JP5828340B2 - Light emitting device and method for manufacturing the light emitting device - Google Patents

Description

  The present invention relates to a light-emitting device and a method for manufacturing the light-emitting device, and more particularly to a light-emitting device that forms a light-emitting layer with quantum dots whose surfaces are coated with a surfactant.

  A quantum dot, which is a nanoparticle having a particle size of 10 nm or less, has excellent carrier (electron, hole) confinement properties. Therefore, excitons can be easily generated by electron-hole recombination. Therefore, light emission from free excitons can be expected, and light emission with high emission efficiency and sharp emission spectrum can be realized. Further, since quantum dots can be controlled in a wide wavelength range using the quantum size effect, their application to light emitting devices such as semiconductor lasers and light emitting diodes (LEDs) has attracted attention.

  In this type of light emitting device, it is important to improve the light emission efficiency by confining carriers in quantum dots (nanoparticles) with high efficiency and recombining them. As a method for producing quantum dots, a method called a self-assembly method is known. This self-assembly method is a method of producing quantum dots by a dry process, and a semiconductor layer is vapor-phase epitaxially grown under a specific condition that causes lattice mismatch, and a three-dimensional quantum dot structure is self-formed.

  FIG. 9 is a cross-sectional view schematically showing a quantum dot structure manufactured by a self-assembly method.

  In the self-assembly method, a plurality of quantum dots 102 are discretely distributed on the surface of the first substrate 101, and a second substrate 103 is formed on the surface of the first substrate 101 so as to cover the quantum dots 102. Yes. That is, in this self-assembling method, distortion is caused by the difference between the lattice constant of the first substrate 101 and the lattice constant of the second substrate 103, and when the epitaxial growth cannot be performed, quantum dots 102 are formed at the locations where the distortion occurs. Is done. This self-assembly method is said to be capable of obtaining a high-quality quantum dot structure in which quantum dots are distributed at a higher density than in the case of artificially performing fine processing.

  However, in such a self-assembly method, since the quantum dots 102 are discretely distributed on the first substrate 101, the quantum dots 102 cannot be integrated on the first substrate 101 with high density. That is, in this self-assembly method, the surface density of the quantum dots 102 is small, and the interval t between the quantum dots 102 tends to be larger than the quantum size of the quantum dots 102. In addition, since the first substrate 101 is bonded to the second substrate 103 at locations other than where the quantum dots 102 are formed, electrons and holes are not injected into the quantum dots 102 but the first substrate 101 or the first substrate 101. 2 is transported to the second substrate 103, which may cause a decrease in luminous efficiency.

  In the self-assembly method, carriers that are not injected into the quantum dots may be recombined outside the quantum dots 102. If the light is recombined outside the quantum dots 102 to emit light as described above, the emission color purity may be reduced, and if the light is not emitted even after recombination, a leakage current may be caused and the emission efficiency may be reduced. There is.

  Therefore, in Patent Document 1, a substrate having a main surface made of a first semiconductor, a plurality of quantum dots distributed discretely on the main surface, and a surface on which the quantum dots are distributed is formed. A covering layer made of a second semiconductor, and disposed in at least a part of a region where the quantum dots are not arranged in a plane in which the quantum dots are distributed, from the band gaps of the first and second semiconductors A semiconductor device having a third semiconductor having a large band gap or a barrier layer formed of an insulating material has been proposed.

  In Patent Document 1, as shown in FIG. 10A, a barrier layer 104 having an insulating property by oxidizing a semiconductor such as AlAs having a larger band gap energy than the first substrate 101 and the second substrate 103. Thus, carriers (electrons and holes) can be easily injected into the quantum dots 102, and emission efficiency is improved by recombination.

  Also, in this type of light emitting device, if the quantum dot and the hole transport layer or the electron transport layer are in ohmic contact, the movement of the phonon is slow at the contact interface, and the high level is controlled by the slow movement of the phonon. The transition of the energy level from low to low is suppressed, and a phenomenon called a phonon bottleneck occurs.

  Therefore, in Patent Document 1, a first quantum well layer 105 and a first tunnel layer 106 are formed between the first substrate 101 and the barrier layer 104 as shown in FIG. A second tunnel layer 107 and a second quantum well layer 108 are formed between the layer 104 and the second substrate 103.

  That is, in Patent Document 1, in order to avoid a phonon bottleneck, the first and second quantum well layers 105 and 108 described above are formed, and carriers are transferred to the first and second quantum well layers 105 and 108. The confinement and the confined carriers are moved by the tunnel effect, thereby increasing the injection efficiency of the carriers into the quantum dots 102.

  Patent Document 2 discloses a light emitting layer that is formed of quantum dots and emits light by recombination of electrons and holes, an n-type inorganic semiconductor layer that transports the electrons to the light emitting layer, and the holes in the light emitting layer. A transporting p-type inorganic semiconductor layer, a first electrode for injecting the electrons into the n-type inorganic semiconductor layer, and a second electrode for injecting the holes into the p-type inorganic semiconductor layer There has been proposed a light emitting device comprising:

  In Patent Document 2, as shown in FIG. 11, a p-type semiconductor layer 111 and an n-type semiconductor layer 112 are formed of an inorganic material, and a light emitting layer and a p-type semiconductor layer 111 are interposed between the p-type semiconductor layer 111 and the n-type semiconductor layer 112. A colloidal quantum dot layer 113 is interposed. That is, in Patent Document 2, a potential barrier is formed between the light-emitting layer and the carrier transport layer by forming the p-type semiconductor layer 111 and the n-type semiconductor layer 112 with an inorganic material having a band structure with good carrier transportability. Even if there is a carrier, carriers are injected into the colloidal quantum dot layer 113 by the tunnel effect, thereby improving the injection efficiency of carriers into the quantum dot layer 113.

  Moreover, in this patent document 2, the colloidal quantum dot layer 113 is formed by immersing the board | substrate with which the semiconductor layer was formed in the colloidal solution containing a quantum dot, pulling up a board | substrate, and evaporating a colloidal solution. .

  Patent Document 3 has a surfactant composed of at least two kinds of ligands localized on the surface of the quantum dot, and at least one of the ligands is a hole transporting ligand. There has been proposed a nanoparticle light-emitting material in which at least one kind is an electron transporting ligand.

  In Patent Document 3, a surfactant having both a hole transporting ligand and an electron transporting ligand (hereinafter referred to as “amphoteric surfactant”) is used. The energy level is devised so as to produce a carrier blocking effect, and carriers are confined in the nanoparticles.

  FIG. 12 shows a case where Patent Document 3 is applied to a light emitting device.

  In this light emitting device, a light emitting layer 126 composed of an assembly of quantum dots 125 is interposed between a hole transport layer 122 formed on the upper surface of the anode 121 and an electron transport layer 124 formed on the lower surface of the cathode 123. Yes. And the surface of the quantum dot 125 is coat | covered with the amphoteric surfactant 130 so that the nanoparticles 129 which consist of the core part 127 and the shell part 128 may not aggregate.

  When a voltage is applied between the anode 121 and the cathode 123, holes are injected into the anode 121 and electrons are injected into the cathode 123. The energy levels of both the electron transporting and hole transporting ligands are devised to confine the holes from the hole transporting layer 122 in the core part 127, and the electrons from the electron transporting layer 124 are confined to the core. By confining in the part 127, electrons and holes are recombined in the core part 127 to emit excitons.

  FIG. 13 is a diagram for explaining the quantum dot confinement principle in Patent Document 3. In FIG.

  As described above, the nanoparticle 129 includes the core portion 127 and the shell portion 128 that covers the core portion 127, and the shell portion 128 is covered with the amphoteric surfactant 130. This surfactant 130 has a hole-transporting ligand 130a and an electron-transporting ligand 130b, and the hole-transporting ligand 130a is localized on the hole transporting layer 122 side. The electron transporting ligand 130b is localized on the layer 124 side.

  In Patent Document 3, the LUMO level 131 of the hole-transporting ligand 130a is set higher than the LUMO level 132 of the electron-transporting ligand 130b, whereby the electrons from the electron transport layer 124 are cored. While injecting into the portion 127, the LUMO level 131 of the hole transporting ligand 130 a is made higher than the lowest electron level 133 in the conduction band (where electrons move) of the core portion 127. The transporting ligand 130 a serves as a barrier against electrons, thereby confining the electrons inside the core portion 127.

  In addition, by making the HOMO level 134 of the electron transporting ligand 130b lower than the HOMO level 135 of the hole transporting layer ligand 130a, the holes from the hole transporting layer 122 are moved into the core portion 127. While the HOMO level 134 of the electron transporting ligand 130b is made lower than the highest electron level 136 in the valence band (where holes move) of the core part 127, The ligand 130b becomes a barrier against holes, thereby confining the holes inside the core portion 127.

  Here, the LUMO level means that when a molecule is irradiated with light, the energy is in an excited state and the molecular orbitals are in an empty state not occupied by electrons. In this case, the molecular orbitals are not occupied by electrons. The energy level corresponding to the lowest lowest orbital (Lowest Unoccupied Molecular Orbital).

  The HOMO level means that in the ground state before the molecule is irradiated with light, electrons are occupied in order from the molecular orbital having the lowest energy. In this case, It refers to the energy level corresponding to the highest highest occupied molecular orbital (Highest Occupied Molecular Orbital).

  As described above, in Patent Document 3, the core portion 127 of the nanoparticle 129 is made to have carriers (electrons and holes) by the electron blocking effect of the hole transporting ligand 130a and the hole blocking effect of the electron transporting ligand 130b. Trapped inside.

  Then, by confining electrons and holes in the core part 127 in this way, the electron-holes can be recombined in the core part 127, and exciton light can be emitted.

JP 2002-184970 A (Claim 1, Claim 2, FIG. 1, FIG. 3) JP 2006-185985 A (Claim 1, FIG. 1, FIG. 3) JP 2008-214363 A (Claims 1 and 3 to 5)

  However, in Patent Document 1, although the barrier layer 104 is formed in order to fill the gap between the quantum dots 102 as shown in FIG. In order to effectively fill the gaps between the dots with the barrier layer 104, the manufacturing process may be complicated.

  That is, in Patent Document 1, the barrier layer 104 is formed after the quantum dot 102 is formed. In this case, the barrier layer on the quantum dot 102 is dry-etched so as not to prevent carrier injection into the quantum dot 102. 104 needs to be removed, resulting in a complicated manufacturing process.

  In Patent Document 1, in order to avoid the occurrence of a phonon bottleneck, the first quantum well layer 105 and the first tunnel layer 106 are formed on the first substrate 101 as shown in FIG. In addition, the second tunnel layer 107 and the second quantum well layer 108 are formed on the surfaces of the quantum dot layer 102 and the barrier layer 104. Therefore, many film formation processes are required, which increases the cost. Invited and inferior in productivity.

  In Patent Document 2 (see FIG. 11), after the substrate is immersed in the colloidal solution, the substrate is pulled up to evaporate the colloidal solution. It is difficult to obtain a colloidal quantum dot layer 113 that is coarsened and has desired emission characteristics.

  On the other hand, in Patent Document 3, as shown in FIG. 12 described above, the quantum dot 125 avoids aggregation of the nanoparticles 129 because the surfaces of the nanoparticles 129 are coated with the amphoteric surfactant 130. Is possible.

  In addition, the quantum dots are not distributed in a discrete manner as in the self-assembly method, and surface defects can be improved while improving surface resistance by inactivating surface defects with a surfactant ligand. Is possible.

  However, since the nanoparticle 129 is coated with the amphoteric surfactant 130 having both the hole transporting ligand 130 a and the electron transporting ligand 130 b, the holes and electrons are in the amphoteric surfactant 130. Will be transported in a coexisting form. For this reason, there is a possibility that electrons and holes approach each other with a certain probability, and holes and electrons may be recombined in the amphoteric surfactant 130 as shown by a in FIG.

  Further, in Patent Document 3, since the light emitting layer 126 is formed only of an assembly of quantum dots 125 and the electron transport layer 124 is formed on the light emitting layer 126, as shown in FIG. In the formation process of the layer 124, when the film density is not sufficiently dense and the quantum dots 125 are open, the light emitting layer 126 may be filled with the electron transporting material 137. In this case, since the size of the surfactant ligand is usually the same as the particle size of the nanoparticle 129, the carrier is not injected into the nanoparticle 129, but travels through the amphoteric surfactant 130 and passes through the quantum dot 125. May flow into the gap between the quantum dots 125 and the quantum dots 125. As a result, carriers may enter the hole transport layer 122 and the electron transport layer 124 without being injected into the nanoparticles 129. Furthermore, as shown in FIG. In the material 137, electrons may combine with holes to emit excitons. That is, in Patent Document 3, excitons do not emit light in the core portion 127 of the nanoparticle 129, and carriers that emit exciton are generated in the filled electron transporting material 137, and therefore, the emission efficiency decreases and the light emission occurs. There is a risk of lowering the color purity.

  This invention is made | formed in view of such a situation, Comprising: It aims at providing the light-emitting device with favorable injection | pouring efficiency of the carrier in a quantum dot, and the manufacturing method of this light-emitting device.

The present inventor conducted intensive studies to achieve the above object, and as a result, two types of surfactants that transport only electrons or holes are used to form ultrafine particles (including oxides, compound semiconductors, and single semiconductors). The surface is coated, thereby forming quantum dots, and by providing an insulating material made of a specific polymer compound that is dense and excellent in voltage endurance between the quantum dots, carrier injection efficiency into ultrafine particles It was found that the light emission characteristics can be improved.

In addition, a phonon bottleneck is generated by moving carriers between the first surfactant having electron transporting property and the second surfactant having hole transporting property and the quantum dot using tunnel resonance. The carrier can be transported quickly and efficiently. For that purpose, it is preferable that at least the first surfactant has a HOMO level that causes tunnel resonance with the valence band of the quantum dot. Specifically, the HOMO level is at the energy level of the valence band. On the other hand, it is preferably −0.2 to +0.2 eV.

The present invention has been made based on such knowledge, and the light-emitting device according to the present invention is a light-emitting device in which a light-emitting layer is formed of an assembly of quantum dots, and the quantum dot has an ultrafine particle surface. It is coated with a first surfactant having a hole transporting property and a second surfactant having an electron transporting property, and the ultrafine particles include any one of an oxide, a compound semiconductor, and a single semiconductor. And the said light emitting layer consists of a high molecular compound formed by 1 or more types selected from the group of acrylic resin, polystyrene resin, polycarbonate resin, polyester resin, polyamide resin, and polyvinyl resin. The insulating material is filled between the quantum dots, and carriers are prevented from passing outside the quantum dots, and the first surfactant is the ultrafine particles. As valence band and tunneling resonance, it is characterized by having a HOMO level of -0.2 to + 0.2 eV with respect to energy levels of the valence band.

As a result, at least the first surfactant moves through carriers using tunnel resonance, so that the phonon bottleneck can be suppressed and carriers can be transported quickly and efficiently. The second surfactant can transport only electrons, and the carrier is injected into the ultrafine particles with high efficiency and can be prevented from passing outside the ultrafine particles. it can.

Therefore, carriers injected into the electrode by applying a voltage can be efficiently transported into the ultrafine particles without recombination of holes and electrons outside the ultrafine particles, thereby making it possible to transport the carrier of the film. Therefore, it is possible to improve the efficiency of injecting the carrier into the ultrafine particles.

In order to suppress the phonon bottleneck described above, it is also preferable to control the LUMO level of the second surfactant instead of controlling the HOMO level of the first surfactant.

That is, the light- emitting device according to the present invention is a light- emitting device in which a light-emitting layer is formed of an aggregate of quantum dots, and the quantum dot includes a first surfactant and an electron whose surface of ultrafine particles has a hole transporting property. The ultrafine particles include any one of an oxide, a compound semiconductor, and a single semiconductor, and are coated with a second surfactant having a transport property, and the light emitting layer includes an acrylic resin, a polystyrene resin, An insulating material made of a polymer compound formed of one or more selected from the group consisting of a polycarbonate resin, a polyester resin, a polyamide resin, and a polyvinyl resin is filled between the quantum dots, In addition to suppressing the passage of carriers through the outside, the second surfactant is capable of energizing the conduction band so as to resonate with the conduction band of the ultrafine particles. It is characterized by having a LUMO level of -0.2 to + 0.2 eV with respect to Energy levels.

  By adjusting the energy level of the ligand in the surfactant in this way, carrier movement using tunnel resonance can be performed, and efficient carrier transport can be realized without causing a phonon bottleneck. Can do. That is, in order to avoid a phonon bottleneck, it is not necessary to form a quantum well layer or a tunnel layer that requires a complicated film formation process, and a light emitting device that can efficiently inject carriers into ultrafine particles can be realized. It becomes possible.

  In the light-emitting device of the present invention, it is preferable that the ultrafine particles have a core-shell structure including a core portion and a shell portion that covers the core portion.

  In the light emitting device of the present invention, it is preferable that a hole transport layer is formed on one main surface of the light emitting layer and an electron transport layer is formed on the other main surface of the light emitting layer.

In addition, the light emitting layer includes first and second surfactants having predetermined HOMO levels and LUMO levels, respectively, and quantum layers fabricated using these first and second surfactants. By preparing a mixed solution in which a dot dispersion solution and an insulating solution are mixed, it can be manufactured inexpensively and efficiently without requiring a plurality of complicated film forming processes.

That is, the method for manufacturing a light-emitting device according to the present invention includes a hole transporting first surfactant having a HOMO level of −0.2 to +0.2 eV with respect to the energy level of the valence band, An electron transporting second surfactant having a LUMO level of −0.2 to +0.2 eV with respect to the energy level of the band is prepared, and ultrafine particles are formed with the first and second surfactants. One or more selected from the group consisting of an acrylic resin, a polystyrene resin, a polycarbonate resin, a polyester resin, a polyamide resin, and a polyvinyl resin, and a quantum dot dispersion solution preparation step for preparing a coated quantum dot dispersion solution An insulating material made of a polymer compound of the above, an insulating solution preparation step of preparing an insulating solution by dissolving the insulating material in a solvent, the quantum dot dispersion solution and the insulating property A mixed solution preparing step of preparing mixed to a mixed solution of a liquid, is characterized by including a light-emitting layer manufacturing step of manufacturing a light-emitting layer using the mixed solution.

  Moreover, the manufacturing method of the light-emitting device of this invention provides the 1st electrode layer formation process which provides a 1st electroconductive material on the surface of a transparent substrate, and forms a 1st electrode layer, The said 1st electrode layer A hole transport layer forming step for forming a hole transport layer by providing a hole transport material to the surface of the substrate, and an electron transport layer for forming an electron transport layer by providing an electron transport material to the surface of the light emitting layer A formation step and a second electrode layer formation step of forming a second electrode layer by applying a second conductive material to the surface of the electron transport layer, the light emitting layer formation step including the hole It is preferable to form the light emitting layer by applying the mixed solution to the surface of the transport layer.

  As a result, regardless of whether the adjacent hole transport layer or electron transport layer is formed of an inorganic material or an organic material, the leakage of the carrier to the adjacent layer is suppressed, and the injection efficiency into the ultrafine particles is high and the quality is high. A light-emitting device can be manufactured inexpensively and with high efficiency.

According to the light-emitting device of the present invention, in the light-emitting device in which the light-emitting layer is formed of an assembly of quantum dots, the quantum dots include the first surfactant having a hole transport property on the surface of the ultrafine particles and electron transport. coated with a second surfactant having a sexual Rutotomoni, the nanoparticle oxide compound comprises semiconductor, and one of the elemental semiconductor, and the emission layer, an acrylic resin, a polystyrene resin An insulating material made of a polymer compound formed of one or more selected from the group consisting of polycarbonate resin, polyester resin, polyamide resin, and polyvinyl resin is filled between the quantum dots, and the quantum dots of the with the carrier inhibits the passage outside said first surfactant, wherein as valence band and tunneling resonance ultrafine particles, of the valence band The energy level of the conduction band has a HOMO level of −0.2 to +0.2 eV with respect to the energy level, or the second surfactant is in tunnel resonance with the conduction band of the ultrafine particles. Since the LUMO level of -0.2 to +0.2 eV with respect to the position, the first or second surfactant moves through the carrier using tunnel resonance, so that a phonon bottleneck occurs. Is suppressed, the carrier can be transported quickly and efficiently, the first surfactant can transport only holes, and the second surfactant can transport only electrons. Then, by filling the insulating material between the quantum dots, the carrier can be prevented from passing outside the ultrafine particles, so that leakage of the carrier to the adjacent layer is suppressed and the ultrafine particles are highly efficient inside. A light-emitting device that can be injected, has good carrier-injection efficiency into the quantum dots, and has good light-emitting efficiency and light-emitting color purity can be obtained.

In other words, carriers injected into the electrode by voltage application can be efficiently transported into the ultrafine particles without recombination of holes and electrons outside the ultrafine particles, thereby making the carrier transportability of the film Therefore, it is possible to improve the efficiency of injecting the carrier into the ultrafine particles.

In addition, according to the method for manufacturing a light-emitting device of the present invention, a hole-transporting first surfactant having a HOMO level of −0.2 to +0.2 eV with respect to the energy level of the valence band, An electron transporting second surfactant having a LUMO level of −0.2 to +0.2 eV with respect to the energy level of the conduction band is prepared, and ultrafine particles are formed using the first and second surfactants. Dot dispersion solution preparation step for preparing a quantum dot dispersion solution coated with a resin, and one kind selected from the group of acrylic resin, polystyrene resin, polycarbonate resin, polyester resin, polyamide resin, and polyvinyl resin An insulating material made of the above polymer compound is prepared, an insulating solution preparing step of preparing the insulating solution by dissolving the insulating material in a solvent, the quantum dot dispersion solution and the insulating solution A mixed solution preparing step of preparing mixed to a mixed solution of the door, since by using the mixed solution containing a light-emitting layer manufacturing step of manufacturing a light-emitting layer, a good injection efficiency which suppresses the occurrence of phonon bottleneck the light-emitting layer having, without requiring a plurality of complicated deposition processes, such as dry process, it is possible to Seisuru created in one process, can be efficiently produced at low cost.

It is sectional drawing which shows typically one Embodiment of the light-emitting device which concerns on this invention. It is an expanded sectional view which shows typically the quantum dot used for the light-emitting device of FIG. It is a figure which shows the relationship between the energy level of surfactant, and the energy level of the quantized carrier of a quantum dot. It is a schematic diagram which shows the principle of the carrier movement by tunnel resonance. It is a figure which shows typically the preparation procedures of the mixed solution which uses a light emitting layer as a raw material. It is a manufacturing process figure (1/2) which shows the manufacturing method of the light emitting device which concerns on this invention. It is a manufacturing process figure (2/2) which shows the manufacturing method of the light-emitting device which concerns on this invention. It is a figure which shows the emission spectrum of an Example sample. It is sectional drawing for demonstrating the general method in the case of producing a quantum dot by the self-assembly method. It is sectional drawing for demonstrating the prior art described in patent document 1. FIG. It is sectional drawing for demonstrating the prior art described in patent document 2. FIG. It is sectional drawing for demonstrating the prior art described in patent document 3. FIG. 10 is a schematic diagram for explaining a carrier confinement principle in Patent Document 3. FIG. 10 is a schematic diagram for explaining the problem of Patent Document 3. FIG.

  Next, an embodiment of the present invention will be described in detail.

  FIG. 1 is a cross-sectional view schematically showing an embodiment of a light emitting diode as a light emitting device according to the present invention.

  In this light emitting diode, an anode 2 is formed on a glass substrate 1 (transparent substrate), and a hole injection layer 3 and a hole transport layer 4 made of a hole transporting material are sequentially formed on the surface of the anode 2, A light emitting layer 6 made of an assembly of quantum dot layers 5 is formed on the surface of the hole transport layer 4, and an electron transport layer 7 made of an electron transporting material is further formed on the surface of the light emitting layer 6. A cathode 8 is formed on the surface of 7.

  As shown in FIG. 2, the quantum dot 5 has a core-shell structure in which nanoparticles (ultrafine particles) 9 have a core portion 10 and a shell portion 11 that protects the core portion 10, and the surface of the shell portion 11 is normal. It is covered with a hole transporting surfactant (first surfactant) 12 having a hole transporting property and an electron transporting surfactant (second surfactant) 13 having an electron transporting property. Then, the holes transported from the hole transport layer 4 and the electrons transported from the electron transport layer 7 are injected into the core part 10 of the nanoparticles 9, and the holes and electrons are injected into the core part 10. Recombines and emits excitons.

  Here, the core material for forming the core portion 10 is not particularly limited as long as it is a semiconductor material having a photoelectric conversion effect, and InP, CdSe, CdS, PbSe, or the like can be used. As a shell material constituting the portion 11, for example, ZnS can be used.

  As the hole transporting surfactant 12, a material in which a ligand is introduced into a low molecular weight hole transport layer material can be used.

  Here, as a material for a low molecular weight hole transport layer, for example, N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl represented by the chemical formula (1) is used. -4,4'-diamine (hereinafter referred to as "TPD"), 4,4'-bis [N- (1-naphthyl) -N-phenyl-amino] biphenyl represented by the chemical formula (2) α-NPD ”), 4,4 ′, 4 ″ -tris (2-naphthylphenylamino) triphenylamine (hereinafter referred to as“ 2-TNATA ”) represented by chemical formula (3), chemical formula (4) N, N′-7-di (1-naphthyl) -N, N′-diphenyl-4,4′-diaminobiphenyl (hereinafter referred to as “Spiro-NPB”) represented by the chemical formula (5) 4,4 ′, 4 ″ -tris (3-methylphenylpheny Ruamino) triphenylamine (hereinafter referred to as “m-MTDATA”) and derivatives thereof can be used.

The ligand is not particularly limited as long as it is a polar group. For example, a thiol group (—SH), an amino group (—NH ₂ ), a carboxyl group (—COOH), a carbonyl group (—CO). ), A nitro group (—NO ₂ ), a phosphino group (—PH ₂ ), a phosphoroso group (—PO), or the like can be used.

  Therefore, as the hole transporting surfactant 12, for example, a TPD-thiol ligand in which a thiol group is introduced into TPD, an α-NPD-amino ligand in which an amino group is introduced into α-NPD, or the like is used. be able to. When the number of introduced ligands is one, it can be dispersed in a nonpolar solvent, and when the number of ligands introduced is two or more, it can also be dispersed in a polar solvent.

  A polymer material such as poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate) (hereinafter referred to as “PEDOT: PSS”) is preferably used as the material for the hole transport layer. Although it can be used, it is not preferable to use it as a material for a hole transporting surfactant. Since the polymer material has a large molecular size, which becomes a steric hindrance, the adjacent distance cannot be shortened. As a result, the surface coverage of the nanoparticles 9 decreases, leading to a decrease in quantum yield, The surface density of the quantum dots 5 cannot be increased.

  Further, as the electron transporting surfactant 13, a material in which a ligand is introduced into the electron transporting layer material can be used.

  Here, as the electron transport layer material, for example, tris (8-hydroxyquinoline) aluminum (hereinafter, referred to as “Alq3”) represented by the chemical formula (6), 2- (4-) represented by the chemical formula (7). Biphenylyl) -5- (4-t-butylphenyl) -1,3,4-oxadiazole (hereinafter referred to as “PBD”), 2,2 ′, 2 ″-(1 represented by the chemical formula (8) , 3,5-benzonitrile) -tris (1-phenyl-1-H-benzimidazole (hereinafter referred to as “TPBi”), 2,9-dimethyl-4,7-diphenyl- represented by the chemical formula (9) 1,10-phenanthroline (hereinafter referred to as “BCP”), 3- (benzothiazol-2-yl) -7- (diethylamino) -2H-1-benzopyran-2- represented by the chemical formula (10) (Hereinafter referred to as “coumarin 6”), bis (2-methyl-8-quinolinolato) -4- (phenylphenolate) aluminum (hereinafter referred to as “BAlq”) represented by chemical formula (11), chemical formula ( 4,4′-bis (9-carbazolyl) -2,2′-dimethylbiphenyl (hereinafter referred to as “CDBP”) represented by 12) and derivatives thereof can be used.

The ligand is not particularly limited as long as it is a polar group, like the hole transporting surfactant 12. For example, a thiol group (—SH), amino group (—NH ₂ ), carboxyl A group (—COOH), a carbonyl group (—CO), a nitro group (—NO ₂ ), a phosphino group (—PH ₂ ), a phosphoroso group (—PO) and the like can be used.

  Therefore, as the electron transporting surfactant 13, for example, a PBD-thiol ligand in which a thiol group is introduced into PBD, a BCP-amino ligand in which an amino group is introduced into BCP, or the like can be used.

  Thus, by covering the surface of the nanoparticle 9 in the state where the hole transporting surfactant 12 and the electron transporting surfactant 13 coexist, only the holes and the electrons only have the respective surfactants ( It is transported via a hole transporting surfactant 12 and an electron transporting surfactant 13). As a result, electron-hole recombination in the surfactant is suppressed, and efficient carrier (electron and hole) transport becomes possible.

  In the light emitting layer 6, the gap between the quantum dots 5 is filled with an insulating material 14.

  In order to recombine carriers in the quantum dot 5, that is, in the core part 10 of the quantum dot 5, to efficiently emit excitons, carriers transported in the vicinity of the quantum dot 5 are efficiently contained in the core part 10. Need to be injected into.

  However, since the surfaces of the nanoparticles 9 are covered with the ligands of the hole transporting surfactant 12 and the electron transporting surfactant 13, even if the surface density of the quantum dots 5 is improved, the space between the nanoparticles 9 is increased. A certain gap is generated in. Therefore, the carriers are not efficiently injected into the core portion 10 of the nanoparticles 9 and recombined outside the core portion 10 or flow into the hole transport layer 3 or the electron transport layer 7 facing each other. As a result, the emission color purity and emission efficiency may be reduced.

  Therefore, in the present embodiment, the gaps between the quantum dots 5 are filled with a dense insulating material 14 having excellent voltage resistance.

  As such an insulating material, a polymer compound is preferable. In the case of an inorganic material, a crystal grain boundary is formed, so that the carrier is not injected into the core part 10 of the nanoparticle 9 and passes around the nanoparticle 9 in such a form as to propagate through the crystal grain boundary, Alternatively, electrons and holes may recombine at the grain boundary, which is not preferable.

Then, as such a polymer compound, Po Li methacrylate (PMMA) or acrylic resins polyacrylates, homopolymers of styrene and acrylonitrile - styrene monomer copolymer (AS) or acrylonitrile - butadiene - styrene copolymer (ABS) or the like of the polystyrene resin, polycarbonate resin, polyamide resin such as nylon, polyester resin, a polyvinyl-based resins such as polyvinyl acetate and polyvinyl chloride may be used.

  In the light emitting diode thus formed, carriers are injected into the anode 2 and the cathode 8 when a voltage is applied. Of the injected carriers, the holes injected into the anode 2 are injected into the nanoparticles 9 along the bulk heterogeneous network of the hole transporting surfactant 12. On the other hand, the electrons injected into the cathode 8 are injected into the nanoparticles 9 through the bulk hetero network of the electron transporting surfactant 13, and the holes and electrons are regenerated in the core 10. Combine and emit light.

  As described above, in the present embodiment, holes and electrons do not flow into the gaps of the quantum dots 5, but are separated through the hole transporting surfactant 12 and the electron transporting surfactant 13 through different paths. Since they are transported inside the particles 9, the holes and electrons do not approach and recombine during transport, and can be transported efficiently even with a relatively thick film thickness of 10 μm level. Thus, photoelectric conversion from an electrical signal to an optical signal can be performed with high efficiency.

  FIG. 3 is a diagram showing the relationship between the energy levels of the surfactants 12 and 13 and the energy levels of the quantized carriers of the nanoparticles 9.

  The hole transporting surfactant 12 tunnels with a valence band energy level 15 (hereinafter referred to as “valence band level”) 15 of the core 10 which is an energy band in which holes can move. The electron transporting surfactant 13 having the HOMO level 16 is an energy level (hereinafter referred to as “conduction band level”) of the conduction band of the core portion 10 of the nanoparticle 9 which is an energy band in which electrons can move. ) Having a LUMO level 18 that is in tunnel resonance with 17.

  By using tunnel resonance in this way, carriers can easily pass through the energy barrier, and efficient carrier movement can be realized.

  FIG. 4 is a schematic diagram showing the principle of carrier movement by tunnel resonance.

  The nanoparticle 9 is composed of the core portion 10 and the shell portion 11 as described above. Since the shell portion 11 is usually an ultra-thin film having a thickness of 1 nm or less, carriers easily pass by the tunnel effect. However, the carrier movement between the core portion 10 and the surfactants 12 and 13 is also performed quickly, so It is desirable to improve transportation efficiency.

  However, when the HOMO level 16 'of the hole transporting surfactant 12 and the valence band level 15 of the core part 10 have a large energy level difference that does not cause tunnel resonance, as indicated by an arrow A'. Holes move so as to overcome the energy barrier. Similarly, when the LUMO level 18 'of the electron transporting surfactant 13 and the conduction band level 17 of the core part 10 have a large energy level difference that does not cause tunnel resonance, as indicated by an arrow B'. Electrons move so as to overcome the energy barrier.

  In addition, in the nanoparticle system, the movement of phonons is slow, and the phonon bottleneck is generated due to the slow movement of phonons, which makes it difficult to move the carriers quickly.

  Therefore, in the present embodiment, the hole transporting surfactant 12 has a HOMO level 16 that is in tunnel resonance with the valence band level 15 of the core portion 10, and the electron transporting surfactant. 13 has a LUMO level 18 that is in tunnel resonance with the conduction band level 17 of the core portion 10, thereby rapidly moving carriers as indicated by arrows A and B, and improving carrier transport efficiency. I am trying.

  In order to generate such tunnel resonance, the HOMO level 16 of the hole transporting surfactant 12 is −0.2 to +0.2 eV with respect to the valence band level 15 of the core 10. For example, when InP (valence band level: 5.7 eV) is used for the core portion 10, a TPD-thiol ligand (HOMO level: 5.6 eV) can be used.

  The LUMO level 18 of the electron transporting surfactant 13 is preferably in the range of −0.2 to +0.2 eV with respect to the conduction band level 17 of the core part 10. For example, the core part 10 has InP (conduction band). When using a level (about 3 eV), a BCP-amino ligand (LUMO level: 3.2 eV) can be used.

  Next, a method for manufacturing the light emitting diode will be described.

  As described above, the nanoparticles 9 can be manufactured using various materials. In the following embodiment, the case where InP is used for the core portion 10 and ZnS is used for the shell portion 11 will be described as an example. .

  FIG. 5 is a production process diagram showing the procedure for producing the quantum dot dispersion solution.

  First, as shown in FIG. 5A, a raw material solution 19 containing InP / ZnS nanoparticles 9 is prepared.

  That is, for example, indium acetate, myristic acid and octadecene are mixed in a container and dissolved by stirring in a nitrogen atmosphere, thereby preparing an indium precursor solution. Further, tristrimethylsilylphosphine, octylamine, and octadecene are mixed in a nitrogen atmosphere, thereby preparing a phosphorus precursor solution.

  Next, the indium precursor solution is heated to a predetermined temperature (for example, 190 ° C.), and the phosphorus precursor solution is injected into the heated solution. Then, precursors with high activity react with each other at a high temperature, indium and phosphorus combine to form nuclei, and then react with surrounding unreacted components to cause crystal growth, thereby producing InP quantum dots. The

  Next, a zinc oxide solution in which zinc oxide is dissolved in stearic acid and a sulfur solution in which sulfur is dissolved in stearic acid are prepared.

  Next, a small amount of zinc oxide solution and sulfur solution are alternately added dropwise to an InP quantum dot solution adjusted to a predetermined temperature (for example, 150 ° C.), heated and cooled, and washed to remove excess organic components in the solution. . After that, while adding a surfactant made of an organic compound such as hexadecylamine (hereinafter referred to as “HDA”), it is dispersed in a dispersion solvent, for example, hexane, whereby InP coated with the surfactant. An InP / ZnS dispersion solution with / nZS as nanoparticles 9, that is, a raw material solution 19 is prepared.

  Next, the hole-transporting surfactant 12 and the electron-transporting surfactant 13 are weighed in equal amounts and dissolved in an organic solvent, for example, hexane. As shown in FIG. Make it.

  Next, the raw material solution 19 and the surfactant solution 20 are mixed so that the surfactant solution 20 has a mixing ratio of about twice that of the raw material solution 19 to perform ligand substitution.

  That is, when the raw material solution 19 and the surfactant solution 20 are mixed in a state where the surfactant solution 20 is about twice as many as the raw material solution 19 and left for a sufficiently long time, the hole transporting surfactant 12 and the electrons are mixed. Since the transporting surfactant 13 is present in an equal amount, the surfactant in the raw material solution 19 is replaced with the hole transporting surfactant 12 and the electron transporting surfactant 13 in the surfactant solution 20. Thus, as shown in FIG. 5C, a ligand substitution solution 21 having quantum dots 5 in which the hole transporting surfactant 12 and the electron transporting surfactant 13 coexist is obtained.

  In order to avoid aggregation of the nanoparticles 9, the nanoparticles 9 are covered with a surfactant made of an organic compound such as HDA, but a light emitting layer is formed using a normal organic compound as the surfactant. Even so, the potential barrier is large due to the low conductivity of the surfactant due to the organic molecules, which may reduce the light emission efficiency via the carriers (holes and electrons).

  In addition, when a conductive polymer or a metal-based material is used as a surfactant, carriers injected into the electrode by voltage application pass through the surfactant from the anode to the cathode or from the cathode to the anode. Therefore, it is difficult to efficiently confine the carriers in the quantum dots.

  On the other hand, in this embodiment, ligand substitution is performed to form nanoparticles 9 as a hole transporting surfactant 12 having a hole transporting ligand and an electron having an electron transporting ligand. It coat | covers with the transportable surfactant 12, and it enables it to transport only an electron or a hole efficiently by this, and the injection | pouring efficiency to the nanoparticle 9 of a carrier is aimed at.

  Next, a large amount of an organic solvent such as methanol is added to the ligand substitution solution 21, separated by a centrifuge, etc., and the supernatant liquid is removed, followed by vacuum drying as shown in FIG. The solvent component is completely removed.

  Next, the quantum dots 5 are dissolved in a dispersion solvent in which the insulating material 14 can be dissolved, thereby producing a quantum dot dispersion solution 22 as shown in FIG.

  On the other hand, as shown in FIG. 5 (f), the insulating material 14 is dissolved in the same organic solvent as the dispersion solvent to produce the insulating solution 23.

  And the quantum dot dispersion | distribution solution 22 and the insulating solution 23 are mixed, and the mixed solution 24 is produced as shown in FIG.5 (g).

  The organic solvent for dissolving the insulating material 14 can be appropriately selected according to the insulating material 14 to be used.

That is, as the organic solvent, For example, an acrylic resin or polycarbonate resin insulation material 14, when using a polyester resin, benzene, toluene, xylene and like aromatic hydrocarbons, trichlorethylene, chlorobenzene, dichloroethane, Chlorine-containing hydrocarbons such as chloroform, ester organic compounds, ketone organic compounds, and the like can be used. In the case where a polystyrene resin is used for the insulating material 14, acetone, methanol, ethanol or the like can be used in addition to the aromatic hydrocarbon and chlorine-containing hydrocarbon described above. Moreover, when using a polyamide-type resin for the insulating material 14, phenol and methanol can be used. Furthermore, when using a polyvinyl acetate resin for the insulating material 14, in addition to the above-mentioned aromatic hydrocarbon and chlorine-containing hydrocarbon, aniline and pyridine can be used, and when using a polyvinyl chloride resin, The chlorine-containing hydrocarbons and acetone described above can be used.

  And the dispersion solvent of the quantum dot dispersion solution 22 is selected according to the organic solvent which melt | dissolves in such a high molecular compound. For example, when PMMA is used for the insulating material 14, toluene in which PMMA is dissolved can be selected as an organic solvent for the insulating solution 23 and a dispersion solvent for the quantum dot dispersion solution 22. Then, a hole transporting surfactant 12 and an electron transporting surfactant 13 dispersible in the selected dispersion solvent are used.

  6 and 7 are manufacturing process diagrams showing the manufacturing method of the light emitting diode.

  As shown in FIG. 6A, an ITO film is formed on the glass substrate 1 by sputtering and UV ozone treatment is performed to form an anode 2 having a thickness of 100 nm to 150 nm.

  Next, a surfactant solution for a hole injection layer (hereinafter referred to as “hole injection layer solution”) is prepared. Here, as the material for the hole injection layer, the same material as the material for the hole transport layer can be used, for example, PEDOT: PSS or the like can be used.

  Then, a hole injection layer solution is applied onto the anode 2 by using a spin coating method or the like to form a hole injection layer 3 having a film thickness of 20 nm to 30 nm as shown in FIG.

  Next, a hole transport layer surfactant solution (hereinafter referred to as a “hole transport layer solution”) having an energy having a lower HOMO level than the hole injection layer material is prepared. Here, for example, when PEDOT: PSS is used as the material for the hole injection layer, poly-TPD having a HOMO level lower than that of the PEDOT: PSS can be used as the material for the hole transport layer. .

  Then, a hole transport layer solution is applied onto the positive electrode injection layer 3 by using a spin coat method or the like to form a hole transport layer 4 having a film thickness of 60 nm to 70 nm as shown in FIG. .

  Since the hole injection layer 3 is provided to improve the hole transportability, the hole transport layer 4 may also be used as the hole injection layer 3. The hole transport layer 4 can be formed of only poly-TPD, and the hole injection layer 3 can be omitted.

  Next, the above-described mixed solution 24 is prepared.

  Then, using a spin coating method or the like, the mixed solution 24 is applied onto the hole transport layer 4 to form the light emitting layer 6 having a laminated structure and a film thickness of 300 nm to 1000 nm as shown in FIG. .

  Next, using an electron transporting material such as Alq3, as shown in FIG. 7E, the electron transporting layer 7 having a film thickness of 50 nm to 70 nm is formed on the surface of the light emitting layer 6 by vacuum deposition.

  And as shown in FIG.7 (f), LiF, Al, etc. are used, The cathode 8 with a film thickness of 100 nm-300 nm is formed by a vacuum evaporation method, Thereby, a light emitting diode is produced.

  As described above, in this embodiment, the quantum dot dispersion solution 22 in which the nanoparticles 9 are coated with the hole transporting surfactant 12 and the electron transporting surfactant 13 is produced, while the insulating material made of a polymer compound is used. 14 is dissolved in a solvent to prepare an insulating solution 23, and the quantum dot dispersion solution 22 and the insulating solution 23 are mixed to prepare a mixed solution 24. The mixed solution 24 is applied to the surface of the hole transport layer 4. Since the light-emitting layer 6 is formed by coating, the light-emitting layer can be produced in one process without requiring a plurality of complicated film forming processes such as a dry process, and the light-emitting layer 6 can be manufactured inexpensively and efficiently. be able to.

  Moreover, even if the hole transport layer 4 and the electron transport layer 7 adjacent to the light emitting layer 6 are formed of either an inorganic material or an organic material, leakage of carriers to the adjacent layer can be suppressed. A high-quality light-emitting device with good injection efficiency can be manufactured at low cost and high efficiency.

  The light-emitting diode thus formed can transport only holes by the hole-transporting surfactant 12 and can transport only electrons by the electron-transporting surfactant 13, and between the quantum dots 5. Is filled with the insulating material 14, it is possible to suppress carriers from being injected into the inside of the nanoparticle 9 with high efficiency and passing through the outside of the nanoparticle 9.

  That is, the carriers injected into the electrode by applying a voltage can be efficiently transported into the quantum dots without recombination of holes and electrons outside the nanoparticles 9. This makes it possible to improve the efficiency of carrier injection into ultrafine particles.

  In addition, by adjusting the energy level of the ligand possessed by the surfactant, carrier transfer using tunnel resonance can be performed, and efficient carrier transport can be realized without causing a phonon bottleneck. it can. That is, to avoid a phonon bottleneck, it is not necessary to form a quantum well layer or a tunnel layer that requires a complicated film formation process, and a light-emitting device that can efficiently inject carriers into nanoparticles 9 is realized. Is possible.

  The present invention is not limited to the above embodiment. In the above embodiment, the nanoparticles 9 have a core-shell structure in which the core portion 10 is covered with the one-layer shell portion 11, but the core portion does not have a two-layer core-shell structure or a shell portion. The same applies to the case.

  Moreover, in the said embodiment, although the compound semiconductor which consists of InP / ZnS was used as the nanoparticle 9, it cannot be overemphasized that an oxide and a single-piece | unit semiconductor may be sufficient.

  Moreover, although the said embodiment demonstrated the case of the light emitting diode as a light emitting device, it cannot be overemphasized that it can use for various light emitting devices, such as a semiconductor laser and various display apparatuses.

  Moreover, in the said embodiment, although the electron carrying layer 7 is performed by the dry process which uses the vacuum evaporation method, you may produce it by wet processes, such as a spin coat method. However, in this case, it is necessary to use a dispersion solvent having the same polarity as the dispersion solution used in the dipping process.

[Sample preparation]
(Sample No. 1)
A raw material solution having a concentration of 5 mg / mL was prepared by coating InP / ZnS nanoparticles having a core part made of InP and a shell part made of ZnS with HDA as a surfactant, and dispersing in a hexane solution.

  Next, a TPD-thiol ligand is prepared as a hole transporting surfactant and a BCP-amino ligand is prepared as an electron transporting surfactant so that the concentration of the surfactant is 0.1 mol / L. These were weighed in equal amounts and dissolved in hexane to prepare a surfactant solution.

  Next, the raw material solution and the surfactant solution were mixed so that the raw material solution: surfactant solution = 1: 2, and allowed to stand for 24 hours, and HDA was mixed with TPD-thiol ligand and BCP-amino coordination. Ligand substitution was performed to obtain a ligand substitution solution containing quantum dots.

  Next, 5 times as much methanol as the ligand substitution solution was added and separated with a centrifuge, and the supernatant was removed, followed by vacuum drying to completely remove the methanol.

  Next, the quantum dots were dispersed in toluene so that the concentration of the quantum dots was 2 to 5 mg / mL to prepare a quantum dot dispersion solution.

  Next, PMMA as an insulating material was dissolved in toluene to prepare an insulating solution having a concentration of 0.1 mol / mL.

  Thereafter, the quantum dot dispersion solution and the insulating solution were mixed to prepare a mixed solution having a quantum dot concentration of 0.8 mg / mL.

  Next, an ITO film was formed on a glass substrate by a sputtering method, UV ozone treatment was performed, and an anode with a thickness of 120 nm was produced.

  Next, PEDOT: PSS as a hole injection layer material was dispersed in pure water to prepare a hole injection layer solution.

  And the solution for positive hole injection layers was apply | coated on the anode using the spin coat method, and the positive hole injection layer with a film thickness of 20 nm was formed.

  Next, poly-TPD as a hole transport layer material was dispersed in chlorobenzene to prepare a hole transport layer solution.

  And the solution for hole transport layers was apply | coated on the positive hole injection layer using the spin coat method, and the 65-nm-thick hole transport layer was produced.

  Next, using the spin coating method, the above-described mixed solution was applied onto the hole transport layer to form a light emitting layer. Specifically, the light emitting layer was formed by spin coating so that the thickness of the light emitting layer was 1 monolayer (monomolecular layer). That is, 0.1 mL of mixed solution was dripped at the positive hole transport layer, and the glass substrate was rotated at 3000 rpm for 60 seconds, and the light emitting layer was produced. In addition, although the thickness of the light emitting layer was made into 1 monolayer in the present Example, this means the state which the nanoparticle is the thickness for 1 particle, and the clearance gap has arisen slightly.

  Next, Alq3 was used as an electron transporting material, and an electron transport layer having a film thickness of 50 nm was formed on the surface of the light emitting layer by vacuum deposition. Although the thickness of the light emitting layer is one monolayer, since this electron transport layer is formed on the light emitting layer, it is assumed that Alq3 forming the electron transport layer flows into a slight gap between the quantum dots. Is done.

  Then, using LiF and Al, a cathode having a film thickness of 250 nm and having a two-layer structure was formed by a vacuum vapor deposition method, thereby preparing a sample of sample number 1.

(Sample No. 2)
Instead of using the mixed solution described above, a quantum dot dispersion solution was used, and the quantum dot dispersion solution was applied on the hole transport layer so as to have a thickness of 1 monolayer, thereby forming a light emitting layer. Other than that, the sample No. 2 was prepared by the same method and procedure as Sample No. 1.

(Sample evaluation)
For Sample Nos. 1 and 2, a direct current voltage was applied, and an emission spectrum was measured using a multichannel analyzer composed of a prism and a CCD.

  FIG. 8 shows the measurement results. The horizontal axis indicates the wavelength (nm), the vertical axis indicates the emission spectrum (au), the upper side indicates the measurement result of sample number 1, and the lower side indicates the measurement result of sample number 2.

  In Sample No. 2, the emission spectrum reached a peak at a wavelength of around 614 nm, but the emission spectrum also appeared at a wavelength of around 535 nm, and the purity of the emission color was lowered. This is because the electron transporting material Alq3 flows between the quantum dots and there are carriers that recombine within the nanoparticle, while some holes are in the electron transporting material filled in the gap or quantum dots It is considered that light recombined with electrons in the electron transport layer adjacent to the layer and emitted light even in the vicinity of 535 nm, which is the absorption wavelength region of Alq3.

  On the other hand, Sample No. 1 is dense and has excellent voltage resistance and is filled between quantum dots, so that it emits light only in the wavelength region near 614 nm of the quantum dot emission, and there is no emission of the adjacent electron transport layer. It was confirmed that good emission color purity was obtained.

  A light emitting device such as a light emitting diode having good luminous efficiency can be realized by improving the efficiency of carrier injection into the nanoparticles.

1 Transparent substrate 2 Anode (first electrode layer)
4 hole transport layer 5 quantum dot 6 light emitting layer 7 electron transport layer 8 cathode (second electrode layer)
9 Nanoparticles (ultrafine particles)
10 Core part 11 Shell part 12 Hole transporting surfactant (first surfactant)
13 Electron transporting surfactant (second surfactant)
14 Insulating Material 15 Valence Band Level 16 HOMO Level 17 Conduction Band Level 18 LUMO Level 22 Quantum Dot Dispersion Solution 23 Insulating Solution 24 Mixed Solution

Claims (6)

In the light emitting device in which the light emitting layer is formed of an assembly of quantum dots,
The quantum dots, is coated with a second surfactant having a first surfactant and an electron-transporting surface of the ultrafine particles has a hole transporting property Rutotomoni,
The ultrafine particles include any one of an oxide, a compound semiconductor, and a single semiconductor,
In addition, the light emitting layer is an insulating layer made of a polymer compound formed of at least one selected from the group consisting of acrylic resins, polystyrene resins, polycarbonate resins, polyester resins, polyamide resins, and polyvinyl resins. Filling the space between the quantum dots, suppress the carrier from passing through the outside of the quantum dots ,
The first surfactant has a HOMO level of −0.2 to +0.2 eV with respect to the energy level of the valence band so as to resonate with the valence band of the ultrafine particles. A light emitting device characterized by that. In the light emitting device in which the light emitting layer is formed of an assembly of quantum dots,
The quantum dots are coated with a first surfactant having a hole transporting property and a second surfactant having an electron transporting property on the surface of the ultrafine particles,
The ultrafine particles include any one of an oxide, a compound semiconductor, and a single semiconductor,
In addition, the light emitting layer is an insulating layer made of a polymer compound formed of at least one selected from the group consisting of acrylic resins, polystyrene resins, polycarbonate resins, polyester resins, polyamide resins, and polyvinyl resins. Filling the space between the quantum dots, suppress the carrier from passing through the outside of the quantum dots,
The second surfactant has a LUMO level of −0.2 to +0.2 eV with respect to the energy level of the conduction band so as to tunnel resonance with the conduction band of the ultrafine particles. A light emitting device characterized . The ultrafine particles according to claim 1 or claim 2 light-emitting device according to, characterized in that it has a core-shell structure comprising a shell part covering the core part and the core part. With the hole transport layer is formed on one main surface of the light-emitting layer, any of claims 1 to 3, characterized in that the electron transport layer on the other main surface of the light emitting layer is formed A light emitting device according to any one of the above. A hole-transporting first surfactant having a HOMO level of −0.2 to +0.2 eV with respect to the energy level of the valence band; and −0.2 to +0 with respect to the energy level of the conduction band. An electron transporting second surfactant having a LUMO level of 2 eV,
A quantum dot dispersion solution preparing step of preparing a quantum dot dispersion solution in which ultrafine particles are coated with the first and second surfactants;
Insulating material comprising one or more polymer compounds selected from the group of acrylic resin, polystyrene resin, polycarbonate resin, polyester resin, polyamide resin, and polyvinyl resin is prepared. An insulating solution preparation step of preparing an insulating solution by dissolving
A mixed solution preparation step of mixing the quantum dot dispersion solution and the insulating solution to prepare a mixed solution;
And a light emitting layer manufacturing step of manufacturing a light emitting layer using the mixed solution. A first electrode layer forming step of forming a first electrode layer by applying a first conductive material to the surface of the transparent substrate;
A hole transport layer forming step of providing a hole transport material on the surface of the first electrode layer to form a hole transport layer;
An electron transport layer forming step of providing an electron transport material on the surface of the light emitting layer and forming an electron transport layer;
A second electrode layer forming step of forming a second electrode layer by applying a second conductive material to the surface of the electron transport layer,
6. The method of manufacturing a light emitting device according to claim 5, wherein the light emitting layer forming step forms the light emitting layer by applying the mixed solution to a surface of the hole transport layer.

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