CN110970567A - Quantum dot light-emitting diode - Google Patents

Quantum dot light-emitting diode Download PDF

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CN110970567A
CN110970567A CN201811150182.5A CN201811150182A CN110970567A CN 110970567 A CN110970567 A CN 110970567A CN 201811150182 A CN201811150182 A CN 201811150182A CN 110970567 A CN110970567 A CN 110970567A
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hole
layer
hole buffer
sublayer
quantum dot
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CN110970567B (en
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苏亮
谢相伟
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TCL Corp
TCL Research America Inc
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TCL Research America Inc
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Priority to PCT/CN2019/107552 priority patent/WO2020063592A1/en
Priority to US16/955,705 priority patent/US20210013437A1/en
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
    • H10K50/115—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers comprising active inorganic nanostructures, e.g. luminescent quantum dots
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/14—Carrier transporting layers
    • H10K50/15—Hole transporting layers

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  • Electroluminescent Light Sources (AREA)
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Abstract

The invention discloses a quantum dot light-emitting diode, which comprises a hole functional layer arranged between an anode and a quantum dot light-emitting layer, wherein the hole functional layer comprises a hole transport layer and a hole buffer layer, the hole transport layer is arranged close to the anode, the hole buffer layer is arranged close to the quantum dot light-emitting layer, the hole buffer layer comprises a first hole buffer sublayer which is attached to the hole transport layer, the first hole buffer sublayer is made of a first hole buffer material or a mixed material consisting of the first hole buffer material and a fourth hole transport material, and the hole mobility of the first hole buffer material is less than 1 multiplied by 10‑6cm2V‑1s‑1. The hole buffer layer can widen a hole accumulation region and reduce a space electric field near an exciton recombination region, so that exciton separation and fluorescence quenching of quantum dots are reduced, the electric resistance of the hole transmission layer can be improved, and the luminous efficiency, stability and service life of the QLED can be improved.

Description

Quantum dot light-emitting diode
Technical Field
The invention relates to the field of light emitting diodes, in particular to a quantum dot light emitting diode.
Background
Because the quantum dots have unique optical properties of continuously adjustable light-emitting wavelength along with size and components, narrow light-emitting spectrum, high fluorescence efficiency, good stability and the like, the quantum-dot-based electroluminescent diode (QLED) is widely concerned and researched. In addition, the QLED display has many advantages that cannot be achieved by LCDs, such as a large viewing angle, a high contrast ratio, a fast response speed, and flexibility, and is thus expected to become a next-generation display technology. Through more than twenty years of continuous research and development, the performance (luminous efficiency and service life) of the QLED is greatly improved, but at present, the QLED is still not a small distance away from commercialization, especially the blue QLED.
At present, a great bottleneck exists in the development of the QLED, that is, no suitable hole transport material exists, because the HOMO energy level of the current hole transport material is not matched with the top energy level of the valence band of the quantum dot, a large hole injection barrier exists between the hole transport layer and the quantum dot layer; in contrast, the electron injection barrier from the electron transport layer to the quantum dot layer is much smaller or even zero, which results in electrons easily moving into the quantum dot and more holes accumulating at the hole transport layer/quantum dot light emitting layer interface. The holes accumulated at the interface form a space charge region, creating a space electric field. On one hand, the existence of the space electric field can further prevent the holes from continuously moving to the quantum dots, so that the charge transmission is more unbalanced; on the other hand, the spatial electric field causes exciton dissociation in the quantum dot, resulting in quenching of the quantum dot fluorescence, both of which degrade the performance of the QLED. In addition, the accumulation of holes at a very narrow interface also puts high requirements on the electric resistance of the hole transport material, and the rapid degradation of the brightness and efficiency of the QLED is often caused by the low electric resistance of the hole transport material.
Accordingly, the prior art is yet to be improved and developed.
Disclosure of Invention
In view of the above disadvantages of the prior art, an object of the present invention is to provide a quantum dot light emitting diode, which aims to solve the problem that the light emitting efficiency of the quantum dot light emitting diode is low due to the easy generation of a space electric field caused by the accumulation of holes at the interface between a hole transport layer and a quantum dot layer.
The technical scheme of the invention is as follows:
a quantum dot light-emitting diode comprises an anode, a cathode, a quantum dot light-emitting layer and a hole functional layer, wherein the anode and the quantum dot light-emitting layer are arranged in a stacked mode, the quantum dot light-emitting layer is arranged between the anode and the cathode, the hole functional layer is arranged between the anode and the quantum dot light-emitting layer and comprises a hole transport layer and a hole buffer layer, the hole transport layer is arranged close to the anode, the hole buffer layer is arranged close to the quantum dot light-emitting layer, the hole buffer layer comprises a first hole buffer sub-layer, the first hole buffer sub-layer is attached to the hole transport layer, the first hole buffer sub-layer is made of a first hole buffer material or a mixed material composed of the first hole buffer material and a fourth hole transport material, and the hole mobility of the first hole buffer material is smaller than-6cm2V-1s-1。
Has the advantages that: the hole function layer in the quantum dot light-emitting diode comprises a hole transmission layer and a hole buffer layer, wherein the hole buffer layer comprises a first hole buffer sublayer which is attached to the hole transmission layer, the first hole buffer sublayer is made of a first hole buffer material or a mixed material consisting of the first hole buffer material and a fourth hole transmission material, and the hole mobility of the first hole buffer material is less than 1 x 10-6cm2V-1s-1. In the invention, the hole buffer layer can widen a hole accumulation region and reduce the accumulated hole density of the hole transport layer in unit volume, thereby phase-changing and enhancing the electric resistance of the hole transport layer; the broadened hole accumulation region also reduces the spatial electric field near the exciton recombination region, thereby reducing quantum dot exciton separation and fluorescence quenching, and improving the luminous efficiency, stability and lifetime of the QLED.
Drawings
Fig. 1 is a schematic diagram of a quantum dot light emitting diode with a first structure according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of a hole accumulation region and an exciton recombination region of the quantum dot light emitting diode shown in fig. 1.
Fig. 3 is a schematic diagram of a quantum dot light emitting diode with a second structure according to an embodiment of the present invention.
Fig. 4 is a schematic diagram of a quantum dot light emitting diode with a third structure according to an embodiment of the present invention.
Fig. 5 is a schematic diagram of a quantum dot light emitting diode with a fourth structure according to an embodiment of the present invention.
Fig. 6 is a current density-voltage (J-V) curve of the QLED in examples 1-5.
Fig. 7 is a graph of luminance versus voltage (L-V) of the QLEDs of examples 1-5.
Fig. 8 is a current efficiency-current density (CE-J) curve of the QLED in examples 1 to 5.
Fig. 9 is a life curve of the QLED in examples 1 to 5.
Detailed Description
The present invention provides a quantum dot light emitting diode, and the present invention will be described in further detail below in order to make the objects, technical solutions, and effects of the present invention clearer and clearer. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The quantum dot light-emitting diode has various forms, and the quantum dot light-emitting diode is divided into a formal structure and a trans structure, and the quantum dot light-emitting diode with the trans structure can comprise a substrate, a cathode, a quantum dot light-emitting layer, a hole functional layer and an anode which are stacked from bottom to top. The embodiments of the present invention will be described mainly by taking quantum dot light emitting diodes with formal structures as examples. Specifically, quantum dot emitting diode includes from down to last range upon range of substrate, positive pole, hole functional layer, quantum dot luminescent layer and negative pole that sets up, wherein, the hole functional layer includes hole transport layer and hole buffer layer, hole transport layer is close to the positive pole setting, the hole buffer layer is close to quantum dot luminescent layer sets up, the hole buffer layer include one deck with the first hole buffering sublayer of hole transport layer laminating setting, the material of first hole buffering sublayer be first hole buffer material or for by first hole buffer material and negative poleA mixed material of a fourth hole transport material, wherein the first hole buffer material has a hole mobility of less than 1 × 10-6cm2V-1s-1。
This embodiment is through setting up a hole functional layer between positive pole and quantum dot luminescent layer, the hole functional layer includes hole transport layer and hole buffer layer, the setting of hole buffer layer both can improve the electric resistance on hole transport layer, can improve QLED's luminous efficacy, stability and life-span again. The mechanism for achieving the above effects is specifically as follows:
in this embodiment, the material of the first hole buffer sublayer is a first hole buffer material or a mixed material composed of a first hole buffer material and a fourth hole transport material, and since the hole mobility of the first hole buffer material is less than 1 × 10-6cm2V-1s-1Therefore, the first hole buffer sublayer can play a role in delaying the motion of the hole to the quantum dot light-emitting layer, the accumulation density of the hole at the interface of the hole transport layer and the quantum dot light-emitting layer is reduced, the hole accumulation region of the quantum dot light-emitting diode is widened, and the following benefits are achieved: on one hand, the requirement on the electric resistance of the hole transport material can be reduced by the widened hole accumulation region, and in other words, the density of accumulated charges of the hole transport layer in unit volume can be reduced by the widened hole accumulation region, so that the electric resistance of the hole transport layer is improved through phase change, and the stability and the service life of the QLED are improved; on the other hand, the broadened hole accumulation region can reduce the electric field intensity close to the interface of the quantum dot light emitting layer, so that exciton separation caused by the electric field is reduced, fluorescence quenching of the quantum dot is reduced, and the luminous efficiency and the service life of the QLED are improved.
Preferably, in this embodiment, the HOMO energy level of the first hole buffer material in the first hole buffer sublayer is greater than the HOMO energy level of the hole transport layer material, and the HOMO energy level of the first hole buffer material is less than the top energy level of the valence band of the quantum dot in the quantum dot light emitting layer. Because the HOMO energy level of the first hole buffer material is greater than that of the hole transport layer material, a hole barrier exists at the interface between the hole transport layer and the first hole buffer sublayer, so that holes are accumulated at the interface, and the purpose of widening a hole accumulation region is achieved. Furthermore, the HOMO energy level of the first hole buffer material is more matched with the top energy level of the valence band of the quantum dot in the quantum dot light-emitting layer, so that the hole in the first hole buffer sublayer is transferred to the quantum dot light-emitting layer to be combined with electrons for light emission, and the light-emitting efficiency of the QLED is improved.
In a preferred embodiment, when the hole buffer layer is a single-layer structure formed by a first hole buffer sublayer and the first hole buffer sublayer is formed of a first hole buffer material, that is, as shown in fig. 1, the quantum dot light emitting diode includes a substrate 101, an anode 102, a hole transport layer 103, a first hole buffer sublayer 104, a quantum dot light emitting layer 105, and a cathode 106, which are sequentially stacked from bottom to top, and the first hole buffer sublayer is formed of a first hole buffer material. In this embodiment, as shown in fig. 2, a single first hole buffer sublayer is disposed between the hole transport layer and the quantum dot light emitting layer, and due to a hole barrier existing at an interface between the hole transport layer and the first hole buffer sublayer, a part of holes output from the anode are accumulated at the interface, and the remaining part of holes move into the first hole buffer sublayer through the interface; however, since the first hole buffer sublayer material has a hole mobility of less than 1 × 10-6cm2V-1s-1The first hole buffer material makes the hole moving to the first hole buffer sublayer, one part of the hole is delayed in the first hole buffer sublayer, and the other part of the hole transits from the first hole buffer sublayer to the quantum dot light-emitting layer to be recombined with the electron to emit light. In the embodiment, due to the introduction of the first hole buffer sublayer, the hole accumulation region in the quantum dot light-emitting diode is widened, the density of the space electric field is reduced, the adverse effect of the space electric field on quantum dot exciton separation and fluorescence quenching is further reduced, and the light-emitting efficiency, the stability and the service life of the QLED are improved.
In this embodiment, although the first hole buffer sublayer is designed to widen the hole accumulation region, its ability to delay hole transport is not favorable for injecting holes into the quantum dot light-emitting layer, which is the key to ensure the luminous intensity and luminous efficiency of the QLED. Based on this, the thickness of the first hole buffer sublayer is selected as the key for balancing the two, and in this embodiment, the thickness of the first hole buffer sublayer is preferably 1 to 6nm, and in this thickness range, the first hole buffer sublayer can both widen the hole accumulation region of the quantum dot light emitting diode and ensure that a sufficient number of holes are injected into the quantum dot light emitting layer, so as to improve the light emitting intensity and the light emitting efficiency of the QLED.
Preferably, in the present embodiment, the first hole buffer material is selected from one or more of TPBi, Bphen, TmPyPb, BCP, and TAZ, but is not limited thereto.
In a preferred embodiment, when the hole buffer layer is a single-layer structure composed of a first hole buffer sublayer and the first hole buffer sublayer is made of a mixed material composed of a first hole buffer material and a fourth hole transport material, that is, as shown in fig. 3, the quantum dot light emitting diode includes a substrate 201, an anode 202, a hole transport layer 203, a first hole buffer sublayer 204, a quantum dot light emitting layer 205, and a cathode 206, which are stacked in sequence from bottom to top, and the first hole buffer sublayer is made of a mixed material composed of a first hole buffer material and a fourth hole transport material. In this embodiment, the hole transport material in the first hole buffer sublayer may serve as a channel for hole transport, and the hole buffer material is responsible for delaying the transport of holes, so that the effect of delaying the hole transport is achieved, and the thickness of the hole buffer layer may be increased, thereby further widening the hole accumulation region, improving the light emitting efficiency of the QLED, and prolonging the service life of the QLED.
Preferably, in this embodiment, the thickness of the first hole buffer sublayer is 1 to 15nm, and in this thickness range, the first hole buffer sublayer can not only further widen the hole accumulation region, but also enable a sufficient number of holes to be injected into the quantum dot light emitting layer, thereby ensuring the luminous intensity and luminous efficiency of the QLED.
Preferably, in this embodiment, the first hole bufferThe punching material is selected from one or more of TPBi, Bphen, TmPyPb, BCP and TAZ, but is not limited to the above. Preferably, the first hole transport material is TAPC, NPB, NPD, TCTA, CBP, NiO, WO3、MoO3And V2O5And the like, but is not limited thereto.
In a preferred embodiment, the hole buffer layer may also be a stacked structure, including a first hole buffer sublayer, a second hole buffer sublayer and a second hole buffer sublayer disposed on the first hole buffer sublayer and the second hole buffer sublayer, the spacer layer is made of a second hole transport material, the second hole buffer sublayer is made of a second hole buffer material or a mixed material composed of the second hole buffer material and a third hole transport material, wherein the hole mobility of the second hole buffer material is less than 1 × 10-6cm2V-1s-1。
Preferably, the first hole buffer material is selected from one or more of TPBi, Bphen, tmpyppb, BCP, TAZ, and the like, but is not limited thereto. Preferably, the second hole buffer material is selected from one or more of TPBi, Bphen, tmpyppb, BCP, TAZ, and the like, but is not limited thereto. Preferably, the second hole transport material is selected from TAPC, NPB, NPD, TCTA, CBP, NiO, WO3、MoO3And V2O5And the like, but is not limited thereto. Preferably, the third hole transport material is selected from TAPC, NPB, NPD, TCTA, CBP, NiO, WO3、MoO3And V2O5And the like, but is not limited thereto.
In a preferred embodiment, as shown in fig. 4, the quantum dot light emitting diode includes a substrate 301, an anode 302, a hole transport layer 303, a first hole buffer sublayer 304, a spacer layer 305, a second hole buffer sublayer 306, a quantum dot light emitting layer 307, and a cathode 308, which are sequentially stacked from bottom to top, where the first hole buffer sublayer is made of a first hole buffer material, the second hole buffer sublayer is made of a second hole buffer material, and hole mobilities of the first hole buffer material and the second hole buffer material are both smallAt 1X 10-6cm2V-1s-1. In this embodiment, a hole barrier exists at an interface between the hole transport layer and the first hole buffer sublayer, a hole barrier also exists at an interface between the spacer layer and the second hole buffer sublayer, and holes can be accumulated at both interfaces, that is, the quantum dot light emitting diode in this embodiment increases a hole accumulation interface, so that a hole accumulation region is further widened, and the light emitting efficiency and the service life of the QLED can be effectively improved.
In order to optimize the performance of the QLED and improve the light emitting efficiency of the QLED, in this embodiment, the thickness of the first hole buffer sublayer is preferably 0.5 to 3nm, and the thickness of the second hole buffer sublayer is preferably 0.5 to 3 nm.
More preferably, the thickness of the spacer layer is 1 to 3 nm.
In a preferred embodiment, as shown in fig. 5, the quantum dot light emitting diode includes a substrate 401, an anode 402, a hole transport layer 403, a first hole buffer sublayer 404, a spacer layer 405, a second hole buffer sublayer 406, a quantum dot light emitting layer 407, and a cathode 408 stacked in sequence from bottom to top, where the first hole buffer sublayer material is a mixed material composed of a first hole buffer material and a fourth hole transport material, the second hole sublayer material is a mixed material composed of a second hole buffer material and a third hole transport material, and hole mobilities of the first hole buffer material and the second hole buffer material are both less than 1 × 10-6cm2V-1s-1. In this embodiment, the first hole transport material in the first hole buffer sublayer can serve as a hole transport channel thereof, and the third hole transport material in the second hole buffer sublayer can serve as a hole transport channel thereof, that is, a hole output from the anode can move to the quantum dot light-emitting layer through the hole transport channels of the first hole buffer sublayer and the second hole buffer sublayer to emit light in combination with an electron; and the other part of the residual holes are distributed in the hole transport layer, the first hole buffer sublayer, the spacing layer and the second hole buffer sublayer, so that the purpose of widening a hole accumulation region is achieved, the luminous efficiency of the QLED is further improved, and the service life of the QLED is further prolonged.
In order to optimize the performance of the QLED and improve the light emitting efficiency of the QLED, in this embodiment, the thickness of the first hole buffer sublayer is preferably 1 to 8nm, and the thickness of the second hole buffer sublayer is preferably 1 to 8 nm.
More preferably, the thickness of the spacer layer is 1 to 5 nm.
In a preferred embodiment, a quantum dot light emitting diode includes a substrate, an anode, a hole transport layer, a first hole buffer sublayer, a spacer layer, a second hole buffer sublayer, a quantum dot light emitting layer, and a cathode stacked in sequence from bottom to top, where the first hole buffer sublayer is made of a first hole buffer material, the second hole sublayer is made of a mixed material of a second hole buffer material and a third hole transport material, and hole mobilities of the first hole buffer material and the second hole buffer material are both less than 1 × 10-6cm2V-1s-1. In this embodiment, a part of holes output from the anode is accumulated on the interface between the hole transport layer and the first hole buffer sublayer, and a part of holes is accumulated on the first hole buffer layer, the spacer layer and the second hole buffer layer, and this embodiment can also achieve the purpose of widening the hole accumulation region, which can reduce the electric field intensity near the interface of the quantum dot light emitting layer, and is beneficial to reducing exciton separation caused by an electric field, and reducing fluorescence quenching of quantum dots, thereby being beneficial to improving the light emitting efficiency of the QLED; the density of accumulated charges of the hole transport layer in unit volume can be reduced, so that the phase change improves the electric resistance of the hole transport layer, and the stability and the service life of the QLED are improved.
Preferably, in order to optimize the performance of the QLED and improve the light emitting efficiency of the QLED, in this embodiment, the thickness of the first hole buffer sublayer is preferably 0.5 to 3nm, the thickness of the second hole buffer sublayer is preferably 1 to 8nm, and the thickness of the spacer layer is preferably 1 to 3 nm.
In a preferred embodiment, the quantum dot light emitting diode comprises a substrate, an anode, a hole transport layer, a first hole buffer sublayer, a spacing layer, a second hole buffer sublayer, a quantum dot light emitting layer and a cathode which are sequentially stacked from bottom to top,the first hole buffer sublayer material is a mixed material composed of a first hole buffer material and a fourth hole transport material, the second hole sublayer material is a second hole buffer material, and the hole mobility rates of the first hole buffer material and the second hole buffer material are both less than 1 multiplied by 10-6cm2V-1s-1. In this embodiment, holes output from the anode may be accumulated on the interface between the hole transport layer and the first hole buffer sublayer, and may also be accumulated on the first hole buffer layer, the spacer layer, and the second hole buffer layer, and this embodiment can also achieve the purpose of widening the hole accumulation region, which can reduce the electric field intensity near the interface of the quantum dot light emitting layer, and is beneficial to reducing exciton separation caused by an electric field, and reducing fluorescence quenching of quantum dots, thereby being beneficial to improving the light emitting efficiency of the QLED; the density of accumulated charges of the hole transport layer in unit volume can be reduced, so that the phase change improves the electric resistance of the hole transport layer, and the stability and the service life of the QLED are improved.
Preferably, in order to optimize the performance of the QLED and improve the light emitting efficiency of the QLED, in this embodiment, the thickness of the first hole buffer sublayer is preferably 1 to 8nm, the thickness of the second hole buffer sublayer is preferably 0.5 to 3nm, and the thickness of the spacer layer is preferably 1 to 3 nm.
In a preferred embodiment, the substrate may be a rigid substrate, such as glass, or a flexible substrate, such as one of PET or PI.
In a preferred embodiment, the anode may be selected from one or more of indium doped tin oxide (ITO), fluorine doped tin oxide (FTO), antimony doped tin oxide (ATO), aluminum doped zinc oxide (AZO), and the like.
In a preferred embodiment, the material of the hole transport layer may be selected from materials having good hole transport properties, such as but not limited to TAPC, NPB, NPD, TCTA, CBP, NiO, WO3、MoO3And V2O5And the like.
Preferably, a space is further provided between the hole transport layer and the anodeA hole injection layer made of PEDOT PSS or WO3、MoO3、V2O5And HAT-CN, but not limited thereto.
In a preferred embodiment, the quantum dot light emitting layer material is one of a group II-VI compound semiconductor, a group III-V compound semiconductor, a group I-III-VI compound semiconductor, or a group IV elemental semiconductor. As an example, the II-VI compound semiconductor is one or more of CdSe, ZnCdS, CdSeS, ZnCdSeS, CdSe/ZnS, CdSeS/ZnS, CdSe/CdS/ZnS, ZnCdS/ZnS, CdS/ZnS, ZnCdSeS/ZnS, and ZnCdSeS/ZnS, etc.; the III-V compound semiconductor is one or more of GaAs, GaN, InP/ZnS and the like; the I-III-VI compound semiconductor is one or more of CuInS, AgInS, CuInS/ZnS, AnInS/ZnS and the like; the IV group elementary substance semiconductor is one or more of Si, C, graphene and the like.
In a preferred embodiment, an electron transport layer is further disposed between the quantum dot light emitting layer and the cathode, and the material of the electron transport layer may be selected from materials having good electron transport properties, such as but not limited to n-type TPBi, Bepp2, BTPS, TmPyPb, ZnO, TiO2、Fe2O3、SnO2、Ta2O3One or more of AlZnO, ZnSnO and InSnO.
Preferably, an electron injection layer is further disposed between the electron transport layer and the cathode, and the material of the electron injection layer is one or more of PEIE, PEI, LiF, NaF, Liq, and the like.
In a preferred embodiment, the cathode may be selected from one of an aluminum (Al) electrode, a silver (Ag) electrode, a gold (Au) electrode, and the like.
The invention also provides an embodiment of a preparation method of the quantum dot light-emitting diode with the formal structure as shown in figure 1, which specifically comprises the following steps:
providing a substrate, and forming an anode on the substrate;
preparing a hole transport layer on the anode;
preparing a first hole buffer sublayer on the hole transport layer, wherein the material of the first hole buffer sublayer is a first hole buffer material, and the hole mobility of the first hole buffer material is less than 1 x 10-6cm2V-1s-1；
Preparing a quantum dot light emitting layer on the first hole buffer sublayer;
and preparing a cathode on the quantum dot light-emitting layer to obtain the quantum dot light-emitting diode.
In the present invention, the preparation method of each layer may 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 continuous ionic 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, one or more of solution method (such as spin coating, printing, knife coating, dip-coating, dipping, spraying, roll coating, casting, slit coating, or bar coating), evaporation method (such as thermal evaporation, electron beam evaporation, magnetron sputtering, or multi-arc ion plating), deposition method (such as physical vapor deposition, atomic layer deposition, pulsed laser deposition, etc.).
The present invention will be described in detail below with reference to examples.
Example 1
A quantum dot light-emitting diode comprises an ITO cathode, an electron transport layer, a quantum dot light-emitting layer, a hole transport layer, a hole injection layer and an anode which are sequentially stacked from bottom to top, and the specific preparation comprises the following steps:
1. depositing a conductive film ITO on a transparent substrate as a cathode, wherein the thickness of the conductive film ITO is 50 nm;
2. depositing 40nm ZnO as electron transport layer on cathode by solution method, N2Annealing at 100 deg.C for 15 min;
3. depositing CdSe/ZnS with the thickness of 25nm on the electron transport layer by a solution method to be used as a quantum dot light-emitting layer, wherein N is2Annealing at 100 deg.C for 15 min;
4. transferring the transparent substrate to an evaporation chamber, and vacuumizing to
Figure DEST_PATH_IMAGE001
Below pa, evaporating NPB as a hole transport layer on the hole buffer layer at the rate of 0.1nm/s, wherein the thickness is 30 nm;
5. evaporating HAT-CN as a hole injection layer on the hole transport layer at the speed of 0.05nm/s, wherein the thickness of the hole injection layer is 10 nm;
6. al was deposited on the hole injection layer at a rate of 0.4nm/s as an anode, and the thickness was 100 nm.
Example 2
A quantum dot light-emitting diode comprises an ITO cathode, an electron transport layer, a quantum dot light-emitting layer, a first hole buffer sublayer, a hole transport layer, a hole injection layer and an anode which are sequentially stacked from bottom to top, and the specific preparation comprises the following steps:
1. depositing a conductive film ITO on a transparent substrate as a cathode, wherein the thickness of the conductive film ITO is 50 nm;
2. depositing 40nm ZnO as electron transport layer on cathode by solution method, N2Annealing at 100 deg.C for 15 min;
3. depositing CdSe/ZnS with the thickness of 25nm on the electron transport layer by a solution method to be used as a quantum dot light-emitting layer, wherein N is2Annealing at 100 deg.C for 15 min;
4. the transparent substrate is moved to an evaporation chamber and is vacuumized to
Figure 669995DEST_PATH_IMAGE001
Below Pa, and then evaporating TPBi on the quantum dot light-emitting layer at the rate of 0.02nm/s to be used as a first hole buffer sublayer with the thickness of 3 nm;
5. evaporating NPB (nitrogen-phosphorus-boron) as a hole transport layer on the first hole buffer sublayer at the speed of 0.1nm/s, wherein the thickness of the hole transport layer is 30 nm;
6. evaporating HAT-CN as a hole injection layer on the hole transport layer at the speed of 0.1nm/s, wherein the thickness of the hole injection layer is 10 nm;
7. al was deposited on the hole injection layer at a rate of 0.4nm/s as an anode, and the thickness was 100 nm.
Example 3
A quantum dot light-emitting diode comprises an ITO cathode, an electron transport layer, a quantum dot light-emitting layer, a first hole buffer sublayer, a hole transport layer, a hole injection layer and an anode which are sequentially stacked from bottom to top, and the specific preparation comprises the following steps:
1. depositing a conductive film ITO on a transparent substrate as a cathode, wherein the thickness of the conductive film ITO is 50 nm;
2. depositing ZnO with the thickness of 40nm as an electron transport layer on a cathode by a solution method, and depositing ZnO on N2Annealing at medium 100 deg.C for 15 min;
3. depositing CdSe/ZnS with the thickness of 25nm on the electron transport layer by a solution method to be used as a quantum dot light emitting layer on N2Annealing at medium 100 deg.C for 15 min;
4. the substrate is moved to a vapor deposition chamber and is vacuumized to
Figure 422050DEST_PATH_IMAGE002
Below Pa, co-evaporating TPBi on the quantum dot light-emitting layer at the rate of 0.02nm/s, wherein NPB is used as a first hole buffer sublayer and has the thickness of 7 nm;
5. evaporating NPB (nitrogen-phosphorus-boron) as a hole transport layer on the first hole buffer sublayer at the speed of 0.1nm/s, wherein the thickness of the hole transport layer is 30 nm;
6. evaporating HAT-CN as a hole injection layer on the hole transport layer at the speed of 0.1nm/s, wherein the thickness of the hole injection layer is 10 nm;
7. al was deposited on the hole injection layer at a rate of 0.4nm/s as an anode, and the thickness was 100 nm.
Example 4
A quantum dot light-emitting diode comprises an ITO cathode, an electron transport layer, a quantum dot light-emitting layer, a first hole buffer sublayer, a spacing layer, a second hole buffer sublayer, a hole transport layer, a hole injection layer and an anode which are sequentially stacked from bottom to top, and the specific preparation comprises the following steps:
1. depositing a conductive film ITO on a transparent substrate as a cathode, wherein the thickness of the conductive film ITO is 50 nm;
2. depositing ZnO with the thickness of 40nm as an electron transport layer on a cathode by a solution method, and depositing ZnO on N2Annealing at medium 100 deg.C for 15 min;
3. in electronDepositing CdSe/ZnS with the thickness of 25nm on the transmission layer by a solution method to be used as a quantum dot light-emitting layer, and depositing CdSe/ZnS on the transmission layer by a solution method to form a quantum dot light-emitting layer2Annealing at medium 100 deg.C for 15 min;
4. the transparent substrate is moved to an evaporation chamber and is vacuumized to
Figure 182196DEST_PATH_IMAGE002
Below Pa, and then evaporating TPBi on the quantum dot light-emitting layer at the rate of 0.01nm/s to be used as a first hole buffer sublayer with the thickness of 1.5 nm;
5. evaporating NPB (nitrogen-phosphorus-boron) as a spacing layer on the first hole buffer sublayer at the speed of 0.01nm/s, wherein the thickness of the NPB is 2 nm;
6. evaporating TPBi on the spacing layer at the rate of 0.01nm/s to be used as a second hole buffer sublayer, wherein the thickness is 1.5 nm;
7. evaporating NPB as a hole transport layer on the second hole buffer sublayer at the speed of 0.1nm/s, wherein the thickness of the hole transport layer is 30 nm;
8. evaporating HAT-CN as a hole injection layer on the hole transport layer at the speed of 0.1nm/s, wherein the thickness of the hole injection layer is 10 nm;
9. al was deposited on the hole injection layer at a rate of 0.4nm/s as an anode, and the thickness was 100 nm.
Example 5
A quantum dot light-emitting diode comprises an ITO cathode, an electron transport layer, a quantum dot light-emitting layer, a first hole buffer sublayer, a spacing layer, a second hole buffer sublayer, a hole transport layer, a hole injection layer and an anode which are sequentially stacked from bottom to top, and the specific preparation comprises the following steps:
1. depositing a conductive film ITO on a transparent substrate as a cathode, wherein the thickness of the conductive film ITO is 50 nm;
2. depositing ZnO with the thickness of 40nm as an electron transport layer on a cathode by a solution method, and depositing ZnO on N2Annealing at medium 100 deg.C for 15 min;
3. depositing CdSe/ZnS with the thickness of 25nm on the electron transport layer by a solution method to be used as a quantum dot light emitting layer on N2Annealing at medium 100 deg.C for 15 min;
4. the transparent substrate is moved to an evaporation chamber and is vacuumized to
Figure 855753DEST_PATH_IMAGE002
Below Pa, co-evaporating TPBi on the quantum dot layer at the rate of 0.02nm/s, wherein NPB is used as a first hole buffer sublayer and has the thickness of 3 nm;
5. evaporating NPB as a spacing layer on the first hole buffer sublayer at the speed of 0.02nm/s, wherein the thickness of the NPB is 3 nm;
6. evaporating TPBi on the spacing layer at the rate of 0.02nm/s, wherein NPB is used as a second hole buffer sublayer and the thickness is 3 nm;
7. evaporating NPB on the second hole buffer sublayer at the speed of 0.1nm/s to be used as a hole transport layer, wherein the thickness of the hole transport layer is 30 nm;
8. evaporating HAT-CN as a hole injection layer on the hole transport layer at the speed of 0.1nm/s, wherein the thickness of the hole injection layer is 10 nm;
9. al was deposited on the hole injection layer at a rate of 0.4nm/s as an anode, and the thickness was 100 nm.
Furthermore, the present invention also tests the performance of the quantum dot light emitting diode in the above examples 1 to 5, and the test results are shown in fig. 6 to 9, where fig. 6 is a current density-voltage (J-V) curve of the QLED in examples 1 to 5; FIG. 7 is a graph of luminance vs. voltage (L-V) of QLEDs in examples 1-5; FIG. 8 is a current efficiency-current density (CE-J) curve of the QLED of examples 1-5; fig. 9 is a life curve of the QLED in examples 1 to 5, in which the QLED in example 1 is a reference device.
As shown in fig. 6, the current of the QLED in each of examples 2 to 5 is larger than that of the reference device in example 1, which is caused by the fact that the HOMO level of the hole buffer layer material is between the HOMO level of the hole transport layer material and the top level of the valence band of the quantum dot, thereby facilitating the transition of holes from the hole buffer layer to the quantum dot.
Due to the introduction of the hole buffer layer, the hole accumulation region is widened, the spatial electric field density is reduced, and the adverse effect of the spatial electric field on the quantum dot excitons is reduced, so that the brightness and the efficiency of the QLED introduced with the hole buffer layer are improved compared with those of a reference device, as shown in fig. 7 and 8. The maximum current efficiency of the QLED shown in example 2 is improved by 28.6% compared with the reference device in example 1, the maximum current efficiency of the QLED shown in example 3 is improved by 45.1% compared with the reference device in example 1, the maximum current efficiency of the QLED shown in example 4 is improved by 42.1% compared with the reference device in example 1, and the maximum current efficiency of the QLED shown in example 5 is improved by 69.2% compared with the reference device in example 1.
As can be seen from fig. 9, the lifetime of the QLED is improved to various degrees after the hole buffer layer is introduced. Wherein, T of QLED shown in example 250Compared with the reference device in example 1, the T of the QLED is improved by 63.3 percent, and the T of the QLED is shown in example 350Compared with the reference device in the embodiment 1, the T of the QLED is improved by 258 percent, and the T of the QLED is shown in the embodiment 450Compared with the reference device in the embodiment 1, the T of the QLED is improved by 163 percent, and the T of the QLED is shown in the embodiment 550Compared with the reference device in the embodiment 1, the improvement is 432%.
In summary, the hole function layer in the quantum dot light emitting diode of the present invention includes a hole transport layer and a hole buffer layer, the hole buffer layer includes a first hole buffer sublayer attached to the hole transport layer, the first hole buffer sublayer is made of a first hole buffer material or a mixed material of the first hole buffer material and a fourth hole transport material, and a hole mobility of the first hole buffer material is less than 1 × 10-6cm2V-1s-1. In the invention, the hole buffer layer can widen a hole accumulation region and reduce the accumulated hole density of the hole transport layer in unit volume, thereby phase-changing and enhancing the electric resistance of the hole transport layer; the broadened hole accumulation region also reduces the spatial electric field near the exciton recombination region, thereby reducing quantum dot exciton separation and fluorescence quenching, and improving the luminous efficiency, stability and lifetime of the QLED.
It is to be understood that the invention is not limited to the examples described above, but that modifications and variations may be effected thereto by those of ordinary skill in the art in light of the foregoing description, and that all such modifications and variations are intended to be within the scope of the invention as defined by the appended claims.

Claims (10)

1. A quantum dot light-emitting diode comprises an anode, a cathode, a quantum dot light-emitting layer and a hole functional layer, wherein the anode and the cathode are arranged in a stacked mode, the quantum dot light-emitting layer is arranged between the anode and the quantum dot light-emitting layer, the hole functional layer comprises a hole transport layer and a hole buffer layer, the hole transport layer is arranged close to the anode, the hole buffer layer is arranged close to the quantum dot light-emitting layer, the quantum dot light-emitting diode is characterized in that the hole buffer layer comprises a first hole buffer sublayer, the first hole buffer sublayer is attached to the hole transport layer, the first hole buffer sublayer is made of a first hole buffer material or a mixed material composed of the first hole buffer material and a fourth hole transport material, and the hole mobility of the first hole buffer material is smaller than 1 x 10-6cm2V-1s-1。
2. The quantum dot light-emitting diode of claim 1, wherein the first hole buffer material is one or more of TPBi, Bphen, TmPyPb, BCP, and TAZ;
and/or the first hole transport material is TAPC, NPB, NPD, TCTA, CBP, NiO, WO3、MoO3And V2O5One or more of;
the fourth hole transport material is TAPC, NPB, NPD, TCTA, CBP, NiO, WO3、MoO3And V2O5One or more of (a).
3. The qd-led of claim 1 or 2, wherein the hole buffer layer is a single-layer structure composed of a first hole buffer sublayer, and when the first hole buffer sublayer material is a first hole buffer material, the thickness of the first hole buffer sublayer is 1-6 nm.
4. The quantum dot light-emitting diode of claim 1, wherein the hole buffer layer is a single-layer structure composed of a first hole buffer sublayer, and when the first hole buffer sublayer is a mixed material composed of a first hole buffer material and a fourth hole transport material, the thickness of the first hole buffer sublayer is 1-15 nm;
and/or when the first hole buffer sub-layer material is a mixed material consisting of a first hole buffer material and a fourth hole transport material, the first hole transport material is TAPC, NPB, NPD, TCTA, CBP, NiO, WO3、MoO3And V2O5One or more of (a).
5. The QED diode of claim 1 or 2, wherein the hole buffer layer is a laminated structure comprising a first hole buffer sublayer, a second hole buffer sublayer and a spacer layer arranged between the first hole buffer sublayer and the second hole buffer sublayer, the spacer layer is made of a second hole transport material, the second hole buffer sublayer is made of a second hole buffer material or a mixed material of the second hole buffer material and a third hole transport material, and the hole mobility of the second hole buffer material is less than 1 x 10-6cm2V-1s-1。
6. The quantum dot light-emitting diode of claim 5, wherein when the first hole buffer sublayer material is a first hole buffer material and the second hole buffer sublayer material is a second hole buffer material, the thickness of the first hole buffer sublayer is 0.5-3nm and the thickness of the second hole buffer sublayer is 0.5-3 nm.
7. The quantum dot light-emitting diode of claim 5, wherein when the first hole buffer sublayer material is a mixed material of a first hole buffer material and a fourth hole transport material, and the second hole sublayer material is a mixed material of a second hole buffer material and a third hole transport material, the thickness of the first hole buffer sublayer is 1-8nm, and the thickness of the second hole buffer sublayer is 1-8 nm.
8. The quantum dot light-emitting diode of claim 5, wherein when the first hole buffer sublayer material is a first hole buffer material and the second hole sublayer material is a mixed material of a second hole buffer material and a third hole transport material, the thickness of the first hole buffer sublayer is 0.5-3nm and the thickness of the second hole buffer sublayer is 1-8 nm.
9. The quantum dot light-emitting diode of claim 5, wherein when the first hole buffer sublayer material is a mixed material consisting of a first hole buffer material and a fourth hole transport material, and the second hole sublayer material is a second hole buffer material, the thickness of the first hole buffer sublayer is 1-8nm, and the thickness of the second hole buffer sublayer is 0.5-3 nm.
10. The quantum dot light-emitting diode according to any one of claims 6 to 9, wherein the second hole buffer material is selected from one or more of TPBi, Bphen, tmpyppb, BCP and TAZ;
and/or the second hole transport material is selected from TAPC, NPB, NPD, TCTA, CBP, NiO, WO3、MoO3And V2O5One or more of;
and/or the third hole transport material is selected from TAPC, NPB, NPD, TCTA, CBP, NiO, WO3、MoO3And V2O5One or more of;
and/or the thickness of the spacing layer is 1-3 nm.
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