CN110783474B - Electroluminescent diode based on quantum dots and photoelectric equipment - Google Patents
Electroluminescent diode based on quantum dots and photoelectric equipment Download PDFInfo
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Abstract
The invention provides an electroluminescent diode and photoelectric equipment based on quantum dots, which comprises a conductive anode, a hole injection layer, a hole transport layer, a quantum dot light-emitting layer, an electron transport layer and an electrode which are connected in sequence. In order to solve the problem of mismatching of electron/hole injection in the traditional quantum dot electroluminescent diode, the invention can effectively reduce the ratio of the number of electron/hole transmission channels by using the core-shell quantum dot light-emitting layer with the directional quantitative transmission channel, so that the injection balance of current carriers can be more easily formed in a light-emitting device, the light-emitting efficiency is improved, and the basic quantum dot core-shell structure based on the tetrapod morphological characteristics, which is provided based on the directional quantitative transmission channel, is used for expanding the application possibility of organic molecule/polymer hole conduction type materials.
Description
Technical Field
The invention relates to the field of semiconductor light emitting diodes, in particular to an electroluminescent diode and photoelectric equipment based on quantum dots.
Background
The quantum dot light emitting diode is expected to become a core device in the next generation display field due to a series of advantages of high color saturation, adjustable light emitting color, low energy consumption and the like.
Through mass search, the applicant finds that in the prior art, for example, a quantum dot light emitting diode and a preparation method thereof are disclosed in the publication number CN106058065B, by mixing a thermal expansion material in packaging glue, the packaging effect can be ensured, heat can be conducted out in time, so that the stability of a QLED device is enhanced, the thickness of the QLED device can be adjusted according to temperature change, the time for light emitted by the QLED device to penetrate through a thermal expansion material layer can be adjusted, the wavelength of the light penetrating through the thermal expansion material layer can be adjusted, and the color rendering property of the light can be optimized. Or as disclosed in CN106384767B, the quantum dot light emitting diode, the method for manufacturing the same, the light emitting module and the display device improve the hole transmission effect by optimizing the hole defect state on the surface of the quantum dot, so that the injection of the holes and the electrons in the QLED device is balanced, thereby improving the light emitting efficiency and stability of the QLED device. Or the quantum dot light emitting diode and the display device including the quantum dot light emitting diode as disclosed in publication No. CN105826480B, since the number of sub-pixels forming one pixel is reduced, the resolution of the display device is improved.
In summary, the quantum dot light emitting diode scheme in the prior art does not effectively and economically solve the problem of adjusting the number of carrier transmission channels of the transmission layer to achieve carrier injection balance. In practice, the difficulty in adjusting the carrier balance is that the difference between the carrier mobility of the organic molecule/polymer material and that of the semiconductor oxide is too large, so that the range of the available organic molecule/polymer material is very limited.
Disclosure of Invention
The present invention proposes a quantum dot based electroluminescent diode and optoelectronic device to solve the problems,
in order to achieve the purpose, the invention adopts the following technical scheme:
an electroluminescent diode based on quantum dots comprises a conductive anode, a hole injection layer, a hole transport layer, a quantum dot light emitting layer, an electron transport layer and an electrode which are sequentially connected; the quantum dot light-emitting layer comprises a plurality of quantum dot core-shell structures, and each quantum dot core-shell structure comprises a quantum dot core and a shell structure wrapped outside the quantum dot core;
the core-shell structure is provided with a plurality of first transmission channels and a plurality of second transmission channels for directional quantification, the first transmission channels are connected to the hole transmission layer, and the second transmission channels are connected to the electron transmission layer.
Further, the number of the second transmission channels is N, and the number of the first transmission channels is 3N.
Furthermore, the N second transmission channels and the 3N first transmission channels are uniformly distributed on the outer surface of the shell structure.
Further, the quantum dot core-shell structure comprises at least one of semiconductor core-shell structure nanocrystals of II-VI, I-III-VI, III-V, or IV groups.
Further, the II-VI group nanocrystals include one of a homogeneous core-shell structure or a heterogeneous core-shell structure.
Furthermore, the diameter of the quantum dot core is 1-5nm, the length of the first transmission channel is 3-20nm, and the length of the second transmission channel is 3-20 nm.
Further, the thickness of the conductive anode is 150-200nm, the thickness of the hole injection layer is 20-50nm, the thickness of the hole transport layer is 20-50nm, the thickness of the quantum dot light emitting layer is 20-40nm, the thickness of the electron transport layer is 20-100nm, and the thickness of the electrode layer is 50-120 nm.
An optoelectronic device comprising the quantum dot electroluminescent diode.
The beneficial technical effects obtained by the invention are as follows:
1. by applying the core-shell quantum dot with the directional quantitative transmission channel, the ratio of the number of the electron/hole transmission channels is effectively reduced, so that under the condition that the hole mobility of various organic micromolecules and conductive polymers is low, the ratio of the number of the electron/hole to 1 can be realized in a quantum dot light-emitting layer, namely, the carrier balance is realized, and the light-emitting efficiency of a device is improved.
2. The basic quantum dot core-shell structure based on the tetrapod morphological characteristics, which is provided by the directional quantitative transmission channel, further expands the application possibility of organic molecule/polymer hole conduction type materials.
3. By applying the quantum dot core-shell structure, the structure improvement and the device optimization with low cost can be facilitated on the premise of not introducing complex interface modification.
Drawings
The invention will be further understood from the following description in conjunction with the accompanying drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the embodiments. Like reference numerals designate corresponding parts throughout the different views.
FIG. 1 is a schematic structural diagram of a quantum dot-based core-shell structure according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a quantum dot based electroluminescent diode according to one embodiment of the present invention;
FIG. 3 is a schematic diagram of a quantum dot based electroluminescent diode according to one embodiment of the present invention;
fig. 4 is a graph comparing a quantum dot based electroluminescent diode according to an embodiment of the present invention with a prior art.
Description of reference numerals: 1-a conductive anode; 2-a hole injection layer; 3-a hole transport layer; 4-a quantum dot light emitting layer; 41-quantum dot core-shell structure; 42-a quantum dot core; 43-shell structure; 44-a first transmission channel; 45-a second transmission channel; 5-an electron transport layer; 6-electrodes.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to embodiments thereof; it should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Other systems, methods, and/or features of the present embodiments will become apparent to those skilled in the art upon review of the following detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. Additional features of the disclosed embodiments are described in, and will be apparent from, the detailed description that follows.
The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there is an orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", etc. based on the orientation or positional relationship shown in the drawings, it is only for convenience of describing the present invention and simplifying the description, but it is not intended to indicate or imply that the device or component referred to must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and are not to be construed as limiting the present patent, and the specific meaning of the terms described above will be understood by those of ordinary skill in the art according to the specific circumstances.
The invention relates to an electroluminescent diode and a photoelectric device based on quantum dots, which are explained according to the following embodiments shown in the accompanying description:
the first embodiment is as follows:
in order to expand the application possibility of organic molecules/polymer materials and achieve a carrier balance state, the charge injection path can be regulated and controlled, namely, a directional and quantitative transmission channel is introduced into a contact structure of the quantum dots and the transmission layer. The traditional spherical core-shell quantum dot cannot provide a transmission structure with the characteristics, and the core-shell quantum dot taking the most basic morphology characteristics of the tetrapods as an example realizes the functions of the structure after physical deposition film forming due to the special orientation of the shell structure, so that the realization method is simple and convenient. By applying the core-shell quantum dot, the structure improvement and the device optimization with low cost can be promoted on the premise of not introducing complex interface modification. This embodiment is explained by using the most basic quantum dots with the core-shell structure having the tetrapod morphology.
An electroluminescent diode based on quantum dots comprises a conductive anode 1, a hole injection layer 2, a hole transport layer 3, a quantum dot light-emitting layer 4, an electron transport layer 5 and an electrode 6 which are connected in sequence; the quantum dot light-emitting layer 4 comprises a plurality of quantum dot core-shell structures 41, wherein each quantum dot core-shell structure 41 comprises a quantum dot core 42 and a shell structure 43 wrapped outside the quantum dot core 42; the core-shell structure 43 has a plurality of first transmission channels 44 and a plurality of second transmission channels 45 for directional quantification, the first transmission channels 44 are connected to the hole transport layer 3, and the second transmission channels 45 are connected to the electron transport layer 5.
The number of the second transmission paths 45 is N, and the number of the first transmission paths 44 is 3N. The N second transmission channels 45 and the 3N first transmission channels 44 are uniformly distributed on the outer surface of the shell structure. Preferably, in this embodiment, N is 1, that is, there are 1 second transmission channels and 3 first transmission channels 44.
The quantum dot core-shell structure 41 comprises at least one of II-VI, I-III-VI, III-V, or IV group semiconductor core-shell structure nanocrystals. The II-VI group nanocrystalline comprises one of a homogeneous core-shell structure or a heterogeneous core-shell structure.
The diameter of the quantum dot core 42 is 1-5nm, the length of the first transmission channel 44 is 3-20nm, and the length of the second transmission channel 45 is 3-20 nm. The thickness of the conductive anode is 150-200nm, the thickness of the hole injection layer is 20-50nm, the thickness of the hole transport layer is 20-50nm, the thickness of the quantum dot light emitting layer is 20-40nm, the thickness of the electron transport layer is 20-100nm, and the thickness of the electrode layer is 50-120 nm.
An optoelectronic device comprising the quantum dot electroluminescent diode.
Example two:
an electroluminescent diode based on quantum dots comprises a conductive anode 1, a hole injection layer 2, a hole transport layer 3, a quantum dot light-emitting layer 4, an electron transport layer 5 and an electrode 6 which are sequentially connected in a stacking manner; the electrode 6 is electrically connected with the conductive anode 1 through each layer;
the conductive anode 1 is deposited on a substrate, which is connected to a base plate. The substrate is a rigid substrate or a flexible substrate, wherein the rigid substrate is glass, a silicon wafer or other rigid materials; the flexible substrate is a plastic substrate, an aluminum foil, an ultrathin metal or an ultrathin glass. The conductive anode is formed by ITO, graphene, indium gallium zinc oxide or other conductive materials and is deposited on the surface of the substrate in a sputtering, evaporation or other modes.
The conductive anode can also be one of fluorine-doped tin oxide (FTO) glass, Indium Tin Oxide (ITO) glass or one of Polyimide (PI)/FTO, polyethylene terephthalate (PET)/FTO, polyethylene naphthalate (PEN)/FTO, PI/ITO, PET/ITO and PEN/ITO flexible substrates which are combined with the substrate into a whole;
the material of the hole injection layer is selected from PEDOT/PSS, NiO and MoO3And WO3One or two of them; the hole transport layer is made of a material selected from CBP (4,4 '-bis (9-carbazole) biphenyl), TPD (N, N' -diphenyl-N, N '-bis (3-methylphenyl) -1,1' -biphenyl-4, 4 '-diamine), Poly-TPD (N, N' -diphenyl-N, N '-bis (4-methylphenyl) biphenyl-4, 4' -diamine), PVK (polyvinylcarbazole) and TFB (Poly [ (N, N '- (4-N-butylphenyl) -N, N' -diphenyl-1, 4-phenylenediamine) -ALT- (9, 9-di-N-octylfluorenyl-2, 7-diyl)]) One or two of (a);
the material of the quantum dot light-emitting layer is II-VI, I-III-VI, III-V or IV group semiconductor core-shell structure nanocrystalline; further, the quantum dot core-shell structure 41 includes at least one of group II-VI, I-III-VI, III-V, or IV semiconductor core-shell structure nanocrystals.
Further, the II-VI group nanocrystals include one of a homogeneous core-shell structure or a heterogeneous core-shell structure.
The material of the electron transport layer is TiO2ZnO nanoparticles, tris (8-hydroxyquinoline) aluminium (Alq3) or 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene (TBPi);
the electrode layer is made of one of silver, aluminum, gold, copper or ITO (indium tin oxide) and aluminum-doped zinc oxide (AZO).
The II-VI group nanocrystal is one of CdSe/CdSe, CdS/CdS, ZnCdSe/ZnCdSe, ZnCdS/ZnCdS, ZnSe/ZnSe homogeneous core-shell structures or CdSe/CdS, CdSe/ZnS, CdS/ZnS, ZnCdS/ZnS or ZnSe/ZnS heterogeneous core-shell structures; the I-III-VI family core-shell structure nanocrystal is CuInSe2/CuInS2、CuInSe2(ii) ZnS or CuInSe2(ii) ZnS; the III-V family core-shell structure nanocrystal is InP/ZnS.
The quantum dot light-emitting layer 4 comprises a plurality of quantum dot core-shell structures 41, wherein each quantum dot core-shell structure 41 comprises a quantum dot core 42 and a shell structure 43 wrapped outside the quantum dot core 42;
the core-shell structure 43 has a plurality of first transmission channels 44 and a plurality of second transmission channels 45 for directional quantification, the first transmission channels 44 are connected to the hole transport layer 3, and the second transmission channels 45 are connected to the electron transport layer 5.
Further, there are N second transmission channels 45, and 3N first transmission channels 44.
Further, the N second transmission channels 45 and the 3N first transmission channels 44 are uniformly distributed on the outer surface of the shell structure 43. In this embodiment, preferably, 1 second transmission channel 45 and 3 first transmission channels 44 are uniformly distributed on the outer surface of the shell structure 43.
The embodiment provides a preparation method of a quantum dot core-shell structure 41 with the morphology characteristics of a tetrapod, which comprises the following steps:
and step 2, wrapping the quantum dot core 42 obtained in the step 1 with the shell layer structure 43 with the morphology characteristics of a tetrapod.
The specific steps are illustrated by the preparation of a CdSe/CdS heterogeneous core-shell structure:
step 1: synthesizing CdSe quantum dot core;
(1.1) 0.1mmol of Se powder and 15mL of octadecene were charged into a 50mL flask, which was then heated to 280 ℃ and incubated for half an hour to give a clear, clear yellow solution.
(1.2) 0.1mmol of cadmium stearate and 5mL of oleic acid were mixed together in a flask, heated to 120 ℃ and 150 ℃ to give a clear solution, which was then rapidly injected into the Se solution. The reaction quickly forms a core to form CdSe nanocrystals. And after the reaction time reaches 3-10 minutes, cooling the reaction liquid to room temperature.
Step 2: coating a four-foot rack shape shell structure;
(2.1) dissolving 0.5mmol of cadmium acetate in 10mL of mixed solution (3:1) of octadecene and trioctylphosphine, and heating to 280-320 ℃ to obtain clear solution;
(2.2) injecting the CdSe core nanocrystal synthesized in the step (1) into the hot solution to grow a CdS shell with the characteristics of a tetrapod for 2-10 min. Finally obtaining the quantum dot core-shell structure with the morphological characteristics of the CdSe/CdS tetrapod.
An optoelectronic device comprising the quantum dot electroluminescent diode.
A preparation method for manufacturing the quantum dot electroluminescent diode comprises the following steps:
s1, taking the conductive anode 1 as a substrate, and preparing and forming a hole injection layer 2 on the conductive anode 1;
s2, forming a hole transport layer 3 on the hole injection layer 2;
s3, depositing the quantum dot structure 41 on the hole transport layer 3 to form a quantum dot light-emitting layer 4;
and S4, sequentially preparing and forming the electron transport layer 5 and the electrode 6 on the quantum dot light-emitting layer 4.
Further, the deposition method of the quantum dot light-emitting layer 4 is one of a spin coating method, a czochralski method, an inkjet printing method, a transfer printing method and a spray coating method. Under a physical deposition method, the core-shell quantum dots with the morphology characteristics of the tetrapods can easily form three ends of a shell layer to be in contact with a hole transport layer, one end of the shell layer is in contact with an electron transport layer, and a special light-emitting layer structure with the number ratio of hole electron transport paths being 3:1 is formed, as shown in fig. 1 and 2. Under the structure, the injection of hole electrons is more controllable, and the excessive injection of electrons can be prevented from damaging the quantum dot light-emitting layer, so that the scheme can effectively improve the light-emitting efficiency and the light-emitting stability of the quantum dot electroluminescent diode.
In the solution processing film-forming process, under the action of gravity, three branch ends of the tetrapod-shaped core-shell quantum dots are in contact with the hole transport layer below to form 3 hole transport channels, namely the first transport channel 44, and the remaining branch end shell layer faces upwards to be in contact with the electron transport layer deposited later to form 1 electron transport channel, namely the second transport channel 45. Such a cavity: compared with the structure of an electron transport channel, the structure provides great convenience for the selection of hole injection and transport materials. In addition, in order to avoid the situation that the charge transmission efficiency is low or the coating effect is not good, the invention strictly regulates the length of the shell layer of the tetrapod and can exert the length of the branch end of the shell layer within a proper range to the maximum extent.
In a preferred embodiment of this embodiment, the diameter of the quantum dot core 42 is 1-5nm, the length of the first transmission channel 44 is 3-20nm, and the length of the second transmission channel 45 is 3-20 nm.
In a preferred embodiment of this embodiment, the thickness of the conductive anode is 150-200nm, the thickness of the hole injection layer is 20-50nm, the thickness of the hole transport layer is 20-50nm, the thickness of the quantum dot light emitting layer is 20-40nm, the thickness of the electron transport layer is 20-100nm, and the thickness of the electrode layer is 50-120 nm. In the present embodiment, the thickness of the quantum dot light emitting layer is preferably 30 nm.
The problem that carrier balance cannot be realized by matching the mobility characteristics of a hole-electron transport material because the electron transport of an electroluminescent device is much faster than the hole transport is solved by a strictly controlled transport channel ratio (hole: electron: 3: 1). Under the guidance of the embodiment, the selection range of organic molecules/polymers can be greatly widened, and good physical basic conditions and structural environments are provided for realizing the carrier balance of the device. In addition, the quantum dot light-emitting layer film is prepared by a solution processing method, has simple and feasible process, is compatible with the current industrial processes such as ink-jet printing, transfer printing and the like, has simple operation, does not need to introduce complicated interface engineering, and can greatly promote the application of quantum dot electroluminescent diodes.
Example three:
an electroluminescent diode based on quantum dots comprises a conductive anode 1, a hole injection layer 2, a hole transport layer 3, a quantum dot light-emitting layer 4, an electron transport layer 5 and an electrode 6 which are sequentially connected in a stacking manner; the electrode 6 is electrically connected with the conductive anode 1 through each layer;
the conductive anode 1 is deposited on a substrate, which is connected to a base plate. The substrate is a rigid substrate or a flexible substrate, wherein the rigid substrate is glass, a silicon wafer or other rigid materials; the flexible substrate is a plastic substrate, an aluminum foil, an ultrathin metal or an ultrathin glass. The conductive anode is formed by ITO, graphene, indium gallium zinc oxide or other conductive materials and is deposited on the surface of the substrate in a sputtering, evaporation or other modes.
The conductive anode can also be one of fluorine-doped tin oxide (FTO) glass, Indium Tin Oxide (ITO) glass or one of Polyimide (PI)/FTO, polyethylene terephthalate (PET)/FTO, polyethylene naphthalate (PEN)/FTO, PI/ITO, PET/ITO and PEN/ITO flexible substrates which are combined with the substrate into a whole;
the material of the hole injection layer is selected from PEDOT/PSS, NiO and MoO3And WO3One or two of them; the hole transport layer is made of a material selected from CBP (4,4 '-bis (9-carbazole) biphenyl), TPD (N, N' -diphenyl-N, N '-bis (3-methylphenyl) -1,1' -biphenyl-4, 4 '-diamine), Poly-TPD (N, N' -diphenyl-N, N '-bis (4-methylphenyl) biphenyl-4, 4' -diamine), PVK (polyvinylcarbazole) and TFB (Poly [ (N, N '- (4-N-butylphenyl) -N, N' -diphenyl-1, 4-phenylenediamine) -ALT- (9, 9-di-N-octylfluorenyl-2, 7-diyl)]) One or two of (a);
the material of the quantum dot light-emitting layer is II-VI, I-III-VI, III-V or IV group semiconductor core-shell structure nanocrystalline; further, the quantum dot core-shell structure 41 includes at least one of group II-VI, I-III-VI, III-V, or IV semiconductor core-shell structure nanocrystals.
Further, the II-VI group nanocrystals include one of a homogeneous core-shell structure or a heterogeneous core-shell structure.
The material of the electron transport layer is TiO2ZnO nanoparticles, tris (8-hydroxyquinoline) aluminium (Alq3) or 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene (TBPi);
the electrode layer is made of one of silver, aluminum, gold, copper or ITO (indium tin oxide) and aluminum-doped zinc oxide (AZO).
As shown in fig. 2 and fig. 3, the quantum dot core-shell structure is divided into a homogeneous core-shell structure and a heterogeneous core-shell structure, and the core-shell structure is composed of the following materials: the II-VI group nanocrystal is one of CdSe/CdSe, CdS/CdS, ZnCdSe/ZnCdSe, ZnCdS/ZnCdS, ZnSe/ZnSe homogeneous core-shell structures or CdSe/CdS, CdSe/ZnS, CdS/ZnS, ZnCdS/ZnS or ZnSe/ZnS heterogeneous core-shell structures; the I-III-VI family core-shell structure nanocrystal is CuInSe2/CuInS2、CuInSe2(ii) ZnS or CuInSe2(ii) ZnS; the III-V family core-shell structure nanocrystal is InP/ZnS.
The quantum dot light-emitting layer 4 comprises a plurality of quantum dot core-shell structures 41, wherein each quantum dot core-shell structure 41 comprises a quantum dot core 42 and a shell structure 43 wrapped outside the quantum dot core 42;
the core-shell structure 43 has a plurality of first transmission channels 44 and a plurality of second transmission channels 45 for directional quantification, the first transmission channels 44 are connected to the hole transport layer 3, and the second transmission channels 45 are connected to the electron transport layer 5.
Further, there are N second transmission channels 45, and 3N first transmission channels 44.
Further, the N second transmission channels 45 and the 3N first transmission channels 44 are uniformly distributed on the outer surface of the shell structure 43. In this embodiment, preferably, 1 second transmission channel 45 and 3 first transmission channels 44 are uniformly distributed on the outer surface of the shell structure 43.
The embodiment provides a preparation method of a quantum dot core-shell structure 41 with the morphology characteristics of a tetrapod, which comprises the following steps:
and step 2, wrapping the quantum dot core 42 obtained in the step 1 with the shell layer structure 43 with the morphology characteristics of a tetrapod.
The specific steps are illustrated by the preparation of a CdSe/CdS heterogeneous core-shell structure:
step 1: synthesizing CdSe quantum dot core;
(1.1) 0.1mmol of Se powder and 15mL of octadecene were charged into a 50mL flask, which was then heated to 280 ℃ and incubated for half an hour to give a clear, clear yellow solution.
(1.2) 0.1mmol of cadmium stearate and 5mL of oleic acid were mixed together in a flask, heated to 120 ℃ and 150 ℃ to give a clear solution, which was then rapidly injected into the Se solution. The reaction quickly forms a core to form CdSe nanocrystals. And after the reaction time reaches 3-10 minutes, cooling the reaction liquid to room temperature.
Step 2: coating a four-foot rack shape shell structure;
(2.1) dissolving 0.5mmol of cadmium acetate in 10mL of mixed solution (3:1) of octadecene and trioctylphosphine, and heating to 280-320 ℃ to obtain clear solution;
(2.2) injecting the CdSe core nanocrystal synthesized in the step (1) into the hot solution to grow a CdS shell with the characteristics of a tetrapod for 2-10 min. Finally obtaining the quantum dot core-shell structure with the morphological characteristics of the CdSe/CdS tetrapod.
An optoelectronic device comprising the quantum dot electroluminescent diode.
A preparation method for manufacturing the quantum dot electroluminescent diode comprises the following steps:
s1, taking the conductive anode 1 as a substrate, and preparing and forming a hole injection layer 2 on the conductive anode 1;
specifically, the method comprises the following steps of carrying out substrate pretreatment: firstly, acetone or isopropylamine is adopted on the conductive anode 1 to easily carry out ultrasonic cleaning; then heating and baking are carried out, the heating temperature is 120-; then transferring the conductive anode 1 into a plasma cleaning machine, and introducing Ar/O2 gas under the radio frequency action of 13.56MHZ to carry out organic matter removal treatment on the conductive anode, wherein the treatment time is 10-20 min;
coating a layer of PEDOT and PSS mixed solution on the pretreated conductive anode 1, spin-coating for 1-3min at 4500rpm, and then heating to 120-150 ℃ to form a PEDOT and PSS uniform film with the thickness of 30nm, namely the hole injection layer 2;
s2, forming a hole transport layer 3 on the hole injection layer 2;
specifically, a mixed solution of PVK (polyvinylcarbazole) and chlorotoluene is spin-coated on the hole injection layer 2, and the mixed solution is heated to 150 ℃ and 200 ℃ to form a PVK polymer film with the thickness of 20nm, namely the hole transport layer 3;
s3, depositing the quantum dot structure 41 on the hole transport layer 3 to form a quantum dot light-emitting layer 4;
specifically, the prepared quantum dot structure 41 is spin-coated on the hole transport layer 3 to form the quantum light emitting layer 4 with the thickness of 30 nm;
s4, preparing and forming the electron transport layer 5 and the electrode 6 on the quantum dot light-emitting layer 4 in sequence;
specifically, the electron transport layer 5 with the thickness of 30nm is formed on the quantum dot light-emitting layer 4 through deposition by a sol-gel method, and the electron transport layer 5 is made of ZnO nanoparticles; and then forming the electrode 6 with the thickness of 120nm on the electron transport layer 5 through vacuum thermal evaporation deposition, wherein the electrode 6 is made of Al, and the electrode 6 is electrically connected with the conductive anode 1.
Under a physical deposition method, the core-shell quantum dots with the morphology characteristics of the tetrapods can easily form three ends of a shell layer to be in contact with a hole transport layer, one end of the shell layer is in contact with an electron transport layer, and a special light-emitting layer structure with the number ratio of hole electron transport paths being 3:1 is formed, as shown in fig. 1 and 2. Under the structure, the injection of hole electrons is more controllable, and the excessive injection of electrons can be prevented from damaging the quantum dot light-emitting layer, so that the scheme can effectively improve the light-emitting efficiency and the light-emitting stability of the quantum dot electroluminescent diode.
In the solution processing film-forming process, under the action of gravity, three branch ends of the tetrapod-shaped core-shell quantum dots are in contact with the hole transport layer below to form 3 hole transport channels, namely the first transport channel 44, and the remaining branch end shell layer faces upwards to be in contact with the electron transport layer deposited later to form 1 electron transport channel, namely the second transport channel 45. Such a cavity: compared with the structure of an electron transport channel, the structure provides great convenience for the selection of hole injection and transport materials. In addition, in order to avoid the situation that the charge transmission efficiency is low or the coating effect is not good, the invention strictly regulates the length of the shell layer of the tetrapod and can exert the length of the branch end of the shell layer within a proper range to the maximum extent.
In a preferred embodiment of this embodiment, the diameter of the quantum dot core 42 is 1-5nm, the length of the first transmission channel 44 is 3-20nm, and the length of the second transmission channel 45 is 3-20 nm.
In a preferred embodiment of this embodiment, the thickness of the conductive anode is 150-200nm, the thickness of the hole injection layer is 20-50nm, the thickness of the hole transport layer is 20-50nm, the thickness of the quantum dot light emitting layer is 20-40nm, the thickness of the electron transport layer is 20-100nm, and the thickness of the electrode layer is 50-120 nm. In this embodiment, it is more preferable that the thickness of the hole injection layer is 30nm, the thickness of the hole transport layer is 20nm, the thickness of the quantum dot light emitting layer is preferably 30nm, the thickness of the electron transport layer is 30nm, and the thickness of the electrode layer is 120 nm.
The problem that carrier balance cannot be realized through material selection because the electron mobility of the oxide is far higher than the hole mobility of organic molecules/polymers is solved through a strictly controlled transport channel ratio (the hole: electron is 3: 1). Under the guidance of the embodiment, the selection range of organic molecules/polymers can be greatly widened, and good physical basic conditions and structural environments are provided for realizing the carrier balance of the device. In addition, the quantum dot light-emitting layer film is prepared by a solution processing method, has simple and feasible process, is compatible with the current industrial processes such as ink-jet printing, transfer printing and the like, has simple operation, does not need to introduce complicated interface engineering, and can greatly promote the application of quantum dot electroluminescent diodes.
As shown in fig. 4(a), it is a J-V characteristic curve of a single electron and single hole device prepared based on the conventional spherical core-shell quantum dot in the prior art. Wherein the electron transport layer is made of ZnO, and the hole injection/transport layer is made of organic molecules/polymers. As can be seen from the figure, the electron transport current density is much higher than the hole transport current density, causing a severe charge imbalance in the light emitting device;
as shown in fig. 4(b), the J-V characteristic curve of the one-electron and one-hole device prepared by the core-shell quantum dot based on the tetrapod morphology features in this embodiment is shown. Similarly, the electron transport layer is made of ZnO, and the hole injection/transport layer is made of organic molecules/polymers;
as can be seen from fig. 4, the transport injection levels of holes and electrons are substantially equivalent by the hole/electron transport channel ratio of 3:1, and the carrier balance is greatly improved, which has an important role in the light efficiency and stability of the light emitting device.
In summary, the invention provides an electroluminescent diode and a photoelectric device based on quantum dots, which effectively reduce the ratio of the number of electron/hole transport channels by using the core-shell quantum dots with directional quantitative transport channels, so that the injection balance of carriers is easier to form in a light emitting device, the light emitting efficiency is improved, and the basic quantum dot core-shell structure based on the tetrapod morphological characteristics, which is proposed based on the directional quantitative transport channels, is used to expand the application possibility of organic molecules/polymer materials. Although the invention has been described above with reference to various embodiments, it should be understood that many changes and modifications may be made without departing from the scope of the invention. That is, the methods, systems, and devices discussed above are examples. Various configurations may omit, substitute, or add various procedures or components as appropriate. For example, in alternative configurations, the methods may be performed in an order different than that described, and/or various components may be added, omitted, and/or combined. Moreover, features described with respect to certain configurations may be combined in various other configurations, as different aspects and elements of the configurations may be combined in a similar manner. Further, elements therein may be updated as technology evolves, i.e., many elements are examples and do not limit the scope of the disclosure or claims.
Specific details are given in the description to provide a thorough understanding of the exemplary configurations including implementations. However, configurations may be practiced without these specific details, e.g., well-known circuits, processes, algorithms, structures, and techniques have been shown without unnecessary detail in order to avoid obscuring the configurations. This description provides example configurations only, and does not limit the scope, applicability, or configuration of the claims. Rather, the foregoing description of the configurations will provide those skilled in the art with an enabling description for implementing the described techniques. Various changes may be made in the function and arrangement of elements without departing from the spirit or scope of the disclosure.
It is intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention. The above examples are to be construed as merely illustrative and not limitative of the remainder of the disclosure. After reading the description of the invention, the skilled person can make various changes or modifications to the invention, and these equivalent changes and modifications also fall into the scope of the invention defined by the claims.
Claims (6)
1. An electroluminescent diode based on quantum dots comprises a conductive anode, a hole injection layer, a hole transport layer, a quantum dot light emitting layer, an electron transport layer and an electrode which are sequentially connected; the quantum dot light-emitting layer is characterized by comprising a plurality of quantum dot core-shell structures, wherein each quantum dot core-shell structure comprises a quantum dot core and a shell structure wrapping the quantum dot core;
the shell structure is provided with a plurality of first transmission channels and a plurality of second transmission channels for directional quantification, the first transmission channels are connected to the hole transmission layer, and the second transmission channels are connected to the electron transmission layer;
the number of the second transmission channels is N, and the number of the first transmission channels is 3N;
the N second transmission channels and the 3N first transmission channels are uniformly distributed on the outer surface of the shell structure, the length of each first transmission channel is 3-20nm, and the length of each second transmission channel is 3-20 nm.
2. A quantum dot based electroluminescent diode as claimed in claim 1 wherein the quantum dot core-shell structure comprises at least one of group II-VI, I-III-VI, III-V, or IV semiconductor core-shell structure nanocrystals.
3. The quantum dot-based electroluminescent diode of claim 2, wherein the group II-VI nanocrystals comprise one of a homogeneous core-shell structure or a heterogeneous core-shell structure.
4. A quantum dot based electroluminescent diode as claimed in claim 1 wherein the quantum dot core diameter is 1 to 5 nm.
5. The quantum dot-based electroluminescent diode as claimed in claim 1, wherein the conductive anode has a thickness of 150-200nm, the hole injection layer has a thickness of 20-50nm, the hole transport layer has a thickness of 20-50nm, the quantum dot light emitting layer has a thickness of 20-40nm, the electron transport layer has a thickness of 20-100nm, and the electrode layer has a thickness of 50-120 nm.
6. An optoelectronic device comprising a quantum dot based electroluminescent diode according to any one of claims 1 to 5.
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