Electron transport layer precursor and electron transport layer for QLED

Abstract

A composition comprising ZnO-based nanoparticles, a polar organic solvent, and a polymer, wherein the ZnO-based nanoparticles are of the formula Li x Mg y M p Zn z The polymer contains O, where 0≦x≦0.2, 0≦y+p≦0.25, z=1-0.5xy-1.5p, M is an element selected from gallium and / or aluminum, the polymer comprises polyvinylpyrrolidone (PVP) and / or poly(ethyl oxazoline) (PEO), and the polymer has an average molecular weight M of 25,000 to 1,300,000 Da. w A composition having the following is provided.

Description

[Technical Field]

[0001] The present invention relates to a composition that is a precursor for an electron transport layer, the use of the composition, a method for manufacturing an electron transport layer for a QLED, an electron transport layer for a QLED, a QLED, and a visual display unit. [Background technology]

[0002] Due to their favorable bandgap and electron transport properties, zinc oxide materials are used as electron transport layers (ETLs) in pixels found in next-generation display devices such as so-called QLED (quantum dot light-emitting diode) displays.

[0003] Pixels in next-generation display devices typically comprise five or more layers, including a quantum dot light-emitting layer, an electron transport layer, and a hole transport layer. Typically, each layer has a thickness of approximately 50 to 150 nanometers.

[0004] An important measure of pixel efficiency in display devices is external quantum efficiency (EQE). EQE can be defined as the ratio of the number of photons emitted by a pixel to the number of electrons passing through the pixel. External quantum efficiency can be considered a measure of the device's efficiency in converting electrons into photons. External quantum efficiency is a measure of the entire pixel. However, equal to all other factors, EQE can be used to measure the effectiveness of zinc oxide ETL.

[0005] The highest EQE reported for experimental QLEDs is approximately 20%. For commercial applications, an external quantum efficiency of over 10% is desirable. Other factors, such as operating lifetime and operating voltage, are also important considerations when preparing the electron transport layer.

[0006] Heng Zhang et al., in J.Mater.Chem.C, 2019, 7, 2291-2298 disclose the use of ZnMgO:PVP (polyvinylpyrrolidone) inorganic-organic hybrid ETLs in an attempt to fabricate improved ETLs for QLEDs. However, there remains a need to further improve the ETLs for QLEDs, and in particular, it is still desired to improve the EQE of such QLEDs.

Summary of the Invention

[0007] One aspect of the present disclosure is a composition comprising ZnO-based nanoparticles, a polar organic solvent, and a polymer, wherein the ZnO-based nanoparticles have the formula Li x Mg y M p Zn z O, where 0 ≦ x ≦ 0.2, 0 ≦ y + p ≦ 0.25, z = 1 - 0.5x - y - 1.5p, M is an element selected from gallium and / or aluminum, the polymer comprises polyvinylpyrrolidone (PVP) and / or poly(ethyl oxazoline) (PEO), and the polymer has an average molecular weight M w ranging from 25,000 to 1,300,000 Da.

[0008] Another aspect of the present disclosure is a method for manufacturing an electron transport layer (ETL) for a QLED, the method comprising providing a composition according to the above aspect, spin-coating the composition to provide a spin-coated composition, and annealing the spin-coated composition.

[0009] Another aspect of the present disclosure is the use of the composition of the above aspect in the manufacture of an electron transport layer (ETL) for a QLED.

[0010] Another aspect of the present disclosure is an electron transport layer (ETL) for a QLED comprising ZnO-based nanoparticles and a polymer, wherein the ZnO-based nanoparticles have the formula Li x Mg y M p Zn zIt has O, where 0 ≦ x ≦ 0.2, 0 ≦ y + p ≦ 0.25, z = 1 - 0.5x - y - 1.5p, M is an element selected from gallium and / or aluminum, the polymer contains polyvinylpyrrolidone (PVP) and / or poly(ethyl oxazoline) (PEO), and the polymer has an average molecular weight M of 25,000 to 1,300,000 Da w is for an electron transport layer (ETL).

[0011] Another aspect of the present disclosure is directed to a QLED including the ETL according to the above aspect.

[0012] Another aspect of the present disclosure is directed to a visual display unit including the QLED according to the above aspect.

Brief Description of the Drawings

[0013] [Figure 1] Shows the measured external quantum efficiency of the QLED of Example 5. [Figure 2] Shows the measured voltage of the QLED of Example 5.

Modes for Carrying Out the Invention

[0014] The present invention aims to address at least some of the problems associated with the prior art or to provide at least a commercially acceptable alternative solution.

[0015] In a first aspect, the present invention is a composition comprising ZnO-based nanoparticles, a polar organic solvent, and a polymer, wherein the ZnO-based nanoparticles have the formula Li x Mg y M p Zn z O, where 0 ≦ x ≦ 0.2, 0 ≦ y + p ≦ 0.25, z = 1 - 0.5x - y - 1.5p, M is an element selected from gallium and / or aluminum, The polymer comprises polyvinylpyrrolidone (PVP) and / or poly(ethyl oxazoline) (PEO), and the polymer has an average molecular weight of 25,000 to 1,300,000 Da. w The present invention provides a composition having the following characteristics:

[0016] Each aspect or embodiment defined herein may be combined with any other aspect or embodiment unless expressly indicated otherwise. Specifically, any feature indicated as preferred or advantageous may be combined with any other feature indicated as preferred or advantageous.

[0017] Through a series of experiments, the inventors of the present invention have surprisingly found that changing the average molecular weight of the polymer in the composition according to the present invention can have a significant effect on the EQE of QLEDs containing ETL prepared using such compositions. The composition is typically a suspension, and the polymer may typically be known as a dispersant or stabilizer. Such terms may be used interchangeably herein.

[0018] The use of PVP as such a stabilizer has been investigated, for example, by Heng Zhang et al., as mentioned above. However, the effect of its molecular weight on stability and / or performance has not been investigated.

[0019] The inventors have discovered that the average molecular weight M is surprisingly 25,000 to 1,300,000 Da. w However, we found that this could result in a composition with significantly increased EQE performance in the resulting QLED.

[0020] While not bound by theory, these unexpected effects may be attributable to the structure of the resulting layer. For example, the packing of the resulting ETL layer can be improved. This is desirable as it can help achieve lower surface roughness in the ETL. wThis may result in a decrease in EQE performance compared to, for example, a QLED prepared using the composition of the present invention. The inventors have found that the dispersant M w We found that increasing the M of the polymer can increase the EQE of such QLEDs. However, w If the value is too high, unexpected effects may not be observed or may be reduced.

[0021] In addition to the beneficial effects of the resulting QLED on EQE, the inventors have also found that the stability of the composition, i.e., its shelf life, can be increased by the use of certain stabilizers of the present invention. Ideally, such a composition should be stable for several months. However, in the absence of such stabilizers, the nanoparticles may separate from the solvent, for example, after about three weeks.

[0022] Furthermore, the nanoparticles may exhibit excellent dispersion within the composition. While not theoretically bound, this may be due to favorable interactions with the specific polymer(s) of the present invention, particularly in the solvents described herein. The composition is typically colorless or translucent, which is thought to be due to the excellent dispersion of the nanoparticles within the composition. Thus, the composition may enable the production of readily dispersible (doped) single-size ZnO particles in polar solvents without the need for sonication.

[0023] Furthermore, it should be noted that peak EQE may degrade after approximately 3 weeks in the absence of a stabilizer. However, with the use of the stabilizer of the present invention, peak EQE can remain stable for 3 months in the presence of the stabilizer.

[0024] Surprisingly, a similar M w It was also found that PEO can achieve stability and EQE (Effective Energy) at a level almost comparable to that of PVP (Photovoltaic Vatilization). Advantageously, both PVP and PEO are non-toxic.

[0025] As used herein, the term “nanoparticles” has the common meaning in the art. For example, nanoparticles may be particles having a diameter in the range of about 1 to 100 nm, as measured by TEM.

[0026] As used herein, the term “ZnO-based nanoparticles” encompasses nanoparticles containing ZnO or doped ZnO. ZnO may be doped with, for example, lithium, magnesium, gallium, and / or aluminum. ZnO-based nanoparticles are derived from the formula Li x Mg y M p Zn z The nanoparticle contains O, where 0 ≤ x ≤ 0.2, 0 ≤ y + p ≤ 0.25, z = 1 - 0.5xy - 1.5p, and M is an element selected from gallium and / or aluminum. The presence of Li is not essential. However, typical methods for producing such nanoparticles may involve the use of lithium-based precursors. Therefore, residual lithium is typically present in ZnO-based nanoparticles. It should be understood that other methods that do not result in the presence of lithium may also be used. The effect of residual lithium on performance is not well understood. However, residual lithium is not considered to have a significant impact on the performance of ZnO-based nanoparticles in ETL. If alternative precursors are used, other unavoidable trace elements may also be present in small amounts.

[0027] Preferably, the composition consists of ZnO-based nanoparticles, a polar organic solvent, and a polymer, and more preferably, ZnO-based nanoparticles, a polar organic solvent, and a polymer.

[0028] As used herein, the term “essentially consisting of” may include certain additional components other than those listed, provided that they do not substantially affect the essential characteristics of the composition.

[0029] The composition could, for example, be a precursor for ETL of QLED.

[0030] Preferably, the polymer is PVP and / or PEO.

[0031] As is known in this field, the average molecular weight M w The formula is:

[0032]

number

[0033] Preferably, the polymer has a molecular weight of 25,000 to 500,000 Da, more preferably 25,000 to 200,000 Da, even more preferably 25,000 to 100,000 Da, even more preferably 25,000 to 75,000 Da, even more preferably 30,000 to 70,000 Da, even more preferably 35,000 to 70,000 Da, even more preferably 40,000 to 65,000 Da, even more preferably 45,000 to 65,000 Da, and even more preferably 50,000 to 63,000 Da. w It has the following properties. Most preferably, the polymer has about 58,000 Da of M w Such molecular weights may result in particularly advantageous stability and improved EQE properties, as described herein.

[0034] Preferably, the polymer contains PVP. More preferably, the polymer is PVP. PVP can provide the best stability and improved EQE properties.

[0035] Preferably, p = 0 and y > 0. In other words, the ZnO-based nanoparticles are preferably doped only with magnesium and optionally with lithium. Magnesium-doped ZnO can provide the best performance in the ETL layer. In an alternative preferred embodiment, M is preferably aluminum. In a further alternative preferred embodiment, y = 0 and p > 0, and preferably M is aluminum. In other words, the ZnO-based nanoparticles are preferably doped only with aluminum and / or gallium, preferably with aluminum, and optionally with lithium.

[0036] In some embodiments, it is a range created by 0 < x ≦ 0.2, 0.01 ≦ x ≦ 0.2, 0.05 ≦ x ≦ 0.15, 0.08 ≦ x ≦ 0.12, or any combination of these endpoints. The amount of lithium is not particularly limited and may depend on the manufacturing method.

[0037] Preferably, 0 < y + p ≦ 0.25, more preferably 0.01 ≦ y + p ≦ 0.25, still more preferably 0.05 ≦ y + p ≦ 0.25, still more preferably 0.10 ≦ y + p ≦ 0.20, still more preferably 0.15 ≦ y + p ≦ 0.20. Of course, for example, if p = 0, it should be understood that 0 < y + p ≦ 0.25 becomes 0 < y ≦ 0.25. In other words, such an equation does not require both y and p to be non-zero. Such amounts of dopants, especially magnesium and / or aluminum, can provide the best EQE performance when used in the ETL layer. The EQE generated by undoped ZnO nanoparticles can generally be smaller than that of doped ZnO nanoparticles. Therefore, it is generally preferred that the ZnO-based nanoparticles are doped with magnesium and / or M, that is, preferably y + p > 0.

[0038] Those skilled in the art can select a suitable polar organic solvent. However, the polar organic solvent preferably includes ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, or a mixture of two or more thereof, more preferably ethanol and / or isopropanol. Preferably, the polar organic solvent is ethanol and / or isopropanol. Most preferably, the solvent is ethanol. Ethanol, for example, can provide the most stable composition.

[0039] Preferably, the weight ratio of ZnO-based nanoparticles to polymer is 1:0.05 to 1:0.5, more preferably 1:0.15 to 1:0.4, and more preferably 1:0.3 to 1:0.4. It has also been found that a higher weight percent of polymer, such as PVP, contained in the composition can increase the optimized properties described above. While not theoretically bound, such weight ratios are thought to optimize, for example, the interaction between the polymer and ZnO-based nanoparticles in the composition. For example, it may be particularly preferable when the total weight of PVP is about 30% by weight of the total weight of ZnO-based nanoparticles in the composition.

[0040] Preferably, the composition contains 0.1 to 10% by weight, more preferably 0.5 to 5% by weight, even more preferably 1 to 4% by weight, even more preferably 2 to 3% by weight, and most preferably about 2.5% by weight of ZnO-based nanoparticles, based on the total weight of the polar organic solvent. Such a concentration of nanoparticles may be particularly suitable, for example, for a spin coating process for producing ETL.

[0041] Preferably, the ZnO-based nanoparticles have an average particle diameter of 1 to 20 nm, preferably 1 to 10 nm. This can be measured using TEM and / or SEM, for example, using standard techniques. Thus, the average particle diameter is typically the number-average particle diameter, i.e., D[1,0]. The particle size distribution of the ZnO-based nanoparticles is preferably monodisperse. In other words, the ZnO-based nanoparticles are preferably substantially uniform in size, for example, each particle having the same particle diameter ±10%. A small average particle diameter is preferred so that the resulting ETL is smooth, i.e., has low surface roughness. Since the ETL is thin, a small particle diameter may be required for a smooth surface.

[0042] In a further aspect of the present invention, a method for manufacturing an electron transport layer (ETL) for a QLED, the method being: To provide a composition according to a first embodiment, To provide a spin-coated composition by spin-coating the composition, A method is provided which includes annealing a spin-coated composition.

[0043] Typically, polar organic solvents can be substantially evaporated and removed during ETL formation.

[0044] Suitable spin coating techniques are known in the art. For example, spin coating may involve a procedure used to deposit a uniform thin film on a flat substrate. Typically, a small amount of coating material is applied to the center of the substrate, which is rotating slowly or not rotating at all. The substrate is then rotated at a speed of up to 10,000 rpm to spread the coating material (and evaporate the solvent) by centrifugal force. The equipment used in spin coating may be called a spin coater or simply a spinner. Spin coating may involve spin coating a composition at about 1000 to about 3000 rpm, for example, about 2000 rpm, for example, for about 30 to about 90 seconds, for example, for example, about 1 minute. Spin coating may also be known as centrifugal rubber mold casting. This method utilizes inertia to produce castings from, for example, a rubber mold.

[0045] Suitable annealing techniques are known in the art. For example, annealing may involve annealing on a hot plate at about 80 to about 120°C, for example, about 100°C, for example, about 5 to about 15 minutes, for example, about 10 minutes. By annealing the spin-coated composition, an ETL is typically formed, which can be incorporated into the QLED.

[0046] Alternatively, on a large scale, ETL can be manufactured using the compositions disclosed herein by using inkjet printing.

[0047] A further aspect of the present invention provides the use of the composition of the first aspect in the manufacture of an electron transport layer (ETL) for QLEDs. Those skilled in the art know suitable techniques for using such compositions.

[0048] In a further aspect of the present invention, an electron transport layer (ETL) for a QLED comprising ZnO-based nanoparticles and a polymer, wherein the ZnO-based nanoparticles are of the formula Li x Mg y M p Zn z It has O, and in the formula, 0 ≤ x ≤ 0.2, 0 ≤ y + p ≤ 0.25, z = 1 - 0.5xy - 1.5p, M is an element selected from gallium and / or aluminum. The polymer comprises polyvinylpyrrolidone (PVP) and / or poly(ethyl oxazoline) (PEO), and the polymer has an average molecular weight of 25,000 to 1,300,000 Da. w An electron transport layer (ETL) having the following is provided.

[0049] Preferred features and advantages described herein with reference to the first embodiment apply equally to this embodiment. It should be understood that the ETL of this embodiment is, for example, the intended product of the precursor composition of the first embodiment.

[0050] ETL preferably has a surface roughness of 2 nm or less, for example, 1.8 nm or less, 1.6 nm or less, 1.4 nm or less, or 1.2 nm or less. Surface roughness can be measured, for example, by atomic force microscopy. Smooth ETL is particularly preferred in QLED technology.

[0051] In a further aspect of the present invention, a QLED is provided which includes ETL according to the above aspect. Such a QLED may exhibit an improved EQE as described herein.

[0052] In a further aspect of the present invention, a visual display unit is provided that includes a QLED according to the above embodiment.

[0053] The present invention will now be described in relation to the following non-limiting embodiments.

[0054] Manufacturing of the composition The compositions according to the present invention were prepared according to the following examples.

[0055] Example 1 - Preparation of 15 mol% Mg-doped ZnO nanoparticles from Zn / Mg acetate / hexane Zinc acetate dihydrate (0.012 mol, 2.63 g, Aldrich 99.999%) and magnesium acetate tetrahydrate (0.45 g, 15 mol%) were added to 120 mL of ethanol and refluxed for 2.5 hours to obtain a clear solution. The solution was then allowed to cool to room temperature.

[0056] Next, lithium hydroxide (0.014 mol, 0.34 g) was dissolved in 120 mL of ethanol and sonicated for approximately 15 minutes. This solution was then added to a zinc acetate / magnesium acetate tetrahydrate solution over 15 minutes with vigorous stirring. No significant changes occurred. This mixture was then left to stir overnight (approximately 17 hours) at room temperature.

[0057] No significant changes occurred after this period.

[0058] 240 mL of the solution was then diluted to 1000 mL with n-hexane to precipitate Mg-doped ZnO, yielding a pale milky white solution. The precipitate was allowed to settle in a Mg-doped ZnO / ethanol / hexane dispersion for 2 hours, and the supernatant was drained. The remaining dispersion was placed in two 50 mL centrifuge tubes and centrifuged at 7000 rpm for 5 minutes. After decantation, the white product in the tubes was rinsed with dry ethanol (2 mL x 2), and 25 mL of ethanol (dried on molecular sieves) was added to obtain a 2.5 wt% dispersion. The tubes were stirred to disperse the product, and in both cases, a clear solution was obtained. The solutions were combined and 10% PVP (M) was added to ethanol. w (=25,000) 1.8 mL was added.

[0059] The composition of ZnO-based nanoparticles is Li 0.07 Mg 0.15 Zn 0.815 It was predicted to be O.

[0060] Example 2 - Preparation of 10 mol% Mg-doped ZnO nanoparticles from Zn / Mg acetate / hexane Zinc acetate dihydrate (0.01 mol, 2.195 g, Aldrich 99.999%) and magnesium acetate tetrahydrate (0.228 g, 10 mol%) were added to ethanol and refluxed for 2.5 hours to obtain a clear solution. The solution was then allowed to cool to room temperature.

[0061] Next, lithium hydroxide (0.01 mol, 0.275 g) was dissolved in 100 mL of ethanol and sonicated for approximately 15 minutes. This solution was then added to a zinc acetate / magnesium acetate tetrahydrate solution over 15 minutes with vigorous stirring. No significant changes occurred. This was then left to stir at room temperature overnight (22.5 hours).

[0062] No significant changes occurred after this period.

[0063] 200 mL of the solution was then diluted to 900 mL with n-hexane to precipitate Mg-doped ZnO, yielding a pale milky white solution. The precipitate was allowed to settle in a Mg-doped ZnO / ethanol / hexane dispersion for 2 hours, and the supernatant was drained. The remaining dispersion was placed in two 50 mL centrifuge tubes and centrifuged at 7000 rpm for 5 minutes. After decantation, the white product in the tubes was rinsed with dry ethanol (2 mL x 2), and ethanol (dried on molecular sieves) was added to obtain a 2.5 wt% dispersion. The tubes were stirred to disperse the product, and in both cases, a clear solution was obtained. The solutions were combined and PVP(M w =25,000), and PVP(M w (=58,000) was added: Tube 1: 0.75 mL of 10% PVP 25,000 / EtOH per 10 mL of nanoparticle dispersion. Tube 2: 0.75 mL of 10% PVP 58,000 / EtOH per 10 mL of nanoparticle dispersion. The composition of ZnO-based nanoparticles is Li 0.07 Mg 0.1 Zn 0.865 It was predicted to be O.

[0064] Example 3 - Preparation of 5 mol% Al-doped ZnO nanoparticles from Zn / acetate / hexane Zinc acetate dihydrate (0.01 mol, 2.195 g, 99.999% Sigma-Aldrich) and Al(acac)3 (0.172 g, 5 mol%) were added to 100 mL of ethanol. The solution was heated to a boil to dissolve the solids and obtain a clear solution.

[0065] After 2.5 hours, the solution was cooled. Then, lithium hydroxide (0.011 mol, 0.252 g) in 100 mL of ethanol was added over 10 minutes. The LiOH had been pre-dissolved in the ethanol by sonication for 15 minutes. The mixture was then stirred overnight for 16 hours.

[0066] 200 mL of the solution was then diluted to 900 mL with n-hexane to precipitate Al-doped ZnO, yielding a pale milky white solution. The precipitate was allowed to settle in the Al-doped ZnO / ethanol / hexane dispersion for 2 hours, and the supernatant was drained. The remaining dispersion was placed in two 50 mL centrifuge tubes and centrifuged at 7000 rpm for 5 minutes. After decantation, the white product in the tubes was rinsed with dry ethanol (2 mL x 2), and ethanol (dried on molecular sieves) was added to obtain a 2.5 wt% dispersion. The tubes were stirred to disperse the product, and in both cases, a clear solution was obtained. The solutions were combined and PVP(M w (=58,000) was added: Tube 1: 0.75 mL of 10% PVP 25,000 / EtOH per 10 mL of nanoparticle dispersion. Tube 2: 0.75 mL of 10% PVP 58,000 / EtOH per 10 mL of nanoparticle dispersion. The composition of ZnO-based nanoparticles is Li 0.07 Al 0.05 Zn 0.89 It was predicted to be O.

[0067] Example 4 - Preparation of 20 mol% Mg-doped ZnO nanoparticles from Zn / Mg acetate / hexane Zinc acetate dihydrate (0.01 mol, 2.195 g, Aldrich 99.999%) and magnesium acetate tetrahydrate (0.536 g, 20 mol%) were added to ethanol and refluxed for 2.5 hours to obtain a clear solution. The solution was then allowed to cool to room temperature.

[0068] Next, lithium hydroxide (0.011 mol, 0.299 g) was dissolved in 100 mL of ethanol and sonicated for approximately 15 minutes. This solution was then added to a zinc acetate / magnesium acetate tetrahydrate solution over 15 minutes with vigorous stirring. No significant changes occurred. This was then left to stir at room temperature overnight (22.5 hours).

[0069] No significant changes occurred after this period.

[0070] 200 mL of the solution was then diluted to 900 mL with n-hexane to precipitate Mg-doped ZnO, yielding a pale milky white solution. The precipitate was allowed to settle in a Mg-doped ZnO / ethanol / hexane dispersion for 2 hours, and the supernatant was drained. The remaining dispersion was placed in two 50 mL centrifuge tubes and centrifuged at 7000 rpm for 5 minutes. After decantation, the white product in the tubes was rinsed with dry ethanol (2 mL x 2), and ethanol (dried on molecular sieves) was added to obtain a 2.5 wt% dispersion. The tubes were stirred to disperse the product, and in both cases, a clear solution was obtained. The solutions were combined and PVP(M w =25,000), and PVP(M w (=58,000) was added: Tube 1: 0.75 mL of 10% PVP 25,000 / EtOH per 10 mL of nanoparticle dispersion. Tube 2: 0.75 mL of 10% PVP 58,000 / EtOH per 10 mL of nanoparticle dispersion. The composition of ZnO-based nanoparticles is Li 0.07 Mg 0.2 Zn 0.765 It was predicted to be O.

[0071] QLED testing Example 5 Bottom-emitting red Cd-free QLEDs were fabricated using Mg0.15ZnO-based ETL containing PVP and PEO of different molecular weights as stabilizer polymers. The layer structure of the red QLEDs is as follows: Al (80 nm), ETL of approximately 50-80 nm, red Cd-free QD of approximately 15-20 nm, hole transport layer (HTL) of 20 nm, PEDOT:PSS (poly(3,4-ethylenedioxythiophene), poly(styrene-sulfonate)) of 40 nm, and indium tin oxide (ITO) of 100 nm. The ETL of each QLED does not contain PVP / PEO, and each contains M w 25,000 PVP, M w 58,000 PVP, and M w They had 50,000 PEO.

[0072] The QLED was tested, and the peak EQE and 10 mA / cm² were measured. 2 The EQE was measured at [location]. The results are shown in Figure 1. The peak EQE value is higher for each QLED and is represented by a square marker. 10 mA / cm 2 The EQE in this case is a lower value for each QLED and is represented by a circular marker. The best EQE performance is M w This was observed for 58,000 PVP. Voltage was also measured under the same conditions, and the results are shown in Figure 2. The voltage produced a peak EQE of 10 mA / cm². 2 This indicates the so-called "driving voltage" that gives the current density.

[0073] Example 6 Red Cd-free QLEDs were also produced using different Mg or M dopants in ETL ZnO nanoparticles, and using PVP with different molecular weights.

[0074] The QLED was tested, and the peak EQE and 10 mA / cm² were measured. 2The EQE was measured. The results are shown in Table 1 below. EQE values ​​are given in 1% units. Magnesium, aluminum, and gallium were used as dopants, respectively. M, y, and p refer to the formulas for ZnO-doped nanoparticles as described herein. Li may have been present in small amounts due to the ETL manufacturing method. The gallium-doped samples did not contain PVP / PEO. Voltage was also measured under the same conditions, and the results are shown in Table 2. Voltage is given in 0.25V units.

[0075] [Table 1]

[0076] [Table 2]

[0077] The dispersions with the highest EQE were Mg0.1ZnO(1367)+PVP25k; Mg0.15ZnO+PVP25k; Mg0.15ZnO+PVP58k; Mg0.2ZnO+PVP25k; Mg0.2ZnO+PVP58k; and Al0.05ZnO+PVP58k. Most driving voltages were less than 5V.

[0078] The detailed description above is provided for illustrative and illustrative purposes only and is not intended to limit the scope of the appended claims. Many modifications of the currently preferred embodiments shown herein will be obvious to those skilled in the art and remain within the scope of the appended claims and their equivalents.

Claims

1. A composition comprising ZnO-based nanoparticles, a polar organic solvent, and a polymer, The ZnO-based nanoparticles, formula Li ｘ Mg ｙ M ｐ Zn ｚ It has O, and in the formula, 0 ≤ x ≤ 0.2, 0 ≤ y + p ≤ 0.25, z = 1 - 0.5x - y - 1.5p, M is an element selected from gallium and / or aluminum. The polymer comprises polyvinylpyrrolidone (PVP) and / or poly(ethyloxazoline) (PEO), and the polymer has an average molecular weight M of 25,000 to 1,300,000 Da. ｗ A composition having the following characteristics.

2. The polymer has a molecular weight of 25,000 to 200,000 Da, preferably 25,000 to 100,000 Da, and more preferably 30,000 to 70,000 Da. ｗ The composition according to claim 1, having the following characteristics.

3. The polymer has an M of 45,000 to 65,000 Da. ｗ A composition according to claim 1 or claim 2, having the following characteristics.

4. The composition according to any prior claim, wherein the polymer comprises PVP.

5. The composition according to any one of claims 1 to 3, wherein p = 0 and y > 0.

6. The composition according to any one of claims 1 to 4, wherein y = 0 and p > 0, and preferably M is aluminum.

7. The composition according to any one of claims 1 to 6, wherein 0.05 ≤ y + p ≤ 0.25, preferably 0.10 ≤ y + p ≤ 0.20, and more preferably 0.15 ≤ y + p ≤ 0.

20.

8. The composition according to any one of claims 1 to 7, wherein the polar organic solvent comprises ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, or a mixture of two or more thereof, preferably ethanol and / or isopropanol.

9. The composition according to any one of claims 1 to 8, wherein the weight ratio of the ZnO-based nanoparticles to the polymer is 1:0.05 to 1:0.5, preferably 1:0.15 to 1:0.4, and more preferably 1:0.3 to 1:0.

4.

10. The composition according to any one of claims 1 to 9, wherein the composition comprises 0.1 to 10% by weight of the ZnO-based nanoparticles based on the total weight of the polar organic solvent.

11. The composition according to any one of claims 1 to 10, wherein the ZnO-based nanoparticles have an average particle size of 1 to 20 nm, preferably 1 to 10 nm.

12. The composition according to any one of claims 1 to 11, wherein 0 ≤ x ≤ 0.2, and preferably 0.01 ≤ x ≤ 0.

2.

13. A method for manufacturing an electron transport layer (ETL) for a quantum dot light-emitting diode (QLED), wherein the method is To provide the composition according to any one of claims 1 to 12, The objective is to provide a spin-coated composition by spin-coating the aforementioned composition, A method comprising annealing the spin-coated composition.

14. Use of the composition according to any one of claims 1 to 12 in the manufacture of an electron transport layer (ETL) for QLEDs.

15. An electron transport layer (ETL) for QLED, comprising ZnO-based nanoparticles and a polymer, wherein the ZnO-based nanoparticles have the formula Li ｘ Mg ｙ M ｐ Zn ｚ O, and in the formula 0 ≤ x ≤ 0.2, 0 ≤ y + p ≤ 0.25, z = 1 - 0.5x - y - 1.5p, M is an element selected from gallium and / or aluminum. The polymer comprises polyvinylpyrrolidone (PVP) and / or poly(ethyloxazoline) (PEO), and the polymer has an average molecular weight M of 25,000 to 1,300,000 Da. ｗ An electron transport layer (ETL) having the following characteristics.

16. The polymer has a molecular weight of 25,000 to 200,000 Da, preferably 25,000 to 100,000 Da, and more preferably 30,000 to 70,000 Da. ｗ The ETL according to claim 15, having the following characteristics.

17. The polymer has an M of 45,000 to 65,000 Da. ｗ The ETL according to claim 15 or claim 16, having the following characteristics.

18. The ETL according to any one of claims 15 to 17, wherein the polymer comprises PVP.

19. The ETL according to any one of claims 15 to 18, wherein p = 0 and y > 0.

20. The ETL according to any one of claims 15 to 18, wherein y = 0 and p > 0, and preferably M is aluminum.

21. The ETL according to any one of claims 15 to 20, wherein 0.05 ≤ y + p ≤ 0.25, preferably 0.10 ≤ y + p ≤ 0.20, and more preferably 0.15 ≤ y + p ≤ 0.

20.

22. The ETL according to any one of claims 15 to 21, wherein the weight ratio of the ZnO-based nanoparticles to the polymer is 1:0.05 to 1:0.5, preferably 1:0.15 to 1:0.4, and more preferably 1:0.3 to 1:0.

4.

23. The ETL according to any one of claims 15 to 22, wherein the ZnO-based nanoparticles have an average particle size of 1 to 20 nm, preferably 1 to 10 nm.

24. A QLED comprising an ETL according to any one of claims 15 to 23.

25. A visual display unit including the QLED described in claim 24.

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