Patent Application
20100245218
1. Technical Field
The present invention relates to a light-emitting device for electroluminescence and a display device using the light emitting device. This light emitting device is available as a variety of light sources for use in communication and illumination.
2. Description of the Related Art
In recent years, electroluminescence elements (hereinafter, referred to as EL elements) have attracted attention as light and thin surface-emitting elements. The EL elements are broadly divided into organic EL elements in which a direct-current voltage is applied to a fluorescent substance made of an organic material to recombine electrons and holes for light emission, and inorganic EL elements in which an alternating voltage is applied to a fluorescent substance made of an inorganic material to induce electrons accelerated in a high electric field of approximately 106 V/cm to collide with the luminescent center of the inorganic fluorescent substance for excitation of the electrons, and permit the inorganic fluorescent substance to emit light in the relaxation process.
Further, the inorganic EL elements include dispersion EL elements in which inorganic fluorescent substance particles are dispersed in a binder made of a polymer organic material to serve as a phosphor layer, and thin-film EL elements in which an insulating layer is provided on one or both sides of a thin-film phosphor layer with a thickness on the order of 1 μm. Among these elements, the dispersion EL elements have attracted attention because of the advantages of their lower power consumption and even lower manufacturing cost due to their simpler manufacturing processes.
The EL element referred to as a dispersion EL element will be described. Conventional EL elements have a layered structure including a substrate, a first electrode, a phosphor layer, an insulator layer, and a second electrode in order from the substrate side. The phosphor layer includes inorganic fluorescent substance particles such as ZnS:Mn dispersed in an organic binder, and the insulator layer includes a strong insulator such as BaTiO3 dispersed in an organic binder. An alternating-current power supply is placed between the first electrode and the second electrode, and a voltage is applied from the alternating-current power supply to the first electrode and the second electrode to permit the EL element to emit light.
In the structure of the dispersion EL element, the phosphor layer is a layer which determines the luminance and efficiency of the dispersion EL element, and particles with a size of 15 μm to 35 μm in particle diameter is used for the inorganic fluorescent substance particles of this phosphor layer. Furthermore, the luminescent color of the phosphor layer of the dispersion EL element is determined by the inorganic fluorescent substance particles used in the phosphor layer. For example, orange light emission is exhibited in the case of using ZnS:Mn for the inorganic fluorescent substance particles, and for example, blue-green light emission is exhibited in the case of using ZnS:Cu for the inorganic fluorescent substance particles. As described above, the luminescent color is determined by the inorganic fluorescent substance particles. Thus, when light of other, white luminescent color is to be emitted, an organic dye is mixed into the organic binder to convert the luminescent color, thereby obtaining the intended luminescent color.
However, light emitters for use in the EL elements have the problems of low light emission luminance and short lifetime.
As a method for increasing the light emission luminance, a method of increasing the voltage applied to the phosphor layer is conceivable. In this case, there is a problem that the half-life of the light output from the light emitter is decreased in proportion to the applied voltage. On the other hand, as a method for making the half-life longer, that is, making the lifetime longer, a method of decreasing the voltage applied to the phosphor layer is conceivable. However, this method has the problem of decrease in light emission luminance. As described above, the light emission luminance and the half-life have a relationship in which when the voltage applied to the phosphor layer is increased or decreased to try to improve one of the light emission luminance and the half-life, the other will be degraded. Therefore, one will have to select either the light emission or the half-life. It is to be noted that the half-time in the specification refers to a period of time until the light output from the light emitter is decreased to the half output of the original luminance.
Thus, suggestions have been made for driving light emitting devices with low voltages, as described in Japanese Patent Laid-Open Publication No. 2006-120328 and Japanese Patent Laid-Open Publication No. 2006-127780. According to this suggestion, in a dispersion EL element, a phosphor layer and a dielectric are interposed between a transparent electrode and a rear electrode, and the phosphor layer has an acicular substance with its conductivity higher than that of a fluorescent substance with being dispersed in an organic binder. Since the acicular substance is dispersed, high-energy electrons are permitted to collide efficiently with the fluorescent substance, thereby allowing for a longer lifetime and a higher efficiency.
However, in the above proposal, it is essential to provide the dielectric layer for constituting dispersion EL, and it is further necessary to apply a high alternating voltage between the electrodes for permitting the phosphor layer to emit light. As a result, the dispersion type EL has a problem that it is hard to obtain long lifetimes and high efficiencies.
An object of the present invention is to solve the problem described above and to provide a light emitting device which is driven at a low voltage, exhibits a high light emission luminance, and has a long lifetime.
A light-emitting device according to the present invention includes:
a first electrode and a second electrode arranged facing each other, at least one of the electrodes being transparent or semi-transparent; and
a phosphor layer provided as being sandwiched between the first electrode and the second electrode, wherein conductive nano particles and phosphor particles are dispersed in a matrix including a hole-transporting material.
A light-emitting device according to the present invention includes:
a first electrode and a second electrode arranged facing each other, at least one of the electrodes being transparent or semi-transparent; and
a phosphor layer sandwiched between the first electrode and the second electrode, the phosphor layer including a phosphor particle powder containing phosphor particles, the phosphor particle having at least surface covered with a coating layer, the coating layer including a hole transport material and conductive nano particles dispersed in the hole transport material.
The phosphor layer may include binder among the phosphor particles.
The conductive nano particles may be interspersed among the respective phosphor particles, the respective phosphor particles may form an electrical connection through the conductive nano particles.
The conductive nano particles may include at least one metal fine particle selected from the group constituting of Ag, Au, Pt, Ni, and Cu. Further, the conductive nano particles may include at least one oxide fine particle selected from the group constituting of an indium tin oxide, ZnO, and InZnO. The conductive nano particles may include at least one carbon substance fine particle selected from the group of fullerene and a carbon nanotube.
The conductive nano particles may have an average particle diameter within the range of 1 to 200 nm.
The hole transport material may include an organic hole transport material including an organic matter.
The organic hole transport material may contain components of the following chemical formula 1 and chemical formula 2.
The organic hole transport material may further include at least one component of the group constituting of the following chemical formula 3, chemical formula 4, and chemical formula 5.
The organic hole transport material may further include at least one component of the group constituting of the following chemical formula 6, chemical formula 7, and chemical formula 8.
The hole transport material may include an inorganic hole transport material including an inorganic matter.
The phosphor particles may include a particle including a Group 13-Group 15 compound semiconductor. The phosphor particles may include at least one light emitting material selected from the group of a nitride, a sulfide, a selenide, and an oxide. The phosphor particles are nitride semiconductor particles may include at least one element of Ga, Al, and In. The phosphor particles may be phosphor particles including GaN.
The phosphor particles may have an average particle diameter within the range of 0.1 μm to 1000 μm.
The conductive nano particles may be selected from the group of metal material particles such as Ag, Au, Pt, Ni, and Cu. The conductive nano particles may be selected from oxide particles such as an indium tin oxide, ZnO, and InZnO. The conductive nano particles may be selected from the group of carbon material particles such as a carbon nanotube.
The conductive nano particles may have an average particle diameter or an average length within the range of 1 to 200 nm.
The light emitting device of the present invention may further include a hole injection layer sandwiched between the first electrode and the phosphor layer. The light emitting of the present invention may further include a support substrate facing the first electrode or the second electrode for support. The support substrate may be a glass substrate or a resin substrate.
The light emitting device of the present invention may further include a thin film transistors connected to the first electrode or the second electrode.
A display device according to the present invention includes:
a light emitting device array in which the light emitting device is two-dimensionally arranged in plural;
a plurality of x electrodes extending parallel to each other in a first direction parallel to a surface of the light emitting device array; and
a plurality of y electrodes extending parallel to a second direction parallel to the surface of the light emitting device array and orthogonal to the first direction,
wherein the thin film transistors of the light emitting device array are each connected to the x electrodes and the y electrodes.
A display device according to the present invention includes:
a light emitting device array in which the light emitting device is two-dimensionally arranged in plural;
a plurality of x electrodes extending parallel to each other in a first direction parallel to a surface of the light emitting device array; and
a plurality of y electrodes extending parallel to a second direction parallel to the surface of the light emitting device array and orthogonal to the first direction.
The display device according to the present invention may further include a color conversion layer anteriorly in a direction of light emission extraction.
The present invention will become readily understood from the following description of preferred embodiments thereof made with reference to the accompanying drawings, in which like parts are designated by like reference numeral and in which:
Light emitting devices according to embodiments of the present invention will be described below with reference to the accompanying drawings. It is to be noted that the practically same members are denoted by the same reference numerals in the drawings.
It is to be noted that the present invention is not limited to the structure described above, and changes can be appropriately made, in such a way that the rear electrode 12 and the transparent electrode 16 are interchanged, transparent electrodes are used for both of the electrode 12 and the electrode 16, or an alternating-current power supply is used as the power supply. Furthermore, changes can be appropriately made, in such a way that a black electrode is used as the rear electrode 12, or a structure is further provided for sealing all or part of the light element 10 with a resin or a ceramic. Furthermore, a modification example as shown in
The respective components of the light emitting device will be described below in detail with reference to
In
Alternatively, when no light is extracted from the substrate side, the light transmitting property described above is not required, and materials without any light transmitting property can also be used.
The electrodes include the rear electrode 12 and the transparent electrode 16. Of the two electrodes, the electrode on the side from which light is extracted is used as the transparent electrode 16. On the other hand, the other is used as the rear electrode 12.
To the rear electrode 12 on the side from which no light is extracted, any well-known conductive material may be applied as a rear electrode. For example, a thin film metal such as Au, Ag, Al, Cu, Ta, Ti, or Pt, or a laminate of one or more of the metals can be used.
The material of the transparent electrode 16 on the side from which light is extracted may be any material having a light transmitting property, and the material preferably has a low resistance. Materials which are particularly preferred as the material of the transparent electrode 16 include, but are not particularly limited to, metal oxides based on an ITO (In2O3 doped with SnO2, which is also referred to as an indium tin oxide), ZnO, ALZnO, GaZnO, or the like; or conductive polymers such as a polyaniline, a polypyrrole, PEDOT/PSS, and a polythiophene.
An ITO can be deposited by a deposition method such as sputtering, electron beam evaporation, or ion plating, for the purpose of improving the transparency or lowering the resistivity. Furthermore, after the deposition, surface treatment such as a plasma treatment may be applied for the purpose of controlling the resistivity. The film thickness of the transparent electrode is determined from the required sheet resistance and visible light transmittance. While the transparent electrode 16 may be directly formed on the phosphor layer 13, a transparent conductive film may be formed on a glass substrate and attached so that the transparent conductive film comes in contact with the phosphor layer 13.
It is to be noted that the rear electrode 12 may be configured to cover the entire surface of the layer, or may be configured to have a plurality of stripe-shaped electrodes in the layer. Furthermore, the rear electrode 12 and the transparent electrode 16 may be configured to have a plurality of stripe-shaped electrodes, in such a way that each stripe-shaped electrode of the rear electrode 12 and all of the strip-shaped electrodes of the transparent electrode 16 have a skew relationship with each other and that projections of each stripe-shaped electrode of the rear electrode 12 onto the light emitting surface and projections of all of the stripe-shaped electrodes of the rear electrode 16 onto the light emitting surface intersect with each other. In this case, the application of a voltage to the electrodes selected respectively from the respective stripe-shaped electrodes of the rear electrode 12 and the respective striped-shaped electrodes of the transparent electrode 16 allows a display to be configured in such a way that light is emitted in a predetermined position.
The phosphor layer 13 is configured in such a way that the phosphor particles 14 and conductive nano particles 18 are each dispersed in the hole transport material 15 as a matrix (
Next, the hole transport material 15 will be described, which covers the surface of each of the phosphor particles 14 or serves as a matrix material existing among the phosphor particles 14. Any organic material having the function of generating and transporting holes can be used for the hole transport material 15. In addition, as the hole transport material 15, organic hole transport materials and inorganic hole transport materials are cited. The hole transport material 15 is preferably a material with a high hole mobility.
This organic hole transport material preferably contains components of the following chemical formula 9 and chemical formula 10.
It is believed that the advantageous effect of the organic hole transport material containing the components of the above chemical formula 9 and chemical formula 10 is efficient injection of holes for the phosphor particles 14.
Furthermore, this organic hole transport material may contain any of the following chemical formula 11, chemical formula 12, and chemical formula 13 as a component.
In addition, the main types of organic hole transport materials are low-molecular-weight materials and high-molecular-weight materials. Low-molecular-weight materials having a hole transport property include diamine derivatives used by Tang et al., such as N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) and N,N′-bis(a-naphthyl)-N,N′-diphenylbenzidine (NPD), in particular, diamine derivatives having a Q1-G-Q2 structure, disclosed in Japanese Patent No. 2037475, where Q1 and Q2 are separately a group having a nitrogen atom and at least three carbon chains (at least one of the carbon chains comes from an aromatic group), and G is a linking group including a cycloalkylene group, an arylene group, an alkylene group or a carbon-carbon bond. Alternatively, the organic hole transport material may be polymers (oligomers) including these structural units. These polymers include polymers having a Spiro structure or a dendrimer structure. Furthermore, the form in which molecules of a low-molecular-weight hole transport material are dispersed in a nonconductive polymer is likewise available. Specific examples of the molecular dispersion system include an example in which molecules of TPD are dispersed in high concentration in a polycarbonate, with the hole mobility on the order of 10−4 to 10−5 cm2/Vs.
Moreover, other examples of the hole transport material include tetraphenyl butadiene materials, hydrazine materials such as 4-(bis(4-methylphenyl)amino)benzaldehyde diphenylhydrazine, stilbene materials such as 4-methoxy-4′-(2,2′-diphenylvinyl)triphenylamines, PEDOT (poly(2,3-dihydrocyano-1,4-dioxin)), α-NPD, DNTPD, and a Cu phthalocyanine.
On the other hand, high-molecular-weight materials having a hole transport property include π-conjugated polymers and σ-conjugated polymers, and for example, a high-molecular-weight material in which an arylamine compound is incorporated. Specifically, the high-molecular-weight materials include, but are not limited to, poly-para-phenylenevinylene derivatives (PPV derivatives), polythiophenes derivatives (PAT derivatives), polyparaphenylene derivatives (PPP derivatives), polyalkylphenylene (PDAF), polyacetylene derivatives (PA derivatives), and polysilane derivatives (PS derivatives). Furthermore, the high-molecular-weight materials may be polymers with a low-molecular-weight hole-transport molecular structure incorporated into their molecular chains, and specific examples of the polymers include polymethacrylamides with an aromatic amine in their side chains (PTPAMMA, PTPDMA) and polyethers with an aromatic amine in their main chains (TPDPES, TPDPEK). Above all, as a particularly preferred example, above all, poly-N-vinylcarbazole (PVK) exhibits an extremely high hole mobility of 10−6 cm2/Vs. Other specific examples include PEDOT/PSS and polymethylphenylsilane (PMPS).
Moreover, more than one type of the hole transport materials mentioned above may be mixed and used. Furthermore, the organic hole transport material may contain a crosslinkable or polymerizable material cross-linked or polymerized by light or heat.
Inorganic hole transport materials will be described. The inorganic hole transport material may be any material being transparent or semi-transparent and having p-type conductivity. Preferred inorganic hole transport materials include metalloid semiconductors such as Si, Ge, SiC, Se, SeTe, and As2Se3; binary compound semiconductor such as ZnSe, CdS, ZnO, and CuI; chalcopyrite semiconductors such as CuGaS2, CuGaSe2, and CuInSe2, and further mixed crystals of these semiconductors; and oxide semiconductors such as CuAlO2 and CuGaO2, and further mixed crystals of these semiconductors. Moreover, a dopant may be added to these materials, in order to control the conductivity.
As the phosphor particles 14, any material having an optical bandgap being as wide as visible light can be used. Specifically, with a nitride such as GaN, InGaN, or AlGaN, ZnSe or ZnS, or further ZnS, ZnSe, GaP, CdSe, CdTe, SrS, CaS, or ZnO as a mother body, the mother body can be used as it is, or phosphor particles with the addition of one or more elements selected from Ag, Al, Ga, Cu, Mn, Cl, Tb, Li, Zn, O, and Si can be used. In addition, multicomponent compounds such as ZnSSe and thiogallate based phosphor can be also used.
The conductive nano particles 18 used for the light emitting devices according to the present invention can use metal material particles such as Ag, Au, Pt, Ni, and Cu, oxide particles such as an indium tin oxide, ZnO, and InZnO, carbon material particles such as carbon nanotubes. The average particle diameter or average length of the conductive nano particles 18 preferably falls within the range of 1 nm to 200 nm. The average particle diameter or average length less than 1 nm results in poor conductivity, decreasing the light emission luminance. On the other hand, the average particle diameter or average length greater than 200 nm increases electrical conduction between the electrodes, while the number of the phosphor particles 14 which are not included in the conductive path is increased, decreasing the light emission luminance and efficiency.
The production of carbon nanotubes is carried out by a method such as a vapor phase synthetic method or plasma method, and depending on the manufacturing conditions, the electrical characteristics, diameters, lengths, and the like of the carbon nanotubes can be arbitrarily varied. As the phosphor particles 14 covered with the hole transmit material 15, p-type carbon nanotubes may be used. The p-type carbon nanotubes are obtained by adding an element such as K or Cs as a dopant to carbon nanotubes.
As an example of the present invention, a method for obtaining the phosphor layer 13 by an application method will be described. As an example, a light emitting device 10 was manufactured as shown in
(a) A silicon substrate 11 with a Pt electrode formed was used as a substrate.
(b) Next, with the use of ITO nano particles with an average particle diameter of 20 to 30 nm as the conductive nano particles 17, the ITO nano particles were added at 10 weight % to a resin paste, and well mixed and dispersed.
(c) Next, as the hole transport material 15, tetraphenylbutadiene T770 dissolved in a resin solution was used. GaN particles with an average particle diameter of 500 to 1000 nm were, as the phosphor particles 14, mixed into the solution, coated and dried, and then mixed into the resin paste with the ITO nano particles 17 dispersed therein to obtain a light emitting paste.
(d) Next, the light emitting paste was applied on a glass substrate with an ITO film deposited thereon. The thickness of the applied film was about 30 μm.
(d) Furthermore, a substrate obtained by depositing an ITO as a transparent conductive film on glass by sputtering was attached to bring the ITO surface into contact with the phosphor layer 13. It is to be noted that the film thickness of the ITO film was about 300 nm.
The light emitting device was obtained in the way described above.
The evaluation of the prepared light emitting device was carried out by applying a direct-current voltage from the power supply 17 between the rear electrode 12 and the transparent electrode 16. Furthermore, the luminance measurement was carried out with the use of a portable luminance meter. It is to be noted that a light emitting device was prepared as a reference without the use of conductive nano particles 18.
It is to be noted that while the positive voltage and the negative voltage were applied respectively to the rear electrode 12 and the transparent electrode 16 in the present example, the light emitting device was allowed to emit light likewise even when the polarity was changed.
The light emitting device according to the present embodiment operates at a lower voltage than conventional light emitting devices, and is thus excellent in corrosion resistance and oxidation resistance and can provide a higher luminance and a longer lifetime than conventional light emitting devices.
A light emitting device according to second embodiment of the present invention will be described with reference to
It is to be noted that the embodiment is not limited to the structure described above, changes can be appropriately made, in such a way that a black electrode is used as the rear electrode 12, or a structure is further provided for sealing all or part of the light element 40 with a resin or a ceramic. Furthermore, a modification example as shown in
The light emitting device according to the present embodiment is able to form a planar shape with relative ease, and can achieve a light emitting device with a high luminance, a high efficiency, and high reliability.
A light emitting device according to third embodiment of the present invention will be described with reference to
Furthermore, in the case of a color display device, the phosphor layers may be deposited separately with the use of phosphor particles for each color of RGB. Alternatively, light emitting units such as electrode/phosphor layer/electrode may be laminated for each of RGB. Moreover, in the case of another color display device, after preparing a display device with phosphor layers for a single color or two colors, color filters and/or color conversion filters can be used to display each color of RGB. For example, RGB display is made possible by providing blue phosphor layers further with filters each for color conversion from a blue color to a green color or from a blue color or a green color to a red color.
In this active matrix display device 90, the phosphor layer 13 constituting the light emitting device of each pixel includes, as described above, the phosphor particles 14 and conductive nano particles 18 dispersed in the organic hole transport material 15 as a matrix, or includes light emitting powder containing the phosphor particles 14 with their surfaces coated with the organic hole transport material 15 with the conductive nano particles 18 dispersed therein. This allows a display device with a high light emission luminance, a high luminous efficiency, and high reliability to be achieved.
A display device according to fifth embodiment of the present invention will be described with reference to
According to this passive matrix display device 100, a display device can be achieved to provide a high light emission luminance, a high luminance efficiency, and high reliability, as in the case of the display device according to fourth embodiment.
It is to be noted that the embodiment is not limited to the structure described above, changes can be appropriately made, in such a way that a black electrode is used as the rear electrode 12, a structure is further provided for sealing all or part of the light element 10 with a resin or a ceramic, or a hole injection layer is further provided between the transparent electrode 16 and the phosphor layer 13.
The respective components constituting this light emitting device 10 will be described.
It is to be noted that the substrate is substantially the same as the substrate in the light emitting device according to first embodiment, and description of the substrate will be thus omitted.
The electrodes include the rear electrode 12 and the transparent electrode 16. Of the two electrodes, the electrode on the side from which light is extracted is used as the transparent electrode 16. On the other hand, the other is used as the rear electrode 12.
The material of the transparent electrode 16 on the side from which light is extracted may be any material having a light transmitting property so that light generated in the phosphor layer 13 can be extracted, and preferably has a high transmittance, in particular, in a visible light region. Furthermore, the material is preferably a low resistance material, and further, preferably has excellent adhesion with the phosphor layer 13. Furthermore, a material is more preferably capable to be deposited on the phosphor layer 13 at a low temperature so as to prevent the phosphor layer 13 from being thermally deteriorated. Particularly preferred materials of the transparent electrode 16 include, but are not particularly limited to, metal oxides based on an ITO (In2O3 doped with SnO2, which is also referred to as an indium tin oxide), InZnO, ZnO, SnO2, or the like; metal thin films such as Pt, Au, Pd, Ag, Ni, Cu, Al, Ru, Rh, and Ir; or conductive polymers such as a polyaniline, a polypyrrole, PEDOT/PSS, and a polythiophene. Furthermore, the transparent electrode 16 desirably has a volume resistivity of 1×10−3 Ωcm or less, a transmittance of 75% or more for wavelengths from 380 to 780 nm, and a refractive index from 1.85 to 1.95. For example, an ITO can be deposited by a deposition method such as sputtering, electron beam evaporation, or ion plating, for the purpose of improving the transparency or lowering the resistivity. Furthermore, after the deposition, surface treatment such as a plasma treatment may be applied for the purpose of controlling the resistivity. The film thickness of the transparent electrode 16 is determined from the required sheet resistance and visible light transmittance. While the transparent electrode 16 may be directly formed on the phosphor layer 13, the transparent electrode 16 including a transparent conductive film may be formed on a glass substrate and attached so that the transparent conductive film comes in contact with the phosphor layer 13.
The rear electrode 12 on the side from which no light is extracted may be any electrode having electrically conductive property and having excellent adhesion with the substrate 11 and the phosphor layer 13. As preferred examples, for example, metal oxides such as ITO, InZnO, ZnO, and SnO2, metals such as Pt, Au, Pd, Ag, Ni, Cu, Al, Ru, Rh, Ir, Cr, Mo, W, Ta, Nb, and laminated structures thereof, conductive polymers such as a polyaniline, a polypyrrole, PEDOT [poly(3,4-ethylene dioxythiophene)]/PSS (polyethylene sulfonic acid), or conductive carbon can be used.
The rear electrode 12 may be configured to cover the entire surface of the layer, or may be configured to have a plurality of stripe-shaped electrodes in the layer. Furthermore, the rear electrode 12 and the transparent electrode 16 may be configured to have a plurality of stripe-shaped electrodes, in such a way that each stripe-shaped electrode of the rear electrode 12 and all of the strip-shaped electrodes of the transparent electrode 16 have a skew relationship with each other and that projections of each stripe-shaped electrode of the rear electrode 12 onto the light emitting surface and projections of all of the stripe-shaped electrodes of the rear electrode 16 onto the light emitting surface intersect with each other. In this case, the application of a voltage to the electrodes respectively selected from the respective stripe-shaped electrodes of the rear electrode 12 and the respective striped-shaped electrodes of the transparent electrode 16 allows a display to be configured in such a way that light is emitted in a predetermined position.
The phosphor layer 13 includes the phosphor particles 14 and the conductive nano particles 23 dispersed in the hole transport material 15 as a medium (
As the phosphor particles 14, any material having an optical bandgap being as wide as visible light can be used. Specifically, AlN, GaN, InN, AlP, GaP, InP, AlAs, GaAs, AlSb, and the like which are Group XIII-Group XV compound semiconductors can be used. In particular, Group XIII nitride semiconductors typified by GaN are preferable. Furthermore, mixed crystals thereof (for example, GaInN, etc.) may be used. Moreover, in order to control the conductivity, the material may contain, as a dopant, one or more elements selected from the group consisting of Si, Ge, Sn, C, Be, Zn, Mg, Ge, and Mn.
Furthermore, with a nitride such as InGaN or AlGaN, ZnSe or ZnS, or further ZnS, ZnSe, GaP, CdSe, CdTe, SrS, CaS, or ZnO as a mother body, the mother body can be used as it is, or phosphor particles with the addition of one or more elements selected from Ag, Al, Ga, Cu, Mn, Cl, Tb, and Li can be used. In addition, multicomponent compounds such as ZnSSe and thiogallate based phosphor can be also used.
Furthermore, the multiple compositions in the phosphor particles 14 may have a laminated structure or a segregated structure. The phosphor particles 14 may have a particle diameter in the range of 0.1 μm to 1000 μm, more preferably, in the range of 0.5 μm to 500 μm.
The conductive nano particles 23 can use metal material particles such as Ag, Au, Pt, Ni, and Cu, oxide particles such as an indium tin oxide, ZnO, and InZnO, carbon material particles such as carbon nanotubes. The shapes of the conductive nano particles 23 may be any shape such as granular, circular, columnar, acicular, or amorphous. The average particle diameter of the conductive nano particles 23 preferably falls within the range of 1 nm to 200 nm, more preferably within the range of 1 nm to 100 nm. The average particle diameter less than 1 nm results in poor conductivity, decreasing the light emission luminance. On the other hand, the average particle diameter greater than 200 nm increases electrical conduction between the electrodes, while the number of the phosphor particles 14 which are not included in the conductive path is increased, decreasing the light emission luminance and efficiency.
The production of carbon nanotubes is carried out by a method such as a vapor phase synthetic method or plasma method, and depending on the manufacturing conditions, the electrical characteristics, diameters, lengths, and the like of the carbon nanotubes can be arbitrarily varied. In the case of holding a carbon nanotube at the electrode interface on the positive electrode side, it is preferable to use a p-type carbon nanotube as the carbon nanotube. In the case of holding a carbon nanotube at the electrode interface on the negative electrode side, it is preferable to use an n-type carbon nanotube as the carbon nanotube. The p-type carbon nanotube is obtained by doping a carbon nanotube with a Group 5 element such as phosphorus, whereas the n-type carbon nanotube is obtained by doping a carbon nanotube with a Group 3 element such as nitrogen.
Next, the hole transport material 15 as a medium in which the phosphor particles 14 and the conductive nano particles 23 are dispersed will be described. As the hole transport material 15, organic hole transport materials and inorganic hole transport materials are cited. The hole transport material 15 is preferably a material with a high hole mobility.
This organic hole transport material preferably contains components of the following chemical formula 14 and chemical formula 15.
It is believed that the advantageous effect of the organic hole transport material containing the components of the above chemical formula 14 and chemical formula 15 is efficient injection of holes for the phosphor particles 14.
Furthermore, this organic hole transport material may contain any of the following chemical formula 16, chemical formula 17, and chemical formula 18 as a component.
In addition, the main types of organic hole transport materials are low-molecular-weight materials and high-molecular-weight materials. Low-molecular-weight materials having a hole transport property include diamine derivatives used by Tang et al., such as N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) and N,N′-bis(α-naphthyl)-N,N′-diphenylbenzidine (NPD), in particular, diamine derivatives having a Q1-G-Q2 structure, disclosed in Japanese Patent No. 2037475, where Q1 and Q2 are separately a group having a nitrogen atom and at least three carbon chains (at least one of the carbon chains comes from an aromatic group), and G is a linking group including a cycloalkylene group, an arylene group, an alkylene group or a carbon-carbon bond. Alternatively, the organic hole transport material may be polymers (oligomers) including these structural units. These polymers include polymers having a spiro structure or a dendrimer structure. Furthermore, the form in which molecules of a low-molecular-weight hole transport material are dispersed in a non-conductive polymer is likewise available. Specific examples of the molecular dispersion system include an example in which molecules of TPD are dispersed in high concentration in a polycarbonate, with the hole mobility on the order of 10−4 to 10−5 cm2/Vs.
On the other hand, high-molecular-weight materials having a hole transport property include π-conjugated polymers and σ-conjugated polymers, and for example, a high-molecular-weight material in which an arylamine compound is incorporated. Specifically, the high-molecular-weight materials include, but are not limited to, poly-para-phenylenevinylene derivatives (PPV derivatives), polythiophenes derivatives (PAT derivatives), polyparaphenylene derivatives (PPP derivatives), polyalkylphenylene (PDAF), polyacetylene derivatives (PA derivatives), and polysilane derivatives (PS derivatives). Furthermore, the high-molecular-weight materials may be polymers with a low-molecular-weight and a hole-transport molecular property incorporated into their molecular chains, and specific examples of the polymers includes polymethacrylamides with an aromatic amine in their side chains (PTPAMMA, PTPDMA) and polyethers with an aromatic amine in their main chains (TPDPES, TPDPEK). Above all, as a particularly preferred example, above all, poly-N-vinylcarbazole (PVK) exhibits an extremely high hole mobility of 10−6 cm2/Vs. Other specific examples include PEDOT/PSS and polymethylphenylsilane (PMPS).
Moreover, multiple types of the hole transport material mentioned above may be mixed and used. Furthermore, the organic hole transport material may contain a crosslinkable or polymerizable material cross-linked or polymerized by light or heat.
Inorganic hole transport materials will be described. The inorganic hole transport material may be any material being transparent or semi-transparent and having p-type conductivity. Preferred inorganic hole transport materials include metalloid semiconductors such as Si, Ge, SiC, Se, SeTe, and As2Se3; binary compounds such as ZnS, ZnSe, CdS, ZnO, and CuI; chalcopyrite semiconductors such as CuGaS2, CuGaSe2, and CuInSe2, and further mixed crystals of these semiconductors; and oxide semiconductors such as CuAlO2 and CuGaO2, and further mixed crystals of these semiconductors. Moreover, a dopant may be added to these materials, in order to control the conductivity.
Next, a method for manufacturing the phosphor layer 13 will be described.
(a) The phosphor particles 14 and the conductive nano particles 23 are mixed and stirred in the hole transport material 15 with any solvent and the like added to prepare a light emitting paste.
(b) Next, the light emitting paste is deposited on the rear electrode 12 provided on the substrate 11, and the solvent and the like are volatilized by drying to form the phosphor layer 13. As the application method in this case, inkjet, dipping, spin coating, screen printing, bar-code, and other various types of application methods can be used. In addition, the application method can be appropriately changed to spray coating, electrostatic painting without the use of a solvent and with the use of a powder material, fluidized bed coating, aerosol deposition, etc. Furthermore, other deposition methods for the organic hole transport material includes vacuum deposition, etc., and it is also possible to form the phosphor layer by the combination of these methods.
A feature of the light emitting device according to sixth embodiment of the present invention is that the phosphor layer 13 includes the phosphor particles 14 and the conductive nano particles 23 dispersed in the hole transport material 15 as a medium, in which the conductive nano particles 23 are present among the phosphor particles 14. Furthermore, the conductive nano particles 23 present among the phosphor particles 14 can reduce the contact resistance among the phosphor particles 14 to improve the hole injection property. In addition, the use of the organic hole transport material 15 as the medium of the phosphor layer 13 makes it easier to enlarge the light emitting device, and allows leakage between the electrode through a path among the particles to be reduced. Therefore, a light emitting device having a higher luminance, a higher efficiency, and high reliability can be achieved.
The light emitting device according to the present invention provides light emission with a higher luminance and a higher efficiency than light emitting devices using conventional compound semiconductor particles or the like.
Phosphor particles mainly containing GaN and inorganic conductive nano fine particles (Cu2S fine particles) were mixed, stirred, and dispersed in an organic hole transport material (a tetraphenylbutadiene derivative). Then, the obtained paste is sandwiched along with spacers between a pair of glass substrates ITO electrodes to prepare a device for EL confirmation. When a direct current voltage was applied to this device for EL confirmation to evaluate the device, the device exhibited a light emission luminance of 180 cd/m2 at 12V. This result was superior to the following comparative examples.
Phosphor particles mainly containing GaN were dispersed in an insulating silicon oil, and sandwiched along with spacers by glass substrates with ITO electrodes to prepare a device for EL confirmation. When a direct current voltage was applied to this device for evaluation of the device, the device exhibited light emission at 50 V (with a light emission luminance less than 1 cd/m2).
Phosphor particles mainly containing GaN were dispersed in an organic hole transport material (a tetraphenylbutadiene derivative), and sandwiched along with spacers by glass substrates with ITO electrodes to prepare a device for EL confirmation. When a direct current voltage was applied to this device for evaluation of the device, the device exhibited a light emission luminance less than 15 cd/m2 at 20 V.
The light emitting devices and display devices according to the present invention provide light emissions with a high light emission luminance and with a high luminous efficiency and provide reliability for long periods of time. In particular, the light emitting devices and display devices are useful as display devices such as televisions and a variety of light sources for use in communication, illumination, etc.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-285084 | Nov 2007 | JP | national |
| 2008-025094 | Feb 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/003134 | 10/31/2008 | WO | 00 | 4/28/2010 |
