Quantum dot and light emitting device including same

Abstract

A quantum dot of a light emitting device includes: a core; and a shell surrounding the core and including at least one type of halogen element, in which a first number of halogen elements per unit volume in a first region of the shell including an outer surface of the shell is greater than a second number of halogen elements per unit volume in a second region of the shell, the second region being a region other than the outer surface of the shell.

Description

Technical Field

[0001] The present disclosure relates to a quantum dot having improved performance by introducing a halogen element and a light emitting device including the quantum dot. Background Art

[0002] A light emitting diode (LED) of a light emitting device may be formed in a pn junction structure of a semiconductor, and electrons and holes injected from an electrode meet at the pn junction and generate light having a wavelength corresponding to an energy band gap (energy difference) between electrons and holes.

[0003] Various types of LEDs, such as organic light emitting diodes (OLEDs) and quantum dot light emitting diodes (QD-LEDs), have been developed and used.

[0004] QD-LED uses quantum dots as a light source, each quantum dot having a core / shell structure consisting of a core including a nanoscale semiconductor crystal and a shell surrounding the periphery of the core. QD-LED provides improved performance by utilizing the quantum confinement effect generated by the size of the nanoscale semiconductor crystals of the quantum dots. QD-LED is able to produce light with different wavelengths by adjusting the size of the nanocrystals without changing the type of material forming the semiconductor crystals. Therefore, QD-LED is able to obtain a variety of colors and has improved effects in terms of color purity and lifespan compared to conventional LEDs.

[0005] Through research on the compounds that make up quantum dots and their synthesis processes, QD-LEDs with improved efficiency and extended lifetime are being developed. Summary of the invention

[0006] According to one aspect of the present disclosure, a quantum dot of a light-emitting device includes: a core; and a shell surrounding the core and including at least one type of halogen element, wherein a first amount of halogen elements per unit volume in a first region of the shell is greater than a second amount of halogen elements per unit volume in a second region of the shell, the first region includes an outer surface of the shell, and the second region is a region excluding the outer surface of the shell.

[0007] The halogen elements in the first region of the shell may include two or more types of halogen elements, and the halogen elements in the second region of the shell may include one type of halogen elements.

[0008] The halogen element may include at least one of fluorine, chlorine, bromine, or iodine, and the halogen element may be in a doped state or a metal halide state inside the shell or on an outer surface of the shell.

[0009] The shell may include a plurality of single layers stacked on each other, and the outer surface of the shell may be an outermost single layer among the plurality of single layers.

[0010] The shell may include a plurality of single layers stacked on each other, and the number of the plurality of single layers may range from 8 to 20.

[0011] The core may include a III-V compound, and the III-V compound may be at least one of the following: a binary element compound selected from the group consisting of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb and a mixture thereof; a ternary element compound selected from the group consisting of GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb and a mixture thereof; or a quaternary element compound selected from the group consisting of GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb and a mixture thereof.

[0012] The core may include a II-VI compound, and the II-VI compound is at least one of: a binary element compound selected from the group consisting of ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS and mixtures thereof; a ternary element compound selected from the group consisting of ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS and mixtures thereof; or a quaternary element compound selected from the group consisting of HgZnTeS, HgZnSeS, HgZnSeTe, HgZnSTe and mixtures thereof.

[0013] The quantum dots may comprise a quantum yield of at least 70%.

[0014] According to one aspect of the present disclosure, a display panel includes: a substrate; and a light-emitting device, which is arranged on the substrate and includes at least one quantum dot, wherein the at least one quantum dot includes: a core; and a shell, which surrounds the core and includes at least one type of halogen element, and a first amount of halogen elements per unit volume in a first region of the shell is greater than a second amount of halogen elements per unit volume in a second region of the shell, the first region may include an outer surface of the shell, and the second region is a region excluding the outer surface of the shell.

[0015] The halogen elements in the first region of the shell may include two or more types of halogen elements, and the halogen elements in the second region of the shell may include one type of halogen elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other aspects, features and advantages of certain embodiments of the present disclosure will become more apparent from the following description in conjunction with the accompanying drawings.

[0017] Figure 1 is a diagram for explaining a structure of a quantum dot and a light emitting device including the quantum dot according to one or more embodiments of the present disclosure, the light emitting device being included in a display panel.

[0018] Figure 2 is a graph for explaining a change in photoluminescence (PL) intensity caused by a ligand removal process in a process of manufacturing quantum dots according to one or more embodiments of the present disclosure.

[0019] Figure 3 is a diagram for explaining the structure of quantum dots surface-treated with a halogen element according to one or more embodiments of the present disclosure.

[0020] Figure 4a is a graph for explaining the results of thermogravimetric analysis (TGA) of quantum dots surface-treated with a halogen element according to one or more embodiments of the present disclosure.

[0021] Figure 4b is a graph for explaining changes in photoluminescence intensity caused by a ligand removal process in a process of manufacturing quantum dots surface-treated with a halogen element according to one or more embodiments of the present disclosure.

[0022] Figure 4c is a graph for illustrating the external quantum efficiency (EQE) of quantum dots generating red light according to one or more embodiments of the present disclosure.

[0023] Figure 4d is a graph for illustrating the external quantum efficiency of quantum dots that generate blue light according to one or more embodiments of the present disclosure.

[0024] Figure 4e is a graph for illustrating the lifetime of quantum dots that generate blue light according to one or more embodiments of the present disclosure.

[0025] Figure 5a is a graph for explaining external quantum efficiency depending on the number of monolayers constituting a quantum dot according to one or more embodiments of the present disclosure.

[0026] Figure 5b is a graph for explaining brightness depending on the number of monolayers constituting quantum dots according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0027] The embodiments may be variously modified and various embodiments may exist, therefore, specific embodiments are shown in the drawings and described in detail in the specific embodiments. However, it should be understood that it is not intended to limit the scope of the present disclosure to the specific forms disclosed herein; on the contrary, the present disclosure should be interpreted as covering various modifications, equivalents and / or substitutions of the embodiments of the present disclosure. When describing the drawings, similar reference numerals may be used to represent similar components.

[0028] In describing the present disclosure, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present disclosure, the detailed description thereof will be omitted.

[0029] In addition, the following embodiments can be modified in many different forms, and the scope of the technical spirit of the present disclosure is not limited to the following embodiments. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the technical spirit of the present disclosure to those skilled in the art.

[0030] The terms used herein are only used to describe specific embodiments and are not intended to limit the scope of the present disclosure. Unless the context clearly indicates otherwise, a singular expression includes a plural expression.

[0031] The expressions “having”, “may have”, “include”, “may include”, etc. used herein indicate the existence of the described features (for example, elements such as values, functions, operations or components), and do not exclude the existence of additional features.

[0032] As used herein, the expressions "A or B", "at least one of A and / or B", "one or more of A and / or B", etc. may include all possible combinations of the items enumerated therein. For example, the expressions "A or B", "at least one of A and B", or "at least one of A or B" indicate (1) only A, (2) only B, or (3) both A and B.

[0033] The expressions “first,” “second,” etc. used herein may modify various components regardless of their order and / or importance and may be used to distinguish one component from another without limiting the components.

[0034] As used herein, the expression "configured to (or set to)" may be used interchangeably with the expressions "suitable to", "capable of", "designed to", "suitable for", "made for", or "capable of...", depending on the context. The term "configured to (set to)" does not necessarily mean "specifically designed to" in hardware.

[0035] When a part (e.g., a layer, film, region, or panel) is referred to herein as being "on" another part, it can be "directly on" the other part, or there can be an intervening part therebetween. Conversely, when a part is referred to as being "directly on" another part, there are no intervening parts therebetween.

[0036] The term "group" corresponding to a compound or an element used herein means a group in the periodic table of elements.

[0037] The various elements and regions in the drawings are schematically shown. Therefore, the technical spirit of the present disclosure is not limited by the relative sizes or distances shown in the drawings.

[0038] Hereinafter, embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings so that those having ordinary skill in the art to which the present disclosure pertains can easily implement the embodiments.

[0039] Figure 1 is a diagram for explaining the structure of a quantum dot and a light emitting device including the quantum dot according to one or more embodiments of the present disclosure.

[0040] refer to Figure 1 , the light emitting device 10 including quantum dots of the display panel may be formed on the substrate. The light emitting device 10 including quantum dots may be a quantum dot light emitting diode (QD-LED), but is not limited thereto. In addition, one or more light emitting devices 10 including quantum dots may constitute RGB pixels and sub-pixels, which are basic units of the display panel.

[0041] In addition, a circuit for controlling the light emitting device 10 including quantum dots may be formed on the substrate. The circuit may include electrodes, diodes (e.g., light emitting diodes (LEDs)), and transistors (e.g., bipolar junction transistors (BJTs), junction field effect transistors (JFETs), insulated gate field effect transistors (IGFETs), metal oxide semiconductor field effect transistors (MOSFETs), and thin film transistors (TFTs)).

[0042] However, the configuration of the circuit is not limited thereto, and various configurations for emitting light to operate as a display panel may also be included, or some configurations may be omitted.

[0043] The light emitting device 10 of the display panel may include: a positive electrode 20 disposed on a substrate; and a negative electrode 30 disposed on the substrate to be spaced apart from the positive electrode 20 .

[0044] Here, the positive electrode 20 may be made of Al and the negative electrode 30 may be made of indium tin oxide (ITO), but the positive electrode 20 and the negative electrode 30 are not limited thereto and they may be made of various materials that can be used as electrodes.

[0045] The light emitting device 10 of the display panel may include a light emitting layer 40 disposed between a positive electrode 20 and a negative electrode 30 on a substrate, the light emitting layer 40 including at least one quantum dot 100 .

[0046] The light emitting device 10 of the display panel may include: an electron transport layer 50 - 1 disposed between the positive electrode 20 and the light emitting layer 40 on the substrate; and a hole transport layer 60 - 1 disposed between the negative electrode 30 and the light emitting layer 40 on the substrate.

[0047] Here, the light emitting device 10 of the display panel may further include an electron injection layer 50 - 2 between the electron transport layer 50 - 1 and the positive electrode 20 , and may further include a hole injection layer 60 - 2 between the hole transport layer 60 - 1 and the negative electrode 30 .

[0048] Electrons may move from the positive electrode 20 to the light emitting layer 40 through the electron injection layer 50 - 2 and the electron transport layer 50 - 1 , and holes may move from the negative electrode 30 to the light emitting layer 40 through the hole injection layer 60 - 2 and the hole transport layer 60 - 1 .

[0049] Here, the light emitting layer 40 may include at least one quantum dot 100, and the quantum dot 100 may include: a core 110 composed of semiconductor nanocrystals; and at least one shell 120 disposed on the core 110 and having a crystalline structure or an amorphous structure. Figure 1 As shown, at least one case 120 may include two cases 120-1 and 120-2. However, the number of cases is not limited to two, and may be one or may be more than two. Hereinafter, the cases 120-1 and 120-2 will be collectively referred to as cases 120.

[0050] The electrons and holes are subjected to a quantum confinement effect of nano-scale semiconductor crystals constituting the quantum dots 100 included in the light emitting layer 40 to emit light having a wavelength corresponding to an energy difference between the electrons and the holes.

[0051] The core 110 of the quantum dot 100 according to one or more embodiments of the present disclosure may include a semiconductor nanocrystal made of a group III-V compound or a group II-VI compound. However, the core 110 of the quantum dot 100 is not limited thereto.

[0052] Here, the III-V group compound constituting the core 110 may be at least one of the following: a binary element compound selected from the group consisting of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb and mixtures thereof; a ternary element compound selected from the group consisting of GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb and mixtures thereof; or a quaternary element compound selected from the group consisting of GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb and mixtures thereof. When the core 110 is made of a group III-V compound, light generated by the quantum dot 100 has a red color.

[0053] In addition, the core 110 may include a II-VI compound, and the II-VI compound may be at least one of: a binary element compound selected from the group consisting of ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS, and mixtures thereof; a ternary element compound selected from the group consisting of ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, and mixtures thereof; or a quaternary element compound selected from the group consisting of HgZnTeS, HgZnSeS, HgZnSeTe, HgZnSTe, and mixtures thereof. When the core 110 is made of a II-VI compound, light generated by the quantum dot 100 has a blue color.

[0054] The shell 120 of the quantum dot 100 may include a crystalline compound or an amorphous compound. According to one or more embodiments, the shell 120 may be made of a compound such as ZnS, ZnSe, or ZnSeS, but is not limited thereto.

[0055] The shell 120 may include a ligand coordinately bonded to a central metal atom of a compound constituting the shell 120. The ligand may be oleic acid (OA), but is not limited thereto, and may include various types of organic ligands.

[0056] The oleic acid ligand included in the shell 120 may include an alkyl chain, and the alkyl chain is a factor that hinders the injection and transmission of electrons and holes. Therefore, in order to solve the aforementioned problem, in the step of synthesizing the quantum dot 100, the oleic acid ligand is reduced by using a halogen element (e.g., chlorine (Cl)), and the oleic acid ligand that is not separated in the synthesis step is removed by a post-treatment process.

[0057] Removing the oleic acid ligands present on the surface of the quantum dot 100 through the post-treatment process as described above may cause defects on the surface of the quantum dot 100 , thereby causing a problem of reducing the photoluminescence intensity (PL) of the quantum dot 100 .

[0058] Figure 2 is a graph for explaining changes in photoluminescence intensity caused by a ligand removal process during the process of manufacturing quantum dots according to one or more embodiments of the present disclosure.

[0059] refer to Figure 2 , when the quantum dot 100 emits red light and chlorine (Cl) is introduced into the quantum dot 100, from the comparison between the curve 210 indicating the photoluminescence intensity of the quantum dot 100 before the ligand removal process and the curve 220 indicating the photoluminescence intensity of the quantum dot 100 after the ligand removal process, it can be seen that within the wavelength range of 620nm to 650nm, the photoluminescence intensity of the quantum dot 100 is reduced by about 50% to 95%.

[0060] The effect of the ligand removal process on the reduction of the photoluminescence intensity of the quantum dot 100 can be shown in Table 1 below.

[0061] Table 1

[0062]

[0063] Therefore, there is a need to find a method for improving the performance of quantum dots 100 and extending the lifetime of quantum dots 100 by more effectively removing oleic acid ligands present on the surface of quantum dots 100 and minimizing surface defects occurring after a post-treatment process for removing oleic acid ligands.

[0064] In order to achieve the above purpose, the halogen element may be introduced into the quantum dot 100 , and specifically, the halogen element may be introduced into the surface of the quantum dot 100 .

[0065] Figure 3is a diagram for explaining the structure of quantum dots surface-treated with a halogen element according to one or more embodiments of the present disclosure.

[0066] refer to Figure 3 To achieve the above-mentioned purpose, the quantum dot 100 according to the present disclosure may include: a core 110 including a semiconductor nanocrystal; and at least one shell 120 formed on the core 110, which is crystalline or amorphous and includes at least one type of halogen element 130. Figure 3 As shown, the at least one shell 120 may include two shells 120 - 1 and 120 - 2 .

[0067] That is, in the step of synthesizing the quantum dot 100 , the halogen element 130 may be introduced into the shell 120 to remove the oleic acid ligand, thereby minimizing the hindrance to the electron and hole transport caused by the alkyl chain of oleic acid.

[0068] The halogen element 130 may be at least one of fluorine (F), chlorine (Cl), bromine (Br), or iodine (I), and may be in a doped state in the shell 120 or on an outer surface of the shell 120 , or in a metal halide state.

[0069] Here, the amount of the halogen element 130 per unit volume present in the first region including the outer surface of the shell 120 may be greater than the amount of the halogen element 130 per unit volume present in the second region of the shell 120 not including the outer surface of the shell 120. Here, the first region may be a region including the outermost surface of the shell 120.

[0070] The first region may be a region referring only to the outermost surface of the shell 120. The second region may be an inner region of the shell 120 excluding the surface of the shell 120. In addition, the first region may be closer to the outermost surface of the shell 120 than the second region. In addition, the point closest to the core 110 in the first region may be closer to the outer surface than the point closest to the outer surface in the second region. However, the above-mentioned first region and second region of the shell 120 are not limited thereto.

[0071] By additionally introducing the halogen element 130 into a region including the surface of the shell 120 immediately after introducing the halogen element 130 to synthesize the shell 120 in the process of manufacturing the quantum dot 100 according to the present disclosure, the amount of the halogen element 130 per unit volume present in the first region including the surface of the shell 120 can be greater than the amount of the halogen element 130 per unit volume present in the second region of the shell 120 that does not include the surface of the shell 120.

[0072] In the first region including the surface of the shell 120, the shell 120 may include two or more types of halogen elements 130. Here, the two or more types of halogen elements included in the first region of the shell 120 may be chlorine (Cl) and fluorine (F), but is not limited thereto.

[0073] The halogen element 130 present in the second region of the shell 120 excluding the surface of the shell 120 may be only chlorine (Cl), which is one type of halogen element, but is not limited thereto.

[0074] The halogen element 130 present on the surface of the shell 120 may be in a doped state or a metal halide state.

[0075] A method of manufacturing the quantum dot 100 in which two or more types of halogen elements 130 are introduced to the surface of the shell 120 will be described below.

[0076] In the case where the core 110 of the quantum dot 100 emitting red light is made of InP, indium acetate and palmitic acid are dissolved in 1-octadecene in a 200 mL reaction bottle, and the reaction bottle is heated to 120 ° C under vacuum. The molar ratio of indium to palmitic acid is 1:3. After 1 hour, the air in the reactor becomes nitrogen. After the reactor is heated to 280 ° C, a mixed solution of tri(trimethylsilyl)phosphine (TMS3P) and trioctylphosphine is quickly injected into the reactor and reacted for 20 minutes. The precipitate obtained by centrifugation in the case of acetone being placed in the reaction solution that is quickly cooled to room temperature is dispersed back into toluene. Each 1 mol of indium contains 0.5 mol of TMS3P. The obtained InP core has a size of about 3nm.

[0077] To obtain ZnSe and ZnS, TOA was placed in a 300 mL reaction bottle, zinc acetate and oleic acid were added in a molar ratio of 1:2, and then the reaction bottle was treated at 120°C under vacuum. The air in the bottle was replaced by nitrogen (N2). The toluene dispersion was quickly added to the ZnSeTe core prepared by heating the reaction bottle to 300°C, followed by the addition of Se / TOP stock solution, and then reacted for 120 minutes. As a result, a ZnSe layer was formed on the core. Next, a ZnS layer was formed on the ZnSe layer by adding S / Top stock solution and zinc acetate, and then reacting for 120 minutes. The molar ratio of the content of the Zn precursor, S precursor, and Se precursor used to form the shell is 3.5:2.5:1.

[0078] By adding three or more times of ethanol, the synthetic solution including InP, ZnSe and ZnS is cleaned twice and then dispersed in cyclohexane. ZnCl2 solution (10 vol% in acetone) and HF dilution solution (10 vol% in acetone) containing 0.1% to 500% content of Zn on the surface are added, and it is reacted for 1 hour at 80°C. After the reaction solution is cooled to room temperature, the reaction solution is cleaned twice by adding three or more times of ethanol and then dispersed in octane. Here, the chlorine (Cl) precursor is not limited to ZnCl2, and the fluorine (F) precursor is not limited to HF.

[0079] In the case where the core 110 of the quantum dot 100 emitting blue light is made of ZnTeSe, selenium, sulfur and tellurium are dispersed in trioctylphosphine (TOP) to obtain 2M Se / TOP stock solution and 2M sulfur / TOP stock solution and 0.1M Te / TOP stock solution. In a 300mL reaction bottle, zinc acetate is dissolved in trioctylamine together with palmitic acid, and the reaction bottle is heated to 120°C under vacuum. After 1 hour, the air in the reactor becomes an inert gas. After the reactor is heated to 300°C, the Se / TOP stock solution and Te / TOP stock solution prepared as described above are quickly injected into the reactor according to a predetermined Te / Se ratio. After 60 minutes, the precipitate obtained by centrifugation in the case of acetone being placed in a reaction solution that is rapidly cooled to room temperature is dispersed in toluene to obtain a ZnSeTe core. The content ratio (Zn:Se) of the Zn precursor and the Se precursor used is 2:1, and the content ratio (Te / Se) of Te to Se is 0.03.

[0080] The method of synthesizing ZnSe and ZnS may be the same as the method described above with respect to the synthesis of the quantum dots 100 that generate red light, but is not limited thereto.

[0081] By adding three or more times of ethanol, the synthetic solution including ZnTeSe, ZnSe and ZnS is washed twice and then dispersed in cyclohexane. A ZnCl2 solution (10 vol% in acetone) and a HF dilution solution (10 vol% in acetone) containing 0.1% to 500% of Zn on the surface are added, and reacted at 80°C for 1 hour. After the reaction solution is cooled to room temperature, the reaction solution is washed twice by adding three or more times of ethanol and then dispersed in octane. Here, the chlorine (Cl) precursor is not limited to ZnCl2, and the fluorine (F) precursor is not limited to HF.

[0082] By additionally introducing the halogen element 130 into the region including the surface of the shell 120 immediately after the halogen element 130 is introduced to synthesize the shell 120 as described above, the oleic acid ligand present in the region including the surface of the shell 120 can be effectively removed, and even after the ligand removal process, there are few defects in the region including the surface of the shell 120, thereby expecting the effect of improving the photoluminescence intensity of the quantum dot 100 and extending the life of the quantum dot 100. The quantum dot 100 may have a quantum yield of 70% or more, but is not limited thereto.

[0083] Reference Figure 4a , Figure 4b , Figure 4c , Figure 4d and Figure 4e To describe the expected effect when the amount of halogen element 130 per unit volume present in a first region including the surface of the shell 120 is greater than the amount of halogen element 130 per unit volume present in a second region of the shell 120 not including the surface of the shell 120 by additionally introducing the halogen element 130 into the region including the surface of the shell 120 immediately after the halogen element 130 is introduced to synthesize the shell 120.

[0084] Figure 4a is a graph for explaining the results of thermogravimetric analysis (TGA) of quantum dots 100 surface-treated with a halogen element according to one or more embodiments of the present disclosure.

[0085] refer to Figure 4a It can be seen that, compared with the curve 410-2 indicating the TGA of the quantum dot 100 introducing chlorine (Cl) and fluorine (F) as the halogen element 130, the curve 410-1 indicating the TGA of the quantum dot 100 introducing only chlorine (Cl) as the halogen element 130 has a larger change in the range of 350°C to 550°C.

[0086] TGA is a method in which the weight of a sample to be analyzed is observed to decrease due to pyrolysis when the temperature is raised while the air environment of the sample to be analyzed is controlled. Here, the object of pyrolysis may be an organic substance.

[0087] Therefore, it can be seen that the weight reduction caused by the pyrolysis of the quantum dot 100 into which only chlorine (Cl) is introduced as the halogen element 130 is greater than the weight reduction caused by the pyrolysis of the quantum dot 100 into which chlorine (Cl) and fluorine (F) are introduced as the halogen element 130. This indicates that the amount of organic matter (i.e., oleic acid ligands including alkyl chains) included in the quantum dot 100 into which chlorine (Cl) and fluorine (F) are introduced as the halogen element 130 is less than the amount of organic matter (i.e., oleic acid ligands including alkyl chains) included in the quantum dot 100 into which only chlorine (Cl) is introduced as the halogen element 130. Therefore, when chlorine (Cl) and fluorine (F) are introduced as the halogen element 130 into the quantum dot 100, the effect of removing oleic acid ligands and the effect of improving the performance of the quantum dot 100 are greater than when only chlorine (Cl) is introduced as the halogen element 130 into the quantum dot 100. Fluorine (F) introduced into the above-mentioned quantum dot 100 may be mainly located on the surface of the shell 120-2.

[0088] Figure 4b is a graph for explaining changes in photoluminescence intensity caused by a ligand removal process in a process of manufacturing quantum dots surface-treated with a halogen element according to one or more embodiments of the present disclosure.

[0089] refer to Figure 4b , compared with the curve 420-1 corresponding to the photoluminescence intensity of the quantum dots 100 introducing only chlorine (Cl) as the halogen element 130, the curve 420-2 corresponding to the photoluminescence intensity of the quantum dots 100 introducing chlorine (Cl) and fluorine (F) as the halogen elements 130 shows a larger photoluminescence intensity value in the entire wavelength range.

[0090] That is, it can be seen that the photoluminescence intensity of the quantum dot 100 introduced with chlorine (Cl) and fluorine (F) as the halogen element 130 has a higher value than the photoluminescence intensity of the quantum dot 100 introduced with only chlorine (Cl) as the halogen element 130 .

[0091] Fluorine (F) introduced into the above-described quantum dot 100 may be mainly located on the surface of the shell 120 - 2 .

[0092] Table 2 below shows the photoluminescence intensity of the quantum dot 100 into which only chlorine (Cl) is introduced as the halogen element 130 and the photoluminescence intensity of the quantum dot 100 into which chlorine (Cl) and fluorine (F) are introduced as the halogen element 130 .

[0093] Table 2

[0094]

[0095] Figure 4cis a graph for illustrating the external quantum efficiency (EQE) of quantum dots generating red light according to one or more embodiments of the present disclosure. Here, the external quantum efficiency refers to the rate at which excitation energy is converted into luminescent energy.

[0096] refer to Figure 4c It can be seen that, compared with the curve 430-1 corresponding to the external quantum efficiency of the quantum dot 100 in which only chlorine (Cl) is introduced as the halogen element 130, the curve 430-2 corresponding to the external quantum efficiency of the quantum dot 100 in which chlorine (Cl) and fluorine (F) are introduced as the halogen element 130 has a larger external quantum efficiency value in the range up to about 9V.

[0097] Furthermore, it is shown that the maximum value of the external quantum efficiency of the quantum dot 100 introducing chlorine (Cl) and fluorine (F) as the halogen element 130 is about 7% higher than the maximum value of the external quantum efficiency of the quantum dot 100 introducing only chlorine (Cl) as the halogen element 130 .

[0098] Figure 4d is a graph for illustrating the external quantum efficiency of quantum dots that generate blue light according to one or more embodiments of the present disclosure.

[0099] refer to Figure 4d It can be seen that, compared with the curve 440-1 corresponding to the external quantum efficiency of the quantum dot 100 introducing only chlorine (Cl) as the halogen element 130, the curve 440-2 corresponding to the external quantum efficiency of the quantum dot 100 introducing chlorine (Cl) and fluorine (F) as the halogen element 130 has a larger external quantum efficiency value.

[0100] In addition, it is shown that the maximum value of the external quantum efficiency of the quantum dot 100 introducing chlorine (Cl) and fluorine (F) as the halogen element 130 is higher by about 1.6% than the maximum value of the external quantum efficiency of the quantum dot 100 introducing only chlorine (Cl) as the halogen element 130 .

[0101] The effect of increasing the maximum value of the external quantum efficiency of quantum dots generating red light when chlorine (Cl) and fluorine (F) are introduced as the halogen element 130 and the effect of increasing the maximum value of the external quantum efficiency of quantum dots generating blue light when chlorine (Cl) and fluorine (F) are introduced as the halogen element 130 can be shown in Table 3 below.

[0102] Table 3

[0103]

[0104] Here, the fluorine (F) introduced into the quantum dot 100 may be mainly located on the surface of the shell 120-2. Therefore, it can be seen that the quantum dot 100 introducing chlorine (Cl) and fluorine (F) as the halogen element 130 has improved efficiency and performance compared to the quantum dot 100 introducing only chlorine (Cl) as the halogen element 130.

[0105] Figure 4e is a graph for illustrating the lifetime of quantum dots that generate blue light according to one or more embodiments of the present disclosure.

[0106] The vertical axis corresponds to the brightness of the light generated by the quantum dots, and the horizontal axis corresponds to time, ie, lifetime.

[0107] refer to Figure 4e It can be observed that the lifetime of the quantum dot 100 introduced with chlorine (Cl) and fluorine (F) as the halogen element 130 is about 0.7 hours longer than the lifetime of the quantum dot 100 introduced with only chlorine (Cl) as the halogen element 130 .

[0108] Therefore, it can be seen that when chlorine (Cl) and fluorine (F) are introduced together as the halogen element 130 , the lifetime of the quantum dot 100 (ie, the light emitting device 10 of the display panel) is improved compared to when only chlorine (Cl) is introduced as the halogen element 130 .

[0109] Hereinafter, regarding the monolayers constituting the shell 120 - 2 included in the quantum dot 100 , the quantum dot 100 in which the halogen element 130 is introduced into the monolayer and the effect of improving the performance of the quantum dot 100 depending on the number of the monolayers will be described.

[0110] The shell 120-2 may include a plurality of stacked monolayers. The amount of the halogen element 130 per unit volume present on the surface of the outermost monolayer of the shell 120-2 may be greater than the amount of the halogen element 130 per unit volume present on monolayers other than the outermost monolayer of the shell 120-2.

[0111] Here, on the outermost single layer of the shell 120-2, the shell 120-2 may include two or more types of halogen elements 130. Here, the two or more types of halogen elements included on the outermost single layer of the shell 120 may be chlorine (Cl) and fluorine (F), but is not limited thereto.

[0112] Furthermore, the halogen element 130 present inside the outermost single layer except the surface of the outermost single layer of the shell 120 - 2 and on other single layers except the outermost single layer may be only chlorine (Cl), but is not limited thereto.

[0113] The halogen element 130 present on the surface of the outermost single layer of the shell 120 - 2 may be in a doped state or a metal halide state.

[0114] In addition, the shell 120-2 may include a plurality of stacked monolayers, and the number of the monolayers may be controlled to achieve the best condition for improving the performance of the quantum dot 100. According to one or more embodiments, the number of the plurality of monolayers may be greater than or equal to 8 and less than or equal to 20, but is not limited thereto.

[0115] Figure 5a is a graph for explaining external quantum efficiency depending on the number of monolayers constituting a quantum dot according to one or more embodiments of the present disclosure.

[0116] refer to Figure 5a It can be seen that, compared with curve 510-1 corresponding to the external quantum efficiency of the quantum dot when the number of monolayers included in the shell 120 is six, curve 510-2 corresponding to the external quantum efficiency of the quantum dot when the number of monolayers included in the shell 120 is ten shows a larger external quantum efficiency value.

[0117] Figure 5b is a graph for explaining brightness depending on the number of monolayers constituting quantum dots according to one or more embodiments of the present disclosure.

[0118] refer to Figure 5b It can be seen that curve 520-2 corresponding to the brightness of the quantum dot when the number of monolayers included in the shell 120 is ten shows a larger brightness value than curve 520-1 corresponding to the brightness of the quantum dot when the number of monolayers included in the shell 120 is six.

[0119] Therefore, it can be seen that when the number of monolayers included in the shell 120 is ten, the effect of improving the performance of the quantum dot 100 is excellent, and when the number of monolayers is in the range of more than or equal to 8 and less than or equal to 20, an excellent performance improvement effect can be exhibited.

[0120] Depending on the number of the above-mentioned monolayers and the amount of the halogen element 130 introduced into the shell 120 of the quantum dot 100 , the effects of improving the efficiency of the quantum dot 100 and extending the life of the quantum dot 100 can be expected.

[0121] In addition, the light emitting device 10 of the display panel including the quantum dot 100 according to the present disclosure may be used in various display devices such as TVs, computers, tablets, smart phones, and wearable devices, but is not limited thereto.

[0122] Although the exemplary embodiments of the present disclosure have been shown and described above, the present disclosure is not limited to the above specific embodiments, and various modifications may be made by those skilled in the art without departing from the subject matter of the present disclosure as claimed in the appended claims. Such modifications should not be understood solely based on the technical spirit or prospect of the present disclosure.

Claims

1. A quantum dot of a light-emitting device, the quantum dot comprising: nuclear; as well as a shell surrounding the core and comprising at least one type of halogen element, The first amount of halogen elements per unit volume in the first region of the shell is greater than the second amount of halogen elements per unit volume in the second region of the shell, the first region includes the outer surface of the shell, and the second region is the region excluding the outer surface of the shell.

2. The quantum dot according to claim 1, wherein The halogen elements in the first region of the shell include two or more types of halogen elements, and the halogen elements in the second region of the shell include one type of halogen elements.

3. The quantum dot according to claim 1, wherein The halogen element includes at least one of fluorine, chlorine, bromine or iodine, and Wherein, inside the shell or on the outer surface of the shell, the halogen element is in a doped state or a metal halide state.

4. The quantum dot according to claim 1, wherein The shell includes a plurality of single layers stacked on top of each other, and Wherein, the outer surface of the shell is the outermost single layer among the multiple single layers.

5. The quantum dot according to claim 1, wherein The shell includes a plurality of single layers stacked on top of each other, and Wherein, the number of the plurality of single layers is in the range from 8 to 20.

6. The quantum dot according to claim 1, wherein The core includes a Group III-V compound, and Wherein, the III-V group compound is at least one of the following: Binary element compounds selected from the group consisting of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, and mixtures thereof; a ternary element compound selected from the group consisting of GaNPs, GaNAs, GaNSb, GaPAs, GaPSb, AlNPs, AlNAs, AlNSb, AlPAs, AlPSb, InNPs, InNAs, InNSb, InPAs, InPSb, and mixtures thereof; or A quaternary element compound selected from the group consisting of GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb and mixtures thereof.

7. The quantum dot according to claim 1, wherein The core comprises a Group II-VI compound, and Wherein, the II-VI group compound is at least one of the following: Binary element compounds selected from the group consisting of ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS, and mixtures thereof; a ternary element compound selected from the group consisting of ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, and mixtures thereof; or A quaternary element compound selected from the group consisting of HgZnTeS, HgZnSeS, HgZnSeTe, HgZnSTe and mixtures thereof.

8. The quantum dot according to claim 1, wherein The quantum dots have a quantum yield of at least 70%.

9. A display panel, comprising: substrate; as well as a light emitting device disposed on the substrate and comprising at least one quantum dot, Wherein, the at least one quantum dot comprises: nuclear; and a shell surrounding the core and comprising at least one type of halogen element, and The first amount of halogen elements per unit volume in the first region of the shell is greater than the second amount of halogen elements per unit volume in the second region of the shell, the first region includes the outer surface of the shell, and the second region is the region excluding the outer surface of the shell.

10. The display panel according to claim 9, wherein: The halogen elements in the first region of the shell include two or more types of halogen elements, and Wherein the halogen elements in the second region of the shell include one type of halogen elements.

11. The display panel according to claim 9, wherein: The halogen element includes at least one of fluorine, chlorine, bromine or iodine, and Wherein, inside the shell or on the outer surface of the shell, the halogen element is in a doped state or a metal halide state.

12. The display panel according to claim 9, wherein: The shell includes a plurality of single layers stacked on top of each other, and Wherein, the outer surface of the shell is the outermost single layer among the multiple single layers.

13. The display panel according to claim 9, wherein: The shell includes a plurality of single layers stacked on top of each other, and Wherein, the number of the plurality of single layers is in the range from 8 to 20.

14. The display panel according to claim 9, wherein: The core includes a Group III-V compound, and Wherein, the III-V group compound is at least one of the following: Binary element compounds selected from the group consisting of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, and mixtures thereof; a ternary element compound selected from the group consisting of GaNPs, GaNAs, GaNSb, GaPAs, GaPSb, AlNPs, AlNAs, AlNSb, AlPAs, AlPSb, InNPs, InNAs, InNSb, InPAs, InPSb, and mixtures thereof; or A quaternary element compound selected from the group consisting of GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb and mixtures thereof.

15. The display panel according to claim 9, wherein: The core comprises a Group II-VI compound, and Wherein, the II-VI group compound is at least one of the following: Binary element compounds selected from the group consisting of ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS, and mixtures thereof; a ternary element compound selected from the group consisting of ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, and mixtures thereof; or A quaternary element compound selected from the group consisting of HgZnTeS, HgZnSeS, HgZnSeTe, HgZnSTe and mixtures thereof.

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