Organic electroluminescence device

1. Field of the Invention

The present invention relates to an organic electroluminescence (EL) device, and more particularly, to an organic EL device which is simply manufactured by forming an electron transport layer by a spin-coating method.

2. Description of the Related Art

An EL device as a spontaneous luminescence type display has a broad viewing angle, good contrast and response time characteristics. Due to these merits, the EL device has been the focus of next generation displays.

The EL device is classified into an inorganic EL device and an organic EL device depending on the material used for a light-emitting layer. In particular, the organic EL device has good luminance, driving voltage and response time, and can display a multitude of colors.

FIG. 1 is a section view showing the structure of a general EL device. Referring to FIG. 1, an anode 12 is formed on a substrate 11 . A hole transport layer 13 , a light-emitting layer 14 , an electron transport layer 15 , and a cathode 16 are formed on the anode 12 in sequence. Here, the hole transport layer 13 , the light-emitting layer 14 and the electron transport layer 15 are organic thin films made of an organic compound.

The organic EL device having the above structure operates based on the following operation principle. When a voltage is applied between the anode 12 and the cathode 16 , holes injected from the anode 12 move through the hole transport layer 13 to the light-emitting layer 14 . Meanwhile, electrons are injected from the cathode 16 through the electron transport layer 15 to the light-emitting layer 14 . Also, carriers are recoupled in the light-emitting layer 14 to generate excitons. The excitons are transited from an excited state to a ground state, so that fluorescent molecules of the light-emitting layer emit light to form a picture.

Also, in general, the electron transport layer is formed of quinolinol complex, benzoquinolinol complex, 1,3,4-oxadiazole derivative, triazole derivative or phenanthroline derivative.

However, when the electron transport layer is formed of the compounds, using a spin coating method is not possible. That is, only a vapor-deposition method should be used. This is because the light-emitting layer is damaged by the solvent used for spin-coating the compounds.

To solve the above problems, it is an object of the present invention to provide an organic electro-luminescence (EL) device which is simply manufactured by forming an electron transport layer by a spin-coating method.

To achieve the above object, there is provided an organic electroluminescence (EL) device comprising an electron transport layer formed between a pair of electrodes, wherein the electron transport layer comprises 50˜99.9 wt % of alcohol-soluble polymer and 0.1˜50 wt % of electron transporting material.

The above object and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:

FIG. 1 is a section view showing the structure of a general organic electroluminescence (EL) device.

Most materials used for a light-emitting layer are almost insoluble in an alcoholic solvent such as a methanol. The point of the present invention is to prepare a composition for an electron transport layer, which is soluble in an alcoholic solvent, and to spin-coat the composition for an electron transport layer to form an electron transport layer. Here, the composition for the electron transport layer is formulated to be stable and soluble in alcohol, and includes an alcohol-soluble polymer and a material capable of transporting electrons.

The alcohol-soluble polymer may be a non-ionic polymer such as polyvinylpyrrolidone, polyvinylpyridine or polyethyleneoxide, or an ionic polymer such as lithium salt of polystyrene sulfonic acid containing 0.01˜50% of average ion per repeating unit, sodium salt thereof, lithium salt of perfluorinated ion exchange powder (so-called Nafion(Aldrich Co.)), or sodium salt thereof. The electron transporting material is not limited to a specific compound. That is, any materials capable of transporting electrons can be used. Preferably, the electron transporting material includes 8-hydroxyquinolino-aluminum (e.g., A/Q), benzoquinolinol complex (e.g., Bebq 2 ), 1,3,4-oxadiazole derivative (e.g., PBD), triazole derivative (e.g., TAZ) or phenanthroline derivative (e.g., MEPHPH), or an ionic compound such as lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium perchlorate (LiClO 4 ), lithium tetrafluoroborate (LiBF 4 ), lithium hexafluorophosphate (LiPF 6 ) or lithium bistrifluoromethanesulfonylamide (LiN(CF 3 SO 2 ) 2 ), represented by the formulae.

The alcohol-soluble polymer and the electron transporting material are mixed at a ratio of 50:50˜99.9:0.1. Here, the content of the alcohol-soluble polymer is out of the range, formation of a film is difficult.

Hereinafter, a method for manufacturing an organic EL device according to the present invention will be described.

First, a material for an anode is coated on a substrate. Here, the substrate is a substrate used for a general organic EL device, preferably, a glass substrate or a transparent plastic substrate which is good in transparency, surface flatness, convenience in handling and waterproofing characteristic. Also, indium tin oxide (ITO), tin oxide (SnO 2 ) or zinc oxide (ZnO), which is good in transparency and conductivity, is used as a material for the anode.

The composition for the hole transport layer is spin-coated on the anode to form a hole transport layer.

The material for the hole transport layer is not limited to a specific material, which may be polyvinylcarbazole (PVK) or poly(p-phenylenevinylene) (PPV). Here, the PVK and PPV may be used as a luminous material. That is, a light-emitting layer capable of transporting holes can be formed by the PVK or PPV. Also, if necessary, an extra emitter layer may further be formed.

The composition for forming an electron transport layer according to the present invention is spin-coated on the hole transporting emitter layer. Then, the resultant structure is dried to form an electron transport layer.

The composition for the electron transport layer according to the present ski invention is prepared by mixing 50˜99.9 wt % of alcohol-soluble polymer with 0.1˜50 wt % of electron transporting material, and then by dissolving the mixture in an alcoholic solvent. Preferably, the alcoholic solvent includes methanol and 2-methoxyethanol.

Then, a metal for forming a cathode is vacuum-deposited or sputtered on the electron transporting layer to form a cathode, thereby completing an organic EL device. Here, the metal for a cathode is lithium (Li), magnesium (Mg), calcium (Ca), aluminum (Al), a magnesium-silver (Mg—Ag) alloy, or an Al—Li alloy.

The organic EL device is formed by stacking in sequence the anode, the hole transport layer, the light-emitting layer, the electron transport layer and the cathode as described above. Alternatively, the order of stacking the respective layers may be reversed such that the cathode, the electron transport layer, the light-emitting layer, the hole transport layer and the anode are stacked in sequence.