WO2020261346A1 - Procédé de production d'élément électroluminescent, et élément électroluminescent - Google Patents

Procédé de production d'élément électroluminescent, et élément électroluminescent Download PDF

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Publication number
WO2020261346A1
WO2020261346A1 PCT/JP2019/025011 JP2019025011W WO2020261346A1 WO 2020261346 A1 WO2020261346 A1 WO 2020261346A1 JP 2019025011 W JP2019025011 W JP 2019025011W WO 2020261346 A1 WO2020261346 A1 WO 2020261346A1
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light emitting
layer
electron transport
transport layer
mixed crystal
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PCT/JP2019/025011
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English (en)
Japanese (ja)
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貴洋 土江
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シャープ株式会社
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
    • H10K50/115—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers comprising active inorganic nanostructures, e.g. luminescent quantum dots
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B33/00—Electroluminescent light sources
    • H05B33/10—Apparatus or processes specially adapted to the manufacture of electroluminescent light sources
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B33/00—Electroluminescent light sources
    • H05B33/12—Light sources with substantially two-dimensional radiating surfaces
    • H05B33/14—Light sources with substantially two-dimensional radiating surfaces characterised by the chemical or physical composition or the arrangement of the electroluminescent material, or by the simultaneous addition of the electroluminescent material in or onto the light source

Definitions

  • the present invention relates to a method for manufacturing a light emitting element and a light emitting element.
  • Patent Document 1 discloses a quantum dot light emitting diode (QLED: Quantum dot Light Emitting Diode) using an inorganic layer such as ZnO (zinc oxide) in the electron transporting layer (ETL: Electron transporting layer).
  • QLED Quantum dot Light Emitting Diode
  • inorganic layer such as ZnO (zinc oxide) in the electron transporting layer
  • ETL Electron transporting layer
  • QLED light emitting element
  • QD Quantum dots
  • the electron transport layer and light emission are the boundaries between the organic layer and the inorganic layer. Defects are likely to occur between the layers and the stability is reduced when the light emitting element is driven. Further, since the organic layer has a slow electron transfer rate and a low electron density, there is a problem that the electron transport efficiency is lower than the hole transport efficiency.
  • Patent Document 1 a solution coating process selected from the group consisting of sol-gel coating, spin coating, printing, casting and spraying, or chemical vapor deposition (CVD), sputtering, is used for forming an electron transport layer.
  • a vapor phase coating process selected from the group consisting of electron beam deposition and vacuum deposition is used.
  • the film forming method by the vacuum method such as sputtering has good film properties, but sputter damage to quantum dots occurs. Further, in such a vapor phase coating process, since a vacuum device is used, the cost is higher than that of the solution coating method.
  • Patent Document 1 also discloses that an electron transport layer is formed by a solution coating process. By using the solution coating process, it is possible to reduce the cost and avoid problems such as spatter damage to the quantum dots.
  • the electron transport layer (ETL) is formed by the solution coating process in this way, the nanoparticles of the separately synthesized ETL material are coated on the light emitting layer.
  • FIG. 6 is a diagram schematically showing problems when an electron transport layer (ETL) is formed by a solution coating process in a QLED using quantum dot QD as a light emitting layer.
  • HTL indicates a hole transport layer.
  • ZnO nanoparticles solution a solution containing ZnO nanoparticles (ZnO-NP) (hereinafter, referred to as “ZnO nanoparticles solution”) is illustrated as an example. ..
  • the contact point at the interface between the quantum dot QD and ZnO-NP is point contact.
  • the resistance component increases, the contact resistance increases, the applied voltage increases, resulting in problems such as a decrease in power consumption and power luminous efficiency, and a decrease in the quality of the interface between the quantum dot QD and ZnO-NP.
  • One aspect of the present disclosure has been made in view of the above problems, and an object thereof is a light emitting device provided with an electron transport layer made of an inorganic layer, which is inexpensive and has excellent coating properties of an electron transport layer.
  • the purpose is to provide a manufacturing method.
  • the method for manufacturing a light emitting element includes an anode forming step of forming an anode on a substrate, a light emitting layer forming step of forming a light emitting layer on the anode, and the like.
  • the electron transport layer forming step comprising an electron transport layer forming step of forming an electron transport layer adjacent to the light emitting layer on the light emitting layer and a cathode forming step of forming a cathode on the electron transport layer.
  • the light emitting element includes an anode, a light emitting layer, an electron transport layer adjacent to the light emitting layer, and a cathode in this order, and the electron transport layer.
  • a light emitting device provided with an electron transport layer made of an inorganic layer, which is inexpensive and has excellent coating properties of the electron transport layer, and a method for manufacturing the same.
  • FIG. 1 is a diagram schematically showing an example of a laminated structure of the light emitting element 1 according to the embodiment.
  • FIG. 2 is a flowchart showing an example of a method for manufacturing the light emitting element 1 according to the embodiment.
  • FIG. 3 is a cross-sectional view schematically showing the steps from step S4 to step S5 shown in FIG.
  • the light emitting element 1 includes an electron transport layer 14 and a light emitting layer 13 as functional layers between the cathode 15 (cathode) and the anode 11 (anode), which are counter electrodes arranged vertically. It is a light emitting element.
  • the light emitting element 1 is provided with an anode 11, a hole transport layer 12 (HTL), a light emitting layer 13, an electron transport layer 14 (ETL), and a cathode 15 on the substrate 10 in this order from the substrate 10 side. ..
  • the electron transport layer 14 is laminated on the light emitting layer 13 adjacent to the light emitting layer 13.
  • the hole transport layer 12 may not be provided.
  • the direction from the substrate 10 to the cathode 15 is defined as the upward direction, and the opposite direction is defined as the downward direction.
  • the layer formed in the process before the layer to be compared is referred to as "lower layer”
  • the layer formed in the process after the layer to be compared is referred to as "upper layer”. ..
  • the anode 11 is formed on the substrate 10 (step S1, anode forming step).
  • the hole transport layer 12 is formed on the anode 11 (step S2, hole transport layer forming step).
  • the light emitting layer 13 is formed on the hole transport layer 12 (step S3, light emitting layer forming step).
  • the electron transport layer 14 is formed on the light emitting layer 13 (electron transport layer forming step).
  • a chemical solution method called a CBD (Chemical bath deposition) method is used for forming the electron transport layer 14.
  • the electron transport layer forming step includes a mask step (step S4), a thin film forming step (step S5, dipping step), a drying step (step S6), and a mask removing step (step S6).
  • a mask step of step S4 as shown in FIG. 3, a part of the surface of the laminate obtained in step S3 is exposed and a part is masked with a mask 21 (mask material).
  • the laminate obtained in step S3 is a laminate including the substrate 10, the anode 11, and the light emitting layer 13, and in the present embodiment, as described above, the anode 11, the hole, and the hole are placed on the substrate 10.
  • a laminated body formed by laminating the transport layer 12 and the light emitting layer 13 in this order is shown.
  • the laminated body will be referred to as "laminated body 20" for convenience of explanation.
  • step S4 specifically, a part of the surface of the light emitting layer 13 which is the surface to be formed of the electron transport layer 14 (in other words, the formed region of the electron transport layer 14) in the light emitting layer 13 of the laminated body 20. (Specifically, the upper surface) is exposed. Then, at least a part of the surface of the laminated body 20 other than the surface to be formed of the electron transport layer 14 (in other words, the electron transport layer non-formed region that does not form the electron transport layer 14) is masked. In addition, in FIG. 3, as an example, the case where the side surface and the back surface of the laminated body 20 are masked is taken as an example.
  • the laminate 20 in which a part of the light emitting layer 13 is exposed is immersed in the reaction solution 23 in the reaction vessel 22.
  • an alkaline aqueous solution containing a zinc source and a sulfur source, which is a base material of the electron transport layer 14, is used as the reaction solution 23.
  • a thin film derived from the alkaline aqueous solution, which becomes the electron transport layer 14, is formed on the light emitting layer 13.
  • the drying step of step S6 the thin film formed in step S5 is dried.
  • the mask removing step of step S7 the mask 21 is removed.
  • the cathode 15 is formed on the electron transport layer 14 thus formed (step S8).
  • the light emitting element 1 shown in FIG. 1 is manufactured by the above steps.
  • the substrate 10 is a support substrate that supports the anode 11, the hole transport layer 12, the light emitting layer 13, the electron transport layer 14, and the cathode 15.
  • the light emitting element 1 may be used as a light source of an electronic device such as a display device, for example.
  • the light emitting element 1 is the light source of the display device, for example, an array substrate on which a thin film transistor is formed is used for the substrate 10, and the anode 11 is electrically connected to the thin film transistor of the array substrate.
  • anode 11 and the cathode 15 For the formation of the anode 11 and the cathode 15, various conventionally known methods such as a sputtering method, a vacuum vapor deposition method, a CVD (chemical vapor deposition) method, a plasma CVD method, and a printing method can be used.
  • the anode 11 and the cathode 15 are connected to a power source 16 (for example, a DC power source), so that a voltage is applied between them.
  • the anode 11 and the cathode 15 contain a conductive material and are electrically connected to the hole transport layer 12 and the electron transport layer 14, respectively.
  • At least one of the anode 11 and the cathode 15 is made of a light transmissive material.
  • Either one of the anode 11 and the cathode 15 may be formed of a light-reflecting material.
  • the light emitting element 1 can extract light from the electrode (specifically, the transparent electrode) side made of a light transmissive material.
  • the upper electrode for example, the cathode 15 is formed of a light transmitting material
  • the lower electrode for example, the anode 11 is formed of a light reflecting material
  • the upper electrode for example, the cathode 15 is formed of a light reflecting material
  • the anode 11 which is a lower electrode is formed of a light transmitting material.
  • the light transmissive material for example, a transparent conductive film material can be used.
  • the light-transmitting material include ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), ZnO (zinc oxide), AZO (aluminum-doped zinc oxide), and BZO (boron-doped zinc).
  • Oxide), GZO (gallium-doped zinc oxide) and the like can be used. Since these materials have high visible light transmittance, the luminous efficiency is improved.
  • the light-reflecting material a material having a high reflectance of visible light is preferable, and for example, a metal material can be used. Specifically, for example, Al (aluminum), Cu (copper), Au (gold), Ag (silver) and the like can be used as the light-reflecting material. Since these materials have high visible light reflectance, the luminous efficiency is improved. Further, by forming either one of the anode 11 and the cathode 15 as a laminate of a layer made of a light-transmitting material and a layer made of a light-reflecting material, an electrode having light reflectivity may be used.
  • the hole transport layer 12 is a layer that transports holes from the anode 11 to the light emitting layer 13.
  • the hole transport layer 12 contains a hole transport material having excellent hole transport properties.
  • the hole transport layer 12 may have a function of inhibiting the transport of electrons.
  • the hole transport layer 12 may also have a function as a hole injection layer (HIL) that promotes hole injection from the anode 11 to the light emitting layer 13, and the anode 11 injects holes. It may also have a function as a layer (EIL).
  • HIL hole injection layer
  • EIL layer
  • the hole transport layer 12 contains, for example, PEDOT: PSS (poly (3,4-ethylenedioxythiophene): poly (4-styrene sulfonic acid)).
  • the hole transport layer 12 may be replaced with PEDOT: PSS, or in addition to PEDOT: PSS, PVK (polyvinylcarbazole), TFB (poly [(9,9-dioctylfluorenyl-2,7-diyl-2,7-diyl)).
  • TPD 4,4'-bis [N-phenyl-N- (3''-methylphenyl)
  • It may contain at least one organic material selected from the group consisting of (amino] biphenyl).
  • the hole transport layer 12 For the formation of the hole transport layer 12, various conventionally known methods such as an inkjet method and a vacuum vapor deposition method can be used.
  • the electron transport layer 14 is a layer that transports electrons from the cathode 15 to the light emitting layer 13.
  • the electron transport layer 14 contains an electron transport material having excellent electron transport properties.
  • the electron transport layer 14 may have a function of inhibiting the transport of holes. Further, the electron transport layer 14 may also have a function as an electron injection layer (EIL) that promotes electron injection from the cathode 15 to the light emitting layer 13, and the cathode 15 is a hole injection layer (EIL). ) May also have the function.
  • EIL electron injection layer
  • the electron transport layer 14 is a mixed crystal layer formed of a solid solution of at least ZnS (zinc sulfide) and Zn (OH) 2 (zinc hydroxide), and has a Zn—S bond and a Zn—OH bond with ZnS. It is formed of mixed crystals containing Zn (OH) 2 .
  • the mixed crystal (mixed crystal layer) may further contain ZnO having a Zn—O bond, and has Zn—S, Zn—OH, and Zn—O bonds, ZnS, ZnO, and Zn. It may be a mixed crystal (mixed crystal layer) with (OH) 2 .
  • the electron transport layer 14 is, for example, a mixed crystal layer containing at least ZnS and Zn (OH) 2 among ZnS, ZnO, and Zn (OH) 2 .
  • a mixed crystal of ZnS and Zn (OH) 2 having a Zn—S bond and a Zn—OH bond is referred to as Zn (S, OH).
  • a mixed crystal of ZnS, ZnO (zinc oxide) and Zn (OH) 2 having a bond of Zn—S, Zn—OH and Zn—O is referred to as Zn (S, O, OH).
  • the electron transport layer 14 contains Zn (S, OH).
  • Zn (S, OH) may be Zn (S, O, OH).
  • the CBD method using an alkaline aqueous solution containing a zinc source and a sulfur source in the reaction solution 23 is used for forming the electron transport layer 14.
  • ZnS is synthesized in an aqueous solution to form a thin film to be an electron transport layer 14, so that at least a hydroxyl group (-OH group) and an oxygen group (-O group) among the hydroxyl groups (-OH group) and the oxygen group (-O group) Group) is always contained in the thin film.
  • ZnO or ZnS is formed by a vacuum method or a vapor deposition method, Zn (OH) 2 is not intentionally mixed.
  • a mask having alkali resistance is used as the mask 21 used in step S4.
  • the material of the mask 21 is not particularly limited as long as it has alkali resistance.
  • a commercially available masking tape can be used.
  • step S4 it is not necessary to mask the entire electron transport layer non-formation region, and the electron transport layer non-formation region of the portion of the electron transport layer non-formation region immersed in the reaction solution 23 in step S5). It is enough if it is masked.
  • the laminate 20 is one of the light emitting layers 13 so that the formed region (in other words, the formed surface) of the electron transport layer 14 in the light emitting layer 13, which is a part of the light emitting layer 13, comes into contact with the reaction solution 23.
  • the part may be immersed in the reaction solution 23. Therefore, the masked portion may be, for example, only the side surface of the laminate 20 including the anode 11, the hole transport layer 12, and the light emitting layer 13 (specifically, a part of the side surface or the entire side surface). It may be a part of the side surface and a part of the back surface of the laminate 20.
  • the entire surface of the laminated body 20 other than the formed region of the electron transport layer 14 (that is, the laminated body) is exposed so that only the formed region of the electron transport layer 14 is exposed. It goes without saying that the entire electron transport layer non-forming region in 20) may be masked.
  • step S5 In the thin film forming step (step S5), first, an alkaline aqueous solution containing a zinc source and a sulfur source is prepared as the reaction solution 23. Then, the reaction solution 23 is placed in the reaction vessel 22. Next, the laminate 20 in which a part of the light emitting layer 13 is exposed is immersed in the reaction solution 23 to form a thin film. Then, the laminate 20 on which the thin film is formed is taken out from the reaction solution 23.
  • the reaction solution 23 is prepared by mixing a zinc source, an alkali source, and a sulfur source so as to have a predetermined concentration.
  • the zinc source and the sulfur source are used as the base material of the electron transport layer 14 as described above.
  • the zinc ion concentration in the reaction solution 23 is preferably 0.001 to 0.5 mol / L, more preferably 0.01 to 0.1 mol / L. If the zinc ion concentration in the reaction solution 23 is smaller than 0.01 mol / L, the chemical reaction rate is very slow and the film formation time may be prolonged. On the other hand, when the zinc ion concentration in the reaction solution 23 exceeds 0.5 mol / L, the reaction time becomes extremely short and the film thickness controllability deteriorates, and the yield of the thin film with respect to the raw material deteriorates. There is a risk of increase.
  • the concentration of sulfide ion in the reaction solution 23 is preferably 0.5 to 5 times, more preferably 1 to 3 times, the zinc ion concentration. If the sulfide ion concentration in the reaction solution 23 is smaller than 0.5 times the zinc ion concentration, the Zn—O bond becomes dominant and the Zn—S bond may not be formed. On the other hand, when the sulfide ion concentration in the reaction solution 23 exceeds 5 times the zinc ion concentration, excess S atoms may be introduced into the ZnS thin film as an acceptor. As a result, the ZnS thin film, which is an n-type semiconductor, behaves like a p-type semiconductor and may not function as the electron transport layer 14.
  • the zinc ion concentration in the reaction solution 23 is preferably smaller than the sulfide ion concentration in the reaction solution 23.
  • the concentration of zinc ions in the reaction solution 23 is smaller than the concentration of sulfide ions in the reaction solution 23, the Zn—S bond becomes the main component, and ZnS / Zn (S, OH) can be brought close to 1.
  • the zinc source at least one selected from the group consisting of a weak acid salt containing zinc and a strong acid salt containing zinc is used.
  • the zinc source include zinc sulfate, zinc acetate, zinc nitrate, zinc chloride and the like.
  • the sulfur source at least one selected from the group consisting of sulfur, thiouric acid, water-soluble thiol, and water-soluble thiocarbonyl compound is used. The water-soluble thiol does not need to be completely dissolved in water.
  • the alkali source for example, salts such as ammonia and NaOH are used.
  • the alkaline aqueous solution is prepared (prepared) by dissolving the alkaline source in water so that a desired pH can be obtained. At this time, the alkaline aqueous solution is preferably prepared so that the pH thereof and the pH of the reaction solution 23 finally prepared are 9 or more.
  • the temperature of the reaction solution 23 while immersing the laminate 20 in the reaction solution 23 may be in the range of 15 to 90 ° C., but is preferably maintained in the range of 70 to 90 ° C. It is more desirable that the temperature is maintained in the range of 75 to 90 ° C.
  • the temperature of the reaction solution 23 By setting the temperature of the reaction solution 23 to 70 ° C. or higher, more preferably 75 ° C. or higher during the immersion of the laminate 20, the formation of the Zn—S bond is promoted over the Zn—O bond (in other words, priority is given). Can grow).
  • the immersion time of the laminate 20 in the reaction solution 23 is the temperature of the reaction solution 23, the concentration of the zinc source and the sulfur source in the reaction solution 23, and the concentration of the alkali source in the reaction solution 23 (in other words, the pH of the reaction solution 23). ) And the like, the thickness of the thin film to be the electron transport layer 14 is appropriately set to be a desired thickness. Therefore, the immersion time is not particularly limited, but is typically 5 minutes or more and 60 minutes or less.
  • ZnSO 4 zinc sulfate
  • ammonia as an alkali source at 7.5 mol / L
  • thiourea as a sulfur source at a concentration of 0.6 mol / L.
  • the reaction solution 23 having a pH of 11 is obtained.
  • ZnS / Zn (S, O, OH) is set to 1 as described above. You can get closer.
  • the temperature of the reaction solution 23 is adjusted to 80 ° C., and the laminate 20 is immersed in the reaction solution 23 for 15 minutes to form a Zn (S, O, OH) thin film having a film thickness of 100 nm.
  • the film thickness of the electron transport layer 14 can be controlled by the concentrations of the zinc source, the sulfur source, and the alkali source in the reaction solution 23, the temperature of the reaction solution 23, the immersion time, and the like. ..
  • the laminate 20 taken out from the reaction solution 23 is dried by, for example, washing the excess reaction solution 23 with water and then allowing it to stand at room temperature. As a result, as shown in FIG. 1, an electron transport layer 14 is formed on the light emitting layer 13.
  • the electron transport layer 14 thus formed is a mixed crystal layer containing ZnS mainly composed of a Zn—S bond as a main component and partially containing Zn (OH) 2 having a Zn—OH bond derived from an aqueous solution. It becomes. Further, not only Zn (OH) 2 but also ZnO having a Zn—O bond derived from an aqueous solution is partially contained.
  • the chemical bond state and abundance of the elements contained in the electron transport layer 14 are determined by X-rays on a sample exposed to the electron transport layer 14 by the XPS (X-ray photoelectron spectroscopy) method or the UPS (ultraviolet photoelectron spectroscopy) method. Alternatively, it can be specified by irradiating with ultraviolet rays and analyzing the composition. Since the electron transport layer 14 contains Zn (S, O, OH), the binding energies between Zn—O / Zn—S and between O—Zn / OH are different. Therefore, the presence of each bond of Zn—S, Zn—OH, and Zn—O in the electron transport layer 14 can be identified by the XPS method or the UPS method. Further, the Fermi level is different between ZnS produced by the CBD method and ZnS produced by the vacuum vapor deposition method.
  • the light emitting layer 13 is a layer that emits light due to recombination of holes transported from the anode 11 and electrons transported from the cathode 15.
  • a forward voltage is applied between the anode 11 and the cathode 15 by the power source 16 (the anode 11 has a higher potential than the cathode 15)
  • the anode 11 goes to the light emitting layer 13 via the hole transport layer 12.
  • holes are supplied, while electrons are supplied from the cathode 15 to the light emitting layer 13 via the electron transport layer 14.
  • the voltage applied by the power supply 16 may be controlled by a thin film transistor (TFT) (not shown).
  • TFT thin film transistor
  • FIG. 4 is a cross-sectional view schematically showing the state of the interface between the light emitting layer 13 and the electron transport layer 14 in the light emitting element 1 according to the embodiment.
  • FIG. 5 is a diagram showing energy bands of each layer of the functional layer in the light emitting element 1 according to the embodiment.
  • the light emitting layer 13 contains quantum dots 13QD as a light emitting material.
  • the quantum dot 13QD used for the light emitting layer 13 in this embodiment is a coating type quantum dot formed by a solution method instead of crystal growth.
  • a dispersion liquid in which quantum dots 13QD are dispersed in a solvent is applied to the upper surface of the hole transport layer 12, a coating film containing the quantum dots 13QD is formed, and then the solvent is volatilized to solidify the coating film. It can be formed by forming (curing).
  • the dispersion liquid is a colloidal solution containing a quantum dot 13QD, a ligand 13R (organic ligand) composed of an organic component, located on the surface of the quantum dot 13QD as a receptor, and a solvent.
  • the surface of the quantum dot 13QD is protected by the ligand 13R, which is a surface modifying group that modifies the surface of the quantum dot 13QD.
  • the ligand 13R is composed of an adsorbing group that adsorbs (coordinates) the surface of the quantum dot 13QD and an alkyl group that binds to the adsorbing group.
  • the adsorbing group include an amino group, a phosphine group, a carboxyl group, a hydroxyl group, a thiol group and the like.
  • an alkyl group having 2 to 50 carbon atoms can be mentioned.
  • the ligand 13R includes, for example, hexadecylamine, oleylamine, octylamine, hexadecanethiol, dodecanethiol, trioctylphosphine, trioctylphosphine oxide, myristic acid, oleic acid and the like.
  • the ligand 13R has a role of protecting the surface of the quantum dots 13QD and preventing deterioration of the quantum dots 13QD, while suppressing aggregation of the quantum dots 13QD in the dispersion liquid and improving dispersibility. Has a role as.
  • the solvent may be water, or may be an organic solvent such as methanol, ethanol, propanol, butanol, pentane, hexane, octane, acetone, toluene, xylene, benzene, chloroform, dichloromethane, and chlorobenzene. Often, it may be a combination thereof.
  • a known coating method such as a spin coating method or an inkjet method can be used for coating the dispersion liquid.
  • the light emitting layer 13 thus formed by the solution method includes a spherical quantum dot 13QD and the above-mentioned ligand 13R. Since the shape of the quantum dot 13QD is spherical rather than island-shaped (lens-shaped) as in the case of crystal growth, the polarization characteristic of light emission can be reduced. Further, since the light emitting layer 13 contains the ligand 13R, the aggregation of the quantum dots 13QD can be suppressed and the quantum dots 13QD can be satisfactorily dispersed when the coating film containing the quantum dots 13QD is formed.
  • the quantum dot 13QD as a receptacle used in the present embodiment is a core-shell type quantum dot (core-shell particle), and as shown in FIG. 4, a nano-sized crystal (semiconductor) of a semiconductor material called a semiconductor nanoparticle. It includes a core 13C as a light emitting portion, which is composed of fine particles of crystals), and a shell 13S that covers the core 13C. Therefore, the light emitting layer 13 includes a core-shell type quantum dot 13QD including a core 13C and a shell 13S covering the core 13C, and a ligand 13R coordinated to the shell 13S in the core-shell type quantum dot 13QD. ..
  • Quantum dot 13QD is, for example, Cd (cadmium), S (sulfur), Te (tellurium), Se (selenium), Zn (zinc), In (indium), N (nitrogen), P (phosphorus), As (arsenic). ), Sb (antimony), Al (aluminum), Ga (gallium), Pb (lead), Si (silicon), Ge (germanium), Mg (magnesium), at least one element selected from the group. It may contain the semiconductor material. For example, nano-sized crystals of the above semiconductor material can be used for the core 13C.
  • the shell 13S preferably contains ZnS, and more preferably consists of ZnS.
  • the red quantum dot 13QD having a CdS (cadmium sulfide) as a core and having a narrow bandgap may have a shell made of, for example, ZnSe.
  • the shell 13S has a double shell structure in which the outermost shell is made of ZnS.
  • the nanocrystal material serving as the core 13C is composed of CdSe (cadmium selenide), CdS, and ZnSe (zinc selenide) in which the conduction band level and the valence band level are present in the bandgap energy of ZnS.
  • Nano-sized crystals of at least one semiconductor material selected from the group are preferred.
  • the wavelength of light emitted by the quantum dot 13QD is proportional to the particle size of the core 13C and does not depend on the particle size of the shell 13S (the outermost particle size of the quantum dot 13QD). ..
  • the particle size of the core 13C is, for example, about 1 to 10 nm
  • the outermost particle size of the quantum dot 13QD which is the particle size of the shell 13S, is, for example, about 1 to 15 nm.
  • the number of overlapping layers of the quantum dots 13QD in the light emitting layer 13 is, for example, 1 to 5 layers.
  • the film thicknesses of the hole transport layer 12, the light emitting layer 13, and the electron transport layer 14 can be conventionally known, but are, for example, about 1 to 50 nm.
  • the film thickness of the light emitting layer 13 is preferably about several times the outermost particle size of the quantum dot QD.
  • the core 13C has a valence band level and a conduction band level.
  • the valence band level is equal to the ionization potential between the vacuum level and the upper end of the valence band indicated as the light emitting layer valence band in FIG.
  • the conduction band level is equal to the electron affinity between the vacuum level and the lower end of the conductor described as the light emitting layer conduction band in FIG.
  • a voltage is applied between the anode 11 and the cathode 15, and holes are generated from the valence band level at the lower end of the hole transport layer 12 (HTL) to the conduction band at the upper end of the electron transport layer 14 (ETL).
  • HTL hole transport layer 12
  • ETL electron transport layer 14
  • the quantum confinement effect can be obtained by making the core 13C smaller than the Bohr radius.
  • the core 13C In the core 13C, electrons located in the conduction band (conduction band of the light emitting layer) of the core 13C and holes located in the valence band (valence band of the light emitting layer) of the core are recombined, and the core 13C It emits light having a wavelength corresponding to the particle size (in other words, light having an emission wavelength corresponding to a band gap between the lower end of the conduction band of the light emitting layer and the upper end of the valence band of the light emitting layer). Since the light emission from the quantum dot 13QD has a narrow spectrum due to the quantum confinement effect, it is possible to obtain light emission with a relatively deep chromaticity.
  • the ligand 13R composed of an organic component and the shell 13S mainly composed of ZnS behave as a blocking layer that reduces the injection efficiency of electrons and holes.
  • the ligand 13R is coordinated on the surface of the quantum dots 13QD, and suppresses aggregation of the quantum dots 13QD and quantum in the dispersion liquid for forming the light emitting layer 13 in which the quantum dots 13QD are dispersed. It is used to prevent deterioration of the dot 13QD, but acts as an insulating component. Therefore, it is desirable that the ligand 13R does not exist at the interface between the light emitting layer 13 and the electron transport layer 14.
  • step S5 the surface of the light emitting layer 13 on which the electron transport layer 14 is laminated is brought into contact with the alkaline aqueous solution. Therefore, the ligand 13R on the surface of the light emitting layer 13 on which the electron transport layer 14 is laminated is etched by the alkaline aqueous solution.
  • the average coordination number of the ligand 13R coordinated to the shell 13S of the quantum dot 13QD included in the interface between the light emitting layer 13 and the electron transport layer 14. Can be less than the average coordination number of the ligand 13R coordinated to the shell 13S of the quantum dot 13QD contained in the portion of the light emitting layer 13 other than the boundary (in other words, the bulk of the light emitting layer 13). ..
  • the ligand 13R at the interface between the light emitting layer 13 and the electron transport layer 14 can be removed.
  • the unnecessary shell 13S at the interface between the light emitting layer 13 and the electron transport layer 14 that comes into contact with the reaction solution 23 is also removed together with the ligand 13R. ..
  • the electron transport layer 14 of a dense thin film can be formed on the spot by a chemical reaction in the aqueous solution, and the interface between the electron transport layer 14 and the light emitting layer 13 can be contacted.
  • the resistance can be reduced, and the ligand 13R and the shell 13S at the interface can be removed to improve the quality of the interface and reduce the resistance component. Therefore, the efficiency of injecting electrons from the electron transport layer 14 into the light emitting layer 13 can be improved.
  • the electron transport layer 14 uses the inorganic layer, defects are unlikely to occur between the electron transport layer 14 and the light emitting layer 13. Moreover, by etching the surface of the quantum dot 13QD with the alkaline aqueous solution as described above, the defects on the surface of the quantum dot 13QD are further reduced as compared with the conventional light emitting device using the inorganic layer for the electron transport layer 14. Can be made to. Therefore, it is possible to obtain a light emitting element 1 having a coating property of the electron transport layer 14 that is superior to that of the conventional light emitting device.
  • the electron transport layer 14 is not formed by laminating nanoparticles of an electron transport material as in the conventional case, but is formed by a zinc source and a sulfur source in an aqueous solution by the CBD method. It is directly formed as a thin film (mixed crystal layer) by a chemical reaction.
  • the electron transport material permeates into the gap between the adjacent quantum dots 13QD at the interface between the light emitting layer 13 and the electron transport layer 14, and the electron transport material becomes quantum. Dot 13QD is coated. Therefore, the contact area between the light emitting layer 13 and the electron transport layer 14 increases.
  • the film property of the electron transport layer 14 can be improved, and the contact resistance between the light emitting layer 13 and the electron transport layer 14 can be reduced. Further, since the vacuum device is not used for forming the electron transport layer 14, the light emitting element 1 can be manufactured at low cost.
  • the energy level can be adjusted by changing the ratio of Zn (S, O, OH) depending on the composition of the reaction solution 23 or the film forming conditions such as the reaction temperature. Therefore, the band gap of Zn (S, O, OH) can be changed by, for example, changing the composition of the reaction solution 23, but the concentration of ZnO contained in Zn (S, O, OH) is large. Therefore, the band gap and the valence band level are lowered, resulting in a decrease in electron injection efficiency. Therefore, a preferable ratio of ZnS, ZnO, and Zn (OH) 2 contained in the mixed crystal (in other words, the electron transport layer 14 which is the mixed crystal layer) constituting the electron transport layer 14 is appropriately set.
  • the mixed crystal contains ZnS as a main component as described above, and the concentration of ZnS contained in the mixed crystal is as described above. It is desirable that the concentration is higher than the concentration of Zn (OH) 2 contained in the mixed crystal.
  • the mixed crystal is Zn (S, O, OH)
  • it is desirable that the concentration of ZnS contained in the mixed crystal is higher than the concentration of ZnO contained in the mixed crystal.
  • the mixed crystal is Zn (S, O, OH)
  • it is desirable that the concentration of Zn (OH) 2 contained in the mixed crystal is higher than the concentration of ZnO contained in the mixed crystal. ..
  • the concentration of ZnS contained in the mixed crystal (Zn (S, OH) or Zn (S, O, OH)) is 50 wt% or more.
  • the value is preferably 50 wt% of ZnS contained in the mixed crystal.
  • the concentration of Zn (OH) 2 is preferably 0.1 wt% or more from the viewpoint of the concentration above the detection limit. Therefore, the concentration of Zn (OH) 2 contained in the mixed crystal (Zn (S, OH) or Zn (S, O, OH)) is based on the concentration of ZnS in the mixed crystal (100 wt%). It is desirable that the value is 0.1 wt% or more and 50 wt% or less with respect to the above reference value.
  • the mixed crystal is Zn (S, O, OH)
  • the electron transport layer 14 is formed by the CBD method, it is possible to form a film at a lower temperature than the conventional film formation method such as a vapor deposition method or a sputtering method, and the hole transport layer 12 or the like which is the lower layer thereof , It becomes possible to use organic materials that are sensitive to heat.
  • the vacuum method such as the vapor deposition method and the sputtering method, the hydroxyl group ( ⁇ OH group) is eliminated as water by heat. Therefore, no hydroxyl group is detected in the electron transport layer formed by a vacuum method such as a vapor deposition method or a sputtering method.

Abstract

L'invention concerne un procédé de production d'un élément électroluminescent comprenant une étape de formation d'électrode positive, une étape de formation de couche électroluminescente, une étape de formation de couche de transport d'électrons et une étape de formation d'électrode négative. L'étape de formation de couche de transport d'électrons comprend une étape d'immersion pour immerger la surface de couche électroluminescente sur laquelle la couche de transport d'électrons sera formée dans une solution alcaline aqueuse contenant une source de zinc et une source de soufre. Dans l'étape de formation de couche de transport d'électrons, une couche de cristaux mixtes qui contient ZnS et Zn(OH) 2 ayant des liaisons Zn-S et des liaisons Zn-OH étant formée en tant que couche de transport d'électrons.
PCT/JP2019/025011 2019-06-24 2019-06-24 Procédé de production d'élément électroluminescent, et élément électroluminescent WO2020261346A1 (fr)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2022143554A1 (fr) * 2020-12-31 2022-07-07 Tcl科技集团股份有限公司 Dispositif électroluminescent et son procédé de préparation

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012160714A1 (fr) * 2011-05-20 2012-11-29 国立大学法人山形大学 Dispositif électronique organique et son procédé de fabrication
KR20150120026A (ko) * 2014-04-16 2015-10-27 희성전자 주식회사 발광 소자 및 발광 소자용 전자수송층 제조 방법

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012160714A1 (fr) * 2011-05-20 2012-11-29 国立大学法人山形大学 Dispositif électronique organique et son procédé de fabrication
KR20150120026A (ko) * 2014-04-16 2015-10-27 희성전자 주식회사 발광 소자 및 발광 소자용 전자수송층 제조 방법

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2022143554A1 (fr) * 2020-12-31 2022-07-07 Tcl科技集团股份有限公司 Dispositif électroluminescent et son procédé de préparation

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