Preparation method of ultra-narrow band Ag-In-Ga-S quantum dot and electroluminescent device

Abstract

The invention provides an Ag-In-Ga-S quantum dot with an ultra-narrow band characteristic and a preparation method of an electroluminescent device, and belongs to the technical field of quantum dot synthesis. The I-III-VI group quantum dots with narrow emission characteristics are synthesized through a one-step method, surface defect and internal defect light emission is inhibited through post-injection of a gallium halide hot solution, narrow-band light emission of the I-III-VI group quantum dots with the half-peak width smaller than 30 nm is achieved, and the light emission peak position is 500-620 nm; the synthesized ultra-narrow-band I-III-VI group quantum dots are changed into short-chain ligands through long-chain ligands, so that charge injection of an electroluminescent device is facilitated; according to the quantum dot light-emitting diode, the defect emission peak of the narrow-band I-III-VI quantum dot light-emitting diode is inhibited in a mode of evaporating multiple layers of small molecules, and the external quantum yield is improved.

Description

Technical Field

[0001] This invention relates to the field of quantum dot synthesis technology, specifically to a method for preparing Ag-In-Ga-S quantum dots with ultra-narrow band characteristics and electroluminescent devices. Background Technology

[0002] Colloidal semiconductor nanocrystals, also known as quantum dots, particularly group I-III-VI quantum dots, have profound significance in the research background of light-emitting diodes (LEDs), especially in high-performance LEDs and quantum dot display technology. These quantum dots are composed of group I, III, and VI elements, such as copper indium selenide (CuInSe2) and silver indium sulfide (AgInS2), and have become key materials for the development of LED technology due to their unique photoelectric properties. Currently, electroluminescent devices based on semiconductor quantum dots mainly use group II-VI cadmium-based quantum dots as the light-emitting layer material. However, the manufacturing, use, and handling of cadmium-based quantum dots may lead to the release of cadmium, causing environmental pollution and bioaccumulation, which poses certain hazards to the environment and human health.

[0003] Therefore, environmentally friendly group I-III-VI quantum dots have attracted widespread attention. These quantum dots are composed of group I, III, and VI elements, such as copper indium selenide (CuInSe2) and copper zinc tin sulfide (CZTS), and have become key materials for the development of light-emitting diode (LED) technology due to their unique photoelectric properties. Firstly, the application of group I-III-VI quantum dots in LEDs mainly benefits from their wide tunable bandgap and high quantum efficiency. This tunable bandgap allows quantum dots to emit light of different wavelengths from ultraviolet to infrared, which is difficult to achieve with traditional light-emitting materials. Therefore, LEDs capable of emitting multiple colors of light can be designed using these quantum dots, which is a major breakthrough for display technology. Furthermore, the application of group I-III-VI quantum dots also helps improve the energy efficiency of LEDs. Due to the high photoelectric conversion efficiency of these quantum dots, their application in LEDs can reduce energy loss, thereby improving the overall energy efficiency ratio. This not only aligns with the current trend of energy conservation and emission reduction but also enhances the market competitiveness of LED products.

[0004] Although group I-III-VI quantum dots have broad application prospects in the LED field, some challenges remain in practical applications, such as low color purity and lack of stability. Traditional silver-based group I-III-VI quantum dots possess a large number of defect states, which act as donor and acceptor levels in the energy level structure. Therefore, the radiative recombination of electrons and holes generally includes two modes: conduction band-vacancy level and donor-acceptor level radiative recombination. The simultaneous existence of these two recombination modes results in generally broad full width at half maximum (FWHM) spectra in both photoluminescence (PL) and photoluminescence (EL) spectra, leading to low color purity in the light-emitting devices and limiting the application of group I-III-VI quantum dots in the display field.

[0005] Currently, existing narrow-band I-III-VI group semiconductor quantum dots, such as multi-element copper-based or silver-based quantum dots (e.g., Cu-Ga-Zn-S, Ag-In-Ga-S), are grown using a seed growth method to first generate broad-spectrum nuclear quantum dots. Then, a shell coating method is used to suppress donor-acceptor radiative recombination, achieving single conduction band-vacancy radiative recombination. The full width at half maximum (FWHM) is between 30-50 nm. Narrow-band quantum dots with FWHM below 30 nm have not yet been reported. Furthermore, narrow-band I-III-VI group quantum dots do not perform ideally in electroluminescent devices, exhibiting low external quantum efficiency (typically less than 1%) and defect peaks that reduce color purity, hindering their effective application in high-definition displays. Therefore, narrowing the FWHM of I-III-VI group quantum dots to below 30 nm and successfully applying them to electroluminescent devices has become a major challenge for researchers.

[0006] In summary, the application of quantum dot materials in high-definition displays using electroluminescent devices requires high color purity, i.e., narrow full width at half maximum (FWHM) for both photoluminescence and electroluminescence. Traditional I-III-VI group semiconductor nanocrystals possess numerous defect states, primarily emitting light from impurity energy levels, resulting in FWHMs generally exceeding 75 nm for both photoluminescence and electroluminescence, thus limiting their display applications. Currently, narrowband I-III-VI group quantum dots typically have FWHMs above 30 nm, and their synthesis is relatively complex, leading to poor performance in electroluminescent devices. Their external quantum efficiency is generally below 1%, and they exhibit strong defect emission peaks, resulting in decreased color purity. Therefore, developing ultra-narrowband quantum dots with FWHMs less than 30 nm, and their successful application in electroluminescent devices, is essential. Summary of the Invention

[0007] The purpose of this invention is to provide a method for fabricating Ag-In-Ga-S quantum dots and electroluminescent devices with ultra-narrow band characteristics, so as to solve at least one of the technical problems existing in the background art.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing Ag-In-Ga-S quantum dots with ultra-narrow band characteristics, comprising the following steps:

[0010] Step 1: Weigh the Ag source, In source, Ga source and the first solvent and place them in a three-necked flask. Heat and degas under vacuum, stirring and dissolving for a period of time.

[0011] Step 2: Weigh the S source, dissolve it in the mixed solution of the first solvent and the ligand, heat and stir for a period of time, weigh the Ga source, dissolve it in the mixed solution of the first solvent and the ligand, heat and stir for a period of time, weigh the short-chain ligand, and dissolve it in the second solvent;

[0012] Step 3: Introduce nitrogen gas, stir magnetically under nitrogen protection, inject the sulfur precursor solution, and maintain the temperature and stir for a period of time.

[0013] Step 4: Set up phased heating and maintain the temperature for a period of time;

[0014] Step 5: Inject Ga source and keep warm for a period of time;

[0015] Step 6: After the reaction is complete, add the short-chain ligand dissolved in the second solvent to the solution, and keep it warm and stirred for a period of time;

[0016] Step 7: Add the final product to the antisolvent and centrifuge. Add the precipitate to the third solvent and antisolvent in sequence and centrifuge repeatedly to obtain narrow-band luminescent quantum dots.

[0017] As a further limitation of the first aspect of the present invention, in step 1, the Ag source is selected from one or more of silver acetate, silver carbonate, silver nitrate, sulfate or silver halide; the In source is selected from one or more of indium acetate, indium nitrate, indium sulfate, indium halide or indium acetylacetonate; and the Ga source is selected from one or more of gallium acetate, gallium nitrate, gallium sulfate, gallium halide or gallium acetylacetonate.

[0018] As a further limitation of the first aspect of the present invention, the molar ratio of the Ag source, the In source, the Ga source, and the S source is 1:(0-20):(0-20):(1-40); 10-100 ml of solvent is added for every 1 mmol of gallium source; the heating temperature is 40-120°C; and the stirring time is 30-90 minutes.

[0019] As a further limitation of the first aspect of the present invention, in step 2, the S source is selected from one or more of thiourea, N,N-dimethylthiourea, dodecyl mercaptan, or elemental sulfur; the Ga source is selected from one or more of gallium acetate, gallium nitrate, gallium sulfate, gallium halide, or gallium acetylacetonate; the first solvent is selected from one or more of oleylamine, octadecylamine, or 1-octadecene; and the ligand is selected from one or a mixture of two of n-decathiol or n-dodecyl mercaptan.

[0020] As a further limitation of the first aspect of the present invention, the volume ratio of solvent to ligand is 1:(0.5-10); 0.5-5 ml of ligand is added for every 1 mmol of sulfur source; the heating temperature is 40-120°C; and the stirring time is 10-60 minutes.

[0021] As a further limitation of the first aspect of the present invention, in step 6, the short-chain ligand includes, but is not limited to, mercaptoethylamine, mercaptoacetic acid, mercaptosuccinic acid, or trioctylphosphine; the second solvent is selected from one or more of methanol, ethanol, chloroform, or acetone and a mixture thereof.

[0022] As a further limitation of the first aspect of the present invention, in step 7, the third solvent is selected from one or more of hexane, toluene, chloroform or dichloromethane; the antisolvent is selected from one or more of methanol, ethanol, isopropanol, tert-butanol or n-butanol.

[0023] In a second aspect, the present invention provides a method for fabricating an electroluminescent device based on Ag-In-Ga-S quantum dots as described in the first aspect, comprising: cleaning a glass substrate coated with indium tin oxide; sequentially spin-coating a PEDOT:PSS solution, a hole transport layer solution, and an Ag-In-Ga-S quantum dot solution; evaporating an electron transport layer; evaporating an electron injection layer and an aluminum electrode; and after evaporation, encapsulating and curing the device with an optical adhesive, thereby completing the fabrication of the electroluminescent device.

[0024] As a further limitation of the second aspect of the present invention, the electron transport layer deposited by vapor deposition includes, but is not limited to, PO-T2T, TPBi, TmPPPyTz or TmPyPB.

[0025] As a further limitation of the second aspect of the present invention, the electron injection layer includes, but is not limited to, LiF, CsCO3 or Li2CO3, with a deposition rate of 0.05-0.2 nm / s and a target thickness of 1 nm; the aluminum electrode is deposited with a deposition rate of 0.5 nm / s and a target thickness of 100 nm.

[0026] The beneficial effects of this invention are as follows: I-III-VI group quantum dots with narrow emission characteristics are synthesized in a one-step process. By post-injecting a gallium halide thermal solution, surface and internal defect luminescence is suppressed, achieving narrow-band emission of I-III-VI group quantum dots with a half-width of less than 30 nm and emission peaks in the 500-620 nm range. For the synthesized ultra-narrow-band I-III-VI group quantum dots, replacing long-chain ligands with short-chain ligands facilitates charge injection into electroluminescent devices. For quantum dot light-emitting diodes, the defect emission peaks of narrow-band I-III-VI quantum dot light-emitting diodes are suppressed by evaporating multiple layers of small molecules, achieving a balance between electron and hole injection and thus improving the external quantum yield.

[0027] The advantages of additional aspects of the invention will be set forth more clearly in the following description or will be learned by practice of the invention. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a flowchart illustrating the preparation process of the ultranarrow band Ag-In-Ga-S quantum dot solution according to an embodiment of the present invention.

[0030] Figure 2 This is a diagram illustrating the preparation process of ultranarrowband Ag-In-Ga-S quantum dots according to an embodiment of the present invention.

[0031] Figure 3 This is a schematic diagram illustrating the construction process of the ultra-narrowband Ag-In-Ga-S quantum dot light-emitting diode according to an embodiment of the present invention.

[0032] Figure 4 This is the fluorescence emission spectrum of the ultranarrowband Ag-In-Ga-S quantum dots described in an embodiment of the present invention.

[0033] Figure 5 This is a transmission electron microscope image of the ultranarrow band Ag-In-Ga-S quantum dots described in an embodiment of the present invention.

[0034] Figure 6 This is an X-ray diffraction pattern of the ultranarrowband Ag-In-Ga-S quantum dots described in an embodiment of the present invention.

[0035] Figure 7 This is the electroluminescence spectrum of the ultranarrowband Ag-In-Ga-S quantum dots described in an embodiment of the present invention.

[0036] Figure 8 The image shows the electroluminescence spectrum of ultranarrowband Ag-In-Ga-S quantum dots prepared using the conventional spin-coating electron transport layer method described in this embodiment of the invention. Detailed Implementation

[0037] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0038] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0039] It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as here.

[0040] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, and / or groups thereof.

[0041] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.

[0042] To facilitate understanding of the present invention, the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. However, the specific embodiments do not constitute a limitation on the embodiments of the present invention.

[0043] Those skilled in the art should understand that the accompanying drawings are merely schematic diagrams of embodiments, and the components in the drawings are not necessarily essential for implementing the present invention.

[0044] Example 1

[0045] In this embodiment 1, a method for preparing ultranarrowband Ag-In-Ga-S quantum dots is provided. An Ag source, In source, and Ga source are preheated in a single batch, followed by injection of a S precursor solution and heating to obtain Ag-In-Ga-S quantum dots. A Ga precursor solution is then injected again, followed by ligand exchange, to obtain ultranarrowband Ag-In-Ga-S quantum dots. The photoluminescence spectrum has a full width at half maximum (FWHM) of less than 30 nm, with the photoluminescence peak located in the 500-620 nm range. Group I-III-VI quantum dots with narrow emission characteristics of 30-40 nm were synthesized in a one-step process. By injecting a gallium halide hydrothermal solution afterward, the excess gallium source diffuses further into the quantum dots at high temperature, passivating the transpose defects that act as donor levels and reducing the luminescence of donor-acceptor levels with broad spectral characteristics. This results in ultra-narrow bandgap luminescence with a full width at half maximum (FWHM) of less than 30 nm. At the same time, halide ions act as ligands on the quantum dot surface, further passivating surface defects and improving the fluorescence quantum yield of the quantum dots. The bandgap size of the quantum dots can be controlled by adjusting the In / Ga ratio, thereby controlling the emission peak position. Replacing long-chain ligands with short-chain ligands with less steric hindrance is beneficial for charge injection into electroluminescent devices.

[0046] Specifically, in this embodiment, as Figure 1 , Figure 2 As shown, the preparation steps of ultranarrowband Ag-In-Ga-S quantum dots are as follows:

[0047] Step 1: Weigh the Ag source, In source, Ga source and solvent and place them in a three-necked flask. Heat and degas under vacuum, stirring and dissolving for a period of time.

[0048] Step 2: Weigh the S source, dissolve it in a mixed solution of solvent and ligand, and heat and stir for a period of time. Weigh the Ga source, dissolve it in a mixed solution of solvent and ligand, and heat and stir for a period of time. Weigh the short-chain ligand and dissolve it in the solvent.

[0049] Step 3: Introduce nitrogen gas, stir magnetically under nitrogen protection, inject sulfur precursor solution, and keep warm and stir for a period of time.

[0050] Step 4: Set the temperature to rise, and keep it warm for a period of time after the temperature rise is complete.

[0051] Step 5: Further inject Ga source and keep warm for a period of time.

[0052] Step 6: After the reaction is complete, add the short-chain ligand solution to the solution and keep it warm and stirred for a period of time.

[0053] Step 7: Add the product obtained from the reaction to the antisolvent and centrifuge. Repeat the centrifugation process by adding solvent and antisolvent to the precipitate in sequence to obtain ultranarrow band light-emitting quantum dots.

[0054] In the drug described in step 1, the Ag source includes, but is not limited to, silver nitrate, silver acetate, silver carbonate, and silver halide; the In source includes, but is not limited to, indium acetylacetonate, indium chloride, indium nitrate, indium sulfate, and indium acetate; the gallium source includes, but is not limited to, gallium acetylacetonate, gallium halide, gallium nitrate, gallium acetate, and gallium sulfate; the ligands include, but are not limited to, n-dodecyl mercaptan, n-decathiol, and octyl mercaptan; the solvents include, but are not limited to, oleylamine, octadecylamine, and 1-octadecene; the molar ratio of silver, indium, gallium, and sulfur precursors is 1:(0-20):(0-20):(1-40), wherein if the molar proportion of indium is too large or the molar proportion of gallium is too small, it will lead to an increase in the half-width at half-maximum, and the ultra-narrow band characteristic cannot be achieved; 10-30 ml of solvent is added for every 1 mmol of gallium source; the heating temperature is 40-120℃ (within this heating temperature, the drug can be fully dissolved in the solvent and will not decompose); the stirring time is 30-90 minutes.

[0055] In step 2, the sulfur source includes, but is not limited to, thiourea, N,N-dimethylthiourea, dodecyl mercaptan, and elemental sulfur; the gallium source includes, but is not limited to, gallium acetylacetonate, gallium halide, gallium nitrate, gallium acetate, and gallium sulfate; the solvent includes, but is not limited to, oleylamine, octadecylamine, and 1-octadecene; the ligands include, but are not limited to, n-dodecyl mercaptan, n-decathyl mercaptan, and octyl mercaptan; the short-chain ligands include, but are not limited to, mercaptoethylamine, mercaptoacetic acid, mercaptosuccinic acid, and trioctylphosphine; the volume ratio of solvent to ligand is 1:(0.5–10); 0.5–5 ml of ligand is added per 1 mmol of sulfur source; the heating temperature is 40–120 °C; and the stirring time is 10–60 minutes.

[0056] In step 3, the sulfur source is dissolved in a mixed solution of solvent and ligand, injected rapidly with a syringe, and stirred for 10–60 min.

[0057] In step 4, the heating process refers to rapidly raising the temperature to 260-330°C within 20 minutes, with a heating rate of 10-20°C / min. Rapidly raising the temperature can cause the gallium precursor to decompose quickly and passivate the quantum dots. The holding time is 0-60 minutes, during which the quantum dots will grow and self-passivate, and the luminescence peak will narrow rapidly.

[0058] In step 5, the heat preservation temperature is 240-330℃, and the heat preservation process lasts for 10-90 minutes.

[0059] In step 6, the heat preservation temperature is 40-120℃, and the heat preservation process lasts for 1-10 hours.

[0060] In step 7, the second solvent includes, but is not limited to, n-hexane, toluene, chloroform, and dichloromethane; the antisolvent includes, but is not limited to, methanol, ethanol, isopropanol, tert-butanol, and n-butanol; all reaction products are added to the antisolvent and centrifuged at 4000–12000 r / min for 2–10 min to separate the precipitate, and washed with the solvent and antisolvent 5–15 times in sequence.

[0061] In this embodiment, the above-mentioned ultranarrowband Ag-In-Ga-S quantum dot preparation process was carried out in an air environment, i.e., at room temperature of 20-30℃ and air humidity of 10-50%. Figure 4 As shown, the electroluminescence of Ag-In-Ga-S quantum dots treated with gallium chloride was significantly enhanced, and the full width at half maximum (FWHM) was successfully narrowed to below 30 nm. The peak position of the Ag-In-Ga-S quantum dots was 530 nm, with a FWHM of 28 nm, exhibiting good color purity. Figure 5 As shown, the Ag-In-Ga-S quantum dots exhibit a uniform size distribution, with a size of 6.4 nm. Figure 6 As shown, the X-ray diffraction peaks of Ag-In-Ga-S quantum dots are located between AIS and AGS, and they exhibit good crystallinity.

[0062] Example 2

[0063] In this embodiment 2, a method for constructing an ultra-narrowband Ag-In-Ga-S based narrowband quantum dot light-emitting diode is provided. The quantum dots synthesized in embodiment 1 are used to further construct the quantum dot light-emitting diode, achieving an efficiency greater than 1%, an electroluminescence half-width of less than 30 nm, and no obvious defect emission peaks.

[0064] Specifically, in this embodiment, as Figure 3 As shown, the fabrication steps for electroluminescent devices using the aforementioned ultranarrow band Ag-In-Ga-S quantum dots are as follows:

[0065] Step 1: Clean the glass substrate coated with indium tin oxide.

[0066] Step 2: Spin-coat PEDOT:PSS solution, hole transport layer solution, and quantum dot solution in sequence.

[0067] Step 3: Multiple evaporation depositions of small organic molecules to act as electron transport layers.

[0068] Step 4: Evaporate LiF and aluminum electrodes, and encapsulate with optical adhesive to complete device fabrication.

[0069] In step 1, the cleaning agents include, but are not limited to, deionized water, acetone, isopropanol, dichloromethane, and chloroform; after cleaning 3 to 5 times and drying, the product is placed in an ozone cleaner for 5 to 50 minutes.

[0070] In step 2, the hole transport layer includes, but is not limited to, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), poly(9,9-dioctylfluorene-co-bis-N,N'-phenyl-bis-N,N'-phenyl-1,4-phenylenediamine) (TFB), poly(9-vinylcarbazole) (PVK), and poly(9,9-dioctylfluorene-co-carbazole) (PF8CZ). After fixing the substrate to a spin coater, 20–60 μL of the hole transport layer solution (2–12 mg / ml) is spin-coated at 2000–6000 rpm for 0.5–2 minutes, followed by annealing at 100–180°C for 20–40 minutes. The prepared Ag-In-Ga-S solution (5–400 mg / ml) is then spin-coated at 2000–4000 rpm for 0.5–2 minutes without annealing.

[0071] In step 3, the vapor-deposited electron transport layers include, but are not limited to, 2,4,6-tris[3'-(pyridin-3-yl)-1,1'-biphenyl-3-yl]-1,3,5-triazine (PO-T2T), 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi), 2,4,6-tris[3-(3-methylpyridinyl)phenyl]-1,3,5-triazine (TmPPPyTz), and 1,3,5-tris[(3-methyl-5-(3-pyridinyl)phenyl]benzene (TmPyPB). The number of vapor-deposited electron transport layers is 1-5. The advantage of vapor deposition is that it avoids the destruction of quantum dots by the solvent, thereby suppressing the appearance of defect peaks. Multiple electron transport layers are conducive to achieving step-like matching of energy levels, which is beneficial for electron transport and achieving high external quantum efficiency, such as... Figure 7 As shown, the electroluminescence spectrum is 29 nm, and no obvious tail peak appears. If a conventional spin-coating electron transport layer method is used, such as... Figure 8 As shown, this will result in noticeable tail emission, leading to a decrease in color purity.

[0072] In step 4, the electron injection layer includes, but is not limited to, LiF, CsCO3, and Li2CO3, with a deposition rate of 0.05-0.2 nm / s and a target thickness of 1 nm. The aluminum electrode is then deposited at a deposition rate of 0.2 nm / s, with a target thickness of 100 nm. After deposition, the device is simply encapsulated. An appropriate amount of optical adhesive is applied to the front side of the device (spin-coated side), bonded to another cover glass, and then cured under a UV lamp. The electroluminescent device is now complete.

[0073] Example 3

[0074] In this embodiment 3, a method for preparing an ultranarrowband Ag-In-Ga-S quantum dot electroluminescent device is provided, comprising the following steps: Silver nitrate, indium chloride, gallium acetylacetonate, and zinc chloride are weighed and mixed in 20 ml of oleylamine solution, and transferred to a four-necked flask. The amount of silver nitrate added is 0.12 mmol, the amount of indium chloride added is 0.24 mmol, and the amount of gallium acetylacetonate added is 1.2 mmol. 2.32 mmol of sulfur powder is dissolved in a mixed solution of 3 ml oleylamine and 5 ml n-dodecyl mercaptan, and stirred at 70°C for half an hour. 1.2 mmol of GaCl3 is dissolved in 6 ml oleylamine, and stirred at 70°C for 1 hour. Further, the reaction system is degassed at 90°C for 1 hour, then protected with nitrogen gas. The prepared sulfur powder solution is injected using a syringe, kept at this temperature for 20 minutes, and then heated to 300°C at a rate of 30°C / min and kept at this temperature for 40 minutes. Further, the prepared GaCl3 solution was injected using a syringe, the temperature was adjusted to 270℃, and maintained at this temperature for 30 minutes. After the reaction was completed, the solution was cooled to room temperature. 20 mg of 1-mercaptosuccinic acid was dissolved in ethanol solution, stirred until transparent, and then injected into the quantum dot solution. The solution was stirred at 50℃ for 10 hours. After the reaction product cooled, 3 volumes of isopropanol were added to the reaction product solution to precipitate the quantum dots. The solution was then centrifuged at 9000 r / min for 5 minutes, the supernatant was discarded, and the precipitate was retained. The obtained precipitate was dissolved in a small amount of n-hexane, and then ethanol was added until complete precipitation. The solution was centrifuged at 9000 r / min for 5 minutes, and the precipitate was retained. This process was repeated 5 times, followed by washing 3 times alternately with ethanol and n-octane to obtain the Ag-In-Ga-S quantum dot solution dissolved in n-octane. The glass substrate coated with indium tin oxide (ITO) was cleaned with deionized water, acetone, and isopropanol, respectively, for 30 minutes each. After drying, the substrate was placed in an ozone cleaner for 20 minutes. 150 µL of LPEDOT:PSS was uniformly coated onto a cleaned glass substrate. After spin-coating at 5000 rpm for 1 minute, the substrate was placed on a heating stage and annealed at 150°C for 15 minutes. After cooling, the substrate was transferred to a glove box. The substrate was then fixed in the spin coater, and 60 µL of a chlorobenzene solution of PTAA (8 mg / ml) was spin-coated at 4000 rpm for 1 minute, followed by annealing at 120°C for 30 minutes. A prepared Ag-In-Ga-S n-octane solution (20 mg / ml) was then spin-coated at 3000 rpm for 1 minute without annealing. After the device returned to room temperature, it was transferred to a vapor deposition chamber. 20 nm of TmPPPyTz was deposited at a deposition rate of 0.2 nm / s. 20 nm of PO-T2T was also deposited at a deposition rate of 0.2 nm / s. LiF was deposited at a deposition rate of 0.1 nm / s, with a target thickness of 1 nm. Aluminum electrodes were deposited by vapor deposition at a rate of 0.1 nm / s, with a target thickness of 100 nm.After the vapor deposition is completed, the device is simply packaged. An appropriate amount of optical adhesive is applied to the front of the device (spin-coated surface) and bonded to another cover glass sheet. The device is then placed under a UV lamp for curing, and the electroluminescent device is thus completed.

[0075] In summary, the quantum dot preparation method described in this invention effectively overcomes the drawback of generally large full width at half maximum (FWHM) of the electroluminescence spectrum of group I-III-VI semiconductor nanocrystals. It prepares group I-III-VI semiconductor nanocrystals with narrow emission characteristics in a one-step process. Subsequent gallium halide treatment further passivates the donor-acceptor radiative recombination with broad spectral characteristics, further narrowing the FWHM to within 30 nm. Ligand exchange replaces long-chain ligands on the quantum dot surface with short-chain ligands that are more conducive to charge injection. By controlling the appropriate elemental ratio, the photoluminescence peak position can be in the 500-620 nm range, demonstrating good application potential in electroluminescent devices. By evaporating multiple layers of small organic molecules as an electron transport layer, electron injection is suppressed, and interface defects between the quantum dot and the electron transport layer are passivated, achieving a balance between electron and hole injection. This results in an electroluminescence spectrum FWHM of less than 30 nm, significant suppression of long-wavelength defect peaks, and an external quantum efficiency greater than 1%. The quantum dot synthesis method of this invention is simple, the materials are inexpensive and readily available, the raw materials are all non-toxic and harmless, the reaction time is short, it is easy to produce on a large scale, and it has good application prospects.

[0076] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that, based on the technical solutions disclosed in the present invention, various modifications or variations that can be made by those skilled in the art without creative effort should be included within the scope of protection of the present invention.

Claims

1. A method for preparing Ag-In-Ga-S quantum dots with ultra-narrow band characteristics, characterized in that, Includes the following steps: Step 1: Weigh the Ag source, In source, Ga source and the first solvent and place them in a three-necked flask. Heat and degas under vacuum, stirring and dissolving for a period of time. Step 2: Weigh the S source, dissolve it in the mixed solution of the first solvent and the ligand, heat and stir for a period of time, weigh the Ga source, dissolve it in the mixed solution of the first solvent and the ligand, heat and stir for a period of time, weigh the short-chain ligand, and dissolve it in the second solvent; Step 3: Introduce nitrogen gas, stir magnetically under nitrogen protection, inject the sulfur precursor solution, and maintain the temperature and stir for a period of time. Step 4: Set the heating process, and after the heating is completed, keep it at the temperature for a period of time; wherein, the heating process refers to heating at a rate of 10-20℃ / min to 260-330℃, so that the gallium precursor is rapidly decomposed and the quantum dots are passivated; the holding process is 0-60 minutes, during which the quantum dots will grow and self-passivate at the same time, and the luminescence peak will narrow rapidly. Step 5: Inject Ga source and keep warm for a period of time; Step 6: After the reaction is complete, add the short-chain ligand dissolved in the second solvent to the solution, and keep it warm and stirred for a period of time; Step 7: Add the final product to the antisolvent and centrifuge. Add the precipitate to the third solvent and antisolvent in sequence and centrifuge repeatedly to obtain narrow-band luminescent quantum dots.

2. The method for preparing Ag-In-Ga-S quantum dots with ultra-narrow band characteristics according to claim 1, characterized in that, In step 1, the Ag source is selected from one or more of silver acetate, silver carbonate, silver nitrate, sulfate, or silver halide; the In source is selected from one or more of indium acetate, indium nitrate, indium sulfate, indium halide, or indium acetylacetonate; and the Ga source is selected from one or more of gallium acetate, gallium nitrate, gallium sulfate, gallium halide, or gallium acetylacetonate.

3. The method for preparing Ag-In-Ga-S quantum dots with ultra-narrow band characteristics according to claim 2, characterized in that, The molar ratio of the Ag source, the In source, the Ga source, and the S source is 1:(0-20):(0-20):(1-40); 10-100 ml of solvent is added for every 1 mmol of gallium source; the heating temperature is 40-120°C; and the stirring time is 30-90 minutes.

4. The method for preparing Ag-In-Ga-S quantum dots with ultra-narrow band characteristics according to claim 1, characterized in that, In step 2, the S source is selected from one or more of thiourea, N,N-dimethylthiourea, dodecyl mercaptan, or elemental sulfur; the Ga source is selected from one or more of gallium acetate, gallium nitrate, gallium sulfate, gallium halide, or gallium acetylacetonate; the first solvent is selected from one or more of oleylamine, octadecylamine, or 1-octadecene; and the ligand is selected from one or a mixture of two of n-decathiol or n-dodecyl mercaptan.

5. The method for preparing Ag-In-Ga-S quantum dots with ultra-narrow band characteristics according to claim 4, characterized in that, The volume ratio of solvent to ligand is 1:(0.5-10); 0.5-5 ml of ligand is added for every 1 mmol of sulfur source; the heating temperature is 40-120℃; and the stirring time is 10-60 minutes.

6. The method for preparing Ag-In-Ga-S quantum dots with ultra-narrow band characteristics according to claim 4, characterized in that, In step 6, the short-chain ligands include, but are not limited to, mercaptoethylamine, mercaptoacetic acid, mercaptosuccinic acid, or trioctylphosphine; the second solvent is selected from one or more of methanol, ethanol, chloroform, or acetone and a mixture thereof.

7. The method for preparing Ag-In-Ga-S quantum dots with ultra-narrow band characteristics according to claim 6, characterized in that, In step 7, the third solvent is selected from one or more of hexane, toluene, chloroform, or dichloromethane; the antisolvent is selected from one or more of methanol, ethanol, isopropanol, tert-butanol, or n-butanol.

8. A method for fabricating an electroluminescent device based on Ag-In-Ga-S quantum dots as described in any one of claims 1-7, characterized in that, include: Clean the glass substrate coated with indium tin oxide; spin-coate PEDOT:PSS solution, hole transport layer solution, and Ag-In-Ga-S quantum dot solution in sequence; An electron transport layer is deposited by vapor deposition; an electron injection layer and an aluminum electrode are deposited by vapor deposition; after vapor deposition, the electroluminescent device is encapsulated and cured with optical adhesive, and the device is fabricated.

9. The method according to claim 8, characterized in that, The electron transport layer deposited by vapor deposition includes, but is not limited to, PO-T2T, TPBi, TmPPPyTz or TmPyPB, and the number of vapor deposition layers includes, but is not limited to, 1-5 layers.

10. The method according to claim 8, characterized in that, The electron injection layer includes, but is not limited to, LiF, CsCO3 or Li2CO3, with a deposition rate of 0.05-0.2 nm / s and a target thickness of 1 nm; the aluminum electrode is deposited with a deposition rate of 0.5 nm / s and a target thickness of 100 nm.

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