KR100769946B1 - Organic electroluminesecnt device capable of driving in low voltage - Google Patents

Abstract

The present invention provides a multi-layered organic light emitting device in which an anode layer and a cathode layer are positioned on a substrate and a substrate, and an organic material layer of different thin films including an emission layer having at least one light emitting function is disposed between the anode and the cathode. A) an anode comprising a metal or metal oxide having a work function of at least 4.5 eV; b) a buffer layer; And c) a hole injection layer comprising an organic material having a p-type semiconductor property represented by Formula 1, or an organic light emitting device including a hole injection and transport layer, in particular energy between an anode material and a hole injection material. It is possible to drive low voltage even if the barrier structure is large, and it is an organic light emitting device with improved driving life.

Organic light emitting device, hole injection material, buffer layer

Description

Organic light-emitting device driven at low voltage {ORGANIC ELECTROLUMINESECNT DEVICE CAPABLE OF DRIVING IN LOW VOLTAGE}

1 is a cross-sectional view showing one structure of an organic light emitting device of the present invention having a structure including a substrate / anode / buffer layer / hole injection layer / hole transport layer / light emitting layer / electron transport layer / cathode.

2 is a cross-sectional view showing one structure of an organic light emitting device of the present invention having a structure including a substrate / anode / buffer layer / hole injection and transport layer / light emitting layer / electron transport layer / cathode.

3 is a cross-sectional view showing one structure of the organic light emitting device of the present invention having a structure including a substrate / anode / buffer layer / hole injection and transport layer / light emitting layer / hole suppression layer / electron transport layer / cathode.

4 is a cross-sectional view showing one structure of the organic light emitting device of the present invention having a structure including a substrate / anode / buffer layer / hole injection layer / hole transport layer / light emitting layer / hole suppression layer / electron transport layer / cathode.

5 is a cross-sectional view of a general organic light emitting device having a structure including a substrate / anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / cathode.

1 is a substrate, 2 is an anode, 3 is a hole injection layer, 4 is a hole transport layer, 5 is a light emitting layer, 6 is an electron transport layer, 7 is a cathode, and 3 'is hole injection and transport Layer, 8 is a hole suppression layer, and 10 is a buffer layer.

The present invention relates to an organic light emitting device, and more particularly, to an organic light emitting device capable of low voltage driving and having improved driving life.

Hole injection from the anode is required in a variety of devices, and devices such as light emitting diodes (light emitting diode) it is very important to inject holes and electrons stably at low voltage. In particular, the organic light emitting device used as a display is used as an electrode in which metal or metal oxides play a role of hole injection.

The organic light emitting diode is generally composed of a thin film of organic material between two opposite electrodes, and has a multi-layered structure composed of different materials to increase efficiency and stability. As shown in FIG. 5, a multilayer structure of the most representative organic light emitting device includes a hole injection layer (3) receiving holes from the anode 2, a hole transporting layer for transferring holes, ( 4)), a light emitting layer (5) in which holes and electrons are coupled, an electron transporting layer (6) which receives electrons from the cathode 7 and transports them to the light emitting layer, and a cathode 7 ). Such an organic light emitting device may be composed of the above-described layer of the mixed material or to introduce additional layers to further improve the efficiency and life of the device. In addition, the number of layers used may be reduced by using a material having various functions simultaneously to simplify the fabrication of the device.

Each layer of a typical organic light emitting device is formed of a thin film, which is formed by thermal evaporation of a sublimable material under high vacuum or by spin coating after melting in a solution. spin-coating, dip-coating, doctor-blading, inkjet printing, or thermal transfer.

The organic light emitting device uses a transparent substrate and an anode according to the purpose of use and emits light through the anode by using a cathode having high reflectivity, or conversely, light is emitted to the cathode by using a cathode having high reflectivity and a cathode having high transparency. You can get out. In addition, the anode and the cathode may be made of a material having high reflectance at the same time to emit light from the side of the device, or by using both electrodes as a material with high transparency, the device can be manufactured to emit light from both sides.

The stable, high-efficiency light emitting device that is commonly used uses a material having a large work function as an anode and a material having a small work function as a cathode. Generally, indium tin oxide (ITO) is used as a transparent anode, and the work function of the anode is treated by treating the surface of ITO with oxygen plasma to facilitate the injection of holes into the hole injection layer. It is known how to increase. When the anode having a large work function is used as described above, the difference between the valence band of the material forming the hole transport layer and the work function of the anode may be reduced, so that smooth hole injection may be performed at a low voltage. Therefore, in the selection of the material contained in the anode and the hole transport layer, the band position between the two materials and the adhesion or stability of the interface greatly affect the efficiency and life of the device.

Similarly, the material constituting the cathode selects a material having a small work function to facilitate electron injection into the conduction band of the material constituting the electron transport layer. Generally, for this purpose, a metal having a small work function such as calcium (Ca), lithium (Li), magnesium (Mg), potassium (K), sodium (Na), cesium (Cs), or magnesium / silver, aluminum / Alloys such as lithium may also be used. However, these materials are easily oxidized, and when exposed to air, the performance of electron injection can be drastically degraded.

In general, the organic light emitting device emits light through the substrate supporting the anode, so that the substrate is transparent and the anode material is a material having a high transmittance. On the other hand, when emitting light toward the cathode instead of the substrate supporting the anode, a substrate or anode having a high reflectance is used instead of the transparent substrate or the electrode, and instead, the transmittance of the cathode side is increased. To achieve this purpose, a transparent electrode (anode) should be formed on a substrate having a high reflectance or a substrate coated with a high reflectance, or the anode itself should be selected from a material having a high reflectance. In addition, since holes must be injected from the anode to the organic light emitting layer, the material forming the anode is advantageous as the work function is larger (> 4.5 eV), such as conventional ITO or IZO. Appropriate current can be supplied. In addition, a thin film is formed on the anode to maintain strong interfacial adhesion with the material forming the hole injection layer to ensure storage stability and stability while driving.

On the other hand, a metal having a relatively large work function as an anode material, such as aluminum, does not facilitate injection of electrons into the electron transport layer, which requires a high driving voltage and shortens the life of the device. Recently, in order to compensate for these disadvantages, an electrode having an insulating thin film having a thickness of 5 to 100 kW is inserted between the electron transport layer and the aluminum electrode to lower the driving voltage, increase efficiency, and improve the driving life of the device. For this purpose, lithium fluoride, lithium oxide, calcium oxide, strontium oxide, cesium oxide, or magnesium fluoride may be used. It is used. Recently, a method of increasing the performance of an organic light emitting device has been disclosed by adding a small amount of silicon oxide or germanium oxide or a mixture of silicon oxide and germanium oxide to such an insulating ultra thin film (US Patent No. 6,198,219 B1). This ultra-thin insulating layer enables tunneling from the cathode to the electron transport layer when a forward electric field is applied to the device, thereby driving the device at a lower voltage than using aluminum alone, and greatly improving the life of the device. Can be.

In general, ITO, which is used as an anode, is formed using a sputtering process while maintaining the temperature of the substrate at a high temperature (> 150 ° C.), so that a substrate capable of withstanding high temperature process conditions is used. Therefore, glass is generally used as a substrate, and the ITO formed under these process conditions is treated with mixed gas plasma cleaning or UV / Ozone treatment with oxygen or oxygen before fabricating the organic light emitting device. Increasing the work function of or removing contaminants on the surface lowers the drive voltage of the device and improves the reliability of the device.

Attempts have been made to use plastic instead of glass substrates to reduce the weight of organic light emitting devices, but in general, the ITO formed on the plastic is relatively inferior to the ITO formed on the glass because the process is performed at a relatively low temperature. In order to make up for these drawbacks, research has recently been conducted to use indium zinc oxide (hereinafter, abbreviated as IZO) that can be deposited at low temperature instead of ITO. Recently, silicon oxide or germanium oxide having insulating properties between the anode and the hole transport layer or the anode and the light emitting layer, or a mixture of metals having a large work function (> 4.5 eV) is used as a hole injection layer in which a thin film is formed. A method for increasing environmental life and device life is disclosed (US Pat. 6,373,186 B1).

Examples of materials having a high work function in the selection of the anode include ITO, IZO, indium oxide, and tin oxide. These are examples of high transmittance, low transparency, and high work function metals or nonmetals. Materials include boron (B), gold (Au), beryllium (Be), carbon (C), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), germanium (Ge), iridium (Ir) ), Molybdenum (Mo), nickel (Ni), osmium (Os), palladium (Pd), platinum (Pt), rhodium (Rh), silicon (Si), ruthenium (Ru), tin (Sn), tungsten (W ), Aluminum (Al), silver (Ag) and the like.

Materials with low work function and low resistance are aluminum (Al), calcium (Ca), chromium (Cr), copper (Cu), gold (Au), iron (Fe), molybdenum (Mo), nickel (Ni) , Platinum (Pt), silver (Ag), zinc (Zn) and the like. Among them, aluminum (Al) and silver (Ag) are typical materials having high reflectance. Also alloys of the materials listed above as examples or alloys of oxides may be used.

Therefore, it is important to select an appropriate anode material according to the use of the organic light emitting device. However, the choice of an anode material that simultaneously satisfies work function, reflectance or transmittance, high electrical conductivity, and interfacial stability with the material used as the hole injection layer greatly reduces the choice. In addition, when the selected anode material is formed on the substrate by a thin film, if the substrate is subjected to a high temperature process, the selection range of the substrate is also reduced since the substrate should be selected only from a material having high heat resistance.

Therefore, there is a need for an organic light emitting device capable of selecting various substrates such as plastic, metal, ceramic, silicon wafer, aluminum foil, etc. in addition to glass.

Accordingly, an object of the present invention is to provide an organic light emitting device that can be driven at a low voltage and has improved driving life in view of the problems of the prior art.

Another object of the present invention is to provide an organic light emitting device that can use a variety of substrates.

In order to achieve the above object, the present invention provides a multi-layered structure in which an anode layer and a cathode layer are disposed on a substrate and a substrate, and an organic material layer of different thin films including an emission layer having at least one light emitting function between the anode and the cathode. In an organic light emitting device,

a) an anode comprising a metal or metal oxide having a work function of at least 4.5 eV;

b) a buffer layer; And

c) a hole injection layer or a hole injection and transport layer comprising a compound represented by the following formula (1)

It provides an organic light emitting device comprising:

(Formula 1)

In the formula of Formula 1,

R is nitrile (-CN), sulfone (-SO ₂ R '), sulfoxide (-SOR'), sulfonamide (-SO ₂ NR ' ₂ ), sulfonate (-) SO ₃ R ′), nitro (notro: —NO ₂ ), trifluoromethane (—CF ₃ ) group, and the like.

R ′ constituting the substituent is an alkyl group having 1 to 60 carbon atoms or aryl which is unsubstituted or substituted with an amine, an amide, an ether, or an ester. Group, or heterocyclic group.

Hereinafter, the present invention will be described in detail.

The present inventors can select a variety of substrates, while researching an organic light emitting device that can be driven at a low voltage, using a metal having a large work function relative to the anode, the organic material represented by the formula (1) in the hole injection layer When using a buffer layer containing an organic or inorganic material capable of tunneling holes between these anodes and the hole injection layer during use, the driving voltage is lowered and the driving life is greatly increased. It became.

The present invention can be operated at a low voltage by introducing a buffer layer on a cathode having a relatively large work function and simultaneously using a compound having a p-type semiconductor property represented by Chemical Formula 1 in the hole injection layer, thereby improving driving life. It is to provide a light emitting device. It also provides a method for easily forming various anodes on a substrate such as plastic. This concept also makes it applicable to other electronic devices that require the injection and transport of holes.

To this end, the present invention, an anode capable of injecting holes effectively at a low voltage formed of a thin film, including a metal or metal oxide having a work function of at least 4.5 eV layered on the substrate, an organic material located on the anode or A buffer layer formed of a thin film including an inorganic material, a hole injection layer formed of a thin film including an organic material represented by Formula 1 located on the buffer layer, an organic material that can be used in a conventional organic light emitting device positioned on the hole injection layer Including a hole transport layer formed of a thin film, a light emitting layer formed of a thin film, including an organic material that can be used in a conventional organic light emitting device positioned on the hole transport layer, an organic material that can be used in a conventional organic light emitting device located on the light emitting layer An electron transfer layer formed into a thin film, and the electron transfer Including a metal that can be used in conventional organic light emitting device that is located above provides an organic light emitting device which can be driven at a low voltage including a negative electrode formed of a thin film.

In addition, the organic light emitting device may use a hole injection and transport layer for the hole injection layer and the hole transport layer can be used at the same time without distinguishing the role between the hole injection layer and the hole transport layer, and mixing two or more materials A hole injection layer or a hole injection and transport layer may be formed, and if necessary, a hole blocking layer may be separately interposed between the electron transport layer and the light emitting layer to prevent the movement of holes to the electron transport layer. have.

Hereinafter, each layer will be described.

The organic light emitting device of the present invention includes a substrate having a suitable mechanical strength that can serve as a support of the thin film. Such a substrate may select a substrate having a high transmittance or a substrate having a high reflectance depending on the use. If a substrate having a high reflectance is required, the substrate itself may have a high reflectance or may be coated with a material having a high reflectance. Examples of substrates used for this purpose are plastics, glass, metals, ceramics, wafers, metal foils and the like.                     

The substrate used in the conventional organic light emitting device is a glass that can withstand high-temperature process conditions by forming a thin film using a sputtering process while maintaining the temperature of the substrate as an anode at a high temperature (> 150 ℃) The ITO anode formed under these process conditions is subjected to mixed gas plasma cleaning or UV / Ozone treatment with oxygen or oxygen before the organic light emitting device is manufactured. Increasing or removing contaminants present on the surface lowers the driving voltage of the device and improves the reliability of the device. The organic light emitting device of the present invention may use such a conventional glass substrate as it is, or may use various substrates having appropriate mechanical strength and flatness.

The organic light emitting device of the present invention forms a cathode thin film using a cathode material of a metal or metal oxide having a relatively large work function on the substrate. These anodes are transparent and high work function materials such as ITO, IZO, zinc oxide, tin oxide, or chromium (Cr: 4.5 eV), copper (Cu: 4.65 eV), gold (Au). : 5.1 eV), iron (Fe: 4.5 eV), molybdenum (Mo: 4.6 eV), nickel (Ni: 5.15 eV), platinum (Pt: 5.65 eV), carbon (5.0 eV), cobalt (Co: 5.0 eV) , Such as ruthenium (Ru: 4.71 eV), opaque or highly reflective (> 4.5 eV) materials. Depending on their properties, these anode materials may be formed into thin films on a substrate using various thin film formation methods such as chemical vapor deposition (CVD), electron beam vapor depostion (EB), thermal vapor deposition, and sputtering. Can be.                     

The organic light emitting device of the present invention uses a buffer layer on the anode. The buffer layer is interposed between the anode and the hole injection layer to enhance the interfacial strength between the hole injection layer and the anode layer, and refers to a layer that serves to properly maintain the concentration of electrons and holes injected into the device. . That is, it serves to facilitate tunneling by lowering an energy barrier required for hole injection existing between the material constituting the hole injection layer and the anode.

Materials that can be used in such a buffer layer include an organic compound or an inorganic compound having high hole mobility (m> 10 ^-6 cm ² / Vs) as a thin film having a thickness of 5 to 1000 mm, or the hole mobility low ^{(10 -9 cm 2 / Vs <} m <10 -6 cm 2 / Vs) lower (m <10 using an organic or an inorganic compound as a thin film having a thickness of 2 to 500 Å, or the hole mobility of the ^{ultra- 9} cm ² / Vs) Organic or inorganic compounds, thin film insulators, or high-dielectric materials can be used with a thickness of 2 to 100 kPa.

Inorganic compounds that can be used in such a buffer layer are aluminum oxide, titanium oxide, zinc oxide, ruthenium oxide, nickel oxide, zirconium oxide. , Tantalum oxide, magnesium oxide, calcium oxide, strontium oxide, vanadium oxide, yttrium oxide, lithium oxide, lithium oxide, Cesium oxide, chromium oxide, silicon oxide, barium oxide, manganese oxide, cobalt oxide, copper oxide, pra It is in the form of an oxide of a single kind of atom such as sodium oxide (praseodymium oxide), tungsten oxide, germanium oxide, potassium oxide, or lithium Metals and halogenated elements such as fluoride, magnesium fluoride, cesium fluoride, calcium fluoride, sodium chloride, potassium chloride, etc. In the form of compounds, or lithium-boron oxide (lithium metaborate: LiBO ₂ ), potassium-silicon oxide (potassium silicate: K ₂ SiO ₃ ), silicon-germanium oxide, barium titanate ) And a composite oxide of two or more elements such as lithium tantalate (LiTaO ₃ ). In addition, nitrides of elements belonging to Groups 3 and 4 of the periodic table such as silicon nitride (Si ₃ N ₄ ) and boron nitride (BN) may be used. In addition, inorganic materials having semiconductor properties such as zinc sulfide (ZnS), cadmium sulfide (CdS), cadmium selenide (CdSe), gallium phosphide (GaP) and gallium nitride (GaN) may also be used. They can also be used as mixtures by selecting two or more kinds. The minerals exemplified above are merely examples for ease of understanding and are not limited to these.

These inorganic compounds may be formed using various methods of thin film formation such as chemical vapor deposition (CVD), electron beam vapor deposition (EB), thermal vapor deposition, and sputtering, depending on their properties. A buffer layer may be formed, and in particular, when a metal is used as an anode material, an oxide layer may be formed by contacting oxygen on its surface to form a buffer layer of a metal oxide.

In addition, the organic compound contained in the buffer layer should be able to enhance the interfacial strength between the anode and the hole injection layer, and if necessary, the hole mobility is high or, on the contrary, the hole mobility is extremely low (m <10). ^-9 cm ² / Vs) material can be used.

Organics that can be used for this purpose include organic molecules, polymers, or polymers containing at least one element selected from the group consisting of carbon, hydrogen, oxygen, nitrogen, silicon, sulfur, fluorine, boron, and phosphorus. Preference is given to organics selected from the group consisting of complexes.

In addition, depending on the purpose, these molecules form a single bond between atoms to form a large band gap (> 3.0 eV) material, or a double or triple bond partially forms a long conjugate length. Band-gaps of molecules or polymers can be reduced.

In addition, a polymer having a high molecular weight can be used a thin film process using a solution, that is, spin coating, roll-coating, inkjet printing, Langmiur Trough, dip-coating, etc. A substance attached to the organic substance in the form of an organometallic complex or a substance having a charge can also be used.

When the hole mobility of the organic compounds is small as m <10 ^-9 cm ² / Vs, a buffer layer is formed in the form of a thin film having a thickness of 2 to 100 μs between the anode and the hole injection layer, and more preferably 2 to 50 μs. It is formed into a thin film. When the hole mobility of the organic compounds is between 10 ^-9 cm ² / Vs <m <10 ^-6 cm ² / Vs, the thickness of the thin film can be extended to 2 to 500 kPa, but the thickness of 2 to 200 kPa More preferred.

In addition, when the buffer layer is interposed between the hole injection layer of the present invention and an anode layer composed of ITO, which is widely known and commonly used in the related art, the life of the device can be further increased.

The organic light emitting device of the present invention uses a hole injection layer or a hole injection and transport layer containing the organic material represented by the formula (1) on the buffer layer. The hole injection layer (or hole injection and transport layer) of the compound represented by Formula 1 is a layer in which holes are injected from the anode. The hole injection layer (or hole injection and transport layer) is supplied from the anode of the metal or metal oxide having a work function of at least 4.5 eV through the buffer layer. Receive.

Including the organic material represented by Chemical Formula 1 in the hole injection layer (or hole injection and transport layer) maintains a negative charge in the hole injection layer (or hole injection and transport layer) suitable for receiving the hole passing through the buffer layer. Because it can.

Therefore, the organic light emitting device of the present invention simultaneously uses a positive electrode containing a metal or metal oxide having a relatively large work function, introducing a buffer layer thereon, and a hole injection layer including the organic material represented by Chemical Formula 1 thereon. (Or a hole injection and transport layer) can be used to drive at low voltages.

The organic material having the hole injection and hole transport ability represented by the formula (1) has been filed by the present inventors and disclosed in WO 01/49806. The organic material of Formula 1 may have a P-type semiconductor property to form a hole injection layer or a hole injection layer and at the same time the role of a hole injection layer and a hole transport layer.

More specific examples of the compound represented by Chemical Formula 1 used in the present invention are shown in Chemical Formulas 1a to 1g.

(Formula 1a) (Formula 1b) (Formula 1c)

Formula 1d Formula 1e                     

(Formula 1f) (Formula 1g)

R 'as defined in the above formula is an alkyl group having 1 to 60 carbon atoms or an aryl group which is unsubstituted or substituted with an amine, amide, ether, or ester. , Or a heterocyclic group.

Particularly, in the case of a compound in which R 'is an alkyl having 5 or more carbon atoms or a substituted alkyl group, the buffer layer) may be thin film using inkjet printing, spin coating, doctor blading, roll coating, etc., in which a process is performed in solution instead of vacuum deposition. In the case of forming, the thin film may be formed by the hole injection layer or the hole injection and transport layer in the same manner. In addition, a thin film may be formed on an aqueous solution by introducing a functional group having a charge on a substituent forming R ′. Examples of the organic material having the hole injection and hole transport ability represented by the formula (1) is merely for the purpose of understanding and not limited thereto.

The organic material represented by Formula 1 contained in the hole injection layer (or the hole injection and transport layer) of the present invention is preferably selected from compounds having a reduction potential of -0.6 V or more and less than 0 V for smooth hole injection. Preferably from -0.6 V to -0.01 V, even more preferably from compounds having a reduction potential between -0.3 and -0.01 V. When an organic material having a reduction potential of less than -0.6 V is used in the hole injection layer (or the hole injection and transport layer), the hole injection ability may be lowered.

If a conventional organic material used in the conventional hole injection layer is used in the hole injection layer (or the hole injection and transport layer) instead of the organic material having the P-type semiconductor property of Formula 1, the work function is relatively large If an organic light emitting device is manufactured by interposing a buffer layer between an anode and a hole injection layer (or a hole injection and transport layer), and a forward electric field is applied to the device, the device operates only at a relatively high voltage and has a low driving life. do.

The organic light emitting device of the present invention uses a separate hole transport layer on the hole injection layer if the hole injection layer does not serve as a hole transport layer. That is, a hole transport layer is formed after the substrate / anode / buffer layer / hole injection layer.

The organic material having a hole transport ability that can be used in the hole transport layer may use a conventional organic material known in the art as it is. Generally, aryl amine-based materials are known as typical hole transport materials, and polycyclic aromatic compounds are also recently known as materials for transporting holes. Specific examples of representative hole transport materials include 4,4'-bis [(N-1-naphtyl) -N-phenylamino] biphenyl (hereinafter abbreviated as NPB), which is an aryl amine type, 1,3,5-tris [N- (4-diphenylaminophenyl) phenylamino] benzene, 4,4 ', 4-tris (3-methylphenylphenylamino) triphenylamine (hereinafter abbreviated as MTDATA). In addition, it is also possible to use a variety of aryl amine-based materials in which a variety of aryl amines are connected to increase the molecular weight to increase heat resistance or to change the hole mobility. The organic material having a hole transporting capacity suitable for the hole transporting layer of the present invention is a compound having an oxidation potential of 0.01 to 1.5 V and a hole mobility greater than 10 ^-8 cm ² / Vs, more preferably, an oxidation potential of 0.01 to 1.2. V and hole mobility is greater than 10 ⁻⁷ cm ² / Vs.

The organic light emitting device of the present invention uses a light emitting layer that emits light by recombination of holes and electrons on the hole injection and transport layer described above or on the hole transport layer. If necessary, a small amount of fluorescent or phosphorescent material may be doped to further increase luminous efficiency.

As the organic material having a light emitting ability that can be used in the light emitting layer, conventional organic materials known in the art may be used as they are. In general, the material forming the light emitting layer is advantageous in terms of driving life as the stability to holes and electrons is greater, and it is known that the material having a high fluorescence is preferable to manufacture a device having high efficiency. In recent years, instead of the fluorescence that theoretically emits light only when the spins of holes and electrons are reversed, phosphorescence that emits light when the spins of electrons and electrons are in the same direction is used as a dopant constituting the emission layer. It is known to use. In this case, many studies have been conducted to overcome the theoretical limitation of fluorescence that only about 1/4 of the injected electrons and holes can emit light. The present invention can also be used for organic light emitting devices using such phosphorescence.

Tris (8-quinolinoato aluminum; Alq3 hereinafter) is most representatively known as a material constituting the light emitting layer used in the conventional fluorescent organic light emitting device. In addition, a material having a large band gap may be used for light emission of short wavelengths. For example, 4,4'-bis (2,2-diphenylvinyl) biphenyl (4,4'-bis (2,2-diphenylvinyl)). biphenyls (hereinafter referred to as DPVBi) and the 9,10-diaryl anthracene family of blue light emitting materials are widely known, and iridium (Ir) or platinum (Pt) to induce phosphorescence instead of fluorescence. Also known is a method of fabricating a highly efficient organic light emitting device using a molecule containing the same as a dopant (C. Adachi, MA Baldo, and SR Forrest, Applied Physics Letter , 77 , 904, 2000 , C). Adachi, MA Baldo, SR Forrest, S. Lamansky, ME Thompsom, and RC Kwong, Applied Physics Letter , 78 , 1 622, 2001 ).

The organic light emitting device of the present invention forms an electron transporting layer on the light emitting layer and receives electrons from the cathode and transfers the electrons to the light emitting layer, but if necessary, a hole for preventing the movement of holes to the electron transporting layer between the electron transporting layer and the light emitting layer. A hole-blocking layer may be interposed separately. Since the hole suppression layer can be limited to the light emitting layer without expanding the region of light emission to the electron transport layer, it is easy to control the emission spectrum. Particularly, in the case of phosphorescence, recombination of holes and electrons is partially performed in the fluorescent electron transport layer. It can suppress what happens. In addition, even when holes are excessively injected, holes accumulated at the interface between the light emitting layer and the hole suppression layer activate electron injection from the cathode, thereby inducing an appropriate balance of the number of holes and electrons in the device, thereby obtaining high quantum efficiency. As the organic material having the hole suppression ability that can be used in such a hole suppression layer, conventional organic materials known in the art may be used as they are. In particular, it is preferable to use a substance which is difficult to oxidize, that is, has a large oxidation potential and a low hole transport rate.

The organic light emitting device of the present invention uses an electron transport layer that is located between the cathode and the light emitting layer, or between the cathode and the hole suppression layer, and smoothly receives electrons from the cathode and transfers the electrons to the light emitting layer. The electron transport layer must maintain a stable interface with the material forming the cathode, and in particular, the electron transport layer must be excellent in stability to electrons, and the higher the electron transport degree, the higher the voltage can drive the device. The organic material having an electron transport ability that can be used as such an electron transport layer may use a conventional organic material known in the art as it is. It is known that Alq3, which is widely known as a material of the light emitting layer, may be used for the electron transport layer, and a new organic compound represented by the following Chemical Formula 2 having a property of extending the life of the device may be used.

(Formula 2)

The organic light emitting device of the present invention uses a cathode containing a conductive material having a relatively small work function. Such negative electrode materials include magnesium, calcium, lithium, aluminum, indium, potassium, yttrium, strontium, europium (europium), sodium, gallium (Ga), and samarium (Sm). It is also possible.

In addition, such a cathode layer may be formed of a multilayer thin film. For example, an insulating metal oxide such as lithium fluoride (LiF), lithium oxide (Li ₂ O), magnesium fluoride, etc., having a thickness of 0.1 to 10 nm is formed by forming a thin film between the electron transport layer and the electrode. The voltage is lowered and a stable cathode is formed. In this case, the thickness of the insulating layer may vary depending on the type of the electron transport layer and the cathode. Preferably, 0.5 to 7 nm is used. Alternatively, electron injection may be more smoothly formed by forming a layer in which a material capable of forming an electron transport layer and a metal having a low work function are deposited.

In addition, when the generated light has to be emitted through the cathode, a metal cathode having a thickness sufficient to maintain the transmittance is manufactured so as to be a transparent cathode, and then transparent indium tin oxide (ITO) or indium zinc oxide (IZO) is formed thereon. ) May be used by thin film deposition.

Examples of the materials constituting each layer described above are only partly provided for the purpose of understanding the present invention, and the compounds provided by the present invention are not limited thereto.

The organic light emitting device of the present invention includes a multilayer organic layer between the anode and the cathode, and has various structures using the above-described layers. Basically, the substrate / anode / buffer layer / hole injection layer / hole transport layer / light emitting layer / electron transport layer / cathode is manufactured as shown in FIG. 1. In addition, as described in the description of each layer, by using a material that simultaneously plays two or more roles, the number of layers of the organic material may be reduced, or conversely, the number of layers may be increased in order to further improve performance or to achieve special performance. Such a layer structure includes a substrate / anode / buffer layer / hole injection and transport layer / light emitting layer / electron transport layer / cathode as shown in FIG. 2; A substrate / anode / buffer layer / hole injection and transport layer / light emitting layer / hole suppression layer / electron transport layer / cathode as shown in FIG. 3; As shown in FIG. 4, the structure may include a substrate / anode / buffer layer / hole injection layer / hole transport layer / light emitting layer / hole suppression layer / electron transport layer / cathode.

In the organic light emitting device of the present invention, each layer is formed of a thin film, and the formation of such a thin film is performed by thermal vacuum deposition (thermal vacuum) under high vacuum (high vacuum) of a material used in each layer, as in a conventional method of manufacturing an organic light emitting device. evaporation, or dissolved in a solution, followed by spin-coating, dip-coating, doctor-blading, inkjet printing, or thermal transfer It is prepared by forming a layer of a thin film using the method of.

Therefore, the organic light emitting device of the present invention can use a variety of anode materials having a relatively large work function, low voltage driving is possible, the driving life is improved to increase the selection of the substrate can be used a variety of substrates such as plastic .

The present invention will be described in more detail with reference to the following examples and comparative examples. However, an Example is for illustrating this invention and is not limited only to these.

EXAMPLE

Example 1

(Manufacture of an organic light emitting device comprising 4,4 ', 4 "-tris (3-methylphenylphenylamino) triphenylamine as a hole injection layer and including a buffer layer)

(Manufacture of ITO transparent electrode (anode))

A glass substrate (corning 7059 glass) coated with a thin film of ITO (indium tin oxide) at a thickness of 1300 Å was placed in distilled water in which a detergent was dissolved and washed with ultrasonic waves. The detergent used was a product of Fischer Co. and Millipore Co. Secondly filtered distilled water was used as a filter of the product. After washing ITO for 30 minutes, ultrasonic washing was repeated 10 times with distilled water twice. After washing the distilled water, ultrasonic cleaning with a solvent such as isopropyl alcohol, acetone, methanol, dried and transferred to a plasma cleaner. The substrate was washed for 5 minutes at 50 W at a pressure of 14 mtorr using a plasma mixed with argon and oxygen at 2: 1, and then transferred to a vacuum evaporator.

(Formation of the buffer layer)

4,4 ', 4-tris (3-methylphenylphenylamino) triphenylamine (hereinafter referred to as MTDATA), which is known as a hole injection material, was thermally vacuum deposited to a thickness of 200 kPa on the prepared ITO transparent electrode to form a buffer layer.

(Formation of Hole Injection Layer)

A hexanitrile hexaazatriphenylene (hereinafter referred to as HAT), a compound represented by Chemical Formula 1a having a reduction potential of -0.05 V, was thermally vacuum deposited to a thickness of 500 kPa on the buffer layer to form a hole injection layer.

(Formation of hole transport layer)

A hole transport layer was formed by vacuum depositing NPB (400 kPa), which is a material for transporting holes on the hole injection layer.

(Formation of light emitting layer)

An Alq3 serving as a light emitting layer on the hole transport layer was vacuum deposited to a thickness of 300 Å to form a light emitting layer.

(Electron transport layer)

The compound represented by Formula 2, which serves as an electron transporting layer, was deposited on the emission layer to a thickness of 200 Å to complete the formation of a thin film of the organic material layer.

(Cathode formation)                     

Lithium fluoride (LiF) and aluminum having a thickness of 2500 kW were deposited on the electron transport layer sequentially to form a cathode.

In the above process, the deposition rate of the organic material was maintained at 1 Å / sec, the lithium fluoride of the cathode was maintained at 0.3 Å / sec, and the aluminum maintained the deposition rate of 3 to 7 Å / sec. ^-7 was maintained.

This device has a structure of HAT / NPB / Alq3 / Formula 2 / LiF / Al cathode of substrate / ITO anode / MTDATA / Formula 1a.

When the 6.2 V forward electric field was applied to the fabricated device, a green spectrum of 1596 nit brightness corresponding to x = 0.352 and y = 0.541 was observed based on the 1931 CIE color coordinate.

Comparative Example 1

In order to compare the effects of the positive electrode buffer layer and the hole injection layer to be used simultaneously in the present invention Example 1 device removing only the HAT (500 kV) which is a compound represented by the formula (1a) having a reduction potential forming the hole injection layer is -0.05V Produced in the same way as. Therefore, the structure of the device has a structure of substrate / ITO anode / MTDATA / NPB / Alq 3 / Formula 2 / LiF / Al cathode.

When the 9.4 V forward electric field was applied to the fabricated device, a green spectrum of 1056 nit brightness corresponding to x = 0.312 and y = 0.555 was observed based on the 1931 CIE color coordinate.                     

Therefore, it can be seen that the role of the buffer layer can be appropriately performed as a low voltage driving only when using a compound satisfying the structure of Formula 1 as the hole injection layer.

Example 2

The same method as in Example 1 except for forming an anode buffer layer having a thickness of 20 kPa of an organic material represented by Formula 1h, which satisfies Formula 1, instead of MTDATA used as a material of the anode buffer layer of Example 1 An organic light emitting diode was manufactured. This device has a structure of HAT / NPB / Alq3 / Formula 2 / LiF / Al cathode of substrate / ITO anode / Formula 1h / Formula 1a.

Formula 1h

In the formula 1h, Et is an ethyl group.

When the device applied a 6.5 V forward electric field, a green spectrum with a 1702 nit brightness of x = 0.348 and y = 0.537 was observed based on the 1931 CIE color coordinate.

Therefore, when the compound satisfying the structure of Formula 1 is used as the hole injection layer, it can be seen that different materials satisfying Formula 1 may serve as a buffer layer.

Example 3

An organic light emitting display device was manufactured in the same manner as in Example 1, except that an insulating buffer material having a thickness of 8 을 was formed of an insulating inorganic material of LiBO ₂ (lithim metaborate) instead of MTDATA used as the material of the anode buffer layer of Example 1. The device was manufactured. This device has a structure of HAT / NPB / Alq3 / Formula 2 / LiF / Al cathode of substrate / ITO anode / LiBO ₂ / Formula 1a.

When the device applied a 6.5 V forward electric field, a green spectrum with a 1690 nit brightness of x = 0.346 and y = 0.554 was observed based on the 1931 CIE color coordinate.

When the device was subjected to a current concentration of 100 mA / cm ² (constant DC), the initial luminance was 3492 nit, and the time required when the initial luminance dropped to the 80% level was 50 hours.

Therefore, when an appropriate insulating material is used in the buffer layer between the anode and the hole injection layer satisfying Formula 1, it can be seen that the driving life of the device is greatly increased.

Comparative Example 2

Example 3 In order to use the insulating inorganic material of LiBO ₂ (lithim metaborate) as a buffer layer having a thickness of 15 지만, but there is no hole injection material that satisfies Formula 1 Example 3 to see the performance of the organic light emitting device An organic light emitting diode was manufactured by removing only HAT which is a compound represented by Chemical Formula 1a. This device has a structure of substrate / ITO anode / LiBO ₂ / NPB / Alq 3 / Formula 9 / LiF / Al.

 When the 18 V forward electric field was applied to the fabricated device, a green spectrum of 762 nit brightness corresponding to x = 0.311 and y = 0.543 was observed based on the 1931 CIE color coordinate.

Therefore, when an organic light emitting device using an insulating inorganic material as a buffer layer without a compound satisfying the structure of Formula 1 is fabricated, it can be seen that the driving voltage of the device is rapidly increased.

Comparative Example 3

The organic light emitting device was manufactured in the same manner as in Example 1, except that a buffer layer was removed to prepare a device including a hole injection layer made of ITO and HAT satisfying Formula 1. The structure of this device has the structure of HAT / NPB / Alq3 / Formula 2 / LiF / Al of the substrate / ITO anode / Formula 1a.

When a 5.37 V forward field was applied to the device, green light emission corresponding to x = 0.345 and y = 0.553 was observed based on the 1931 CIE color coordinate. At this time, the current density injected into the organic light emitting device was 50 mA / cm ² .

When the device was subjected to a current concentration of 100 mA / cm ² (constant DC), the initial luminance was 3399 nit, and the time required when the initial luminance dropped to the 80% level was 23 hours.

Therefore, it can be seen that the buffer layer can play a role of improving the life of the device.

According to the present invention, the buffer layer is interposed between the anode and the hole injection layer including the organic material represented by Formula 1, thereby enabling low voltage driving and improving driving life even using a structure having a large energy barrier between the anode material and the hole injection material. It has the effect of manufacturing an organic light emitting device.

Claims (6)

In the organic light emitting device having a multi-layer structure in which the anode layer and the cathode layer is positioned on the substrate and the substrate, and the organic material layer of the different thin film including a light emitting layer having a light emitting function between the anode and the cathode, a) an anode comprising a metal or metal oxide having a work function of at least 4.5 eV; b) a buffer layer; And c) a hole injection layer or a hole injection and transport layer comprising a compound represented by the following formula (1) Organic light emitting device comprising: (Formula 1)

In the formula of Formula 1, R is nitrile (-CN), sulfone (-SO ₂ R '), sulfoxide (-SOR'), sulfonamide (-SO ₂ NR ' ₂ ), sulfonate (-) SO ₃ R ′), nitro (notro: —NO ₂ ), trifluoromethane (—CF ₃ ) group, and the like. R ′ constituting the substituent is an alkyl group having 1 to 60 carbon atoms or aryl which is unsubstituted or substituted with an amine, an amide, an ether, or an ester. Group, or heterocyclic group. The method of claim 1, The anode includes ITO, IZO, zinc oxide, tin oxide, chromium (Cr), copper (Cu), gold (Au), iron (Fe), molybdenum (Mo), nickel (Ni) Organic light emitting device comprising a metal or metal oxide selected from the group consisting of platinum (Pt), carbon (C), cobalt (Co), and ruthenium (Ru). The method of claim 1, The buffer layer is aluminum oxide, titanium oxide, zinc oxide, ruthenium oxide, nickel oxide, zirconium oxide, tantalum oxide, magnesium oxide, calcium oxide, strontium oxide, vanadium oxide, yttrium oxide, lithium oxide, cesium oxide, chromium oxide, silicon oxide , Barium oxide, manganese oxide, cobalt oxide, copper oxide, prasodynium oxide, tungsten oxide, germanium oxide, potassium oxide, lithium fluoride, magnesium fluoride, cesium fluoride, calcium fluoride, sodium chloride, potassium chloride, lithium -Boron oxide (lithium metaborate: LiBO ₂ ), potassium-silicon oxide (potassium silicate: K ₂ SiO ₃ ), silicon-germanium oxide, barium titanate, lithium tantalate (LiTaO) ₃ ), silicon nitride (Si ₃ N ₄ ), boron nitride (BN ), Nitrides of elements belonging to Groups 3 and 4, zinc sulfide (ZnS), cadmium sulfide (CdS), cadmium selenide (CdSe), gallium phosphide (GaP), and gallium nitride (GaN) An organic light emitting device comprising at least one inorganic material selected. The method of claim 1, The buffer layer is selected from the group consisting of organic molecules or polymers containing at least one element selected from the group consisting of carbon, hydrogen, oxygen, nitrogen silicon, sulfur, fluorine, boron, and phosphorus, and complexes with metals thereof. An organic light emitting device comprising the organic material selected. The method of claim 1, The hole injection layer or the hole injection and transport layer is an organic light emitting device comprising an organic material with a reduction potential of more than -0.6 V and less than 0 V. A display device comprising the organic light emitting device of claim 1.

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