Method for manufacturing quantum dots, light-emitting device, and manufacturing method thereof, and nanomaterial

Abstract

To provide a quantum dot that achieves high luminescence intensity and a light-emitting device using the quantum dot.SOLUTION: A method for manufacturing quantum dots includes the steps of dispersing cesium acetate, sodium acetate, and indium acetate in a mixture of organic solvents containing a fatty acid having a main chain carbon number of 18 or less and an aliphatic amine having a main chain carbon number of 18 or less in a predetermined ratio to prepare a solution, and injecting chloride into the solution while heating it to synthesize Cs2NaInCl6 perovskite quantum dots.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for producing quantum dots, a light-emitting device and a method for producing the same, and a nanomaterial. [Background technology]

[0002] Lead halide perovskites are used in light-emitting devices such as LEDs (light-emitting diodes). Lead-free perovskites include Cs2NaInCl6 perovskite, in which Pb (lead) is replaced with Na (sodium) and In (indium) and doped with Sb (antimony) (see, for example, Non-Patent Document 1). Cs2NaInCl6 nanocrystals doped with Sb and Mn (manganese) are also known (see, for example, Non-Patent Document 2).

[0003] It is known that Cs2AgInCl6 perovskite can be produced by adding cesium acetate, silver acetate, and indium acetate to a solution of 1-octadecene, oleic acid, and oleylamine, and then injecting chloride (see, for example, Non-Patent Document 3). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] R. Zeng et al., J. Phys. Chem. Letter. 2020, 11, 2053-2061 [Non-patent document 2] X. Liu et al., Small 2020, 16, 2002547 [Non-patent document 3] X. Wang et al., Nano Lett. 2022, 22, 636-643 Summary of the Invention [Problem to be solved by the invention]

[0005] In the nanocrystal manufacturing method described in Non-Patent Document 2, the addition of Mn significantly reduces the PLQY (Photoluminescence quantum yield). Without the addition of Mn, the PLQY is 50%, but at a Mn concentration of 2%, the PLQY drops to 25% or less. When nanocrystals with a low PLQY are used in light-emitting devices, sufficient light emission cannot be obtained.

[0006] An object of the present invention is to provide a quantum dot that achieves high luminescence intensity and a light-emitting device using the quantum dot. [Means for solving the problem]

[0007] In one embodiment, a method for producing quantum dots includes: a step of dispersing cesium acetate, sodium acetate, and indium acetate in a mixture of an organic solvent containing a fatty acid having a main chain carbon number of 18 or less and an aliphatic amine having a main chain carbon number of 18 or less in a predetermined ratio to prepare a solution; synthesizing Cs2NaInCl6 perovskite quantum dots by injecting chloride into the heated solution; Includes:

[0008] In another embodiment, the light emitting element comprises: a light-emitting layer having a thickness of 25 nm or less, the light-emitting layer including Cs2NaInCl6 perovskite quantum dots doped with Sb and at least one element selected from Mn and rare earth elements; a hole transport layer and an electron transport layer sandwiching the light-emitting layer; a first electrode provided on the hole transport layer opposite the light emitting layer; a second electrode provided on the electron transport layer opposite the light emitting layer; Equipped with.

[0009] In yet another embodiment, the nanomaterial is: Cs2NaInCl6 perovskite quantum dots and a ligand bound to the quantum dot and comprising a fatty acid having a main chain carbon number of less than 18 and / or an aliphatic amine having a main chain carbon number of less than 18; Equipped with. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide quantum dots that achieve high luminous intensity and light-emitting devices using the quantum dots. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view of an LED manufactured by the manufacturing method of the first embodiment. [Figure 2] Figure 2 shows the energy diagram of Sb-doped Cs2NaInCl6. [Figure 3] FIG. 3(a) is a flowchart showing a method for producing a quantum dot solution, and FIG. 3(b) is a flowchart of step S10 in FIG. 3(a). [Figure 4] FIG. 4 is a flowchart showing a method for manufacturing an LED. [Figure 5] FIG. 5(a) is a diagram showing the photoluminescence spectrum of the quantum dot solution, and FIG. 5(b) is a diagram showing the PLQY of the quantum dot solution. [Figure 6] FIG. 6(a) shows the photoluminescence spectrum of the quantum dot solution in sample 4:1, and FIG. 6(b) shows the XRD results. [Figure 7] 7(a) to 7(c) are schematic diagrams showing the roles of OA and OAm. [Figure 8] FIG. 8 shows photographs of the quantum dot solutions in Samples A to C after three days. [Figure 9] FIG. 9 is an energy diagram of Sb and Mn doped Cs2NaInCl6. [Figure 10] Figures 10(a) and 10(b) are PYS spectra of the quantum dots. [Figure 11]FIG. 11 is a diagram showing the band structure of an LED with a Mn molar ratio of 10%. [Figure 12] FIG. 12 is a diagram showing the spectrum of electroluminescence from LED_A. [Figure 13] FIG. 13(a) is a graph showing luminance versus voltage for LED_A, and FIG. 13(b) is a graph showing EQE versus voltage. [Figure 14] FIG. 14 is a diagram showing the electroluminescence spectrum of LED_B. [Figure 15] FIG. 15(a) is a graph showing current density and luminance versus voltage for LED_B, and FIG. 15(b) is a graph showing EQE versus voltage. [Figure 16] FIG. 16 is a cross-sectional view of LED_C. [Figure 17] FIG. 17 is a diagram showing the band structure of LED_C. [Figure 18] FIG. 18 is a diagram showing the electroluminescence spectrum of LED_C. [Figure 19] FIG. 19(a) is a graph showing current density and luminance versus voltage for LED_C, and FIG. 19(b) is a graph showing EQE versus voltage. [Figure 20] FIG. 20 is a diagram showing the spectrum of electroluminescence from LED_D. [Figure 21] FIG. 21(a) is a graph showing the current density and luminance versus voltage for LED_D, and FIG. 21(b) is a graph showing the EQE versus voltage. [Figure 22] FIG. 22 is a diagram showing the spectrum of electroluminescence from LED_E. [Figure 23] FIG. 23(a) is a graph showing current density and luminance versus voltage in LED_E, and FIG. 23(b) is a graph showing EQE versus voltage in LED_E. [Figure 24] FIG. 24 is a diagram showing the spectrum of electroluminescence from LED_F. [Figure 25]FIG. 25(a) is a graph showing current density and luminance versus voltage in LED_F, and FIG. 25(b) is a graph showing EQE versus voltage. [Figure 26] FIG. 26(a) shows the XRD results of the quantum dot solution, and FIG. 26(b) is an enlarged view of the peak in the (220) plane. [Figure 27] FIG. 27 shows photoluminescence spectra of quantum dot solutions with different Mn molar ratios. [Figure 28] FIG. 28(a) shows the absorption spectra of quantum dot solutions with different Mn molar ratios, and FIG. 28(b) shows the photoluminescence excitation spectrum of a sample with a 10% Mn molar ratio. [Figure 29] FIG. 29 is a cross-sectional view of the LED fabricated in Experiment 3. [Figure 30] FIG. 30 shows the photoluminescence spectrum of quantum dot solution G. [Figure 31] FIG. 31 is a transmission electron microscope image of quantum dot solution G. [Figure 32] FIG. 32 is a diagram showing the spectrum of electroluminescence from LED_G. [Figure 33] FIG. 33(a) is a graph showing current density and luminance versus voltage for LED_G, and FIG. 33(b) is a graph showing EQE versus voltage for LED_G. [Figure 34] FIG. 34(a) is a graph showing the current density and luminance versus voltage for LED_R, and FIG. 34(b) is a graph showing the EQE versus voltage for LED_R. [Figure 35] 35(a) is a schematic diagram of the nanomaterial in quantum dot solution R, and FIG. 35(b) is a schematic diagram of the nanomaterial in quantum dot solution G. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the embodiments, LEDs (light emitting diodes) will be used as light-emitting elements. However, the following embodiments are merely examples for embodying the technical concepts of the invention, and the present invention is not limited to the described configurations and numerical values. In the drawings, components having the same functions may be given the same reference numerals, and redundant descriptions may be omitted. Partial substitution or combination between different embodiments and configuration examples is possible. The size, positional relationship, etc. of each component shown in each drawing may be exaggerated to facilitate understanding of the invention.

[0013] (Embodiment 1) (LED structure) FIG. 1 is a cross-sectional view of an LED manufactured using the manufacturing method of Embodiment 1. In the LED 100, an electrode 11 is provided on a substrate 10. However, the substrate 10 is not essential and may be removed after device fabrication. In this example, the substrate 10 is a transparent insulating substrate to extract light from the substrate 10 side. The electrode 11 is a transparent conductive layer. An oxide conductive substrate such as ITO (indium tin oxide), IZO (indium zinc oxide), or IZTO (indium zinc tin oxide) may be used to serve as both the substrate 10 and the electrode 11. A hole transport layer 12 is provided on the electrode 11. The hole transport layer 12 is an organic semiconductor layer. A light-emitting layer 13 is provided on the hole transport layer 12. The light-emitting layer 13 contains perovskite quantum dots 18. The light-emitting layer 13 has a thickness T13. The quantum dots 18 are provided throughout the light-emitting layer 13, but FIG. 1 schematically illustrates only a portion of the quantum dots 18. An electron transport layer 14 is provided on the light-emitting layer 13. The electron transport layer 14 is an organic semiconductor. An electrode 15 is provided on the electron transport layer 14. The electrode 15 is a conductive layer. The hole transport layer 12 and the electron transport layer 14 sandwich the light-emitting layer 13, with the electrode 11, which is a first electrode, being provided on the side of the hole transport layer 12 opposite the light-emitting layer 13, and the electrode 15, which is a second electrode, being provided on the side of the electron transport layer 14 opposite the light-emitting layer 13.

[0014] When a positive voltage relative to the potential of electrode 15 is applied to electrode 11, holes are injected from electrode 11 into hole transport layer 12. Hole transport layer 12 transports the holes from electrode 11 to light-emitting layer 13. Electrons are injected from electrode 15 into electron transport layer 14. Electron transport layer 14 transports electrons from electrode 15 to light-emitting layer 13. Light is emitted by recombination of holes and electrons in quantum dots 18 in light-emitting layer 13. Light emitted in light-emitting layer 13 passes through hole transport layer 12, electrode 11, and substrate 10 and is emitted downward in FIG. 1.

[0015] The quantum dots 18 in the light-emitting layer 13 are double perovskite quantum dots in which Sb is doped into Cs2NaInCl6. Double perovskite has the general formula ABO3, and two elements are contained in the B site of the perovskite. In general perovskite, Pb (lead) is used in the B site. However, Pb is toxic, and perovskite containing Pb lacks stability. Therefore, Pb 2+ Na + and In 3+ By replacing Cs2AgInCl6 with Cs2AgInCl6, Pb-free perovskite quantum dots can be realized. Quantum dots 18 are inexpensive because they do not contain Ag, like Cs2AgInCl6 double perovskite quantum dots.

[0016] Figure 2 is an energy diagram of Sb-doped Cs2NaInCl6. As shown in Figure 2, in Cs2NaInCl6 double perovskite quantum dots, the ground state GS forms the valence band, and the FE (free exciton) level forms the conduction band. The energy Ef between GS and FE is approximately 320 nm in wavelength. When ultraviolet light with a wavelength of approximately 320 nm is irradiated, holes are generated in GS and electrons are generated in FE. When Sb is doped, In is replaced by Sb, forming a STE (self-trapped exciton) level. The energy Es between GS and STE is smaller than the energy Ef. When the electron in FE is bound to the STE as shown by arrow T1, and the electron in STE recombines with the hole in GS, blue light Lb with a wavelength of approximately 450 nm corresponding to Es is emitted.

[0017] As described above, when In in Cs2NaInCl6 double perovskite quantum dots is replaced with Sb, blue light Lb is emitted.

[0018] In Non-Patent Document 1, a hydrothermal synthesis method is used to mix cesium chloride, sodium chloride, antimony chloride, and indium chloride in a hydrochloric acid solution, and the mixture is heated to 180°C for 2 hours and then cooled to room temperature over 10 hours to produce Sb 3+ In this paper, we synthesized a doped Cs2NaInCl6 double perovskite. In Non-Patent Document 1, a PLQY of nearly 76% was obtained, but further improvement of the PLQY is required. In Embodiment 1, we provide a manufacturing method for manufacturing an LED with improved PLQY.

[0019] (Method for preparing quantum dot solution) Fig. 3(a) is a flowchart showing a method for preparing a quantum dot solution. Fig. 3(b) is a flowchart of step S10 in Fig. 3(a). As shown in Fig. 3(a), a solution is prepared (step S10).

[0020] Figure 3(b) is a flowchart of step S10 in Figure 3(a). As shown in Figure 3(b), an organic medium containing an organic solvent and a predetermined ratio of oleic acid (OA) and oleylamine (OAm) is prepared (step S30). The organic solvent is, for example, 1-octadecene. Using 1-octadecene as the organic solvent improves the PLQ of the quantum dots, resulting in an LED with high luminous intensity.

[0021] Next, acetates such as cesium acetate, sodium acetate, indium acetate, and antimony acetate are mixed with the organic solvent (step S32). As described below, when adding at least one element selected from Mn and rare earth elements in addition to Sb to Cs2NaInCl6, cesium acetate, sodium acetate, indium acetate, and antimony acetate, as well as acetates of at least one element selected from Mn and rare earth elements, can be dispersed in the mixed solution prepared in step S30. Next, the mixed solution is stirred under predetermined conditions (step S34). The temperature at which the solution is stirred is, for example, 100°C to 120°C, and the stirring time is, for example, 50 minutes or more.

[0022] Next, returning to FIG. 3(a), a chloride is injected into the prepared solution (step S12). The injection of the chloride may be performed by heating. The chloride is, for example, germanium chloride. The heating temperature during injection is, for example, 170°C to 230°C. The heating time is, for example, 1 minute or more. In addition to germanium chloride, benzoyl chloride or chlorotrimethylsilane may also be used as the chloride used in step S12. By using germanium chloride as the chloride, the PLQ of the quantum dots can be improved, resulting in an LED with high luminous intensity.

[0023] Next, the chloride and the solution are reacted to synthesize quantum dots (step S14). The quantum dots are synthesized by heating. The heating temperature is, for example, 170°C to 230°C, which is higher than the temperature at the time of injection in step S12. The heating time is, for example, 1 minute or more.

[0024] Next, the synthesized quantum dots are dispersed in an organic solvent (step S16). The quantum dots from step S14 may be washed using a centrifugal method before being dispersed in an organic solvent. The organic solvent is, for example, hexane. Using hexane as the organic solvent improves the PLQ of the quantum dots, resulting in an LED with high luminous intensity.

[0025] (LED manufacturing method) 4 is a flowchart showing a method for manufacturing an LED. As shown in FIG. 4, an electrode 11 is formed on a substrate 10 (step S20). The electrode 11 is formed by, for example, vacuum deposition. Next, a hole transport layer 12 is formed on the electrode 11 (step S22). To form the hole transport layer 12, for example, a solution containing a hole transport material is applied onto the electrode 11, and the applied solution is heat-treated.

[0026] Next, the light-emitting layer 13 is formed on the hole transport layer 12 (step S24). In forming the light-emitting layer 13, for example, the dispersion liquid produced in step S16 of FIG. 3 is applied onto the hole transport layer 12, and the applied dispersion liquid is heat-treated. Next, the electron transport layer 14 is formed on the light-emitting layer 13 (step S26). In forming the electron transport layer 14, for example, a solution containing an electron transport material is applied onto the light-emitting layer 13, and the applied solution is heat-treated. Next, the electrode 15 is formed on the electron transport layer 14 (step S28). The electrode 15 is formed by, for example, vacuum deposition.

[0027] In the first embodiment, as in step S10 described above, a first solution is prepared by dispersing cesium acetate, sodium acetate, indium acetate, and antimony acetate in a mixture of organic solvents containing oleic acid and oleylamine in a predetermined ratio. As in steps S12 and S14, chlorides are added to the first solution while it is heated, synthesizing Sb-doped Cs2NaInCl6 double perovskite quantum dots. The quantum dot dispersion is then applied to a substrate 10 and heat-treated, easily forming a thin film of the light-emitting layer 13 containing quantum dots 18. This allows for the realization of an LED with high emission intensity, as shown in Experiment 1 below.

[0028] Next, we consider the ratio of OA to OAm that increases the PLQY of Sb-doped Cs2NaInCl6 quantum dots.

[0029] (Experiment 1) The quantum dot solution was prepared as follows. Process S30 An organic solvent was prepared by mixing 9 mL of 1-octadecene with a predetermined ratio of oleic acid and oleylamine. The total volume of the oleic acid and oleylamine was 3.5 mL.

[0030] Process S32 The organic solvent prepared in step S30 was mixed with 0.71 mmol of cesium acetate, 0.5 mmol of sodium acetate, 0.495 mmol of indium acetate, and 0.055 mmol of antimony acetate.

[0031] Process S34 In step S32, the mixed liquid was stirred under vacuum at 110° C. for 50 minutes to disperse cesium acetate, sodium acetate, indium acetate, and antimony acetate in the mixed liquid.

[0032] Process S12 77 μL of germanium chloride and 1 mL of 1-octadecene are mixed in advance. The solution prepared in step S10 is heated to 170° C., and the germanium chloride mixed with 1-octadecene is poured into the solution.

[0033] Process S14 The solution containing germanium chloride was heated at 180°C for 5 minutes. This resulted in the synthesis of Sb-doped Cs2NaInCl6 double perovskite quantum dots. The quantum dots were approximately 10 nm in size.

[0034] Process S16 The mixed solution prepared in step S14 was washed as follows: The mixed solution from step S14 was placed in a centrifuge tube and centrifuged at 9,500 rpm for 5 minutes. The supernatant was discarded, and the precipitate was dissolved in 10 mL of chlorobenzene. This was further centrifuged at 9,500 rpm for 5 minutes. The supernatant was discarded, and the precipitate was thoroughly dried. This completes the washing process. The dried precipitate was dispersed in 4 mL of hexane. The dispersed hexane was centrifuged at 9,500 rpm for 2 minutes. The supernatant after centrifugation is the quantum dot solution.

[0035] Quantum dot solution samples were prepared in which the volume ratios of oleic acid (OA) to oleylamine (OAm) in the mixed solution in step S10 were 4:1, 2:1, 1:1, 1:2, and 1:4. The samples with OA:OAm volume ratios of 4:1, 2:1, 1:1, 1:2, and 1:4 are designated Sample 4:1, Sample 2:1, Sample 1:1, Sample 1:2, and Sample 1:4, respectively.

[0036] (Photoluminescence results) The photoluminescence of the prepared quantum dot solution was measured. Figure 5(a) shows the photoluminescence spectrum of the quantum dot solution. The horizontal axis represents wavelength, and the vertical axis represents normalized intensity. The normalized intensity is the photoluminescence intensity normalized by the maximum photoluminescence intensity of OA:OAm = 1:4. As shown in Figure 5(a), the normalized peak intensity of Sample 2:1 is smaller than that of Sample 4:1. The normalized peak intensity of Sample 1:1 is larger than that of Sample 2:1. The normalized peak intensity of Sample 1:2 and Sample 1:4 is larger than that of Sample 1:1.

[0037] Figure 5(b) shows the PLQY of the quantum dot solution. The horizontal axis represents the volume ratio of OA to OAm (OA:OAm) used in the sample. The vertical axis represents the PLQY (%). The PLQY of each sample is shown along with the data variability. As shown in Figure 5(b), the data variability is smaller for Sample 2:1 than for Sample 4:1. The PLQY improves from Sample 2:1 to Sample 1:1, Sample 1:2, and Sample 1:4. The average PLQY for Sample 1:4 is over 90%. Thus, in step S10, increasing the volume ratio of oleylamine OAm to oleic acid OA (OAm / OAm) improves the PLQY. All samples exhibited PLQY comparable to that of Non-Patent Document 1, which was prepared by hydrothermal synthesis. In particular, Samples 1:2 and 1:4 exhibited high PLQYs exceeding approximately 76% of that of Non-Patent Document 1.

[0038] Next, we examined the stability of the quantum dot solution. After leaving the quantum dots for one month, we measured the photoluminescence again. Table 1 compares the photoluminescence peak intensity in the initial state and after one month.

[0039] [Table 1]

[0040] As shown in Table 1, for samples 4:1, 2:1, and 1:1, the peak intensity barely changes between the initial state and one month later. For sample 1:2, the peak intensity after one month decreases only slightly from the initial state. For sample 1:4, the peak intensity after one month decreases slightly from the initial state. Thus, in step S10, by increasing the volume ratio of oleylamine OAm to oleic acid OA (OAm / OAm), the luminescence intensity is maintained and the stability of the quantum dot solution is maintained.

[0041] Figure 6(a) shows the photoluminescence spectrum of the quantum dot solution in sample 4:1. As shown in Figure 6(a), the peak position is approximately 450 nm and the peak intensity is approximately 2900 nm both in the initial state and after one month. The waveform of the photoluminescence spectrum shows almost no change even after one month from the initial state.

[0042] Figure 6(b) shows the X-ray diffraction (XRD) results for the quantum dot solution of sample 4:1. As shown in Figure 6(b), the 2θ of the peak remains almost unchanged from the initial state even after one month, indicating that the crystalline structure of the quantum dots remains stable even after one month.

[0043] Figures 7(a) to 7(c) are schematic diagrams showing the roles of OA and OAm. Figure 7(b) shows the OA:OAm 4:1 state, and Figure 7(c) shows the OA:OAm 1:4 state. As shown in Figures 7(b) and 7(c), Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR) analyses of the quantum dots reveal that oleylamine (OAm) 20 binds to the surface of the quantum dots 18, while oleic acid (OA) 22 hardly binds to the surface of the quantum dots 18.

[0044] As shown in Figure 7(c), when there is a large amount of OAm20, OAm20 binds to the surface of the quantum dots 18 and acts as a ligand, so that OAm20 fills the defects of the quantum dots 18, which is thought to improve the PLQY.

[0045] As shown in FIG. 7(a), oleic acid OA22 ionizes oleylamine OAm20 as indicated by arrow 60. As a result, OAm20 becomes a cation OAm20 as indicated by arrow 61. + 21, and OA22 is the anion OA - As shown by arrow 63 in FIG. 7(b), even if OAm 20a leaves the quantum dot 18, OA 22a ionizes OAm 20a as shown by arrows 64 and 65. As shown by arrow 66, the ionized OAm + 21a rebinds to quantum dots 18. Therefore, oleic acid (OA) contributes to the stability of the quantum dot solution.

[0046] 7(c), even if OAm20a leaves the quantum dots 18 as indicated by arrow 66, the OAm20a is not ionized because there is little OA20. In this case, the quantum dots 18 aggregate and tend to precipitate.

[0047] From the above, from the viewpoint of improving PLQY, the volume ratio of oleylamine OAm to oleic acid OA, OAm / OA, is preferably 1 / 4 or more, more preferably 1 / 2 or more, and even more preferably 1 or more. From the viewpoint of improving the stability of the quantum dot solution, OAm / OA is preferably 10 or less, more preferably 4 or less, and even more preferably 2 or less.

[0048] As can be seen from Table 1, increasing the OAm / OA ratio may decrease the stability of the quantum dot solution. If we consider that oleic acid stabilizes the quantum dot solution by promoting the recombination of oleylamine that has left the quantum dots back into the quantum dots, then it should be possible to add oleic acid to the quantum dot solution after synthesizing the quantum dots.

[0049] Therefore, we prepared a quantum dot solution with an OA:OAm ratio of 1:4, and created three samples: Sample A with no additions, Sample B with 10 μL of oleylamine OAm added, and Sample C with 10 μL of oleic acid OA added. Samples A to C were left for three days, and then the quantum dot solutions were observed.

[0050] Figure 8 shows photographs of the quantum dot solutions in Samples A to C after three days. From left to right are Samples A, B, and C. As shown in Figure 8, precipitation occurred in Samples A and B, as indicated by arrow 50. In Sample C, no precipitation occurred, as indicated by arrow 52.

[0051] As shown in Figure 7(c), when OAm20a is released from the quantum dots 18, the quantum dots 18 aggregate together and form precipitates. In samples A and B, even though OAm20a is released from the quantum dots 18, OAm20a does not recombine with the quantum dots 18, so it is thought that the quantum dots 18 aggregate together and form precipitates. In sample C, even though OAm20a is released from the quantum dots 18, OAm20a is ionized by the added oleic acid, and as in Figure 7(b), OAm + 21a recombines with the quantum dots 18. It is believed that this is why the quantum dots 18 do not aggregate with each other and no precipitate is formed.

[0052] As described above, by adding oleic acid to the quantum dot solution after step S16 in Figure 3(a), it is believed that the stability of the quantum dot solution can be ensured even when quantum dots are synthesized using a mixed solution with a high OAm / OA ratio.

[0053] (Embodiment 2) The second embodiment is a light-emitting device using Cs2NaInCl6 doped with Sb and Mn (or a rare earth element). Figure 9 is an energy diagram of Cs2NaInCl6 doped with Sb and Mn. As shown in Figure 9, when Cs2NaInCl6 is doped with Mn in addition to Sb, the level is increased by the d electrons of Mn. 6 A1 and 4 T1 is formed. 6 A1 and 4 The energy Em between T1 and Mn is smaller than Es. Energy is transferred from the electron of STE to Mn as shown by the arrow T2, and the level 6 A1 electron level 4 Excited to T1. 6 A1 electrons and levels 4 When the electrons recombine with holes in T1, red light Lr is emitted with a wavelength of approximately 630 nm, corresponding to Em. In Non-Patent Document 2, white light is obtained by doping Cs2NaInCl6 with Sb and Mn, but sufficient PLQY is not obtained and the Mn concentration range is limited. Therefore, in the LED of Embodiment 2, the mixing ratio of OA and OAm is adjusted as in Embodiment 1, and the thickness T13 of the light-emitting layer 13 in Figure 1 is set to 25 nm or less, thereby expanding the range of color adjustment for the white light while maintaining the light-emitting intensity from the light-emitting layer 13.

[0054] (Experiment 2) The method of Experiment 1 was used, with the OAm / OA ratio set to 4. The appropriate amounts for step S10 in Figure 3 were 9 mL of 1-octadecene, 0.7 mL of oleic acid, 2.8 mL of oleylamine, 0.71 mmol of cesium acetate, 0.5 mmol of sodium acetate, and 0.055 mmol of antimony acetate. The total amount of indium acetate and manganese acetate was 0.495 mmol, and the molar ratio of Mn / (In + Mn) [%] was varied. The molar ratio of Sb / (In + Sb) was 10%.

[0055] Using the manufacturing method shown in FIG. 4, an LED was fabricated as follows. Process S20 An ITO layer was formed as an electrode 11 on a glass substrate as a substrate 10. The thickness of the electrode 11 was 180 nm. The total thickness of the substrate 10 and the electrode 11 was 1.1 mm.

[0056] Process S22 A solution of PVK (poly(9-vinylcarbazole)) dissolved in chlorobenzene at a concentration of 5.5 mg / mL is applied onto the electrode 11 by spin coating. The spin coating conditions are a rotation speed of 3000 rpm and a rotation time of 30 seconds. The resulting film is then heat-treated at 150°C for 20 minutes. This forms a hole transport layer 12 including a PVD layer on the electrode 11.

[0057] Process S22 A dispersion liquid in which quantum dots are dispersed in hexane is applied onto the hole transport layer 12 using a spin coating method. The spin coating conditions are a rotation speed of 3000 rpm and a rotation time of 30 seconds. This is then heat-treated at 150°C for 10 minutes. This results in the formation of a light-emitting layer 13 on the hole transport layer 12. Three types of LEDs with different thicknesses T1 of the light-emitting layer 13 were fabricated by varying the quantum dot concentrations in the dispersion liquid to 50 mg / mL, 10 mg / mL, and 1.5 mg / mL.

[0058] Process S24 A solution of TPBi (2,2',2''-(1,3,5-benzinetriyl)tris(1-phenyl-1-H-benzimidazole)) dispersed in ethyl acetate at a concentration of 5.0 mg / mL is applied onto the light-emitting layer 13 by spin coating. The spin coating conditions are a rotation speed of 1000 rpm and a rotation time of 30 seconds. As a result, an electron transport layer 14 including a TPBi layer is formed on the light-emitting layer 13.

[0059] Process S26 On the electron transport layer 14, Al (aluminum) is formed as an electrode 15 by vacuum deposition. The thickness of the electrode 15 is 100 nm. In this way, an LED was fabricated.

[0060] (Band structure of quantum dots with a Mn molar ratio of 10%) Photoemission Yield Spectroscopy (PYS) measurements were performed to investigate the band structure of quantum dots with a 10% Mn molar ratio. Figures 10(a) and 10(b) show the PYS spectra of the quantum dots. The horizontal axis of Figure 10(a) is the light energy, and the vertical axis is (αhν). 1 / 2 The line 54 fitted to the spectrum and (αhν) 1 / 2 The energy at the intersection 55 with the line = 0 is the band gap energy Eg. The band gap energy Eg is 3.55 eV.

[0061] The horizontal axis of Figure 10(b) is the light energy (eV), and the vertical axis is the yield. 1 / 3 The optical energy at the intersection 57 of the baseline line 58 in Figure 10(b) and the line 56 fitted to the spectrum corresponds to the ionization energy of the highest occupied molecular orbital (HOMO), which is -6.85 eV. From the HOMO level and the band gap energy Eg, the lowest unoccupied molecular orbital (LUMO) level can be calculated to be -3.3 eV.

[0062] The Fermi level energy Ef was measured using the Gerbin probe method and found to be -4.29 eV. Figure 11 shows the band structure of an LED with a 10% Mn molar ratio. The known work functions of ITO and Al are listed as the work functions of electrodes 11 and 15. The known HOMO and LUMO levels of PVK and TPBi are listed as the VBM (Valence Band Maximum) and CBM (Conduction Band Minimum) of hole transport layer 12 and electron transport layer 14. By applying a positive voltage to electrode 11 relative to electrode 15, holes are injected from electrode 11 through hole transport layer 12 into light-emitting layer 13. Electrons are injected from electrode 15 through electron transport layer 14 into light-emitting layer 13. Electrons and holes recombine in light-emitting layer 13, causing light to be emitted from light-emitting layer 13.

[0063] (LED with 10% Mn molar ratio) In step S24, the thicknesses T13 of the light-emitting layer 13 were 40 nm, 25 nm, and 10 nm when the quantum dot concentrations in the dispersion were 50 mg / mL, 10 mg / mL, and 1.5 mg / mL, respectively. The thickness T13 was measured using a scanning electron microscope (SEM). However, if SEM measurement was not possible, it was measured using a scanning white light interference microscope. The scanning white light interference microscope measured the sum of the thickness of the hole transport layer 12 and the thickness T1 of the light-emitting layer 13. Because the thickness of the hole transport layer 12 was 3 nm or less, the thickness of the hole transport layer 12 was assumed to be 1.5 nm to calculate the thickness T13. Thus, the thickness T13 of the light-emitting layer 13 could be controlled by changing the quantum dot concentration in the dispersion. The LED fabricated using a quantum dot dispersion with a concentration of 1.5 mg / mL emitted light, but the other LEDs did not. Thus, to improve the emission intensity, it is important to thin the light-emitting layer 13.

[0064] (LED_A with a Mn mole ratio of 10% and a thickness T13 of 10 nm) An LED with a molar ratio of Mn of 10% and a light-emitting layer thickness T13 of 10 nm is designated LED_A. Figure 12 shows the electroluminescence spectrum of LED_A. The horizontal axis represents wavelength, and the vertical axis represents light emission intensity. The obtained spectrum was fitted using two Gaussian curves, resulting in two curves 30 and 31. Curve 30 is considered to represent light emission from Sb STE, and curve 31 is considered to represent light emission from Mn. In this way, by using quantum dots in which Sb and Mn are doped into Cs2NaInCl6 in the light-emitting layer 13, light emission with two wavelength components can be obtained.

[0065] FIG. 13(a) is a graph showing the luminance versus voltage for LED_A. The horizontal axis is the voltage applied to electrode 11 relative to electrode 15, and the vertical axis is the luminance of the light-emitting layer 13. As shown in FIG. 13(a), the light-emitting layer 13 begins to emit light when the voltage reaches 6 V or higher. When the voltage exceeds 10 V, the luminance decreases. FIG. 13(b) is a graph showing the EQE (External Quantum Efficiency) versus voltage for LED_A. The horizontal axis is the voltage applied to electrode 11 relative to electrode 15, and the vertical axis is the EQE. As shown in FIG. 13(b), the EQE improves as the voltage increases. The EQE peaks at a voltage of 9 V, with a maximum EQE of 0.0011%.

[0066] (LED_B with a Mn mole ratio of 10% and a thickness T13 of 10 nm) LED_B was fabricated using the same conditions as LED_A, but with a different quantum dot solution prepared. Figure 14 shows the electroluminescence spectrum of LED_B. The horizontal axis represents wavelength, and the vertical axis represents luminous intensity. The voltage was varied from 9.5V to 11.5V in 0.5V steps. As shown in Figure 14, LED_B begins to emit light at a voltage of 9.5V. As the voltage increases, the luminous intensity increases. When the voltage exceeds 10.5V, the luminous intensity decreases.

[0067] Figure 15(a) shows the current density and luminance versus voltage for LED_B. The horizontal axis represents the voltage applied to electrode 11 relative to electrode 15, and the vertical axis represents the current density flowing between electrodes 15 and 11 and the luminance of the light-emitting layer 13. Black circles represent current density, and white circles represent luminance. As shown in Figure 15(a), current begins to flow when the voltage reaches 9.5 V or higher, and luminance increases as the voltage increases. Luminance decreases when the voltage exceeds 10.5 V. Figure 15(b) shows the EQE versus voltage for LED_B. As shown in Figure 15(b), the EQE improves with increasing voltage. The maximum EQE is 0.0040% at a voltage of 10.5 V. Note that at voltages of 11 V or higher, the current limiter of the voltage source may be reached. Even with different production lots, LEDs such as LED_A and LED_B emit light, and the maximum EQE is 0.001% or higher.

[0068] (LED_C using PEDOT:PSS as the hole injection layer) LED_C, which has a hole injection layer, was fabricated using the same quantum dot solution as LED_B. FIG. 16 is a cross-sectional view of LED_C. As shown in FIG. 16, LED 102, which is LED_C, has a hole injection layer 16 between the electrode 11 and the hole transport layer 12. PEDOT:PSS (poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid) was used as the hole injection layer 16. The other configurations are the same as those in FIG. 1, and therefore their explanations are omitted. In fabricating LED_C, after step S20 in FIG. 4, PEDOT:PSS was applied to the electrode 11 by spin coating. The spin coating conditions were a rotation speed of 3000 rpm and a rotation time of 30 seconds. Then, a heat treatment was performed at 150°C for 10 minutes. This formed the hole injection layer 16 on the electrode 11. In step S22, a hole transport layer 12 was formed on the hole injection layer 16. The other fabrication methods were the same as those in LED_B.

[0069] Figure 17 shows the band structure of LED_C. The known work function of PEDOT:PSS is shown for the hole injection layer 16. The work function of PEDOT:PSS is between the work function of ITO and the VBM of PVK. This facilitates the injection of holes from the electrode 11 into the hole transport layer 12.

[0070] Figure 18 shows the electroluminescence spectrum of LED_C. The voltage was changed from 9.5V to 14.5V in 0.5V steps. As shown in Figure 18, light emission begins at a voltage of 9.5V. As the voltage increases, the light emission intensity increases. The peak at a wavelength of around 400nm is light emission from PVK, and the peak at a wavelength of 500nm is light emission from the light-emitting layer 13. The overall light emission is white.

[0071] Figure 19(a) shows the current density and brightness versus voltage for LED_C. Black circles indicate current density, and white circles indicate brightness. As shown in Figure 19(a), current begins to flow when the voltage is 9.5V or higher, and brightness increases as the voltage increases. At a voltage of 15V, LED_C no longer emits light. The maximum brightness is 13.21cd / m when the voltage is 14.5V. 2 19(b) is a graph showing the EQE versus voltage for LED_C. As shown in FIG. 19(b), the EQE improves as the voltage increases. The maximum EQE is 0.01296% when the voltage is 11.5 V. The EQE decreases when the voltage exceeds 11.5 V. Thus, LED_C has a higher maximum EQE than LED_A and LED_B. This is thought to be because the hole injection layer 16 improves the efficiency of hole injection into the light-emitting layer 13.

[0072] (Quantum dots with TPPO passivation LED_D) LED_D was fabricated using the same quantum dot solution as LED_B, with the quantum dots passivated by TPPO. In the fabrication of LED_D, in step S24 of Figure 4, 5 wt% of TPPO (triphenylphosphine oxide) was added to the hexane in which the quantum dot solution to be applied to the hole transport layer 12 was dispersed. The rest of the fabrication method was the same as for LED_B.

[0073] Figure 20 shows the electroluminescence spectrum of LED_D. The voltage was changed from 8.5V to 11V in 0.5V steps. As shown in Figure 20, LED_D begins to emit light at a voltage of 9V. As the voltage increases, the luminous intensity increases. When the voltage exceeds 10V, the luminous intensity decreases.

[0074] Figure 21(a) shows the current density and brightness versus voltage for LED_D. Black circles indicate current density, and white circles indicate brightness. As shown in Figure 21(a), current begins to flow when the voltage is 9V or higher, and brightness increases as the voltage increases. When the voltage exceeds 10V, the brightness becomes uniform, and at a voltage of 11.5V, no light is emitted. The maximum brightness is 38.09cd / m when the voltage is 10V. 2 FIG. 21(b) shows the EQE versus voltage for LED_D. As shown in FIG. 21(b), the EQE improves as the voltage increases. The maximum EQE is 0.00513% when the voltage is 10V. As such, the maximum brightness is higher than LED_A to LED_C.

[0075] (LED_E using PEDOT:PSS and TPPO) Using the same quantum dot solution as LED_B, LED_E was fabricated, which had a hole injection layer 16 using PEDOT:PSS and TPPO passivation on the quantum dots. In fabricating LED_E, the hole injection layer 16 was formed in the same manner as LED_C, and the light-emitting layer 13 was formed in the same manner as LED_D.

[0076] Figure 22 shows the electroluminescence spectrum of LED_E. The voltage was changed from 7.5V to 14V in 0.5V steps. As shown in Figure 22, LED_E begins to emit light at a voltage of 7.5V. As the voltage increases, the luminous intensity increases. When the voltage exceeds 11.5V, the luminous intensity decreases.

[0077] Figure 23(a) shows the current density and brightness versus voltage for LED_E. Black circles indicate current density, and white circles indicate brightness. As shown in Figure 23(a), current begins to flow when the voltage exceeds 8V, and brightness increases as the voltage increases. The current decreases when the voltage exceeds 12.5V, and increases again when the voltage exceeds 16V. Brightness decreases when the voltage exceeds 10.5V. Since almost no light is emitted at voltages of 14V or higher, it is thought that current at voltages of 14V or higher does not contribute to light emission. The maximum brightness is 6.991cd / m when the voltage is 11.5V. 2 Figure 23(b) shows the EQE versus voltage for LED_E. As shown in Figure 23(b), the EQE improves as the voltage increases. The maximum EQE is 0.01244% at a voltage of 8.5V. Thus, LED_E has a higher maximum EQE than LED_A, B, and D. LED_E has the highest luminance and the highest EQE at low voltages, making it possible to drive it at a low voltage.

[0078] As in LED_C and LED_E, by providing a poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid layer between the hole transport layer 12 and the electrode 11, the maximum EQE can be improved.

[0079] Like LED_D and LED_E, the light-emitting layer 13 contains triphenylphosphine oxide as a passivation agent for the quantum dots, which can increase the maximum brightness.

[0080] (LED_F with a thickness T13 of 25 nm and using PEDOT:PSS and TPPO) LED_F was fabricated by setting the concentration of quantum dots in the dispersion liquid in step S24 to 10 mg / mL, providing a hole injection layer 16 using PEDOT:PSS, and passivating the quantum dots with TPPO. In fabricating LED_F, the method for forming the hole injection layer 16 was the same as for LED_C, and the method for forming the light-emitting layer 13 was the same as for LED_D, except that the concentration of quantum dots in the dispersion liquid in step S24 was 10 mg / mL.

[0081] Figure 24 shows the electroluminescence spectrum of LED_F. The voltage was changed from 9.5V to 11.5V in 0.5V steps. As shown in Figure 24, there was some light emission at voltages of 10V and 11.5V. At other voltages, there was little light emission.

[0082] Figure 25(a) shows the current density and luminance versus voltage for LED_F. Black circles indicate current density, and white circles indicate luminance. As shown in Figure 25(a), luminance increases when the voltage is 9V or higher. When the voltage exceeds 10V, the current saturates and luminance decreases. When the voltage is 12V or higher, almost no light is emitted. Figure 25(b) shows the EQE versus voltage for LED_F. As shown in Figure 25(b), the EQE improves as the voltage increases. When the voltage exceeds 10V, the EQE decreases. The maximum EQE is 0.000215% at a voltage of 10V. As shown, the maximum luminance and maximum EQE for LED_F are at least one order of magnitude smaller than those for LED_A to LED_E.

[0083] In the second embodiment, as shown in Figures 24 to 25(b), when the thickness T13 of the light-emitting layer 13 containing Sb- and Mn-doped Cs2NaInCl6 double perovskite quantum dots 18 is 25 nm, LED_F using PEDOT:PSS and TPPO barely emits light, but does not emit light when either PEDOT:PSS or TPPO is not used. When the thickness T13 is 10 nm, the light-emitting layer 13 emits light even without the hole injection layer 16 and TPPO, as shown in Figures 12 to 15(b) of LED_A and LED_B. Thus, when the thickness T13 is 25 nm or less, the light-emitting layer 13 emits light. When the thickness T13 is 15 nm or less, the light-emitting layer 13 emits more light. When the thickness T13 is 10 nm, as shown in Figures 24 to 25(b), the light-emitting layer 13 emits even more light. This is thought to be because a high resistance of the light-emitting layer 13 makes it difficult for current to flow through the light-emitting layer 13. Since the light-emitting layer 13 emits light, the thickness T13 is preferably 1 nm or more.

[0084] (Quantum dot Mn molar ratio dependence) Quantum dot solutions were prepared with different Mn molar ratios. The ratio of indium acetate to manganese acetate in step S10 was varied to prepare quantum dot solutions. The molar ratio of Sb to In + Sb + Mn was constant at 10%. Quantum dot solutions were prepared with the molar ratio of Mn to In + Mn set to 0%, 1%, 2.5%, 5%, 10%, 20%, 30%, 40%, and 50%.

[0085] Figure 26(a) shows the XRD results of the quantum dot solution. Figure 26(b) shows an enlarged view of the peak in the (220) plane. (111), (220), (222), (400), (422), and (440) represent the diffracted peaks in each crystal plane. The vertical dashed line in Figure 26(b) indicates the 2θ position of the (200) plane peak for a sample with a 10% Sb molar ratio and no Mn content. As shown in Figure 26(a), the 2θ values in each diffraction plane are almost the same, indicating that the quantum dot crystal structures are almost the same.

[0086] Table 2 shows the molar ratio of Mn and the 2θ of the (220) plane calculated from FIG. 26(b).

[0087] [Table 2]

[0088] As shown in Figure 26(b) and Table 2, when the Mn molar ratio is in the range of 5% or less, the 2θ shifts slightly in the smaller direction as the Mn molar ratio increases. This is because Mn, which has an ionic radius of 0.830 Å, 2+ The ion is In, with an ionic radius of 0.800 Å. 3+ This is thought to be because the lattice expands when the Mn molar ratio is substituted at the site. When the Mn molar ratio is 30% or more, the 2θ shifts slightly in the larger direction as the Mn molar ratio increases. This is because Mn 2+ The ion is In 3+ In addition, Na has a large ionic radius of 1.03 Å. + This is thought to be because the lattice shrinks when the ions are substituted into the sites.

[0089] Figure 27 shows the photoluminescence spectra of quantum dot solutions with different Mn molar ratios. The horizontal axis represents wavelength, and the vertical axis represents normalized luminescence intensity. The normalized luminescence intensity is the value obtained by normalizing the luminescence intensity of each quantum dot solution to 1 at 450 nm. The peak wavelengths of the Sb-induced luminescence and the Mn-induced luminescence are approximately 430 nm and 630 nm, respectively, and remain almost unchanged even when the Mn molar ratio is changed. As the Mn molar ratio increases, the peak at approximately 630 nm becomes higher than the peak at approximately 450 nm. In this way, by appropriately setting the Pb / Mn molar ratio, the LED's emission spectrum can be freely adjusted.

[0090] Table 3 shows the molar ratio of Mn and the total PLQY.

[0091] [Table 3]

[0092] As shown in Table 3, when the Mn molar ratio is 5% or less, the PLQY is 90% or more. At a Mn molar ratio of 10%, the PLQY exceeds 80%, and even at a Mn molar ratio of 20%, a PLQY of nearly 70% is obtained. Even at a Mn molar ratio of 50%, the PLQY is approximately 45%. Thus, Table 3 shows that a higher PLQY is obtained compared to Non-Patent Document 2. The PLQY tends to decrease with increasing Mn doping amount, which is thought to be due to the substitution of some of the Mn for Na sites.

[0093] The absorption spectrum of the quantum dot solution was measured. Figure 28(a) shows the absorption spectrum of quantum dot solutions with different Mn molar ratios. The vertical axis in the upper panel of Figure 28(a) shows the normalized absorption coefficient, where the absorption coefficient at a wavelength of 300 nm is set to 1, and the vertical axis in the lower panel shows the second-order derivative of the upper panel. The wavelength at which the second-order derivative is minimum indicates the wavelength at which the absorption coefficient peaks. The undoped sample is a quantum dot solution that is not doped with Sb or Mn. The Sb molar ratio of the samples other than the undoped sample is 10%. No absorption peak is observed in the undoped sample. Absorption peaks are observed at approximately 320 nm and approximately 335 nm in the samples other than the undoped sample. The absorption peak is largest when the Mn molar ratio is 1%. Although the magnitude of the absorption peak changes depending on the Mn molar ratio, the position of the absorption peak wavelength does not change.

[0094] Figure 28(b) shows the photoluminescence excitation (PLE) spectrum of a sample with a 10% Mn mole fraction. The vertical axis represents the PLE intensity at photoluminescence wavelengths of 450 nm and 630 nm, normalized to a maximum intensity of 1. As shown in Figure 28(b), the PLE intensity peaks at approximately 320 nm and 335 nm for both photoluminescence wavelengths of 450 nm and 630 nm. Thus, the PLE spectra of the emission from Sb and the emission from Mn are almost identical. This indicates that the Mn level receives energy from the STE level due to Sb, as shown in Figure 9, and emits light from the Mn level.

[0095] As described above, by setting the Mn molar ratio to, for example, 1% or more and 50% or less, the photoluminescence spectrum can be made to have a desired waveform, and not only can the color of the emitted light be adjusted, but the color of the white light can also be adjusted from cool to warm colors. As shown in Table 3, from the viewpoint of prioritizing PLQY, the Mn molar ratio may be set to 30% or less. From the viewpoint of forming the STE level, the Sb molar ratio is preferably, for example, 1% or more and 20% or less.

[0096] Although the quantum dots 18 have been described as Sb- and Mn-doped Cs2NaInCl6 double perovskite quantum dots, the quantum dots 18 may also be Sb- and rare earth element-doped Cs2NaInCl6 double perovskite quantum dots. Examples of rare earth elements include scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). In scandium and yttrium, the d orbital, and in lanthanides, the f orbital, form a level lower than the STE level, similar to Mn in Figure 2. Therefore, similar to Mn, energy is transferred from the STE level to the rare earth element level, and light emission with a wavelength different from that of Sb can be obtained.

[0097] (Embodiment 3) In the third embodiment, quantum dots are produced using a fatty acid having a smaller number of carbon atoms in its main chain than oleic acid. In the first and second embodiments, oleic acid and oleylamine are used as the ligands for the quantum dots. However, if the ligand is long, the distance between the quantum dots increases, making it difficult for carriers to flow between the quantum dots. This makes it difficult for carriers to be injected into the quantum dots. Therefore, instead of oleic acid, the fatty acid in the organic solvent prepared in step S30 of FIG. 3(b) is replaced with a fatty acid having a shorter number of carbon atoms in its main chain than oleic acid. Alternatively, instead of oleylamine, the aliphatic amine in the organic solvent prepared in step S30 is replaced with an aliphatic amine having a shorter number of carbon atoms in its main chain than oleylamine. Alternatively, instead of oleic acid, a fatty acid having a shorter number of carbon atoms in its main chain than oleic acid may be used, and instead of oleylamine, an aliphatic amine having a shorter number of carbon atoms in its main chain than oleylamine may be used.

[0098] (Experiment 3) (Preparation of quantum dot solution) Quantum dot solutions G and R were prepared. For quantum dot solution G, 2.8 mL of 2-ethylhexanoic acid and 0.7 mL of oleylamine were mixed with 9 mL of 1-octadecene in step S30 of Figure 3(b). For quantum dot solution R, 2.8 mL of oleic acid and 0.7 mL of oleylamine were mixed with 9 mL of 1-octadecene.

[0099] Next, in step S32, 0.71 mmol of cesium acetate, 0.5 mmol of sodium acetate, 0.483 mmol of indium acetate, 0.055 mmol of antimony acetate, and 0.012 mmol of manganese acetate were mixed with the organic solvent prepared in step S30. The other steps were the same as in Experiment 1.

[0100] (LED manufacturing) Fig. 29 is a cross-sectional view of an LED fabricated in Experiment 3. As shown in Fig. 29, the LED 104 includes an electron injection layer 17 between the electron transport layer 14 and the electrode 15. The CBM of the electron injection layer 17 is located between the CBM of the electron transport layer 14 and the work function of the electrode 15. This facilitates injection of electrons from the electrode 15 into the electron transport layer 14. Lithium fluoride (LiF) was used as the electron injection layer 17.

[0101] In step S26 of FIG. 4, the electron transport layer 14 and the electron injection layer 17 were formed using vacuum deposition. The remaining manufacturing methods for the LED were the same as those for LED-E. In the LED fabricated in Experiment 3, the electrode 11 was ITO. The hole injection layer 16 was PEDOT:PSS. The hole transport layer 124 was PVD. The light-emitting layer 13 was Cs2NaInCl6 double perovskite quantum dots doped with Sb and Mn and passivated with TPPO. The electron transport layer 14 was TPBi, and the electron injection layer 17 was LiF. The electrode 15 was Al.

[0102] In LED-G, quantum dot solution G was used to form the light-emitting layer 13. In LEG-R, quantum dot solution R was used to form the light-emitting layer 13.

[0103] (Results for quantum dot solution G) Figure 30 shows the photoluminescence spectrum of quantum dot solution G. The horizontal axis represents wavelength, and the vertical axis represents normalized intensity. The maximum normalized intensity is set to 1. As shown in Figure 30, emission due to Sb with a peak wavelength of approximately 430 nm and emission due to Mn with a peak wavelength of approximately 630 nm can be observed. The PLQY was nearly 100%.

[0104] Figure 31 is a transmission electron microscope image of quantum dot solution G. As shown in Figure 31, the quantum dots 18 are squares with sides each measuring approximately 10 nm. Multiple quantum dots 18 are aligned. The quantum dots 18 are spaced apart by approximately 1 nm.

[0105] (Results of LED-G using 2-ethylhexanoic acid) Figure 32 shows the electroluminescence spectrum of LED_G. The horizontal axis represents wavelength, and the vertical axis represents emission intensity. The voltage was changed from 8V to 14V in 0.5V steps. As shown in Figure 32, at a voltage of 8V, the emission intensity at a peak wavelength of approximately 430nm is greater than the emission intensity at a peak wavelength of approximately 500nm. As the voltage increases from 8V, the emission intensity at a peak wavelength of approximately 430nm decreases. The emission intensity at peak wavelengths of approximately 500nm to 550nm also decreases as the voltage increases. The emission intensity at peak wavelengths of approximately 500nm to 550nm decreases more gradually with increasing voltage than the emission intensity at a peak wavelength of approximately 430nm. At voltages of 10.5V or higher, the emission intensity at peak wavelengths of approximately 500nm to 550nm is greater than the emission intensity at a peak wavelength of approximately 430nm.

[0106] Figure 33(a) shows the current density and brightness versus voltage for LED_G. Black circles indicate current density, and white circles indicate brightness. As shown in Figure 33(a), current begins to flow when the voltage reaches 7.5V or higher, and brightness increases as the voltage increases. Brightness decreases when the voltage exceeds 10.5V. The maximum brightness is 19.1cd / m when the voltage is 10V. 2 Figure 33(b) shows the EQE versus voltage for LED_G. As shown in Figure 33(b), the EQE improves as the voltage increases. The highest EQE is 0.5862% when the voltage is 8V.

[0107] (Results of LED-R using oleic acid) Figure 34(a) shows the current density and brightness versus voltage for LED_R. Black circles indicate current density, and white circles indicate brightness. As shown in Figure 34(a), current begins to flow when the voltage reaches 6.5V or higher, and brightness increases as the voltage increases. Brightness decreases when the voltage exceeds 9V. The maximum brightness is 8.4cd / m when the voltage is 9V. 2 Figure 34(b) shows the EQE versus voltage for LED_R. As shown in Figure 34(b), the EQE improves as the voltage increases. The highest EQE is 0.1623% when the voltage is 7.5V.

[0108] The maximum luminance and maximum EQE of LED-R are greater than those of LED-E in Figures 23(a) and 23(b), respectively. This is thought to be due to the fact that, compared to LED-E, the electron injection layer 17 is provided and the electron transport layer 14, the electron injection layer 17, and the electrode 15 are formed by vacuum deposition.

[0109] The maximum brightness and maximum EQE of LED-G are greater than those of LED-R, which is thought to be due to the use of 2-ethylhexanoic acid instead of oleic acid as the organic solvent in step S30.

[0110] Chemical formula 1 is the chemical formula for 2-ethylhexanoic acid, and chemical formula 2 is the chemical formula for oleic acid.

[0111] [ka]

[0112] [ka]

[0113] As shown in Chemical Formula 1, 2-ethylhexanoic acid is a saturated fatty acid with a terminal carboxyl group, a main chain of six carbon atoms, and a branched saturated fatty acid with an ethyl group attached to a branch of the main chain. As shown in Chemical Formula 2, oleic acid is a monounsaturated fatty acid with a terminal carboxyl group, a main chain of 18 carbon atoms, an unbranched straight-chain fatty acid, and one double bond. The double bond is located in the center of the main chain.

[0114] Oleylamine used as the aliphatic amine is a straight-chain monounsaturated aliphatic amine having an amino group at the terminal, 18 carbon atoms in the main chain, no branches, and one double bond.

[0115] (Schematic diagram of nanomaterials) FIG. 35(a) is a schematic diagram of a nanomaterial in quantum dot solution R. As shown in FIG. 35(a), nanomaterial 25R in quantum dot solution R uses oleic acid and oleylamine as ligands 19 around quantum dots 18. Therefore, the length L1 of the ligands 19 is large. The spacing L2 between quantum dots 18 is approximately twice the length L1 of the ligands 19. Oleic acid and oleylamine each have 18 carbon atoms, and the length L1 is approximately 1.5 nm, so the spacing L2 between quantum dots 18 is thought to be approximately 3 nm. Because the spacing L2 between quantum dots 18 is large, electron and hole carriers do not easily flow between the quantum dots 18. This is thought to increase the resistance of the light-emitting layer 13 and reduce the luminous efficiency.

[0116] Figure 35(b) is a schematic diagram of the nanomaterial in quantum dot solution G. As shown in Figure 35(b), nanomaterial 25G in quantum dot solution G uses 2-ethylhexanoic acid and oleylamine as ligands 19 around the quantum dots 18. Therefore, the length L1 of the ligands 19 is shorter than that of nanomaterial 25R. The main chain of 2-ethylhexanoic acid has six carbon atoms, and its length L1 is approximately 0.5 nm, approximately one-third that of oleic acid. Although the length of the oleylamine is the same as that of nanomaterial 25R, the spacing L2 between the quantum dots 18 is smaller than that of nanomaterial 25R. For example, the spacing L2 between the quantum dots 18 is thought to be approximately 1 nm. Because the spacing L2 between the quantum dots 18 is small, electron and hole carriers, for example, tunnel between the quantum dots 18. This is thought to reduce the resistance of the light-emitting layer 13 and improve the luminous efficiency.

[0117] In this way, it is believed that the luminous efficiency can be improved by shortening the main chains of the fatty acids and aliphatic amines contained in the organic solvent in step S30.

[0118] To summarize embodiments 1 to 3, the quantum dot solution is produced in step S30 of Fig. 3(b) by dispersing cesium acetate, sodium acetate, and indium acetate in a mixture of organic solvents containing a fatty acid having a main chain carbon number of 18 or less and an aliphatic amine having a main chain carbon number of 18 or less in a predetermined ratio. In step S32, chloride is injected into the heated solution to synthesize Cs2NaInCl6 perovskite quantum dots. This allows for the realization of an LED with high luminous intensity.

[0119] The fatty acid has a carboxyl group at the end of the main chain, and the aliphatic amine has an amino group at the end of the main chain. Note that the main chain is the longest chain when the fatty acid or aliphatic amine is branched.

[0120] The fatty acid may be a saturated fatty acid or an unsaturated fatty acid. The more double bonds there are, the more curvature of the main chain becomes. From this viewpoint, the fatty acid is preferably a saturated fatty acid or a monovalent or divalent unsaturated fatty acid having one or two double bonds. The fatty amine may be a saturated fatty amine or an unsaturated fatty amine. The fatty amine is preferably a saturated fatty amine or a monovalent or divalent unsaturated fatty amine having one or two double bonds.

[0121] The fatty acid may be a straight-chain fatty acid without branches, or a branched fatty acid. When the carbon number of the main chain is small, quantum dots are more likely to precipitate in the quantum dot solution. Therefore, when the carbon number of the main chain is 8 or less or 6 or less, the fatty acid is preferably a branched fatty acid. The number of branches is, for example, 1 or 2. The aliphatic amine may be a straight-chain aliphatic amine or a branched aliphatic amine. When the carbon number of the main chain is 8 or less or 6 or less, the aliphatic amine is preferably a branched aliphatic amine. The number of branches is, for example, 1 or 2. The branch is preferably, for example, a methyl group or an ethyl group.

[0122] As shown in Figure 34(b), from the viewpoint of reducing the length L1 of the ligand 19, the number of carbon atoms in the main chain of the fatty acid is preferably less than 18, more preferably 10 or less, even more preferably 8 or less, and even more preferably 6 or less. Generally, the number of carbon atoms in the main chain of the fatty acid is 4 or more. The number of carbon atoms in the main chain of the aliphatic amine is preferably less than 18, more preferably 10 or less, even more preferably 8 or less, and even more preferably 6 or less. Generally, the number of carbon atoms in the main chain of the aliphatic amine is 4 or more.

[0123] By using a fatty acid with six carbon atoms in the main chain as the fatty acid, the length L1 of the ligand 19 can be one-third that of oleic acid. This allows for high PLQY and EQE, as in quantum dot solution G and LED-G. A linear saturated fatty acid with six carbon atoms in the main chain is hexanoic acid. An alkyl group such as a methyl group or an ethyl group may be bonded to the main chain of hexanoic acid. The carbon atom to which the alkyl group is bonded may be any of the carbon atoms 2 to 4, with the carbon atom in the carboxyl group being 1. The alkyl group may be bonded to multiple carbon atoms. An aliphatic amine with six carbon atoms in the main chain may also be used as the aliphatic amine.

[0124] The nanomaterial in the quantum dot solution comprises Cs2NaInCl6 perovskite quantum dots 18 and ligands 19 bound to the quantum dots 18 and made of a fatty acid having a main chain with less than 18 carbon atoms and / or an aliphatic amine having a main chain with less than 18 carbon atoms, thereby improving luminescence efficiency.

[0125] The size of the quantum dots 18 is, for example, 6 nm or more and 20 nm or less, and the distance L2 between the quantum dots 18 is, for example, 2 nm or less.

[0126] The above describes in detail preferred embodiments, but the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims. [Explanation of symbols]

[0127] 10: Circuit board 11: Electrode 12: Hole transport layer 13: Light-emitting layer 14:Electron transport layer 15: Electrode 16: Hole injection layer 17:Electron injection layer 18: Quantum dots 19: Ligand

Claims

1. a step of dispersing cesium acetate, sodium acetate, and indium acetate in a mixture of an organic solvent containing a fatty acid having a main chain carbon number of 18 or less and an aliphatic amine having a main chain carbon number of 18 or less in a predetermined ratio to prepare a solution; By injecting chloride into the heated solution, Cs ２ NaInCl ６ synthesizing perovskite quantum dots; A method for producing quantum dots, comprising:

2. The method for producing quantum dots according to claim 1 , wherein at least one of the fatty acid and the aliphatic amine has a main chain having less than 18 carbon atoms.

3. The method for producing quantum dots according to claim 1 , wherein the aliphatic amine is oleylamine.

4. The method for producing quantum dots according to claim 3 , wherein the fatty acid has a main chain having six carbon atoms.

5. The solution has antimony acetate dispersed therein, Cs ２ NaInCl ６ Perovskite quantum dots are Sb-doped Cs ２ NaInCl ６ Perovskite quantum dots, The method for producing quantum dots according to claim 3 , wherein the fatty acid is oleic acid.

6. 6. The method for producing quantum dots according to claim 5, wherein the volume ratio of oleylamine to oleic acid in the solution is 1 / 4 or more and 1 / 10 or less.

7. The method for producing quantum dots according to claim 6, wherein the chloride is germanium chloride.

8. 7. The method for producing quantum dots according to claim 6, wherein the organic solvent is 1-octadecene.

9. the step of preparing the solution includes a step of preparing a solution in which cesium acetate, sodium acetate, indium acetate, antimony acetate, and an acetate of at least one element selected from Mn and rare earth elements are dispersed in the mixed liquid; The step of synthesizing the quantum dots includes the step of doping Sb and at least one element selected from Mn and rare earth elements with Cs ２ NaInCl ６ The method for producing quantum dots according to claim 6, comprising the step of synthesizing perovskite quantum dots.

10. the step of preparing the solution includes a step of preparing a solution in which cesium acetate, sodium acetate, indium acetate, antimony acetate, and manganese acetate are dispersed in the mixed liquid; The step of synthesizing the quantum dots includes synthesizing Sb and Mn doped Cs ２ NaInCl ６ The method for producing quantum dots according to claim 6, comprising the step of synthesizing perovskite quantum dots.

11. The method for producing quantum dots according to claim 6 , further comprising the step of mixing oleic acid into a quantum dot solution containing the quantum dots after the step of synthesizing the quantum dots.

12. A dispersion liquid is produced by dispersing the quantum dots synthesized by the method for producing quantum dots according to any one of claims 1 to 11 in an organic solvent; The dispersion is applied onto a substrate and heat-treated to form a light-emitting layer. A method for manufacturing a light-emitting device.

13. Cs doped with Sb and at least one element selected from Mn and rare earth elements ２ NaInCl ６ an emitting layer containing perovskite quantum dots and having a thickness of 25 nm or less; a hole transport layer and an electron transport layer sandwiching the light-emitting layer; a first electrode provided on the hole transport layer opposite the light emitting layer; a second electrode provided on the electron transport layer opposite the light emitting layer; A light-emitting element comprising:

14. The quantum dots are Cs doped with Sb and Mn. ２ NaInCl ６ The light-emitting device according to claim 13, which is a perovskite quantum dot.

15. the hole transport layer comprises a poly(9-vinylcarbazole) layer; 15. The light-emitting device of claim 14, wherein the electron transport layer comprises a layer of 2,2',2''-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole).

16. 16. The light-emitting device according to claim 15, further comprising a poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid layer between the hole transport layer and the first electrode.

17. The light-emitting element according to claim 15 or 16, wherein the light-emitting layer contains triphenylphosphine oxide as a passivation agent for the quantum dots.

18. Cs ２ NaInCl ６ Perovskite quantum dots and a ligand bound to the quantum dot and comprising a fatty acid having a main chain carbon number of less than 18 and / or an aliphatic amine having a main chain carbon number of less than 18; A nanomaterial comprising:

19. A light-emitting device comprising a light-emitting layer comprising the nanomaterial of claim 18.

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