KR100261539B1 - Organic light emitting device having good stability - Google Patents

Abstract

PURPOSE: An organic light-emitting device having improved stability is provided to have excellent heat resistance, thin film property and stability by forming a hole carrier layer as a mixed layer composed of hole carrier material and fluoro polymer and making a light emission/electron carrier film as a mixed layer of light-emitting material and polyimide polymer. CONSTITUTION: The organic light-emitting device comprises a flat glass(a), an ITO layer(b), a hole carrier film(c), a light emission/electron carrier film(d) and a cathode(e). The hole carrier film(c) comprises hole carrier material and fluoro polymer. The light emission/electron carrier film(d) comprises light-emitting material and polyimide. A host-guest system is applied to the hole carrier film(c) and light emission/electron carrier film(d) for the stability of the organic light-emitting device.

Description

Excellent organic light emitting device

The present invention relates to an organic light emitting device having excellent stability, and more particularly, in an organic light emitting device including an anode electrode, a hole transport layer, a light emitting / electron transporting layer, and a cathode, the hole transporting layer includes a hole transporting material and a fluorine polymer. The electron transport layer is characterized in that it comprises an organometallic light emitting material and polyimide.

Conventional organic electroluminescent devices include (1) a device having a monomolecular emission layer between an anode and a cathode, (2) a device having a monomolecular hole transport layer and a monomolecular emission / electron transport layer, (3) a device having a polymer light emitting layer, (4) a device having a polymer hole transport layer and a polymer light emitting / electron transport layer, (5) a device having a polymer hole transport / light emitting layer and a polymer electron transport layer, and a device having an organic thin film multilayer structure other than (6).

In the device in which the double hole transport layer, the light emitting layer, and the electron transport layer are vacuum-deposited with a monomolecular material, the stability of the device is very deteriorated due to deterioration such as crystallization, and the device including the polymer material is also poly (p-phenylene vinylene). The use of the (PPV) family does not solve the stability problem.

Accordingly, an object of the present invention is to provide an organic light emitting device having excellent stability.

1 shows a structure of an organic light emitting device of the present invention,

2A and 2B show energy band structures before and after voltage application of the organic light emitting diode of the present invention, respectively.

Figure 3 shows the photoluminescence spectrum of the Alq3 vacuum deposition thin film and Alq3 / PEI thin film,

4a and 4b show the change in current density of the organic light emitting device according to the applied voltage of the organic light emitting device of the present invention,

5a and 5b show the change in the electroluminescence intensity according to the applied voltage of the organic light emitting device of the present invention,

6 shows a change in electroluminescence intensity according to the current density of the organic light emitting device of the present invention.

In order to achieve the above object, in the present invention, in the organic light emitting device comprising an anode electrode, a hole transport layer, a light emitting / electron transport layer and a cathode, the hole transport layer comprises a hole transport material and a fluorine polymer, the light emitting / electron transport layer is an organic metal light emitting Provided is a device comprising a material and a polyimide.

Hereinafter, the organic light emitting diode of the present invention will be described in detail.

The organic light emitting device according to the present invention includes a hole transport layer, a light emitting / electron transporting layer and an electron transporting electrode made of organic materials on a glass-ITO substrate, and a host-guest system in the hole transporting layer and the light emitting / electron transporting layer for stability. Was applied.

In the light emitting device of the present invention, the hole transport layer to which the host-guest system is applied forms a thin film in which a fluorine polymer and a guest hole transport material are uniformly mixed as a polymer material used as a host, and another host-guest system is applied. The light emitting / electron transport layer is a polymer material used as a host to form a thin film in which polyimide and an organometallic light emitting material having not only light emitting characteristics but also electron transfer characteristics are uniformly mixed.

Examples of the hole transport material include N, N'-diphenyl-N, N'-di (m-tolyl) benzidine (TPD), 4,4 ', 4' '-tris (3-methylphenyl-phenyl) Amino) triphenylamine (MTDATA), poly (9-vinylcarbazole), and the like, with TPD being preferred.

The fluorine polymer is poly (vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) or poly (vinylidene fluoride) (PVdF) having a repeating unit of the following structural formula (II).

In addition, as a light emitting material having an electron transporting property used in the present invention, tris (8-hydroxyquinolinato) aluminum (Alq3), bis (8-hydroxyquinolinato) zinc (II) of formula (III) (Znq2), bis (8-hydroxyquinolinato) beryllium (II) (Beq2), bis (8-hydroxyquinolinato) magnesium (Mgq2), bis (8-hydroxy-2-methylquinolinato Zinc (II) (ZnMq2), bis (8-hydroxy-2-quinolinato) beryllium (BeMq2), bis (8-hydroxy-2-propylquinolinato) aluminum (AlPrq2), and the like. Alq3 is preferred.

Examples of the polyimide used for the light emitting / electron transport layer include poly (etherimide) (PEI) having a repeating unit represented by the following structural formula (IV).

The device of the present invention can be manufactured as follows.

A hole transport material is prepared by dispersing a molecular weight at a weight ratio of 5:95 to 60:40, preferably 30:70 using a solvent in a fluorine polymer. In this case, the solid content is 0.2 to 10% by weight, preferably 0.3% by weight, and dimethylacetamide, N-methyl-2-pyrrolidone, tetrahydrofuran or acetone may be used as the solvent. The solution is coated on a glass-ITO substrate to prepare a polymer hole transport layer thin film. As the coating method, a method such as spin-coating, doctor-blading or screen printing may be used, and preferably spin-coating for 1 to 5 minutes at 1,000 to 5,000 rpm. More preferably, spin-coating for 3 minutes at 3,000 rpm. The coated thin film is dried at 40 to 90 ° C. for at least 30 minutes.

Subsequently, a solution in which the organometallic luminescent material is dispersed at a molecular level in a weight ratio of 5:95 to 75:25, preferably 70:30 in a soluble polyimide using a solvent such as chloroform is prepared. At this time, the solid content is 0.5 to 10% by weight, preferably 0.5% by weight. The solution is coated on the hole transport layer thin film to prepare a double polymer layer thin film of a polymer hole transport layer and a polymer electron transport layer. Coating and drying methods are the same as in the case of hole transport thin films.

The metal is vacuum deposited on the bilayer thin film at a rate of 0.5 to 1 nm / sec so that the thickness of the final metal layer is 300 to 500 nm, preferably 400 nm. In this case, aluminum, silver, calcium, magnesium, copper and alloys of these metals may be used.

Further protective / conductive layers may be deposited on the devices of the present invention.

As shown in FIG. 1, the schematic structure of the device manufactured as described above is composed of a glass (a), an ITO layer (b), a hole transport layer (c), a light emitting / electron transport layer (d), and a cathode (e). .

Hereinafter, the present invention will be described in detail by way of examples, but the content of the present invention is not limited thereto.

Example

Spin a solution (containing about 0.3 wt% solids) of TPD dispersed in a weight ratio of 30:70 (TPD: PVdF-HFP) by using dimethylacetamide in PVdF-HFP on a glass-ITO substrate prepared in advance for 3 minutes at 3,000 rpm. After coating, it was dried at 50 ° C. for 1 hour.

Subsequently, a solution in which Alq3 was dispersed in PEI using chloroform in a weight ratio of 70:30 (Alq3: PEI) (containing about 0.5 wt% of solid content) was spin-coated on the TPD / PVdF-HFP thin film at 3,000 rpm for 3 minutes. And dried at 50 ° C. for 1 hour.

The substrate was placed in a vacuum chamber and aluminum was vacuum deposited at 10 ⁻⁶ torr to produce an organic light emitting diode having a final thickness of 400 nm.

The energy band structures before and after applying the DC voltage to the organic light emitting diodes manufactured as described above were observed and shown in FIGS. 2A and 2B, respectively. The dashed line is the highest Occupied Molecular Orbital (HOMO) level expected. As shown here, when the DC voltage is not applied to the device, as shown in FIG. 2A, the HOMO and LUMO energy states are parallel, but when the voltage is applied, the energy band structure is changed to the inclined structure as shown in FIG. 3B. Electrons are injected from the cathode) and holes are injected into the organic thin film from the ITO electrode (anode). Most of the electrons injected from the cathode accumulate in the organic thin film interface due to the high LUMO energy level of the TPD / PVdF-HFP layer. Ultimately, the light is recombined with electrons already accumulated inside the Alq3 / PEI layer.

On the other hand, in order to examine the effect of the polyimide polymer on the electroluminescence of the device, by first vacuum-depositing only Alq3, an organic metal light emitting material on a quartz substrate to prepare a thin film containing no PEI with a final thickness of 50 nm, Alq3 was dissolved in PEI with chloroform at a molecular weight of 50: 50 (Alq3: PEI) in a molecular level solution (solid content: 1 wt%) on a quartz substrate by spin-coating and drying the polyimide to 50 nm thickness. Thin films were prepared, the photoluminescence spectra of these thin films were measured, and the results are shown in FIG. 3. In FIG. 3, the dotted line is an Alq3 thin film and the solid line is an Alq3 / PEI thin film. As shown here, the light emitting peak was observed at around 520 nm for the thin film without PEI, whereas the light emission peak was observed at around 510 nm for the thin film containing PEI, indicating that the blue shifted toward the higher energy. Can be. This phenomenon is due to the "dilution effect" caused by the intermolecular distance caused by the light-emitting molecules PEI substrate. Therefore, it can be seen that the thin film in which the light emitting material is dispersed in the PEI is capable of color tunning.

In addition, the change of the current density according to the voltage applied when driving the device manufactured above, the results are shown in Figures 4a and 4b. 4A and 4B, 1 is a hole transport layer, 2 is a light emitting / electron transport layer, h + is a hole, and e− is an electron. As shown here, a typical diode characteristic was observed in which the leakage current gradually increased as soon as voltage was applied, and then the current rapidly increased from about 13 volts. Therefore, it can be estimated that light emission starts from this voltage.

In addition, the change in electroluminescent intensity according to the applied voltage when driving the device manufactured above was examined, and the results are shown in FIGS. 5A and 5B. As shown here, photons were detected at 12 volts (FIG. 5A), but it can be seen that 13 volts is a more accurate ON voltage (FIG. 5B).

The change in electroluminescent intensity according to the current density of the device manufactured above is shown in FIG. 6. As shown here, a section of 0 to 4 ㎃ / ㎠ is a leakage current section in which current flows into the device but no light is emitted, and a region of 4 to 45 ㎃ / ㎠ is injected. In particular, the slope of the high voltage section of 20 to 45 mA / cm 2 was 0.368, while the slope of the low voltage range of 4 to 20 mA / cm 2 was 0.018. Accordingly, it can be seen that the contribution of the electrons to light emission is higher in the high voltage section than in the low voltage section.

The organic light emitting device of the present invention is made of a mixed layer made of a hole transport material and a fluorine polymer and a light emitting / electron transport layer made of a mixed layer made of a light emitting material and a polyimide polymer. Excellent

In addition, the device of the present invention can be manufactured in a large area and made of only a polymer, so that a bendable or foldable display device can be manufactured.

The present invention can be utilized in large area solar cells and photodiodes as well as organic electronic devices.

Claims (6)

An organic light emitting device comprising an anode electrode, a hole transport layer, a light emitting / electron transporting layer and a cathode, wherein the hole transporting layer comprises a hole transporting material and a fluorine polymer, and the light emitting / electron transporting layer comprises an organometallic light emitting material and a polyimide An organic light emitting device. The method of claim 1, An organic light emitting device, wherein the fluorine polymer is poly (vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) having a repeating unit represented by the following structural formula (II). Formula 2

The method of claim 1, An organic light emitting device, characterized in that the polyimide is a polyetherimide (PEI) having a repeating unit of the following structural formula (IV). Formula 4

The method of claim 1, The hole transport material is N, N'-diphenyl-N, N'-di (m-tolyl) benzidine (TPD) of formula (I), and the luminescent material is tris (8-hydroxy) of formula (III) Quinolinato) aluminum (Alq3), the organic light emitting device characterized in that. Formula 1

Formula 3

The method of claim 1, The hole transport layer is an organic light emitting device, characterized in that the hole transport material and the fluorine polymer is mixed in a weight ratio of 5: 95 to 60: 40. The method of claim 1, The organic light emitting device, characterized in that the light emitting / electron transport layer is an organic metal light emitting material and a polyimide is mixed in a weight ratio of 5: 95 to 75: 25.

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