Quantum dot light-emitting diode and preparation method thereof

Abstract

The present invention 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 provided between the hole transport layer and the quantum dot light-emitting layer. The interface layer material is a sulfide. The general structural formula of the sulfide is Li x B y S z , where B is one or more of P, Si, Ge, and Sn; 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. In the present invention, the interface layer can effectively reduce the hole injection barrier, increase the hole injection rate, and effectively prevent electron tunneling and recombination with holes in the non-quantum dot light-emitting area, thereby improving the luminous efficiency of the device.

Description

Technical Field

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

[0002] Quantum dot light-emitting diodes (QLEDs) boast excellent characteristics such as high color purity, a narrow half-peak width, high luminous efficiency, tunable luminescent color, and stable devices, making them promising for broad application in fields such as flat-panel displays and solid-state lighting. With the continuous advancement of research and development, the external quantum efficiency (EQE) of quantum dot LEDs has significantly improved. The external quantum efficiency of red and green quantum dot LEDs is above 25%, making them comparable to organic light-emitting diodes (OLEDs) in terms of efficiency. However, the external quantum efficiency and lifespan of blue quantum dot LEDs still do not meet the requirements.

[0003] Similar to OLED devices, the QLED device structure typically consists of an anode, a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer, and a cathode. Electrons and holes are injected from the cathode and anode, respectively, and recombine in the quantum dot light-emitting layer to emit light. The existing electron transport layer is typically composed of nano-zinc oxide particles, which have a high carrier concentration and mobility. The organic polymer materials used in the hole transport layer, such as PVK and TFB, have difficulty injecting holes due to the low carrier mobility of the hole transport layer and the deep energy levels of the quantum dots. This causes holes to accumulate in the hole transport layer or at the interface between the hole transport layer and the quantum dot light-emitting layer for a long time. Excessive electron injection makes it easy for them to jump to the hole transport layer or its interface with the quantum dot light-emitting layer, ultimately leading to electron and hole recombination in the non-light-emitting layer, seriously affecting the efficiency and lifespan of the QLED device.

[0004] Therefore, the prior art needs to be improved. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a quantum dot light emitting diode and a preparation method thereof, aiming to solve the problem of low luminous efficiency of existing quantum dot light emitting diodes.

[0006] The technical solutions of the present invention are as follows:

[0007] A quantum dot light-emitting diode comprises 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, wherein an interface layer is disposed between the hole transport layer and the quantum dot light-emitting layer, the interface layer material being a sulfide having a general structural formula of Li x B y S z, wherein B is one or more of P, Si, Ge and Sn; 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 method for preparing a quantum dot light-emitting diode, comprising the steps of:

[0009] providing an anode substrate, and a hole transport layer on the anode substrate;

[0010] An interface layer is prepared on the hole transport layer, wherein the interface layer material is sulfide, and the general structural formula of the sulfide is Li x B y S z , wherein B is one or more of P, Si, Ge and Sn;

[0011] preparing a quantum dot light-emitting layer on the interface layer;

[0012] preparing a cathode on the quantum dot light-emitting layer to obtain the quantum dot light-emitting diode;

[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. The interface layer material is sulfide. The general structural formula of the sulfide is Li x B y S z , wherein B is one or more of P, Si, Ge and Sn;

[0015] preparing a hole transport layer on the interface layer;

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

[0017] Beneficial effects: The present invention provides an interface layer between the hole transport layer and the quantum dot light-emitting layer. Since 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, it can effectively reduce the hole injection barrier, thereby reducing the material and device degradation caused by the accumulation of holes at the barrier interface; the interface layer can also effectively block electron tunneling, avoiding the recombination of electrons and holes in the non-quantum dot light-emitting layer, thereby improving the luminous efficiency of the quantum dot light-emitting diode. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a structural schematic diagram of a preferred embodiment of a positive-type quantum dot light-emitting diode of the present invention.

[0019] Figure 2This is a structural schematic diagram of a preferred embodiment of an inversion structure quantum dot light emitting diode of the present invention.

[0020] Figure 3 The present invention is a flow chart of a preferred embodiment of a method for preparing a positive-type quantum dot light-emitting diode.

[0021] Figure 4 The present invention is a flowchart of a preferred embodiment of a method for preparing an inversion structure quantum dot light-emitting diode. DETAILED DESCRIPTION

[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 more clear and explicit, the present invention is further described below in detail. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0023] There are many forms of quantum dot light emitting diodes, and the quantum dot light emitting diodes are divided into regular structures and inverted structures. The inverted structure quantum dot light emitting diodes 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 embodiment of the present invention, the following will be mainly used: Figure 1 The positive-type quantum dot light-emitting diode shown in the figure is introduced as an example. Specifically, the positive-type quantum dot light-emitting diode includes an anode arranged on the surface of a substrate, a hole transport layer arranged on the surface of the anode, an interface layer arranged on the surface of the hole transport layer, a quantum dot light-emitting layer arranged on the interface layer, and a cathode arranged on the surface of the quantum dot light-emitting layer, wherein the interface layer material is a sulfide, and the general structural formula of the sulfide is Li x B y S z , wherein B is one or more of P, Si, Ge and Sn, 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, due to the large potential barrier between the highest occupied energy level (HOMO) of the commonly used hole transport layer and the work function of the quantum dot light-emitting layer, it becomes difficult for holes to be injected from the hole transport layer into the quantum dot light-emitting layer, resulting in an imbalance in the injection of holes and electrons, which seriously affects the luminous efficiency of the quantum dot light-emitting diode. In this embodiment, an interface layer made of sulfide is provided 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 hole injection barrier, thereby reducing the material and device degradation caused by the accumulation of holes at the barrier interface, thereby effectively improving the luminous efficiency and service life of the quantum dot light-emitting diode. The HOMO energy level in this 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 this 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] Furthermore, since the energy barrier between the electron transport material and the quantum dot light-emitting layer is usually small, electron injection is more likely to occur, which causes some electrons to easily tunnel to the hole transport layer or the interface between the hole transport layer and the quantum dot light-emitting layer, and recombine with holes in the non-quantum dot light-emitting layer area, thereby affecting the overall luminous efficiency of the quantum dot light-emitting diode. In this embodiment, an interface layer composed of sulfide is provided between the hole transport layer and the quantum dot light-emitting layer. The interface layer material is sulfide, and the general structural formula of the sulfide is Li x B y S z , wherein B is one or more of P, Si, Ge and Sn. The sulfide has the property of conducting ions and holes but not electrons. Therefore, the sulfide can not only effectively assist hole injection, but also effectively prevent electrons from tunneling to the hole transport layer, avoiding the device from emitting light in the non-luminescent area, thereby improving the overall luminous efficiency of the quantum dot light-emitting diode.

[0026] Furthermore, since the material used for the hole transport layer of the quantum dot light-emitting diode is usually an organic material, such as PEDOT (polythiophene), which is sensitive to water and oxygen, the gradual penetration of water and oxygen from the encapsulation glue will affect the stability of hole injection and transport. In this embodiment, an interface layer composed of sulfide is provided between the hole transport layer and the quantum dot light-emitting layer to further effectively block the penetration of water and oxygen, thereby improving the service life of the device.

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

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

[0029] In some specific embodiments, the interface layer material is Li3PS4. In this embodiment, the HOMO energy level of the Li3PS4 is between the HOMO energy levels of the hole transport layer and the quantum dot light-emitting layer. Therefore, the interface layer can effectively lower the hole injection barrier and promote the hole injection rate, thereby reducing the material and device degradation caused by hole accumulation at the barrier interface, thereby effectively improving the luminous 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-carbazol)biphenyl (CBP), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD), and N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (NPB), but is 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 is not limited thereto. For example, the binary phase quantum dots are at least one of CdS, CdSe, CdTe, InP, AgS, PbS, PbSe, and HgS; and / or the ternary phase quantum dots are 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; and / or, the quaternary phase quantum dots are 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 / ZnS, wherein 0 <X<1。

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

[0033] In some embodiments, a hole injection layer is further provided between the anode and the hole transport layer.

[0034] In some embodiments, the hole injection layer is one or more of PEDOT:PSS, WO3, MoO3 and V2O5, but is not limited thereto.

[0035] In some embodiments, the hole injection layer has a thickness of 30-120 nm.

[0036] In some embodiments, the cathode may be Au, Ag, Al, Cu, Mo, or alloys thereof, but is not limited thereto.

[0037] In some embodiments, the thickness of the anode is 5-120 nm.

[0038] In some embodiments, the hole transport layer has a thickness of 30-120 nm.

[0039] In some embodiments, the thickness of the quantum dot light-emitting layer is 10-200 nm.

[0040] In some embodiments, the thickness of the electron transport layer is 5-100 nm; the thickness of the cathode is 5-120 nm.

[0041] In some embodiments, the anode is one or more of ITO, FTO, ATO, AZO, GZO, IZO, MZO, and AMO, but is not limited thereto.

[0042] In some embodiments, the present invention also provides a quantum dot light emitting diode with an inversion structure, such as Figure 2 As shown, the inversion structure quantum dot light-emitting diode includes a cathode arranged on the surface of the substrate, a quantum dot light-emitting layer arranged on the surface of the cathode, an interface layer arranged on the surface of the quantum dot light-emitting layer, a hole transport layer arranged on the surface of the interface layer, and an anode arranged on the surface of the hole transport layer, wherein the interface layer material is sulfide, and the general structural formula of the sulfide is Li x B y S z , wherein B is one or more of P, Si, Ge and Sn, 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.

[0043] In this embodiment, an interface layer made of sulfide is provided 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 hole injection barrier, thereby reducing the material and device degradation caused by the accumulation of holes at the barrier interface, thereby effectively improving the luminous efficiency and service life of the quantum dot light-emitting diode. The interface layer material is sulfide, and the general structural formula of the sulfide is Li x B y S z , wherein B is one or more of P, Si, Ge and Sn, and the sulfide has the property of conducting ions and holes but not electrons, and the hole and ion conductivity of the sulfide at room temperature is close to 10 -2 S / cm, and its electronic conductivity is more than 4-5 orders of magnitude lower than the ion / hole conductivity. Therefore, the sulfide can not only effectively assist hole injection, but also effectively prevent electron tunneling to the hole transport layer, avoiding the device from emitting light in the non-luminescent area, thereby improving the overall luminous efficiency of the quantum dot light-emitting diode.

[0044] In some embodiments, there is also provided a Figure 1 The preparation method of the quantum dot light emitting diode of the positive structure shown in FIG. Figure 3 As shown, it includes the steps of:

[0045] S10, providing an anode substrate, and a hole transport layer on the anode substrate;

[0046] S20, preparing an interface layer on the hole transport layer, wherein the interface layer material is sulfide, and the general structural formula of the sulfide is Li x B y S z , wherein B is one or more of P, Si, Ge and Sn;

[0047] S30, preparing a quantum dot light-emitting layer on the interface layer;

[0048] S40, preparing a cathode on the quantum dot light-emitting layer to obtain the quantum dot light-emitting diode.

[0049] In this embodiment, the preparation methods of the above-mentioned layers can be chemical methods or physical methods, wherein the chemical method includes but is not limited to one or more of chemical vapor deposition, continuous ion layer adsorption and reaction, anodization, electrolytic deposition, and co-precipitation; the physical method includes but is not limited to physical plating or solution method, wherein the solution method includes but is not limited to spin coating, printing, scraping, dip pulling, immersion, spraying, roll coating, casting, slit coating, and strip coating; the physical plating method includes but is not limited to one or more of thermal evaporation coating, electron beam evaporation coating, magnetron sputtering, multi-arc ion plating, physical vapor deposition, atomic layer deposition, and pulsed laser deposition.

[0050] In some specific embodiments, a spin coating method is used to prepare an interface layer on the hole transport layer, which specifically includes the steps of: dispersing the sulfide in an organic solvent to prepare a sulfide solution; spin coating the sulfide solution on the surface of the hole transport layer, and thermally annealing at 100°C for 30 minutes to prepare the interface layer. In this embodiment, the organic solvent includes ethanol, methanol, butanol, acetone, isopropyl ketone, butyronitrile, chlorobenzene, toluene, xylene, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, and ethyl acetate, but is not limited thereto. In this embodiment, the concentration of the sulfide solution is 1-2 wt%. Within this concentration range, the prepared interface layer can both reduce the interfacial impedance and effectively improve the luminescence performance of the quantum dot light-emitting diode.

[0051] In some embodiments, a method for preparing a quantum dot light-emitting diode with an inverted structure is also provided, which comprises the following steps: Figure 2The preparation method of the inverted structure QLED shown in FIG. Figure 4 As shown, it includes the following steps:

[0052] S100, providing a cathode substrate, and preparing a quantum dot light-emitting layer on the cathode substrate;

[0053] S200, preparing an interface layer on the surface of the quantum dot light-emitting layer, wherein the interface layer material is sulfide, and the general structural formula of the sulfide is Li x B y S z , wherein B is one or more of P, Si, Ge and Sn;

[0054] S300, preparing a hole transport layer on the interface layer;

[0055] S400, preparing an anode on the hole transport layer to obtain the quantum dot light emitting diode.

[0056] In one embodiment of the present invention, the cathode substrate includes a substrate and a bottom electrode arranged on the substrate, and the bottom electrode is a cathode; in another embodiment of the present invention, the cathode substrate may include a substrate, a bottom electrode stacked on the surface of the substrate, and an electron injection layer stacked on the surface of the substrate; in another embodiment of the present invention, the cathode substrate may include a substrate, a bottom electrode stacked on the surface of the substrate, an electron injection layer stacked on the surface of the substrate, and an electron transport layer stacked on the surface of the electron injection layer; in another embodiment of the present invention, the anode substrate may include a substrate, a bottom electrode stacked on the surface of the substrate, an electron injection layer stacked on the surface of the substrate, an electron transport layer stacked on the surface of the electron injection layer, and a hole blocking layer stacked on the surface of the electron transport layer.

[0057] The preparation methods of the above-mentioned layers can be chemical or physical methods, among which the chemical method includes but is not limited to one or more of chemical vapor deposition, continuous ion layer adsorption and reaction, anodization, electrolytic deposition, and co-precipitation; the physical method includes but is not limited to physical plating or solution method, among which the solution method includes but is not limited to spin coating, printing, doctor blade coating, dip pulling, immersion, spraying, roll coating, casting, slit coating, and strip coating; the physical plating method includes but is not limited to one or more of thermal evaporation coating, electron beam evaporation coating, magnetron sputtering, multi-arc ion plating, physical vapor deposition, atomic layer deposition, and pulsed laser deposition.

[0058] The following is a further explanation of a quantum dot light-emitting diode and a preparation method thereof according to the present invention through specific embodiments:

[0059] Example 1

[0060] A method for preparing a quantum dot light-emitting diode with an upright bottom-emitting structure comprises the following steps:

[0061] Step S1: depositing a hole injection layer on a transparent anode substrate, wherein 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;

[0062] Step S2: depositing a hole transport layer on the hole injection layer, wherein the hole transport layer material is PFB and the thickness of the hole transport layer is 60 nm;

[0063] Step S3: depositing an interface layer on the hole transport layer, wherein the interface layer material is Li3PS4 and the thickness of the interface layer is 100 nm;

[0064] Step S4: depositing a quantum dot light-emitting layer on the interface layer, wherein the material of the quantum dot light-emitting layer is PbSe and the thickness of the quantum dot light-emitting layer is 50 nm;

[0065] Step S5: depositing an electron transport layer on the quantum dot light-emitting layer, wherein the electron transport layer material is TiO and the thickness of the electron transport layer is 60 nm;

[0066] Step S6: depositing a metal cathode on the electron transport layer, wherein the cathode material is Ag, the thickness of the cathode is 100 nm, and the cathode reflects no less than 98% of visible light.

[0067] Example 2

[0068] A method for preparing a quantum dot light-emitting diode with a top-emitting structure comprises the following steps:

[0069] Step S1: depositing a hole injection layer on a transparent anode substrate, wherein 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;

[0070] Step S2: depositing a hole transport layer on the hole injection layer, wherein the hole transport layer material is TCTA and the thickness of the hole transport layer is 60 nm;

[0071] Step S3: depositing an interface layer on the hole transport layer, wherein the interface layer material is Li3PS4 and the thickness of the interface layer is 100 nm;

[0072] Step S4: depositing a quantum dot light-emitting layer on the interface layer, wherein the material of the quantum dot light-emitting layer is InP and the thickness of the quantum dot light-emitting layer is 50 nm;

[0073] Step S5: depositing an electron transport layer on the quantum dot light-emitting layer, wherein the electron transport layer material is NiO and the thickness of the electron transport layer is 60 nm;

[0074] Step S6: depositing a cathode on the electron transport layer, wherein the cathode material is Ag, the thickness of the cathode is 100 nm, and the transmittance of the cathode to visible light is not less than 90%.

[0075] Example 3

[0076] A method for preparing a quantum dot light-emitting diode with an inverted bottom emission structure comprises the following steps:

[0077] Step S1: depositing a Ag layer on the substrate by evaporation, wherein the thickness of the Ag layer is 5 nm;

[0078] Step S2: depositing an electron transport layer on the Ag layer, wherein the electron transport layer material is SnO and the thickness of the electron transport layer is 50 nm;

[0079] Step S3: depositing a quantum dot light-emitting layer on the electron transport layer, wherein the material of the quantum dot light-emitting layer is CdSe and the thickness of the quantum dot light-emitting layer is 50 nm;

[0080] Step S4: depositing an interface layer on the quantum dot light-emitting layer, wherein the material of the interface layer is Li3PS4 and the thickness of the interface layer is 80 nm;

[0081] Step S5: depositing a hole transport layer on the interface layer, wherein the hole transport layer material is PVK and the thickness of the hole transport layer is 80 nm;

[0082] Step S6: depositing a hole injection layer on the hole transport layer, wherein the hole injection layer material is PEDOT:PSS and the thickness of the hole injection layer is 60 nm;

[0083] Step S7: depositing an anode on the hole injection layer, wherein the anode material is ITO and the thickness of the anode is 120 nm; and the anode reflects no less than 98% of visible light.

[0084] Example 4

[0085] A method for preparing a quantum dot light-emitting diode with an inverted top-emitting structure comprises the following steps:

[0086] Step S1: depositing a Ag layer on the substrate by evaporation, wherein the thickness of the Ag layer is 5 nm;

[0087] Step S2: depositing an electron transport layer on the Ag layer, wherein the electron transport layer material is TiO and the thickness of the electron transport layer is 60 nm;

[0088] Step S3: depositing a quantum dot light-emitting layer on the electron transport layer, wherein the material of the quantum dot light-emitting layer is CdTe, and the thickness of the quantum dot light-emitting layer is 50 nm;

[0089] Step S4: depositing an interface layer on the quantum dot light-emitting layer, wherein the material of the interface layer is Li3PS4 and the thickness of the interface layer is 80 nm;

[0090] Step S5: depositing a hole transport layer on the interface layer, wherein the hole transport layer material is PFB and the thickness of the hole transport layer is 80 nm;

[0091] Step S6: depositing a hole injection layer on the hole transport layer, wherein the hole injection layer material is MoO3 and the thickness of the hole injection layer is 60 nm;

[0092] Step S7: depositing an anode on the hole injection layer, wherein the anode material is ITO, the thickness of the anode is 120 nm, and the visible light transmittance of the anode is not less than 90%.

[0093] Comparative Example 1

[0094] A method for preparing a quantum dot light-emitting diode with an upright bottom-emitting structure comprises the following steps:

[0095] Step S1: depositing a hole injection layer on a transparent anode substrate, wherein 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;

[0096] Step S2: depositing a hole transport layer on the hole injection layer, wherein the hole transport layer material is PFB and the thickness of the hole transport layer is 60 nm;

[0097] Step S3: depositing a quantum dot light-emitting layer on the hole transport layer, wherein the material of the quantum dot light-emitting layer is PbSe and the thickness of the quantum dot light-emitting layer is 50 nm;

[0098] Step S4: depositing an electron transport layer on the quantum dot light-emitting layer, wherein the electron transport layer material is TiO and the thickness of the electron transport layer is 60 nm;

[0099] Step S5: depositing a metal cathode on the electron transport layer, wherein the cathode material is Ag, the thickness of the cathode is 100 nm, and the cathode reflects no less than 98% of visible light.

[0100] Comparative Example 2

[0101] A method for preparing a quantum dot light-emitting diode with a top-emitting structure comprises the following steps:

[0102] Step S1: depositing a hole injection layer on a transparent anode substrate, wherein 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;

[0103] Step S2: depositing a hole transport layer on the hole injection layer, wherein the hole transport layer material is TCTA and the thickness of the hole transport layer is 60 nm;

[0104] Step S3: depositing a quantum dot light-emitting layer on the hole transport layer, wherein the material of the quantum dot light-emitting layer is InP and the thickness of the quantum dot light-emitting layer is 50 nm;

[0105] Step S4: depositing an electron transport layer on the quantum dot light-emitting layer, wherein the electron transport layer material is NiO and the thickness of the electron transport layer is 60 nm;

[0106] Step S5: depositing a cathode on the electron transport layer, wherein the cathode material is Ag, the thickness of the cathode is 100 nm, and the transmittance of the cathode to visible light is not less than 90%.

[0107] Comparative Example 3

[0108] A method for preparing a quantum dot light-emitting diode with an inverted bottom emission structure comprises the following steps:

[0109] Step S1: depositing a Ag layer on the substrate by evaporation, wherein the thickness of the Ag layer is 5 nm;

[0110] Step S2: depositing an electron transport layer on the Ag layer, wherein the electron transport layer material is SnO and the thickness of the electron transport layer is 50 nm;

[0111] Step S3: depositing a quantum dot light-emitting layer on the electron transport layer, wherein the material of the quantum dot light-emitting layer is CdSe and the thickness of the quantum dot light-emitting layer is 50 nm;

[0112] Step S4: depositing a hole transport layer on the quantum dot light-emitting layer, wherein the hole transport layer material is PVK and the thickness of the hole transport layer is 80 nm;

[0113] Step S5: depositing a hole injection layer on the hole transport layer, wherein the hole injection layer material is PEDOT:PSS and the thickness of the hole injection layer is 60 nm;

[0114] Step S6: depositing an anode on the hole injection layer, wherein the anode material is ITO and the thickness of the anode is 120 nm; and the anode reflects no less than 98% of visible light.

[0115] Comparative Example 4

[0116] A method for preparing a quantum dot light-emitting diode with an inverted top-emitting structure comprises the following steps:

[0117] Step S1: depositing a Ag layer on the substrate by evaporation, wherein the thickness of the Ag layer is 5 nm;

[0118] Step S2: depositing an electron transport layer on the Ag layer, wherein the electron transport layer material is TiO and the thickness of the electron transport layer is 60 nm;

[0119] Step S3: depositing a quantum dot light-emitting layer on the electron transport layer, wherein the material of the quantum dot light-emitting layer is CdTe, and the thickness of the quantum dot light-emitting layer is 50 nm;

[0120] Step S4: depositing a hole transport layer on the quantum dot light-emitting layer, wherein the hole transport layer material is PFB and the thickness of the hole transport layer is 80 nm;

[0121] Step S5: depositing a hole injection layer on the hole transport layer, wherein the hole injection layer material is MoO3 and the thickness of the hole injection layer is 60 nm;

[0122] Step S6: depositing an anode on the hole injection layer, wherein the anode material is ITO, the thickness of the anode is 120 nm, and the visible light transmittance of the anode is not less than 90%.

[0123] The performance of the quantum dot light-emitting diodes prepared in Examples 1-4 and Comparative Examples 1-4 was tested, and the results are shown in Table 1:

[0124] Table 1 Performance test results of quantum dot light-emitting diodes

[0125] External quantum efficiency - EQE (%) LT95(h) Example 1 10.2 6.3 Example 2 16.3 5.0 Example 3 9.4 6.8 Example 4 16.9 5.8 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

[0126] Comparing the data in Table 1, it can be seen that the difference between Example 1 and Comparative Example 1 is that an interface layer formed of Li3PS4 material is added between the hole transport layer and the quantum dot light-emitting layer, and its external quantum efficiency is increased from 7.9% to 10.2%, and its service life is increased from 5.4h to 6.3h; the difference between Example 2 and Comparative Example 2 is that an interface layer formed of Li3PS4 material is added between the hole transport layer and the quantum dot light-emitting layer, and its external quantum efficiency is increased from 14.6% to 16.3%, and its service life is increased from 3.9h to 1. to 5.0h; the only difference between Example 3 and Comparative Example 3 is that an interface layer formed of Li3PS4 material is added between the hole transport layer and the quantum dot light-emitting layer, and its external quantum efficiency is increased from 8.3% to 9.4%, and its service life is increased from 5.9h to 6.8h; the only difference between Example 4 and Comparative Example 4 is that an interface layer formed of Li3PS4 material is added between the hole transport layer and the quantum dot light-emitting layer, and its external quantum efficiency is increased from 15.8% to 16.9%, and its service life is increased from 4.1h to 5.8h. From the above data, it can be found that by providing an interface layer between the hole transport layer and the quantum dot light-emitting layer, the external quantum efficiency and service life of the quantum dot light-emitting diode can be effectively improved.

[0127] In summary, the present invention optimizes quantum dot light-emitting diode devices by adding an interface layer to the hole transport layer and the quantum dot light-emitting layer to reduce the hole injection barrier, improve hole injection, avoid hole accumulation at the interface, and effectively reduce the recombination of electrons that tunnel into the hole transport layer in the non-quantum dot light-emitting area, thereby improving device efficiency and life. The interface layer can also effectively block the influence of water and oxygen on the organic hole injection and transport layers, thereby improving device stability.

[0128] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

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 provided between the hole transport layer and the quantum dot light-emitting layer, and the interface layer material is Li3PS4; 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.

2. The quantum dot light emitting diode according to claim 1, characterized in that The thickness of the interface layer is 10-200 nm.

3. The quantum dot light-emitting diode according to any one of claims 1-2, characterized in that: The hole transport layer material is selected from one or more of TFB, PVK, Poly-TPD, PFB, TCTA, CBP, TPD and NPB.

4. The quantum dot light-emitting diode according to claim 3, characterized in that The hole transport material is selected from TFB.

5. The quantum dot light-emitting diode according to any one of claims 1-2, characterized in that: 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.

6. The quantum dot light-emitting diode according to any one of claim 5, characterized in that: The binary phase quantum dots are at least one of CdS, CdSe, CdTe, InP, AgS, PbS, PbSe, and HgS; and / or the ternary phase quantum dots are 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; and / or, the quaternary phase quantum dots are 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 / ZnS, wherein 0 <X<1。 7. The quantum dot light-emitting diode according to claim 1, characterized in that An electronic functional layer is provided between the quantum dot light-emitting layer and the cathode; and / or a hole injection layer is provided between the anode and the hole transport layer.

8. A method for preparing a quantum dot light-emitting diode, characterized in that: Including steps: providing an anode substrate, and a hole transport layer on the anode substrate; An interface layer is prepared on the hole transport layer, wherein the interface layer material is Li3PS4; 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, and a quantum dot light-emitting layer is prepared on the cathode substrate; An interface layer is prepared on the surface of the quantum dot light-emitting layer, wherein the interface layer material is Li3PS4; 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 is less than the HOMO energy level of the quantum dot light-emitting layer.

9. The method for preparing a quantum dot light-emitting diode according to claim 8, characterized in that: The step of preparing an interface layer on the hole transport layer comprises: Dispersing the Li3PS4 in an organic solvent to prepare a Li3PS4 solution; An interface layer is prepared on the surface of the hole transport layer, wherein the interface layer material is the Li3PS4; Alternatively, the step of preparing an interface layer on the surface of the quantum dot light-emitting layer comprises: Dispersing the Li3PS4 in an organic solvent to prepare a Li3PS4 solution; An interface layer is prepared on the surface of the quantum dot light-emitting layer, and the interface layer material is the Li3PS4.

10. The method for preparing a quantum dot light-emitting diode according to claim 9, characterized in that: The concentration of the Li3PS4 solution is 1-2 wt%.

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