KR102148534B1 - Organic electro luminescence device - Google Patents

Abstract

The present invention is a positive electrode; cathode; And one or more organic material layers interposed between the anode and the cathode, and at least one of the one or more organic material layers includes a first host and a second host.

Description

Organic electroluminescent device {ORGANIC ELECTRO LUMINESCENCE DEVICE}

The present invention relates to an organic electroluminescent device including one or more organic material layers.

In the organic electroluminescent device, when a voltage is applied between two electrodes, holes are injected into the organic material layer from the anode and electrons are injected into the organic material layer from the cathode. When injected holes and electrons meet, excitons are formed, and when these excitons fall to the ground state, light is emitted. In this case, the material used as the organic material layer may be classified into a light emitting material, a hole injection material, a hole transport material, an electron transport material, an electron injection material, and the like according to their function.

In order to increase the luminous efficiency of the organic electroluminescent device, color purity and energy transfer are required. To this end, a light emitting material in which a host material and a dopant material are mixed may be used.

The dopant material may be classified into a fluorescent dopant using an organic material and a phosphorescent dopant using a metal complex compound containing heavy atoms such as Ir and Pt. At this time, since the phosphorescent material can theoretically improve the luminous efficiency up to four times as compared to the fluorescent material, a lot of research has been conducted on a phosphorescent host as well as a phosphorescent dopant.

Currently, a metal complex compound including Ir such as Firpic, Ir(ppy) ₃ , and (acac)Ir(btp) ₂ is known as a phosphorescent dopant material of the emission layer, and CBP is known as a phosphorescent host material.

In particular, compared to green or red phosphorescent hosts, a blue phosphorescent host requires a larger band gap, which makes it difficult to obtain a highly efficient device because charge injection and exciton confinement are inefficient. When Firpic is used as a blue phosphorescent dopant and mCP is used as a blue phosphorescent host, it has been reported that high photoluminescence quantum efficiency is obtained. However, since there is no material with a large bandgap for efficient charge carrier injection and exciton confinement suitable for such a system, it has been difficult to implement highly efficient blue phosphorescence.

As described above, conventional materials do not have satisfactory light emission characteristics in the organic electroluminescent device, and thus development of an organic electroluminescent device including a light emitting material having excellent performance is required.

In order to solve the above problems, an object of the present invention is to provide an organic electroluminescent device having improved characteristics such as driving voltage, luminous efficiency and lifetime.

In order to achieve the above object, the present invention is a positive electrode; cathode; And at least one organic material layer interposed between the anode and the cathode, wherein at least one of the at least one organic material is a blue phosphorescent emission layer including a first host and a second host, and the second host is a HOMO -An organic electroluminescent device characterized in that the LUMO energy gap is the same as the first host or greater than the first host, or the LUMO energy level is greater than that of the first host.

In the organic electroluminescent device of the present invention, a first host and a second host having a HOMO-LUMO energy gap equal to or greater than the first host are used in combination, or the first host and the LUMO energy level are the first host. By including an emission layer using a mixture of a larger second host, characteristics such as driving voltage, luminous efficiency, and lifespan may be further improved compared to a conventional organic electroluminescent device using only one type of host. Accordingly, when a display panel is manufactured using the organic electroluminescent device of the present invention, it is possible to provide a display panel with improved performance and lifetime.

Hereinafter, the present invention will be described.

In the present invention, the HOMO-LUMO energy gap means the energy difference between HOMO and LUMO.

The organic electroluminescent device according to the present invention includes a blue phosphorescent emission layer using a mixture of a first host and a second host, wherein the second host has a HOMO-LUMO energy gap equal to the first host or the first host It is characterized in that the greater than, or the LUMO energy level is greater than that of the first host.

In an organic electroluminescent device, the HOMO (highest occupied molecular orbital) energy level of the hole injection/transport layer material is between the HOMO energy level of the surrounding organic material layer (especially the light-emitting layer) and the HOMO energy level of the anode to facilitate hole injection. The LUMO (lowest unoccupied molecular orbital) energy level of the injection/transport layer material is preferably between the LUMO energy level of the surrounding organic material layer (especially the light emitting layer) and the LUMO energy level of the cathode in order to facilitate electron transfer.

However, in the blue phosphorescent light emitting layer, the host material must have a singlet and triplet energy level higher than that of the dopant material. This is to prevent the phenomenon that the excitons in the triplet of the dopant are reversed back to the host. However, it has been difficult to develop a single host having high triplet energy, wide HOMO-LUMO energy gap, and high charge mobility.

Accordingly, in the present invention, instead of using the host of the emission layer alone, one host (hereinafter,'first host') and the first host and a host having the same HOMO-LUMO energy gap or a larger HOMO-LUMO energy gap ( Hereinafter,'second host') or a host having a higher LUMO energy level than the first host is used to balance the holes and electrons flowing into the organic electroluminescent device. The lifespan of the electroluminescent device may be improved, and efficiency may be improved.

In this case, the second host preferably has a HOMO-LUMO energy gap greater than 0.1 to 2.0 eV than the first host, or a LUMO energy level greater than 0.1 to 1.0 eV than the first host.

Here, among the first host and the second host, the second host having a relatively upper energy band gap (HOMO-LUMO) has a strong hole dominant, and a second host having a relatively lower energy band gap. 1 A host has a strong electron dominant.

The HOMO-LUMO energy gap of the first host is not particularly limited, but is preferably 3.0 to 5.0 eV. In this case, the HOMO energy level of the first host may be 5.0 to 7.0 eV, and the LUMO energy level may be 1.0 to 3.0 eV.

In addition, the triplet energy of the first host is not particularly limited, but in the case of 2.8 eV or more, preferably 2.8 to 4.0 eV, since energy transfer from the host to the dopant is easily made, the light emission of the organic electroluminescent device Efficiency, driving voltage, and lifespan may be further improved.

Examples of the compound used as the first host include carbazole-based compounds, phosphine oxide-based compounds, nitrogen-containing heterocyclic compounds (eg, pyrimidine-based compounds), and the like, but is not limited thereto.

Since the carbazole-based compound has a triplet energy of 3.2 eV, it can be applied to all light-emitting layers including red phosphorescence as well as blue phosphorescence, and has excellent thermal stability, thereby improving device stability.

The phosphine oxide-based compound is prevented by π-π conjugation due to a phosphine oxide group, thereby having a large energy band gap and may have a triplet energy of 3.0 eV or more. In addition, the phosphine oxide-based compound has excellent electron transport characteristics due to the phosphine oxide group, and thus, the efficiency of the device is excellent, and further, the stability of the device is also excellent.

Further, the nitrogen-containing heterocyclic compound has a large energy band gap and may have a triplet energy of 2.8 eV or more. In addition, since the nitrogen-containing heterocyclic compound is a material having high electron absorbing properties, it has excellent electron transport properties, and thus, the efficiency of the device is excellent, and further, the stability of the device is also excellent.

The HOMO-LUMO energy gap of the second host is not particularly limited as long as it is the same as the above-described first host or larger than the first host, but the HOMO-LUMO energy gap of the second host is preferably 3.0 to 6.0 eV. In this case, the HOMO energy level of the second host may be 5.0 to 7.0 eV, and the LUMO energy level may be 0.5 to 3.0 eV.

In addition, the triplet energy of the second host is not particularly limited, but in the case of 2.8 eV or more, preferably 2.8 to 4.0 eV, since energy transfer from the host to the dopant is easily made, the light emission of the organic electroluminescent device Efficiency, driving voltage, and lifespan may be further improved.

Examples of the compound used as the second host include, but are not limited to, a carbazole compound, a silane compound, or a carboline compound.

The silane-based compound is suitable for blue phosphorescence emission because the Si atom contained in the molecule can interfere with the π-π conjugation in the molecule, so that the energy band gap is large and has triplet energy of 3.0 eV or more.

However, the silane-based compound has a disadvantage in that charge mobility is inferior, but by introducing moieties such as carbazole, triphenylene, and phenyl into the molecule, the charge mobility is improved and at the same time has a wide band gap, thereby exhibiting excellent light emission characteristics. Eggplant can be used as a host.

In addition, carbazole-based compounds and carboline-based compounds have a triplet energy of 3.2 eV or more, and can be applied to all light-emitting layers up to red phosphorescence and blue phosphorescence, and have excellent thermal stability in terms of device stability. Have.

The mixing ratio of the first host and the second host described above is not particularly limited, but may be a weight ratio of 1:99 to 99:1, and in this case, it is preferable that the use ratio of the second host is higher. Preferably, the mixing ratio of the first host and the second host may be a weight ratio of 20:40 to 80:60.

The emission layer of the present invention may further include a dopant other than the above-described first host and second host.

The material usable as the dopant is not particularly limited, but there are metals, metal oxides, and metal complex compounds. It is preferable to use a metal complex compound.

Non-limiting examples of the metal complex compound include a platinum-containing metal complex compound, a zinc-containing metal complex compound, an iridium-containing metal complex compound, and the like. Using a metal complex compound containing iridium (Ir) desirable.

Non-limiting examples of the iridium-containing metal complex compound include Firpic, Ir(ppy) ₃ , (acac)Ir(btp) ₂ and the like.

In this case, the mixing ratio of the first host, the second host, and the dopant is not particularly limited, but the first host, the second host, and the dopant may be 70 to 99:30 to 1 weight ratio. Preferably, the mixing ratio of the first host, the second host, and the dopant may be 80 to 95:20 to 5 weight ratio.

A method of manufacturing a light emitting layer including such a first host and a second host, and optionally further including a dopant is not particularly limited as long as it is a method known in the art, and for example, a co-deposition method, a vacuum vapor deposition method, a solution coating method, etc. There is this. Examples of the co-deposition method include the following methods.

As an example, the first host and the second host are respectively positioned in first and second heat sources, and a dopant is positioned in the third heat source, and heat is simultaneously applied to co-deposit to form a light emitting layer.

Specifically, at a vacuum degree of 1×10 ^-0.6 torr or less, a first host with high electron mobility and good electron injection efficiency is placed in the first heat source, and hole mobility is high and hole injection This is a method of co-depositing at an appropriate rate by simultaneously controlling the evaporation rate per second of each material after placing a second host with good efficiency in a second heat source, and placing a dopant in a third heat source. At this time, the number of hosts to be co-deposited may be two or more depending on the characteristics of the emission layer.

As another example, the first host and the second host used for forming the light emitting layer are mixed at an appropriate ratio, placed in one heat source, and co-deposited by applying heat to form a light emitting layer. Compared to the above-described method, this method has fewer heat sources and a simpler formation process.

Specifically, a host (first host + second host) mixed with a first heat source is placed at a vacuum degree of 1×10 ^-0.6 torr or less, a dopant is placed in a second heat source, and the evaporation rate per second of each material is At the same time, it is adjusted to form a light emitting layer. In this method, when one or more types of hosts are used, an error in the mixing ratio of one or more types of hosts can be reduced, and a light emitting layer can be formed using a small number of heat sources.

The organic electroluminescent device of the present invention includes an anode, a cathode, and one or more organic material layers interposed between the anode and the cathode.

The one or more organic material layers may be any one or more of a hole injection layer, a hole transport layer, an emission layer, an electron transport layer, and an electron injection layer, wherein the emission layer includes the aforementioned first host and second host. By including such a light emitting layer, the organic electroluminescent device of the present invention can further improve efficiency (luminescence efficiency and power efficiency), lifespan, luminance, and driving voltage as compared to a conventional organic electroluminescent device having a light emitting layer including a single host. I can.

The structure of the organic EL device is not particularly limited, and for example, a substrate, an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode may be sequentially stacked. In this case, the emission layer includes a first host and a second host, as described above, and the second host has a HOMO-LUMO energy gap equal to or greater than the first host, or It is a material having a LUMO energy level greater than that of the first host. In some cases, an electron injection layer may be additionally stacked on the electron transport layer. In addition, an insulating layer or an adhesive layer may be further inserted at the interface between the electrode and the organic material layer.

The organic electroluminescent device according to the present invention may be manufactured by forming other organic material layers and electrodes using materials and methods known in the art, except for forming the emission layer as described above.

An organic material layer other than the light emitting layer may be formed by a vacuum deposition method or a solution coating method. Examples of the solution coating method include, but are not limited to, spin coating, dip coating, doctor blading, inkjet printing, or thermal transfer method.

The substrate usable in the present invention is not particularly limited, and a silicon wafer, quartz, glass plate, metal plate, plastic film and sheet, and the like may be used.

In addition, as the anode material, metals such as vanadium, chromium, copper, zinc, and gold, or alloys thereof; Metal oxides such as zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); Combinations of metals and oxides such as ZnO:Al or SnO ₂ :Sb; Conductive polymers such as polythiophene, poly(3-methylthiophene), poly[3,4-(ethylene-1,2-dioxy)thiophene] (PEDT), polypyrrole or polyaniline; And carbon black, but are not limited thereto.

In addition, as a negative electrode material, a metal such as magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, aluminum, silver, tin, or lead, or an alloy thereof; And a multi-layered material such as LiF/Al or LiO ₂ /Al, but is not limited thereto.

In addition, the hole injection material is a material capable of well injecting holes from the anode at a low voltage, and it is preferable that the HOMO (highest occupied molecular orbital) of the hole injection material is between the work function of the anode material and the HOMO of the surrounding organic material layer. . Specific examples of hole injection materials include metal porphyrine, oligothiophene, arylamine-based organic substances, hexanitrile hexaazatriphenylene-based organic substances, quinacridone-based organic substances, and perylene-based organic substances. Organic substances, anthraquinone, polyaniline, and polythiophene-based conductive polymers, etc., but are not limited thereto.

In addition, as the hole transport material, a material capable of transporting holes from an anode or a hole injection layer to the light emitting layer and having high mobility for holes is suitable. Specific examples include an arylamine-based organic material, a conductive polymer, and a block copolymer including a conjugated portion and a non-conjugated portion, but are not limited thereto.

As the electron transport material, a material capable of receiving electrons well from the cathode and transferring them to the light emitting layer, and a material having high mobility for electrons is suitable. Specific examples include Al complex of 8-hydroxyquinoline; Complexes containing Alq ₃ ; Organic radical compounds; Hydroxyflavone-metal complexes and the like, but are not limited thereto.

Hereinafter, the present invention will be described in detail through examples, but the following examples are only illustrative of the present invention, and the present invention is not limited by the following examples.

[ Example 1] organic Electric field Manufacturing of light emitting devices

The glass substrate coated with ITO (Indium tin oxide) with a thickness of 1500 Å was ultrasonically washed with distilled water. After washing with distilled water, ultrasonically clean with a solvent such as isopropyl alcohol, acetone, methanol, etc., dry, transfer to a UV OZONE cleaner (Power Sonic 405, Hwashin Tech), and clean the substrate for 5 minutes using UV. The substrate was transferred to a vacuum evaporator.

CuPc (10 nm) / TPAC (30 nm) / first host (PBH-1) + second host (PBH-4) + 10% Flrpic (30 nm) / Alq ₃ (30 nm) on the ITO transparent substrate prepared as above )/ LiF (0.2 nm)/Al (150 nm) were stacked in order to fabricate an organic EL device. Here, the mixing ratio of the first host and the second host was 3:7 weight ratio.

At this time, the structures of CuPc, TPAC, Flrpic and PBH-1 and PBH-4 used are as follows, and their HOMO energy level, LUMO energy level, and band gap are shown in Table 1 below.

[Example 2] ~ [Example 9] Fabrication of an organic electroluminescent device

An organic electric field device was manufactured in the same manner as in Example 1, except that each compound shown in Table 2 below was used instead of PBH-1 and PBH-4 used as hosts of the emission layer in Example 1.

At this time, the structures of PBH-1 to PBH-6 used are as described in Example 1.

[Comparative Example 1] Fabrication of an organic electroluminescent device

An organic electroluminescent device was manufactured in the same manner as in Example 1, except that CBP was used instead of PBH-1 and PBH-4 used for forming the emission layer in Example 1. At this time, the structure of the used CBP is as follows.

[Comparative Example 2] Fabrication of an organic electroluminescent device

An organic electroluminescent device was manufactured in the same manner as in Example 1, except that PBH-5 was used instead of PBH-1 and PBH-4 used for forming the emission layer in Example 1.

[Comparative Example 3] Fabrication of an organic electroluminescent device

An organic electroluminescent device was manufactured in the same manner as in Example 1, except that PBH-2 was used instead of PBH-1 and PBH-4 used for forming the emission layer in Example 1.

[Experimental Example]

For the organic electroluminescent devices prepared in Examples 1 to 9 and Comparative Examples 1 to 3, respectively, driving voltage and current efficiency at a current density of 10 mA/cm 2 were measured, and the results are shown in Table 2 below.

Sample Host Driving voltage (V) EL peak
(nm) Current efficiency (cd/A) First host Second host Example 1 30% PBH-1 70% PBH-4 6.50 480 6.99 Example 2 30% PBH-1 70% PBH-5 6.45 485 6.85 Example 3 30% PBH-1 70% PBH-6 6.70 471 7.34 Example 4 30% PBH-2 70% PBH-4 6.10 475 6.90 Example 5 30% PBH-2 70% PBH-5 6.50 479 7.34 Example 6 30% PBH-2 70% PBH-6 6.20 470 6.55 Example 7 30% PBH-3 70% PBH-4 6.00 482 6.94 Example 8 30% PBH-3 70% PBH-5 6.40 485 7.25 Example 9 30% PBH-3 70% PBH-6 6.20 472 7.47 Comparative Example 1 CBP 7.80 474 5.80 Comparative Example 2 PBH-5 7.50 473 6.20 Comparative Example 3 PBH-2 7.40 474 6.10

Referring to Table 2, the organic electroluminescent devices (Examples 1 to 9) of the present invention using the emission layer including the first host and the second host include conventional CBP or PBH-2, PBH-5 as a single host material. It was confirmed that the organic electroluminescent devices using the light emitting layer (Comparative Examples 1 to 3) exhibited superior performance in terms of current efficiency and driving voltage.

Claims (8)

anode; cathode; And one or more organic material layers interposed between the anode and the cathode,
At least one of the one or more organic material layers includes a blue phosphorescent emission layer including a first host and a second host,
The first host and the second host each have a singlet energy in the range of 3.185 to 4.110 eV,
The second host has a HOMO-LUMO energy gap equal to or greater than the first host, or an LUMO energy level greater than that of the first host. The method of claim 1,
The second host is an organic electroluminescent device, characterized in that the HOMO-LUMO energy gap is 0.1 to 2.0 eV greater than the first host, or the LUMO energy level is 0.1 to 1.0 eV greater than the first host. The method of claim 1,
The first host has a HOMO-LUMO energy gap in a range of 3.0 to 5.0 eV, a LUMO energy level in a range of 1.0 to 3.0 eV,
The second host is an organic electroluminescent device, characterized in that the HOMO-LUMO energy gap is in the range of 3.0 ~ 6.0 eV, the LUMO energy level is in the range of 0.5 ~ 3.0 eV. The method of claim 1,
Each of the first host and the second host has a triplet energy of 2.8 eV or more. The method of claim 1,
The first host is selected from the group consisting of a carbazole-based compound, a phosphine oxide-based compound, and a bipyrimidine-based compound,
The second host is an organic electroluminescent device, characterized in that the silane-based compound, carbazole-based compound, or carboline-based compound. The method of claim 1,
The first host and the second host is an organic electroluminescent device, characterized in that included in a weight ratio of 1 ~ 99: 99 ~ 1. The method of claim 1,
The blue phosphorescent emission layer further includes a dopant,
The dopant is an organic electroluminescent device, characterized in that the iridium-containing metal complex compound. The method of claim 7,
The (a) first host, the second host, and (b) the dopant is an organic electroluminescent device, characterized in that included in a weight ratio of 70 ~ 99:30 ~ 1.