Hydrophilic quantum dots, hydrophilic solvent-based quantum dot ink composition containing the same, and light-emitting device and display containing the same

Abstract

To provide a hydrophilic quantum dot, a hydrophilic solvent-type quantum dot ink composition including the same, and a light-emitting device and a display including the same.SOLUTION: The disclosure relates to hydrophilic quantum dots, a hydrophilic solvent-type quantum dot ink composition including the same, and a light-emitting device and a display that are manufactured by including the same, and more particularly, to hydrophilic quantum dots that are dispersible in a polar solvent with high viscosity, allowing for easy control of viscosity, a hydrophilic solvent-type quantum dot ink composition including the same, and a light-emitting device and a display that include the same.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to hydrophilic quantum dots, a hydrophilic solvent-based quantum dot ink composition containing the same, and a light-emitting device and a display manufactured using the same. Specifically, the present invention relates to hydrophilic quantum dots that are dispersible in a highly viscous polar solvent and whose viscosity is easily adjusted, a hydrophilic solvent-based quantum dot ink composition containing the same, and a light-emitting device and a display including the same. [Background technology]

[0002] Quantum dots (QDs) are semiconductor nanocrystals that can generate various colors by emitting light of different wavelengths according to particle size without changing the type of material. They are also attracting attention as a next-generation light-emitting device due to their advantages of higher color purity and light stability than existing light-emitting materials.

[0003] In particular, quantum dots, which have become a new trend in the display field, are dispersed in a polymer matrix and can be used in the form of a composite in a variety of displays and electronic devices in addition to TVs and LEDs. Meanwhile, materials for color filters require high sensitivity, adhesion to the substrate, chemical resistance, heat resistance, etc. Conventionally, color filters used in displays have generally been formed through a patterning process in which a desired pattern is formed using a photosensitive resist composition through an exposure process using a photomask, and then the unexposed areas are dissolved and removed through a development process, but this has led to the problem of increased costs due to wasted material.

[0004] Recently, to address the increasing sophistication of materials used in pixels and the resulting rise in costs, methods that minimize material usage by using materials only in desired areas, rather than conventional patterning methods such as spin coating or slit coating, have been attracting attention. The most representative method is the inkjet method, which can be broadly divided into the bubble jet method and the piezo method. The inkjet method uses materials only in desired pixels, thereby preventing unnecessary material waste. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Korean Patent No. 10-2340892 Summary of the Invention [Problem to be solved by the invention]

[0006] The quantum dot composition used in the inkjet method is required to have a viscosity of 100 cps or less, preferably 50 cps or less, so achieving low viscosity is essential. Since it is difficult to use solvent-free inks to develop self-luminous ELQD ink materials, development of solvent-based inks is underway. However, there are technical limitations, such as difficulty in adjusting viscosity with non-polar solvents used in solvent-based inks and reduced dispersibility with polar solvents, and related research is currently insufficient.

[0007] In this regard, a prior invention (Korean Patent No. 10-2340892, published on December 17, 2021) has been published relating to a quantum dot microcapsule ink that can achieve a low viscosity of 10 cps or less and is electrically charged and can be dispersed in resins and binders, etc. However, further processes were required, such as performing processes such as frictional charging to cause the shell region of the quantum dot capsule to be positively or negatively charged, or coating the capsule surface with a charge control agent, etc.

[0008] Furthermore, the type of solvent for quantum dot emissive layers used in self-luminous displays for inkjet printing is unclear, and many solvent types are being researched and developed. However, when a non-polar solvent-based emissive layer is used, there is a technical problem that the emissive layer may be etched if a non-polar solvent-based electron transport layer ink composition with the same properties is used. Therefore, there is a need for hydrophilic quantum dots and hydrophilic solvent-based quantum dot ink compositions that are dispersible in polar solvents.

[0009] The problem to be solved by the present invention is to provide hydrophilic quantum dots and a hydrophilic solvent-based quantum dot ink composition that can be easily inkjet printed by modifying the surface of quantum dots to make them dispersible in a highly viscous polar solvent, and that have easy viscosity control. [Effects of the Invention]

[0010] According to an embodiment of the present invention, quantum dots can be dispersed in polar solvents through surface modification, and can have properties (such as viscosity) that are suitable for inkjet printing.

[0011] The solvent-based quantum dot ink composition can be prepared using a polar solvent, making it easy to adjust the viscosity.

[0012] Furthermore, when manufacturing an emissive layer using the hydrophilic solvent-based quantum dot ink composition according to the present invention, even if a non-polar solvent-based electron transport layer is formed on top of the emissive layer, etching of the emissive layer does not occur.

[0013] Therefore, the polar solvent-based ink composition of the present invention can be effectively applied to the preparation of light-emitting devices, specifically, self-luminous displays, through an inkjet printing process, and can also exhibit advantageous effects in terms of commercialization and large-scale production through the application of a simple and inexpensive inkjet process.

[0014] The effects of the present invention are not limited to the above-mentioned examples, and a wider variety of effects are included within the present specification. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a graph showing the results of Experimental Example 4 for the ink composition of Example 4. [Figure 2] 1 is a graph showing the results of Experimental Example 4 for the ink composition of Example 4-a. [Figure 3] 1 is a graph showing the results of Experimental Example 4 for the ink composition of Example 4-b. [Figure 4] 10 is a diagram showing the results of Experimental Example 5. [Figure 5] 10 is a diagram showing the results of Experimental Example 6. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described below. Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in the same manner as commonly understood by those skilled in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries should not be interpreted ideally or excessively unless otherwise clearly defined.

[0017] Furthermore, throughout this specification, when a part is described as "comprising" a certain component, this does not mean that it excludes other components, but that it may further include other components, unless otherwise specified.

[0018] As used herein, the term "organic group" refers to a C1-C10 linear or branched alkyl group, a C2-C10 linear or branched alkenyl group, or a C2-C10 linear or branched alkynyl group, each of which may be substituted or unsubstituted.

[0019] As used herein, "alkyl" refers to a monovalent substituent derived from a straight or branched chain saturated hydrocarbon having 1 to 10 carbon atoms. Examples include, but are not limited to, methyl, ethyl, propyl, isobutyl, sec-butyl, pentyl, iso-amyl, or hexyl.

[0020] As used herein, "alkenyl" refers to a monovalent substituent derived from a straight- or branched-chain unsaturated hydrocarbon having 2 to 10 carbon atoms and one or more carbon-carbon double bonds. Examples include, but are not limited to, vinyl, allyl, isopropenyl, or 2-butenyl.

[0021] As used herein, "alkynyl" refers to a monovalent substituent derived from a straight- or branched-chain unsaturated hydrocarbon having 2 to 10 carbon atoms and one or more carbon-carbon triple bonds. Examples include, but are not limited to, ethynyl, n-propynyl, n-but-2-enyl, or n-hex-3-enyl.

[0022] <Hydrophilic Solvent-Based Quantum Dot Ink Composition> The quantum dot ink composition according to an embodiment of the present invention is an ink composition that can form an emissive layer by discharging it using inkjet printing, roll-to-roll coating, screen printing, spray coating, dip coating, or spin coating.

[0023] A quantum dot ink composition according to an embodiment of the present invention includes hydrophilic quantum dots surface-modified with a ligand and a polar solvent, and the hydrophilic quantum dots can be dispersed in the polar solvent.

[0024] The composition of the quantum dot composition will be specifically described below.

[0025] quantum dots Quantum dots (QDs) are nano-sized semiconductor materials that can have different energy bandgaps depending on their size and composition, and thus can emit light of various emission wavelengths.

[0026] Such quantum dots may have a homogeneous single-layer structure, a multilayer structure such as a core-shell structure or a gradient structure, or a mixture of these. In the core-shell structure, the shell may be multilayered (e.g., core / shell / shell), and each layer may contain a different component, e.g., a (semi)metal oxide.

[0027] The quantum dots can be freely selected from II-VI compounds, III-V compounds, IV-VI compounds, Group IV elements, Group IV compounds, and combinations thereof. When the quantum dots have a core-shell structure, the core and shell can be freely composed of the following exemplified components.

[0028] By way of example, the II-VI compound may be a binary compound selected from the group consisting of CdO, CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, MgSe, MgS and mixtures thereof; CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdH ternary compounds selected from the group consisting of CdZnSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, and mixtures thereof; and quaternary compounds selected from the group consisting of CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, and mixtures thereof. As another example, the III-V compound may be selected from the group consisting of binary compounds selected from the group consisting of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, and mixtures thereof; ternary compounds selected from the group consisting of GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNPs, AlNAs, AlNSb, AlPAs, AlPSb, InNPs, InNAs, InNSb, InPAs, InPSb, and mixtures thereof; and quaternary compounds selected from the group consisting of GaAlNPs, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNPs, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNPs, InAlNAs, InAlNSb, InAlPAs, InAlPSb, and mixtures thereof.

[0029] As another example, the IV-VI compound may be selected from the group consisting of binary compounds selected from the group consisting of SnS, SnSe, SnTe, PbS, PbSe, PbTe, and mixtures thereof; ternary compounds selected from the group consisting of SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, and mixtures thereof; and quaternary compounds selected from the group consisting of SnPbSSe, SnPbSeTe, SnPbSTe, and mixtures thereof.

[0030] As another example, the group IV element may be selected from the group consisting of Si, Ge, and mixtures thereof. The group IV compound may also be a binary compound selected from the group consisting of SiC, SiGe, and mixtures thereof.

[0031] As another example, the alloy type compound is a ternary compound selected from InZnP, etc.

[0032] The surface of the quantum dots may contain a divalent to tetravalent metal, such as a metal from Groups 2 to 14, such as Mg, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Cd, In, or Sn. By adding more metal to the surface of the quantum dots before surface modification, the sites to which ligands can be attached can be expanded, thereby effectively modifying the surface of the quantum dots.

[0033] The two-element compound, three-element compound, or four-element compound may be present in a particle at a uniform concentration, or may be present in the same particle with partially different concentration distributions. Also, quantum dots may have a core / shell structure in which one quantum dot surrounds another. The interface between the core and shell may have a concentration gradient in which the concentration of the element present in the shell decreases toward the center.

[0034] The shape of quantum dots is not particularly limited as long as it is a shape commonly used in the art, and examples thereof include spherical, rod-shaped, pyramidal, disc-shaped, multi-arm, or cubic nanoparticles, nanotubes, nanowires, nanofibers, and nanoplate particles.

[0035] The size of the quantum dots is not particularly limited and can be appropriately adjusted within a conventional range known in the art. For example, the average particle size (D50) of the quantum dots is approximately 2 to 10 nm. Thus, when the particle size of the quantum dots is controlled within the range of approximately 2 to 10 nm, light of a desired hue can be emitted. For example, when the particle size of the quantum dot core / shell containing InP is approximately 5 to 6 nm, light with a wavelength of approximately 520 to 550 nm can be emitted. On the other hand, when the particle size of the quantum dot core / shell containing InP is approximately 7 to 8 nm, light with a wavelength of approximately 620 to 640 nm can be emitted. For example, non-cadmium (Cd)-based III-V QDs (e.g., InP, InGaP, InZnP, GaN, GaAs, GaP) can be used as blue-emitting QDs.

[0036] The quantum dots may have an emission wavelength spectrum full width at half maximum (FWHM) of about 40 nm or less, which can improve color purity and color reproducibility. Furthermore, light emitted through such quantum dots is emitted in all directions, which can improve a wide viewing angle.

[0037] Organic ligands such as oleic acid, myristic acid, lauric acid, palmitic acid, stearic acid, oleylamine, n-octylamine, hexadecylamine, hexylphosphonic acid, n-octylphosphonic acid, tetradecylphosphonic acid, octadecylphosphonic acid, or combinations thereof may be attached to the surface of the quantum dots.

[0038] According to one embodiment of the present invention, the content of the quantum dots is 1 to 20 wt %, preferably 1 to 10 wt %, and more preferably 1 to 5 wt %, based on the total weight of the quantum dot composition, depending on the properties of the quantum dots.

[0039] A metal constituting the surface of the quantum dots can be added to the quantum dot solution, and the content of the added metal is 1 to 20 wt %, preferably 1 to 10 wt %, and more preferably 1 to 5 wt % based on the total weight of the quantum dot composition. For example, if Zn metal is contained on the surface of the quantum dots, ZnCl2 can be added.

[0040] The weight ratio of the quantum dots to the metal compound that forms the surface of the quantum dots and is added to the quantum dots is 3:1 to 1:3, preferably 2:1 to 1:2, and more preferably 1:1.

[0041] Ligand In the quantum dot composition according to the present invention, the ligand serves to modify the surface of the quantum dots. Quantum dots have a barrier to dispersion in hydrophilic or polar solvents due to their hydrophobic surface characteristics, but by modifying the surface of the quantum dots with an appropriate ligand, the miscibility of the quantum dots in hydrophilic solvents can be improved, and the viscosity can be adjusted, making the composition suitable for inkjet printing.

[0042] According to one embodiment of the present invention, the ligand comprises a reactive group capable of bonding to the surface of the quantum dot and a hydrophilic organic group, preferably comprising a reactive group capable of bonding to the surface of the quantum dot on one side and a hydrophilic organic group on the other side, and more preferably comprising one or more reactive groups capable of bonding to the surface of the quantum dot on one side and one or more hydrophilic organic groups at the end.

[0043] Non-limiting examples of functional groups capable of binding to the surface of a quantum dot may include those selected from the group including -COOH, -CN, NH, NH, N, SH, PO, P, OH, COOR' (wherein R' is an alkyl group), -C(=O)-, PO(OH), POOH, and combinations thereof.

[0044] The hydrophilic organic group contained in the ligand is an organic group having 3 to 10 carbon atoms, and preferably contains one or more elements selected from the group consisting of nitrogen (N), oxygen (O), and sulfur (S). Specific examples include a carboxy group, a hydroxy group, a sulfo group, a sulfonyl group, an ammonium group, an amine group, ethylene glycol, and polyethylene glycol (PEG).

[0045] The hydrophilic organic group contained in the ligand is contained in the ligand as 1 to 20 independently selected moieties as part of the ligand.

[0046] Examples of ligands include bifunctional molecules containing a carboxylic acid-containing organic group and a thiol group, such as, but not limited to, 3-mercaptopropionic acid, 6-mercaptohexanoic acid, 7-mercaptoheptanoic acid, 8-mercaptooctanoic acid, 12-mercaptododecanoic acid, mercaptosuccinic acid, or dimercaptosuccinic acid.

[0047] According to one embodiment of the present invention, the content of the ligand is 1 to 40 wt %, preferably 1 to 20 wt %, more preferably 1 to 10 wt %, based on the total weight of the quantum dot composition, depending on the properties of the quantum dots.

[0048] The weight ratio of the quantum dots to the ligand is 1:1 to 1:5, preferably 1:1 to 1:3, and more preferably 1:1.5 to 1:2.5.

[0049] Polar solvents Highly viscous polar solvents have excellent properties for preparing ink compositions suitable for use in inkjet printing processes, but have presented problems in uniformly dispersing quantum dots.

[0050] According to one embodiment of the present invention, the polar solvent contains two or more kinds, preferably propylene glycol, and more preferably one or more solvents containing one or more functional groups selected from the group consisting of a carboxy group, a hydroxy group, a sulfo group, an ester group, and a ketone group. In this case, the volume ratio of propylene glycol to the remaining polar solvent is 1:0.5 to 1:5, preferably 1:1 to 1:3. The optimal volume ratio may vary depending on the physical properties of the remaining polar solvent to be added.

[0051] The viscosity of the quantum dot ink composition according to the present invention is approximately 2 to 20 cps, preferably 2 to 16 cps, and more preferably 2.1 to 15 cps, and within this range, the quantum dot ink composition is suitable for use in inkjet printing methods.

[0052] Furthermore, the quantum dot ink composition according to the present invention has a roughness of 0.5 to 5 nm, preferably 1 to 3 nm, and more preferably 1 to 2 nm. The more uniform the roughness after thinning, the more uniform the thin film can be realized when applied to light-emitting devices and display devices, resulting in uniform color reproduction and no leakage when the device is operated, thereby improving the driving characteristics of the device.

[0053] <Light-emitting element and display device> The light emitting device according to one embodiment of the present invention is distinguished from conventional light emitting devices in that it includes a light emitting layer formed from the quantum dot ink composition described above.

[0054] The light emitting device according to an embodiment of the present invention may be applied to various types of light emitting devices, including, but not limited to, quantum dot light emitting devices and organic light emitting devices.

[0055] In general, a light-emitting device includes a first electrode, a second electrode facing the first electrode, a light-emitting layer disposed between the first electrode and the second electrode and formed by inkjet printing the quantum dot ink composition, a hole transport layer disposed between the first electrode and the light-emitting layer, and an electron transport layer disposed between the light-emitting layer and the second electrode. Optionally, the light-emitting device may further include at least one of a hole injection layer and an electron injection layer.

[0056] The present invention also provides a display device comprising the quantum dot ink composition, where the display device may be, but is not limited to, a liquid crystal display (LCD), an electroluminescent display (EL), a plasma display (PDP), a field emission display (FED), or an organic light emitting diode (OLED). [Example]

[0057] The present invention will be described in more detail with reference to the following Preparation Examples and Examples. However, the following Preparation Examples and Examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0058] <Production Example 1. Polar Solvent A> Polar solvent A was prepared by mixing propylene glycol (hereinafter referred to as PG), butanol, and propylene glycol monomethyl acetate (hereinafter referred to as PGMEA) in a volume ratio of 1:1:1 to a total volume of 2 ml.

[0059] <Production Example 2. Polar Solvent B> Polar solvent B was prepared by mixing PG and butanol in a volume ratio of 1:3.

[0060] <Production Example 3. Polar Solvent C> Polar solvent C was prepared by mixing PG and PGMEA in a volume ratio of 1:1.

[0061] <Production Example 4. Polar Solvent D> Polar solvent D was prepared by mixing PG and hexanol in a volume ratio of 1:1.

[0062] <Production Example 5. Polar Solvent E> Polar solvent E was prepared by mixing PG and ethanol in a volume ratio of 1:3.

[0063] <Production Example 6. Polar Solvent F> Polar solvent F was prepared by mixing PG and butyl acetate in a volume ratio of 1:1.

[0064] <Production Example 7. Polar Solvent G> Polar solvent G was prepared by mixing PG and heptanol in a volume ratio of 1:1.

[0065] <Production Example 8. Polar Solvent H> Polar solvent H was prepared by mixing PG and acetone in a volume ratio of 1:1.

[0066] Example 1: Hydrophilic Solvent-Based Quantum Dot Ink Composition The quantum dots used were a green quantum dot solution dispersed in colloidal form in toluene, with a core of indium phosphide (InP), a shell of zinc selenide (ZnSe) and zinc sulfide (ZnS), and a ligand of oleic acid, approximately 0.025 g in total.

[0067] Approximately 0.025 g of ZnCl2 (5 wt% in ethanol) was added to the green quantum dot solution dispersed in toluene, and the mixture was stirred for approximately 10 minutes. After stirring, ethanol was added and the mixture was centrifuged.

[0068] After centrifugation, the mixture was redispersed in toluene, and approximately 0.05 g of mercaptosuccinic acid was added as a surface-modifying ligand. After stirring for 10 minutes, hexane was added and the mixture was centrifuged to obtain the surface-modified quantum dots. These were then dispersed in the polar solvent A.

[0069] <Example 2> The production was carried out in the same manner as in Example 1, except that the surface-modified quantum dots were dispersed in polar solvent B.

[0070] Example 3 The production was carried out in the same manner as in Example 1, except that the surface-modified quantum dots were dispersed in polar solvent C.

[0071] Example 4 The production was carried out in the same manner as in Example 1, except that the surface-modified quantum dots were dispersed in polar solvent D.

[0072] <Example 5> The production was carried out in the same manner as in Example 1, except that the surface-modified quantum dots were dispersed in polar solvent E.

[0073] Example 6 The production was carried out in the same manner as in Example 1, except that the surface-modified quantum dots were dispersed in polar solvent F.

[0074] Example 7 The production was carried out in the same manner as in Example 1, except that the surface-modified quantum dots were dispersed in polar solvent G.

[0075] Example 8 The production was carried out in the same manner as in Example 1, except that the surface-modified quantum dots were dispersed in polar solvent H.

[0076] <Comparative Example> A solution of green quantum dots dispersed in colloidal form in cyclohexylbenzene was used without surface modification. The core consisted of indium phosphide (InP), the shell of zinc selenide (ZnSe) and zinc sulfide (ZnS), and the ligand was oleic acid.

[0077] <Experimental Example 1. Quantum Efficiency Evaluation> Using a QE 2100 device, the quantum efficiency (QE) of the ink compositions prepared in Examples 1 to 8 was measured (excitation wavelength 450 nm) under absorption conditions of 0.6 to 0.8. The results are shown in Table 1 below.

[0078] [Table 1]

[0079] In all examples, the quantum efficiency was 70% or more, and examples 3 to 8 showed extremely excellent quantum efficiencies of approximately 98 to 100%.

[0080] <Experimental Example 2. Viscosity Evaluation> The viscosity of the ink composition was measured using a rheometer (MARS-40) by the CP (convex and plate) measurement method, with the set temperature at 25°C and the shear rate at Start 10 sec. -1 ~End 20sec -1 I did.

[0081] In addition to Examples 1 to 8, polar solvents were further produced by varying the mixing ratio of each polar solvent, and the respective mixing ratios and viscosity results are shown in Table 2 below.

[0082] [Table 2]

[0083] The remaining solvents other than PG have lower polarity than PG, so the viscosity tends to decrease as the specific gravity of the mixture ratio increases. The viscosity of the examples shown in Table 2 all fell within the range of 2 to 16 cps, and were deemed suitable for use in inkjet printing.

[0084] <Experimental Example 3. Evaluation of organic matter content / TGA analysis> TGA analysis is a thermal analysis method that measures the mass change of a sample due to temperature change. The temperature at which a rapid change in weight occurs can be interpreted as the decomposition temperature of the organic matter, and the weight percentage of the organic matter can be numerically determined based on the degree of total weight loss.

[0085] The ink compositions prepared in Example 1 (ZC-MSA GQD) and Comparative Example (Ref GQD) were dried in a vacuum oven for at least 1 hour to form powder, and then the organic content was evaluated using a TGA 550. The results are shown in Table 3 and a graph below. Measurement conditions: Mass flow 240 mL / min, equilibrate 40°C, ramp 10°C / min to 700°C / min

[0086] [Table 3]

[0087] Referring to Table 3 and the first graph, only the oleic acid (third peak) attached to the initial quantum dots was observed in the quantum dots produced in the comparative example, and there was a weight loss of about 16% of the organic material. From this, it can be determined that about 16.3% of the total weight of the initial quantum dots was oleic acid attached.

[0088] In the case of Example 1, there was a weight loss of about 15% of the organic matter, and three peaks (1st to 3rd peaks) were observed. The first peak was associated with oleic acid that had been detached from the quantum dots by substitution with the ligand, the second peak was associated with the newly attached ligand to the surface of the quantum dots, and the third peak was associated with oleic acid that had not yet been substituted.

[0089] While the weight loss of the total organic matter in Example 1 and the comparative example is almost similar, the third peak values ​​are 2.767 and 14.348, respectively, which is about 5.2 times different. This indicates that ligand substitution on the surface of the quantum dots is very effective in Example 1.

[0090] Furthermore, referring to the second graph, a rapid weight loss occurs in Example 1 at approximately 180°C, while a rapid weight loss occurs in Comparative Example at approximately 400°C, indicating that the combustion points of the main organic compounds are different.

[0091] <Experimental Example 4. Roughness Evaluation> After cleaning the ITO glass, the ink composition was applied to a thin film using a spin coater (3500 rpm / 20 s), dried on a hot plate at 70°C for about 15 minutes, and the roughness of the thin film was measured using a Zygo NewView 9000 device.

[0092] For the roughness evaluation, ink compositions containing polar solvents shown in Table 4 below were used, and the results are shown in FIGS.

[0093] [Table 4]

[0094] 1 to 3, the roughness value of the thickest part of an arbitrary cross section of each thin film was measured and displayed. In Example 4 (FIG. 1), the maximum roughness value was measured to be about 2.73 nm, in Example 4-a (FIG. 2), it was measured to be about 2.02 nm, and in Example 4-b (FIG. 3), it was measured to be about 1.73 nm.

[0095] This confirms that the roughness value of the ink composition can be uniformly adjusted by adjusting the mixing ratio of the polar solvent.

[0096] <Experimental Example 5. Evaluation of ejection properties> After mounting the head on a Fuji Film Dimatix 2.4pl (DMC-11610), ejection performance was evaluated using an Omnijet 200 device. The ink composition of Example 1 was used and ejected in the form of one drop. Time-division photography was performed according to the time it took for one drop of ink to be ejected, and the results are shown in Figure 4.

[0097] Referring to FIG. 4, it can be seen that a tail is formed in the ink at the beginning of ejection, but it can be seen that the ink is gradually ejected into a balanced sphere with a diameter of approximately 18.307 μm.

[0098] <Experimental Example 6. Inkjet Shape (CRF) Evaluation> As in Experimental Example 5, after mounting on a Fuji Film Dimatix 2.4pl (DMC-11610) head, the ink composition of Example 1 was ejected using an Omnijet 200 device, and pattern evaluation was carried out.

[0099] During pattern evaluation, ITO glass was used as the lower substrate, and the size and height of the pattern on the substrate were measured using a Zygo New View 9000. In this case, the following equation 1 was introduced to quantify the degree of the coffee-ring effect, and the results are shown in Figure 5. [Formula 1] CRF (Coffee Ring Factor)=Hmax / Hmin In the above formula, Hmax represents the maximum thickness of the pattern, Hmin represents the minimum thickness of the pattern, and the CRF value represents the degree of the coffee ring effect, i.e., CRF=1 indicates that the coffee ring effect is completely eliminated.

[0100] 5, the Hmax of the inkjet shape of Example 1 was approximately 41.62 nm and Hmin was approximately 39.78 nm. Therefore, the CRF was approximately 1.047, a value very close to 1, and it was determined that the coffee ring effect had almost no effect. Also, when observing the three-dimensional shape, it was confirmed that the shape was uniform overall, not just a cross section.

[0101] It is obvious to those skilled in the art to which the present invention pertains that the present invention is not limited to the above-described embodiments and can be modified or altered in various ways without departing from the technical scope of the present invention.

Claims

1. 1. A surface-modified quantum dot, comprising: The quantum dots are surface-modified with a ligand containing a reactive group capable of bonding to the surface of the quantum dots and a hydrophilic organic group; The quantum dots have a core made of InP and a shell made of ZnSe and ZnS, and a hydrophilic quantum dot, wherein the ligand is mercaptosuccinic acid; a polar solvent, The quantum dot ink composition, wherein the polar solvent comprises propylene glycol and one or more additional solvents other than propylene glycol having one or more functional groups selected from the group consisting of a carboxyl group, a hydroxyl group, a sulfo group, an ester group, and a ketone group.

2. The quantum dot ink composition of claim 1 , wherein the quantum dot ink composition is for use in inkjet printing.

3. 10. The quantum dot ink composition of claim 1, wherein the surface of the quantum dots comprises Mg, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Cd, In, or Sn.

4. 2. The quantum dot ink composition according to claim 1, wherein the polar solvent has a total volume ratio of propylene glycol to the other solvents of 1:0.5 to 1:

5.

5. The quantum dot ink composition according to claim 1, wherein the viscosity of the ink composition is 2 to 20 cps.

6. The quantum dot ink composition of claim 1 , wherein the ink composition has a roughness of 0.5 to 5 nm.

7. The quantum dot ink composition of claim 1 , wherein the quantum dots are dispersed in the polar solvent.

8. The quantum dot ink composition of claim 1 , wherein the ink composition is for inkjet printing.

9. 10. The quantum dot ink composition of claim 1, wherein the ink composition has a quantum efficiency (QE) of 70% or greater.

10. A light-emitting device comprising a light-emitting layer formed from the composition according to any one of claims 1 to 9.

11. A display comprising the light-emitting element of claim 10.

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