Quantum dot light emitting device and preparation method thereof, display substrate and display device

Abstract

The application discloses a quantum dot light-emitting device and a preparation method thereof, a display substrate and a display device, so as to improve the light-emitting efficiency and service life of the quantum dot light-emitting device. The quantum dot light-emitting device provided by an embodiment of the application comprises a substrate, a first electrode, a quantum dot light-emitting functional layer and a second electrode which are arranged in a stack on one side of the substrate; the quantum dot light-emitting functional layer comprises a quantum dot layer and a first transfer layer obtained by ion exchange on a surface of the quantum dot layer close to the second electrode.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of display, in particular to a quantum dot light-emitting device, a preparation method thereof, a display substrate and a display device. BACKGROUND

[0002] Quantum dots have the advantages of narrow emission spectrum, wide adjustable color range, wide color gamut and long fluorescence lifetime, and are expected to become the next generation of mainstream display technology.

[0003] In the prior art, in the preparation process of a quantum dot device, an electron transport layer or a hole transport layer needs to be deposited after forming a quantum dot layer, however, the process of depositing the electron transport layer or the hole transport layer will generate a large number of defects, leading to unbalanced carrier injection, causing quantum dot fluorescence quenching and thus reducing the efficiency and service life of the device. SUMMARY

[0004] Embodiments of the present application provide a quantum dot light-emitting device, a preparation method thereof, a display substrate and a display device, to improve the light-emitting efficiency and service life of the quantum dot light-emitting device.

[0005] The quantum dot light-emitting device provided by an embodiment of the present application comprises: a substrate, a first electrode, a quantum dot light-emitting functional layer and a second electrode which are sequentially arranged on one side of the substrate.

[0006] The quantum dot light-emitting functional layer comprises: a quantum dot layer, and a first transport layer obtained by ion exchange on a surface of the quantum dot layer close to the second electrode.

[0007] In some embodiments, the quantum dot layer comprises core-shell quantum dots.

[0008] The first transport layer is a shell layer obtained by ion exchange on a shell layer of the core-shell quantum dots.

[0009] In some embodiments, the first electrode is an anode, the second electrode is a cathode, and the first transport layer comprises an electron transport layer.

[0010] The electron transport layer comprises: a first shell layer obtained by anion exchange on a shell layer of the core-shell quantum dots.

[0011] In some embodiments, the material of the shell layer of the core-shell quantum dots comprises a zinc compound.

[0012] The material of the first shell layer comprises zinc oxide.

[0013] In some embodiments, the first electrode is a cathode, the second electrode is an anode, and the first transport layer comprises a hole transport layer.

[0014] The hole transport layer comprises: a second shell layer obtained by anion exchange and then cation exchange on a shell layer of the core-shell quantum dots.

[0015] In some embodiments, the material of the shell layer of the shell-core quantum dot comprises a zinc compound.

[0016] The material of the second shell layer comprises nickel oxide or tungsten oxide.

[0017] The embodiment of the present application provides a preparation method of a quantum dot light-emitting device, which comprises the following steps:

[0018] forming a first electrode on one side of a substrate;

[0019] forming a quantum dot layer on the side, away from the substrate, of the first electrode;

[0020] forming a first transport layer by performing an ion exchange process on the surface of the quantum dot layer;

[0021] forming a second electrode layer on the side, away from the quantum dot layer, of the first transport layer.

[0022] In some embodiments, the quantum dot layer is formed on the side, away from the substrate, of the first electrode, and specifically comprises the following steps:

[0023] coating the quantum dot layer comprising shell-core quantum dots on the side, away from the substrate, of the first electrode;

[0024] forming the first transport layer by performing an ion exchange process on the surface of the quantum dot layer, and specifically comprising the following steps:

[0025] coating an ion exchange solution on the surface of the quantum dot layer, and performing annealing treatment, so that the shell layer on the surface of the quantum dot layer, away from the first electrode, undergoes an ion exchange reaction to form the first transport layer;

[0026] coating a cleaning solution on the surface of the first transport layer to remove the remaining products formed by the ion exchange reaction.

[0027] In some embodiments, the first electrode is an anode, and the second electrode is a cathode; the ion exchange solution is coated on the surface of the quantum dot layer, and the first transport layer is formed by performing annealing treatment, and specifically comprising the following steps:

[0028] coating an anion exchange solution on the surface of the quantum dot layer, and performing annealing treatment, so that the shell layer on the surface of the quantum dot layer, away from the first electrode, undergoes an anion exchange reaction to form the electron transport layer.

[0029] In some embodiments, the material of the shell of the shell-core quantum dot comprises a zinc compound; the anion exchange solution is coated on the surface of the quantum dot layer, and the electron transport layer is formed by performing annealing treatment, so that the shell layer on the surface of the quantum dot layer, away from the first electrode, undergoes an anion exchange reaction, and specifically comprising the following steps:

[0030] A first preset concentration of sodium hydroxide solution is spin-coated on the surface of the quantum dot layer, and annealing treatment is performed at a first preset temperature for a first preset duration to form a zinc oxide shell layer as an electron transport layer.

[0031] In some embodiments, the first electrode is a cathode, and the second electrode is an anode; an ion exchange solution is coated on the surface of the quantum dot layer, and annealing treatment is performed to form a first transport layer, specifically including:

[0032] The anion exchange solution is coated on the surface of the quantum dot layer, and annealing treatment is performed to cause an anion exchange reaction of the shell layer on the surface of the side of the quantum dot layer away from the first electrode to form a first shell layer;

[0033] The cleaning solution is coated on the surface of the first shell layer to remove the remaining products formed by the anion exchange reaction;

[0034] The cation exchange solution is coated on the surface of the first shell layer, and annealing treatment is performed to cause a cation exchange reaction of the first shell layer to form a hole transport layer.

[0035] In some embodiments, the material of the shell of the core-shell quantum dot includes a zinc compound; the anion exchange solution is coated on the surface of the quantum dot layer, and annealing treatment is performed to cause an anion exchange reaction of the shell layer on the surface of the side of the quantum dot layer away from the first electrode to form a first shell layer, specifically including:

[0036] A first preset concentration of sodium hydroxide solution is spin-coated on the surface of the quantum dot layer, and annealing treatment is performed at a first preset temperature for a first preset duration to form a zinc oxide shell layer;

[0037] The cleaning solution is coated on the surface of the zinc oxide shell layer to remove the remaining products formed by the ion exchange reaction;

[0038] The cation exchange solution is coated on the surface of the first shell layer, and annealing treatment is performed to cause a cation exchange reaction of the first shell layer to form a hole transport layer, specifically including:

[0039] A second preset concentration of nickel nitrate solution or tungsten nitrate solution is spin-coated on the surface of the zinc oxide shell layer, and annealing treatment is performed at a second preset temperature for a second preset duration to cause a cation exchange reaction of the zinc oxide shell layer to form a nickel oxide shell layer or a tungsten oxide shell layer as a hole transport layer.

[0040] The display substrate provided by the embodiments of the present application includes the quantum dot light emitting device provided by the embodiments of the present application.

[0041] The display device provided by the embodiments of the present application includes the display substrate provided by the embodiments of the present application.

[0042] The quantum dot light-emitting device, the preparation method thereof, the display substrate and the display device provided by the embodiments of the present application can obtain the first transport layer by ion exchange on the surface of the quantum dot layer close to the second electrode, so that the first transport layer can be formed without the deposition process on the surface of the quantum dot layer, and the quenching of quantum dot fluorescence caused by defects of the first transport layer formed by the deposition process on the quantum dot layer can be avoided, thereby improving the efficiency of the quantum dot light-emitting device. Moreover, the ion exchange on the surface of the quantum dot layer is equivalent to in-situ ion exchange on the quantum dot layer, so that the first transport layer formed can be combined closely with the quantum dots, the carrier injection can be promoted, the carrier injection can be balanced, and the efficiency and the service life of the quantum dot light-emitting device can be further improved. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0044] Figure 1 A structure schematic diagram of a quantum dot light-emitting device provided by the embodiments of the present application is shown in the figure.

[0045] Figure 2 A structure schematic diagram of another quantum dot light-emitting device provided by the embodiments of the present application is shown in the figure.

[0046] Figure 3 A structure schematic diagram of another quantum dot light-emitting device provided by the embodiments of the present application is shown in the figure.

[0047] Figure 4 A structure schematic diagram of another quantum dot light-emitting device provided by the embodiments of the present application is shown in the figure.

[0048] Figure 5 A flowchart of a preparation method of a quantum dot light-emitting device provided by the embodiments of the present application is shown in the figure.

[0049] Figure 6 A schematic diagram of a cored-shell quantum dot undergoing anion exchange reaction to form an electron transport layer is shown in the figure.

[0050] Figure 7 A schematic diagram of a cored-shell quantum dot undergoing anion exchange reaction and then cation exchange reaction to form a hole transport layer is shown in the figure. DETAILED DESCRIPTION

[0051] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will be combined with the accompanying drawings for the embodiments of the present application to make a clear and complete description of the technical solutions of the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. And the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. Based on the described embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0052] Unless otherwise defined, technical terms or scientific terms used in the present application shall have the common meaning understood by one of ordinary skill in the art to which the present application pertains. The terms "first", "second", and similar terms used in the present application do not denote any order, quantity, or importance, but are used to distinguish different components. The terms "include", "contain", and similar terms mean that the elements or objects before the terms encompass the elements or objects listed after the terms and their equivalents, without excluding other elements or objects. The terms "connect" or "connected" and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect.

[0053] It should be noted that the sizes and shapes of the figures in the drawings do not reflect the true proportions, but only serve to illustrate the content of the present application. And the same or similar reference numbers represent the same or similar elements or elements with the same or similar functions throughout.

[0054] The embodiments of the present application provide a quantum dot light emitting device, as shown in the following figure. Figure 1 As shown in the figure, the quantum dot light emitting device comprises: a substrate 1, a first electrode 2, a quantum dot light emitting functional layer 3, and a second electrode 4 stacked on one side of the substrate 1.

[0055] The quantum dot light emitting functional layer 3 comprises: a quantum dot layer 5 and a first transport layer 6 obtained by ion exchange on the surface of the quantum dot layer 5 close to the second electrode 4.

[0056] It should be noted that the principle of ion exchange is the substitution of one ion for another ion in the lattice position. It is usually divided into cation exchange and anion exchange. Cation exchange is the exchange of cations in the lattice position by cations, and anion exchange is the exchange of anions in the lattice position by anions. The ion exchange process is a mild and controllable process, and a clear and defect-free exchange interface can be obtained after ion exchange on the surface of the quantum dot layer close to the second electrode.

[0057] The quantum dot light-emitting device provided in this application obtains a first transport layer by performing ion exchange on the surface of the quantum dot layer near the second electrode. This eliminates the need for a deposition process on the surface of the quantum dot layer to form the first transport layer, avoiding the quantum dot fluorescence quenching caused by defects in the first transport layer formed during deposition, thereby improving the efficiency of the quantum dot light-emitting device. Furthermore, performing ion exchange on the surface of the quantum dot layer is equivalent to in-situ ion exchange within the quantum dot layer, ensuring a tight bond between the formed first transport layer and the quantum dots, promoting and balancing carrier injection, and further improving the efficiency and lifetime of the quantum dot light-emitting device.

[0058] In some embodiments, such as Figure 1 As shown, quantum dot layer 5 includes shell-core quantum dots 7; shell-core quantum dots 7 includes: shell layer 8 and core layer 9;

[0059] The first transport layer 6 is a shell obtained by ion exchange of the shell layer 8 of the shell-core quantum dot.

[0060] In some embodiments, the height of the first transport layer in the direction perpendicular to the substrate is greater than or equal to 1 nanometer and less than or equal to 10 nanometers.

[0061] In some embodiments, the shell material of the core-shell quantum dot includes a zinc compound. In specific embodiments, the zinc compound may be, for example, zinc sulfide (ZnS).

[0062] In some embodiments, the core material of the shell-core quantum dot includes one of the following: cadmium sulfide (CdS), (CdSe), indium phosphide (InP), lead sulfide (PbS), cesium lead chloride (CsPbCl3), cesium lead bromide (CsPbBr3), and cesium lead iodide (CsPbI3).

[0063] In some embodiments, such as Figure 2 As shown, the first electrode 2 is the anode 10, the second electrode 4 is the cathode 11, and the first transport layer 6 includes an electron transport layer 12.

[0064] The electron transport layer 12 includes a first shell 13 obtained by anion exchange of the shell 8 of the core-shell quantum dot 7.

[0065] The quantum dot light-emitting device provided in this application obtains an electron transport layer by performing anion exchange on the surface of the quantum dot layer near the second electrode. This eliminates the need to deposit an electron transport layer on the surface of the quantum dot layer, avoiding quantum dot fluorescence quenching caused by defects and thus improving the efficiency of the quantum dot light-emitting device. Furthermore, the in-situ ion exchange on the surface of the quantum dot layer to form the electron transport layer ensures a tight bond between the formed electron transport layer and the quantum dots, promoting and balancing electron injection, further improving the efficiency and lifetime of the quantum dot light-emitting device.

[0066] In some embodiments, when the material of the shell of the core-shell quantum dot includes a zinc compound, the material of the first shell includes zinc oxide (ZnO).

[0067] In practical implementation, taking ZnS as the shell layer of the core-shell quantum dot as an example, it is necessary to exchange the S in ZnS for oxygen (O) through an ion exchange reaction. Sodium hydroxide solution can be used as the ion exchange solution coated on the surface of the core-shell quantum dot layer. The anion exchange reaction equation is: ZnS + 2NaOH → ZnO + Na₂S + H₂O. Since Zn is an active metal, and the bond dissociation energy of ZnS is lower than that of ZnO, ZnO is more stable than ZnS, and the ZnO product can exist stably.

[0068] In some embodiments, when the first electrode is the anode and the second electrode is the cathode, the anode is a transparent electrode, and the material of the transparent electrode includes, for example, indium tin oxide (ITO); the material of the cathode includes, for example, aluminum (Al), magnesium silver alloy (MgAg), etc.

[0069] In some embodiments, when the material of the second electrode includes a magnesium-silver alloy, such as Figure 3 As shown, the quantum dot light-emitting device also includes a capping layer (CPL) 17 on the side of the second electrode 4 facing away from the substrate 1.

[0070] In practical implementation, CPL typically includes a high refractive index material and a capping layer is provided on the side of the second electrode away from the substrate, which can enhance the light extraction efficiency of the second electrode and further improve the efficiency and lifespan of the device.

[0071] In some embodiments, such as Figure 2 , Figure 3 As shown, the quantum dot light-emitting device further includes: a hole injection layer 16 located between the substrate 1 and the anode 10, and a hole transport layer 14 located between the hole injection layer 16 and the anode 10.

[0072] In some embodiments, such as Figure 4 As shown, the first electrode 2 is the cathode 11, the second electrode 4 is the anode 10, and the first transport layer 6 includes a hole transport layer 14.

[0073] The hole transport layer 14 includes a second shell 15 obtained by first performing anion exchange and then cation exchange on the shell 8 of the core-shell quantum dot 7.

[0074] The quantum dot light-emitting device provided by the embodiments of the present application can obtain a hole transport layer by cation exchange on the surface of the quantum dot layer close to the second electrode, so that the hole transport layer does not need to be deposited on the surface of the quantum dot layer, and the quenching of quantum dot fluorescence caused by defects can be avoided, thereby improving the efficiency of the quantum dot light-emitting device. Moreover, the hole transport layer is formed by in-situ ion exchange on the surface of the quantum dot layer, so that the hole transport layer formed can be tightly combined with the quantum dots, the hole injection can be promoted, the hole injection can be balanced, and the efficiency and the service life of the quantum dot light-emitting device are further improved.

[0075] In some embodiments, when the material of the shell layer of the core-shell quantum dot includes a zinc compound, the material of the second shell layer includes nickel oxide (NiO) or tungsten oxide (WO3).

[0076] In specific implementation, taking the shell layer of the core-shell quantum dot as ZnS for example, S in ZnS is exchanged into oxygen (O) to obtain ZnO by anion exchange reaction, and then Zn in ZnO is exchanged into nickel (Ni) or tungsten (W) by cation exchange reaction. In specific implementation, in the anion exchange process, a sodium hydroxide solution can be used as an ion exchange solution to be coated on the surface of the core-shell quantum dot layer, and the anion exchange reaction equation is: ZnS+2NaOH→ZnO+Na2S+H2O. When NiO is needed to be obtained as the hole transport layer, a nickel nitrate (Ni(NO3)2) solution is coated on the surface of the ZnO shell layer after the anion exchange reaction, and the cation exchange reaction equation is: ZnO+2Ni(NO3)2→Zn(NO3)2+NiO. When WO3 is needed to be obtained as the hole transport layer, a tungsten nitrate (Ni(NO3)2) solution is coated on the surface of the ZnO shell layer after the anion exchange reaction, and the cation exchange reaction equation is: 3ZnO+2W(NO3)3→3Zn(NO3)2+2WO3.

[0077] In some embodiments, when the first electrode is a cathode and the second electrode is an anode, the cathode is a transparent electrode, and the material of the transparent electrode includes, for example, indium tin oxide (ITO); and the material of the anode includes, for example, aluminum (Al), magnesium silver alloy (MgAg), etc.

[0078] In some embodiments, when the material of the anode includes magnesium silver alloy, as shown in FIG. 2, the quantum dot light-emitting device can further include a CPL 17 on the side of the second electrode 4 away from the substrate 1. Figure 5

[0079] In specific implementation, the CPL generally includes a high refractive index material, and a capping layer is arranged on the side of the second electrode away from the substrate, so that the light extraction efficiency of the second electrode can be improved, and the efficiency and the service life of the device are further improved.

[0080] In some embodiments, as shown in FIG. 3, the quantum dot light-emitting device can further include a capping layer 18 on the side of the second electrode 4 away from the substrate 1. Figure 4 ,​Figure 5 As shown, the quantum dot light emitting device further comprises an electron transport layer 12 between the cathode 11 and the substrate 1, and a hole injection layer 16 between the hole transport layer 14 and the anode.

[0081] In some embodiments, the substrate is, for example, a transparent substrate. The material of the transparent substrate includes, for example, glass or polyimide, etc.

[0082] In some embodiments, the material of the hole injection layer includes, for example, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT: PSS).

[0083] Based on the same inventive concept, the embodiments of the present application further provide a preparation method of a quantum dot light emitting device, which comprises the following steps: Figure 6 As shown, the preparation method comprises the following steps:

[0084] S101, forming a first electrode on one side of a substrate;

[0085] S102, forming a quantum dot layer on the side of the first electrode away from the substrate;

[0086] S103, performing ion exchange process on the surface of the quantum dot layer to form a first transport layer;

[0087] S104, forming a second electrode layer on the side of the first transport layer away from the quantum dot layer.

[0088] The preparation method of the quantum dot light emitting device provided by the embodiments of the present application performs ion exchange process on the surface of the quantum dot layer to obtain the first transport layer, so that the first transport layer is formed on the surface of the quantum dot layer without deposition process, and the quenching of quantum dot fluorescence caused by defects in the first transport layer formed on the quantum dot layer by deposition process can be avoided, thereby improving the efficiency of the quantum dot light emitting device. Moreover, the ion exchange on the surface of the quantum dot layer is equivalent to in-situ ion exchange on the quantum dot layer, which can ensure that the first transport layer is tightly combined with the quantum dots, promote carrier injection, balance carrier injection, and further improve the efficiency and service life of the quantum dot light emitting device.

[0089] In some embodiments, the step S102 of forming the quantum dot layer on the side of the first electrode away from the substrate specifically comprises:

[0090] coating the quantum dot layer including core-shell quantum dots on the side of the first electrode away from the substrate;

[0091] The step S103 of performing ion exchange process on the surface of the quantum dot layer to form the first transport layer specifically comprises:

[0092] coating an ion exchange solution on the surface of the quantum dot layer, and performing annealing treatment, so that ion exchange reaction occurs on the shell layer on the surface of the side of the quantum dot layer away from the first electrode to form the first transport layer.

[0093] The remaining product formed by the ion exchange reaction is removed by coating a cleaning solution on the surface of the first transport layer.

[0094] It should be noted that, in addition to forming the first transport layer, the ion exchange reaction between the quantum dots and the ion exchange solution also forms other products. The preparation method of the quantum dot light-emitting device provided in the embodiments of the present application removes the remaining products by coating a cleaning solution on the surface of the first transport layer after the ion exchange reaction forms the first transport layer, thereby avoiding the influence of the remaining products of the ion exchange reaction on the carrier transport.

[0095] In some embodiments, before forming the second electrode, the method further includes: performing X-ray diffraction (XRD) characterization on the film layer after the ion exchange reaction is completed. In this way, it can be determined from the XRD characterization result whether the quantum dot shell material and the first transport layer material coexist, and if they do, it indicates that the ion exchange reaction is completed. If the first transport layer material does not exist, the steps of coating the ion exchange solution and performing annealing can be performed again to continue the ion exchange reaction.

[0096] Next, the preparation method of the quantum dot light-emitting device provided in the embodiments of the present application is described by taking the first electrode as the anode and the second electrode as the cathode as an example.

[0097] In some embodiments, the ion exchange solution is coated on the surface of the quantum dot layer, and annealing is performed to form the first transport layer, specifically including:

[0098] The anion exchange solution is coated on the surface of the quantum dot layer, and annealing is performed to cause the shell layer on the surface of the side of the quantum dot layer away from the first electrode to undergo an anion exchange reaction to form an electron transport layer.

[0099] In some embodiments, the material of the shell of the core-shell quantum dot includes a zinc compound, the anion exchange solution is coated on the surface of the quantum dot layer, and annealing is performed to cause the shell layer on the surface of the side of the quantum dot layer away from the first electrode to undergo an anion exchange reaction to form an electron transport layer, specifically including:

[0100] The first pre-set concentration of sodium hydroxide solution is spin-coated on the surface of the quantum dot layer, and annealing is performed at the first pre-set temperature for a first pre-set time length to form a zinc oxide shell layer as the electron transport layer.

[0101] In a specific implementation, a schematic diagram of the anion exchange reaction of the core-shell quantum dot to form the electron transport layer is as shown in Figure 6The ion exchange reaction equation is ZnS+2NaOH→ZnO+Na2S+H2O, for example, the first preset concentration can be 5 mg / mL, the first preset temperature can be 100 degrees Celsius (℃), and the first preset time length can be 10 minutes (min); that is, spin coating a NaOH solution with a concentration of 5 mg / mL on the surface of the quantum dot layer, and then performing 100℃ annealing for 10 min, so as to complete the ion exchange reaction.

[0102] It should be noted that the height of the first transport layer in the direction perpendicular to the substrate is related to the first preset concentration, the first preset temperature, and the first preset time length. In specific implementation, the first preset concentration, the first preset temperature, and the first preset time length can be set according to the actual required height of the first transport layer in the direction perpendicular to the substrate.

[0103] In specific implementation, before forming the second electrode, the film layer after the ion exchange reaction is completed is characterized by XRD; if there are two phases of ZnS and ZnO, it indicates that the ion exchange reaction is completed; if there is no ZnO, the steps of coating sodium hydroxide solution and annealing can be performed again to continue the ion exchange reaction.

[0104] In specific implementation, after forming the zinc oxide shell layer as the electron transport layer, a cleaning solution is coated on the surface of the first transport layer to remove the remaining products formed by the ion exchange reaction, which specifically includes:

[0105] Ethanol is spin-coated on the surface of the first transport layer to remove the remaining products formed by the ion exchange reaction. That is, sodium sulfide (Na2S) generated by the ion exchange reaction is removed by ethanol.

[0106] In some embodiments, before forming the quantum dot layer on the side of the first electrode away from the substrate, the method further includes:

[0107] The hole injection layer and the hole transport layer are spin-coated on the side of the first electrode away from the substrate in sequence. The quantum dot layer is formed on the side of the first electrode away from the substrate, that is, the quantum dot layer is formed on the side of the hole transport layer away from the hole injection layer.

[0108] In some embodiments, the first electrode and the second electrode can be formed by a vapor deposition process.

[0109] In some embodiments, after forming the second electrode layer on the side of the first transport layer away from the quantum dot layer, the method further includes:

[0110] The CPL is formed on the side of the second electrode layer away from the substrate.

[0111] Next, taking the first electrode as the cathode and the second electrode as the anode as an example, the preparation method of the quantum dot light-emitting device provided in the embodiments of the present application is exemplarily described.

[0112] In some embodiments, the surface of the quantum dot layer is coated with an ion exchange solution, and annealing treatment is performed to form the first transport layer, specifically including:

[0113] The surface of the quantum dot layer is coated with an anion exchange solution, and annealing treatment is performed to cause an anion exchange reaction of the shell layer on the surface of the side of the quantum dot layer away from the first electrode to form a first shell layer;

[0114] A cleaning solution is coated on the surface of the first shell layer to remove the remaining products formed by the anion exchange reaction;

[0115] A cation exchange solution is coated on the surface of the first shell layer, and annealing treatment is performed to cause a cation exchange reaction of the first shell layer to form a hole transport layer.

[0116] In specific implementation, a schematic diagram of the core-shell quantum dot first undergoing an anion exchange reaction and then undergoing a cation exchange reaction to form a hole transport layer is shown in Figure 7 .

[0117] In some embodiments, the material of the shell of the core-shell quantum dot includes a zinc compound; the surface of the quantum dot layer is coated with an anion exchange solution, and annealing treatment is performed to cause an anion exchange reaction of the shell layer on the surface of the side of the quantum dot layer away from the first electrode to form a first shell layer, specifically including:

[0118] A first pre-set concentration of sodium hydroxide solution is spin-coated on the surface of the quantum dot layer, and annealing treatment is performed at a first pre-set temperature for a first pre-set duration to form a zinc oxide shell layer;

[0119] A cleaning solution is coated on the surface of the zinc oxide shell layer to remove the remaining products formed by the ion exchange reaction;

[0120] A cation exchange solution is coated on the surface of the first shell layer, and annealing treatment is performed to cause a cation exchange reaction of the first shell layer to form a hole transport layer, specifically including:

[0121] A second pre-set concentration of nickel nitrate solution is spin-coated on the surface of the zinc oxide shell layer, and annealing treatment is performed at a second pre-set temperature for a second pre-set duration to cause a cation exchange reaction of the zinc oxide shell layer to form a nickel oxide shell layer as a hole transport layer.

[0122] In a specific implementation, taking the shell layer of the core-shell quantum dot as an example, the S in the ZnS is exchanged into oxygen (O) to obtain ZnO through an anion exchange reaction, and then the Zn in the ZnO is exchanged into nickel (Ni) through a cation exchange reaction. In a specific implementation, the anion exchange process can be performed by coating a sodium hydroxide solution on the surface of the core-shell quantum dot layer as an ion exchange solution. The anion exchange reaction equation is: ZnS+2NaOH→ZnO+Na2S+H2O. The first preset concentration can be, for example, 5 milligrams per milliliter (mg / mL), the first preset temperature can be, for example, 100 degrees Celsius (℃), and the first preset time length can be, for example, 10 minutes (min); that is, a 5 mg / mL NaOH solution is spin-coated on the surface of the quantum dot layer, and then annealing treatment is performed at 100 ℃ for 10 min, so as to complete the anion exchange reaction and form a first shell layer. After the anion exchange reaction, a nickel nitrate (Ni(NO3)2) solution is coated on the surface of the ZnO shell layer, and the cation exchange reaction equation is: ZnO+2Ni(NO3)2→Zn(NO3)2+NiO; the second preset concentration can be, for example, 5 milligrams per milliliter (mg / mL), the second preset temperature can be, for example, 100 degrees Celsius (℃), and the second preset time length can be, for example, 10 minutes (min); that is, a 5 mg / mL Ni(NO3)2 solution is spin-coated on the surface of the first shell layer, and then annealing treatment is performed at 100 ℃ for 10 min, so as to complete the cation exchange reaction.

[0123] In a specific implementation, the first preset concentration, the first preset temperature, the first preset time length, the second preset concentration, the second preset temperature, and the second preset time length can be set according to the actual height of the first transport layer in the direction perpendicular to the substrate.

[0124] In a specific implementation, before the cation exchange reaction is performed, the film layer after the anion exchange reaction is characterized by XRD; if there are two phases of ZnS and ZnO, it indicates that the ion exchange reaction is completed; if there is no ZnO, the sodium hydroxide solution coating, annealing, and other steps can be performed again to continue the ion exchange reaction. Before the second electrode is formed, the film layer after the cation exchange reaction is characterized by XRD; if there are two phases of ZnS and NiO, it indicates that the ion exchange reaction is completed; if there is no NiO, the Ni(NO3)2 solution coating, annealing, and other steps can be performed again to continue the ion exchange reaction.

[0125] Alternatively, in some embodiments, the material of the shell of the core-shell quantum dot includes a zinc compound; an anion exchange solution is coated on the surface of the quantum dot layer, and annealing treatment is performed to cause the shell layer on the surface of the side of the quantum dot layer away from the first electrode to undergo an anion exchange reaction to form a first shell layer, which specifically includes:

[0126] spin-coat a first pre-set concentration of sodium hydroxide solution on the surface of the quantum dot layer, and perform annealing treatment at a first pre-set temperature for a first pre-set duration to form a zinc oxide shell layer;

[0127] coat a cleaning solution on the surface of the zinc oxide shell layer to remove residual products formed in the ion exchange reaction;

[0128] coat a cation exchange solution on the surface of the first shell layer, and perform annealing treatment to cause the first shell layer to undergo a cation exchange reaction to form a hole transport layer, specifically including:

[0129] spin-coat a second pre-set concentration of tungsten nitrate solution on the surface of the zinc oxide shell layer, and perform annealing treatment at a second pre-set temperature for a second pre-set duration to cause the zinc oxide shell layer to undergo a cation exchange reaction to form a tungsten oxide shell layer as the hole transport layer.

[0130] In specific implementation, taking the shell layer of the core-shell quantum dot as an example, which is ZnS, S in ZnS needs to be exchanged into oxygen (O) to obtain ZnO through an anion exchange reaction, and then Zn in ZnO needs to be exchanged into tungsten (W) through a cation exchange reaction. In specific implementation, the anion exchange process can use sodium hydroxide solution as the ion exchange solution to coat on the surface of the core-shell quantum dot layer, and the anion exchange reaction equation is: ZnS+2NaOH→ZnO+Na2S+H2O. The first pre-set concentration can be, for example, 5 milligrams per milliliter (mg / mL), the first pre-set temperature can be, for example, 100 degrees Celsius (℃), and the first pre-set duration can be, for example, 10 minutes (min); that is, spin-coat 5 mg / mL NaOH solution on the surface of the quantum dot layer, and then perform 100℃ annealing treatment for 10 min to complete the anion exchange reaction and form the first shell layer. After the anion exchange reaction, coat tungsten nitrate (Ni(NO3)2) solution on the surface of the ZnO shell layer, and the cation exchange reaction equation is: 3ZnO+2W(NO3)3→3Zn(NO3)2+2WO3. The second pre-set concentration can be, for example, 5 milligrams per milliliter (mg / mL), the second pre-set temperature can be, for example, 100 degrees Celsius (℃), and the second pre-set duration can be, for example, 10 minutes (min); that is, spin-coat 5 mg / mL W(NO3)3 solution on the surface of the first shell layer, and then perform 100℃ annealing treatment for 10 min to complete the cation exchange reaction.

[0131] In specific implementation, the first pre-set concentration, the first pre-set temperature, the first pre-set duration, the second pre-set concentration, the second pre-set temperature, and the second pre-set duration can be set according to the actual need of the first transport layer in the height direction perpendicular to the substrate.

[0132] In a specific implementation, before the cation exchange reaction is performed, the film layer after the anion exchange reaction is completed is characterized by XRD; if both ZnS and ZnO phases exist, it indicates that the ion exchange reaction is completed; if ZnO does not exist, the ion exchange reaction can be continued by performing the steps of coating with a sodium hydroxide solution, annealing, etc. again. Before the second electrode is formed, the film layer after the cation exchange reaction is completed is characterized by XRD; if both ZnS and WO3 phases exist, it indicates that the ion exchange reaction is completed; if WO3 does not exist, the ion exchange reaction can be continued by performing the steps of coating with a W(NO3) solution, annealing, etc. again.

[0133] In a specific implementation, after the zinc oxide shell layer is formed, a cleaning solution is coated on the surface of the zinc oxide shell layer to remove the remaining products formed in the ion exchange reaction, specifically including: ethanol is spin-coated on the surface of the zinc oxide shell layer to remove the remaining products formed in the ion exchange reaction. That is, sodium sulfide (Na2S) generated in the ion exchange reaction is removed by ethanol. After the NiO or WO3 is formed, a cleaning solution is coated on the surface of the hole transport layer to remove the remaining products formed in the ion exchange reaction, specifically including: ethanol is spin-coated on the surface of the hole transport layer to remove the remaining products formed in the ion exchange reaction. That is, zinc nitrate (Zn(NO3)2) generated in the ion exchange reaction is removed by ethanol.

[0134] In some embodiments, before the quantum dot layer is formed on the side of the first electrode away from the substrate, the method further includes:

[0135] The electron transport layer is spin-coated on the side of the first electrode away from the substrate. The quantum dot layer is formed on the side of the first electrode away from the substrate, that is, the quantum dot layer is formed on the side of the electron transport layer away from the first electrode.

[0136] In some embodiments, the first electrode and the second electrode can be formed by a vapor deposition process.

[0137] In some embodiments, after the second electrode layer is formed on the side of the first transport layer away from the quantum dot layer, the method further includes:

[0138] The CPL is formed on the side of the second electrode layer away from the substrate.

[0139] Based on the same inventive concept, the embodiments of the present application also provide a display substrate including a plurality of quantum dot light emitting devices provided by the embodiments of the present application.

[0140] In some embodiments, the display substrate further includes: a substrate substrate, a pixel driving circuit layer located above the substrate substrate, and a planarization layer located on the side of the driving circuit layer away from the substrate substrate. In a specific implementation, the planarization layer is multiplexed as a substrate of the quantum dot light emitting device.

[0141] In some embodiments, the display substrate comprises a plurality of sub-pixels arranged in an array; each sub-pixel comprises at least one quantum dot light emitting device; the pixel driving circuit layer comprises, for example, a pixel driving unit corresponding to each sub-pixel, and the pixel driving unit comprises, for example, a plurality of thin film transistors and a storage capacitor; the first electrode of the quantum dot light emitting device is electrically connected to the source or drain of the thin film transistor in the pixel driving unit.

[0142] In specific implementation, the plurality of quantum dot light emitting devices comprises, for example, a red quantum dot light emitting device, a blue quantum dot light emitting device, and a green quantum dot light emitting device.

[0143] Alternatively, in some embodiments, the display substrate comprising a plurality of quantum dot light emitting devices is used as a light emitting substrate of a display product backlight module. In specific implementation, the plurality of quantum dot light emitting devices comprises, for example, a red quantum dot light emitting device, a blue quantum dot light emitting device, and a green quantum dot light emitting device.

[0144] Based on the same inventive concept, the embodiments of the present application also provide a display device comprising the display substrate provided by the embodiments of the present application.

[0145] In specific implementation, when the display substrate is used as a light emitting substrate, the display device further comprises a liquid crystal display panel located on the light emitting side of the display substrate.

[0146] The display device provided by the embodiments of the present application is any product or component with display function, such as a mobile phone, a tablet computer, a television, a display, a notebook computer, a digital photo frame, a navigator, etc. Other essential components of the display device should be understood by those skilled in the art and are not described herein in detail, nor should they be considered as limitations on the present application. The implementation of the display device can refer to the embodiments of the display substrate and the quantum dot light emitting device described above, and repeated descriptions are omitted.

[0147] In summary, the quantum dot light emitting device and the preparation method thereof, the display substrate, and the display device provided by the embodiments of the present application can obtain the first transport layer by ion exchange on the surface of the quantum dot layer close to the second electrode, thereby avoiding the quenching of quantum dot fluorescence caused by defects in the deposition process of the first transport layer on the quantum dot layer, and improving the efficiency of the quantum dot light emitting device. Moreover, the ion exchange on the surface of the quantum dot layer is equivalent to in-situ ion exchange of the quantum dot layer, which can ensure that the first transport layer is tightly combined with the quantum dots, promote carrier injection, balance carrier injection, and further improve the efficiency and lifetime of the quantum dot light emitting device.

[0148] While the preferred embodiments of the application have been described, additional variations and modifications can be made to these embodiments by those skilled in the art once they have the benefit of the present disclosure without departing from the spirit and scope of the application. Accordingly, it is intended that the appended claims include all such modifications and variations as fall within the scope of the present application.

[0149] It is apparent that many modifications and variations of this application can be effected although only a few have been chosen for purposes of disclosure. Thus, it is intended that this application include all such modifications and variations as fall within the scope of the claims and their equivalents.

Claims

1. A quantum dot light emitting device, comprising: The quantum dot light-emitting device comprises: a substrate, a first electrode, a quantum dot light-emitting functional layer, and a second electrode which are sequentially arranged on one side of the substrate; The quantum dot light-emitting functional layer comprises: a quantum dot layer, and a first transport layer obtained by ion exchange on a surface of the quantum dot layer close to the second electrode; The quantum dot layer comprising core-shell quantum dots is coated on a side of the first electrode away from the substrate; an ion exchange solution is coated on a surface of the quantum dot layer, and annealing treatment is performed to cause ion exchange reaction of the shell layer on the surface of the quantum dot layer away from the first electrode to form the first transport layer; and a cleaning solution is coated on the surface of the first transport layer to remove the remaining products formed by the ion exchange reaction.

2. The quantum dot light emitting device of claim 1, wherein, The first electrode is an anode, the second electrode is a cathode, and the first transport layer comprises an electron transport layer; The electron transport layer comprises a first shell layer obtained by anion exchange on the shell layer of the core-shell quantum dots.

3. The quantum dot light emitting device of claim 2, wherein, The material of the shell layer of the core-shell quantum dots comprises a zinc compound; The material of the first shell layer comprises zinc oxide.

4. The quantum dot light emitting device of claim 1, wherein, The first electrode is a cathode, the second electrode is an anode, and the first transport layer comprises a hole transport layer; The hole transport layer comprises a second shell layer obtained by anion exchange and then cation exchange on the shell layer of the core-shell quantum dots.

5. The quantum dot light emitting device of claim 4, wherein the first and second quantum dots are configured to emit light having a peak wavelength of 450 nm or less. The material of the shell layer of the core-shell quantum dots comprises a zinc compound; The material of the second shell layer comprises nickel oxide or tungsten oxide.

6. A method of fabricating a quantum dot light emitting device, comprising: The method comprises: forming a first electrode on one side of a substrate; coating a quantum dot layer comprising core-shell quantum dots on a side of the first electrode away from the substrate; coating an ion exchange solution on a surface of the quantum dot layer, and performing annealing treatment to cause ion exchange reaction of the shell layer on the surface of the quantum dot layer away from the first electrode to form a first transport layer; and coating a cleaning solution on the surface of the first transport layer to remove the remaining products formed by the ion exchange reaction; forming a second electrode layer on a side of the first transport layer away from the quantum dot layer.

7. The method of claim 6, wherein, The first electrode is an anode, the second electrode is a cathode; coating an ion exchange solution on a surface of the quantum dot layer, and performing annealing treatment to form the first transport layer, specifically comprising: coating an anion exchange solution on a surface of the quantum dot layer, and performing annealing treatment to cause anion exchange reaction of the shell layer on the surface of the quantum dot layer away from the first electrode to form an electron transport layer.

8. The method of claim 7, wherein, The material of the shell of the core-shell quantum dots comprises a zinc compound; coating an anion exchange solution on a surface of the quantum dot layer, and performing annealing treatment to cause anion exchange reaction of the shell layer on the surface of the quantum dot layer away from the first electrode to form an electron transport layer, specifically comprising: spin coating a first predetermined concentration of sodium hydroxide solution on a surface of the quantum dot layer, and performing annealing treatment at a first predetermined temperature for a first predetermined time length to form a zinc oxide shell layer as an electron transport layer.

9. The method of claim 6, wherein, The first electrode is a cathode, the second electrode is an anode; coating an ion exchange solution on a surface of the quantum dot layer, and performing annealing treatment to form the first transport layer, specifically comprising: coating an anion exchange solution on the surface of the quantum dot layer, and performing annealing treatment, so that an anion exchange reaction occurs on the shell layer of the surface of the quantum dot layer away from the first electrode side to form a first shell layer; coating a cleaning solution on the surface of the first shell layer to remove the remaining products formed by the anion exchange reaction; coating a cation exchange solution on the surface of the first shell layer, and performing annealing treatment, so that a cation exchange reaction occurs on the first shell layer to form a hole transport layer.

10. The method of claim 9, wherein, The material of the shell of the core-shell quantum dot includes a zinc compound; coating an anion exchange solution on the surface of the quantum dot layer, and performing annealing treatment, so that an anion exchange reaction occurs on the shell layer of the surface of the quantum dot layer away from the first electrode side to form a first shell layer, specifically including: spinning a first pre-set concentration of sodium hydroxide solution on the surface of the quantum dot layer, and performing annealing treatment at a first pre-set temperature for a first pre-set time length to form a zinc oxide shell layer; coating a cleaning solution on the surface of the zinc oxide shell layer to remove the remaining products formed by the ion exchange reaction; coating a cation exchange solution on the surface of the first shell layer, and performing annealing treatment, so that a cation exchange reaction occurs on the first shell layer to form a hole transport layer, specifically including: spinning a second pre-set concentration of nickel nitrate solution or tungsten nitrate solution on the surface of the zinc oxide shell layer, and performing annealing treatment at a second pre-set temperature for a second pre-set time length, so that a cation exchange reaction occurs on the zinc oxide shell layer to form a nickel oxide shell layer or a tungsten oxide shell layer as a hole transport layer.

11. A display substrate, comprising: The display substrate includes a plurality of quantum dot light emitting devices according to any one of claims 1-5.

12. A display device, characterized by comprising: The display substrate includes a plurality of display substrates according to claim 11.

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