JP4956151B2 - Light emitting element - Google Patents

Description

  The present invention relates to a light emitting element using an organic compound.

  In the organic EL element, a process of applying a voltage to the positive electrode and the negative electrode and injecting carriers (holes and electrons) from the electrode to the organic layer with high efficiency is important for high efficiency light emission. Therefore, a carrier injection material having high performance is desired.

  As the electron injection material, an inorganic compound containing a highly reducible metal such as an aluminum lithium alloy (AlLi), a magnesium silver alloy (AgMg), or lithium fluoride is used. However, these compounds have high reactivity, are unstable in the air, are difficult to handle, and have problems such as poor light emission stability of the organic EL element.

A typical example of the hole injection material is copper phthalocyanine (Non-Patent Document 1 ). Copper phthalocyanine improves hole injectability, but has a problem of absorption in the visible light region and absorption of EL light emission from the light emitting layer. Copper phthalocyanine has a radical localized to Cu ions. The property of copper phthalocyanine that oxidizes is mainly governed by the property of phthalocyanine, which is a ligand, and the radical of Cu ions does not dominate the property of oxidation.

Recently, Non-Patent Document 2 published a study using a nickel complex having a specific structure for an active layer of an organic transistor. Since this nickel complex has a radical in the ligand, it is electrochemically active and oxidation / reduction is easily performed. A transistor with good performance is obtained by using a film formed by vacuum deposition for a transistor. However, although there is a description regarding carrier transportability in the transistor, there is no description about an application example to the organic LED as in the present invention.

Coordination Chemistry Reviews, 171, 161-174 (1998) Journal of American Chemical Society (ASAP DOI No. 10.1021 / ja052663s)

  An object of the present invention is to provide a carrier injection material capable of realizing high luminous efficiency, and to provide a light emitting element with high luminous efficiency.

［Ｍは、ＮｉまたはＰｔである。
Ｒは水素原子である。
ｎは２である。
式（２）および（６）において、配位子中のＣＨ基の水素原子はｔｅｒｔ−ブチル基に置換されてもよい。
・はラジカルを表す。］ That is, the light-emitting element of the present invention is a light-emitting element having a light-emitting layer and a layer other than the light-emitting layer between two electrodes, and the layer other than the light-emitting layer is represented by either of the following general formulas (2) or (6). have a metal coordination compound, a layer other than the light emitting layer is characterized by contacting the either one of the two electrodes.

[M is Ni or Pt.
R is a hydrogen atom.
n is 2.
In the formulas (2) and (6), the hydrogen atom of the CH group in the ligand may be substituted with a tert-butyl group.
-Represents a radical. ]

  The metal coordination compound of the present invention has high luminous efficiency, high stability, and low cost, and is useful for a carrier injection layer of an organic EL device. Therefore, the light-emitting element of the present invention exhibits high light emission efficiency.

  Hereinafter, the present invention will be described in detail.

  First, the characteristics of the metal coordination compound used in the present invention will be described using the nickel metal coordination compound (8) shown below as an example.

  The nickel ion of this coordination compound has a formal charge of divalent (Ni (II)) and is neutralized in the whole complex by two minus monovalent bidentate ligands. Ni (II) usually has a planar four-coordinate structure, and this complex also has a planar structure.

  What is characteristic is that the ligand has a radical, and due to the presence of the radical in this ligand, (a) the band gap is very narrow (1.01 eV), (b) electrochemically. It is active and easily oxidized and reduced. The radical in the chemical structural formula (8) is delocalized throughout the ligand because of various resonance structures. The resonance structure is represented by the following structural formula.

  As understood from this formula, the ligand in the chemical structural formula (8) is formally minus monovalent and has one radical, and the radical and minus monovalent charge are Is delocalized.

  Furthermore, the structural formula of the metal coordination compound also has several resonance structures, some of which are shown below.

  In the above formula, the leftmost structural formula is a representative example of the resonance structural formula of the ligand containing the above radical.

  Therefore, the chemical structural formulas shown in the general formulas (1) to (7) described later show one of the resonance structures for convenience.

  The details of the electronic state of the metal coordination compound of the present invention are described in Journal of American Chemical Society, 125, 10997-11005 (2003). Metal coordination compounds such as Ni, Pd, and Pt have two radicals in total, but their spins are antiparallel to each other, and the ground state is singlet. Therefore, these compounds are diamagnetic.

  In Ni, Pd, Pt, and Cu, two bidentate ligands are coordinated in a plane, whereas in Co, Rh, and Ir, three bidentate ligands are coordinated in an octahedral form. Co, Rh, and Ir are paramagnetic because there are three (odd) radicals on the ligand.

  Since the radical delocalized on the ligand as described above is active in both oxidation and reduction, it can be used for both the electron injection layer and the hole injection layer. Oxidation reduction is represented by the following chemical reaction formula.

  In these layers, the metal coordination compound of the present invention may be used alone, or may be used by blending with an organic material or metal complex material having a hole or electron transport capability. When blended, it is easy not only to receive holes or electrons from the electrode, but also oxidizes / reduces other compounds blended with the metal coordination compound of the present invention, and the redox species of the other compounds become holes or electrons. In some cases, injection from the electrodes may be promoted.

  Further, since the metal coordination compound of the present invention can promote the injection of both holes and electrons, the same compound can be arranged on both the cathode side and the anode side to improve the hole / electron injection efficiency.

Further, when applied to a light emitting element, if other constituent materials absorb the light emitted in the light emitting layer, it may cause a decrease in light emission efficiency. When this metal coordination compound is used, since the band gap is very small, the absorption spectrum peak is at 790 nm (12660 cm ⁻¹ ) and is in the infrared region, and thus the light emission of the organic EL element that emits visible light is strongly absorbed. There is nothing. For reference, copper phthalocyanine, which is a typical hole injection material, has a problem that the wavelength has a strong absorption near 600 nm, and absorbs red light emission, resulting in a decrease in efficiency. Even if the copper phthalocyanine film is made very thin in order to minimize the absorption of EL emission, the EL emission is affected by the absorption of the carrier transport layer due to the multiple reflection in the emission layer, and the emission efficiency decreases. Invite. Therefore, the present inventors consider that the metal coordination compound of the present invention is suitable for a carrier injection material in consideration of the strong redox property and absorption in the weak visible light region, which are the characteristics of the metal coordination compound of the present invention. This led to the present invention.

  The metal coordination compound used in the present invention may be a nonionic metal coordination compound or diamagnetic. Moreover, you may have multiple ligands which have a radical.

  Examples of the metal coordination compound used in the present invention include a metal coordination compound having a partial structural formula represented by the following general formula (1). And it is preferably a metal coordination compound represented by any one of the following general formulas (2) to (6), more preferably a metal coordination compound represented by the following general formula (7).

[M is a transition metal, X and Y are N, O or S atoms, and n is 2 or 3. Moreover,-represents a radical. ]

[M is Ni, Pd, Pt, Cu, Co, Rh, or Ir.

  R is hydrogen, a branched or straight chain alkyl group or an aromatic ring group.

  n is 2 when M is Ni, Pd, Pt, or Cu, and 3 when Co, Rh, or Ir.

  The hydrogen atom of the CH group in the ligand may be substituted. The substituent is deuterium, amino group, nitro group, trimethylsilyl group, halogen atom, or optionally substituted phenyl group, fluorenyl group, or linear or branched alkyl having 5 or less carbon atoms. Group or alkoxyl group (the hydrogen atom of the alkyl group or alkoxyl group may be replaced by a halogen atom). ]

  Specific examples of the metal coordination compound used in the present invention are shown in the following table (in Table 1, n = 2), but are not limited thereto. In addition, the ligand in a table | surface is shown below.

  An example of the configuration of the organic EL device of the present invention is shown in FIG. FIG. 1A shows an organic LED in which a hole injection layer 605 and an electron injection layer 602 are arranged above and below the light emitting layer 603. Each of the injection layers 602 and 605 may be disposed as necessary, and either one may be omitted. FIGS. 1B and 1C show a device configuration in which a hole transport layer 604 and an electron transport layer 608 are added in addition to the light emitting layer 603. The configuration, material, and film thickness of each layer determine element characteristics such as element efficiency and stability, and must be carefully designed.

  In the light-emitting element of the present invention, a layer other than the light-emitting layer 603, preferably a layer in contact with the electrodes 601 and 606, that is, one or both of the hole injection layer 605 and the electron injection layer 602 contains the metal coordination compound. To do.

  The structural formulas and abbreviations of the organic compounds used in this example are shown below.

<Example 1, comparative example 1>
In this example, the metal coordination compound of the present invention is used for a hole injection layer.

  [Synthesis of Exemplary Compound 1001]

  The synthesis | combination of exemplary compound 1001 followed Journal of American Chemical Society, 88, 5201-5209 (1966). That is, a 500 ml aqueous solution of 3 g of o-phenylenediamine was added to a mixed solution of 5 g of nickel chloride hexahydrate and 30 ml of aqueous ammonia in 30 ml, and stirred for 9 hours using a magnetic stirrer. The deep blue precipitate was collected by filtration and washed well with acetone and water. After purification by recrystallization method, purification was performed by sublimation purification method.

[Manufacture of elements]
A device having five organic layers as shown in FIG. On the glass substrate (substrate 607), 100 nm of ITO (positive electrode 606) was patterned so that the opposing electrode area was 3 mm ² . On the ITO substrate, the following organic layer and electrode layer were vacuum-deposited by resistance heating in a vacuum chamber of 10 ⁻⁴ Pa to form a continuous film.

Hole injection layer 605 (5 nm): exemplary compound 1001
Hole transport layer 604 (40 nm): Compound FL01
Light emitting layer 603 (40 nm): CBP: Ir (ppy) 3 (weight ratio 10% by weight)
Electron transport layer 608 (50 nm): BPhen
Electron injection layer 602 (1 nm): KF
Metal electrode (cathode 601) (100 nm): Al

  As Comparative Example 1, an element having the same configuration as that described above except that the hole injection layer 605 was not provided was created, and the effect of improving the current characteristics by the exemplified compound 1001 was observed.

  The device characteristics were evaluated by applying a DC voltage with the positive electrode 606 as positive and the negative electrode 601 as negative. The emission intensity was measured with a spectrum measuring machine SR1 and BM7 manufactured by Topcon Corporation. The current value at the time of voltage application was measured by 4140Bd manufactured by Hured Packard. Table 4 shows the measurement results.

In the case of Example 1 using Exemplified Compound No. 1001 as the hole injection material, the current density was improved by 2.1 times when the voltage of 5 V was applied as compared with the device of Comparative Example 1, and the power efficiency was 1.8. Improved twice. Illustrative compound number 1001 was shown to have high performance as a hole injection material, and it was found that the hole injection property was improved and the light emission efficiency was improved. Further, stable light emission was confirmed when the device was energized with a brightness of 1000 cd / m ² .

<Examples 2 to 4>
A device was prepared in the same manner as in Example 1 except that the hole injection layer 605 was a compound layer shown in Table 4 (Example 2 was a co-deposition layer).

  When the element was measured in the same manner as in Example 1, as shown in Table 4, a higher current density and higher power efficiency were obtained than in Comparative Example 1.

  In addition, regarding the synthesis | combination of exemplary compound, the synthesis method of Journal of American Chemical Society, 88, 5201-5209 (1966) was followed. A reaction formula of the compounds of exemplary compounds 2001 and 3001 is shown below.

<Examples 5 and 6>
In this example, the metal coordination compound of the present invention is used for an electron injection layer.

  A device was produced in the same manner as in Example 1 except that the hole injection layer 605 was not provided and the electron injection layer 602 was changed to the compound layer shown in Table 5.

For comparison, the characteristics of the device of Comparative Example 1 and the device of this example were examined. The results are shown in Table 5. When the element was measured in the same manner as in Example 1, it was found that higher current density and higher power efficiency were obtained than in Comparative Example 1, and that exemplary compounds 1001 and 1005 were useful for the electron injection layer. It was. In addition, an experiment for stability of light emission was performed by emitting light with a luminance of 500 cd / m ² , and it was confirmed that stable light emission was obtained.

<Example 7>
In this example, a device was fabricated in the same manner as in Example 1 except that the co-deposited film of the exemplary compound 1001 and Bphen was used for the electron injection layer 602.

By comparing with Comparative Example 1, the effect of the element of this example was examined. The results are shown in Table 5. When the device was measured in the same manner as in Example 1, it was found that a higher current density and higher power efficiency were obtained than in Comparative Example 1, and that the co-deposited film of Example Compound 1001 was useful for the electron injection layer. Became. In addition, an experiment for stability of light emission was performed by emitting light with a luminance of 500 cd / m ² , and it was confirmed that stable light emission was obtained.

<Example 8>
A device was prepared in the same manner as in Example 1 except that the layer of the exemplified compound 1017 was formed by spin coating as the hole injection layer.

  That is, a 0.2% solution of chlorobenzene and Exemplified Compound 1017 was prepared and applied with a spin coater to form the hole injection layer 605. From the hole transport layer 604, elements were formed by sequentially forming layers by the vacuum evaporation method as in Example 1.

  The effect of the device of this example was examined by measuring the device in the same manner as in Example 1 and comparing it with Comparative Example 1. The results are shown in Table 6.

  Good hole injection characteristics were obtained, and it was revealed that the exemplified compound 1017 is useful as a material used for the hole injection layer.

<Example 9, Comparative Example 2>
The element shown in FIG. 1A was manufactured.

  On the same ITO substrate as in Example 1, PEDOT (for organic EL) manufactured by Bayer was applied to a film thickness of 40 nm with a spin coater under the condition of 1000 rpm (20 seconds). It was dried in a vacuum chamber at 120 ° C. for 1 hour to form a hole injection layer 605.

  On top of that, an organic film (light-emitting layer 603) having a thickness of 120 nm was formed by spin coating using the following solution under a nitrogen atmosphere at 2000 rpm for 20 seconds. After film formation, the film was dried under the same conditions as those for forming the hole injection layer 605.

[solution]
Dehydrated chlorobenzene: 6g
PVK (average molecular weight 9600): 92 mg
_{Ir (C 4 -ppy) 3:} 8mg

  Next, the following organic layer and electrode layer were vacuum-deposited under the same conditions as in Example 1 to form a continuous film.

Electron injection layer 602 (5 nm): exemplary compound 1001
Metal electrode (cathode 601) (100 nm): Al
As Comparative Example 2, an element using an AlLi alloy was created instead of the exemplified compound 1001.

The results evaluated in the same manner as Example 1 are shown in Table 7. High current density and high power efficiency were obtained as compared with Comparative Example 2, and it was revealed that the exemplary compound 1001 is useful for the electron injection layer. In addition, an experiment for stability of light emission was performed by emitting light with a luminance of 500 cd / m ² , and it was confirmed that stable light emission was obtained.

<Example 10>
A device was prepared in the same manner as in Example 1 except that the exemplified compound 1001 was used for the electron injection layer 602.

The results evaluated in the same manner as Example 1 are shown in Table 8. The device of Example 10 was improved in both current density and power efficiency as compared with the device of Comparative Example 1. It has been shown that by using Exemplified Compound No. 1001 for both the hole and electron layers, it has high performance. Further, stable light emission was confirmed when the device was energized with a brightness of 1000 cd / m ² .

It is a figure which shows an example of the light emitting element of this invention.

Claims (3)

In the light-emitting element having a layer other than the light-emitting layer and the light-emitting layer between the two electrodes, a layer other than the emission layer have a metal coordination compound represented by any of the following general formula (2) or (6) A layer other than the light emitting layer is in contact with one of the two electrodes .

[M is Ni or Pt.
R is a hydrogen atom.
n is 2.
In the formulas (2) and (6), the hydrogen atom of the CH group in the ligand may be substituted with a tert-butyl group.
-Represents a radical. ] The light emitting device according to claim 1 , wherein the metal coordination compound is a metal coordination compound represented by the following general formula (7).

The organic light-emitting device according to claim 1, wherein the metal coordination compound is represented by the following structural formula.

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