KR100659072B1 - Organic electroluminescent element - Google Patents

Abstract

The present invention provides an organic electroluminescent device having a light emitting layer between a pair of electrodes, wherein the light emitting layer includes at least two light emitting host materials, a dopant and a light emitting assistant. By using the light emission aid according to the present invention it is possible to increase the energy transfer efficiency to improve the efficiency and life characteristics of the device.

Description

Organic electroluminescence display

1 is a cross-sectional view of an organic electroluminescent device according to an embodiment of the present invention.

2 is a view showing an embodiment and a comparative example according to the present invention for the efficiency characteristics of the organic electroluminescent device.

3 is a view showing an embodiment and a comparative example according to the present invention for the life characteristics of the organic EL device.

The present invention relates to an organic electroluminescent device, and more particularly, to an organic electroluminescent device having improved efficiency and lifespan characteristics by using a light emission aid.

Electroluminescent devices (EL devices) are self-luminous display devices that have a wide viewing angle, excellent contrast, and fast response time. EL elements are classified into inorganic EL elements and organic EL elements according to materials for forming an emitting layer. Herein, the organic EL device has an advantage of excellent luminance, driving voltage, and response speed, and multicoloring, compared to the inorganic EL device.

A typical organic electroluminescent device has an anode formed on the substrate, and the hole transport layer (HTL), the light emitting layer (EML), the electron transport layer (ETL) and the cathode (cathode) are sequentially formed on the anode. Have Here, the hole transport layer, the light emitting layer, and the electron transport layer are organic thin films made of an organic compound.

The driving principle of the organic EL element is that when a voltage is applied between the anode and the cathode, holes injected from the anode are moved to the light emitting layer via the hole transport layer. On the other hand, electrons are injected into the light emitting layer from the cathode via the electron transport layer, and carriers are recombined in the light emitting layer to generate excitons. The exciton is changed from the excited state to the ground state, whereby the fluorescent molecules in the light emitting layer emit light to form an image. At this time, the excited state falls to the ground state through the singlet excited state and emits light is called 'fluorescence', and the triplet excited state falls to the ground state through the excited state is called 'phosphorescence'. In the case of fluorescence, the probability of singlet excited state is 25% (triple state 75%) and there is a limit of luminous efficiency, whereas phosphorescence can be used to triplet 75% and singlet excited state 25%. Can be up to 100% internal quantum efficiency. Referring to Nature 750 (2000, vol. 75), the triplet state using a phosphorescent pigment Ir (ppy) ₃ and PtOEP as a dopant, which has heavy elements such as Ir and Pt with large spin-orbit coupling, is used as a dopant. An organic electroluminescent device having excellent efficiency has been developed by emitting light effectively even in (phosphorescence).

Recently, a method of using a carbazole compound having a triplet energy band gap larger than CBP as a host when forming an emission layer using a phosphorescent material is known.

However, when the carbazole compound known to date is used, there is much room for improvement because the efficiency and lifespan characteristics of the phosphorescent device do not reach a satisfactory level.

The technical problem to be achieved by the present invention is to solve the above problems to provide an organic EL device having excellent efficiency and life characteristics.

In order to achieve the above technical problem, the present invention is an organic electroluminescent device having a light emitting layer between a pair of electrodes,

The light emitting layer provides an organic electroluminescent device comprising at least two light emitting host materials, a dopant and a light emitting agent.

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

In the present invention, the efficiency and lifespan characteristics of the organic EL device are improved by using two or more host materials and forming a light emitting agent (sensitizer) together when forming a light emitting layer including a phosphorescent dopant between a pair of electrodes.

According to one embodiment of the present invention, the material having the characteristics of the light emission aid is a transition metal compound. The transition metal serves to assist energy transfer between two or more mixed hosts and the light emitting dopant in the light emitting layer of the organic light emitting device in the form of an organometallic complex.

In general, an organic light emitting device has a light emitting layer composed of only one host and a dopant, and the energy transfer used in the light emission is performed between the host and the dopant and is driven using only the dopant light emission.

In the present invention, the light-emitting aid is added to the energy that can not be used for light emission in addition to the direct energy transfer between the general host and the dopant, it is a method that can be used for light emission by indirectly to the dopant through the light-emitting assistant. This increases the energy transfer efficiency and increases the luminous properties and device life of the device.

In order to be used as a luminescent aid, it is preferable that the luminescent aid has an absorption spectrum in the luminescent spectral region exiting the host, and that the luminescent spectrum of the luminescent aid matches the absorption spectrum of the luminescent dopant. This is to absorb energy from the host well and to convert it into an energy region where the luminescent dopant is advantageous to absorb.

The luminescent aid is a transition metal element Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg and Lanthanide Elements Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu It can be selected from the group. It is used in the form of the said transition metal and organometallic complex compound, Preferably it is a transition metal complex compound chosen from Ir, Pt, and Tm. For example, luminescent aids include Ir (ppy) ₃ [tris (2-phenylpyridine) Iridium], PtOEP [2,3,7,8,12,13,17,18-octaethyl-12H, 23H-porhine platium (II). )] And Btp2Ir (acac) [bis (2- (20-benzo [4,5-a] thienyl) pyridinato-N, C30) Iridium (acetylactonate)].

In particular, among the light emission aids usable in the present invention, various iridium metal compounds may be used, and these materials are also materials usable as green light emitting dopants. For example, Ir (ppy) ₃ [tris (2-phenylpyridine) Iridium], Ir (ppz) ₃ [tris (phenylpyrazole) Iridium], etc. are mentioned.

Materials used as luminescent aids should be materials with a wider energy bandgap (energy gap between HOMO and LUMO) than luminescent dopants. Here, the HOMO of the adjuvant is located between the host and the HOMO of the light emitting dopant, and the LUMO of the adjuvant is also preferably located between the host and the LUMO of the light emitting adjuvant. That is, a blue light emitting dopant having a wide energy band gap may be used as an adjuvant to any of green and red light emitting dopants provided that the energy level is matched with the host.

In the present invention, the preferred amount of the light-emitting assistant used depends on the combination of the light-emitting assistant and the light-emitting dopant, but generally from 0.1 to 100 parts by weight based on the total weight of the light-emitting layer forming material (ie, the total weight of the host, the dopant and the light-emitting assistant). It is preferable that it is 50 weight part. If it is less than 0.1 part by weight, the effect is insignificant, and the efficiency and life characteristics do not appear. If the content is more than 50 parts by weight, the luminescent aid emits light or acts as a luminescent attenuator.

According to one embodiment of the present invention, the two or more host materials are preferably two or more low molecular materials selected from a hole transport material, an electron transport material.

The hole transporting material having the hole transporting property uses a carbazole compound, and examples of the carbazole compound include 1,3,5-tricarbazolylbenzene and 4,4'-biscarbazolyl. Biphenyl {4,4'-biscarbazolylbiphenyl (CBP)}, m-biscarbazolylphenyl, 4,4'-biscarbazolyl-2,2'-dimethylbiphenyl {(4,4'- biscarbazolyl-2,2'-dimethylbiphenyl) [dmCBP]}, 4,4 ', 4 "-tri (N-carbazolyl) triphenylamine {4,4', 4" -tri (N-carbazolyl) triphenylamine}, 1,3,5-tri (2-carbazolylphenyl) benzene {1,3,5-tris (2-carbazolylphenyl) benzene}, 1,3,5-tris (2-carbazolyl-5-methoxyphenyl) It is preferably at least one selected from the group consisting of benzene {1,3,5-tris (2-carbazolyl-5-methoxyphenyl) benzene} and bis (4-carbazolylphenyl) silane}.

The material having an electron transporting property may be at least one compound selected from an organometallic complex including a metal and an organic ligand, a spirofluorene compound, an oxadiazole compound, a phenanthroline compound, a triazine compound, and a triazole compound. Can be.

Examples of the organometallic complex include bis (8-hydroxyquinolato) biphenoxy metal and bis (8-hydroxyquinolato) phenoxy metal. -hydroxyquinolato) phenoxy metal}, bis (2-methyl-8-hydroxyquinolato) biphenoxy metal {bis (2-methyl-8-hydroxyquinolato) biphenoxy metal}, bis (2-methyl-8-hydroxy Quinolato) phenoxy metal) {bis (2-methyl-8-hydroxyquinolato) phenoxy metal}, bis (2-methyl-8-quinolinolato) (para-phenyl-phenolato) metal {Bis (2- group consisting of methyl-8-quinolinolato) (para-phenyl-phenolato) metal} and bis (2- (2-hydroxyphenyl) quinolato) metal {bis (2- (2-hydroxyphenyl) quinolato) metal} At least one selected from, and the metal is Al, Zn, Be, or Ga.

The electron transporting materials are bis (8-hydroxyquinolato) biphenoxy aluminum, bis (8-hydroxyquinolato) phenoxy aluminum, bis (2-methyl-8-hydroxyquinolato) biphenoxy Ci aluminum, bis (2-methyl-8-hydroxyquinolato) phenoxy aluminum, bis (2-methyl-8-quinolinolato) (para-phenyl-phenolato) aluminum (BAlq), or bis ( Preference is given to 2- (2-hydroxyphenyl) quinolato) zinc.

The spirofluorene-based compound is a structure having a linking ring between two spirofluorenes, the linkage is triazole, oxadiazole, naphthalene, anthracene ), Phenyl, or the like, and the position 9 of each fluorene is substituted with O, S, Se, NR, PR, or the like, or NR or PR is directly connected between two spirofluorenes. It can be a structure that connects. Each R is H, or a C 6 to C 20 alkyl group, a C 5 to 20 aryl group having 1 to 20 carbon atoms, a C 2 to 20 heteroaryl group, and a C 1 to 20 alkoxy group having 6 carbon atoms It is a substituent selected from the group which consists of the aryl group of 20. Preferably, the spirofluorene-based compound is 2,5-disspirobifluorene-1,3,4-oxadiazole (2,5-Dispirobifluorene-1,3,4-oxadiazole).

Examples of the oxadiazole-based compound include (4-biphenylyl) -5- (4-tertbutylphenyl) -1,3,4-oxadiazole and the like, and examples of the phenanthroline-based compound include 2,9-dimethyl-4,7-diphenyl-9,10-phenanthroline (BCP), and the like. Examples of the triazine-based compound include 2,4,6-tris (diphenylamino) -1. , 3,5-triazine, 2,4,6-tricarbazolo-1,3,5-triazine, 2,4,6-tris (N-phenyl-2-naphthylamino) -1,3, 5-triazine or 2,4,6-tris (N-phenyl-1-naphthylamino) -1,3,5-triazine, etc. are mentioned. Examples of the triazole-based compound include 3-phenyl-4- (1'-naphthyl) -5-phenyl-1,2,4-triazole.

The content of two or more hosts in the light emitting layer is preferably 50 to 99 parts by weight based on 100 parts by weight of the total weight of the light emitting layer forming material. If less than 50 parts by weight of the triplet quenching phenomenon occurs, the efficiency is lowered, if more than 99 parts by weight is insufficient because the light emitting material is insufficient efficiency and life characteristics is not preferable.

The dopant used in forming the light emitting layer of the present invention is a light emitting material, and non-limiting examples thereof include bisthienylpyridine acetylacetonate Iridium, bis (benzothienylpyridine) acetylacetonate iridium {bis (benzothienylpyridine) acetylacetonate Iridium}, bis (2-phenylbenzothiazole) acetylacetonate iridium {Bis (2-phenylbenzothiazole) acetylacetonate Iridium}, bis (1-phenylisoquinoline) iridium acetylacetonate {bis (1-phenylisoquinoline) Iridium acetylacetonate} , Tris (1-phenylisoquinoline) Iridium}, and tris (2-phenylpyridine) Iridium} (Ir (ppy) ₃ ) One or more phosphorescent dopants.

Hereinafter, the manufacturing method of the organic EL device of the present invention will be described.

Referring to Figure 1 describes a method for manufacturing an organic EL device according to an embodiment of the present invention.

First, an anode is formed on a substrate by coating an anode material, which is a first electrode. Herein, a substrate used in a conventional organic electroluminescent device is used, but a glass or organic substrate or a transparent plastic substrate having excellent transparency, surface smoothness, ease of handling, and waterproofness is preferable. The anode material may be a high work function metal (≥4.5 eV), or a transparent and highly conductive indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO ₂ ), and zinc oxide. (ZnO) or the like is used.

Each organic thin film layer on top of the anode is subjected to thermal evaporation in high vacuum, or dissolved in a solution depending on the type of material used, followed by spin-coating, dip-coating, It may be formed using a method such as doctor-blading, inkjet printing, or thermal transfer, and it is preferable to use thermal evaporation.

A hole injection layer HIL is selectively formed on the anode. It is preferable that the thickness of a hole injection layer is 50-1500 kPa here. If the thickness of the hole injection layer is less than 50 kV, the hole injection characteristic is lowered.

The hole injection layer material is not particularly limited, and copper phthalocyanine (CuPc) or Starburst type amines such as TCTA, m-MTDATA, IDE406 (Idemitsu Corp. material), and the like may be used as the hole injection layer.

A hole transport layer (HTL) is selectively formed by vacuum thermal evaporation or spin coating of the hole transport layer material on the hole injection layer formed by the above process. The hole transport material is not particularly limited, and N, N'-bis (3-methylphenyl) -N, N'-diphenyl- [1,1-biphenyl] -4,4'-diamine (TPD), N, N'-di (naphthalen-1-yl) -N, N'-diphenyl benzidine, IDE320 (made by Idemitsu Corp.), etc. are used. It is preferable that the thickness of a positive hole transport layer is 50-1500 kPa here. If the thickness of the hole transport layer is less than 50 kV, the hole transport property is deteriorated. If the hole transport layer is more than 1500 kV, it is not preferable because of the increase in driving voltage.

Subsequently, the light emitting layer EML is formed on the hole transport layer using a conventional light emitting material. The light emitting material may use two or more host materials. As described above, it may be one of two or more hole transport materials, hole transport materials and electron transport materials, or two or more electron transport materials. A light emitting layer (EML) is formed using phosphorescent dopants with two or more host materials. The light emitting layer forming method is not particularly limited, but vacuum deposition, spin-coating, dip-coating, doctor-blading, inkjet printing, laser transfer, photolithography or photolithography.

It is preferable that the thickness of the said light emitting layer is 100-800 GPa. If the thickness of the light emitting layer is less than 100 kW, the efficiency and lifetime are lowered, and if the thickness of the light emitting layer exceeds 800 kW, the driving voltage increases, which is not preferable.

A hole blocking layer (HBL) is selectively formed on the light emitting layer by coating using a material for hole blocking. The material for the hole blocking layer used at this time is not particularly limited, but should have an ionization potential higher than that of the light emitting compound while having an electron transport ability, and typically Balq, BCP, TPBI, and the like are used. If the thickness of the hole blocking layer is preferably 30 to 500 kPa. If the thickness of the hole blocking layer is less than 30 kW, the hole blocking property is not good and the efficiency is lowered.

An electron transport layer forms an electron transport layer (ETL) on the hole blocking layer as a vacuum deposition method or a spin coating method. It does not restrict | limit especially as an electron carrying layer material, Alq3 can be used. It is preferable that the thickness of the said electron carrying layer is 50-600 GPa. If the thickness of the electron transport layer is less than 50 kW, the lifespan characteristics are lowered. If the electron transport layer is more than 600 kW, it is not preferable to increase the driving voltage.

In addition, an electron injection layer EIL may be selectively stacked on the electron transport layer. As the electron injection layer forming material, materials such as LiF, NaCl, CsF, Li ₂ O, BaO, and Liq can be used. It is preferable that the thickness of the said electron injection layer is 1-100 kPa. If the thickness of the electron injection layer is less than 1 kW, the driving voltage is not high because it does not serve as an effective electron injection layer, and if it exceeds 100 kW, the driving voltage acts as an insulating layer.

Subsequently, the cathode, which is the second electrode, is deposited on the electron injection layer using a method such as vacuum thermal deposition, sputtering, and metal-organic chemical vapor deposition. By forming, an organic electroluminescent element is completed.

The cathode metal is lithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium (Al-Li), calcium (Ca), magnesium-indium (Mg-In), magnesium-silver (Mg-Ag ) And the like are used.

The organic electroluminescent device of the present invention may further form or omit an intermediate layer of one or two layers according to the needs of the anode, the hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer, the electron injection layer, and the cathode.

Hereinafter, the present invention will be described with reference to the following examples, but the present invention is not limited only to the following examples.

Example 1

The anode cuts a corning 15Ω / cm ² (1200Å) ITO glass substrate to 50mm x 50mm x 0.7mm and ultrasonically cleans for 5 minutes in isopropyl alcohol and pure water, followed by UV and ozone cleaning for 30 minutes. Was used.

N, N'-di (1-naphthyl) -N, N'-diphenylbenzidine (N, N'-di (1-naphtyl) -N, N'-diphenylbenzidine (NPD)) was vacuum deposited on the substrate. Thus, a hole transport layer was formed to a thickness of 600 kPa.

66 parts by weight of two host materials CBP and 22 parts by weight of BAlq and 11 parts by weight of a phosphorescent dopant Ir (pq) 2 (acac) on top of the hole transport layer, together with 1% of tris (2-phenylpyridine) as a luminescent aid. 1 part by weight of iridium Ir (ppy) ₃ was vacuum deposited to form a light emitting layer having a thickness of about 400 GPa.

Alq ₃ , an electron transporting material, was deposited on the emission layer to form an electron transporting layer having a thickness of about 300 μs.

LiF 10 전극 (electron injection layer) and Al 1000 Å (cathode) were sequentially vacuum deposited on the electron transport layer to form a LiF / Al electrode, thereby manufacturing an organic EL device as shown in FIG. 1.

Example 2

An organic electroluminescent device was manufactured in the same manner as in Example 1, except that 3 parts by weight of Ir (ppy) ₃ was used as a light emission aid.

Comparative Example 1

The anode cuts a corning 15Ω / cm ² (1200Å) ITO glass substrate to 50mm x 50mm x 0.7mm and ultrasonically cleans for 5 minutes in isopropyl alcohol and pure water, followed by UV and ozone cleaning for 30 minutes. Was used.

N, N'-di (1-naphthyl) -N, N'-diphenylbenzidine (N, N'-di (1-naphtyl) -N, N'-diphenylbenzidine (NPD)) was vacuum deposited on the substrate. Thus, a hole transport layer was formed to a thickness of 600 kPa.

A light emitting layer was formed on the hole transport layer by vacuum depositing 12 parts by weight of phosphorescent dopant Ir (pq) 2 (acac) at 66 parts by weight of the host CBP and 22 parts by weight of BAlq.

Alq3, an electron transporting material, was deposited on the emission layer to form an electron transporting layer having a thickness of about 300 kHz.

LiF 10 전극 (electron injection layer) and Al 1000 Å (cathode) were sequentially vacuum deposited on the electron transport layer to form a LiF / Al electrode, thereby manufacturing an organic EL device as shown in FIG. 1.

In the organic EL device manufactured according to Example 1-2 and Comparative Example 1, the luminous efficiency, power efficiency and lifespan characteristics were investigated.

As a result, the luminance of the organic electroluminescent elements of Examples 1 and 2 was 5.6 cd / A at 800 cd / m 2, respectively. And 5.7 cd / A, and the luminance of the organic electroluminescent device of Comparative Example 1 is 4.7 cd / A at 800 cd / m 2, and the above examples have improved efficiency compared to the comparative example.

In addition, the power efficiency of the organic EL device of Comparative Example 1 is 2.4lm / W, the organic EL device of Example 1 and Example 2 has a power efficiency of 2.71lm / W and 2.95lm / W of Comparative Example 1 Compared to the case, the power efficiency is improved.

In addition, the lifespan characteristics are represented by the time when the initial emission luminance decreases by 50%. The organic electroluminescent device of Example 1 is 1,500 hours at 4,000 cd / m ² , and the organic electroluminescent device of Comparative Example 1 is 4,000 cd / m. ^{It was found that 2} to 300 hours, Example 1 was significantly improved life characteristics compared to the case of Comparative Example 1.

Luminescent aids are used in addition to at least two hosts and dopants in forming the light emitting layer of the organic light emitting device. By using a light emitting aid in the light emitting layer, energy that cannot be used for light emission other than the direct energy transfer between the general host and the dopant can be used for light emission by transferring energy to the dopant in an indirect manner through the light emitting aid. By using the light emission aid according to the present invention it is possible to increase the energy transfer efficiency to increase the efficiency and life characteristics.

Claims (10)

In an organic electroluminescent device having a light emitting layer between a pair of electrodes, The light emitting layer is an organic electroluminescent device comprising at least two low molecular host materials selected from a hole transport material, an electron transport material, a dopant and a light emitting aid (sensitizer), the light emitting aid is tris (2-phenylpyridine) iridium [Ir (ppy ) ₃ ], 2,3,7,8,12,13,17,18-octaethyl-12H, 23H-phosphine platinum (II) [PtOEP], and bis (2- (20-benzo [4, 5-a] thienyl) pyridinato-N, C30) iridium (acetylacetonate) [Btp2Ir (acac)] It is an organic electroluminescent device characterized by the above-mentioned. delete delete delete delete The organic electroluminescent device according to claim 1, wherein the content of the light emitting assistant in the light emitting layer is 0.1 to 50 parts by weight based on 100 parts by weight of the total weight of the light emitting layer forming material. delete The method of claim 1, wherein the hole transport material is 1,3,5-tricarbazolylbenzene, 4,4'-biscarbazolylbiphenyl, m-biscarbazolylphenyl, 4,4'-biscarbazolyl-2 , 2'-dimethylbiphenyl, 4, 4 ', 4 "-tri (N-carbazolyl) triphenylamine, 1,3,5-tri (2-carbazolylphenyl) benzene, 1,3,5-tris An organic electroluminescent device, characterized in that at least one carbazole compound selected from the group consisting of (2-carbazolyl-5-methoxyphenyl) benzene, and bis (4-carbazolylphenyl) silane. The method of claim 1, wherein the electron transporting material is bis (8-hydroxyquinolato) biphenoxy aluminum, bis (8-hydroxyquinolato) phenoxy aluminum, bis (2-methyl-8-hydroxy Quinolato) biphenoxy aluminum, bis (2-methyl-8-hydroxyquinolato) phenoxy aluminum, bis (2-methyl-8-quinolinolato) (para-phenyl-phenololato) aluminum, An organic electroluminescent device, which is 2,5-disspirobifluorene-1,3,4-oxadiazole or bis (2- (2-hydroxyphenyl) quinolato) zinc. The method of claim 1, wherein the dopant in the light emitting layer, bisthienylpyridine acetylacetonate iridium, bis (benzothienylpyridine) acetylacetonate iridium, bis (2-phenylbenzothiazole) acetylacetonate iridium, bis (1 -Phenyl isoquinoline) iridium acetylacetonate, tris (1-phenylisoquinoline) iridium, and tris (2-phenylpyridine) iridium organic electroluminescent device characterized in that at least one selected from the group consisting of.

Images