Quantum dot light emitting diode and preparation method thereof

Abstract

The application discloses a quantum dot light emitting diode and a preparation method thereof. The quantum dot light emitting diode comprises a quantum dot light emitting layer arranged between a cathode and an anode, and a hole transport layer arranged between the anode and the quantum dot light emitting layer. An interface layer is arranged between the hole transport layer and the quantum dot light emitting layer. The interface layer is made of a lithium lanthanum titanium oxide compound. The structural general formula of the lithium lanthanum titanium oxide compound is Li 3x La 2 / 3‑x TiO3, wherein 0

Description

TECHNICAL FIELD

[0001] The present application relates to the field of quantum dots, in particular to a quantum dot light emitting diode and a preparation method thereof. BACKGROUND

[0002] Quantum dot light emitting diode (QLED) has high color purity, narrow half-peak width, high light emitting efficiency, adjustable light emitting color and good device stability, etc., which makes it have wide application prospects in the fields of flat panel display, solid state lighting, etc. With the continuous development of research and development, the external quantum efficiency (EQE) of quantum dot light emitting diode has been significantly improved, among which the external quantum efficiency of red quantum dot light emitting diode and green quantum dot light emitting diode is higher than 25%, which is comparable to organic light emitting diode (OLED) in efficiency, but the external quantum efficiency and lifetime of blue quantum dot light emitting diode are still insufficient to meet the requirements.

[0003] Similar to OLED devices, the structure of QLED devices is usually composed of anode, hole injection layer, hole transport layer, quantum dot light emitting layer, electron transport layer and cathode, and electrons and holes are injected from the cathode and anode respectively, and recombine and emit light in the quantum dot light emitting layer. The existing electron transport layer is usually composed of nano-zinc oxide particles, which has a high carrier concentration and mobility; the organic polymer materials used in the hole transport layer, such as PVK, TFB, etc., due to the low carrier mobility of the hole transport layer and the deep energy level of the quantum dots, which leads to the difficulty of hole injection, so that the holes are accumulated in the hole transport layer or the interface layer between the hole transport layer and the quantum dot light emitting layer for a long time, and the excessive injection of electrons leads to the transition of electrons to the hole transport layer or the interface layer between the hole transport layer and the quantum dot light emitting layer, which eventually leads to the recombination of electrons and holes in the non-light emitting layer, which seriously affects the efficiency and lifetime of QLED devices.

[0004] Therefore, the prior art still needs to be improved. SUMMARY

[0005] In view of the deficiencies of the prior art described above, the purpose of the present application is to provide a quantum dot light emitting diode and a preparation method thereof, which aims to solve the problem of low light emitting efficiency of the existing quantum dot light emitting diode.

[0006] The technical scheme of the present application is as follows:

[0007] A quantum dot light emitting diode, comprising a cathode, an anode, a quantum dot light emitting layer arranged between the cathode and the anode, and a hole transport layer arranged between the anode and the quantum dot light emitting layer, wherein an interface layer is arranged between the hole transport layer and the quantum dot light emitting layer, the material of the interface layer is lithium lanthanum titanium oxide compound, and the general structure of the lithium lanthanum titanium oxide compound is Li 3x La 2 / 3-xTiO3, wherein 0 < x < 0.16; the HOMO energy level of the interface layer is greater than the HOMO energy level of the hole transport layer and less than the HOMO energy level of the quantum dot light emitting layer.

[0008] A preparation method of a quantum dot light emitting diode, comprising the steps of:

[0009] Providing an anode substrate, and a hole transport layer is prepared on the anode substrate;

[0010] An interface layer is prepared on the hole transport layer, and the material of the interface layer is a lithium lanthanum titanium oxide compound, and the general structure of the lithium lanthanum titanium oxide compound is Li 3x La 2 / 3-x TiO3, wherein 0 < x < 0.16;

[0011] A quantum dot light emitting layer is prepared on the interface layer;

[0012] A cathode is prepared on the quantum dot light emitting layer, and the quantum dot light emitting diode is prepared;

[0013] Alternatively, a cathode substrate is provided, and a quantum dot light emitting layer is prepared on the cathode substrate;

[0014] An interface layer is prepared on the surface of the quantum dot light emitting layer, and the material of the interface layer is a lithium lanthanum titanium oxide compound, and the general structure of the lithium lanthanum titanium oxide compound is Li 3x La 2 / 3-x TiO3, wherein 0 < x < 0.16;

[0015] A hole transport layer is prepared on the interface layer;

[0016] An anode is prepared on the hole transport layer, and the quantum dot light emitting diode is prepared.

[0017] Beneficial effects: the interface layer is arranged between the hole transport layer and the quantum dot light emitting layer, the HOMO energy level of the interface layer is located between the HOMO energy levels of the hole transport layer and the quantum dot light emitting layer, the injection barrier of holes can be effectively reduced, the material and the device degradation caused by the accumulation of holes at the barrier interface can be reduced, the interface layer can effectively block the electron tunneling, the recombination of electrons and holes in the non-quantum dot light emitting layer can be avoided, and the light emitting efficiency of the quantum dot light emitting diode is improved. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a structure schematic diagram of a preferred embodiment of a quantum dot light emitting diode with a positive structure of the application.

[0019] Figure 2 It is a structure schematic diagram of a preferred embodiment of a quantum dot light emitting diode with a reverse structure of the application.

[0020] Figure 3 This is a flowchart of a preferred embodiment of a method for preparing a normal-structure quantum dot light-emitting diode according to the present invention.

[0021] Figure 4 This is a flowchart of a preferred embodiment of a method for preparing an inverted-structure quantum dot light-emitting diode according to the present invention. Detailed implementation manners

[0022] The present invention provides a quantum dot light-emitting diode and a method for preparing the same. To make the objectives, technical solutions and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] The quantum dot light-emitting diode has various forms, and the quantum dot light-emitting diode is divided into a normal structure and an inverted structure. The inverted-structure quantum dot light-emitting diode may include a substrate, a cathode, a quantum dot light-emitting layer, a hole transport layer, and an anode stacked from bottom to top. In the specific implementation manners of the present invention, the normal-structure quantum dot light-emitting diode as shown in Figure 1 will be mainly introduced as an embodiment. Specifically, the normal-structure quantum dot light-emitting diode includes an anode disposed on the surface of a substrate, a hole transport layer disposed on the surface of the anode, an interface layer disposed on the surface of the hole transport layer, a quantum dot light-emitting layer disposed on the interface layer, and a cathode disposed on the surface of the quantum dot light-emitting layer. Among them, the material of the interface layer is lithium lanthanum titanium oxide, and the structural general formula of the lithium lanthanum titanium oxide is Li 3x La 2 / 3-x TiO3, where 0 < x < 0.16, and the HOMO energy level of the interface layer is greater than the HOMO energy level of the hole transport layer and less than the HOMO energy level of the quantum dot light-emitting layer.

[0024] Specifically, because there is a large potential barrier between the highest occupied molecular orbital (HOMO) of the commonly used hole transport layer and the work function of the quantum dot light emitting layer, it is difficult for holes to be injected from the hole transport layer to the quantum dot light emitting layer, leading to an imbalance between the injection of holes and electrons, which seriously affects the light emitting efficiency of the quantum dot light emitting diode. The embodiment sets an interface layer made of a lithium lanthanum titanium oxide compound between the hole transport layer and the quantum dot light emitting layer, the HOMO energy level of the interface layer is greater than the HOMO energy level of the hole transport layer and less than the HOMO energy level of the quantum dot light emitting layer, the interface layer can effectively reduce the injection potential barrier of holes, thereby reducing the material and device degradation caused by the accumulation of holes at the potential barrier interface, and effectively improving the light emitting efficiency and service life of the quantum dot light emitting diode. The size of the HOMO energy level in the embodiment refers to the absolute value of the HOMO energy level. That is, the absolute value of the HOMO energy level of the interface layer in the embodiment is greater than the absolute value of the HOMO energy level of the hole transport layer and less than the absolute value of the HOMO energy level of the quantum dot light emitting layer.

[0025] Further, because the energy level potential barrier between the electron transport material and the quantum dot light emitting layer is usually small, electron injection occurs easily, which leads to some electrons easily tunneling to the hole transport layer or the interface between the hole transport layer and the quantum dot light emitting layer, and recombining with holes in the non-quantum dot light emitting layer region, thereby affecting the overall light emitting efficiency of the quantum dot light emitting diode. The embodiment sets an interface layer composed of a lithium lanthanum titanium oxide compound between the hole transport layer and the quantum dot light emitting layer, the general structure of the lithium lanthanum titanium oxide compound is Li 3x La 2 / 3-x TiO3, where 0 < x < 0.16, the lithium lanthanum titanium oxide compound has the properties of being able to conduct ions and holes, but not electrons, and the hole conductivity of the lithium lanthanum titanium oxide compound is as high as 10 -2 S / cm, which is 5 orders of magnitude greater than its electron conductivity, so the lithium lanthanum titanium oxide compound not only effectively helps hole injection, but also effectively prevents electron tunneling to the hole transport layer, avoiding the device emitting light in the non-light emitting region, thereby improving the overall light emitting efficiency of the quantum dot light emitting diode.

[0026] Further, because the material used in the hole transport layer of the quantum dot light emitting diode is usually an organic material, such as PEDOT (polythiophene), etc., such materials are sensitive to water and oxygen, and the gradual penetration of water and oxygen from the encapsulating glue will affect the stability of hole injection and transport, the embodiment sets an interface layer composed of a lithium lanthanum titanium oxide compound between the hole transport layer and the quantum dot light emitting layer, which can further effectively block the penetration of water and oxygen, thereby improving the service life of the device.

[0027] In some embodiments, the interface layer has a thickness of 10-200 nm. Within this range, the interface layer can both increase the hole injection rate and block the electron tunneling. If the thickness of the interface layer is less than 10 nm, the interface layer has a poor effect of blocking the electron tunneling to the hole transport layer. If the thickness of the interface layer is greater than 200 nm, the hole injection distance is increased, which affects the efficiency of the hole transport to the quantum dot light-emitting layer.

[0028] In some embodiments, the HOMO energy level of the interface layer is 4.9-6.0 eV. In this embodiment, the HOMO energy level of the hole transport layer is generally 4.9-5.4 eV, and the HOMO energy level of the quantum dot light-emitting layer is generally 5.9-6.5 eV. In this case, the HOMO energy level of the interface layer is between the HOMO energy levels of the hole transport layer and the quantum dot light-emitting layer. Therefore, the hole injection barrier can be effectively reduced, the hole injection rate can be promoted, the material and device degradation caused by the accumulation of holes at the barrier interface can be reduced, and the light-emitting efficiency and service life of the quantum dot light-emitting diode can be effectively improved. As an example, when TFB (HOMO energy level of 5.4 eV) is used as the hole transport layer material and Cds-ZnSe quantum dots (HOMO energy level of 5.9-6.1 eV) are used as the quantum dot light-emitting layer material, the HOMO energy level of the interface layer can be 5.4-6 eV.

[0029] In some specific embodiments, the interface layer material is Li 0.33 La 0.56 TiO3. In this embodiment, the HOMO energy level of the Li 0.33 La 0.56 TiO3 is between the HOMO energy levels of the hole transport layer and the quantum dot light-emitting layer. Therefore, the interface layer can effectively reduce the hole injection barrier, promote the hole injection rate, reduce the material and device degradation caused by the accumulation of holes at the barrier interface, and effectively improve the light-emitting efficiency and service life of the quantum dot light-emitting diode.

[0030] In some embodiments, the hole transport layer material is selected from one or more of poly(9,9-dioctylfluorene-CO-N-(4-butylphenyl)diphenylamine) (TFB), polyvinylcarbazole (PVK), poly(N,N'bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine) (Poly-TPD), poly(9,9-dioctylfluorene-co-bis-N,N-phenyl-1,4-phenylenediamine) (PFB), 4,4',4"-tris(carbazol-9-yl)triphenylamine (TCTA), 4,4'-bis(9-carbazolyl) biphenyl (CBP), N,N'-diphenyl-N,N'-di(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD), N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (NPB), but not limited thereto.

[0031] In some embodiments, the quantum dot light emitting layer is selected from one or more of binary phase quantum dots, ternary phase quantum dots, and quaternary phase quantum dots, but not limited thereto. As an example, the binary phase quantum dots are at least one of CdS, CdSe, CdTe, InP, AgS, PbS, PbSe, HgS; and / or, the ternary phase quantum dots are at least one of Zn X Cd 1-X S, Cu X In 1- X S, Zn X Cd 1-X Se, Zn X Se 1-X S, Zn X Cd 1-X Te, PbSe X S 1-X at least one of Zn X Cd 1-X S / ZnSe, Cu X In 1-X S / ZnS, Zn X Cd 1-X Se / ZnS, CuInSeS, Zn X Cd 1-X Te / ZnS, PbSe X S 1-X at least one of Zn

[0032] In some embodiments, an electron functional layer is disposed between the quantum dot light emitting layer and the cathode, the electron functional layer including a hole blocking layer, an electron injection layer, and an electron transport layer, but not limited thereto.

[0033] In some embodiments, the electron transport layer material is selected from one or more of ZnO, TiO, NiO, W2O3, Mo2O3, TiO2, SnO, ZrO2, and Ta2O3, but not limited thereto.

[0034] In some embodiments, a hole injection layer is further provided between the anode and the hole transport layer.

[0035] In some embodiments, the hole injection layer is one or more of PEDOT:PSS, WO3, MoO3, and V2O5, but not limited thereto.

[0036] In some embodiments, the thickness of the hole injection layer is 30-120 nm.

[0037] In some embodiments, the cathode can be Au, Ag, Al, Cu, Mo, or alloys thereof, but not limited thereto.

[0038] In some embodiments, the thickness of the anode is 5-120 nm.

[0039] In some embodiments, the thickness of the hole transport layer is 30-120 nm.

[0040] In some embodiments, the thickness of the quantum dot light emitting layer is 10-200 nm.

[0041] In some embodiments, the thickness of the electron transport layer is 5-100 nm; and the thickness of the cathode is 5-120 nm.

[0042] In some embodiments, the anode is one or more of ITO, FTO, ATO, AZO, GZO, IZO, MZO, AMO, but not limited thereto.

[0043] In some embodiments, the present application further provides a quantum dot light emitting diode with an inverted structure, as shown in FIG. 1. Figure 2 As shown in FIG. 1, the quantum dot light emitting diode with the inverted structure includes a cathode provided on a surface of a substrate, a quantum dot light emitting layer provided on a surface of the cathode, an interface layer provided on a surface of the quantum dot light emitting layer, a hole transport layer provided on a surface of the interface layer, and an anode provided on a surface of the hole transport layer, wherein the interface layer material is a lithium lanthanum titanium oxide compound, the structure general formula of the lithium lanthanum titanium oxide compound is Li 3x La 2 / 3-x TiO3, wherein 0 < x < 0.16; the HOMO energy level of the interface layer is greater than the HOMO energy level of the hole transport layer and less than the HOMO energy level of the quantum dot light emitting layer.

[0044] The embodiment sets an interface layer made of lithium lanthanum titanium oxide between the hole transport layer and the quantum dot light-emitting layer, the HOMO energy level of the interface layer is greater than the HOMO energy level of the hole transport layer and less than the HOMO energy level of the quantum dot light-emitting layer, the interface layer can effectively reduce the injection barrier of holes, thereby reducing the material and device degradation caused by the accumulation of holes at the barrier interface, thereby effectively improving the light-emitting efficiency and service life of the quantum dot light-emitting diode. The interface layer material is lithium lanthanum titanium oxide, the general structure of the lithium lanthanum titanium oxide is Li 3x La 2 / 3-x TiO3, wherein 0 < x < 0.16; the lithium lanthanum titanium oxide has the properties of ion and hole conduction but not electron conduction, therefore, the lithium lanthanum titanium oxide can not only effectively help the hole injection, but also effectively prevent the electron tunneling to the hole transport layer, avoiding the device emitting light in the non-light-emitting area, thereby improving the overall light-emitting efficiency of the quantum dot light-emitting diode.

[0045] In some embodiments, a preparation method of a quantum dot light-emitting diode with the positive structure as shown in Figure 1 is also provided, which comprises the steps of: Figure 3

[0046] S10, providing an anode substrate, a hole transport layer is prepared on the anode substrate;

[0047] S20, preparing an interface layer on the hole transport layer, the interface layer material is lithium lanthanum titanium oxide, the general structure of the lithium lanthanum titanium oxide is Li 3x La 2 / 3-x TiO3, wherein 0 < x < 0.16;

[0048] S30, preparing a quantum dot light-emitting layer on the interface layer;

[0049] S40, preparing a cathode on the quantum dot light-emitting layer, thereby obtaining the quantum dot light-emitting diode.

[0050] In the embodiment, the preparation method of each layer can be a chemical method or a physical method, wherein the chemical method includes but is not limited to one or more of chemical vapor deposition, successive ion layer adsorption and reaction, anodic oxidation, electrolytic deposition, and coprecipitation; the physical method includes but is not limited to physical coating or solution method, wherein the solution method includes but is not limited to spin coating, printing, blade coating, dip-coating, immersion, spraying, roll coating, casting, slot coating, and strip coating; the physical coating method includes but is not limited to one or more of thermal evaporation coating, electron beam evaporation coating, magnetron sputtering, multi-arc ion coating, physical vapor deposition, atomic layer deposition, and pulsed laser deposition.

[0051] ​In some specific embodiments, the interface layer is prepared on the hole transport layer by a spin coating method, which specifically comprises the following steps: dispersing the lithium lanthanum titanium oxide compound in an organic solvent to prepare a lithium lanthanum titanium oxide compound solution; spin coating the lithium lanthanum titanium oxide compound solution on the surface of the hole transport layer, and annealing at 100°C for 30 minutes to prepare the interface layer. In the present embodiment, the organic solvent includes ethanol, methanol, butanol, acetone, isopropyl ketone, butyronitrile, chlorobenzene, toluene, dimethylbenzene, dimethylformamide, dimethyl sulfoxide, N-methyl pyrrolidone, ethyl acetate, and the like, but is not limited thereto. In the present embodiment, the concentration of the lithium lanthanum titanium oxide compound solution is 1-2 wt%, and within the concentration range, the prepared interface layer can not only reduce the interface impedance, but also effectively improve the light emitting performance of the quantum dot light emitting diode.

[0052] In some embodiments, a preparation method of a quantum dot light emitting diode with an inverted structure is also provided, which comprises the following steps: Figure 2 As shown in the preparation method of the QLED with an inverted structure as shown in Figure 4 As shown in the preparation method of the QLED with an inverted structure as shown in

[0053] S100, providing a cathode substrate, and preparing a quantum dot light emitting layer on the cathode substrate;

[0054] S200, preparing an interface layer on the surface of the quantum dot light emitting layer, wherein the interface layer material is a lithium lanthanum titanium oxide compound, and the general structure of the lithium lanthanum titanium oxide compound is Li 3x La 2 / 3-x TiO3, wherein 0 < x < 0.16;

[0055] S300, preparing a hole transport layer on the interface layer;

[0056] S400, preparing an anode on the hole transport layer to obtain the quantum dot light emitting diode.

[0057] In an embodiment of the present application, the cathode substrate comprises a substrate, a bottom electrode provided on the substrate, and the bottom electrode is a cathode. In another embodiment of the present application, the cathode substrate can comprise a substrate, a bottom electrode provided on the surface of the substrate, and an electron injection layer provided on the surface of the substrate. In another embodiment of the present application, the cathode substrate can comprise a substrate, a bottom electrode provided on the surface of the substrate, an electron injection layer provided on the surface of the substrate, and an electron transport layer provided on the surface of the electron injection layer. In another embodiment of the present application, the anode substrate can comprise a substrate, a bottom electrode provided on the surface of the substrate, an electron injection layer provided on the surface of the substrate, an electron transport layer provided on the surface of the electron injection layer, and a hole blocking layer provided on the surface of the electron transport layer.

[0058] The preparation method of each layer can be a chemical method or a physical method, wherein the chemical method includes but is not limited to one or more of a chemical vapor deposition method, a sequential ion layer adsorption and reaction method, an anodic oxidation method, an electrolytic deposition method, and a coprecipitation method; the physical method includes but is not limited to a physical coating method or a solution method, wherein the solution method includes but is not limited to a spin coating method, a printing method, a blade coating method, a dip-coating method, an immersion method, a spray coating method, a roll coating method, a casting method, a slot coating method, and a bar coating method; the physical coating method includes but is not limited to one or more of a thermal evaporation coating method, an electron beam evaporation coating method, a magnetron sputtering method, a multi-arc ion coating method, a physical vapor deposition method, an atomic layer deposition method, and a pulsed laser deposition method.

[0059] The preparation method of the quantum dot light-emitting diode and the quantum dot light-emitting diode are further explained and described below through specific embodiments:

[0060] Embodiment 1

[0061] A preparation method of a quantum dot light-emitting diode with a bottom-emitting structure includes the following steps:

[0062] Step S1: Depositing a hole injection layer on a transparent anode substrate, the transparent anode is ITO, the hole injection layer material is WO3, the thickness of the transparent anode is 20 nm, and the thickness of the hole injection layer is 60 nm;

[0063] Step S2: Depositing a hole transport layer on the hole injection layer, the hole transport layer material is PFB, and the thickness of the hole transport layer is 60 nm;

[0064] Step S3: Depositing an interface layer on the hole transport layer, the interface layer material is Li 0.33 La 0.56 TiO3, and the thickness of the interface layer is 100 nm;

[0065] Step S4: Depositing a quantum dot light-emitting layer on the interface layer, the quantum dot light-emitting layer material is PbSe, and the thickness of the quantum dot light-emitting layer is 50 nm;

[0066] Step S5: Depositing an electron transport layer on the quantum dot light-emitting layer, the electron transport layer material is TiO, and the thickness of the electron transport layer is 60 nm;

[0067] Step S6: Depositing a metal cathode on the electron transport layer, the cathode material is Ag, the thickness of the cathode is 100 nm, and the cathode has a visible light reflection of not less than 98%.

[0068] Embodiment 2

[0069] A preparation method of a quantum dot light-emitting diode with a top-emitting structure includes the following steps:

[0070] Step S1: depositing a hole injection layer on a transparent anode substrate, the transparent anode being FTO, the hole injection layer material being WO3, the thickness of the transparent anode being 20 nm, the thickness of the hole injection layer being 60 nm;

[0071] Step S2: depositing a hole transport layer on the hole injection layer, the hole transport layer material being TCTA, the thickness of the hole transport layer being 60 nm;

[0072] Step S3: depositing an interface layer on the hole transport layer, the interface layer material being Li 0.33 La 0.56 TiO3, the thickness of the interface layer being 100 nm;

[0073] Step S4: depositing a quantum dot light-emitting layer on the interface layer, the quantum dot light-emitting layer material being InP, the thickness of the quantum dot light-emitting layer being 50 nm;

[0074] Step S5: depositing an electron transport layer on the quantum dot light-emitting layer, the electron transport layer material being NiO, the thickness of the electron transport layer being 60 nm;

[0075] Step S6: depositing a cathode on the electron transport layer, the cathode material being Ag, the thickness of the cathode being 100 nm, the transmission of the cathode to visible light being not less than 90%.

[0076] Embodiment 3

[0077] A preparation method of a quantum dot light-emitting diode with an inverted bottom emission structure, comprising the following steps:

[0078] Step S1: depositing an Ag layer on a substrate by evaporation, the thickness of the Ag layer being 5 nm;

[0079] Step S2: depositing an electron transport layer on the Ag layer, the electron transport layer material being SnO, the thickness of the electron transport layer being 50 nm;

[0080] Step S3: depositing a quantum dot light-emitting layer on the electron transport layer, the quantum dot light-emitting layer material being CdSe, the thickness of the quantum dot light-emitting layer being 50 nm;

[0081] Step S4: depositing an interface layer on the quantum dot light-emitting layer, the interface layer material being Li 0.33 La 0.56 TiO3, the thickness of the interface layer being 80 nm;

[0082] Step S5: depositing a hole transport layer on the interface layer, the hole transport layer material being PVK

[0083] The thickness of the hole transport layer is 80 nm.

[0084] Step S6: depositing a hole injection layer on the hole transport layer, the material of the hole injection layer is PEDOT:PSS, and the thickness of the hole injection layer is 60 nm.

[0085] Step S7: depositing an anode on the hole injection layer, the material of the anode is ITO, the thickness of the anode is 120 nm, and the anode has a visible light reflection of not less than 98%.

[0086] Example 4

[0087] A preparation method of a quantum dot light emitting diode with an inverted top emission structure includes the following steps:

[0088] Step S1: depositing an Ag layer on a substrate by evaporation, and the thickness of the Ag layer is 5 nm.

[0089] Step S2: depositing an electron transport layer on the Ag layer, the material of the electron transport layer is TiO, and the thickness of the electron transport layer is 60 nm.

[0090] Step S3: depositing a quantum dot light emitting layer on the electron transport layer, the material of the quantum dot light emitting layer is CdTe, and the thickness of the quantum dot light emitting layer is 50 nm.

[0091] Step S4: depositing an interface layer on the quantum dot light emitting layer, the material of the interface layer is Li 0.33 La 0.56 TiO3, and the thickness of the interface layer is 80 nm.

[0092] Step S5: depositing a hole transport layer on the interface layer, the material of the hole transport layer is PFB, and the thickness of the hole transport layer is 80 nm.

[0093] Step S6: depositing a hole injection layer on the hole transport layer, the material of the hole injection layer is MoO3, and the thickness of the hole injection layer is 60 nm.

[0094] Step S7: depositing an anode on the hole injection layer, the material of the anode is ITO, the thickness of the anode is 120 nm, and the anode has a visible light transmission of not less than 90%.

[0095] Comparative Example 1

[0096] A preparation method of a quantum dot light emitting diode with a normal bottom emission structure includes the following steps:

[0097] Step S1 : Depositing a hole injection layer on a transparent anode substrate, the transparent anode is ITO, the hole injection layer material is WO3, the thickness of the transparent anode is 20 nm, and the thickness of the hole injection layer is 60 nm;

[0098] Step S2: Depositing a hole transport layer on the hole injection layer, the hole transport layer material is PFB, the thickness of the hole transport layer is 60 nm;

[0099] Step S3: Depositing a quantum dot light-emitting layer on the hole transport layer, the quantum dot light-emitting layer material is PbSe, the thickness of the quantum dot light-emitting layer is 50 nm;

[0100] Step S4: Depositing an electron transport layer on the quantum dot light-emitting layer, the electron transport layer material is TiO, the thickness of the electron transport layer is 60 nm;

[0101] Step S5: Depositing a metal cathode on the electron transport layer, the cathode material is Ag, the thickness of the cathode is 100 nm, and the cathode has a visible light reflection of not less than 98%.

[0102] Comparative Example 2

[0103] A preparation method of a quantum dot light-emitting diode with an upside-down top emission structure, comprising the following steps:

[0104] Step S1 : Depositing a hole injection layer on a transparent anode substrate, the transparent anode is FTO, the hole injection layer material is WO3, the thickness of the transparent anode is 20 nm, and the thickness of the hole injection layer is 60 nm;

[0105] Step S2: Depositing a hole transport layer on the hole injection layer, the hole transport layer material is TCTA, the thickness of the hole transport layer is 60 nm;

[0106] Step S3: Depositing a quantum dot light-emitting layer on the hole transport layer, the quantum dot light-emitting layer material is InP, the thickness of the quantum dot light-emitting layer is 50 nm;

[0107] Step S4: Depositing an electron transport layer on the quantum dot light-emitting layer, the electron transport layer material is NiO, the thickness of the electron transport layer is 60 nm;

[0108] Step S5: Depositing a cathode on the electron transport layer, the cathode material is Ag, the thickness of the cathode is 100 nm, and the cathode has a visible light transmission of not less than 90%.

[0109] Comparative Example 3

[0110] A preparation method of a quantum dot light-emitting diode with an upside-down bottom emission structure, comprising the following steps:

[0111] Step S1: depositing an Ag layer on the substrate by evaporation, the thickness of the Ag layer being 5 nm;

[0112] Step S2: depositing an electron transport layer on the Ag layer, the electron transport layer material being SnO, the thickness of the electron transport layer being 50 nm;

[0113] Step S3: depositing a quantum dot light-emitting layer on the electron transport layer, the quantum dot light-emitting layer material being CdSe, the thickness of the quantum dot light-emitting layer being 50 nm;

[0114] Step S4: depositing a hole transport layer on the quantum dot light-emitting layer, the hole transport layer material being PVK, the thickness of the hole transport layer being 80 nm;

[0115] Step S5: depositing a hole injection layer on the hole transport layer, the hole injection layer material being PEDOT:PSS, the thickness of the hole injection layer being 60 nm;

[0116] Step S6: depositing an anode on the hole injection layer, the anode material being ITO, the thickness of the anode being 120 nm; the anode reflecting no less than 98% of visible light.

[0117] Comparative Example 4

[0118] A preparation method of a quantum dot light-emitting diode of an inverted top-emitting structure, comprising the following steps:

[0119] Step S1: depositing an Ag layer on the substrate by evaporation, the thickness of the Ag layer being 5 nm;

[0120] Step S2: depositing an electron transport layer on the Ag layer, the electron transport layer material being TiO, the thickness of the electron transport layer being 60 nm;

[0121] Step S3: depositing a quantum dot light-emitting layer on the electron transport layer, the quantum dot light-emitting layer material being CdTe, the thickness of the quantum dot light-emitting layer being 50 nm;

[0122] Step S4: depositing a hole transport layer on the quantum dot light-emitting layer, the hole transport layer material being PFB, the thickness of the hole transport layer being 80 nm;

[0123] Step S5: depositing a hole injection layer on the hole transport layer, the hole injection layer material being MoO3, the thickness of the hole injection layer being 60 nm;

[0124] Step S6: depositing an anode on the hole injection layer, the anode material is ITO, the thickness of the anode is 120 nm; the transmittance of the anode to visible light is not less than 90%.

[0125] The performance of the quantum dot light emitting diodes prepared in Examples 1-4 and Comparative Examples 1-4 is tested, and the results are shown in Table 1:

[0126] Table 1: Performance test results of quantum dot light emitting diodes

[0127] External Quantum Efficiency - EQE (%) LT95 (h) Example 1 9.3 5.6 Example 2 15.1 4.4 Example 3 8.9 6.3 Example 4 16.5 5.2 Comparative Example 1 7.9 5.4 Comparative Example 2 14.6 3.9 Comparative Example 3 8.3 5.9 Comparative Example 4 15.8 4.1

[0128] Comparing the data in Table 1, the difference between Example 1 and Comparative Example 1 is only that an interface layer formed by Li 0.33 La 0.56 TiO3 material is added between the hole transport layer and the quantum dot light emitting layer, and the external quantum efficiency is increased from 7.9% to 9.3%, and the service life is increased from 5.4h to 5.6h; the difference between Example 2 and Comparative Example 2 is only that an interface layer formed by Li 0.33 La 0.56 TiO3 material is added between the hole transport layer and the quantum dot light emitting layer, and the external quantum efficiency is increased from 14.6% to 15.1%, and the service life is increased from 3.9h to 4.4h; the difference between Example 3 and Comparative Example 3 is only that an interface layer formed by Li 0.33 La 0.56 TiO3 material is added between the hole transport layer and the quantum dot light emitting layer, and the external quantum efficiency is increased from 8.3% to 8.9%, and the service life is increased from 5.9h to 6.3h; the difference between Example 4 and Comparative Example 4 is only that an interface layer formed by Li 0.33 La 0.56 TiO3 material is added between the hole transport layer and the quantum dot light emitting layer, and the external quantum efficiency is increased from 15.8% to 16.5%, and the service life is increased from 4.1h to 5.2h. From the above data, it can be found that by setting an interface layer between the hole transport layer and the quantum dot light emitting layer, the external quantum efficiency and the service life of the quantum dot light emitting diode can be effectively improved.

[0129] In summary, the quantum dot light emitting diode device is optimized by adding an interface layer between the hole transport layer and the quantum dot light emitting layer to reduce the hole injection barrier, improve the hole injection, avoid the accumulation of holes at the interface, and effectively reduce the recombination of electrons in the non-quantum dot light emitting region which have tunneled to the hole transport layer, thereby improving the device efficiency and service life. The interface layer can also effectively block the influence of water and oxygen on the organic hole injection and transport layer, thereby improving the stability of the device.

[0130] It is to be understood that the application is not limited to the examples described above, which can be modified or adapted in several ways by those skilled in the art without departing from the scope of the present application, as defined by the appended claims.

Claims

1. A quantum dot light emitting diode comprising a cathode, an anode, a quantum dot light emitting layer disposed between the cathode and the anode, and a hole transport layer disposed between the anode and the quantum dot light emitting layer, characterized in that, An interface layer is arranged between the hole transport layer and the quantum dot light-emitting layer, the interface layer material is a lithium lanthanum titanium oxide compound, a general structure of the lithium lanthanum titanium oxide compound is Li 3x La 2 / 3-x TiO3, wherein 0 < x < 0.16; a HOMO energy level of the interface layer is greater than a HOMO energy level of the hole transport layer and less than a HOMO energy level of the quantum dot light-emitting layer.

2. The quantum dot light emitting diode of claim 1, wherein, The interface layer has a thickness of 10-200 nm.

3. The quantum dot light emitting diode of claim 1, wherein the quantum dot light emitting diode is a quantum dot light emitting diode on silicon. The HOMO energy level of the interface layer is 4.9-6.0 eV.

4. The quantum dot light emitting diode of claim 1, wherein, The interface layer material is Li 0.33 La 0.56 TiO3.

5. The quantum dot light emitting diode of any one of claims 1-3, wherein, The hole transport layer material is selected from one or more of TFB, PVK, Poly-TPD, PFB, TCTA, CBP, TPD and NPB.

6. The quantum dot light emitting diode of any one of claims 1-3, wherein, The quantum dot light emitting layer material is selected from one or more of binary phase quantum dots, ternary phase quantum dots and quaternary phase quantum dots.

7. The quantum dot light emitting diode of claim 6, wherein the quantum dot layer is disposed on the first electrode layer. CdS, CdSe, CdTe, InP, AgS, PbS, PbSe, HgS; and / or, the ternary quantum dot is Zn X Cd 1-X S, Cu X In 1-X S, Zn X Cd 1-X Se, Zn X Se 1-X S, Zn X Cd 1-X Te, PbSe X S 1-X at least one of Zn X Cd 1-X S / ZnSe, Cu X In 1-X S / ZnS, Zn X Cd 1-X Se / ZnS, CuInSeS, Zn X Cd 1-X Te / ZnS, PbSe X S 1-X at least one of Zn wherein 0 < X < 1.

8. The quantum dot light emitting diode of claim 1, wherein, An electron functional layer is arranged between the quantum dot light emitting layer and the cathode; and / or, a hole injection layer is arranged between the anode and the hole transport layer.

9. A method of fabricating a quantum dot light emitting diode, the method comprising: forming a quantum dot light emitting diode on a substrate; and forming a quantum dot light emitting diode on the substrate. The method comprises the steps of: providing an anode substrate, on which a hole transport layer is prepared; An interface layer is prepared on the hole transport layer, the interface layer material is lithium lanthanum titanium oxide, the general structure of the lithium lanthanum titanium oxide is Li 3x La 2 / 3-x TiO3, wherein 0 < x < 0.16; preparing a quantum dot light emitting layer on the interface layer; preparing a cathode on the quantum dot light emitting layer to obtain the quantum dot light emitting diode; Alternatively, a cathode substrate is provided, on which a quantum dot light emitting layer is prepared; An interface layer is prepared on the surface of the quantum dot light-emitting layer, the interface layer material is a lithium lanthanum titanium oxide compound, the general structure of the lithium lanthanum titanium oxide compound is Li 3x La 2 / 3-x TiO3, wherein 0 < x < 0.

16. preparing a hole transport layer on the interface layer; preparing an anode on the hole transport layer to obtain the quantum dot light emitting diode; The HOMO energy level of the interface layer is greater than the HOMO energy level of the hole transport layer and less than the HOMO energy level of the quantum dot light emitting layer.

10. The method for fabricating a quantum dot light-emitting diode according to claim 9, characterized in that, The step of preparing the interface layer on the hole transport layer comprises: dispersing the lithium lanthanum titanium oxide compound in an organic solvent to obtain a lithium lanthanum titanium oxide compound solution; spin coating the lithium lanthanum titanium oxide compound solution on the surface of the hole transport layer to obtain the interface layer; Alternatively, the step of preparing the interface layer on the surface of the quantum dot light emitting layer comprises: dispersing the lithium lanthanum titanium oxide compound in an organic solvent to obtain a lithium lanthanum titanium oxide compound solution; spin coating the lithium lanthanum titanium oxide compound solution on the surface of the quantum dot light emitting layer to obtain the interface layer.

11. The method for fabricating a quantum dot light-emitting diode according to claim 10, characterized in that, The concentration of the lithium lanthanum titanium oxide compound solution is 1-2 wt%.

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