Method for manufacturing quantum dot display device

Abstract

According to a method for manufacturing a quantum dot display device, according to exemplary embodiments of the present invention, a quantum dot light-emitting layer is formed on a first substrate. A double layer is formed by laminating an electron transport layer on the upper surface of the quantum dot light-emitting layer. The double layer is picked up using a stamp having a surface portion with a higher Young's modulus than a center portion. The double layer picked up using the stamp is transferred onto a second substrate. After the step of transferring onto the second substrate, the surface roughness of the lower surface of the quantum dot light-emitting layer is 0.1 nm to 10 nm.

Description

Method for manufacturing quantum dot display devices

[0001] The present invention relates to a method for manufacturing a quantum dot display device.

[0002]

[0003] Quantum dots are being applied to the display field by utilizing the photoluminescence and electroluminescence phenomena of various types of quantum dot materials, and are particularly being applied to products that aim for color conversion and brightness enhancement using photoluminescence.

[0004] Quantum dots are being actively researched in a wide range of fields, including light-absorbing layers in solar cells, biosensors, optical sensors, and lighting, and their achievements in the display field are particularly notable.

[0005] In the past, when forming a quantum dot pattern by picking up a thin film of quantum dot nanoparticles coated on a donor substrate with a relief stamp or a full-face stamp and transferring it to the final substrate, polydimethylsiloxane (PDMS), a silicone rubber, was used.

[0006] Since quantum dots for general light-emitting devices are surrounded by long carbon chain organic ligands, a positive stamp or a full-surface stamp can pick up a thin film of quantum dots for light-emitting devices from a donor substrate and transfer it to a final substrate.

[0007] However, it is difficult to implement high-efficiency light-emitting devices for wearable electronic devices using these technologies.

[0008]

[0009] One object of the present invention is to provide a method for manufacturing a quantum dot display device having improved external quantum efficiency (EQE) and ultra-high resolution based on a double layer including quantum dots and a charge transfer layer formed by a transfer process.

[0010]

[0011] According to a method for manufacturing a quantum dot display device according to exemplary embodiments of the present invention, a quantum dot light-emitting layer is formed on a first substrate. An electron transport layer is laminated on the upper surface of the quantum dot light-emitting layer to form a double layer. The double layer is picked up using a stamp having a surface portion having a higher Young's modulus than the center portion. The double layer picked up by the stamp is transferred onto a second substrate. After the step of transferring onto the second substrate, the surface roughness (R) of the lower surface of the quantum dot light-emitting layer is measured. q ) is 0.1 nm to 10 nm.

[0012] In exemplary embodiments, the surface roughness (R) of the upper surface of the electron transport layer q ) can be from 0.1 nm to 15 nm.

[0013] In a method for manufacturing a quantum dot display device according to some embodiments, a step of forming a double layer pattern by bringing the picked-up double layer into contact with a negative trench may be further included after the picking-up step.

[0014] In a method for manufacturing a quantum dot display device according to some embodiments, the stamp may be subjected to oxygen plasma treatment or UV-ozone treatment.

[0015] In a method for manufacturing a quantum dot display device according to some embodiments, the stamp may be subjected to UV-ozone treatment for 3 to 300 seconds.

[0016] In a method for manufacturing a quantum dot display device according to some embodiments, the Young's modulus of the surface of the stamp may be 2.0 MPa to 3.3 MPa.

[0017] In a method for manufacturing a quantum dot display device according to some embodiments, the central Young's modulus of the stamp may be 0.5 MPa to 2.0 MPa.

[0018] In a method for manufacturing a quantum dot display device according to some embodiments, the stamp may include an elastomer of the siloxane series, the acrylic series, the epoxy series, the triblock copolymer series, or a composite thereof.

[0019] In a method for manufacturing a quantum dot display device according to some embodiments, the stamp may include PDMS (polydimethylsiloxane).

[0020] In a method for manufacturing a quantum dot display device according to some embodiments, the electron transport layer may include ZnO, ZnMgO, or an organic semiconductor.

[0021] A display device according to exemplary embodiments can be manufactured using the method for manufacturing a quantum dot display device of claim 1.

[0022]

[0023] According to a method for manufacturing a quantum dot display device according to exemplary embodiments, external quantum efficiency (EQE) can be improved by controlling the surface roughness of a quantum dot light-emitting layer.

[0024] In exemplary embodiments, charge injection can also be smoothly achieved by controlling the surface roughness of the lower surface of the electron transport layer.

[0025]

[0026] FIG. 1 is a schematic flowchart of a method for manufacturing a quantum dot display device according to embodiments of the present invention.

[0027] FIG. 2 is a schematic diagram of a method for manufacturing a quantum dot display device according to one embodiment of the present invention.

[0028] FIG. 3 is a schematic cross-sectional view showing a double layer manufactured according to exemplary embodiments.

[0029] FIG. 4 is a schematic cross-sectional view showing the appearance of a double layer manufactured according to exemplary embodiments immediately before pickup.

[0030] FIG. 5 is a schematic cross-sectional view showing the appearance of a double layer manufactured according to exemplary embodiments immediately before transfer.

[0031] FIG. 6 and FIG. 7 are cross-sectional images of the interface between a quantum dot light-emitting layer (110) and a hole transport layer (HTL) in a spin coating process and a method for manufacturing a quantum dot display device, respectively.

[0032] FIG. 8 is a schematic cross-sectional view showing the arrangement of a negative trench (200) on the lower surface of a quantum dot light-emitting layer (110) and an electron transport layer (120) picked up by a stamp (130) before transfer of a double layer manufactured according to exemplary embodiments.

[0033] Figure 9 shows the work of adhesion (W) between each layer during the double-layer transfer process. A / B ) is a graph comparing the sizes.

[0034] Figure 10 is a schematic cross-sectional view of a display element.

[0035] Figures 11 to 13 are atomic force microscopy (AFM) analysis images of the surface of the stamps in Examples 1 to 2 and Comparative Example 1, respectively.

[0036] Figures 14 to 16 are photographs after pickup of a double-layer film manufactured by transferring with the stamps of Examples 1 to 2 and Comparative Example 1, respectively.

[0037] Figures 17 and 18 are scanning electron microscope (SEM) analysis images of the upper surface of the electron transport layer (120) in the double layer of Example 3 and Comparative Example 2, respectively.

[0038] Figures 19 and 20 are atomic force microscopy (AFM) analysis images of the lower surface of the quantum dot light-emitting layer (110) among the double layers of Example 3 and Comparative Example 2, respectively.

[0039] Figure 21 is a graph showing the results of measuring the impedance of a double layer manufactured by a spin coating process and a double layer transfer printing method.

[0040] Figure 22 is a graph showing changes in current density and luminance according to changes in voltage for each QLED manufactured by a spin coating process and a double-layer transfer printing method.

[0041] Figure 23 is a graph showing the change in external quantum efficiency (EQE) according to the change in luminance for each QLED manufactured by the spin coating process and the double-layer transfer printing method of Manufacturing Example 5.

[0042]

[0043] Embodiments of the present invention provide a method for manufacturing a quantum dot display device, comprising the step of transferring a bilayer including quantum dots and an electron transport layer.

[0044] The terms "top surface," "bottom surface," "upper part," and "lower part" used in this application do not designate absolute locations, but are used in a relative sense. For example, the terms are used relatively to designate different areas with respect to a specific reference plane.

[0045] The term "surface roughness (R)" used in this application q )" can mean root mean square roughness.

[0046] <Method for manufacturing quantum dot display devices>

[0047] A method for manufacturing a quantum dot display device according to one embodiment of the present invention comprises the steps of: forming a quantum dot light-emitting layer on a first substrate; forming a bilayer by laminating an electron transport layer on the quantum dot light-emitting layer; picking up the bilayer using a stamp having a surface portion having a higher Young's modulus than a center portion; and transferring the bilayer picked up by the stamp onto a second substrate; and after the step of transferring onto the second substrate, the surface roughness (R) of the lower surface of the quantum dot light-emitting layer is determined. q ) is 0.1 nm to 10 nm.

[0048] Hereinafter, embodiments of the present invention will be described in more detail.

[0049] FIG. 1 is a schematic flowchart of a method for manufacturing a quantum dot display device according to embodiments of the present invention.

[0050] FIG. 2 is a schematic diagram of a method for manufacturing a quantum dot display device according to one embodiment of the present invention.

[0051] FIG. 3 is a schematic cross-sectional view showing a double layer manufactured according to exemplary embodiments.

[0052] Referring to FIG. 3, the double layer includes a quantum dot light-emitting layer (110) and an electron transport layer (120).

[0053] Referring to FIGS. 1 to 3, a quantum dot light-emitting layer (110) is formed on a first substrate (100).

[0054] The first substrate (100) is made of glass, quartz, Al2O3, SiC, polydimethlysiloxane (PDMS), ecoflex (polybutylene adipate terephthalate, PBAT), polyurethane (PU), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polysilane, polysiloxane, polysilazane, polycarbosilane, cyclic olefin copolymer (COC), cyclic olefin polymer (COP), polyethylene (PE), polypropylene (PP), polyimide (PI), polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), polycarbonate (PC), polyvinylidene fluoride (PVDF), It may include perfluoroalkyl polymer (PFA) and styrene acrylonitrile copolymer (SAN).

[0055] The quantum dot light-emitting layer (110) may include a colloidal nanocrystal material including quantum dot particles.

[0056] Quantum dot particles can refer to nano-sized semiconductor materials. For example, atoms can form molecules, and molecules can form clusters, which are collections of small molecules, forming nanoparticles. When the aforementioned nanoparticles possess semiconductor properties, they are called quantum dot particles.

[0057] The above quantum dot particles can receive energy from the outside and reach an excited state, and can emit energy (e.g., light) according to the energy band gap of the quantum dot itself. In one embodiment, the quantum dot particles can emit light by photoluminescence when irradiated with light or emit light by electroluminescence when applied with current. Due to the above-described luminescent properties, the quantum dot particles can be applied as luminescent materials in various fields such as display devices, energy devices, or bioluminescent devices.

[0058] For example, quantum dot particles can be used in displays based on LCD (Liquid Crystal Diodes) using photoluminescent elements or displays based on QLED (Quantum dot Light Emitting Diodes) using electroluminescent elements.

[0059] The quantum dot light-emitting layer (110) according to exemplary embodiments can emit light on its own, for example, by irradiating light, by including the above-described quantum dot particles.

[0060] The energy bandgap emitted from quantum dot particles can be selected by controlling the nanocrystal size and / or composition of the quantum dot particles. For example, as the size of the quantum dot particle decreases, the energy bandgap can be widened and the emission wavelength can decrease. Therefore, by controlling the particle size and / or composition of the quantum dot particle, it is possible to create a quantum dot particle that emits light of a desired wavelength.

[0061] For example, the quantum dot particles may include blue quantum dots that emit blue light, green quantum dots that emit green light, or red quantum dots that emit red light. For example, the green quantum dots or red quantum dots may be irradiated with blue light and photoconverted into green light or red light.

[0062] According to exemplary embodiments, the quantum dot particle may include a material that emits light when stimulated by light. For example, the material may include a group II-VI compound, a group III-V compound, a group IV-VI compound, a group I-III-VI2 compound, a group IV element or a compound containing the same, and mixtures thereof. These may be used alone or in combination of two or more.

[0063] The above II-VI group compound is a binary compound selected from CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS, and mixtures thereof; a ternary compound selected from CdSeS, CdSeTe, CdSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, HgZnS, HgZnSe, HgZnTe, and mixtures thereof; and may be selected from the group consisting of four-element compounds selected from CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, and mixtures thereof.

[0064] The above III-V group compound may be selected from the group consisting of a binary compound selected from GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, and mixtures thereof; a ternary compound selected from GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, and mixtures thereof; and a quaternary compound selected from GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, and mixtures thereof.

[0065] The above IV-VI group compound may be selected from the group consisting of a binary compound selected from SnS, SnSe, SnTe, PbS, PbSe, PbTe, and mixtures thereof; a ternary compound selected from SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, and mixtures thereof; and a quaternary compound selected from SnPbSSe, SnPbSeTe, SnPbSTe, and mixtures thereof.

[0066] The above I-III-VI2 group compound can be selected from CuInSe2.

[0067] The above group IV element or compound containing the same may be selected from the group consisting of an element compound selected from Si, Ge and mixtures thereof; and a binary element compound selected from SiC, SiGe and mixtures thereof.

[0068] According to exemplary embodiments, the quantum dot particle may have a homogeneous single structure, a core-shell structure, a gradient structure, or a mixed structure thereof.

[0069] In some embodiments, the quantum dot particle may have a core-shell structure comprising a core and a shell covering the core. The core may be a portion where light emission occurs. The shell may prevent oxidation of the core and reduce trap energy levels on the surface. Therefore, the stability and efficiency of the quantum dot particle may be enhanced by the shell.

[0070] The core and the shell may be composed of different compounds. For example, the core may include one or more materials selected from the group consisting of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, InNP, InZnP, InNAs, InNSb, InPAs, InPSb GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb and mixtures thereof. The shell may include one or more materials selected from the group consisting of ZnSe, ZnS, ZnTe, CdTe, PbS, TiO, SrSe, HgSe, ZnSe, ZnS, ZnSeS and mixtures thereof. Preferably, the core may include In and P, and the shell may include Zn, Se and / or S.

[0071] In some embodiments, the shell may be a multi-layered shell structure comprising one or more shell layers. For example, the quantum dot particle may include a core, a first shell layer covering the core, and a second shell layer covering the first shell layer.

[0072] In some embodiments, adjacent core and shell layers in the multilayer shell structure may have different compositions. For example, the core may include InP and / or InZnP, the first shell layer may include ZnSe and / or ZnSeS, and the second shell layer may include ZnS.

[0073] According to exemplary embodiments, the quantum dot particle may include a concentration gradient region formed between the center and the surface of the particle. For example, at least one specific element of the quantum dot particle may have a concentration gradient that varies from the center of the particle to the surface of the particle.

[0074] In some embodiments, the concentration of Se may continuously decrease from the center of the particle toward the surface of the particle, and the concentration of S may continuously increase. For example, the shell may have an intersection where the concentrations of Se and S intersect. The intersection may have equal concentrations of Se and S.

[0075] When Se is present on the surface of a quantum dot particle, prolonged exposure to external light and oxygen can cause the Se to be oxidized, thereby causing the structure of the quantum dot particle to collapse. According to exemplary embodiments, the optical properties of the quantum dot particle can be improved, and the durability and structural stability can be enhanced as the concentration of Se decreases and the concentration of S increases toward the surface of the particle.

[0076] The quantum dot light-emitting layer (110) can be manufactured by spin-coating passivated quantum dot particles dispersed in a dispersion medium onto a first substrate (100).

[0077] Next, an electron transport layer (120) is laminated on the upper surface of the quantum dot light-emitting layer (110) to form a double layer.

[0078] The electron transport layer (120) transports electrons to the quantum dot light-emitting layer (110) to cause the quantum dot light-emitting layer (110) to emit light.

[0079] The electron transport layer (120) may include a metal-containing material. The metal-containing material may include an alkali metal complex, an alkaline earth metal complex, or a combination thereof. The metal ion of the alkali metal complex may be a Li ion, a Na ion, a K ion, an Rb ion, or a Cs ion, and the metal ion of the alkaline earth metal complex may be a Be ion, a Mg ion, a Ca ion, a Sr ion, or a Ba ion. The ligands coordinated to the metal ions of the alkali metal complex and alkaline earth metal complex may independently include hydroxyquinoline, hydroxyisoquinoline, hydroxybenzoquinoline, hydroxyacridine, hydroxyphenanthridine, hydroxyphenyloxazole, hydroxyphenylthiazole, hydroxyphenyloxadiazole, hydroxyphenylthiadiazole, hydroxyphenylpyridine, hydroxyphenylbenzoimidazole, hydroxyphenylbenzothiazole, bipyridine, phenanthroline, cyclopentadiene, and the like.

[0080] In some embodiments, the electron transport layer (120) may include metal oxides such as ZnO, TiO2, ZrO2, HfO2, ZnMgO, or inorganic materials including Si3N4 or n-type semiconductor organic molecules and polymers.

[0081] In one embodiment, the electron transport layer (120) may include ZnO, ZnMgO, an organic semiconductor, or the like.

[0082] In some embodiments, the electron transport layer (120) may include a nanoparticle film.

[0083] The electron transport layer (120) can be manufactured by spin-coating metal-containing nanoparticles dispersed in a dispersion medium onto the quantum dot light-emitting layer (110).

[0084] Next, the double layer is picked up using a stamp having a surface portion with a higher Young's Modulus than the center portion.

[0085] FIG. 4 is a schematic cross-sectional view showing the appearance of a double layer manufactured according to exemplary embodiments immediately before pickup.

[0086] Referring to FIG. 4, the double layer on the first substrate (100) can be picked up by a stamp (130).

[0087] In embodiments of the present invention, not only can the display device production process be efficiently performed by simultaneously transferring the double layer, but the function of the transferred double layer can also be excellently maintained.

[0088] When picking up the double layer through the above stamp (130), high pressure (>2 kg·cm-) is applied during the picking process. 2 ) may cause cracks due to deformation of the stamp (130). The reason for the cracks is that, during the bilayer pick-up process, the electron transport layer (120) without organic ligands is more fragile than the long-chain ligand-passivated quantum dot light-emitting layer (110) capable of intermolecular interaction.

[0089] To prevent cracks from occurring, the distortion of the stamp (130) must be minimized. However, as the Young's modulus of the stamp increases, the interfacial adhesion between the stamp (130) and the double layer decreases, so if the Young's modulus of the stamp is too high, problems may arise during the double layer pickup process. To address this issue, the Young's modulus of the surface portion of the stamp (130) can be selectively increased compared to the center portion.

[0090] In exemplary embodiments, the stamp (130) may have its surface treated with oxygen plasma, UV-ozone, or the like to increase the modulus of the surface.

[0091] For example, the stamp (130) may be subjected to UV-ozone treatment for 3 to 300 seconds, or 3 to 100 seconds, or 3 to 30 seconds, or 5 to 25 seconds, or 10 to 20 seconds, or 12 to 18 seconds. In the above range, the surface portion of the stamp (130) can be selectively hardened, thereby preventing cracks or the like due to excessive deformation of the stamp during the double-layer pick-up step.

[0092] According to exemplary embodiments, the stamp (130) may optionally have a surface portion that is hardened, and the Young's modulus of the surface portion may be 2.0 MPa to 3.3 MPa, or 2.0 MPa to 3.1 MPa, or 2.0 MPa to 3.0 MPa, or 2.1 MPa to 2.9 MPa, or 2.1 MPa to 2.8 MPa, or 2.1 MPa to 2.5 MPa. In the case of a stamp having a surface portion Young's modulus in the above range, cracks in the double layer due to excessive deformation of the stamp in the double layer pickup step can be prevented, thereby enabling more efficient double layer transfer printing.

[0093] According to exemplary embodiments, the central Young's Modulus of the stamp (130) may be 0.5 MPa to 2.0 MPa, or 0.7 MPa to 1.8 MPa, or 0.8 MPa to 1.7 MPa, or 0.9 MPa to 1.6 MPa, or 1.0 MPa to 1.5 MPa.

[0094] In exemplary embodiments, when the surface of a stamp is subjected to oxygen plasma treatment or UV-ozone treatment, the Young's modulus at the center of the stamp may be identical to the overall Young's modulus of the stamp before treatment. In this case, the Young's modulus at the center of the stamp may be adjusted, for example, by changing the content of the curing agent, the curing time for photocuring, or the amount of light irradiation.

[0095] The stamp (130) may include an elastomer of the siloxane series, acrylic series, epoxy series, triblock copolymer series, or a composite thereof. In exemplary embodiments, the stamp (130) may include polyurethaneacrylate, polydimethylsiloxane (PDMS). In one embodiment, the stamp (130) may include polydimethylsiloxane (PDMS). Accordingly, the pickup of the double layer by the stamp (130) may be facilitated.

[0096] According to exemplary embodiments, the stamp (130) may include a curing agent. The curing agent may be, for example, 5 wt% to 25 wt%, or 10 wt% to 20 wt% of the total weight of the stamp.

[0097] According to exemplary embodiments, the stamp (130) can form a micropattern on a nano to micron scale to reduce the contact area between the double layer and the stamp (130) so that it can be easily transferred onto another substrate.

[0098] According to exemplary embodiments, the stamp (130) may be an elastic stamp patterned to correspond to the pixel size to be formed. Using the patterned elastic stamp, a double layer including a patterned quantum dot layer of multiple color elements can be formed by repeating the process of double layer pickup and transfer printing.

[0099] Next, the double layer picked up by the above stamp (130) is transferred onto the second substrate (300).

[0100] FIG. 5 is a schematic cross-sectional view showing the appearance of a double layer manufactured according to exemplary embodiments immediately before transfer.

[0101] Referring to FIG. 5, the double layer can be transferred onto a second substrate (300).

[0102] According to exemplary embodiments, the second substrate (300) may include a metal, a metal oxide, a semiconductor, an insulator, and the like. According to exemplary embodiments, the second substrate (300) may include gold, palladium, platinum, glass, ceramic, germanium, silicon, plastic, and the like.

[0103] According to exemplary embodiments, when the double layer is used in an electroluminescent device, the second substrate (300) may be a transparent, flat-surfaced glass substrate, a transparent plastic substrate, transparent silicon, or the like. In this case, the second substrate (300) may be a hole transport layer.

[0104] According to exemplary embodiments, the second substrate (300) can be used after removal of contaminants through ultrasonic cleaning using a solvent such as isopropyl alcohol, acetone, or methanol and UV-Ozone cleaning.

[0105] When the double layer is picked up and transferred onto the second substrate (300) using the stamp (130), the pressure applied during the picking process causes particle packing in the horizontal and vertical directions, thereby reducing cracks and voids within the film. In addition, the packing significantly reduces internal resistance compared to the conventional spin process, and reduces electron movement, thereby reducing charge leakage. Accordingly, a device having high external quantum efficiency can be manufactured.

[0106] According to exemplary embodiments, in the bilayer transferred on the second substrate, the surface roughness (R) of the lower surface of the quantum dot light-emitting layer (110) q ) is 0.1 nm to 10 nm.

[0107] According to exemplary embodiments, in the bilayer transferred onto the second substrate, the surface roughness (R) of the upper surface of the electron transport layer q ) can be from 0.1 nm to 15 nm.

[0108] For example, the surface roughness of the lower surface of the quantum dot light-emitting layer (110) may be 0.3 nm to 5 nm, or 0.5 nm to 1 nm.

[0109] For example, the surface roughness (R) of the upper surface of the electron transport layer q ) may be 0.3 nm to 10 nm, or 0.5 nm to 5 nm.

[0110] The surface roughness within the above range can be achieved by the pressure applied to the double layer during the process of transferring onto the second substrate. Accordingly, the surface roughness of the quantum dot light-emitting layer (110) can be alleviated and the interface resistance can be reduced, thereby reducing the electron injection resistance into the quantum dot light-emitting layer (110) and reducing the leakage charge. Accordingly, a display device having high external quantum efficiency can be manufactured.

[0111] If the surface roughness of the lower surface of the quantum dot light-emitting layer (110) exceeds 10 nm, the leakage charge may not be sufficiently reduced, so the external quantum efficiency may be low.

[0112] Surface roughness (R) of the upper surface of the electron transport layer q ) exceeds 15 nm, the interface area may be small and charge injection may not be smooth.

[0113] In order for the surface roughness of the lower surface of the quantum dot light-emitting layer (110) to be less than 0.1 nm, the force applied to the bilayer must increase in the step of picking up and transferring the bilayer, so cracks may occur on the surface of the picked up bilayer.

[0114] In order for the surface roughness of the upper surface of the electron transport layer to be less than 0.1 nm, the force applied to the bilayer must increase during the step of picking up and transferring the bilayer, so cracks may occur on the surface of the picked up bilayer.

[0115] FIG. 6 and FIG. 7 are cross-sectional images of the interface between a quantum dot light-emitting layer (110) and a hole transport layer (HTL) in a spin coating process and a method for manufacturing a quantum dot display device, respectively.

[0116] Referring to FIGS. 6 and 7, it can be seen that the interface between the quantum dot light-emitting layer (110) and the hole transport layer (HTL) is more distinct in the case of the method for manufacturing a quantum dot display device.

[0117] Among the methods for manufacturing a quantum dot display device according to one embodiment of the present invention, the double-layer transfer method may be a dry transfer method, and accordingly, since the hole transport layer (HTL) described below is not dissolved by a solvent, the interface is well formed, so that leakage charge can be reduced and external quantum efficiency can be increased.

[0118] According to exemplary embodiments, the stamp (130) can be removed by applying heat so that the bilayer picked up on the stamp (130) can be easily transferred onto the second substrate (300). To facilitate the bilayer detachment from the stamp (130), the piezoelectric effect can be utilized or micro-vibrations such as sound waves or ultrasonic waves can be applied to the stamp (130).

[0119] FIG. 8 is a schematic cross-sectional view showing the arrangement of a negative trench (200) on the lower surface of a quantum dot light-emitting layer (110) and an electron transport layer (120) picked up by a stamp (130) before transfer of a double layer manufactured according to exemplary embodiments.

[0120] Referring to FIG. 8, a step of forming a double layer pattern by bringing the picked-up double layer into contact with the negative trench (200) after the picking-up step may be further included. Accordingly, a portion not in contact with the negative trench (200) can be transferred onto the second substrate (300).

[0121] Figure 9 shows the work of adhesion (W) between each layer during the double layer transfer process. A / B ) is a graph comparing the sizes.

[0122] In exemplary embodiments, the adhesion between the first substrate (100) and the quantum dot light-emitting layer (110), the adhesion between the electron transport layer (120) and the stamp (130), the adhesion between the engraved trench (200) and the quantum dot light-emitting layer (110), and the adhesion between the second substrate (300) and the quantum dot light-emitting layer (110) may have values ​​within a range appropriate for performing the double-layer transfer printing method of the present invention.

[0123] In exemplary embodiments, the adhesion between the first substrate (100) and the quantum dot light-emitting layer (110) is less than the adhesion between the electron transport layer (120) and the stamp (130).

[0124] In exemplary embodiments, the bonding time between the electron transport layer (120) and the stamp (130) is less than the bonding time between the engraved trench (200) and the quantum dot light-emitting layer (110).

[0125] In exemplary embodiments, the adhesion between the electron transport layer (120) and the stamp (130) is less than the adhesion between the second substrate (300) and the quantum dot light-emitting layer (110).

[0126] <Display device>

[0127] A display device manufactured by a method for manufacturing a quantum dot display device according to embodiments of the present invention and a display device including the device are provided.

[0128] Figure 10 is a schematic cross-sectional view of a display element.

[0129] Referring to FIG. 10, the display element may include elements stacked in the following order: a first electrode (310), a hole transport region (320), a light-emitting layer (330), an electron transport region (340), and a second electrode (350).

[0130] The first electrode (310) has conductivity. The first electrode (310) may be a cathode or an anode.

[0131] A hole transport region (320) is provided on the first electrode (310). The hole transport region (320) may be the second substrate (300) described above. The hole transport region (320) may have a single layer or multiple layers made of a single material or multiple different materials. For example, the hole transport region (320) may include a hole transport layer (HTL).

[0132] The light-emitting layer (330) is provided on the hole transport region (320). The light-emitting layer (330) may include the quantum dot light-emitting layer (110) described above.

[0133] An electron transport region (340) is provided on the light-emitting layer (330). The electron transport region (340) may include the electron transport layer (120) described above.

[0134] A second electrode (350) is provided on the electron transport region (340). The second electrode (350) has conductivity. The second electrode (350) may be a cathode or an anode.

[0135] The display element according to an embodiment of the present invention can be manufactured into a display device by adding a configuration known in the art.

[0136] Hereinafter, embodiments of the present invention will be further described with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present invention and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various modifications and variations of the examples are possible within the scope and technical spirit of the present invention, and it is also natural that such modifications and variations fall within the scope of the appended claims.

[0137] Manufacturing Example 1: Formation of colloidal quantum dots

[0138] Manufacturing Example 1-1: Green light-emitting quantum dots

[0139] A solution containing cadmium oleate (Cd(oleate)2) and zinc oleate (Zn(oleate)2) complexes was prepared by heating a mixture of 0.14 mmol of cadmium acetate (Cd(OAc)2, 99.995%), 3.41 mmol of zinc oxide (ZnO, 99.99%), 7.0 mL of oleic acid (OA, 90%), and 15.0 mL of 1-octadecene (ODE, 90%) at 120°C in a vacuum for 1.5 h.

[0140] A mixture of 2.0 mL of trioctylphosphine-Se (TOP-Se, 1 M) and trioctylphosphine-S (TOP-S, 1 M) was rapidly injected into the above solution heat-treated with argon (Ar) at 290°C to form a quantum dot core.

[0141] After 10 minutes, 2.4 mL of 1-octadecene solution (0.4 M) containing sulfur (S) was slowly injected into the quantum dot core, and the shell was grown by reacting for 12 minutes, and then 6.0 mL of zinc oleate solution (0.5 M) and 0.1 mL of trioctylphosphine-S (TOP-S) solution (2 M) were slowly injected, and the shell was further grown by reacting for 20 minutes, forming a quantum dot core / shell.

[0142] Manufacturing Example 1-2: Red-emitting quantum dots

[0143] A solution containing cadmium myristate was prepared by heating a mixture of 1.2 mmol of myristic acid (MA, >99%), 0.4 mmol of cadmium oxide (CdO, >99.99%), and 6.0 mL of 1-octadecene (ODE) at 120 °C in vacuum for 1.5 h.

[0144] 0.1 mL of trioctylphosphine-Se (TOP-Se, 2 M) was rapidly injected into the above solution heat-treated with argon (Ar) at 270°C to form a quantum dot core.

[0145] After 90 seconds, a mixture of 1.6 mL of zinc oleate (0.5 M) and 0.1 mL of 1-octanethiol (OT, 98.5%) was slowly injected and reacted for 30 minutes to grow the shell of the quantum dot core, and then 2.4 mL of cadmium oleate solution (0.5 M) and 0.6 mL of trioctylphosphine-S (TOP-S) solution (2 M) were slowly injected and reacted for an additional 15 minutes to form a quantum dot core / shell with additional shell growth.

[0146] Manufacturing Example 1-3: Blue-emitting quantum dots

[0147] A solution containing cadmium oleate (Cd(oleate)2) and zinc oleate (Zn(oleate)2) complexes was prepared by heating a mixture of 1.0 mmol of cadmium oxide (CdO, >99.99%), 9.0 mmol of zinc acetate (Zn(OAc)2, 99.99%), 8.0 mL of oleic acid (OA, 90%), and 15.0 mL of 1-octadecene (ODE, 90%) at 120°C in a vacuum for 1.5 h.

[0148] A quantum dot core was formed by rapidly injecting 3.0 mL of a 1-octadecene solution containing 1.8 mmol of sulfur (S) and 0.2 mmol of selenium (Se) into the above solution heat-treated with argon (Ar) at 300°C.

[0149] After 10 minutes, 4.0 mL of trioctylphosphine-S (TOP-S) solution (2 M) was slowly injected into the quantum dot core and reacted for 50 minutes to grow a shell, and then 5.0 mL of zinc oleate solution (0.5 M) and 1.0 mL of 1-octanethiol (OT, 98.5%) were slowly injected and reacted for 10 minutes to further grow a shell, forming a quantum dot core / shell.

[0150] Manufacturing Example 1-4: Quantum Dot Passivation

[0151] 1.0 mL of 1-dodecanethiol (DDT, 98%) (or 2-ethylhexanethiol (EHT, 97%), or 1-octanethiol (OT, 98.5%)) was added to 1.0 mL of cyclohexane in which 68.7 mg of the green, red, or blue quantum dot core / shell was dispersed, and the mixture was stirred at 70° C. in an inert atmosphere for 1 hour.

[0152] Quantum dots passivated with 1-dodecanethiol (or 2-ethylhexanethiol, or 1-octanethiol) were purified through multiple centrifugations using chloroform and acetone.

[0153] Manufacturing Example 2: Synthesis of ZnO nanoparticles

[0154] 55 mL of methanol containing 1.23 g of Zn(OAc)2·2(H2O) and 0.48 g of potassium hydroxide (KOH) were added to 25 mL of methanol at 57°C over 1 hour, and then heated for 2 hours. After heating, the product was purified through several rounds of centrifugation using a mixed solution of hexane and isopropyl alcohol, thereby producing ZnO nanoparticles.

[0155] Manufacturing Example 3: Double-layer fabrication

[0156] The passivated quantum dots dispersed in cyclohexane and the ZnO nanoparticles dispersed in anhydrous butanol were sequentially spin-coated on a silicon (Si) substrate surface-treated with octadecyltrichlorosilane (ODTS), and then annealed at 150°C for 30 minutes to produce a double layer.

[0157] Manufacturing Example 4: Double-layer transfer

[0158] The above-described double layer was picked up using a flat stamp of the examples and comparative examples described below. The picked-up double layer film was pressed against a patterned negative trench with minimal pressure and then slowly removed to form a double layer pattern. The double layer pattern formed on the stamp was imprinted onto a target substrate described below.

[0159] Manufacturing Example 5: QLED Manufacturing

[0160] Indium tin oxide (ITO) substrates were ultrasonically treated with detergent, deionized water, and isopropyl alcohol for 10 minutes, followed by UV-ozone treatment. Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS, Clevios VP AI 4083) was spin-coated at 5,000 rpm onto the ozone-treated ITO substrates, followed by annealing at 150 °C for 30 minutes to prepare preliminary substrates. All subsequent processes were performed in a glovebox.

[0161] After annealing, poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4`-(N-(p-butylphenyl))diphenylamine)]; TFB, 0.5 mg mL was added onto the pre-substrate. -1 , Solaris-Chem) and poly(9-vinylcarbazole); PVK, 5 mg·mL -1 , Sigma-Aldrich) was spin-coated at 3,000 rpm in dissolved chlorobenzene and baked at 150°C for 30 minutes to prepare a target substrate.

[0162] The above double layer was transfer-printed onto the target substrate according to the method of Manufacturing Example 4. After transfer, 100 nm thick Al was deposited as the upper electrode using a thermal evaporator.

[0163] Example 1

[0164] A preliminary stamp was fabricated using 10 parts by weight of a curing agent per 100 parts by weight of polydimethylsiloxane (PDMS). The surface of the preliminary stamp was subjected to UV-ozone treatment (UVO treatment) for 15 seconds. After ozone treatment, the stamp was immersed in ethanol for 30 minutes to remove hydroxyl groups, thereby fabricating a stamp. The stamp was stored under ambient conditions for 12 hours before use.

[0165] Comparative Example 1

[0166] A stamp was manufactured in the same manner as in Example 1, except that the surface of the above-mentioned preliminary stamp was not subjected to UV-ozone treatment for 15 seconds.

[0167] Example 2

[0168] A stamp was manufactured in the same manner as in Example 1, except that the surface of the above-mentioned preliminary stamp was UV-ozone treated for 35 seconds.

[0169] Figures 11 to 13 are atomic force microscopy (AFM) analysis images of the surface of the stamps in Examples 1 to 2 and Comparative Example 1, respectively.

[0170] The above atomic force microscope used a Dimension ICON device from Bruker.

[0171] The Young's modulus (MPa) of the surface area according to the UV-ozone treatment time (seconds) of the stamp surface in Examples 1 to 2 and Comparative Example 1 is shown in Table 1 below.

[0172] UV-Ozone treatment time (sec) Surface Young's modulus (MPa) Center Young's modulus (MPa) Example 1 152.1 11.93 Example 2 353.5 5 1.93 Comparative example 101.93 1.93

[0173] Example 3

[0174] The double layer of Manufacturing Example 3 was picked up using the stamp of Example 1 and then transferred onto the target substrate of Manufacturing Example 5 to produce a double layer.

[0175] Comparative Example 2

[0176] A double layer was fabricated in the same manner as in Manufacturing Example 3, except that the target substrate of Manufacturing Example 5 was used instead of the silicon (Si) substrate surface-treated with octadecyltrichlorosilane (ODTS).

[0177]

[0178] Experimental Example 1: Confirming Double-Layer Pickup Results

[0179] Figures 14 to 16 are photographs after pickup of a double-layer film manufactured by transferring with the stamps of Examples 1 to 2 and Comparative Example 1, respectively.

[0180] According to Figures 14 to 16, in the case of Example 1, no cracks occurred during the double-layer pickup step. In the case of Example 2, fine cracks occurred during the double-layer pickup step. In the case of Comparative Example 1, cracks occurred during the double-layer pickup step, making it unusable as a product.

[0181]

[0182] Experimental Example 2: Measurement of adhesion time

[0183] The work of adhesion between A and B can be expressed by the following mathematical formula 1.

[0184]

[0185] In mathematical expression 1, , are the dispersion components (mJ / m) of A and B, respectively. 2 ), , is the polar component of each substance (mJ / m 2 )am.

[0186] The bonding time for each layer of the QLED device manufactured according to Example 1 was measured and shown in Table 2 below.

[0187] Material contact angle (°) Dispersion factor (mJ / m) 2 )Polar element (mJ / m) 2 ) Ultrapure distilled water Glycerol ZnO 3 3.2 30.6 15.9 4 5.5 Quantum Dot 10 6.9 9 5.8 13.2 1.5 HTL 8 8.5 8 1.7 11.9 8.8 SiO 2 7 3.4 6 4.4 18.5 13.9 ODTS-Si 10 3.9 9 9.9 5.4 5.5 Stamp (Example 1) 111.6 110.6 2.15.1

[0188] Table 1 shows the contact angle, dispersion factor, and polarity factor for each substance in ultrapure distilled water and glycerol.

[0189] In Table 1, when measuring the contact angle, a fixed volume of ultrapure distilled water or glycerol was slowly dropped onto each material. The dispersion factor and polar factor were obtained using the following mathematical equation 2.

[0190]

[0191] In equation 2, is the total surface free energy in ultrapure distilled water or glycerol, , are the dispersive and polar components of surface free energy in ultrapure distilled water or glycerol.

[0192] The measured contact days are shown in Table 3.

[0193] Measurement target contact date (mJ / m) 2 ) Adhesion between the first substrate and the quantum dot emitting layer 20.2 Adhesion between the electron transport layer and the stamp 22.6 Adhesion between the engraved trench and the quantum dot emitting layer 36.4 Adhesion between the second substrate and the quantum dot emitting layer 30.3

[0194] Experimental Example 3: Measurement of surface roughness according to pressure

[0195] For the double layers of Example 3 and Comparative Example 2, the pressure applied to the double layers and the surface roughness (R) of the quantum dot light-emitting layer and electron transport layer according to the pressure applied to the double layers q ) are shown in Table 4 below.

[0196] Pressure (kgf / cm 2 ) Surface roughness (R) of the lower surface of the quantum dot light-emitting layer q ) (nm) Surface roughness (R) of the upper surface of the electron transport layer q ) (nm) Example 32.00.676.6 Comparative Example 20.02.596.9

[0197]

[0198] Experimental Example 4: Surface Characteristics Evaluation

[0199] Figures 17 and 18 are scanning electron microscope (SEM) analysis images of the upper surface of the electron transport layer (120) in the double layer of Example 3 and Comparative Example 2, respectively.

[0200] Referring to FIGS. 17 and 18, it can be seen that the internal pores of the electron transport layer of the double layer of Example 3 are filled and the particles are densely packed.

[0201] Figures 19 and 20 are atomic force microscopy (AFM) analysis images of the lower surface of the quantum dot light-emitting layer (110) among the double layers of Example 3 and Comparative Example 2, respectively.

[0202] Referring to FIGS. 19 and 20, it can be confirmed that the bilayer of Example 3 has particles of the quantum dot light-emitting layer densely packed, thereby reducing the surface roughness of the lower surface of the quantum dot light-emitting layer.

[0203]

[0204] Experimental Example 5: Impedance Measurement

[0205] Figure 21 is a graph showing the results of measuring the impedance of a double layer manufactured by a spin coating process and a double layer transfer printing method.

[0206] Referring to Fig. 21, it can be confirmed that the impedance of the double layer produced by the double layer transfer printing method is measured to be lower.

[0207]

[0208] Experimental Example 6: Measurement of External Quantum Efficiency

[0209] Figure 22 is a graph showing changes in current density and luminance according to changes in voltage for each QLED manufactured by a spin coating process and a double-layer transfer printing method.

[0210] Figure 23 is a graph showing the change in external quantum efficiency (EQE) according to the change in luminance for each QLED manufactured by the spin coating process and the double-layer transfer printing method of Manufacturing Example 5.

[0211] Referring to FIGS. 22 and 23, the QLED manufactured by the double-layer transfer printing method had a high external quantum efficiency with reduced leakage current.

Claims

1. A step of forming a quantum dot light-emitting layer on a first substrate; A step of forming a double layer by laminating an electron transport layer on the upper surface of the quantum dot light-emitting layer; A step of picking up the double layer using a stamp having a surface portion having a higher Young's Modulus than the center portion; and A step of transferring the double layer picked up by the above stamp onto a second substrate; Including, After the step of transferring onto the second substrate, the surface roughness (R) of the lower surface of the quantum dot light-emitting layer q ) is 0.1 nm to 10 nm, a method for manufacturing a quantum dot display device.

2. In claim 1, after the step of transferring onto the second substrate, the surface roughness (R) of the upper surface of the electron transport layer q ) is 0.1 nm to 15 nm, a method for manufacturing a quantum dot display device.

3. A method for manufacturing a quantum dot display device according to claim 1, further comprising a step of forming a double layer pattern by bringing the picked-up double layer into contact with a negative trench after the picking-up step.

4. A method for manufacturing a quantum dot display device according to claim 1, wherein the stamp is treated with oxygen plasma or UV-ozone.

5. A method for manufacturing a quantum dot display device according to claim 4, wherein the stamp is subjected to UV-ozone treatment for 3 to 300 seconds.

6. A method for manufacturing a quantum dot display device according to claim 1, wherein the surface modulus of the stamp is 2.0 MPa to 3.3 MPa.

7. A method for manufacturing a quantum dot display device according to claim 1, wherein the central Young's modulus of the stamp is 0.5 MPa to 2.0 MPa.

8. A method for manufacturing a quantum dot display device according to claim 1, wherein the stamp comprises an elastomer of siloxane series, acrylic series, epoxy series, triblock copolymer series, or a composite thereof.

9. A method for manufacturing a quantum dot display device according to claim 8, wherein the stamp comprises PDMS (polydimethylsiloxane).

10. A method for manufacturing a quantum dot display device according to claim 1, wherein the electron transport layer comprises ZnO, ZnMgO, or an organic semiconductor.

11. A display device manufactured by the method for manufacturing a quantum dot display device of claim 1.

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