Light-emitting unit, preparation method thereof and light-emitting device

Abstract

The invention discloses a light-emitting unit, a preparation method thereof and a light-emitting device. The light-emitting unit comprises first quantum dots and inorganic nanoparticles, and the average particle size of the inorganic nanoparticles is smaller than that of the first quantum dots.

Description

Technical Field

[0001] This application relates to the technical field of quantum dots, and particularly to a light-emitting unit, a preparation method thereof, and a light-emitting device. Background Art

[0002] Currently, the widely used light-emitting devices are organic light-emitting devices (OLEDs) and quantum dot light-emitting devices (QLEDs). Due to their excellent display performances such as self-luminescence, simple structure, ultra-thinness, fast response speed, wide viewing angle, low power consumption, and flexible display, OLEDs have become the mainstream technology in the display technology field. QLEDs have the advantages of saturated emission light color, adjustable wavelength, low turn-on voltage, good solution processability, easy fine control of quantum dots, etc., and have high photoluminescence and electroluminescence quantum yields. In recent years, they have become strong competitors of OLEDs.

[0003] The light-emitting unit is the main light-emitting component of the light-emitting device. However, the light-emitting efficiency of the existing light-emitting units is relatively low and needs to be further improved. Summary of the Invention

[0004] In view of this, this application provides a light-emitting unit, a preparation method thereof, and a light-emitting device.

[0005] An embodiment of this application is implemented as follows. A light-emitting unit includes a first quantum dot and an inorganic nanoparticle. The emission peak wavelength of the first quantum dot is 430 - 480 nm, and the average particle size of the inorganic nanoparticle is smaller than the average particle size of the first quantum dot.

[0006] Optionally, in some embodiments, the average particle size of the first quantum dot is 10 - 25 nm;

[0007] and / or, the average particle size of the inorganic nanoparticle is 5 - 10 nm;

[0008] and / or, the mass ratio of the inorganic nanoparticle to the first quantum dot is (0.1 - 0.5):1.

[0009] and / or, the inorganic nanoparticle includes one or more of a P-type inorganic nanoparticle and a second quantum dot. The emission peak wavelength of the second quantum dot is 600 - 640 nm.

[0010] Optionally, in some embodiments, the PLQY of the first quantum dot is 50 - 100%, and the PLQY of the second quantum dot is greater than 0 and less than or equal to 10%; preferably, the PLQY of the first quantum dot is 75 - 85%, and the PLQY of the second quantum dot is greater than 0 and less than or equal to 5%;

[0011] and / or, the full width at half maximum of the first quantum dot is 10 - 30 nm;

[0012] and / or, the full width at half maximum of the second quantum dot is 10 to 40 nm.

[0013] Optionally, in some embodiments, the p-type inorganic nanoparticles include one or more of doped metal oxide particles, undoped metal oxide particles, metal sulfides, and metal nitrides, wherein the metal oxides in the doped metal oxide particles and the metal oxides in the undoped metal oxide particles independently include one or more of MoO3, WO3, NiO, CrO3, CuO, Cu2O, and V2O5, the doping elements in the doped metal oxide particles include one or more of Mo, W, Ni, Cr, Cu, and V, the metal sulfides include one or more of CuS, MoS3, and WS3, and the metal nitrides include p-type gallium nitride;

[0014] And / or, the first quantum dot and the second quantum dot each independently include one or more of a single-structure quantum dot, a core-shell structure quantum dot, and a perovskite semiconductor material. Among them, the material of the single-structure quantum dot, the core material of the core-shell structure quantum dot, and the shell material of the core-shell structure quantum dot may each include one or more of II-VI group compounds, IV-VI group compounds, III-V group compounds, and I-III-VI group compounds. The II-VI group compounds include one or more of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, and HgZnSTe. The IV-VI group compounds include one or more of SnS, SnSe, SnTe, PbS, PbSe, PbTe, SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, SnPbSSe, SnPbSeTe, and SnPbSTe. The III-V group compounds include one or more of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, and InAlPSb. The I-III-VI group compounds include one or more of CuInS2, CuInSe2, and AgInS2. The perovskite semiconductor material includes doped or undoped inorganic perovskite semiconductors, or organic-inorganic hybrid perovskite semiconductors. The structural general formula of the inorganic perovskite semiconductor is AMX3, where A is Cs + ions, M is a divalent metal cation, including Pb 2+ 、Sn 2+, Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2 + , Yb 2+ , Eu 2+ One or more of the following, X is a halogen anion, including Cl - , Br - , I - One or more of the following. The structural general formula of the organic-inorganic hybrid perovskite semiconductor is BMX3, where B is an organic amine cation, including CH3(CH2) n-2 NH3 + or [NH3(CH2) n NH3] 2+ , where n≥2, M is a divalent metal cation, including Pb 2+ , Sn 2+ , Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2+ , Yb 2+ , Eu 2+ One or more of the following, X is a halogen anion, including Cl - , Br - , I - One or more of the following;

[0015] Optionally, in some embodiments, ligands are separately and independently attached to the surfaces of the first quantum dot and the second quantum dot. The ligands include substituted or unsubstituted C6-C 24 fatty acids, substituted or unsubstituted C6-C 24 fatty amines, substituted or unsubstituted C6-C 24 aliphatic thiols, substituted or unsubstituted C6-C 24 aliphatic thioethers, substituted or unsubstituted C6-C 24 aliphatic phosphines, substituted or unsubstituted C6-C 24 aliphatic phosphine oxides, substituted or unsubstituted C8-C 20 aliphatic phosphoric acids, substituted or unsubstituted C6-C 24 aliphatic phosphates, substituted or unsubstituted C6-C 24at least one of aliphatic phosphorous acid and substituted or unsubstituted C6-C 24 at least one of aliphatic phosphite esters, wherein the substituents of the substituted ones are selected from at least one of C1-C6 alkyl, C1-C6 alkoxy, and halogen;

[0016] Optionally, the substituted or unsubstituted C6-C 24 fatty acids include at least one of capric acid, undecylenic acid, myristic acid, oleic acid, linoleic acid, and stearic acid;

[0017] Optionally, the substituted or unsubstituted C6-C 24 aliphatic thiols include at least one of octanethiol, dodecyl mercaptan, and octadecyl mercaptan;

[0018] Optionally, the substituted or unsubstituted C6-C 24 fatty amines include at least one of oleylamine, octadecylamine, octylamine, dioctylamine, and trioctylamine;

[0019] Optionally, the substituted or unsubstituted C6-C 24 aliphatic phosphines include trioctylphosphine;

[0020] Optionally, the substituted or unsubstituted C6-C 24 aliphatic phosphine oxides include trioctylphosphine oxide.

[0021] Correspondingly, the embodiments of the present application further provide a method for preparing a light-emitting unit, including the following steps:

[0022] Providing inorganic nanoparticles, first quantum dots, and a solvent, mixing to obtain a quantum dot solution, wherein the average particle size of the inorganic nanoparticles is smaller than the average particle size of the first quantum dots; and

[0023] Preparing a thin film using the quantum dot solution to obtain a light-emitting unit.

[0024] Optionally, in some embodiments, the average particle size of the first quantum dots is 10-25 nm;

[0025] and / or, the average particle size of the inorganic nanoparticles is 5-10 nm;

[0026] and / or, the mass ratio of the inorganic nanoparticles to the first quantum dots is (0.1-0.5):1;

[0027] and / or, the inorganic nanoparticles include one or more of P-type inorganic nanoparticles and second quantum dots.

[0028] Optionally, in some embodiments, the method for preparing the second quantum dots includes:

[0029] Provide an initial second quantum dot; and

[0030] Expose the initial second quantum dot to water and oxygen for a period of time T under ultraviolet light illumination conditions to obtain the second quantum dot.

[0031] Optionally, in some embodiments, the wavelength of the ultraviolet light is 365 - 405 nm;

[0032] And / or, the PLQY of the initial second quantum dot is 50 - 100%;

[0033] And / or, the PLQY of the first quantum dot is 50 - 100%, and the PLQY of the second quantum dot is greater than 0 and less than or equal to 10%;

[0034] And / or, the time T is 1 - 48 h.

[0035] Correspondingly, an embodiment of the present application further provides a light-emitting device including the light-emitting unit.

[0036] The light-emitting unit described in the present application includes the first quantum dot and the inorganic nanoparticles, and the average particle size of the inorganic nanoparticles is smaller than the average particle size of the first quantum dot, and has a relatively high PLQY. Description of the Drawings

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0038] Figure 1 is a flowchart of a preparation method of a light-emitting unit provided by an embodiment of the present application;

[0039] Figure 2 is a schematic structural diagram of a light-emitting device provided by an embodiment of the present application;

[0040] Figure 3 is a schematic structural diagram of another light-emitting device provided by an embodiment of the present application;

[0041] Figure 4 is a schematic structural diagram of yet another light-emitting device provided by an embodiment of the present application;

[0042] Figure 5 is a schematic structural diagram of yet another light-emitting device provided by an embodiment of the present application;

[0043] Figure 6 is a schematic structural diagram of yet another light-emitting device provided by an embodiment of the present application.

[0044] Reference numerals

[0045] Light-emitting device 100; anode 10; light-emitting unit 20; cathode 30; hole transport layer 40; electron transport layer 50; hole injection layer 60. Detailed implementation manners

[0046] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application. In addition, it should be understood that the specific implementation manners described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0047] In the present application, unless otherwise stated, the orientation terms such as "upper" and "lower" generally refer to the upper and lower in the actual use or working state of the device, specifically the drawing direction in the accompanying drawings; while "inner" and "outer" refer to the outline of the device. In addition, in the description of the present application, the term "comprising" means "including but not limited to". The terms first, second, third, etc. are only used as labels and do not impose numerical requirements or establish an order.

[0048] In the present application, "and / or" describes the association relationship of associated objects and indicates that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. Wherein A and B may be singular or plural.

[0049] In the present application, "at least one" means one or more, and "a plurality" means two or more. "At least one kind", "at least one of the following items" or similar expressions refer to any combination of these items, including any combination of single item (s) or plural item (s). For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0050] In this application, when forming another layer "on" a certain layer, the so-called "on" is a broad concept, which can mean that the formed another layer is adjacent to the certain layer, or there are other spacer structure layers between the another layer and the certain layer. For example, when forming a second electrode "on" the first charge carrier functional layer, the so-called "on" can mean that the formed second electrode is adjacent to the first charge carrier functional layer, or there are other spacer structure layers between the second electrode and the first charge carrier functional layer, such as a light-emitting layer.

[0051] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within that range, such as 1, 2, 3, 4, 5, and 6, which applies regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0052] Due to the excellent solution processability of quantum dots, quantum dots are very suitable for film formation by the solution method. A thin film with high luminous efficiency is an important guarantee for high-performance devices. However, when quantum dots are prepared into a thin film from a solution, Förster energy resonance transfer (FRET) occurs between the quantum dots, which will not only cause the fluorescence of some quantum dots to be quenched, resulting in a significant decrease in the PLQY (photoluminescence quantum yield) of the quantum dot film compared to the PLQY of the quantum dot solution, but also cause a significant red shift in the wavelength from the photoluminescence spectrum to the electroluminescence spectrum of the quantum dot film, thus seriously affecting the size of the luminous color gamut value. In addition, due to the relatively wide bandgap of the light-emitting core of blue quantum dots, it is difficult for the PLQY of blue quantum dot solutions to rival that of red quantum dot solutions. Therefore, when a blue quantum dot solution is prepared into a quantum dot film from a solution, there will be a problem of a significant decrease in PLQY, resulting in easy quenching of charge carriers in the device, thereby affecting the luminous efficiency and lifespan and other performance of the device.

[0053] The technical solution of this application is as follows:

[0054] An embodiment of this application provides a quantum dot solution, which includes first quantum dots, inorganic nanoparticles, and a solvent. The emission peak wavelength of the first quantum dots is 430 - 480 nm. In other words, the first quantum dots are blue quantum dots. The average particle size of the inorganic nanoparticles is smaller than the average particle size of the first quantum dots.

[0055] The quantum dot solution described in this application includes the first quantum dots and the inorganic nanoparticles, and the average particle size of the inorganic nanoparticles is smaller than that of the first quantum dots. Since FRET (Förster resonance energy transfer) is inversely proportional to the distance between the particles that undergo energy transfer, when the first quantum dots are mixed with inorganic nanoparticles having a smaller particle size, the distance between the blue light quantum dots can be increased, thereby significantly suppressing the FRET phenomenon when the film layer is prepared using the quantum dot solution.

[0056] In some embodiments, the average particle size of the first quantum dots is 10 - 25 nm. Within this average particle size range, the first quantum dots have fewer defects and higher luminescence efficiency.

[0057] In some embodiments, the average particle size of the inorganic nanoparticles is 5 - 10 nm. The FRET phenomenon can be effectively suppressed within this average particle size range.

[0058] The inorganic nanoparticles include one or more of P-type inorganic nanoparticles and second quantum dots.

[0059] In at least one embodiment, the inorganic nanoparticles are the second quantum dots.

[0060] In some embodiments, the emission peak wavelength of the second quantum dots is 600 - 640 nm. In other words, the second quantum dots are red light quantum dots.

[0061] Within the emission peak wavelength range of the blue light quantum dots and the red light quantum dots described in this application, a large distance can be achieved both between the emission spectrum of the blue light quantum dots and the absorption spectrum of the red light quantum dots, and between the emission spectrum of the red light quantum dots and the absorption spectrum of the blue light quantum dots, thereby effectively reducing or even avoiding the problem of energy resonance transfer from blue light quantum dots to red light quantum dots inside the quantum dot film.

[0062] It can be understood that the blue light quantum dots described in this application are quantum dots that can emit blue light, and the red light quantum dots described in this application are quantum dots that can emit red light.

[0063] In some embodiments, the PLQY of the first quantum dots is 50 - 100%, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, etc. Within this range, the quantum dot film can have better luminescence performance.

[0064] In some embodiments, the PLQY of the second quantum dots is greater than 0 and less than or equal to 10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc. Within this range, the quantum dot film can have better blue light color purity.

[0065] The quantum dot solution described in this application includes both the first quantum dots and the second quantum dots. On the one hand, since FRET is inversely proportional to the distance between the particles undergoing energy transfer, when red quantum dots with a lower PLQY are mixed in the blue light quantum dots, the distance between the blue light quantum dots can be increased, thus significantly suppressing the FRET phenomenon. On the other hand, since the emission peak of the blue light quantum dots does not overlap with the absorption peak of the red light quantum dots, when red light quantum dots with a lower PLQY are doped into the blue light quantum dots, the presence of the red light quantum dots can significantly suppress the occurrence of FRET, thereby avoiding the problem of a significant decrease in PLQY when the blue light quantum dot solution is converted from a solution to a thin film, and thus providing a quantum dot film with high luminous efficiency for high-performance blue light devices. On the further hand, when the quantum dot film prepared from the quantum dot solution is used in a light-emitting device, the valence band of the red light quantum dots with a lower PLQY is between the valence band of the hole transport layer material known to be used in the light-emitting device and the valence band of the blue light quantum dots, which can effectively reduce the hole injection barrier from the hole transport layer to the blue light quantum dot film, improve the hole injection level of the device, promote the balance of electrons and holes, and further enhance the performance such as the efficiency and lifespan of the light-emitting device.

[0066] In at least one preferred embodiment, the PLQY of the first quantum dots is 75 - 85%, and the PLQY of the second quantum dots is less than or equal to 5%. In this way, the quantum dot film prepared from the quantum dot solution can have both higher blue light color purity and higher stability.

[0067] In some embodiments, the full width at half maximum (FWHM) of the first quantum dots is 10 - 30 nm. The blue light quantum dots with such an FWHM not only help improve the color gamut of optoelectronic devices but also enable a large distance between the emission spectrum of the blue light quantum dots and the absorption spectrum of the red light quantum dots, avoiding the problem of energy resonance transfer from blue light quantum dots to red light quantum dots inside the quantum dot film.

[0068] In some embodiments, the full width at half maximum (FWHM) of the second quantum dots is 10 - 40 nm. The red light quantum dots with such an FWHM can enable a large distance between the emission spectrum of the red light quantum dots and the absorption spectrum of the blue light quantum dots, avoiding the problem of energy resonance transfer from blue light quantum dots to red light quantum dots inside the quantum dot film.

[0069] In some embodiments, in the quantum dot solution, the mass ratio of the inorganic nanoparticles to the first quantum dots is (0.1 to 0.5):1. For example, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1, 0.5:1, etc. Within the range of this mass ratio, the quantum dot film prepared from the quantum dot solution can emit blue light, and the blue light emitted by the quantum dot film prepared from the quantum dot solution has a high color purity.

[0070] Due to the synergistic effect of the specific PLQY, emission wavelength, particle size, and mass ratio of the blue-light quantum dots and red-light quantum dots in the quantum dot solution of the present application, the quantum dot film prepared therefrom can emit blue light, the emitted blue light has a high color purity, and the quantum dot film can also have a long lifespan.

[0071] It can be understood that the solvent is a solvent known in the art for preparing or dispersing quantum dots, and can include but is not limited to at least one of alkanes, alkenes, ethers, and aromatic compounds with a carbon atom number greater than or equal to 10. As an example, the first solvent can include but is not limited to one or more of n-hexane, n-octane, toluene, tetradecene, hexadecene, octadecene, eicosene, and paraffin oil.

[0072] The concentration of the quantum dot solution is not limited. In at least some embodiments, the concentration of the quantum dot solution is 30 to 50 mg / mL. Within this concentration range, it is beneficial to prepare a quantum dot film with good film-forming effect and luminescence performance.

[0073] The first quantum dots and the second quantum dots can be independently selected from but are not limited to one or more of single-structure quantum dots, core-shell structure quantum dots, and perovskite semiconductor materials.

[0074] The materials of the single-structure quantum dots, the core materials of the core-shell structure quantum dots, and the shell materials of the core-shell structure quantum dots may respectively include, but are not limited to, one or more of II-VI group compounds, IV-VI group compounds, III-V group compounds, and I-III-VI group compounds. The II-VI group compounds may include, but are not limited to, one or more of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, and HgZnSTe. The IV-VI group compounds may include, but are not limited to, one or more of SnS, SnSe, SnTe, PbS, PbSe, PbTe, SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, SnPbSSe, SnPbSeTe, and SnPbSTe. The III-V group compounds may include, but are not limited to, one or more of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, and InAlPSb. The I-III-VI group compounds may include, but are not limited to, one or more of CuInS2, CuInSe2, and AgInS2.

[0075] It can be understood that the materials of the core and the shell of the core-shell structure quantum dots may be the same or different. In at least one embodiment, the materials of the core and the shell of the core-shell structure quantum dots are different.

[0076] As an example, the quantum dots of the core-shell structure may include, but are not limited to, one or more of CdSe / ZnSe, CdTe / ZnSe, CdZnSe / ZnSe, ZnSe / ZnS, ZnSeTe / ZnS, CdSe / ZnS, CdSe / CdSeS / CdS, InP / ZnSeS / ZnS, CdZnSe / ZnSe / ZnS, CdSeS / ZnSeS / ZnS, CdSe / ZnSe / ZnSCdZnTe / ZnSe, CdSe / CdZnSe / ZnSe, CdSe / CdZnSeS / ZnS, CdTe / CdZnTe / ZnSe, CdTe / CdZnSe / ZnSe, and InP / ZnSe / ZnS.

[0077] The perovskite semiconductor material may include, but is not limited to, doped or undoped inorganic perovskite semiconductors, or organic-inorganic hybrid perovskite semiconductors. The general structural formula of the inorganic perovskite semiconductor is AMX3, where A is Cs + ions, M is a divalent metal cation, including Pb 2+ , Sn 2+ , Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2+ , Yb 2+ , Eu 2+ and one or more of the like, and X is a halogen anion, including Cl - , Br - , I - and one or more of the like. The general structural formula of the organic-inorganic hybrid perovskite semiconductor is BMX3, where B is an organic amine cation, including CH3(CH2) n-2 NH3 + or [NH3(CH2) n NH3] 2+ , where n≥2, M is a divalent metal cation, including Pb 2+ , Sn 2+ , Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2+ , Yb 2+ , Eu 2+one or more of them, X is a halogen anion, including Cl - , Br - , I - one or more of them.

[0078] In some embodiments, the red quantum dots are CdSe / CdZnSe / CdZnS, the core of the red quantum dots is CdSe (particle size is 5 nm); the amount of Se used in the first shell is 1.5 mmol, and the molar ratio of Cd to Se elements is 0.3:1; the amount of S used in the second shell CdZnS is 1 mmol, and the molar ratio of Cd to S elements is 0.3:1, and the average particle size is 8 nm.

[0079] In some other embodiments, the core of the red quantum dots is CdSe (particle size is 5 nm); the amount of Se used in the first shell is 1.5 mmol, and the molar ratio of Cd to Se elements is 0.3:1; the amount of S used in the second shell CdZnS is 1 mmol, and the molar ratio of Cd to S elements is 0.3:1; the amount of S used in the outermost shell ZnS is 1 mmol. The average particle size of the red quantum dots is 8.5 nm.

[0080] In still some other embodiments, the structure of the red quantum dots is CdZnSe / CdZnSe / CdZnS, the core of the red quantum dots is CdZnSe (particle size is 6 nm), the amount of Se used is 0.8 mmol, and the molar ratio of Cd to Se elements is 0.5:1; the amount of Se used in the first shell is 1 mmol, and the molar ratio of Cd to Se elements is 0.3:1; the amount of S used in the second shell CdZnS is 1 mmol, and the molar ratio of Cd to S elements is 0.3:1; the average particle size of the red quantum dots is 8.5 nm.

[0081] In still some other embodiments, the structure of the red quantum dots is CdZnSe / CdZnS, the core of the red quantum dots is CdZnSe (average particle size is 8 nm), the amount of Se used is 1.2 mmol, and the molar ratio of Cd to Se elements is 0.6:1; the amount of S used in the first shell CdZnS is 2 mmol, and the molar ratio of Cd to S elements is 0.4:1; the average particle size of the red quantum dots is 9.8 nm.

[0082] In some embodiments, ligands are independently connected to the surfaces of the first quantum dots and the second quantum dots, and the ligands include substituted or unsubstituted C6-C 24 fatty acids, substituted or unsubstituted C6-C 24 fatty amines, substituted or unsubstituted C6-C 24 aliphatic thiols, substituted or unsubstituted C6-C 24 aliphatic thioethers, substituted or unsubstituted C6-C 24 aliphatic phosphines, substituted or unsubstituted C6-C24 aliphatic phosphine oxides, substituted or unsubstituted C8 - C 20 aliphatic phosphoric acids, substituted or unsubstituted C6 - C 24 aliphatic phosphates, substituted or unsubstituted C6 - C 24 aliphatic phosphites, substituted or unsubstituted C6 - C 24 and at least one of aliphatic phosphonites, substituted or unsubstituted C6 - C.

[0083] Among them, "substituted or unsubstituted" means that the defined group can be substituted or unsubstituted. When the defined group is substituted, it should be understood that the defined group can be substituted by one or more substituents.

[0084] Among them, the substituted substituents are selected from at least one of C1 - C6 alkyl, C1 - C6 alkoxy, and halogen.

[0085] In some embodiments, the substituted or unsubstituted C6 - C 24 fatty acids include at least one of capric acid, undecylenic acid, myristic acid, oleic acid, linoleic acid, and stearic acid.

[0086] In some embodiments, the substituted or unsubstituted C6 - C 24 aliphatic thiols include at least one of octanethiol, dodecyl mercaptan, and octadecyl mercaptan.

[0087] In some embodiments, the substituted or unsubstituted C6 - C 24 fatty amines include at least one of oleylamine, octadecylamine, octylamine, dioctylamine, and trioctylamine.

[0088] In some embodiments, the substituted or unsubstituted C6 - C 24 aliphatic phosphines include trioctylphosphine.

[0089] In some embodiments, the substituted or unsubstituted C6 - C 24 aliphatic phosphine oxides include trioctylphosphine oxide.

[0090] The P-type inorganic nanoparticles include one or more of doped metal oxide particles, undoped metal oxide particles, metal sulfides, and metal nitrides. Among them, the metal oxides in the doped metal oxide particles and the metal oxides in the undoped metal oxide particles independently include one or more of MoO3, WO3, NiO, CrO3, CuO, Cu2O, and V2O5. The doping elements in the doped metal oxide particles include one or more of Mo, W, Ni, Cr, Cu, and V. The metal sulfides include one or more of CuS, MoS3, and WS3. The metal nitrides include P-type gallium nitride.

[0091] In a second aspect, an embodiment of the present application further provides a method for preparing a quantum dot solution, including: providing inorganic nanoparticles, a first quantum dot, and a solvent, and mixing them to obtain a quantum dot solution.

[0092] The materials and proportions of the inorganic nanoparticles, the first quantum dot, and the solvent refer to those described above.

[0093] In some embodiments, when the inorganic nanoparticles are second quantum dots, the second quantum dots are prepared by the following preparation method:

[0094] Providing an initial second quantum dot, and under UV conditions, exposing the initial second quantum dot to water and oxygen for a period of time T to cause photodegradation of the initial second quantum dot, thereby obtaining the second quantum dot.

[0095] In some embodiments, the wavelength of the ultraviolet light is 365 - 405 nm.

[0096] In some embodiments, the PLQY of the initial second quantum dot is 50 - 100%.

[0097] In some embodiments, the time T is 1 - 48 h.

[0098] In a third aspect, an embodiment of the present application further provides a quantum dot film, which is prepared by a solution film-forming method from the quantum solution described above. The quantum dot film includes the first quantum dot and the second quantum dot.

[0099] The PLQY, emission wavelength, full width at half maximum, average particle size, mass ratio, and material selection of the first quantum dot and the second quantum dot refer to those described above, and will not be elaborated here.

[0100] In some embodiments, the solution film-forming method can be spin coating, printing, inkjet printing, doctor blading, printing, dip coating, immersion, spraying, roll coating, casting, slot die coating, bar coating, etc.

[0101] Fourthly, an embodiment of the present application further provides a light-emitting unit, including a blue quantum dot and an inorganic nanoparticle.

[0102] The first quantum dot, the inorganic nanoparticle and their ratios are as described above, and will not be elaborated here.

[0103] The light-emitting unit described in the present application includes the first quantum dot and the inorganic nanoparticle, and the average particle size of the inorganic nanoparticle is smaller than that of the first quantum dot, and it has a relatively high PLQY and a good color gamut value.

[0104] Furthermore, when the inorganic nanoparticle is the second quantum dot, since the emission peak of the blue quantum dot does not overlap with the absorption peak of the red quantum dot, when a red quantum dot with a relatively low PLQY is doped into the blue quantum dot, the presence of the red quantum dot can significantly inhibit the occurrence of FRET, thereby avoiding the problem of a significant decrease in PLQY when the blue quantum dot solution is converted from a solution to a thin film, thus providing a quantum dot film with high luminous efficiency for high-performance blue devices. In addition, when the quantum dot film prepared from the quantum dot solution is used in a light-emitting device, the valence band of the red quantum dot with a relatively low PLQY is between the valence band of the hole transport layer material known for use in light-emitting devices and the valence band of the blue quantum dot, which can effectively reduce the hole injection barrier from the hole transport layer to the blue quantum dot film, improve the hole injection level of the device, promote the balance of electrons and holes, and further improve the performance such as the efficiency and lifespan of the light-emitting device.

[0105] Fifthly, please refer to Figure 1 , an embodiment of the present application further provides a preparation method of the light-emitting unit, including the following steps:

[0106] Step S11: Provide an inorganic nanoparticle, a first quantum dot and a solvent, and mix them to obtain a quantum dot solution;

[0107] Step S12: Use the quantum dot solution to prepare a thin film to obtain a light-emitting unit.

[0108] The types and ratios of the inorganic nanoparticle, the first quantum dot and the solvent are as described above, and will not be elaborated here.

[0109] Sixthly, please refer to Figure 2 , an embodiment of the present application further provides a light-emitting device 100, including the light-emitting unit 20 described above.

[0110] In at least one embodiment, the light-emitting device 100 includes an anode 10, a light-emitting unit 20 and a cathode 30 stacked in sequence.

[0111] Please refer to Figure 3, in some embodiments, the light-emitting device 100 further includes a hole transport layer 40 located between the anode 10 and the light-emitting unit 20. In other words, the light-emitting device 100 includes an anode 10, a hole transport layer 40, a light-emitting unit 20, and a cathode 30 that are stacked in sequence.

[0112] Please refer to Figure 4 , in some embodiments, the light-emitting device 100 further includes an electron transport layer 50 located between the light-emitting unit 20 and the cathode 30. In other words, the light-emitting device 100 includes an anode 10, a light-emitting unit 20, an electron transport layer 50, and a cathode 30 that are stacked in sequence.

[0113] Please refer to Figure 5 , in some embodiments, the light-emitting device 100 includes an anode 10, a hole transport layer 40, a light-emitting unit 20, an electron transport layer 50, and a cathode 30 that are stacked in sequence.

[0114] Please refer to Figure 6 , in some embodiments, the light-emitting device 100 further includes a hole injection layer 60 located between the anode 10 and the hole transport layer 40.

[0115] The anode 10 and the cathode 30 are anodes and cathodes known in the art for light-emitting devices. For example, they can independently include, but are not limited to, doped metal oxide particle electrodes, composite electrodes, graphene electrodes, carbon nanotube electrodes, metal elemental electrodes, or alloy electrodes. The material of the doped metal oxide particle electrode can include, but is not limited to, one or more of indium-doped tin oxide (ITO), fluorine-doped tin oxide (FTO), antimony-doped tin oxide (ATO), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), indium-doped zinc oxide (IZO), magnesium-doped zinc oxide (MZO), and aluminum-doped magnesium oxide (AMO). The composite electrode is a composite electrode in which doped or undoped transparent metal oxide particles sandwich a metal, such as AZO / Ag / AZO, AZO / Al / AZO, ITO / Ag / ITO, ITO / Al / ITO, ZnO / Ag / ZnO, ZnO / Al / ZnO, TiO2 / Ag / TiO2, TiO2 / Al / TiO2, ZnS / Ag / ZnS, ZnS / Al / ZnS, etc. Here, " / " represents a stacked structure. For example, AZO / Ag / AZO represents a composite electrode including an AZO layer, an Ag layer, and an AZO layer stacked in sequence. The material of the metal elemental electrode can include, but is not limited to, one or more of Ag, Al, Cu, Mo, Au, Pt, Ca, Mg, and Ba.

[0116] The material of the hole transport layer 40 may also be a material known in the art for hole transport layers, and may include, for example, but not limited to, 4,4'-N,N'-dicarbazolyl-biphenyl (CBP), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4”-diamine (α-NPD), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD), poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine) (Poly-TPD), N,N'-bis(3-methylphenyl)-N,N'-bis(phenyl)-spiro(spiro-TPD), N,N'-bis(4-(N,N'-diphenyl-amino)phenyl)-N,N'-diphenylbenzidine (DNTPD), 4,4',4'-tris(N-carbazolyl)-triphenylamine (TCTA), 4,4',4'-tris(N-3-methylphenyl-N-phenylamino)triphenylamine (m-MTDATA), poly[(9,9'-dioctylfluorene-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl)diphenylamine))] (TFB), poly(N-vinylcarbazole) (PVK) and its derivatives, N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4-4'-diamine (NPB), spiro-NPB, poly(phenylene vinylene) (PPV), poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV), poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene vinylene] (MOMO-PPV), 2,2',7,7'-tetrakis[N,N-bis(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-omeTAD), 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)aniline] (TAPC), 1,3-bis(carbazol-9-yl)benzene (MCP), polyaniline, polypyrrole, poly(p-phenylene vinylene), aromatic tertiary amines, polynuclear aromatic tertiary amines, 4,4'-bis(p-carbazolyl)-1,1'-biphenyl compounds, N,N,N',N'-tetraarylbenzidine, PEDOT:PSS and its derivatives, polymethacrylate and its derivatives, poly(9,9-octylfluorene) and its derivatives, poly(spirofluorene) and its derivatives, doped graphene, undoped graphene, C60, doped or undoped NiO, doped or undoped MoO3, doped or undoped WO3, doped or undoped V2O5, doped or undoped p-type gallium nitride, doped or undoped CrO3, doped or undoped CuO, or one or more of them.

[0117] The material of the electron transport layer 50 is a material known in the art for electron transport layers. For example, it may include, but is not limited to, one or more of inorganic electron transport materials and organic electron transport materials. The inorganic electron transport materials include one or more of metal oxides, doped metal oxides, IIB-VIA group semiconductor materials, IIIA-VA group semiconductor materials, and IB-IIIA-VIA group semiconductor materials. The metal oxides include one or more of ZnO, TiO2, SnO2, ZrO2, Ta2O5; the metal oxides in the doped metal oxides include one or more of ZnO, TiO2, SnO2, ZrO2, Ta2O5, Al2O3, and the dopants in the doped metal oxides include one or several of Al, Mg, Li, Mn, Y, La, Cu, Ni, Zr, Ce, In, Ga, Sn; the IIB-VIA group semiconductor materials include one or more of ZnS, ZnSe, CdS; the IIIA-VA group semiconductor materials include one or more of InP, GaP; the IB-IIIA-VIA group semiconductor materials include one or more of CuInS, CuGaS; the organic electron transport materials include one or more of quinoxaline compounds, imidazole compounds, triazine compounds, fluorene-containing compounds, hydroxyquinoline compounds.

[0118] The material of the hole injection layer 60 can be a material known in the art for hole injection layers. For example, it can be selected from, but is not limited to, 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HAT-CN), PEDOT, PEDOT:PSS, a derivative of PEDOT:PSS doped with s-MoO3 (PEDOT:PSS:s-MoO3), 4,4',4'-tris(N-3-methylphenyl-N-phenylamino)triphenylamine (m-MTDATA), tetracyanoquinodimethane (F4-TCQN), copper phthalocyanine, nickel oxide, molybdenum oxide, tungsten oxide, vanadium oxide, molybdenum sulfide, tungsten sulfide, and copper oxide, etc.

[0119] In some embodiments, the thickness of the anode 10 is 20 - 200 nm; the thickness of the hole injection layer 60 is 20 - 200 nm; the thickness of the hole transport layer 40 is 30 - 180 nm; the total thickness of the light-emitting unit 20 is 30 - 180 nm; the thickness of the electron transport layer 50 is 20 - 100 nm; the thickness of the cathode 30 is 40 - 190 nm.

[0120] It can be understood that the light-emitting device 100 can also be provided with some functional layers that are commonly used in light-emitting devices and are helpful for improving the performance of the light-emitting device, such as an electron blocking layer, a hole blocking layer, an electron injection layer, an interface modification layer, etc.

[0121] It can be understood that the materials of the respective layers of the light-emitting device 100 can be adjusted according to the light-emitting requirements of the light-emitting device 100.

[0122] In some embodiments, the light-emitting device 100 further includes a substrate, which is disposed on a side of the anode 10 away from the light-emitting unit 20, or the substrate is disposed on a side of the cathode 30 away from the light-emitting unit 20.

[0123] The substrate can be a rigid substrate or a flexible substrate. In some embodiments, the material of the substrate can include, but is not limited to, one or more of glass, silicon wafer, polycarbonate, polymethyl methacrylate, polyethylene terephthalate, polyethylene naphthalate, polyamide, and polyethersulfone.

[0124] It can be understood that the light-emitting device 100 can be a front-emitting light-emitting device or an inverted light-emitting device. The light-emitting device 100 can be a quantum dot light-emitting device or an organic light-emitting device.

[0125] The light-emitting unit 20 of the light-emitting device 100 is the quantum dot film described in the present application, so that blue light with higher color purity can be emitted, and it has higher luminous efficiency and longer lifespan.

[0126] In a fourth aspect, an embodiment of the present application further provides a display device, which includes the light-emitting device 100.

[0127] The display device can be any electronic product with a display function, and the electronic product includes, but is not limited to, a smart phone, a tablet computer, a notebook computer, a digital camera, a digital video camera, a smart wearable device, a smart weighing electronic scale, a vehicle-mounted display, a television, or an e-book reader. Among them, the smart wearable device can be, for example, a smart bracelet, a smart watch, a virtual reality (VR) helmet, etc.

[0128] The present application will be specifically described below through specific embodiments. The following embodiments are only partial embodiments of the present application and do not limit the present application.

[0129] Embodiment 1

[0130] Provide an ITO anode substrate, where the thickness of the ITO anode is 120 nm. Ultrasonically clean the ITO substrate with acetone and ethanol for 15 min, then wash it with deionized water and blow it dry, then dry it on a hot plate at 150 °C for 10 min, and then perform ultraviolet light irradiation for 20 min to increase the ITO work function;

[0131] Spin-coat PEDOT:PSS material on the cleaned ITO substrate at a rotation speed of 4000 rpm for 30 s, and then heat it on a hot plate at 210 °C for 20 min to obtain a hole injection layer with a thickness of 25 nm;

[0132] In an inert atmosphere, spin-coat TFB material on the hole injection layer at a rotation speed of 3000 rpm for 30 s, and then heat it on a hot plate at 200 °C for 30 min to obtain a hole transport layer with a thickness of 25 nm;

[0133] Provide a quantum dot solution with a concentration of 30 mg / ml. The quantum dot solution includes red light quantum dots, blue light quantum dots and solvent n-octane. Spin-coat the quantum dot solution on the hole transport layer at a rotation speed of 2000 rpm for 30 s, and then heat it on a hot plate at 80 °C for 5 min to obtain a quantum dot film with a thickness of 40 nm, that is, obtain a light-emitting layer;

[0134] Among them, the mass ratio of red light quantum dots to blue light quantum dots is 0.3:1;

[0135] The structure of the blue light quantum dots is CdZnSe / ZnSe / CdZnS / ZnS. The core of the blue light quantum dots is CdZnSe, and the amount of Se used in the core is 1.3 mmol. The molar ratio of Cd to Se elements is 0.1:1; the amount of Se used in the first shell is 2.5 mmol; the amount of S used in the second shell CdZnS is 1.8 mmol, and the molar ratio of Cd to S used is 0.35:1; the amount of S used in the outermost shell ZnS is 1 mmol. The emission wavelength is 472 nm, the full width at half maximum is 21 nm, the PLQY is 75%, and the average particle size of the blue light quantum dots is 11.5 nm;

[0136] The structure of the initial red light quantum dots is CdSe / CdZnSe / CdZnS. The core of the red light quantum dots is CdSe (particle size is 5 nm); the amount of Se used in the first shell is 1.5 mmol, and the molar ratio of Cd to Se elements is 0.3:1; the amount of S used in the second shell CdZnS is 1 mmol, and the molar ratio of Cd to S elements is 0.3:1. The average particle size of the red light quantum dots is 8 nm. The emission wavelength of the initial red light quantum dots is 635 nm, the full width at half maximum of the initial red light quantum dots is 23 nm, the PLQY of the initial red light quantum dots is 80%, and the red light quantum dots with a PLQY of 5% are obtained by exposing the initial red light quantum dots to air under 365 nm UV for 12 h;

[0137] Spin-coat a doped Mg ZnO colloid with a concentration of 20 mg / mL (the mass fraction of Mg is 15%) on the light-emitting layer at a rotation speed of 4000 rpm for 30 s, and then evacuate it under a low pressure of 0.001-10 Pa for 15 min to obtain an electron transport layer with a thickness of 30 nm;

[0138] Deposit Ag by evaporation on the electron transport layer, where the vacuum degree is not higher than 3x10 -4 Pa, the evaporation rate is 1 Å / s, and the time is 1000 s to obtain a cathode with a thickness of 100 nm;

[0139] Encapsulate, and then anneal at 120 °C for 30 min to obtain a light-emitting device.

[0140] Example 2

[0141] This example is basically the same as Example 1, except that in this example, the mass ratio of red light quantum dots to blue quantum dots is 0.1:1.

[0142] Example 3

[0143] This example is basically the same as Example 1, except that in this example, the mass ratio of red light quantum dots to blue quantum dots is 0.5:1.

[0144] Example 4

[0145] This example is basically the same as Example 1, except that in this example, the mass ratio of red light quantum dots to blue quantum dots is 0.05:1.

[0146] Example 5

[0147] This example is basically the same as Example 1, except that in this example, the mass ratio of red light quantum dots to blue quantum dots is 0.8:1.

[0148] Example 6

[0149] This example is basically the same as Example 1, except that in this example, the PLQY of the blue light quantum dots is 50%.

[0150] Example 7

[0151] This example is basically the same as Example 1, except that in this example, the PLQY of the blue light quantum dots is 90%.

[0152] Example 8

[0153] This example is basically the same as Example 1, except that in this example, the PLQY of the red light quantum dots is 1%.

[0154] Example 9

[0155] This example is basically the same as Example 1, except that in this example, the PLQY of the red light quantum dots is 10%.

[0156] Example 10

[0157] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the emission wavelength of the blue quantum dots is 430 nm.

[0158] Embodiment 11

[0159] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the emission wavelength of the blue quantum dots is 480 nm.

[0160] Embodiment 12

[0161] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the emission wavelength of the red quantum dots is 600 nm.

[0162] Embodiment 13

[0163] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the emission wavelength of the red quantum dots is 640 nm.

[0164] Embodiment 14

[0165] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the structure of the red quantum dots is CdSe / CdZnSe / CdZnS / ZnS, and the structure of the blue quantum dots is CdZnSe / CdZnSe / CdZnS / ZnS.

[0166] The core of the red quantum dots is CdSe (average particle size is 5 nm); the amount of Se used in the first shell is 1.5 mmol, and the molar ratio of Cd to Se elements is 0.3:1; the amount of S used in the second shell CdZnS is 1 mmol, and the molar ratio of Cd to S is 0.3:1; the amount of S used in the outermost shell ZnS is 1 mmol. The average particle size of the red quantum dots is 8.5 nm. The emission wavelength of the initial red quantum dots is 635 nm, the full width at half maximum of the initial red quantum dots is 23 nm, the PLQY of the initial red quantum dots is 85%, and the red quantum dots with a PLQY of 6% are obtained by exposing the initial red quantum dots to air under 365 nm UV for 12 h.

[0167] The core of the blue quantum dots is CdZnSe, the amount of Se used in the core is 1.3 mmol, and the molar ratio of Cd to Se elements is 0.1:1; the amount of Se used in the first shell CdZnSe is 2.5 mmol, and the molar ratio of Cd to Se is 0.08:1; the amount of S used in the second shell CdZnS is 1.8 mmol, and the molar ratio of Cd to S used is 0.35:1; the amount of S used in the outermost shell ZnS is 1 mmol. The emission wavelength of the blue quantum dots is 475 nm, the full width at half maximum is 21 nm, the PLQY is 80%, and the average particle size of the blue quantum dots is 11.9 nm.

[0168] Embodiment 15

[0169] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the thickness of the ITO anode is 100 nm, the thickness of the hole injection layer is 90 nm, the thickness of the hole transport layer is 90 nm, the structure of the blue quantum dots is CdZnS / CdZnS / ZnS, the full width at half maximum is 18 nm, and the PLQY of the red quantum dots is 6%.

[0170] The core of the blue quantum dots is CdZnS, the amount of S used in the core is 1.2 mmol, and the molar ratio of Cd to S elements is 0.66:1; the amount of S used in the first shell layer CdZnS is 2 mmol, and the molar ratio of Cd to S is 0.5:1; the amount of S used in the outermost shell layer ZnS is 0.5 mmol. The emission wavelength of the blue quantum dots is 475 nm, the full width at half maximum is 18 nm, the PLQY is 85%, and the average particle size of the blue quantum dots is 9 nm.

[0171] Example 16

[0172] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the structure of the red quantum dots is CdZnSe / CdZnSe / CdZnS, the core of the red quantum dots is CdZnSe (average particle size is 6 nm), the amount of Se used is 0.8 mmol, and the molar ratio of Cd to Se elements is 0.5:1; the amount of Se used in the first shell layer is 1 mmol, and the molar ratio of Cd to Se elements is 0.3:1; the amount of S used in the second shell layer CdZnS is 1 mmol, and the molar ratio of Cd to S elements is 0.3:1; the average particle size of the red quantum dots is 8.5 nm. The emission wavelength of the initial red quantum dots is 636 nm, and the full width at half maximum of the initial red quantum dots is 22 nm.

[0173] Example 17

[0174] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the structure of the red quantum dots is CdZnSe / CdZnS, the core of the red quantum dots is CdZnSe (average particle size is 8 nm), the amount of Se used is 1.2 mmol, and the molar ratio of Cd to Se elements is 0.6:1; the amount of S used in the first shell layer CdZnS is 2 mmol, and the molar ratio of Cd to S elements is 0.4:1; the average particle size of the red quantum dots is 9.8 nm. The emission wavelength of the initial red quantum dots is 637 nm, and the full width at half maximum of the initial red quantum dots is 25 nm.

[0175] Comparative Example 1

[0176] This comparative example is basically the same as Embodiment 1, except that the quantum dot solution in this comparative example does not include red quantum dots.

[0177] Comparative Example 2

[0178] This comparative example is basically the same as Example 1, except that the PLQY of the red quantum dots in this comparative example is 38%.

[0179] Comparative Example 3

[0180] This comparative example is basically the same as Example 1, except that the PLQY of the red quantum dots in this comparative example is 65%.

[0181] Comparative Example 4

[0182] This comparative example is basically the same as Example 14, except that the quantum dot solution in this comparative example does not include red quantum dots.

[0183] Comparative Example 5

[0184] This comparative example is basically the same as Example 15, except that the quantum dot solution in this comparative example does not include red quantum dots.

[0185] The PLQY of the quantum dot solutions and quantum dot films of Examples 1 to 17 and Comparative Examples 1 to 5 were respectively detected, and the detection results are shown in Table 1.

[0186] The emission wavelength (PL) of the quantum dot solutions of Examples 1 to 17 and Comparative Examples 1 to 5 was tested, and the detection results are shown in Table 1.

[0187] The external quantum efficiency EQE, lifetime T95@1000nit, and electroluminescence spectrum EL of the light-emitting devices of Examples 1 to 17 and Comparative Examples 1 to 5 were respectively detected, and the detection results are shown in Table 1.

[0188] The test method for the emission wavelength (PL) is as follows: Using n-hexane as the solvent, an appropriate amount of the quantum dot solution is added. After shaking well, it is scanned in an appropriate wavelength range using a fluorescence spectrophotometer (Hitachi F-7000), and the excitation wavelength is 350 nm.

[0189] The test method for the external quantum efficiency EQE is as follows: The ratio of the number of electron-hole pairs injected into the quantum dots to the number of emitted photons, with the unit of %, is an important parameter for measuring the quality of electroluminescent devices, and it can be obtained by measuring with an EQE optical test instrument. The specific calculation formula is as follows:

[0190]

[0191] Among them, ηe is the light output coupling efficiency, ηr is the ratio of the number of recombined carriers to the number of injected carriers, χ is the ratio of the number of excitons generating photons to the total number of excitons, K R is the radiation process rate, K NR is the non-radiation process rate.

[0192] The test method for the lifetime T95@1000nit is as follows: in CDA gas, under constant current drive, the time it takes for the device brightness to decay to a certain proportion of the maximum brightness is measured. The time when the brightness decays to 95% of the maximum brightness is defined as T95, and this lifetime is the measured lifetime. To shorten the lifetime test cycle, the device lifetime test is usually carried out by accelerating the device aging at high brightness, and the lifetime at low brightness is obtained by fitting through the decay fitting formula. For example, the lifetime at 1000 nits is denoted as T95@1000nits, and the calculation formula is:

[0193]

[0194] where T95 L is the lifetime at low brightness, generally taking the lifetime at 1000 nits, T95 H is the lifetime at high brightness, that is, the measured lifetime, L H is the maximum brightness to which the device is accelerated, L L is generally 1000 nits, A is the acceleration factor, taking 1.7. Among them, the constant current is 2 mA.

[0195] The test method for the electroluminescence spectrum (EL) is as follows: use an optical fiber spectrometer (Ocean Optics QE65000) to measure the electroluminescence spectrum of the QLED.

[0196] The environmental conditions for the above tests are: carried out at room temperature, and the air humidity is 30 - 60%.

[0197] Table 1:

[0198]

[0199] As can be seen from Table 1:

[0200] Compared with Comparative Examples 1, 4 - 5, the PLQY of the quantum dot film formed after the quantum dot solution is formed into a film in Examples 1 - 17 decreases less. In other words, compared with Comparative Examples 1, 4 - 5, the PLQY of the quantum dot film in Examples 1 - 17 is higher. It can be seen that doping red quantum dots into blue quantum dots can not only significantly inhibit the energy resonance transfer phenomenon in the quantum dot film and greatly inhibit the occurrence of the PL - to - EL red - shift phenomenon, thereby effectively improving the PLQY of the prepared quantum dot film;

[0201] Compared with the light-emitting devices of Comparative Example 1, the light-emitting devices of Examples 1 to 10, 12 to 13, and 16 to 17 have higher luminous efficiency and longer lifespan; compared with the light-emitting devices of Comparative Example 4, the light-emitting device of Example 14 has higher luminous efficiency and longer lifespan; compared with the light-emitting devices of Comparative Example 5, the light-emitting device of Example 15 has higher luminous efficiency and longer lifespan. It can be seen that doping red quantum dots into blue quantum dots can not only significantly inhibit the energy resonance transfer phenomenon in the quantum dot film and greatly suppress the occurrence of the PL-to-EL red shift phenomenon, thereby effectively improving the luminous efficiency and lifespan of the light-emitting device;

[0202] The luminous efficiency of the light-emitting device of Example 11 is lower and the lifespan is shorter compared with that of the light-emitting device of Comparative Example 1 because the emission wavelength of the blue quantum dots of the light-emitting device of Example 11 is shorter;

[0203] Red impurity peaks appear in the light-emitting device of Example 5. The reason may be that the doping concentration of the red quantum dots is relatively high, resulting in the problem of red impurity peaks in the EL spectrum of the light-emitting device and a relatively high CIEy value of the blue QLED device, which is not conducive to the development of high-color gamut display devices.

[0204] The technical solutions provided by the embodiments of the present application have been introduced in detail above. Specific examples are used in this article to elaborate on the principles and implementation manners of the present application. The descriptions of the above embodiments are only used to help understand the method and its core idea of the present application; at the same time, for those skilled in the art, according to the idea of the present application, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A light-emitting unit, characterized in that, It includes a first quantum dot and inorganic nanoparticles. The emission peak wavelength of the first quantum dot is 430 - 480 nm, and the average particle size of the inorganic nanoparticles is smaller than that of the first quantum dot.

2. The light-emitting unit according to claim 1, characterized in that, The average particle size of the first quantum dot is 10 - 25 nm; and / or, the average particle size of the inorganic nanoparticles is 5 - 10 nm; and / or, the mass ratio of the inorganic nanoparticles to the first quantum dot is (0.1 - 0.5):

1. and / or, the inorganic nanoparticles include one or more of P-type inorganic nanoparticles and a second quantum dot. The emission peak wavelength of the second quantum dot is 600 - 640 nm.

3. The light-emitting unit according to claim 2, characterized in that, The PLQY of the first quantum dot is 50 - 100%, and the PLQY of the second quantum dot is greater than 0 and less than or equal to 10%; preferably, the PLQY of the first quantum dot is 75 - 85%, and the PLQY of the second quantum dot is greater than 0 and less than or equal to 5%; and / or, the full width at half maximum of the first quantum dot is 10 - 30 nm; and / or, the full width at half maximum of the second quantum dot is 10 - 40 nm.

4. The light-emitting unit according to claim 2, characterized in that, The P-type inorganic nanoparticles include one or more of doped metal oxide particles, undoped metal oxide particles, metal sulfides, and metal nitrides. Among them, the metal oxides in the doped metal oxide particles and the metal oxides in the undoped metal oxide particles independently include one or more of MoO3, WO3, NiO, CrO3, CuO, Cu2O, V2O5. The doping elements in the doped metal oxide particles include one or more of Mo, W, Ni, Cr, Cu, V. The metal sulfides include one or more of CuS, MoS3, WS3. The metal nitrides include P-type gallium nitride; And / or, the first quantum dots and the second quantum dots each independently include one or more of single-structure quantum dots, core-shell structure quantum dots, and perovskite semiconductor materials. Among them, the materials of the single-structure quantum dots, the core materials of the core-shell structure quantum dots, and the shell materials of the core-shell structure quantum dots may each include one or more of II-VI group compounds, IV-VI group compounds, III-V group compounds, and I-III-VI group compounds. The II-VI group compounds include one or more of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, and HgZnSTe. The IV-VI group compounds include one or more of SnS, SnSe, SnTe, PbS, PbSe, PbTe, SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, SnPbSSe, SnPbSeTe, and SnPbSTe. The III-V group compounds include one or more of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, and InAlPSb. The I-III-VI group compounds include one or more of CuInS2, CuInSe2, and AgInS2. The perovskite semiconductor materials include doped or undoped inorganic perovskite semiconductors or organic-inorganic hybrid perovskite semiconductors. The structural general formula of the inorganic perovskite semiconductors is AMX3, where A is Cs + ions, M is a divalent metal cation, including Pb 2+ and Sn 2+ , Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2 + , Yb 2+ , Eu 2+ One or more of the following, X is a halogen anion, including Cl - , Br - , I - One or more of the following. The structural general formula of the organic-inorganic hybrid perovskite semiconductor is BMX3, where B is an organic amine cation, including CH3(CH2) n-2 NH3 + or [NH3(CH2) n NH3] 2+ , where n≥2, M is a divalent metal cation, including Pb 2+ , Sn 2+ , Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2+ , Yb 2+ , Eu 2+ One or more of the following, X is a halogen anion, including Cl - , Br - , I - One or more of the following.

5. The light-emitting unit according to claim 2, characterized in that, The surface of the first quantum dot and the second quantum dot is independently connected with a ligand, and the ligand includes substituted or unsubstituted C6-C 24 fatty acid, substituted or unsubstituted C6-C 24 fatty amine, substituted or unsubstituted C6-C 24 aliphatic thiol, substituted or unsubstituted C6-C 24 aliphatic thioether, substituted or unsubstituted C6-C 24 aliphatic phosphine, substituted or unsubstituted C6-C 24 aliphatic phosphine oxide, substituted or unsubstituted C6-C 20 aliphatic phosphoric acid, substituted or unsubstituted C8-C 24 aliphatic phosphate, substituted or unsubstituted C6-C 24 aliphatic phosphorous acid, and substituted or unsubstituted C6-C 24 at least one of aliphatic phosphite, wherein the substituent of the substitution is selected from at least one of C1-C6 alkyl, C1-C6 alkoxy and halogen; Optionally, the substituted or unsubstituted C6-C 24 fatty acids include at least one of capric acid, undecylenic acid, myristic acid, oleic acid, linoleic acid, and stearic acid; Optionally, the substituted or unsubstituted C6-C 24 aliphatic thiols include at least one of octanethiol, dodecyl mercaptan, and octadecyl mercaptan; Optionally, the substituted or unsubstituted C6-C 24 The fatty amines include at least one of oleylamine, octadecylamine, octylamine, dioctylamine, and trioctylamine; Optionally, the substituted or unsubstituted C6-C 24 aliphatic phosphines include trioctylphosphine; Optionally, the substituted or unsubstituted C6-C 24 aliphatic oxygen phosphine includes trioctylphosphine oxide.

6. A method for preparing a light-emitting unit, characterized in that, It includes the following steps: Providing inorganic nanoparticles, a first quantum dot, and a solvent, mixing them to obtain a quantum dot solution, where the average particle size of the inorganic nanoparticles is smaller than that of the first quantum dot; and Using the quantum dot solution to prepare a thin film to obtain a light-emitting unit.

7. The preparation method according to claim 6, characterized in that, The average particle size of the first quantum dot is 10 - 25 nm; and / or, the average particle size of the inorganic nanoparticles is 5 - 10 nm; and / or, the mass ratio of the inorganic nanoparticles to the first quantum dot is (0.1 - 0.5):1; and / or, the inorganic nanoparticles include one or more of P-type inorganic nanoparticles and a second quantum dot.

8. The preparation method according to claim 7, characterized in that, The preparation method of the second quantum dot includes: Providing an initial second quantum dot; and Under ultraviolet light illumination conditions, exposing the initial second quantum dot to water and oxygen for a period of time T to obtain the second quantum dot.

9. The preparation method according to claim 8, characterized in that, The wavelength of the ultraviolet light is 365 - 405 nm; and / or, the PLQY of the initial second quantum dot is 50 - 100%; and / or, the PLQY of the first quantum dot is 50 - 100%, and the PLQY of the second quantum dot is greater than 0 and less than or equal to 10%; and / or, the time T is 1 - 48 h.

10. A light-emitting device, characterized in that, The light-emitting unit according to any one of claims 1 to 5 or the light-emitting unit prepared by the preparation method according to any one of claims 6 to 9.

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