JP2010055900A - Electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroluminescent element having high light emission efficiency and high purity of color. <P>SOLUTION: The electroluminescent element includes a pair of a first electrode and a second electrode, at least one of them has light transmission characteristics, and a light-emitting layer pinched between the first electrode and the second electrode. The light-emitting layer is an electroluminescent element containing light-emitting nanoparticles and non-light-emitting nanoparticles. Preferably, the light emitting nanoparticles include a quantum dot light emitting material, and the non-light-emitting nanoparticles containing metal oxide nanoparticles. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an electroluminescent device. More specifically, the present invention relates to an electroluminescent device suitable for an electroluminescent device containing nanoparticles.

2. Description of the Related Art In recent years, electroluminescence elements (EL elements; electroluminescent elements) have attracted attention as surface-emitting elements that are lightweight and thin, have low power consumption, and are excellent in shape flexibility. Such an EL element has many excellent features such as high luminance light emission, high speed response, wide viewing angle, thin and light weight, and high resolution, and is applied to flat panel displays.

As such an EL element, an organic electroluminescence element (hereinafter also referred to as “organic EL element”) is generally known. The organic EL element is usually a self-luminous and all-solid-state light-emitting element including a pair of electrodes composed of an anode and a cathode and a light-emitting layer sandwiched between the pair of electrodes, and has high visibility. It is high and resistant to impacts, so it is expected to be widely applied to fields such as displays and lighting.

The manufacturing process of the organic EL element is roughly classified into a dry method using a vapor deposition method and a wet method using a coating method depending on a film forming method. In an organic EL device manufactured by a dry method, a low molecular light emitting material is usually used as a light emitting material. On the other hand, in an organic EL device manufactured by a wet method, a polymer light emitting material is usually used as a light emitting material. Is used.

As for the low-molecular light-emitting material, highly efficient green light-emitting materials and red light-emitting materials using phosphorescent materials have been proposed. On the other hand, a blue light-emitting material requires a host material having a high band gap, and currently there is no blue light-emitting material with high color purity and high efficiency. In addition, there is a technique using a microcavity effect as a technique for realizing high color purity, but in this case, there is room for improvement in terms of improving viewing angle characteristics.

On the other hand, polymer light emitting materials have many problems in terms of efficiency and demand. Moreover, since the polymer light emitting material has a large half-value width of the emission wavelength, there is room for improvement in terms of improving color purity. In addition to the material as the chromophore, the polymer phosphorescent material requires a host skeleton with a high bandgap as a host. Therefore, it is necessary to focus on development more than the low-molecular light-emitting material.

Further, in organic light emitting materials such as low molecular light emitting materials and polymer light emitting materials, there are fluctuations of bands peculiar to organic substances, and the emission wavelength tends to be broad. In addition, in order to cause the phosphorescent material to emit light, a material having a high band gap is required, and there is room for further development in terms of realizing this material with an organic material.

On the other hand, luminescent nanoparticles (nanoluminescent materials) such as quantum dots have been proposed as light-emitting materials with high efficiency and high color purity. In this luminescent nanoparticle, the color purity depends on the luminescent nanoparticle system, and light emission having a sharp peak with a small half-value width is possible. In addition, in any of blue, green and red light emission, the band gap of the material itself does not change, so light can be emitted without distinction between blue, green and red.

As a material, quantum dots can emit light with high efficiency by a quantum confinement effect, and can emit light with high efficiency by photoluminescence. At present, the quantum yield of quantum dots is about 50%, but this is due to structural defects of the shell (i.e. immature manufacturing), and in principle, 100% is possible. Development is underway.

Under such circumstances, a charge injection type EL element using a quantum dot as a light emitting layer is disclosed (for example, see Non-Patent Document 1 and Patent Document 1). In addition, an EL element having a light-emitting layer in which semiconductor ultrafine particles are dispersed in a polymer compound is disclosed (see, for example, Patent Document 2 and Non-Patent Documents 2 and 3).
“Organic Electronics”, Vol. 4, (2003), p. 123-130 JP 2005-502176 Gazette JP 2004-172102 A “Applied Physics letters”, 1995, Vol. 66, p. 1316-1318 “Science” (USA), February 22, 2002, Vol. 295, p. 1506-1508

However, in an EL device using luminescent nanoparticles such as quantum dots, sufficient efficiency could not be exhibited.

For example, with respect to the technique described in Non-Patent Document 1, (1) the quantum dot layer that is the light emitting layer is a single layer, and even if they are arranged closely, gaps are generated and vertical leakage occurs. When the layer is a single layer, there are many charges penetrating the quantum dot layer, and the efficiency is not improved. (3) The ionization potential of the quantum dot is low, and holes are injected using an organic material used in an organic EL element. (4) Although the quantum dots emit light due to the quantum confinement effect, there is a problem that the quantum dots cannot be stacked because no current flows by themselves.

In the technique described in Patent Document 1, it is necessary to provide a capping molecule with a functional unit that causes injection of an excited state into the quantum dot on the surface of the quantum dot in order to inject charge into the quantum dot. However, in such a configuration, in particular, in an organic material-based capping molecule as described in the claims and specifications of Patent Document 1, the ionization potential wall of the quantum dot is crossed into the quantum dot. It was difficult to inject charges.

Furthermore, for the techniques described in Patent Document 2 and Non-Patent Documents 2 and 3, a system in which semiconductor ultrafine particles are dispersed in a polymer material (polyvinylcarbazole or polyphenylene vinylene) is used, and a charge transporting compound is contained. The device has a device structure in which the layer is inserted between the light emitting layer and the electrode. Light emission was observed even with these configurations, but the efficiency of the light emission itself was low. This is thought to be due to the lack of charge injection into the quantum dots and the current flowing through the system.

This invention is made | formed in view of the said present condition, and it aims at providing the electroluminescent element which has high luminous efficiency and high color purity.

The inventors of the present invention have studied various electroluminescent elements having high luminous efficiency and high color purity, and have focused on luminescent nanoparticles such as quantum dots. The light emitting layer contains not only light emitting nanoparticles but also non-light emitting nanoparticles having a function of flowing charges and a function of injecting charges into the light emitting nanoparticles, so that light emitting nanoparticles such as quantum dots can be obtained. The present inventors have found that the above-described problems can be solved brilliantly, and have reached the present invention.

That is, the present invention provides an electroluminescent device comprising a pair of first electrode and second electrode, at least one of which has optical transparency, and a light emitting layer sandwiched between the first electrode and the second electrode. And the said light emitting layer is an electroluminescent element containing a luminescent nanoparticle and a nonluminous nanoparticle. Thereby, an electroluminescent element having high efficiency and high color purity can be realized.

In the light emitting layer, at least one kind of each of the light emitting nanoparticles and the non-light emitting nanoparticles may be used, and the number of the kinds is not particularly limited.

The configuration of the electroluminescent device of the present invention is not particularly limited as long as such components are formed as essential, and other components may or may not be included. is not.
The preferable form in the electroluminescent element of this invention is demonstrated in detail below. In addition, each form shown below may be combined suitably.

From the viewpoint of more efficient charge injection from the non-luminescent nanoparticle to the luminescent nanoparticle, the non-luminescent nanoparticle preferably has a charge transporting property, and the non-luminescent nanoparticle is an electron transporter. Preferably, the light-emitting nanoparticle is electrically connected to the electron-transporting nanoparticle and the hole-transporting nanoparticle. Preferably, the non-luminescent nanoparticle includes a metal oxide nanoparticle, and the non-luminescent nanoparticle has a size equal to or larger than the band gap of the luminescent nanoparticle. It preferably has a band gap.

In addition, the non-light-emitting nanoparticles can improve the light emission efficiency by having a band gap that is the same as or larger than the band gap of the light-emitting nanoparticles. If the non-luminescent nanoparticle has a band gap that is less than or equal to the band gap of the luminescent nanoparticle, excitons formed by the luminescent nanoparticle will transfer energy toward the non-luminescent nanoparticle. There is a possibility that the luminous efficiency of the luminescent nanoparticles may be reduced.

From the viewpoint of more efficient hole injection from the non-luminescent nanoparticle to the luminescent nanoparticle, the ionization potential (IP) of the non-luminescent nanoparticle is greater than the ionization potential (IP) of the luminescent nanoparticle. From the viewpoint of more efficiently injecting electrons from the non-luminescent nanoparticle to the luminescent nanoparticle, the electronegativity of the non-luminescent nanoparticle is the same as that of the luminescent nanoparticle. It is preferably smaller (shallow) than the electronegativity. In any case, since an energy barrier at the time of charge injection can be eliminated, charge injection can be performed more effectively.

Note that the electron-transporting nanoparticles and the hole-transporting nanoparticles may be at least one kind in the light-emitting layer, and the number of kinds is not particularly limited. Thus, it is preferable that the said nonluminous nanoparticle contains at least 2 or more types of nanoparticle.

From the viewpoint of achieving particularly excellent efficiency and color purity, it is preferable that the luminescent nanoparticles include a quantum dot luminescent material.

From the viewpoint of realizing a light-emitting layer having excellent film forming properties, the light-emitting layer preferably includes a support material.

From the viewpoint of improving the electrical conductivity of the light emitting layer, the support material preferably has a charge transport property.

From the viewpoint of reducing manufacturing costs, the first electrode and the second electrode preferably include the same material.

From the viewpoint of more efficient charge injection into the light emitting layer, the first electrode and the second electrode preferably include materials having different work function values.

From the viewpoint of further improving the light emission efficiency, the electroluminescent element preferably further includes a charge injection / transport layer between one of the first electrode and the second electrode and the light emitting layer.

From the viewpoint of further improving the luminous efficiency, the charge injecting and transporting layer preferably contains nanoparticles.

In the charge injecting and transporting layer, there may be at least one kind of the nanoparticles, and the number of kinds is not particularly limited.

From the viewpoint of further improving the light emission efficiency, the electroluminescence element includes a first charge injection transport layer and a first charge layer between the first electrode and the light emitting layer and between the second electrode and the light emitting layer, respectively. It is preferable to further include a two-charge injection transport layer.

From the viewpoint of further improving the luminous efficiency, it is preferable that the first charge injection transport layer and the second charge injection transport layer contain nanoparticles.

In each of the first charge injecting and transporting layer and the second charge injecting and transporting layer, there may be at least one kind of the nanoparticles, and the number of kinds is not particularly limited.

From the viewpoint of performing charge injection into the light emitting layer more efficiently, the first charge injection transport layer and the second charge injection transport layer include the same material as the non-light emitting nanoparticles contained in the light emitting layer. Is preferred.

From the viewpoint of further improving the light emission efficiency, one of the first charge injection transport layer and the second charge injection transport layer has an electron transport property, and the first charge injection transport layer and the second charge injection transport The other of the layers preferably has a hole transporting property.

From the viewpoint of further improving the light emission efficiency, the electroluminescent element preferably further includes a charge blocking layer between the light emitting layer and one of the first electrode and the second electrode.

From the viewpoint of further improving the light emission efficiency, the electroluminescent element includes a first charge blocking layer and a second charge layer between the first electrode and the light emitting layer and between the second electrode and the light emitting layer, respectively. It is preferable to further include a charge blocking layer.

From the viewpoint of suppressing deterioration of the element, the electroluminescent element preferably has a plurality of emission centers in the light emitting layer, and the light emitting layer has electron transport properties and holes that have a difference in transport performance from each other. It is preferable that the light-emitting layer has an electron transport property and a hole transport property that have a difference of 10 times or more in mutual transport performance, and the electroluminescent element is driven by alternating current. It is preferable. From the same point of view, the light emitting layer may have a form in which the electron transport property is larger than the hole transport property and contains metal oxide nanoparticles having an electron transport property. The hole transport property may be larger than the electron transport property, and the metal oxide nanoparticles containing the hole transport property may be included.

Note that the emission center is a region where recombination of electrons and holes occurs in the actual light emitting region with a particularly high probability, that is, a point where light emission is strongest in the light emitting region.

The electron-transporting metal oxide nanoparticles and the hole-transporting metal oxide nanoparticles may be at least one kind in the light emitting layer, and the number of kinds is not particularly limited.

From the viewpoint of improving visibility, the electroluminescent element is preferably AC driven at a driving frequency of 60 Hz or more.

From the viewpoint of realizing a layer having excellent in-plane uniformity, at least one of the layers sandwiched between the first electrode and the second electrode is preferably formed by a spray method. The layer sandwiched between the first electrode and the second electrode is more preferably formed by a spray method.

According to the electroluminescent element of the present invention, high luminous efficiency and high color purity can be realized.

Embodiments will be described below, and the present invention will be described in more detail with reference to the drawings. However, the present invention is not limited only to these embodiments.

(Embodiment 1)
1A and 1B are schematic cross-sectional views of an EL element according to Embodiment 1. FIG. 1A is a stacked structure, and FIG. 1B is an enlarged view of a light emitting layer. As shown in FIG. 1A, the EL element of the present embodiment has a structure in which a first electrode 2, a light emitting layer 3, and a second electrode 4 are laminated in this order from the substrate 1 side on a substrate 1. That is, the basic configuration of the EL element of the present embodiment includes a pair of upper and lower electrodes 2 and 4 and a light emitting layer 3. The light emitting layer 3 is composed of luminescent nanoparticles (nanoluminescent material) 5 and non-luminescent nanoparticles 6.

As shown in FIG.1 (b), the luminescent nanoparticle 5 contains the quantum dot provided with the quantum effect, and the nonluminous nanoparticle 6 is a metal oxide nanoparticle which has at least 1 or more types of electron transport property. And at least one kind of metal oxide nanoparticles having a hole transport property. In addition, the nonluminous nanoparticle 6 may contain some fluorides, such as NaF, CaF, and MgF, as a nanoparticle with a charge transport function.

As described above, quantum dots are attracting attention as light-emitting materials with high efficiency and high color purity. However, quantum dots are inefficient with conventional electroluminescent methods. The conventional device structure including quantum dots has the following problems (1) to (4).
(1) The quantum dot layer, which is the light emitting layer, is a single layer, and even if they are arranged closely, a gap is generated and vertical leaks occur.
(2) If the quantum dot layer is a single layer, there are many charges penetrating the quantum dot layer, and the efficiency is not improved.
(3) The ionization potential of the quantum dots is low, and it is difficult to inject holes using an organic material used in an organic EL element.
(4) Although the quantum dot emits light due to the quantum confinement effect, the quantum dot itself cannot be stacked because no current flows.

In order to overcome these problems, the following concepts (A) to (C) are necessary.
(A) The light emitting layer is not a single layer, and a structure in which electricity sufficiently flows even when quantum dots are deposited is formed, and leakage between the upper and lower electrodes is suppressed by stacking the quantum dots.
(B) In order to promote the injection of charges into the quantum dots, particularly the injection of holes, an injection method other than the conventional injection type is applied.
(C) Although it is synonymous with said (A) and (B), the element design which flows many electric currents into a system is performed, and the production amount of an exciton is increased.
The configuration of the present embodiment is a configuration that realizes these concepts and allows the quantum dots to emit light efficiently.

In addition, the present inventors have found that metal oxide nanoparticles have high conductivity. Metal oxide nanoparticles can have different electron and hole transport properties depending on the type of material and the metal oxide production process. Therefore, by mixing the light emitting layer 3 with quantum dots that do not pass electricity and metal oxide nanoparticles with good conductivity, it is possible to achieve both a function of flowing charge and a function of emitting light within the light emitting layer 3. it can. As a result, since the light emitting layer 3 can be thickened, leakage between the upper and lower electrodes 2 and 6 can be suppressed.

Furthermore, in the configuration of the present embodiment, the internal charge of the metal oxide nanoparticles can be used as the current without depending on the charge injection from the electrodes 2 and 4. For this reason, it is possible to flow a current through the element system significantly, compared to a conventional organic EL element in which a current is supplied by charge injection from an electrode.

The configuration of the present embodiment is also effective for injecting charges into the quantum dot material. As described above, the quantum dot usually has a deep ionization potential compared to the charge transport layer used in the conventional organic EL device, and when the core-shell structure is used, the band gap of the material constituting the shell portion is large, Furthermore, since there are cases in which passivation molecules for preventing aggregation are added around the quantum dots, it is difficult to inject charges into the quantum dots, particularly with respect to holes, with the conventional method. there were. That is, it is difficult to inject charges into the quantum dots using a material selected from an energy diagram as considered in conventional organic EL elements. In contrast, the present inventors have found that a new charge injection mechanism for quantum dots can be realized with this configuration. That is, the metal oxide nanoparticles have an internal charge, and a potential difference is generated between the metal oxide nanoparticles present in the light emitting layer 3 and the quantum dots. Using this potential difference and an externally applied electric field, metal oxidation occurs despite the existence of an energy barrier due to the internal Schottky effect and tunneling effect between the nanoparticles (metal oxide nanoparticles and quantum dots). We found that charge injection from quantum nanoparticles to quantum dots can be performed. And since the charge injected into the quantum dot cannot escape from the quantum dot due to the quantum effect, if the hole is injected first, it emits light when the electron is injected, while the electron is injected first. In this case, light is emitted when holes are injected.

The quantum dot is a semiconductor nanometer crystal (crystal of nanometer order made of a semiconductor), and MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe. II-VI group semiconductor compounds such as CdS, CdSe, CdTe, HgS, HgSe, HgTe, and / or III-V group semiconductor compounds such as GaAs, GaP, InN, InAs, InP, InSb, and / or It can have a crystal of a group IV semiconductor compound such as Si, Ge. In addition, the semiconductor compound can be doped with cations of rare earth metals or transition metals such as Eu ³⁺ , Tb ³⁺ , Ag ⁺ and Cu ⁺ . A quantum dot can consist of two or more semiconductor compounds. The quantum dots are preferably prepared by a wet chemical process. Most practically, the quantum dots contain InN, InGaP or GaAs. The quantum dot radius is smaller than the exciton Bohr radius of the bulk material. It is most practical for quantum dots to have a radius not greater than about 10 nm. Most preferably, the quantum dots have a radius of 1 to 6 nm. The quantum dot can have a core-shell structure. In this case, the quantum dot is a light emitting core material (eg, ZnS) overcoated with a high bandgap shell material (eg, ZnS) so that electrons and / or holes and / or excitons are confined in the core of the quantum dot. CdSe).

Passivation molecules can also be linked to the surface of the quantum dot in order to stabilize the quantum dot (eg prevent aggregation). Examples of such passivation molecules include fluoride ions, molecules having non-aromatic hydrocarbon moieties, coordination solvents, phosphanes, and phosphane oxides. A capping molecule having a functional unit or a molecule having a non-aromatic hydrocarbon moiety can also be linked to the surface of the quantum dot through a binding unit. Examples of such a binding unit include thiol, sulfate, sulfite, sulfide, carboxylic acid, aldehyde, alcohol, ester, phosphine, phosphate, amine, and non-fused polynuclear pyridine. Can be mentioned.

The quantum dot electrons have an energy range, and the concepts such as energy levels, band gaps, conduction bands, and valence bands apply to conventional bulk semiconductors as they are, but there is one major difference. In the bulk state, the grain size of the semiconductor crystal is significantly larger than Exciton Bohr Radius, and excitons reach the natural limit. However, as the semiconductor crystal becomes smaller, it approaches the size of the substance Exciton Bohr Radius, the electron energy levels are no longer continuous, and a small separation occurs between discrete, ie energy levels. This discrete energy level state is called quantum confinement, in which the semiconductor material is no longer bulk but instead is a quantum dot. In this state, the absorption and emission of the semiconductor material are greatly affected. Similar to bulk semiconductor materials, electrons tend to move from end to end in a band gap, but in quantum dots, the size of the band gap can be controlled by simply changing the particle size of the quantum dots. Since the emission wavelength of the quantum dot depends on the band gap of the light emitting part (for example, the core part), the emission wavelength of the quantum dot can be adjusted very precisely. The emission spectrum of the quantum dots has a narrow full width at half maximum and becomes a symmetrical emission spectrum. For example, in the case of a quantum dot having a core portion made of CdSe and a shell portion made of ZnS, the full width at half maximum is 30 to 40 nm. FIG. 2 is a schematic diagram illustrating the band gap of the quantum dots according to the first embodiment in which the core portion is made of CdSe and the shell portion is made of ZnS. In this case, the band gap Eg of the core portion 5a is 2.1 eV, and the band gap Eg of the shell portion 5b is 4.1 eV. Then, electrons e are injected from the conduction band of the shell portion 5b into the core portion 5a, holes h are injected from the valence band of the shell portion 5b into the core portion 5a, and the electrons e and holes h are injected into the core portion 5a. Recombine and emit light.

As a material of the metal oxide nanoparticles, those having an electron transporting property include barium titanate (for example, BaTiO ₃ ), titanium oxide (for example, TiO ₂ ), cerium oxide (for example, CeO ₂ ), yttrium oxide (for example, Y _2). O ₃ ), gallium oxide (Ga ₂ O ₃ ), and the like, and those having hole transporting properties include ITO, copper oxide (for example, Cu ₂ O), molybdenum oxide (for example, MoO ₂ (3)), and zinc oxide. (For example, ZnO ₂ ). However, even with the same oxide, the charge transport property varies depending on the manufacturing method and the state of the material, and may have an electron transport property or a hole transport property. As a product nanoparticle, it can be suitably used as needed irrespective of the material.

Further, the number of types of electron-transporting metal oxide nanoparticles contained in the light-emitting layer 3 and the number of types of hole-transporting metal oxide nanoparticles are not particularly limited, and can be set as appropriate. Good.

The reason why the metal oxide nanoparticles have conductivity and can be charged is considered as follows.
(Cause 1)
Metal oxide nanoparticles form a charge transfer complex at the interface with the electrode or quantum dot. More specifically, a charge transfer complex (metal complex) is formed between the oxide on the metal oxide nanoparticle and the electrode, or between the metal on the metal oxide nanoparticle and the quantum dot. For this reason, charge is injected into the light emitting layer through this charge transfer complex, and charge injection is considered to occur even if there is a band gap between the electrode and the metal oxide nanoparticle or between the metal oxide nanoparticle and the quantum dot. .
(Cause 2)
The metal oxide itself is a dielectric, but may be in an incomplete oxide state in the nanoparticulate process, or a part of the material may be in an incomplete oxide state. The presence of this incomplete oxide generates excessive electrons and holes when viewed as an electronic material. That is, when the metal oxide nanoparticles are formed into a film shape, a layer containing a large amount of internal charges is formed. By applying an electric field to this layer, the internal charges move to the counter electrode and become a current.

The average particle diameter of the metal oxide nanoparticles is not particularly limited as long as it is nano-order, but in order to perform charge injection from the metal oxide nanoparticles to the quantum dots more efficiently, the metal oxide nanoparticles are applied to the quantum dots. It is preferable to contact as many as possible. A configuration in which at least one kind of hole-transporting metal oxide nanoparticles and electron-transporting metal oxide nanoparticles are connected to the quantum dots is preferable. A quantum dot that emits visible light usually has a size of about 2 to 3 nm for blue light emission and a size of about 10 nm for red light emission. Therefore, if the size of the metal oxide nanoparticles is extremely larger than that of the quantum dots, many metal oxide nanoparticles cannot be connected around the quantum dots. Therefore, it is preferable that the metal oxide nanoparticles have a size of about several nm to several tens of nm, more specifically about 2 to 30 nm.

In addition, the metal oxide nanoparticles may aggregate to form secondary particles that are aggregates. In this case, the particle size, that is, the particle size of the secondary particles is within the wavelength range of visible light (usually, 400 to 700 nm) is preferable, whereby the transmittance of the light emitting layer 3 can be improved. In addition, about the particle size of nanoparticles, such as a metal oxide nanoparticle and a quantum dot, it can measure by methods, such as a BET measuring method.

From the viewpoint of more efficient charge injection from the metal oxide nanoparticles into the quantum dots, the size of the band gap of the metal oxide nanoparticles is preferably equal to or greater than the size of the band gap of the quantum dots. . This is because charge injection is easily performed without an energy barrier from a large band gap to a small band gap. Moreover, since it can suppress effectively that the exciton formed by the quantum dot moves to the direction of a metal oxide nanoparticle, luminous efficiency can also be improved.

Further, from the viewpoint of more efficiently injecting holes from the metal oxide nanoparticles into the quantum dots, the ionization potential (IP) of the metal oxide nanoparticles is larger than the ionization potential (IP) of the quantum dots (deeper). From the viewpoint of more efficient electron injection from the metal oxide nanoparticles into the quantum dots, the electronegativity of the metal oxide nanoparticles should be smaller (shallow) than that of the quantum dots. Is preferred. In any case, since an energy barrier at the time of charge injection can be eliminated, charge injection can be performed more effectively.

As described above, according to the EL element of the present embodiment, it is possible to realize an element in which a large amount of current can flow through the element and leakage between the upper and lower electrodes 2 and 4 is sufficiently suppressed. In addition, since the charge can be efficiently injected from the metal oxide nanoparticles into the quantum dots, efficient light emission is possible. In addition, since light-emitting nanoparticles such as quantum dots are used, light emission with excellent color purity is possible.

In metal oxide nanoparticles, the charge transport process due to internal charges plays a major role in charge transport or injection, and therefore the influence on the injection characteristics and transport characteristics due to the type (material) of the adjacent electrode is small. That is, in the configuration of the present embodiment, the direction of charge injection into the light emitting layer 3 can be determined by the direction of the current flowing between the upper and lower electrodes 2 and 4. That is, for example, when the organic EL element of the present embodiment is AC driven, electrons and holes are injected into the light emitting layer 3 in both electric field directions, and these are passed through the metal oxide nanoparticles. Recombines within the quantum dot and emits light.

Note that the metal oxide nanoparticles in the present invention have a function of injecting and / or transporting charges, but the mechanism of charge injection and / or transport by the metal oxide nanoparticles in the present invention is currently clear. This principle is not established. However, the mechanism in the present invention is a mechanism of electron injection and / or electron transport by a layer such as a so-called electron injection layer, electron transport layer, or electron injection transport layer used in an organic EL device produced by a conventional dry method. Are considered different. However, in this specification, in order to avoid complicated explanation, for the sake of convenience, “metal oxide nanoparticles have a charge (hole or electron) injection property and / or a charge (hole or electron) transport property. Or “charge (hole or electron) injection property and / or charge (hole or electron) transport property metal oxide nanoparticle”.

FIG. 3 is a schematic cross-sectional view showing a modification of the EL element of Embodiment 1, and is an enlarged view of the light emitting layer. The light emitting layer 3 may include a support 7, and the light emitting nanoparticles 5 and the non-light emitting nanoparticles 6 may be dispersed in the support 7. Metal oxide nanoparticles usually have a modification layer of about several nanometers on the surface layer of the particles. As a result, even metal oxide nanoparticles alone are fixed in a film by self-supporting force. Often done. However, since this adhesive force is small, many films made of metal oxide nanoparticles alone are easily peeled off. Therefore, usually, the light emitting layer 3 can be firmly fixed to the device by using a polymer material having a strong self-supporting force as a binder in combination with the quantum dot material and the metal oxide nanoparticle material. In the EL device of the present embodiment, the metal oxide nanoparticles used for the light emitting layer 3 need to be provided with both functions of electron transporting property and hole transporting property. In this way, by blending multiple metal oxide nanoparticles with different characteristics to the polymer support (binder resin), the functionality of either charge can be demonstrated more effectively. Can be made. As described above, by using a polymer material as a binder, it is possible to easily form a stable film on the light-emitting layer 3 that has excellent film formability and can disperse a mixture of metal oxide nanoparticles substantially uniformly. Can do.

As the binder resin, polystyrene, polyimide, polycarbonate, acrylic resin, inactive resin, or the like can be used.

Further, the binder resin may have a charge transport property, and a charge transport material may be mixed in the binder resin. In these cases, the conductivity of the light emitting layer 3 can be improved as compared with the case where the binder resin is insulative. The metal oxide nanoparticles themselves have sufficient charge transport performance. However, when the minute nanoparticles are uniformly dispersed in the binder at a low concentration, the charges possessed by the nanoparticles may not be transported effectively. Therefore, by using a material having charge transport properties as a material constituting the light emitting layer other than the metal oxide nanoparticles, the high charge transport properties of the metal oxide nanoparticles can be further effectively extracted. .

Examples of the charge transporting binder resin and the charge transporting material mixed in the binder resin include polythiophene and derivatives thereof, polypyrrole and derivatives thereof, polyaniline and derivatives thereof, and conjugated polymer materials based on these. .

In addition, the support body 7 should just be at least 1 type, and the number of the types is not specifically limited. That is, the support 7 may contain a plurality of materials.

In the configuration of the present embodiment, since current is passed through the light emitting layer 3 using the internal charges of the metal oxide nanoparticles, there is no particular condition for selecting the material of the upper and lower electrodes 2 and 4. However, since the present embodiment is a light emitting element, at least one of the upper and lower electrodes 2 and 4 needs to be transparent. Further, for example, if a transparent conductive film such as ITO is used as the upper and lower electrodes 2 and 4, a transparent light emitting element can be obtained. Even if at least one of the upper and lower electrodes 2 and 4 is formed using a metal material, it is possible to impart transparency to at least one of the upper and lower electrodes 2 and 4 by forming a thin metal film. Even in this case, the same material can be used by making the upper and lower electrodes 2 and 4 the same, so the number of film forming apparatuses and types of materials can be reduced, and as a result, cost reduction can be realized. it can.

Further, since the light emitting layer 3 is basically formed of an inorganic material, the film formation method of the upper and lower electrodes 2 and 4 can be freely set. In a conventional organic EL element, for example, when an ITO film is formed by sputtering on the organic layer, the organic layer may be deteriorated. On the other hand, in the configuration of this embodiment, even if sputtering is used for forming the electrode 4, the light emitting layer 3 is not deteriorated.

As materials for the upper and lower electrodes 2 and 4, in addition to ITO, Al, Ag, Mo, Au, or the like may be used.

On the other hand, from the viewpoint of improving charge injection, different materials can be used for the upper and lower electrodes 2 and 4. Thereby, depending on the material of the metal oxide nanoparticles or the material of the charge transporting resin used as the binder, charges can be injected into the light emitting layer 3 more efficiently. In this case, the anode preferably includes a material having a work function of 5 eV or less, and the cathode preferably includes a metal having a work function of 4 eV or more. More specifically, the material of the upper and lower electrodes 2 and 4 includes ITO as the anode, Al, MgAg alloy as the cathode, and Ba / Al laminated in which Ba and Al are laminated in this order from the light emitting layer 3 side. Examples include an electrode, a Ca / Al laminated electrode in which Ca and Al are laminated in this order from the light emitting layer 3 side, and a LiF / Al laminated electrode in which LiF and Al are laminated in this order from the light emitting layer 3 side.

Below, the manufacturing method of the organic EL element of this embodiment and a more specific Example (Example 1) are demonstrated.

The substrate 1 preferably has an insulating surface, for example, a substrate formed from an inorganic material such as glass or quartz, a substrate formed from a plastic such as polyethylene terephthalate, or a substrate formed from ceramics such as alumina. A substrate in which a metal substrate such as aluminum or iron is coated with an insulator such as SiO ₂ or an organic insulating material, a substrate in which the surface of the metal substrate is subjected to an insulation process by an anodic oxidation method, or the like can be widely used. .

First, an electrode 2 is formed by sputtering ITO (indium-tin oxide) having a thickness of 150 nm on the entire surface of the substrate 1 and patterning it into a desired shape and size by a photolithography process. In the present embodiment, patterning is performed with 2 × 2 mm pixels.

In addition, as a material of the electrode 2, in addition to ITO, a metal having a high work function such as gold (Au), platinum (Pt), nickel (Ni), or IDIXO (indium-indium zinc oxide; In ₂ O ₃ A transparent conductive material such as (ZnO) _n ) or SnO ₂ may be used.

Next, cleaning is performed after ITO patterning. Examples of the cleaning method include a method in which ultrasonic cleaning is performed for 10 minutes using acetone, isopropyl alcohol (IPA), etc., and then ultraviolet (UV) -ozone cleaning is performed for 30 minutes.

Next, barium titanate nanoparticles, which are electron-transporting metal oxide nanoparticles, copper oxide (Cu ₂ O) nanoparticles, which are hole-transporting metal oxide nanoparticles, and CdSe quantum dots ( Evident Technology, peak wavelength 520 nm), and polyarinine-based hole transport material ND1501 (Nissan Chemical Co., Ltd.) containing a binder resin and having hole transportability, mass ratio 1: 1: 0.3: A mixture in which 0.1 is mixed is prepared, and a solution in which this mixture is dissolved and / or dispersed in NMP (N-methylpyrrolidone) so as to have a solid content ratio of 20% is sprayed. The light emitting layer 3 having a film thickness of 100 nm is formed by coating on the substrate 2. As application conditions at this time, for example, the N ₂ flow rate is 10 l / min, the solution flow rate is 0.2 l / min, the spray nozzle moving speed is 2 mm / sec, and the nozzle height is 130 cm. That's fine. Then, a solvent is evaporated by baking (200 degreeC, 10 minutes) on a hotplate. The average particle diameter of the barium titanate nanoparticles and the copper oxide nanoparticles is about 20 nm, and the average particle diameter of the quantum dots is about 10 nm.

Here, a green light emitting material is used as the quantum dots, but blue and red light emitting materials may be used as necessary. Even if the quantum dot itself is the same material, the emission color can be changed depending on the particle diameter. That is, in the injection process, any color of green, blue and red can be injected by the same mechanism.

An aluminum (Al) film having a film thickness of 100 nm was formed as the electrode 4 on the light emitting layer 3 thus formed by a vacuum vapor deposition method, thereby completing the device of this embodiment.

As described above, according to the EL element of this embodiment, high light emission efficiency and high color purity can be realized.

(Embodiment 2)
The EL element of this embodiment has the same configuration as that of the EL element of Example 1 except that an ITO film having a thickness of 100 nm is formed as the electrode 4 by a sputtering apparatus.

In the EL element of the present embodiment, since the light emitting layer 3 is made of an inorganic material, the light emitting layer 3 is not damaged even if the sputter film is formed directly on the light emitting layer 3. That is, a transparent conductive film such as ITO can be formed without damaging the light emitting layer 3.

According to the EL element of this embodiment, since the electrodes 2 and 4 are both transparent, a double-sided light emitting element can be realized. Moreover, since the apparatus (sputtering apparatus) in which the electrode 2 is formed can be used as the apparatus for forming the electrode 4 as it is, the apparatus for forming the electrode 4 is not required.

(Embodiment 3)
The EL element of this embodiment is the same as the EL element of Example 1 except that a Ba film having a film thickness of 100 nm and an Al film having a film thickness of 100 nm are formed in this order as the electrode 4 by the vacuum evaporation method. It has a configuration.

In the EL element of the present embodiment, it is possible to easily inject electrons into the light emitting layer 3 as compared with the case where only the Al film is provided as the electrode 4. As a result, the current value of the element can be improved.

(Embodiment 4)
FIG. 4 is a schematic cross-sectional view of an EL element according to the fourth embodiment. The EL device according to the present embodiment includes nanoparticles of barium titanate, which are electron-transporting metal oxide nanoparticles, and copper oxide (Cu ₂ O) nanoparticles, which are hole-transporting metal oxide nanoparticles. , CdSe quantum dots (Evident Technology, peak wavelength: 520 nm), and polyarinine-based hole transport material ND1501 (Nissan Chemical Co., Ltd.) containing a binder resin and having hole transportability, have a mass ratio of 1: 0. .3: The structure is the same as that of the EL element of Example 1 as shown in FIG. As described above, since the amount of the metal oxide nanoparticles having a hole transporting property is reduced, the light emitting layer 3 becomes an electron-rich system, and the electron flow in the light emitting layer 3 flows 10 times as much as the holes. became. In addition, the EL element of the present embodiment is AC driven (AC driven) at a frequency of 60 Hz.

The light emitting region in the light emitting layer 3 is mainly determined by the balance of electron and hole transport in the light emitting layer 3. That is, in the conventional organic EL element, when a light emitting material in which electrons flow more easily is used, a light emission center is formed in the vicinity of the interface on the one electrode (anode) side.

According to the EL element of this embodiment, by performing AC driving, (1) when the electrode 2 is an anode and the electrode 4 is a negative electrode, the emission center (the region surrounded by the broken line in FIG. 4) is the electrode 2. (2) When the electrode 2 is a negative electrode and the electrode 4 is an anode, the light emission center is formed at the interface portion between the electrode 4 and the light emitting layer 3, and as a result, depending on the direction of the electrode The position of the light emission center can be changed.

On the other hand, for example, when a general conventional organic EL element is AC driven, the conventional organic EL element can emit light in the direction of the electric field to emit light (forward bias), but the electric field in the opposite direction (reverse bias). ) Could not emit light.

Therefore, when the element is aged by direct current (DC) and constant current driving, in a general conventional organic EL element, DC continues to flow in the forward direction in the light emitting layer and the light emission center in the light emitting layer is constant. In other words, only a certain point in the light emitting layer continues to emit light. And if aging is continued, the luminescent material in this luminescent center will deteriorate, As a result, luminescent brightness will fall.

On the other hand, in the EL element of the present embodiment, an alternating current (AC) electric field can be applied when constant current driving is performed. Further, according to the above-described light emitting mechanism, in the EL element of the present embodiment, the light emitting position in the light emitting layer 3 can be changed depending on the direction of the electric field applied to the upper and lower electrodes 2 and 4. Of course, in the EL element of this embodiment, a constant luminance can be obtained in each electric field direction. That is, at least two emission centers can be formed in the light emitting layer 3. As a result, it is possible to theoretically at least double the time for the emission luminance to decrease.

Further, it is considered that the stress caused by applying a DC electric field to the light emitting layer 3 only from a certain direction, that is, the stress due to the electric charge on the light emitting layer 3 is also a cause of deterioration of the element. On the other hand, in the EL element of this embodiment, the AC drive can eliminate the stress caused by the permanent application of such an electric field, so that deterioration of the element can be further suppressed.

Thus, it is preferable that the EL element of the present embodiment is AC driven (AC driven).

According to the EL element of the present embodiment, by forming a plurality of light emission centers, it is possible to theoretically at least double the time during which the light emission luminance decreases, and to eliminate the stress caused by the DC electric field. Therefore, the lifetime of the element can be further extended, more specifically, it can be extended by twice or more.

AC driving means driving by applying an AC voltage between the upper and lower electrodes 2 and 4, and the frequency in AC driving is not particularly limited. That is, when the EL element of the present embodiment is AC driven, it may be a slow switching of the electric field direction of 1 Hz level, or a switching of the electric field direction of 60 Hz or more, and the element life can be extended similarly. However, it is considered that AC driving at a certain frequency (preferably 60 Hz) or more increases the effect of preventing deterioration due to the stress due to the charge. Visibility can be improved by AC driving at a certain frequency or higher. That is, by performing AC driving at 60 Hz or higher, the non-lighting state at the time of switching of the electric field cannot be recognized by the human eye due to the afterimage, and it can be recognized that it is always lit. Moreover, in the conventional organic EL element, the shape of the spectrum changes when the emission center changes due to the optical effect. However, in the light emission of quantum dots, even if the emission center changes, the original spectrum peak is steep, so even if the emission center changes, it is hardly affected by the optical effect. Therefore, by using quantum dots, the shape of the spectrum can be prevented from changing even if the emission center changes.

The AC driving can be realized by applying an electric field to the light emitting layer 3 using voltage switching means such as a pulse generator capable of switching the voltage between positive and negative. This also makes it possible to apply an arbitrary pulse such as a rectangular wave, a pulse waveform having a duty ratio, or a sine wave.

When permanent light emission is desired by a DC electric field, light is sufficiently emitted in one electric field direction, and after deterioration, the electric field direction is reversed and light emission is performed at different emission centers. Also by this, the lifetime of the element can be extended as compared with the conventional organic EL element.

As described above, in order to separate the emission center in the light emitting layer 3, it is preferable that the light emitting layer 3 has an electron transporting property and a hole transporting property, and that there is a difference in transporting property between the two. In the present embodiment, the light emitting layer 3 has an electron transporting property and a hole transporting property that are different from each other in transport performance. The light emitting layer 3 has an electron transporting property and a hole transporting property in some form. The larger the difference in the transporting properties, the greater the change in the position of the light emission center depending on the electric field direction. In the present embodiment, since the electron transporting property of the light emitting layer 3 is larger than the hole transporting property (electron transporting property> hole transporting property), the negative charge from the upper part of the element (electrode 4) and the lower part (electrode 2) When a more positive electric field is applied, the emission center is formed on the lower side (substrate 1 side) of the light emitting layer 3. Conversely, when an electric field in the reverse direction is applied, a light emission center is formed on the upper side of the light emitting layer 3. That is, when the injection direction of holes and electrons into the light emitting layer 3 is reversed, the location of the light emission center in the light emitting layer 3 changes greatly. Thus, if the two light emission centers can be formed so as not to overlap in the light emitting layer 3, the light emission characteristics at each light emission center can be effectively exhibited, so that the lifetime can be improved more efficiently.

As described above, the EL element of this embodiment can emit light to the light emitting layer 3 at a plurality of light emission centers (at least two light emission centers). That is, the EL element of this embodiment can have a plurality of emission centers of the light emitting layer 3. Note that the emission center is usually a region in which recombination of electrons and holes in the film thickness direction of the light emitting layer 3 occurs most actively.

Moreover, the light emitting layer 3 has an electron transport property and a hole transport property which have a difference 10 times or more in mutual transport performance. Thereby, the emission center can be almost limited to the interface between the light emitting layer 3 and the upper and lower electrodes 2 and 4. That is, the position of the light emission center can be set to the upper end side or the lower end side (end portion on the substrate 1 side) of the light emitting layer 3 depending on the electric field direction. Therefore, the difference in the emission center depending on the electric field direction can be made clearer.

Furthermore, the light emitting layer 3 has a higher electron transport property than a hole transport property, and contains metal oxide nanoparticles having an electron transport property. For example, like a quantum dot, depending on the characteristics, there are many cases where the charge transporting property itself cannot be improved or the difference between the electron transporting property and the hole transporting property cannot be made due to the characteristics. In such a case, in order to draw out the difference in charge transportability of the light emitting layer 3, the metal oxide nanoparticles having electron transporting property or hole transporting property are mixed in the light emitting layer 3, thereby In addition to improving the charge transportability, it is possible to provide a difference in electron and hole transport characteristics. As a result, the difference in the emission center depending on the electric field direction can be made clearer.

(Embodiment 5)
FIG. 5 is a schematic cross-sectional view of an EL element according to the fifth embodiment. The EL device according to the present embodiment includes nanoparticles of barium titanate, which are electron-transporting metal oxide nanoparticles, and copper oxide (Cu ₂ O) nanoparticles, which are hole-transporting metal oxide nanoparticles. , CdSe quantum dots (Evident Technology, peak wavelength: 520 nm), and a polyarinin-based hole transport material ND1501 (Nissan Chemical Co., Ltd.) containing a binder resin and having hole transportability, have a mass ratio of 0.3. Except for the change to 1: 0.3: 0.1, the EL device has the same configuration as the EL device of Example 1 as shown in FIG. As described above, since the amount of the electron-transporting metal oxide nanoparticles is reduced, the light emitting layer 3 becomes a hole-rich system, and the hole flow in the light emitting layer 3 flows 10 times as much as the electrons. became. In addition, the EL element of the present embodiment is AC driven (AC driven) at a frequency of 60 Hz.

In the EL device of this embodiment, the light emitting layer 3 has an electron transport property and a hole transport property, and there is a difference in transport properties between the two, as in the EL device of Embodiment 4. Moreover, the light emitting layer 3 has an electron transport property and a hole transport property which have a difference 10 times or more in mutual transport performance. Furthermore, the light emitting layer 3 has a larger hole transport property than an electron transport property, and contains metal oxide nanoparticles having a hole transport property. Therefore, the same effect as the EL element of Embodiment 4 can be produced. However, the light emission center (the region surrounded by the broken line in FIG. 5) is formed at a location opposite to that of the fourth embodiment in each electric field direction. That is, when a negative charge is applied from the upper part (electrode 4) of the device and a positive electric field is applied from the lower part (electrode 2), the emission center is formed on the upper side of the light emitting layer 3. Conversely, when an electric field in the opposite direction is applied, a light emission center is formed on the lower side (substrate 1 side) of the light emitting layer 3.

In addition, when the electrode 2 or the electrode 4 is formed using an active metal film such as Ba as in the third embodiment, an exciton quenching site can be obtained if there is an emission center near the active metal film. There is. In such a case, the balance of the metal oxide nanoparticles in the light emitting layer 3 can be adjusted to separate the light emission center from the active metal film. As described above, the deterioration of the element can be further prevented by changing the position of the light emission center according to the material of the electrodes 2 and 4.

(Embodiment 6)
FIG. 6 is a schematic cross-sectional view of an EL element according to the sixth embodiment. As shown in FIG. 6, the EL element of the present embodiment has a hole injection / transport layer 8 that is a layer for injecting or transporting holes between the electrode 2 and the light emitting layer 3, The structure is the same as that of the EL element of Example 1. More specifically, PEDOT-PSS was formed on the electrode 2 to have a film thickness of 60 nm by spin coating, and the hole injection / transport layer 8 was formed by baking at 200 ° C. for 10 minutes.

The material of the hole injection / transport layer 8 is not limited to PEDOT-PSS, and a hole transport material, a hole injection material, and a hole injection / transport material that are generally used in an organic EL element may be used. Alternatively, hole transporting metal oxide nanoparticles may be used. Further, the hole injecting and transporting layer 8 may be mixed with a plurality of materials. Thus, the hole injection transport layer 8 may be a hole injection layer or a hole transport layer.

According to the EL device of this embodiment, holes can be efficiently injected from the electrode 2 into the device. Moreover, when the electron inject | poured from the electrode 4 penetrates the light emitting layer 3, an electron blocking effect can be exhibited. Therefore, the hole injection property to the light emitting layer 3 is improved and the electrons penetrating the light emitting layer 3 can be blocked, so that the light emission efficiency can be further improved.

Here, the hole injecting and transporting layer 8 is inserted between the electrode 2 and the light emitting layer 3, but instead of the hole injecting and transporting layer 8, electrons are injected between the electrode 4 and the light emitting layer 3. An electron injecting and transporting layer that is a layer for transporting may be inserted. The electron injecting and transporting layer is formed by a spray method. Also in this case, as a material of the electron injection / transport layer, an electron transport material, an electron injection material, an electron injection / transport material generally used in an organic EL element may be used, or an electron transporting metal oxide nano material may be used. Particles may be used. The electron injecting and transporting layer may be mixed with a plurality of materials. Thus, the electron injection / transport layer may be an electron injection layer or an electron transport layer. Also by this, luminous efficiency can be further improved.

(Embodiment 7)
FIG. 7 is a schematic cross-sectional view of an EL element according to the seventh embodiment. In the EL device of this embodiment, as shown in FIG. 7, a hole injection transport layer 8 is inserted between the electrode 2 and the light emitting layer 3, and an electron injection transport is performed between the electrode 4 and the light emitting layer 3. The structure is the same as that of the EL element of Example 1 except that the layer 9 is inserted. More specifically, a polyalinin-based hole transport material ND1501 containing copper oxide (Cu ₂ O) nanoparticles, which are hole transportable metal oxide nanoparticles, and a binder resin and having hole transportability. (Manufactured by Nissan Chemical Co., Ltd.) is mixed so that the mass ratio is 1: 0.1, and this mixture is dissolved in NMP (N-methylpyrrolidone) so that the solid content ratio is 20%. And the hole injection transport layer 8 with a film thickness of 100 nm is formed by apply | coating the dispersed solution on the electrode 2 with a spray method. The coating conditions at this time are the same as the film forming conditions of the light emitting layer 3. Then, a solvent is evaporated by baking (200 degreeC, 10 minutes) on a hotplate.

In addition, it does not specifically limit as a material of the positive hole injection transport layer 8, You may use metal oxide nanoparticles other than the above, The positive hole transport material generally used by an organic EL element, a positive hole injection material Alternatively, a hole injecting and transporting material may be used. Further, the hole injecting and transporting layer 8 may be mixed with a plurality of materials. Thus, the hole injection transport layer 8 may be a hole injection layer or a hole transport layer.

Next, after forming the light emitting layer 3 on the hole injecting and transporting layer 8 in the same manner as in Example 1, it contains barium titanate nanoparticles that are electron transporting metal oxide nanoparticles and a binder resin. In addition, a material prepared by mixing polyallynin-based hole transport material ND1501 (manufactured by Nissan Chemical Co., Ltd.) having a hole transporting property so as to have a mass ratio of 1: 0.1 is prepared, and this mixture is mixed with NMP (N An electron injecting and transporting layer 9 having a thickness of 20 nm is formed by applying a solution dissolved and / or dispersed in methylpyrrolidone) on the light emitting layer 3 by a spray method. The coating conditions at this time are the same as the film forming conditions of the light emitting layer 3. Then, a solvent is evaporated by baking (200 degreeC, 10 minutes) on a hotplate.

In addition, it does not specifically limit as a material of the electron injection transport layer 9, You may use metal oxide nanoparticles other than the above, The electron transport material generally used with an organic EL element, an electron injection material, an electron injection A transport material may be used. The electron injecting and transporting layer 9 may be mixed with a plurality of materials. Thus, the electron injection / transport layer 9 may be an electron injection layer or an electron transport layer.

According to the EL device of this embodiment, holes can be efficiently injected from the electrode 2 into the device. Further, electrons can be efficiently injected from the electrode 4 into the device. Further, when electrons injected from the electrode 4 penetrate the light emitting layer 3, an electron blocking effect can be exhibited. And when the hole inject | poured from the electrode 2 penetrates the light emitting layer 3, a hole blocking effect can be exhibited. Therefore, the hole and electron injection property to the light emitting layer 3 is improved and the holes and electrons penetrating the light emitting layer 3 can be blocked, so that the light emission efficiency can be further improved.

In addition, the hole injecting and transporting layer 8 and the electron injecting and transporting layer 9 each include the same material as the non-light emitting nanoparticle 6 (metal oxide nanoparticle) included in the light emitting layer 3. As a result, electrons and holes are directly injected from the hole injecting and transporting layer 8 and the electron injecting and transporting layer 9 into the non-light emitting nanoparticles 6 included in the light emitting layer 3, so that more efficient electron injection and holes are possible. An injection can be performed.

As in the present embodiment, at least one of the layers sandwiched between the electrodes 2 and 4 (charge injection transport layer and charge blocking layer described later) is preferably formed by a spray method. More preferably, the layer sandwiched between the four layers is formed by a spray method. As materials constituting these layers, materials that are soluble in organic solvents are usually used. For example, when these layers are formed by a method such as a spin coating method or an ink jet method, the solution and the lower layer are mixed. In addition to being unable to make a laminated structure, the in-plane uniformity is significantly impaired. Therefore, a laminated film is produced by spray coating. The spray method is a method in which a solution is formed in a micro mist state. For this reason, the solvent is almost evaporated at the time of dropping onto the substrate. For example, even if a charge injecting and transporting layer is formed on the light emitting layer 3, they can be laminated almost without crossing each other. Therefore, a high-performance EL element having a stacked structure in which functionality is ensured can be manufactured. Further, the charge injecting and transporting layer and the charge blocking layer can be formed using the same solvent as the organic solvent used for forming the light emitting layer 3.

(Embodiment 8)
FIG. 8 is a schematic cross-sectional view of an EL element according to the eighth embodiment. As shown in FIG. 8, the EL device of this embodiment has the same configuration as the EL device of Example 1 except that an electron blocking layer 10 is inserted between the electrode 2 and the light emitting layer 3. The electron blocking layer 10 is a layer having an effect of suppressing the transport of only electrons without suppressing the flow of holes.

In addition, as a material of the electron blocking layer 10, the electron blocking material generally used with an organic EL element can be used. The electron blocking layer 10 may be mixed with a plurality of materials.

According to the EL element of the present embodiment, when electrons injected from the electrode 4 penetrate the light emitting layer 3, an electron blocking effect can be exhibited. Therefore, the luminous efficiency can be further improved.

Here, although the electron blocking layer 10 is inserted between the electrode 2 and the light emitting layer 3, a hole blocking layer is inserted between the electrode 4 and the light emitting layer 3 instead of the electron blocking layer 10. Also good. The hole blocking layer is a layer having an effect of suppressing the transport of only holes without suppressing the flow of electrons. The hole blocking layer is formed by a spray method.
Also in this case, as a material of the hole blocking layer, a hole blocking material generally used in an organic EL element can be used. The hole blocking layer may be mixed with a plurality of materials. Also by this, luminous efficiency can be further improved.

(Embodiment 9)
FIG. 9 is a schematic cross-sectional view of an EL element according to the ninth embodiment. As shown in FIG. 9, in the EL element of this embodiment, an electron blocking layer 10 is inserted between the electrode 2 and the light emitting layer 3, and a hole blocking layer 11 is interposed between the electrode 4 and the light emitting layer 3. The structure is the same as that of the EL element of Example 1 except that is inserted. The electron blocking layer 10 and the hole blocking layer 11 are formed by a spray method.

In addition, as a material of the electron blocking layer 10, the electron blocking material generally used with an organic EL element can be used. The electron blocking layer 10 may be mixed with a plurality of materials.

As a material of the hole blocking layer 11, a hole blocking material generally used in an organic EL element can be used. The hole blocking layer 11 may be mixed with a plurality of materials.

According to the EL element of the present embodiment, when electrons injected from the electrode 4 penetrate the light emitting layer 3, an electron blocking effect can be exhibited. Moreover, when the hole injected from the electrode 2 penetrates the light emitting layer 3, a hole blocking effect can be exhibited. Therefore, the luminous efficiency can be further improved.

(Embodiment 10)
FIG. 10 is a schematic cross-sectional view of an EL element according to the tenth embodiment. As shown in FIG. 10, the EL element of the present embodiment is a form that covers all of the sixth to ninth embodiments. Specifically, in the EL device of this embodiment, the hole injection / transport layer 8 and the electron blocking layer 10 are inserted in this order between the electrode 2 and the light emitting layer 3 from the electrode 2 side, Except that the hole blocking layer 11 and the electron injecting and transporting layer 9 are inserted in this order between the light emitting layer 3 and the light emitting layer 3, it has the same configuration as the EL element of Example 1. The hole injection / transport layer 8, the electron blocking layer 10, the light emitting layer 3, the hole blocking layer 11 and the electron injection / transport layer 9 are all formed by a spray method.

Since the EL element of this embodiment has a configuration in which the charge injection efficiency and the charge blocking effect are maximized, the light emission efficiency can be particularly improved.

In addition, the EL element of this embodiment may be in a form in which at least one of the hole injection / transport layer 8, the electron blocking layer 10, the hole blocking layer 11 and the electron injection / transport layer 9 is not appropriately formed. That is, for example, the EL element of the present embodiment may not have the electron blocking layer 10 and the electron injection transport layer 9 but may have the hole injection transport layer 8 and the hole blocking layer 11. The hole injection / transport layer 8 and the hole blocking layer 11 may not be provided, and the electron blocking layer 10 and the electron injection / transport layer 9 may be included. One of the blocking layer 11 and the electron injecting and transporting layer 9 may not be formed.

It is a cross-sectional schematic diagram of the EL element of Embodiment 1, (a) shows a laminated structure, (b) is an enlarged view of a light emitting layer. It is a schematic diagram which shows the band gap of the quantum dot which concerns on Embodiment 1 whose core part consists of CdSe and whose shell part consists of ZnS. It is a cross-sectional schematic diagram which shows the modification of the EL element of Embodiment 1, and is an enlarged view of a light emitting layer. 6 is a schematic cross-sectional view of an EL element according to Embodiment 4. FIG. 6 is a schematic cross-sectional view of an EL element according to Embodiment 5. FIG. 10 is a schematic cross-sectional view of an EL element according to Embodiment 6. FIG. 10 is a schematic cross-sectional view of an EL element according to Embodiment 7. FIG. 10 is a schematic cross-sectional view of an EL element according to Embodiment 8. FIG. 10 is a schematic cross-sectional view of an EL element according to Embodiment 9. FIG. 10 is a schematic cross-sectional view of an EL element according to Embodiment 10. FIG.

Explanation of symbols

1: Substrate 2, 4: Electrode 4: Luminescent layer 5: Luminescent nanoparticles (nanoluminescent body)
5a: Core part 5b: Shell part 6: Non-luminescent nanoparticle 7: Support 8: Hole injection / transport layer 9: Electron injection / transport layer 10: Electron blocking layer 11: Hole blocking layer e: Electron h: Hole

Claims (29)

An electroluminescent device comprising a pair of a first electrode and a second electrode, at least one of which is light transmissive, and a light emitting layer sandwiched between the first electrode and the second electrode,
The light-emitting layer contains a light-emitting nanoparticle and a non-light-emitting nanoparticle. The electroluminescent device according to claim 1, wherein the non-light-emitting nanoparticles have a charge transport property. The electroluminescent device according to claim 1, wherein the non-light-emitting nanoparticles include electron-transporting nanoparticles and hole-transporting nanoparticles. The electroluminescent device according to claim 3, wherein the light-emitting nanoparticles are electrically connected to the electron-transporting nanoparticles and the hole-transporting nanoparticles. The electroluminescent device according to claim 1, wherein the non-light-emitting nanoparticles include metal oxide nanoparticles. 6. The electroluminescent device according to claim 1, wherein the non-light-emitting nanoparticles have a band gap that is equal to or larger than a band gap of the light-emitting nanoparticles. Sense element. The electroluminescent device according to claim 1, wherein the luminescent nanoparticle contains a quantum dot luminescent material. The electroluminescent element according to claim 1, wherein the light emitting layer includes a support material. 9. The electroluminescent device according to claim 8, wherein the support material has charge transportability. The electroluminescent element according to claim 1, wherein the first electrode and the second electrode contain the same material. The electroluminescent device according to claim 1, wherein the first electrode and the second electrode include materials having different work function values. The said electroluminescent element is further equipped with the electric charge injection transport layer between the layers of one of said 1st electrode and said 2nd electrode, and said light emitting layer, The Claim 1 characterized by the above-mentioned. Electroluminescence element. The electroluminescent device according to claim 12, wherein the charge injection transport layer includes nanoparticles. The electroluminescence device further includes a first charge injection transport layer and a second charge injection transport layer between the first electrode and the light emitting layer and between the second electrode and the light emitting layer, respectively. The electroluminescence device according to claim 1, wherein the electroluminescence device is a device. The electroluminescent device according to claim 14, wherein the first charge injection transport layer and the second charge injection transport layer include nanoparticles. 16. The electroluminescent device according to claim 14, wherein the first charge injecting and transporting layer and the second charge injecting and transporting layer contain the same material as the non-light emitting nanoparticle contained in the light emitting layer. . One of the first charge injection transport layer and the second charge injection transport layer has an electron transport property,
The other of said 1st charge injection transport layer and said 2nd charge injection transport layer has hole transport property, The electroluminescent element in any one of Claims 14-16 characterized by the above-mentioned. The electroluminescence device according to any one of claims 1 to 17, wherein the electroluminescence element further includes a charge blocking layer between one of the first electrode and the second electrode and the light emitting layer. Luminescence element. The electroluminescent device further includes a first charge blocking layer and a second charge blocking layer between the first electrode and the light emitting layer and between the second electrode and the light emitting layer, respectively. The electroluminescent element according to claim 1. The organic electroluminescent element according to claim 1, wherein the electroluminescent element has a plurality of emission centers in the light emitting layer. The electroluminescent device according to any one of claims 1 to 20, wherein the light emitting layer has an electron transporting property and a hole transporting property that are different from each other in transport performance. The electroluminescent device according to claim 21, wherein the light emitting layer has an electron transporting property and a hole transporting property having a difference of 10 times or more in the transport performance of each other. 23. The electroluminescent device according to claim 21, wherein the light emitting layer has a higher electron transport property than a hole transport property and contains metal oxide nanoparticles having an electron transport property. The electroluminescent device according to claim 21 or 22, wherein the light emitting layer has a hole transport property larger than an electron transport property and contains metal oxide nanoparticles having a hole transport property. The electroluminescent element according to claim 1, wherein the electroluminescent element is AC driven. 26. The electroluminescent device according to claim 25, wherein the electroluminescent device is AC driven at a driving frequency of 60 Hz or more. 27. The electroluminescent device according to claim 1, wherein at least one of the layers sandwiched between the first electrode and the second electrode is formed by a spray method. The electroluminescence device according to any one of claims 1 to 27, wherein an ionization potential of the non-light-emitting nanoparticles is larger than an ionization potential of the light-emitting nanoparticles. The electroluminescent device according to any one of claims 1 to 28, wherein the electronegativity of the non-light-emitting nanoparticles is smaller than the electronegativity of the light-emitting nanoparticles.

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