WO2008013069A1

WO2008013069A1 - El device

Info

Publication number: WO2008013069A1
Application number: PCT/JP2007/063971
Authority: WO
Inventors: Miho Ikenishi; Satoshi Kobayashi; Yuki Iguchi
Original assignee: Hoya Corporation
Priority date: 2006-07-28
Filing date: 2007-07-13
Publication date: 2008-01-31
Also published as: JPWO2008013069A1; CN101449626A

Abstract

Disclosed is an EL device which emits light when an alternating current field is applied thereto. In the EL device, a light-emitting layer contains a quantum dot having a core-shell structure wherein the surface of a core portion is covered with a shell layer. The shell layer is made of a material having a wider band gap than the material for the core portion, and the thickness of the shell layer is 5-100 nm.

Description

Specification

EL element

Technical field

TECHNICAL FIELD [0001] The present invention relates to an EL element (electric mouth luminescence element) of a type that emits light by injecting carriers into luminescent particles by applying an alternating electric field.

Background art

[0002] EL devices that emit light by injecting carriers into light-emitting fine particles by applying an alternating electric field are being actively studied because of the possibility of obtaining high emission luminance. As such an EL element, there is one described in Patent Document 1, for example.

[0003] In the EL element of Patent Document 1, at least one dielectric layer and a light emitting layer are laminated between two electrodes, and in this light emitting layer, the second semiconductor fine particles are made of the first semiconductor. Dispersed in the continuous phase. When an alternating electric field is applied to the EL element, carriers generated from the first semiconductor collide with the second semiconductor fine particles, and the second semiconductor fine particles are excited to emit light when returning to the ground state. Arise.

Patent Document 1: Japanese Patent Laid-Open No. 2003-249373

Patent Document 2: Japanese Patent Laid-Open No. 2003-173878

Disclosure of the invention

Problems to be solved by the invention

[0004] However, the EL element of Patent Document 1 cannot realize the light emission efficiency expected to reduce the carrier injection efficiency into the fine particles of the second semiconductor. This is because the scattering of carriers due to impurities mixed during the formation of the light emitting layer and the low continuity at the interface between the first semiconductor and the second semiconductor fine particles, resulting in a decrease in the “quantum confinement effect”. It is thought to be due to this.

Means for solving the problem

[0005] A first aspect of the present invention is an EL device in which a light emitting layer includes a quantum dot having a core-shell structure in which a surface of a core portion is covered with a shell layer, and emits light by applying an alternating electric field. The layer is made of a material having a larger band gap than the material of the core portion, and the shell This is an EL device with a film thickness of 5 nm to 100 nm.

[0006] A second aspect of the present invention is an EL device in which the light emitting layer includes a quantum dot having a core-shell structure in which the surface of the core portion is covered with a shell layer, and emits light by applying an alternating electric field. The layer is made of a material having a band gap larger than that of the material of the core portion, and is an EL element that emits light when intrinsic charge carriers existing in the shell layer are supplied to the core portion.

[0007] A third aspect of the present invention is the EL device according to the first or second aspect, wherein the light-emitting layer has core-shell structured particles mixed with a binder material.

[0008] A fourth aspect of the present invention is the EL element according to the third aspect, wherein the binder material is a dielectric.

[0009] A fifth aspect of the present invention is the EL device according to any one of the first to third aspects, in which the quantum dot has an organic side chain outside the shell.

[0010] A sixth aspect of the present invention is the EL device according to any one of the first to fifth aspects, wherein the core portion has a particle size of 1 to: LOnm.

The invention's effect

[0011] According to the present invention, by using a quantum dot having a core-shell structure including a thick shell layer, the core portion and the carrier injection that are hardly affected by the contamination of impurities during the formation of the light-emitting layer can be obtained by a simple manufacturing method. The continuity of the interface of the shell layer as a layer can be ensured, and carriers present in the shell layer can be efficiently injected into the core portion. As a result, it is possible to provide an EL device that achieves high luminous efficiency and utilizes the intrinsic high luminance of the core including the quantum dots.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments according to the present invention will be described in detail.

The EL element (electric aperture luminescence element) according to this embodiment has a configuration in which a first insulating layer, a light emitting layer, and a second insulating layer are sequentially stacked between a pair of electrodes.

[0013] As the pair of electrodes, for example, an Au (gold) metal electrode and an ITO (indium stannate) transparent electrode can be used. The Au electrode is formed by vacuum evaporation using a normal resistance heating evaporation source. The ITO electrode used is a film formed on a glass substrate. You may form by sputtering method and other well-known means.

[0014] The two insulating layers are formed, for example, by sputtering or the like using silicon nitride, tantalum oxide, silicon oxide, yttrium oxide, alumina, hafnium oxide, or norium tantalum oxide. be able to.

[0015] It is preferable that the light emitting layer also constitutes only a core-shell quantum dot force. This eliminates the need to uniformly disperse the particles in the needle and reduces the possibility of impurities being mixed. However, if it is difficult to form a light-emitting layer using only core-shell quantum dots, it is advisable to improve the adhesion to the insulating layer by mixing with a binder.

[0016] The core-shell structure quantum dot has a structure in which the surface of the core portion is covered with a shell layer.

For example, CdS, PbSe, HgTe, CdTe, InP, GaP, InG aP, GaAs, InGaN, GaN, ZnO, CsSe, ZnSe, ZnTe, and mixed crystals thereof. The material and the particle size are appropriately determined according to the emission wavelength required for the EL element. The particle size of the core portion is formed in a spherical shape by a known method (for example, a wet chemical synthesis method (liquid phase synthesis method), a laser ablation method), which is preferably selected based on a force within the range of 1 to lOnm.

[0017] The Chenole layer is composed of ZnS, ZnSe, CaS, SrS, BaS, CaGa S, SrGa S, ZnM

2 4 2 4 gS, BaAl S, and mixed crystals of these materials,

2 2 4

A material having a large band gap is used, for example, formed by a liquid phase synthesis method, a vapor deposition method, an aerosol deposition method or a spray coating method. The quantum dot obtained by the liquid phase synthesis method usually has a ligand having an organic side chain force around the shell layer so that the solvent dispersibility is high. In the EL device of the present embodiment, the supply power of intrinsic charge carriers to the core portion is a shell layer formed around the core portion. It will not contribute. Therefore, the quantum dots can be used for the light emitting layer while the organic side chain exists around the shell layer. The specific charge carriers supplied to the core portion are naturally supplied from the shell layer formed around the core portion, but the adjacent quantum dots or remote quantum dot shells are used. Even layer strength will be supplied. [0018] As the binder, a dielectric is preferred from the viewpoint of application of an alternating electric field. For example, epoxy resin, vinylidene fluoride resin, cyanocellulose, cyanopolyvinyl alcohol, Polyethylene, polypropylene, polystyrene resin, and silicone resin can be used. The binder can be formed by a relatively simple film formation method such as spin coating, screen printing, dip coating, or spray coating.

The EL device of this embodiment is excited and emits light by applying an alternating electric field between a pair of electrodes and injecting carriers into the core portion. The injected carriers exist in the shell layer. In order to limit the thickness of the shell, the shell layer can have a predetermined thickness and an alternating electric field can be generated at a predetermined period. In this case, the predetermined thickness of the shell layer is 5ηπ! It is selected from the range of ˜10 Onm, and the predetermined period can be selected so that only the carriers existing in the shell can be injected into the core portion in combination with the predetermined film thickness. In this way, when only the carriers present in the shell layer are injected into the core part surrounded by the shell layer, it is possible to prevent the carriers from being scattered by impurities, thereby realizing high light emission efficiency. It is possible to provide an EL device that utilizes the intrinsic high emission luminance of the core. In addition, even in an EL device in which the thickness of the shell layer is designed in this manner, by changing the period of the AC electric field, the intrinsic charge carriers from the adjacent or remote quantum dot shell layer are used as the core part. It is also possible to supply. It is also possible to change the luminance of the EL element by changing the period of the AC electric field.

Example 1

[0020] Example 1 of the above embodiment will be described.

An ITO electrode formed on a glass substrate (crystallite size film thickness; approximately lOOnm, surface roughness Ra; approximately 50nm) is used. On this ITO-attached glass substrate, a TaO film was grown as an insulating layer and the substrate was grown at room temperature using a high-frequency magnetron 'sputtering apparatus. The film thickness of the insulating layer was about 400 nm. On top of this, CdSe (core part) ZZnS (shell layer) quantum dots having a CoreZShell structure surface-modified with TOPO (trioctylphosphine oxide) are dispersed in a cyanoethylcellulose solution (binder). Was spin-coated and dried to form a film. The substrate temperature during drying can be selected from room temperature to around 200 ° C However, it is preferably 100 ° C or lower. This is because if it is too high, the light emission activity of the quantum dots deteriorates. The thickness of the deposited film was about 1 μm. On this, an insulating layer TaO film was grown to a thickness of about 400 ηm, and an Au electrode having a thickness of about 500 nm was formed by vacuum deposition using a shadow mask.

[0021] In this way, TaO Z (CdSe (core diameter: about 5.2 nm) ZZnS (shell thickness: about 15 nm) quantum dot-cyanoethyl cellulose binder) ZTaO ZAu is laminated in this order to form an EL device. Produced. An EL spectrum (single peak centered around 600 nm), which is the emission color originating from the quantization level of the quantum dot core, was obtained.

Next, a method for measuring the luminescence spectrum and intensity will be described. The photoluminescence (PL) of the EL device was measured using a fluorescence spectrophotometer FP-6500DS manufactured by JASCO Corporation using monochromatic light with a wavelength of 350 nm as excitation light. All sample temperatures at the time of measurement are room temperature. At this time, the PL spectrum of the used raw material dispersion was also measured. The EL measurement was performed by applying a low-frequency sine wave voltage between the ITO and Au electrodes. The size of the Au electrode is a square with a length of lmm each in length and width, and a voltage of f = 100kHz (period 0.01 ms) and voltage V = 100V (AC electric field) is applied to both electrodes via In. And light emission (EL)

PP

When measured, light emission at about 600 nm was confirmed. When the light emitted from the glass substrate surface of the device was taken into the detector of the fluorescence spectrophotometer with a single optical fiber and measured, the PL spectrum of the device and the PL spectrum of the raw material solution almost coincided.

Example 2

[0023] In Example 2, CdSe (core part) ZZnS (shell layer) quantum dots having a CoreZShell structure surface-modified with TOPO (trioctylphosphine oxide) in Example 1 described above! Instead of, EL elements were formed in the same manner except that InP (core part) ZZnSe (shell layer) quantum dots having a CoreZShell structure surface-modified with TOPO were used. The quantum dots used in Example 2 had a core diameter of about 2.6 nm and a shell thickness of about 12 nm. When voltage f = 10kHz and voltage V = 150V is applied,

PP

Luminescence was confirmed.

[0024] Although the present invention has been described with reference to the above-described embodiment, the present invention is not limited to the above-described embodiment, and the present invention is improved within the scope of the idea of the present invention or the idea of the present invention. Or it can be changed.

Claims

The scope of the claims

[1] An EL element that includes a quantum dot having a core-shell structure in which a surface of a core portion is covered with a shell layer and that emits light by applying an alternating electric field,

The shell layer has a material force having a larger band gap than the material of the core portion, and

An EL device having a thickness of the shell layer of 5 nm to 1 OO nm.

[2] The EL element includes a quantum dot having a core-shell structure in which the surface of the core portion is covered with a shell layer, and emits light by applying an alternating electric field,

An EL device that emits light by supplying intrinsic charge carriers present in the shell layer to the core portion.

[3] The EL device according to [1] or [2], wherein the light emitting layer is formed by mixing particles of the core-shell structure with a binder material.

4. The EL device according to claim 3, wherein the binder material also has a dielectric force.

[5] The quantum dot has an organic side chain outside the shell.

3. EL element according to item 1!

[6] The EL device according to any one of [1] to [5], wherein the core portion has a particle size of 1 to LOnm.