Light-emitting diode comprising double-doped oxide hole injection layer and manufacturing method therefor

Abstract

The present invention relates to a light-emitting diode comprising a double-doped oxide hole injection layer and a manufacturing method therefor and, more specifically, to a light-emitting diode comprising a first electrode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and a second electrode, wherein the hole injection layer comprises a self-assembled monolayer (SAM) formed thereon and contains nickel oxide doped with nickel and magnesium.

Description

Light-emitting device comprising a double-doped oxide hole injection layer and a method for manufacturing the same

[0001] The present invention relates to a light-emitting device comprising a double-doped oxide hole injection layer and a method for manufacturing the same.

[0002]

[0003] Quantum dots (QDs) possess various advantages, including high color purity, a narrow emission bandwidth, tunable emission wavelength, solution processability, high photoluminescence quantum yield, and robust optical stability. These characteristics establish them as ideal candidates not only for quantum dot light-emitting diodes (QLEDs) but also for other applications such as biosensors and luminescent solar concentrators. In QLEDs, an electric field induces carrier injection from the electrodes into the QDs, forming excitons. These excitons emit photons as they relax from an excited state to a ground state. However, if charge balance is disrupted or excitons are quenched by other mechanisms, non-radiative recombination occurs, which can induce carrier recombination in adjacent layers and reduce luminous efficiency. Therefore, maintaining charge balance within the emissive layer is critical for optimal device performance.

[0004] Modern QLEDs generally utilize organic-based hole injection layers (HILs). However, these materials exhibit low stability when exposed to moisture, heat, and chemicals, leading to shortened device lifespans. In contrast, inorganic materials, particularly metal oxides, offer higher stability and light transmittance across the entire visible light spectrum. Consequently, p-type oxides such as CuO, MoO3, V2O5, and NiO are being studied as alternatives to organic HILs. Among these, NiO is known to possess intrinsic p-type conductivity regardless of doping. Furthermore, it combines excellent transparency in the visible light region with strong heat, chemical, and moisture resistance. Due to these advantages, NiO is a subject of extensive research as a potential HIL material. Nevertheless, there are several limitations hindering the practical application of NiO. For example, its low electrical conductivity and significant hole injection barriers to the HTL can lead to electron accumulation within the quantum dots (QDs). Such accumulation generates heat that can damage the device or induce recombination in HTLs (e.g., poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl)diphenylamine)](TFB)), which ultimately degrades overall performance. Furthermore, NiOOH species on the NiO surface promote non-radiative recombination through surface trap states. Therefore, to effectively replace organic HILs, it is essential to improve the electrical behavior of metal oxides, lower the hole injection barrier, and minimize surface defects.

[0005] In response to this, various doping strategies are being introduced to improve the properties of NiO. In particular, such doping is known to enhance the electrical conductivity of NiO and improve charge balance by shifting the valence electron band to deeper energy levels. Nevertheless, the performance of QLED devices remains insufficient, requiring further improvement. Among available deposition techniques, sputtering is known to produce smooth, high-quality thin films through excellent thickness control, while simultaneously enabling multi-target configurations for multi-component layer fabrication.

[0006]

[0007] The present invention aims to provide a light-emitting device that uses nickel oxide doped with lithium and magnesium by a sputtering method as a hole injection layer.

[0008] The technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art from the description below.

[0009]

[0010] To achieve the above objective, the present invention provides a light-emitting device comprising a first electrode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and a second electrode, wherein the hole transport layer comprises self-assembled monolayers (SAM) formed on the hole injection layer and comprises nickel oxide double-doped with nickel and magnesium.

[0011] The above self-assembled monolayer may include [2-(9H-carbazole-9-yl)ethyl]phosphonic acid (2PACz).

[0012] The hole injection layer can be formed by depositing nickel and magnesium-doped nickel oxide by co-sputtering a nickel oxide target containing lithium and a magnesium oxide target on the first electrode through radio frequency (RF) magnetron sputtering.

[0013] The nickel oxide target containing lithium can be sputtered with a power of 1 to 150 W, and the magnesium oxide target can be sputtered with a power of 1 to 150 W.

[0014] The thickness of the hole injection layer above may be 5 to 80 nm.

[0015] In the nickel and magnesium double-doped nickel oxide above, the lithium content may be 0.1% to 25% based on the total composition, and the magnesium content may be 0.1% to 25% based on the total composition.

[0016] In addition, the present invention provides a method for manufacturing a light-emitting device comprising the steps of: forming a first electrode on a substrate; forming a hole injection layer on the first electrode; forming a hole transport layer on the hole injection layer; forming a light-emitting layer on the hole transport layer; forming an electron transport layer on the light-emitting layer; and forming a second electrode on the electron transport layer, wherein the hole injection layer comprises a self-assembled monolayer formed on the hole injection layer and comprises nickel oxide doped with nickel and magnesium.

[0017] The step of forming a hole injection layer on the first electrode can be performed by co-sputtering a nickel oxide target containing lithium and a magnesium oxide target through radio frequency (RF) magnetron sputtering to deposit nickel oxide doped with nickel and magnesium, thereby forming the hole injection layer.

[0018] The nickel oxide target containing lithium can be sputtered with a power of 1 to 150 W, and the magnesium oxide target can be sputtered with a power of 1 to 150 W.

[0019] The step of forming a hole injection layer on the first electrode can be performed by sputtering under room temperature conditions in an argon-oxygen atmosphere, with a pressure of 1 to 20 mTorr and flow rates of argon gas and oxygen gas of 1 to 80 sccm.

[0020] The self-assembled monolayers (SAM) described above comprise [2-(9H-carbazole-9-yl)ethyl]phosphonic acid (2PACz), and the thickness of the self-assembled monolayers may be 1 to 5 nm.

[0021]

[0022] By means of the solution to the above problem, the present invention can manufacture a uniformly doped thin film through a sputtering method, and thereby provide a light-emitting device with improved performance.

[0023] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description in the claims.

[0024]

[0025] Figure 1 shows (a) a schematic diagram of the cavity sputtering process used for depositing NiMgLiO thin films, (b) a GIXRD spectrum of the NiMgLiO thin film showing the crystal structure, (c) an AFM image and RMS roughness of the ITO / NiMgLiO thin film deposited with 0W MgO sputtering power, and (d) an AFM image and RMS roughness of the ITO / NiMgLiO thin film deposited with 6W MgO sputtering power.

[0026] Figure 2 shows the results of atomic force microscopy (AFM) analysis showing the RMS (root mean square) roughness of (a) bare ITO, (b) ITO / NiMgLiO with 3W MgO sputtering power, and (c) ITO / NiMgLiO with 9W MgO sputtering power.

[0027] Figure 3 shows the XPS spectrum of a NiMgLiO+2PACz thin film showing the effect of MgO sputtering power on the surface composition, with (a) Ni 2p 3 / 2 Spectrum (dotted line is Ni) 2+ and Ni 3+ (b) C 1s spectrum (indicating the position), (c) Mg 1s spectrum (indicating the characteristic carbon bonding environment), and (c) Mg 1s spectrum (indicating changes in Mg incorporation).

[0028] Figure 4 shows the XPS spectra of NiMgLiO+2PACz thin films as a function of MgO sputtering power. (a) Ni 2p 3 / 2 Spectrum, (b) C 1s spectrum showing carbon bonds, (c) Mg 1s spectrum showing magnesium bonds, (d) Li 1s, (e) P 2p spectrum highlighting the chemical state of phosphorus in 2PACz, (f) N 1s spectrum showing the nitrogen bonding environment.

[0029] Figure 5 shows (a) a Tauc plot of a NiMgLiO thin film, (b) a UPS spectrum of a NiMgLiO thin film (secondary electron block (left) and Fermi edge (right)), (c) an energy level diagram of a NiMgLiO thin film, (d) a steady-state PL spectrum of glass / NiMgLiO+2PACz / QD with an MgO sputtering power of 0.6 W, (e) a glass / NiMgLiO+2PACz / TFB / QD with an MgO sputtering power of 0.6 W, and (f) a TRPL spectrum of glass / NiMgLiO+2PACz / TFB / QD with an MgO sputtering power of 0.6 W.

[0030] Figure 6 shows (a) the UPS spectrum of the NiMgLiO+2PACz thin film (secondary electron blocking (left) and Fermi edge (right)), (b) the energy level diagram of the NiMgLiO+2PACz thin film, (c) the steady-state PL spectrum, and (d) the TRPL spectrum of the glass / NiMgLiO+2PACz / TFB / QD thin film.

[0031] Figure 7 shows (a) the JV characteristics of an ITO / NiMgLiO+2PACz / Au device, (b) the conductivity of a NiMgLiO+2PACz thin film derived from Hall measurements, (c) the JV characteristics of an HOD with an ITO / NiMgLiO+2PACz / TFB / QD / MoO3 / Ag structure and an EOD with an ITO / ZnO / QD / ZnMgO / Al structure at 0W and 6W MgO sputtering powers, and (d) the impedance spectrum of a QLED with a NiMgLiO HIL at various MgO sputtering powers.

[0032] Figure 8 shows (a) the current density-voltage (JV) characteristics of an ITO / NiMgLiO / Au device, (b) the conductivity values ​​extracted from Figure 7(a) (ITO / NiMgLiO+2PACz / Au), (c) the conductivity values ​​derived from Figure 8a, and (d) the JV characteristics of an ITO / NiMgLiO+2PACz / TFB / QD / MoO₃ / Ag HOD.

[0033] Figure 9 shows the results of a comparison of reported green QLED performance indicators, including EQE and luminance, highlighting (a) a schematic diagram of the ITO / NiMgLiO+2PACz / TFB / QD / ZnMgO / Al QLED device structure, (b) an energy level diagram of the QLED, (c) JVL characteristics, (d) EQE-luminance-current efficiency characteristics, (e) a histogram of EQE values ​​of a QLED with a sputtered NiMgLiO+2PACz thin film at 6W MgO power, and (f) a device using a sputtered NiO-based HIL.

[0034] Figure 10 shows the performance of a SAM-free QLED (without 2PACz) with an ITO / NiMgLiO / TFB / QD / ZnMgO / Al structure at various MgO sputtering powers, and shows a box chart showing (a) JVL characteristics, (b) EQE-luminance-current efficiency characteristics, and (c) EQE distribution.

[0035] Figure 11 compares the performance of QLEDs with various HILs (NiMgLiO3+2PACz(MgO 6W), PEDOT:PSS and 2PACz) in an ITO / HIL / TFB / QD / ZnMgO / Al structure, showing (a) JVL characteristics, (b) EQE-luminance-current efficiency characteristics, and (c) a box chart showing the distribution of EQE.

[0036] Figure 12 shows the operating life of a QLED with various HIL layers (NiMgLiO+2PACz or PEDOT:PSS deposited with MgO sputtering power of 0W and 6W).

[0037]

[0038] The terms used in this invention have been selected based on currently widely used general terms, taking into account their functions within the invention; however, these terms may vary depending on the intent of those skilled in the art, case law, the emergence of new technologies, etc. Additionally, in specific cases, terms have been arbitrarily selected by the applicant, and in such cases, their meanings will be described in detail in the relevant description of the invention. Therefore, the terms used in this invention should be defined not merely by their names, but based on their meanings and the overall content of the invention.

[0039] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0040] When a part of a specification is described as “comprising” a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0041] Embodiments of the present invention are described below with reference to the attached drawings so that those skilled in the art can easily implement them. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0042]

[0043] The present invention will be described in detail below.

[0044]

[0045] The present invention provides a light-emitting device comprising a first electrode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and a second electrode, wherein the hole transport layer comprises self-assembled monolayers (SAM) formed on the hole injection layer and comprises nickel oxide double-doped with nickel and magnesium.

[0046] The self-assembled monolayer may include [2-(9H-carbazole-9-yl)ethyl]phosphonic acid (2PACz). The self-assembled monolayer can passivate surface defects of the hole injection layer and lower the hole injection barrier by changing the state of nickel oxide and shifting the energy level to a deeper position.

[0047] The hole injection layer can be formed by depositing nickel and magnesium double-doped nickel oxide by co-sputtering a nickel oxide target containing lithium and a magnesium oxide target on the first electrode through radio frequency (RF) magnetron sputtering.

[0048] By using the above nickel and magnesium double-doped nickel oxide as a hole injection layer, the electrical and optical properties of the oxide-based hole injection layer can be improved. When lithium is introduced into nickel oxide (NiO), Ni 2+ Ni ions 3+ It is oxidized into a species to maintain charge balance, and this is Ni 3+ Concentration can be increased to improve electrical properties. At the same time, magnesium oxide (MgO), which has a wide bandgap of 7.8 eV, can shift the valence band maximum (VBM) of nickel oxide to deeper energy levels when added as a dopant. The addition of magnesium can improve the electrical conductivity of nickel oxide thin films. The increase in conductivity due to magnesium doping is related to Ni 3+ This is because the p-type conductivity of nickel and magnesium double-doped nickel oxide improves as the ion concentration increases. Therefore, the double doping of lithium and magnesium is Ni 3+ By increasing ion concentration, deepening the VBM, and improving electrical conductivity, the hole injection barrier can be reduced, thereby enhancing the electrical performance of nickel oxide thin films. This ultimately improves charge balance within the quantum dot layer, which is essential for stable and efficient device operation.

[0049] The nickel oxide target containing lithium can be sputtered with a power of 1 to 150 W, and the magnesium oxide target can be sputtered with a power of 1 to 150 W. Preferably, it can be sputtered with a power of 30 to 70 W, and the magnesium oxide target can be sputtered with a power of 1 to 20 W.

[0050] The nickel oxide target containing the above lithium may contain 0.1 to 15 at% of lithium. Preferably, it may contain 1 to 10 at% of lithium, and more preferably, 2 to 7 at% of lithium, but is not limited thereto.

[0051] According to one embodiment of the present invention, the light-emitting layer may be a quantum dot light-emitting layer.

[0052] The above quantum dots may be one or more selected from the group consisting of CdSe / ZnS, InP / ZnSe / ZnS, CdZnSe / CdZnS, CdSe / CdZnS / ZnS, ZnSe / CdS / ZnS, ZnCdSe / ZnSe / ZnS, CdZnSe / CdZnS / ZnS, ZnSeTe / ZnSe / ZnS, ZnSe / ZnS, InP / GaP / Zns, AgGaInS2, and CuInZnS / ZnS, and preferably may be CdSe / ZnS, but is not limited thereto.

[0053] The thickness of the hole injection layer above may be 5 to 80 nm.

[0054] In the nickel and magnesium double-doped nickel oxide above, the lithium content may be 0.1% to 25% based on the total composition, and the magnesium content may be 0.1% to 25% based on the total composition.

[0055] The light-emitting device according to the present invention can be applied to optoelectronic devices such as quantum dot light-emitting diodes (QLEDs), organic light-emitting diodes (OLEDs), perovskite light-emitting diodes (PELEDs), perovskite solar cells, and photodetectors.

[0056] According to one embodiment of the present invention, the light-emitting element may be a nickel oxide-based green quantum dot light-emitting element manufactured by a sputtering method.

[0057] The light-emitting device according to the present invention can control the electronic structure and improve charge transport characteristics by co-doping Mg and Li into a NiO matrix. This co-doping method is Ni 3+ By significantly increasing the ion concentration and deepening the valence band maximum, the hole injection barrier can be lowered, and the electrical conductivity of the nickel oxide thin film can be improved. This modification can promote charge injection into the quantum dot emissive layer in a more balanced manner, thereby improving device efficiency.

[0058] The above light-emitting device may have a maximum external quantum efficiency (EQE) of 9% or higher and a maximum brightness of 55,000 cd / m² 2 Magnesium doping can shift the VBM to deeper energy levels, thereby improving hole injection and achieving better charge balance in the emissive layer, and this improved balance can reduce exciton quenching and promote more efficient radiative recombination.

[0059] 100 mA / cm of the above light-emitting element 2 The expected lifespan can be over 1,000 hours. This improvement is attributed to improved electrical characteristics and improved charge balance within the device.

[0060] In addition, the present invention provides a method for manufacturing a light-emitting device comprising the steps of: forming a first electrode on a substrate; forming a hole injection layer on the first electrode; forming a hole transport layer on the hole injection layer; forming a light-emitting layer on the hole transport layer; forming an electron transport layer on the light-emitting layer; and forming a second electrode on the electron transport layer, wherein the hole injection layer comprises a self-assembled monolayer formed on the hole injection layer and comprises nickel oxide double-doped with nickel and magnesium.

[0061] The first electrode may be ITO (Indium Tin Oxide). The substrate coated with the ITO may be washed with detergent, acetone, ethanol, and deionized water for 5 to 15 minutes each, dried with a nitrogen gun, and then treated with UV-ozone for 20 to 40 minutes to remove residues and enhance hydrophilicity.

[0062] The step of forming a hole injection layer on the first electrode can be performed by co-sputtering a nickel oxide target containing lithium and a magnesium oxide target through radio frequency (RF) magnetron sputtering to deposit nickel oxide double-doped with nickel and magnesium, thereby forming the hole injection layer.

[0063] The nickel oxide target containing lithium can be sputtered at a power of 1 to 150 W, and the magnesium oxide target can be sputtered at a power of 1 to 150 W. Preferably, the nickel oxide target can be sputtered at a power of 30 to 70 W, and the magnesium oxide target can be sputtered at a power of 1 to 20 W. When the magnesium oxide target is sputtered at a power within the above range, the surface morphology can be improved, and the surface smoothness can be best. This improvement is attributed to the reduced thin film growth rate during the sputtering of magnesium oxide, which can facilitate more uniform deposition and better step coverage. Additionally, if the sputtering power of the magnesium oxide target is less than the above range, magnesium may not be sufficiently deposited.

[0064] The step of forming a hole injection layer on the first electrode can be performed by sputtering under room temperature conditions in an argon-oxygen atmosphere, with a pressure of 1 to 20 mTorr and flow rates of argon gas and oxygen gas of 1 to 80 sccm.

[0065] The step of forming self-assembled monolayers (SAM) on the hole injection layer may include: spin-coating a self-assembled monolayer precursor solution dissolved in anhydrous ethanol at 2000 to 4000 rpm for 10 to 60 seconds; annealing at 80 to 120 ℃ for 5 to 15 minutes after spin-coating; and spin-coating with ethanol at 5000 to 7000 rpm for 20 to 60 seconds after annealing to remove weakly bound 2PACz.

[0066] The self-assembled monolayers (SAM) described above comprise [2-(9H-carbazole-9-yl)ethyl]phosphonic acid (2PACz), and the thickness of the self-assembled monolayers may be 1 to 5 nm.

[0067] The step of forming a hole transport layer on the self-assembled monolayer above can be performed by spin-coating TFB (poly(9,9-dioctylfluorene-alt-N-(4-sec-butylphenyl)-diphenylamine) dissolved in chlorobenzene at 3000 to 5000 rpm for 20 to 50 seconds and annealing at 100 to 200 ℃ for 20 to 40 minutes to form the hole transport layer.

[0068] According to one embodiment of the present invention, the light-emitting layer may be a quantum dot light-emitting layer.

[0069] The above quantum dots may be one or more selected from the group consisting of CdSe / ZnS, InP / ZnSe / ZnS, CdZnSe / CdZnS, CdSe / CdZnS / ZnS, ZnSe / CdS / ZnS, ZnCdSe / ZnSe / ZnS, CdZnSe / CdZnS / ZnS, ZnSeTe / ZnSe / ZnS, ZnSe / ZnS, InP / GaP / Zns, AgGaInS2, and CuInZnS / ZnS, and preferably may be CdSe / ZnS, but is not limited thereto.

[0070] According to one embodiment of the present invention, the step of forming a light-emitting layer on the hole transport layer can be performed by spin-coating quantum dots dispersed in hexane at 1000 to 3000 rpm for 10 to 30 seconds and then annealing at 60 to 100 ℃ for 10 to 30 minutes.

[0071] The electron transport layer facilitates electron injection from the cathode and serves to transfer electrons to the light-emitting layer. According to one embodiment of the present invention, the electron transport layer may be zinc magnesium oxide (ZnMgO).

[0072] According to one embodiment of the present invention, the step of forming an electron transport layer on the light-emitting layer may be performed by dispersing zinc magnesium oxide in anhydrous ethanol, spin-coating at 1500 to 4000 rpm for 40 to 80 seconds, and then annealing at 60 to 100 ℃ for 10 to 40 minutes to form the electron transport layer.

[0073] The second electrode above may be aluminum (Al).

[0074] According to one embodiment of the present invention, the step of forming a second electrode on the electron transport layer comprises 1x10 aluminum having a thickness of 80 to 120 nm. -7 It can be deposited via thermal deposition at a growth rate of 1 to 5 Å / s at a pressure of less than torr.

[0075] Hereinafter, the present invention will be described in detail with reference to examples to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention is not to be interpreted as being limited to the embodiments described below. The embodiments of this specification are provided to more completely explain the present invention to those with average knowledge in the art.

[0076]

[0077] <Example>

[0078] ingredient

[0079] Li-doped NiO (5 at%) target (2 inch diameter, 5 mm thickness), MgO target (99.99%, 2 inch diameter, 5 mm thickness), Al pellets (99.999%), Ag granules (99.99%, 3–5 nm), Indium Tin Oxide (ITO) coated glass substrate (50 nm thickness, sheet resistance: 27–30 Ω), Zinc acetate dihydrate (99%), Magnesium acetate tetrahydrate (98%), Tetramethylammonium hydroxide pentahydrate (TMAH, 97%), Dimethyl sulfoxide (DMSO, 99.9%), MoO3 (99.5%), TFB (OMI259BE), Green CdSe / ZnS (CZO-530H) QDs dispersed in n-hexane, n-hexane (95%) and ethanol (99.9%), 2PACz (>98%)

[0080]

[0081] <Preparation Example> Preparation of ZnMgO nanoparticles

[0082] ZnMgO nanoparticles were prepared by dissolving zinc acetate dihydrate (8.5 mmol) and magnesium acetate tetrahydrate (1.5 mmol) in 40 mL of DMSO. Separately, 10 mmol of TMAH was dissolved in 10 mL of anhydrous ethanol. This TMAH solution was added to the DMSO mixture at a rate of 1 mL / min using a syringe pump, and the mixture was stirred continuously at room temperature for 1 hour. The resulting nanoparticles were precipitated by adding acetone, and then centrifuged to remove residual impurities. Finally, the ZnMgO nanoparticles were redispersed in anhydrous ethanol at a concentration of 30 g / L, filtered through a 0.2 μm polytetrafluoroethylene membrane, and refrigerated until use.

[0083]

[0084] <Example 1> Preparation of NiMgLiO Thin Film

[0085] The ITO-coated glass substrate was ultrasonically cleaned using a detergent diluted in distilled water, followed by sequential treatment with acetone, ethanol, and distilled water for 10 minutes each. The cleaned substrate was dried with a nitrogen gun and treated with ultraviolet (UV) ozone for 30 minutes. Co-sputtered NiMgLiO thin films were deposited via radio frequency (RF) magnetron sputtering by maintaining a constant power of 50 W on a lithium-doped NiO (5 at%) target and adjusting the RF power applied to the MgO target to 0, 3, 6, or 9 W. During deposition, the substrate temperature was maintained at room temperature in an Ar-O2 atmosphere, the total pressure was maintained at 5 mTorr, and the gas flow rate of Ar and O2 (1:1 ratio) was maintained at 18 sccm. No post-deposition treatment was performed.

[0086]

[0087] <Example 2> Fabrication of a light-emitting device containing a NiMgLiO thin film

[0088] After depositing the NiMgLiO layer, the substrate was transferred to a glove box filled with nitrogen. A 2PACz solution (dissolved in anhydrous ethanol at a concentration of 0.5 mg / mL) was spin-coated onto the NiMgLiO layer at 3000 rpm for 30 seconds, followed by heat treatment at 100 °C for 10 minutes. To remove weakly bound 2PACz, ethanol was spin-coated at 6000 rpm for 30 seconds. A TFB solution (dissolved in chlorobenzene at a concentration of 8 mg / mL) was spin-coated at 4000 rpm for 30 seconds, followed by heat treatment at 150 °C for 30 minutes. CdSe / ZnS quantum dots were deposited by spin-coating a hexane dispersion at 2000 rpm for 20 seconds, followed by annealing at 80 °C for 20 minutes. ZnMgO nanoparticles dispersed in ethanol were spin-coated at 3000 rpm for 60 seconds and then annealed at 80 °C for 30 minutes. Finally, a 100 nm thick aluminum anode was subjected to a high vacuum (<1 × 10⁻⁶ -7Thermal evaporation was performed at a deposition rate of 2-2.5 Å / s in Torr. Subsequently, the device was encapsulated using a UV-curing resin and measured without an additional aging process.

[0089] A device composed of glass / ITO / NiMgLiO+2PACz / Au was fabricated for conductivity measurement. 2 × 10⁻⁶ Au (100 nm) -6 It was deposited at a rate of 1.0 Å / s under a vacuum of less than Pa. Hole-only devices (HODs) with a glass / ITO / NiMgLiO+2PACz / TFB / QD / MoO3 / Ag structure were also fabricated. MoO3 (10 nm) and Ag (100 nm) were deposited at rates of 0.1 Å / s and 1.0 Å / s, respectively.

[0090]

[0091] <Comparative Example 1> Preparation of NiLiO Thin Film

[0092] The ITO-coated glass substrate was ultrasonically cleaned using a detergent diluted in distilled water, and then sequentially treated with acetone, ethanol, and distilled water for 10 minutes each. The cleaned substrate was dried with a nitrogen gun and treated with ultraviolet (UV) ozone for 30 minutes. NiLiO thin films were deposited on a lithium-doped NiO (5 at%) target via radio frequency (RF) magnetron sputtering at a constant power of 50 W. During deposition, the substrate temperature was maintained at room temperature in an Ar-O2 atmosphere, the total pressure was maintained at 5 mTorr, and the gas flow rates of Ar and O2 (1:1 ratio) were kept constant at 18 sccm. No post-deposition treatment was performed.

[0093]

[0094] <Comparative Example 2> Fabrication of a light-emitting device containing a NiLiO thin film

[0095] It was prepared in the same manner as Example 2, except that a substrate on which the NiLiO thin film prepared in Comparative Example 1 was deposited was used.

[0096]

[0097] <Experimental Example 1> GIXRD and AFM Analysis of NiMgLiO Thin Films

[0098] Figure 1a shows the deposition process of a NiMgLiO thin film serving as the hole injection layer (HIL) for a QLED. This thin film was deposited using RF magnetron co-sputtering without applying additional heating to the substrate. To fabricate the NiMgLiO thin film, a NiO target containing 5 at% Li and a separate MgO target were co-sputtered simultaneously. The RF power of the NiLiO target was kept constant at 50 W, while the power applied to the MgO target was varied stepwise to 0, 3, 6, and 9 W to control the Mg content. The growth rates measured throughout the deposition process were 2.50, 2.17, 2.22, and 2.25 nm / min at MgO sputtering powers of 0, 3, 6, and 9 W, respectively. Meanwhile, the total thin film thickness was consistently maintained at 55 nm under all conditions.

[0099] As shown in Fig. 1b, the structural phase of the co-sputtered thin film was investigated using GIXRD. According to the JCPDS pattern for NiO (No. 00-047-1049), the deposited thin film exhibited a single-phase rock salt NiO structure. However, upon co-sputtering with MgO, the intensity of the (200) diffraction peak decreased, and as indicated by the XRD data, the preferential orientation gradually shifted toward the (111) plane. In particular, in the rock salt structure, the (200) plane has a higher atomic packing density than the (111) plane, but the (111) plane grows faster because it generally has lower surface energy. At an MgO sputtering power of 0 W, the thin film growth rate was high enough to promote crystal growth along the (200) direction, which is less kinetically favorable. In contrast, the introduction of MgO reduced the overall deposition rate, resulting in preferential growth along the (111) direction, which is energetically and kinetically advantageous under low flux conditions.

[0100] AFM measurements were performed to evaluate the surface roughness of the thin films after sputtering (Figs. 1(c), 1(d), and 2). The RMS (Root Mean Square) roughness values ​​were 0.768 nm for the bare ITO substrate and 0.943 nm, 0.854 nm, 0.639 nm, and 0.706 nm for the thin films deposited at MgO sputtering powers of 0 W, 3 W, 6 W, and 9 W, respectively. These results indicate that MgO co-sputtering improves surface morphology, with the most pronounced smoothing observed at 6 W. This improvement is attributed to the reduced thin film growth rate during MgO co-sputtering, which facilitates more uniform deposition and better step coverage. Additionally, Mg incorporation suppresses NiO particle aggregation, which can reduce surface defects and minimize leakage paths when the thin film is used as a HIL in QLEDs.

[0101]

[0102] <Experimental Example 2> XPS Analysis of NiMgLiO+2PACz Thin Film

[0103] XPS analysis was performed on NiMgLiO + 2PACz thin films to investigate surface chemical changes induced by Mg doping (Figs. 3 and 4). Ni 2p 3 / 2 The XPS spectrum shows Ni with satellite peaks due to multiplexing of transition metal energy levels. 2+ (NiO) and Ni 3+ It was decomposed into peaks corresponding to (related to Ni2O3 and NiOOH) (Figs. 3a and 4a). As the MgO sputtering power increased, Ni 3+ / Ni 2+ An increase in the ratio was observed, which is Ni in the lattice. 2+ g Mg 2+ This is because it was substituted with . In particular, as indicated in Table 1, this substitution is Mg 2+ (0.72 Å) and Ni 2+The mismatch in ionic radius between (0.69 Å) causes lattice distortion and is accompanied by an increase in nickel vacancy concentration.

[0104] FilmsNi ratio (%)Li ratio (%)Mg ratio (%)Ni 3+ / Ni 2+ MgO 0 W+2PACz77.9122.0902.78MgO 3 W+2PACz78.8821.1202.84MgO 6 W+2PACz83.1915.930.882.93MgO 9 W+2PACz81.7516.751.502.88MgO 0 W3.25MgO6W3.85

[0105]

[0106] Also, Ni 2p 3 / 2 The peak shifted toward a binding energy approximately 0.15 eV higher, which is Ni 3+ This appears to reflect a decrease in surface electron density due to the increased content. However, as the MgO sputtering power increases, Ni 3+ The fraction decreased slightly. This trend is due to the presence of Mg lowering the formation energy of oxygen vacancies, thereby inhibiting the formation of nickel vacancies. After self-assembled monolayer (SAM) treatment, Ni 3+ The fraction decreased further. This decrease is due to the consumption of NiOOH and passivation of surface defects caused by the interaction between the hydroxyl group (-OH) of the phosphonic acid head group of 2PACz and the NiOOH species on the NiO surface. Additionally, the core-level binding energy shifted to a higher value after SAM deposition compared to a surface without SAM, which is because the strong dipole moment of 2PACz attracts electrons from the surface, lowering the local electron density.

[0107] In the absence of 2PACz, the C 1s spectrum exhibited peaks attributed to CC, COC, and C=O bonds, which are likely related to residual surface contamination. After SAM deposition, additional peaks corresponding to CP and CN bonds appeared, confirming the presence of 2PACz (Figs. 3b and 4b). The intensity of the Mg 1s peak increased with increasing MgO sputtering power, indicating that there was more Mg bonding (Figs. 3c and 4c). At a sputtering power of 3W, no Mg was detected, suggesting that the deposition was insufficient. On the other hand, at 6W and 9W, the Mg content increased to approximately 0.88% and 1.50%, respectively, as summarized in Table 1.

[0108] The Li 1s spectrum confirmed the presence of Li under all deposition conditions, indicating that Li was effectively absorbed from the sputtering target (Fig. 4d). In addition, the appearance of P 2p and N 1s signals confirmed that the 2PACz layer was successfully integrated (Figs. 4e and 4f).

[0109] The optical bandgap of the NiMgLiO thin films was measured by converting absorbance data into a Tauc plot (Fig. 5a). Pure NiLiO exhibited a bandgap of 3.64 eV, whereas all co-sputtered NiMgLiO thin films exhibited a consistent bandgap of 3.72 eV regardless of Mg content.

[0110]

[0111] <Experimental Example 3> Analysis of VBM and Fermi Energy Levels of NiMgLiO+2PACz and NiMgLiO Thin Films

[0112] The valence band maximum (VBM) and Fermi energy levels of the NiMgLiO+2PACz and NiMgLiO thin films were evaluated using UPS (Figs. 6a and 5b). The work function (Φ) was calculated using the following equation.

[0113] Work function (Φ) = hν - (Ecutoff - E F ).

[0114] The work function of the NiMgLiO+2PACz thin film was 4.77 eV at an MgO sputtering power of 0 W. As the MgO sputtering power was increased to 3, 6, and 9 W, it rose to 4.80, 4.83, and 4.78 eV, respectively. Meanwhile, VBM is VBM = hν - (E cutoff - E onset It was determined using ) and shifted to -5.75, -5.78, and -5.76 eV, respectively, as the MgO sputtering power increased. In the absence of 2PACz, the work function was 4.68, 4.80, 4.74, and 4.73 eV at 0, 3, 6, and 9 W, respectively, and the corresponding VBM values ​​were -5.44, -5.46, -5.47, and -5.46 eV. This trend is attributed to the inherent characteristics of MgO, which has a wide bandgap (~7.8 eV) and a VBM deeper than that of NiO. As Mg is bonded to the NiO matrix, the overall VBM shifts downward accordingly. Introducing 2PACz at a given MgO power results in an additional work function and a deeper VBM, which is consistent with the surface dipole effect of SAM.

[0115] This deeper VBM alignment lowers the hole injection barrier at the HTL and TFB interfaces, thereby enhancing hole injection. The energy level diagram of the NiMgLiO+2PACz thin film was constructed using the optical bandgap (Fig. 5a) and UPS data (Figs. 6a and 5b), which are presented in Figs. 6b and 5c.

[0116] The effect of MgO sputtering power on the interfacial and optical properties of the thin films was evaluated by performing steady-state PL and time-resolved PL (TRPL) measurements (Figs. 6c, d and Figs. 5d-f). Although Mg was incorporated into the NiMgLiO+2PACz and NiMgLiO thin films, no peak shift was observed compared to the original NiLiO. However, the Mg-doped thin films exhibited enhanced PL intensity. In particular, in the TRPL spectrum, decay components A1, A2, and A3 correspond to surface trap-mediated non-radiative recombination (τ1), inter-band radiative recombination (τ2), and deep trap-assisted recombination (τ3), respectively. In the presence of 2PACz, increasing the MgO power from 0 W to 6 W resulted in a decrease in A1 from 28.66% to 16.51%, an increase in A2 from 41.11% to 59.84%, and τ avg While α increases from 8.06 ns to 9.75 ns, τ2 increases from 7.93 ns to 9.12 ns (Fig. 6d). In the absence of 2PACz, increasing from 0 W to 6 W causes A1 to decrease from 49.51% to 42.73%. A2 increases from 28.40% to 39.61%, and τ avg τ2 increases from 6.05 ns to 7.02 ns, and increases from 8.21 ns to 9.18 ns (Table 2). These results suggest that Mg doping and SAM functionalization mitigate surface defects and improve interfacial charge carrier dynamics.

[0117] τ1(ns)A1(%)τ2(ns)A2(%)τ3(ns)A3(%)τ ave (ns)MgO 0W0.3449.518.2128.4016.0522.086.05MgO 6W0.4142.739.1839.6118.1917.667.02MgO 0W+2PACz0.4828.667.9341.1115.4130.238.06MgO 6W+2PACz0.6916.519.1259.8417.6823.659.75

[0118]

[0119] <Experimental Example 4> Analysis of Electrical Conductivity of NiMgLiO According to MgO Sputtering Power

[0120] To evaluate the electrical conductivity of NiMgLiO according to MgO sputtering power, devices with ITO / NiMgLiO+2PACz / Au and ITO / NiMgLiO / Au structures were fabricated as shown in Figs. 7a and 8a. In both structures, the current density showed the same order of 6W > ​​9W > 3W > 0W, regardless of whether 2PACz was functionalized. The extracted conductivity also showed this trend (Figs. 8b and c). The increase in conductivity due to Mg doping was Ni 3+ This is presumed to be because the p-type conductivity of NiMgLiO improves as the ion concentration increases. Additionally, the downward shift of the VBM due to Mg doping facilitates hole injection, contributing to the improvement of electrical performance. Results of Hall effect measurements performed on NiMgLiO+2PACz thin films (Fig. 7b) showed that the conductivity of the Mg-doped samples increased significantly compared to undoped NiLiO, which is due to Ni 3+ It further supports the role of facilitating charge transport.

[0121]

[0122] <Experimental Example 5> Evaluation of Hole Injection and Charge Balance in QLED Structure

[0123] To evaluate hole injection and charge balance in QLED structures, HODs and electron-only devices (EODs) with ITO / NiMgLiO+2PACz / TFB / QD / MoO3 / Ag and ITO / ZnO / QD / ZnMgO / Al structures were fabricated (Figs. 7c and 8d). The HODs exhibited enhanced hole injection at a MgO sputtering power of 6 W, which is consistent with the conductivity results. Although ZnMgO in the EOD structure possesses high electron concentration and mobility, the samples sputtered at 6 W showed similar injection characteristics, indicating improved charge balance. Impedance measurements were performed to evaluate the hole injection capability and electrical characteristics of the QLEDs (Fig. 7d). As the MgO sputtering power increased, the device resistance decreased, indicating that hole injection from the NiMgLiO+2PACz HIL to the TFB was facilitated. Among all conditions, the NiMgLiO thin film co-sputtered with MgO at 6 W exhibited the lowest resistance. These results suggest that the NiMgLiO thin film co-sputtered with MgO at 6 W provides optimal electrical performance and promotes more balanced charge injection in QLEDs.

[0124]

[0125] <Experimental Example 6> Performance evaluation of electroluminescent device according to MgO sputtering power

[0126] To evaluate the performance of the electroluminescent device according to the MgO sputtering power, a green QLED with an ITO / NiMgLiO+2PACz / TFB / QD / ZnMgO / Al structure was fabricated. Here, the NiMgLiO+2PACz layer acts as a hole injection layer (HIL) as shown in Fig. 9a. The energy level diagram in Fig. 9b shows a downward energy shift of approximately 0.29 eV due to the strong dipole moment of 2PACz, which facilitates hole injection from the NiMgLiO layer to the TFB layer.

[0127]

[0128] <Experimental Example 7> JVL ​​characteristics of QLEDs fabricated with various MgO sputtering powers

[0129] The JVL characteristics of QLEDs fabricated with various MgO sputtering powers are presented in Fig. 9c, and the corresponding EQE, luminance, and current efficiency are shown in Fig. 9d. In particular, a device containing NiLiO+2PACz without Mg doping exhibited a turn-on voltage of approximately 3.0 V, a maximum energy efficiency (EQE) of 6.83%, and 41,711 cd / m² 2 It exhibited a maximum brightness. In contrast, a device containing a NiMgLiO+2PACz thin film deposited with an MgO sputtering power of 6 W showed significantly improved performance, such as a decrease in turn-on voltage to approximately 2.5 V. The maximum EQE increased to 9.02%, approximately 1.32 times higher, and the brightness improved by approximately 1.38 times to 57,636 cd / m². 2 It reached. The performance of NiMgLiO without 2PACz is shown in Fig. 10. At an MgO power of 6 W, NiMgLiO HIL exhibited a turn-on voltage of 4.0 V, an EQE of 2.54%, and 21,869 cd / m². 2 It indicates the brightness to emphasize the interface role of 2PACz. As shown in Fig. 11, the device using only 2PACz exhibits a turn-on voltage of 3.0 V, an EQE of 4.21%, and 32,786 cd / m². 2The brightness was shown. For external benchmarking using conventional HIL, the PEDOT:PSS device exhibited a turn-on voltage of 3.0 V, an EQE of 4.85%, and a brightness of 36,650 cd / m² (Fig. 11). This improvement is attributed to the Mg doping effect, which shifts the VBM to deeper energy levels to improve hole injection and achieve better charge balance in the QD layer. This improved balance reduces exciton quenching and promotes more efficient radiative recombination. To evaluate the reproducibility of the improved performance, 10 QLEDs containing NiMgLiO+2PACz HIL deposited with an MgO sputtering power of 6 W were fabricated and characterized. As can be seen in Fig. 9e, this device exhibited a narrow EQE distribution with an average EQE of 8.53%, confirming the high uniformity and reliability of the cavity-sputtering process. A summary of device performance according to various MgO sputtering powers is presented in Table 3.

[0130] HILEQE max (%)L max (cd / m 2 )CE max (cd / A)MgO 0 W6.834171128.22MgO 3 W7.344458029.99MgO 6 W9.025763636.84MgO 9 W8.354560834.23

[0131] The QLED device lifetime was measured as shown in Fig. 12. PEDOT:PSS L0 = 5,028 cd / m² 2 T at 182 seconds 50 NiLiO showed a T of 851 seconds at a current density of 100 mA / cm². 50 9,255 cd / m 2 Represents the initial luminance of. 100 mA / cm 2 At NiMgLiO(MgO 6 W), L0 = 10,840 cd / m² 2 T at 911 seconds 50 Represents. Lifetime scaling relationship L n T50 = If using the constant (n=1.8), 100 cd / m 2 The expected lifetime of PEDOT:PSS is approximately 58 hours, NiLiO is 818 hours, and NiMgLiO (MgO 6 W) is 1,164 hours. These improvements are attributed to enhanced electrical characteristics and improved charge balance within the device. QLED devices fabricated under 6 W MgO conditions exhibited the highest EQE and brightness among existing sputtered NiO-based green QLEDs. This is shown in Fig. 9f.

[0132]

[0133] Specific embodiments of the present invention have been examined so far. Those skilled in the art will understand that the present invention may be embodied in modified forms without departing from the essential characteristics of the invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the claims, not by the foregoing description, and all variations within the scope of equivalents should be interpreted as being included in the present invention.

Claims

1. It includes a first electrode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and a second electrode, A light-emitting device characterized in that the hole transport layer comprises self-assembled monolayers (SAM) formed on a hole injection layer, and comprises nickel oxide double-doped with nickel and magnesium.

2. In Paragraph 1, A light-emitting device characterized in that the self-assembled monolayer comprises [2-(9H-carbazole-9-yl)ethyl]phosphonic acid (2PACz).

3. In Paragraph 1, A light-emitting device characterized in that the hole injection layer is formed by co-sputtering a nickel oxide target containing lithium and a magnesium oxide target on the first electrode through radio frequency (RF) magnetron sputtering to deposit nickel oxide double-doped with nickel and magnesium.

4. In Paragraph 3, A light-emitting device characterized by sputtering the nickel oxide target containing lithium at a power of 1 to 150 W and sputtering the magnesium oxide target at a power of 1 to 150 W.

5. In Paragraph 1, A light-emitting device characterized by the thickness of the hole injection layer being 5 to 80 nm.

6. In Paragraph 1, A light-emitting device characterized in that the nickel oxide double-doped with nickel and magnesium has a lithium content of 0.1% to 25% based on the total composition and a magnesium content of 0.1% to 25% based on the total composition.

7. A step of forming a first electrode on a substrate; A step of forming a hole injection layer on the first electrode; A step of forming a hole transport layer on the hole injection layer above; A step of forming a light-emitting layer on the hole transport layer above; A step of forming an electron transport layer on the light-emitting layer; and The method includes the step of forming a second electrode on the electron transport layer, The hole injection layer comprises a self-assembled monolayer formed on the hole injection layer, and A method for manufacturing a light-emitting device characterized in that the hole injection layer comprises nickel oxide double-doped with nickel and magnesium.

8. In Paragraph 7, The step of forming a hole injection layer on the first electrode is, A method for manufacturing a light-emitting device characterized by forming a hole injection layer by depositing nickel oxide double-doped with nickel and magnesium by co-sputtering a nickel oxide target containing lithium and a magnesium oxide target through radio frequency (RF) magnetron sputtering.

9. In Paragraph 8, A method for manufacturing a light-emitting device characterized by sputtering the nickel oxide target containing lithium at a power of 1 to 150 W and sputtering the magnesium oxide target at a power of 1 to 150 W.

10. In Paragraph 7, The step of forming a hole injection layer on the first electrode is, A method for manufacturing a light-emitting device characterized by performing sputtering under room temperature conditions in an argon-oxygen atmosphere, with a pressure of 1 to 20 mTorr and flow rates of argon gas and oxygen gas of 1 to 80 sccm.

11. In Paragraph 7, A method for manufacturing a light-emitting device, characterized in that the self-assembled monolayers (SAM) comprise [2-(9H-carbazole-9-yl)ethyl]phosphonic acid (2PACz), and the thickness of the self-assembled monolayers is 1 to 5 nm.

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