'-bis (4-aminobiphenyl)-(1,1'-biphenyl) -4,4'-diamine (DBABBD) was vacuum deposited to polymerize poly [N, N'-di Phenyl-N, N'-bis (4-aminobiphenyl)-(1,1'-biphenyl) -4,4'-diamine pyromellimidide] (PMDA-DBABBD PI) can be used.

Wherein n is an integer of 2 or more.

Conventional electron transport materials may be used for the electron transport layer of the present invention, and specific examples thereof include 2- (4-biphenyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole (butyl -PBD), oxadiazole derivatives (OXD), 2,5-bis (aminostyryl) -1,3,4-oxadiazole (BAPOXD) and the like. These may be vacuum-deposited in a conventional manner to produce an electron transport layer, or may be dispersed and used in a polymer such as polyimide.

The metal electrode of the present invention is made of aluminum, magnesium, calcium, silver alloy and the like.

In the organic light emitting layer of the present invention, the blue organic light emitting material used is 2- (2-hydroxyphenyl) benzoxazolato lithium (LiPBO), 4,4'-bis (2,2-diphenylvinyl) -1,1 '. Biphenyls, mixtures thereof, and the like.

As the organic doping material, a compound having a smaller electron affinity than the light emitting material and a band gap of 2.65 eV or more is used, and the amount of the organic doping material is 0.1 to 10% by weight based on the weight of the blue organic light emitting material.

Examples of specific doping materials include 1,1,4,4-tetraphenyl-1,3-butadiene (TPB), 2- (4-biphenyl) -5- (4-t-butylphenyl) -1,3, 4-oxadiazole (BPBP-OXD), 2- (4-biphenyl) -5-phenyl-1,3,4-oxadiazole (BPBP-OXD), 1,4-bis (2-methylstyryl ) Benzene (bis-MSB), oligo-phenylene vinylene (oligo-PV), 9-hydroxyquinolinate lithium (LiQ), 1,4-di (2-thienyl) -1,3-butadiene (DTB), 2,5-bis (5-t-butyl-2-benzoxazolyl) thiophene (BBBOT), 2- (4-thiazoyl) benzimidazole (TBI), 5-isoquinolene sulfonic acid (5IQSA), 1,4-bis (4-methylene-5-phenyl-2-oxazole) benzene (DMI-POPOP), 2,5-bis (2-naphthyl) -1,3,4-oxadia Sol (BNP-OXD), triamterene, 8-hydroxy-2-methyl-quinolinate lithium (LiMQ), mixtures thereof, and the like, and their structural formulas are shown in Table 1 below.

The organic light emitting layer according to the method of the present invention can form a thin film by a variety of methods, such as conventional spin coating method, vacuum thermal deposition method, sputtering or electron-beam deposition method.

In the present invention, the step of doping the doping material to the organic light emitting material may be carried out by selecting appropriately according to the organic light emitting layer manufacturing method. For example, in the case of using the spin coating method for manufacturing the organic light emitting layer, the doping material is mixed with the organic light emitting material and then coated by dispersing it in an appropriate solvent. In addition, when a thermal evaporation method is used, two materials may be put in each evaporator and thermally evaporated at the same time. At this time, the thin film is grown by determining an appropriate mixing ratio in consideration of the deposition rate of the main organic light emitting material and the doping material.

In addition to the blue light emitting material, the organic light emitting layer may include conventional green and / or red light emitting materials, and may adjust various amounts thereof to implement various colors.

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

Example

It was prepared by patterning an ITO transparent electrode on a transparent glass in a conventional manner.

On the transparent electrode, pyromellitic dianhydride (PMDA) and N, N'-diphenyl-N, N'-bis (4-aminobiphenyl)-(1,1'-biphenyl) -4, 4'-diamine (DBABBD) was vacuum-deposited to polymerize poly [N, N'-diphenyl-N, N'-bis (4-aminobiphenyl)-(1,1'-biphenyl) -4,4 ' -Diamine pyromellitimide] (PMDA-DBABBD PI) layer was formed to a thickness of 300 mm 3 to prepare a hole transport layer.

A blue light emitting material, 2- (2-hydroxyphenyl) benzoxazolato lithium (LiPBO), is mixed with 1,4-bis (2-methylstyryl) benzene as a doping material in an amount of 1% by weight, and the holes are Deposition was carried out on the transport layer to form an organic light emitting layer having a thickness of 400 kHz.

A blue light emitting device according to the present invention was manufactured by forming a metal electrode by forming a magnesium-silver alloy on the organic light emitting layer to a thickness of 2500 kV.

Comparative example

The organic light emitting layer was prepared in the same manner as in Example 1 except for using only 2- (2-hydroxyphenyl) benzoxazolato lithium (LiPBO) without a doping material.

FIG. 2A is an absorbance (●) and photoluminescence (○) spectrum of a 2- (2-hydroxyphenyl) benzoxazolato lithium (LiPBO) thin film, and FIG. 2B is an electrical diagram when the light emitting layer includes only LiPBO according to a comparative example. Emission spectrum. It can be seen from FIG. 2B that the maximum electroluminescence wavelength of the light emitting layer without the doping material is 456 and 492 nm, and the spectrum has a wide range.

FIG. 3A shows absorption and photoluminescence (?) Of a thin film comprising 2- (2-hydroxyphenyl) benzoxazolato lithium (LiPBO) and a dopant 1,4-bis (2-methylstyryl) benzene. 3B is an electroluminescence spectrum when the light emitting layer includes LiPBO and 1,4-bis (2-methylstyryl) benzene as a doping material according to an embodiment. The maximum emission wavelengths that can be seen from FIG. 3b are 445 and 486 nm, and the wavelengths shift toward shorter wavelengths compared with the case without undoping, and the wavelengths are narrower in the spectral range, so that the color is closer to the actual blue color with improved color purity. .

The organic electroluminescent device of the present invention has a narrow spectral range of the emission color and improves color purity by shifting the emission region toward shorter wavelengths, and thus it is possible to emit light closer to actual blue color, and to realize various colors when combined with red, green, and blue. Can be. Furthermore, the luminance of light emitted can be increased by preventing a self-quenching phenomenon generated when the density of the blue light emitter itself is high, and thus it can be applied to various devices using an organic semiconductor such as an organic light emitting display.

Claims (5)

An organic electroluminescent device comprising a transparent electrode, an organic light emitting layer, and a metal electrode sequentially formed on a transparent substrate, wherein the organic light emitting layer has a lower electron affinity and a band gap than the blue organic light emitting material and the blue organic light emitting material. An organic electroluminescent device comprising an organic doping material that is 2.65 eV or more. The method of claim 1, The organic doped material is characterized in that the organic doped material is used in an amount of 0.1 to 10% by weight based on the weight of the blue organic light emitting material. The method of claim 1, An organic electroluminescent device, wherein the organic light emitting material is 2- (2-hydroxyphenyl) benzoxazolato lithium, 4,4'-bis (2,2-diphenylvinyl) biphenyl, or a mixture thereof. The method of claim 1, The doping material is 1,1,4,4-tetraphenyl-1,3-butadiene (TPB), 2- (4-biphenyl) -5- (4-t-butylphenyl) -1,3,4- Oxadiazole (BPBP-OXD), 2- (4-biphenyl) -5-phenyl-1,3,4-oxadiazole (BPBP-OXD), 1,4-bis (2-methylstyryl) benzene (Bis-MSB), oligo-phenylene vinylene (oligo-PV), 9-hydroxyquinolinate lithium (LiQ), 1,4-di (2-thienyl) -1,3-butadiene (DTB ), 2,5-bis (5-t-butyl-2-benzoxazolyl) thiophene (BBBOT), 2- (4-thiazoyl) benzimidazole (TBI), 5-isoquinolene sulfonic acid (5IQSA ), 1,4-bis (4-methylene-5-phenyl-2-oxazole) benzene (DMI-POPOP), 2,5-bis (2-naphthyl) -1,3,4-oxadiazole ( BNP-OXD) and triamterene and 8-hydroxy-2-methyl-quinolinate lithium (LiMQ) and a mixture thereof. The method of claim 1, An organic electroluminescence device further comprising green and red light emitting materials in the organic light emitting layer.