CN114695694A - Quantum dot light-emitting diode and preparation method thereof - Google Patents
Quantum dot light-emitting diode and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a quantum dot light-emitting diode and a preparation method thereof. The quantum dot light emitting diode includes: the quantum dot light-emitting diode comprises an anode, a quantum dot light-emitting layer arranged on the anode and a cathode arranged on the quantum dot light-emitting layer; the spacing of the quantum dots in the quantum dot light-emitting layer in a first direction is greater than the spacing in a second direction; or the spacing of the quantum dots in the first direction is greater than 0.1nm and less than or equal to 20nm, and the spacing of the quantum dots in the second direction is greater than 0.1nm and less than or equal to 20 nm; wherein the first direction and the second direction are perpendicular to each other. The invention can avoid the phenomenon of luminous red shift caused by the close packing of quantum dots, thereby improving the color performance of the quantum dot light-emitting diode.
Description
Technical Field
The invention relates to the technical field of quantum dots, in particular to a quantum dot light-emitting diode and a preparation method thereof.
Background
Quantum dots are nanocrystalline particles with a radius that is smaller than or close to the bohr exciton radius. The quantum dots have quantum confinement effect and can emit fluorescence after being excited. And the quantum dots have unique luminescence characteristics, such as wide excitation peak, narrow emission peak, adjustable luminescence spectrum and the like, so that the quantum dots have wide application prospect in the field of photoelectric luminescence.
The quantum dot light emitting diode is a device using colloidal quantum dots as a light emitting layer, and the light emitting layer is introduced between different conductive materials to obtain light with required wavelength. The quantum dot light emitting diode has the advantages of high color gamut, self-luminescence, low starting voltage, high response speed and the like. However, in the application process of the quantum dot light emitting diode, the problem that the red shift of the light emitting wavelength is easy to occur exists, and the color gamut of the display device based on the quantum dot light emitting diode is further influenced.
Accordingly, the prior art is yet to be improved and developed.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, the present invention is directed to a quantum dot light emitting diode and a method for manufacturing the same, which is intended to solve the problem of red shift of emission wavelength when a quantum dot light emitting layer emits light in the quantum dot light emitting diode.
A quantum dot light-emitting diode comprises an anode, a cathode and a quantum dot light-emitting layer arranged between the anode and the cathode, wherein the interval of quantum dots in the quantum dot light-emitting layer in a first direction is larger than the interval in a second direction;
or the spacing of the quantum dots in the first direction is more than 0.1nm and less than or equal to 20nm, and the spacing of the quantum dots in the second direction is more than 0.1nm and less than or equal to 20 nm;
wherein the first direction and the second direction are perpendicular to each other.
The quantum dot light-emitting diode is characterized in that when the distance between quantum dots in the quantum dot light-emitting layer in the first direction is larger than that in the second direction, the distance between the quantum dots in the first direction is 5-20 nm, and the distance between the quantum dots in the second direction is 0.1-1 nm.
The quantum dot light-emitting diode, wherein when the distance between the quantum dots in the first direction and the distance between the quantum dots in the second direction are both greater than 0.1nm and less than or equal to 20nm, the distance between the quantum dots in the first direction and the distance between the quantum dots in the second direction are equal.
The quantum dot light emitting diode, wherein the quantum dot light emitting diode further comprises: a barrier layer disposed between the anode and the quantum dot light emitting layer for reducing leakage current.
The quantum dot light-emitting diode is characterized in that the band gap of the material of the barrier layer is more than or equal to 3 eV.
The quantum dot light-emitting diode is characterized in that the barrier layer material is selected from one or more of polymethyl methacrylate and polyvinylpyrrolidone.
A method for preparing a quantum dot light-emitting diode comprises the following steps:
providing an anode;
forming a quantum dot light emitting layer on the anode;
forming a cathode on the quantum dot light emitting layer;
alternatively, a cathode is provided;
forming a quantum dot light emitting layer on the cathode;
forming an anode on the quantum dot light emitting layer;
wherein the interval of the quantum dots in the quantum dot light-emitting layer in the first direction is larger than the interval in the second direction, or the interval of the quantum dots in the first direction and the interval in the second direction are both larger than 0.1nm and less than or equal to 20nm, wherein the first direction and the second direction are perpendicular to each other.
The preparation method of the quantum dot light-emitting diode comprises the following steps:
depositing quantum dots on a substrate, and stretching the substrate to form a quantum dot light-emitting layer;
transferring the quantum dot light emitting layer onto the anode or the cathode.
The preparation method of the quantum dot light-emitting diode is characterized in that the stretching of the substrate comprises the following steps:
stretching the substrate in a first direction;
alternatively, the substrate is stretched in both the first direction and the second direction.
The preparation method of the quantum dot light-emitting diode is characterized in that the temperature for stretching the substrate is a preset stretching temperature;
the preset stretching temperature is greater than or equal to the glass transition temperature of the substrate.
Has the beneficial effects that: the distance in the first direction is larger than the distance in the second direction, so that the accumulation of the quantum dots in the first direction is reduced, or the distance of the quantum dots in the first direction and the distance of the quantum dots in the second direction are both larger than 0.1nm, so that the accumulation of the quantum dots in the first direction and the second direction is reduced, the phenomenon of light-emitting red shift caused by the close accumulation of the quantum dots can be avoided, and the color performance of the quantum dot light-emitting diode is improved.
Drawings
Fig. 1 is a schematic diagram of quantum dot arrangement mode in a close-packed quantum dot light-emitting layer prepared by a spin coating method.
Fig. 2 is a schematic diagram of quantum dots arranged in rows to form a quantum dot grating in the embodiment of the present invention.
Fig. 3 is a schematic diagram of quantum dots arranged at intervals to form a quantum dot interval lattice in the embodiment of the present invention.
Fig. 4 is a schematic structural diagram of a qd-led in an embodiment of the present invention.
Fig. 5 is a schematic structural diagram of another quantum dot light-emitting diode in an embodiment of the invention.
Fig. 6 is a flow chart of manufacturing a quantum dot light emitting diode according to an embodiment of the invention.
Fig. 7 is a schematic diagram of a process of forming a quantum dot grating by stretching a substrate according to an embodiment of the present invention.
Fig. 8 is a schematic diagram of a stamp adsorption process in the embodiment of the present invention.
FIG. 9 is a schematic diagram illustrating a stamping process according to an embodiment of the present invention.
Fig. 10 is a schematic structural diagram of a device after a quantum dot light-emitting layer is transferred to a barrier layer in the embodiment of the present invention.
Detailed Description
The invention provides a quantum dot light-emitting diode and a preparation method thereof, and the invention is further described in detail below in order to make the purpose, technical scheme and effect of the 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.
In the current preparation of quantum dot light-emitting diodes, a quantum dot light-emitting layer is generally prepared by adopting a spin coating method, quantum dot particles are dispersed in a solution and then directly spin-coated on the surface of a device, and after drying, the quantum dots form a film in a close-packed manner, so that the close-packed quantum dot light-emitting layer shown in fig. 1 is obtained, wherein the distance between the quantum dots in the quantum dot light-emitting layer is less than or equal to 0.1 nm.
Researches show that when the quantum dots of the densely packed quantum dot light emitting layer are closer, a stronger energy resonance transfer phenomenon can occur during light emitting, so that the light emitting wavelength is red-shifted, and the color gamut of a display device based on the quantum dot light emitting diode is influenced. Moreover, when the quantum dot light-emitting diode works, the quantum dots can be charged, the density of the equivalent quantum dots is too high, the charge density of the quantum dot light-emitting layer is high, the electric field intensity is high, auger recombination is obvious, the efficiency of the quantum dot light-emitting diode is reduced, the material aging is aggravated, and the service life of the quantum dot light-emitting diode is shortened.
With reference to fig. 2 to 4, an embodiment of the present invention provides a quantum dot light emitting diode, which includes an anode 1, a cathode 7, and a quantum dot light emitting layer 5 disposed between the anode 1 and the cathode 7, where a distance between quantum dots in the quantum dot light emitting layer 5 in a first direction is greater than a distance between quantum dots in a second direction, for the purpose of avoiding red shift of light emitting wavelength and obvious auger recombination of quantum dots in the quantum dot light emitting diode;
or the spacing of the quantum dots in the first direction is greater than 0.1nm and less than or equal to 20nm, and the spacing of the quantum dots in the second direction is greater than 0.1nm and less than or equal to 20 nm;
wherein the first direction and the second direction are perpendicular to each other.
The pitch refers to a distance (a gap distance between two adjacent quantum dots) between two adjacent quantum dots, that is, a shortest distance between an edge of one quantum dot and an edge of an adjacent quantum dot. For example, the quantum dots are spherical quantum dots, and the distance is the shortest distance between two adjacent quantum dot spheres.
Compared with the prior art that the quantum dots are closely stacked in both the first direction and the second direction in the close-packed quantum dot light-emitting layer 5, the interval of the quantum dots in the first direction is larger than that in the second direction, so that the interval of the quantum dots in the first direction is increased relative to that in the second direction, the packing of the quantum dots in the first direction can be reduced, the phenomenon of red shift of light emission caused by the close-packed quantum dots can be avoided, and the color performance of the quantum dot light-emitting diode is improved. When the quantum dot light-emitting diode works, the problem that the charge density of the quantum dot light-emitting layer 5 is high due to the fact that the density of the quantum dots is too high can be avoided, the purpose of reducing Auger recombination is achieved, the efficiency of the quantum dot light-emitting diode is improved, the aging of materials is slowed down, and the service life of the quantum dot light-emitting diode is prolonged.
The interval of quantum dot on the first direction and the interval in the second direction all are greater than 0.1nm, make quantum dot have and have great interval in first direction and second direction, can avoid because the luminous red-shift phenomenon that quantum dot close-packed leads to, have improved quantum dot emitting diode's color performance. When the quantum dot light-emitting diode works, the problem that the charge density of the quantum dot light-emitting layer 5 is high due to the fact that the density of the quantum dots is too high can be avoided, the purpose of reducing Auger recombination is achieved, the efficiency of the quantum dot light-emitting diode is improved, the aging of materials is slowed down, and the service life of the quantum dot light-emitting diode is prolonged.
For example, the first direction is a transverse direction (left-right direction), the second direction is a longitudinal direction (front-back direction), and the gap width between a quantum dot and a left-side or right-side adjacent quantum dot in the quantum dot light-emitting layer 5 (the pitch of the quantum dot in the left-right direction) is larger than the gap width between a quantum dot and a front-side or back-side adjacent quantum dot (the pitch of the quantum dot in the front-back direction). The gap width between the quantum dots and the left or right adjacent quantum dots in the quantum dot light-emitting layer 5 is greater than 0.1nm, and compared with the gap of the existing densely-packed quantum dots being less than or equal to 0.1nm, the gap of the quantum dots in the left and right directions is increased, the arrangement density (the number of the quantum dots in a unit area) of the quantum dots is reduced, and the phenomenon of red shift of light emission caused by the close packing of the quantum dots can be effectively avoided.
Referring to fig. 2, when the distance between the quantum dots in the quantum dot light emitting layer 5 in the first direction is greater than the distance between the quantum dots in the second direction, the quantum dots in the quantum dot light emitting layer 5 of the present invention may implement linear arrangement of the quantum dots, so as to form a quantum dot grating. Specifically, the quantum dots are arranged in an end-to-end connection manner to form a plurality of lines due to the small distance between the quantum dots in the front-back direction, and the quantum dots are arranged in a left-right direction to form a slit between two adjacent lines due to the large distance between the quantum dots, so that a grating is formed. The quantum dots which are arranged in a linear shape are opaque parts of the grating, and a gap between two adjacent lines is a light-transmitting slit of the grating. The linear arrangement can be irregular curve arrangement or regular straight line arrangement. The linear arrangement of the quantum dots can also be called as the quantum dots are arranged in rows, that is, the quantum dots are arranged in a plurality of rows.
In one embodiment of the present invention, the quantum dot grating is formed such that the quantum dots are spaced apart from each other in the first direction and arranged in a line in the second direction, when the pitch of the quantum dots in the first direction is large and the pitch of the quantum dots in the second direction is small, and optionally, the pitch of the quantum dots in the first direction is 5nm to 20nm and the pitch of the quantum dots in the second direction is 0.1 nm. Specifically, the spacing between the quantum dots in the first direction may be 6nm, 10nm or 15nm, and the spacing between the quantum dots in the second direction may be 0.1-1 nm.
For example, for the quantum dots arranged in rows to form the quantum dot grating, the spacing between the quantum dots in the same row is smaller, specifically, the spacing between the adjacent quantum dots in the same row is 0.1 to 1nm, such as 0.5 nm; and the quantum dot spacing between two adjacent rows (spacing between two rows) is larger, specifically, the spacing between two adjacent rows is 15-20 nm, such as 18 nm.
Moreover, the quantum dots are arranged to form a grating, and the luminous efficiency and the visual angle of the device can be improved. Specifically, the quantum dots are arranged in the light emitting diode to form a quantum dot grating, and the quantum dot grating has a light splitting effect, so that emergent light can be uniformly distributed in a larger angle, and the visual angle is improved; the quantum dot grating can generate a coupling effect, so that the light extraction rate can be improved, and the light emitting efficiency is improved.
Referring to fig. 3, the quantum dots in the quantum dot light emitting layer 5 are arranged at intervals to form a quantum dot interval lattice, specifically, the quantum dots are spaced to form independent quantum dots, that is, the quantum dots are not in contact with neighboring quantum dots, but are spaced to distribute. That is, compared with the existing close-packed quantum dots, the quantum dots are separated from each other by a certain distance, so that the distance between the quantum dots is increased, the phenomenon of red shift of the light-emitting wavelength caused by close-packed quantum dots is avoided, and the color performance of the quantum dot light-emitting diode is improved.
For the quantum dots arranged at intervals to form the quantum dot interval lattice, the adjacent quantum dots are separated by a certain distance, and specifically, the quantum dots may be uniformly distributed, that is, the quantum dots may have the same pitch with the adjacent quantum dots around. In an embodiment of the present invention, the pitch in the first direction is the same as the pitch in the second direction, optionally, the pitch in the first direction and the pitch in the second direction are both 1nm to 20nm, for example, the pitch in the first direction and the pitch in the second direction are both 5nm, 10nm, or 15 nm. The quantum dots are arranged at the same interval and at a larger interval, so that a uniform quantum dot interval lattice is formed. Therefore, compared with the existing quantum dots which are densely packed, the quantum dot light-emitting diode disclosed by the invention can reduce the light-emitting red shift phenomenon caused by energy resonance transfer among the quantum dots, and improves the color performance of the quantum dot light-emitting diode. In addition, the quantum dot light-emitting diode increases the quantum dot gap, effectively reduces the charge density of the quantum dot light-emitting layer 5, reduces Auger recombination and material aging, and improves the efficiency and the service life of the quantum dot light-emitting diode.
The distance between the quantum dots in the quantum dot light-emitting layer in the first direction is larger than or equal to the distance between the quantum dots in the second direction, wherein the distance between the quantum dots in the first direction is larger than 0.1nm and smaller than or equal to 20nm, the red shift phenomenon of the light-emitting wavelength caused by the close packing of the quantum dots can be avoided, and the color performance of the quantum dot light-emitting diode is improved.
In one embodiment of the present invention, the quantum dots include, but are not limited to, nanocrystals of II-VI semiconductors such as CdS quantum dots, CdSe quantum dots, CdTe quantum dots; the quantum dots may also be perovskite quantum dots or the like. Optionally, the diameter (size) of the quantum dots is 3-20 nm.
Referring to fig. 5, in an embodiment of the present invention, the quantum dot light emitting diode further includes: and a barrier layer 4 (electron barrier layer) arranged between the anode 1 and the quantum dot light-emitting layer 5. In the invention, the quantum dot interval is large, which may cause the leakage current of the quantum dot light-emitting diode to increase, and influence the device performance of the quantum dot light-emitting diode. The leakage current of the quantum dot light-emitting diode is reduced by arranging a barrier layer 4 between the anode 1 and the quantum dot light-emitting layer 5 (between HTL/QD).
In order to achieve the blocking effect of the blocking layer 4 for electrons, the blocking layer material needs to satisfy a certain band gap and a conduction band top level (LOMO level). In one embodiment of the present invention, the band gap of the barrier layer material is not less than (not less than) 3eV, such as 3-10 eV, and the band gap of the barrier layer material is not less than-2 eV, such as-2-1 eV.
In one embodiment of the present invention, the barrier material has a certain adsorptivity to the quantum dots, which facilitates the transfer of the quantum dots during the preparation process. Optionally, the barrier layer material is one or more of polymethyl methacrylate (PMMA), polyvinylpyrrolidone (PVP).
In the invention, the quantum dot spacing is increased, the barrier layer 4 is too thin to effectively block electrons, so that the electrons can directly tunnel to the hole side, the efficiency of the quantum dot light-emitting diode is reduced, the conductivity of the device is poor due to too thick quantum dot light-emitting diode, and the performance of the device is poor due to the reduction of hole injection. In one embodiment of the present invention, the thickness of the barrier layer 4 is 0.1 to 5 nm.
In one embodiment of the present invention, in order to improve device performance of a quantum dot light emitting diode, the quantum dot light emitting diode further includes: a hole function layer located between the anode 1 layer and the barrier layer 4; and the electronic function layer is positioned between the quantum dot light-emitting layer 5 and the cathode 7 layer. Specifically, the hole function comprises a hole injection layer 2 and a hole transport layer 3, wherein the hole injection layer 2 is positioned on the anode 1 layer, and the hole transport layer 3 is positioned on the hole injection layer 2; the electron functional layer comprises an electron transport functional layer.
Compared with the existing quantum dot light-emitting layer 5 which is densely packed, in the quantum dot light-emitting layer 5 provided by the invention, quantum dots form the quantum dot light-emitting layer 5 at a larger interval, so that the light-emitting red shift phenomenon caused by energy resonance transfer among the quantum dots can be reduced, and the effects of reducing Auger recombination and reducing material aging are realized.
Referring to fig. 6, a method for manufacturing a quantum dot light emitting diode according to an embodiment of the present invention includes: preparing a front functional layer, transferring a quantum dot light-emitting layer 5, and preparing a rear functional layer; the preparation of the quantum dot light-emitting layer 5 comprises the following steps: depositing quantum dots on the substrate 8 to prepare a quantum dot substrate 8; and stretching the quantum dot substrate 8 to obtain the quantum dot light-emitting layer 5 formed on the substrate 8. In one embodiment of the present invention, a method for manufacturing a quantum dot light emitting diode includes:
s101, providing an anode 1;
s201, forming a quantum dot light-emitting layer 5 on the anode 1;
s301, forming a cathode 7 on the quantum dot light emitting layer 5;
alternatively, S102, providing the cathode 7;
s202, forming a quantum dot light-emitting layer 5 on the cathode 7;
s302, forming an anode 1 on the quantum dot light-emitting layer 5;
wherein the interval of the quantum dots in the quantum dot light-emitting layer in the first direction is larger than that in the second direction, or the interval of the quantum dots in the first direction is larger than 0.1nm and less than or equal to 20nm, and the interval of the quantum dots in the second direction is larger than 0.1nm and less than or equal to 20nm, wherein the first direction and the second direction are perpendicular to each other.
Compared with the prior art of preparing the close-packed quantum dots, the interval of the quantum dots in the quantum dot light-emitting layer 5 in the first direction is larger than that in the second direction, or the interval of the quantum dots in the first direction and the interval of the quantum dots in the second direction are both larger than 0.1nm and less than or equal to 20nm, so that the gap of the quantum dots in the first direction is increased, the accumulation (arrangement) of the quantum dots is reduced, the phenomenon of light-emitting red shift caused by close-packed quantum dots can be avoided, and the color performance of the quantum dot light-emitting diode is improved. When the quantum dot light-emitting diode prepared based on the preparation method works, the problem that the charge density of the quantum dot light-emitting layer 5 is high due to the fact that the density of the quantum dots is too high can be avoided, and the effects of reducing Auger recombination, improving the efficiency of the quantum dot light-emitting diode, slowing down material aging and prolonging the service life of the quantum dot light-emitting diode are achieved.
Referring to fig. 7 to 10, in an embodiment of the present invention, the method for forming the quantum dot light emitting layer 5 includes:
s211, depositing the quantum dots on a substrate 8, and stretching the substrate 8 to form a quantum dot light-emitting layer 5;
s221, transferring the quantum dot light-emitting layer 5 to the anode 1 or the cathode 7.
In the embodiment of the invention, the quantum dot light emitting diode is prepared by increasing the interval between quantum dots in the quantum dot light emitting layer 5 by stretching the substrate and transferring the quantum dot light emitting layer 5 to the anode 1 or the cathode 7. Therefore, the method for combining stretching and transferring of the substrate can increase the distance of the quantum dots in the stretching direction, and cannot damage other functional layers and influence the performance of other functional layers.
In one embodiment of the present invention, the S211 includes:
s2111, stretching the substrate in a first direction;
alternatively, S2112, stretching the substrate in the first direction and the second direction.
The S2111 stretches the substrate 8 in the first direction, so that the pitch of the quantum dots in the first direction is increased, and the pitch in the second direction is maintained. That is, the S2111 unidirectionally stretches the substrate to form quantum dot linear arrangement, thereby obtaining the quantum dot grating. Optionally, in S2111 of the embodiment of the present invention, the quantum dots may be deposited on the substrate 8, and the substrate 8 is heated and then transversely stretched, so that the transverse distance between the quantum dots on the substrate 8 is increased, and the quantum dot light emitting layer 5 in which the quantum dots are arranged in rows is formed; and then the quantum dot light emitting layer 5 is transferred to a device (such as an anode 1 or a cathode 7) prepared in the previous process, thereby preparing a quantum dot light emitting diode.
Optionally, in the preparation method of the quantum dot light emitting diode according to the embodiment of the present invention, quantum dots are deposited on the substrate 8, and the substrate 8 is heated and then transversely stretched to increase the distance between the quantum dots on the substrate 8, so as to form the quantum dot light emitting layer 5 in which the quantum dots are linearly arranged; and then the quantum dot light emitting layer 5 is transferred to a device (such as an anode 1 or a cathode 7) prepared in the previous process, thereby preparing a quantum dot light emitting diode. Generally, if the quantum dots on the substrate 8 are regularly arranged, the quantum dot light-emitting layer 5 with quantum dots arranged in lines (linearly arranged) can be obtained after the substrate is transversely stretched; if the quantum dots on the substrate 8 are regularly arranged, the quantum dot light-emitting layer 5 with quantum dots arranged in a curve can be obtained after transverse stretching.
The S2112 stretches the substrate 8 in the first direction and the second direction, so that the pitches of the quantum dots in the first direction and the second direction are increased. That is, the S2111 biaxially stretches the substrate, and when the stretching distances in the first direction and the second direction are the same, a quantum dot lattice with uniformly distributed quantum dots is formed; when the stretching distance in the first direction is greater than the stretching distance in the second direction, the quantum dot light-emitting layer 5 having the quantum dot pitch in the first direction greater than the quantum dot pitch in the second direction can be obtained, for example, the stretching distance in the second direction is greater so that the pitch of the quantum dots in the first direction is greater than 5nm, and the stretching distance in the second direction is smaller so that the pitch of the quantum dots in the second direction is 0.1 to 1 nm.
Optionally, in S2112 of the embodiment of the present invention, quantum dots are deposited on the substrate 8, and the substrate 8 is heated and then stretched transversely and longitudinally, so that the distance between the quantum dots on the substrate 8 is increased, and the quantum dot light emitting layers 5 in which the quantum dots are arranged at intervals are formed; and then the quantum dot light emitting layer 5 is transferred to a device (such as an anode 1 or a cathode 7) prepared in the previous process, thereby preparing a quantum dot light emitting diode.
In one embodiment of the present invention, the anode 1 may specifically be Indium Tin Oxide (ITO).
In S200, the substrate 8 is required to be made of a material with good ductility and stability, for example, the substrate 8 is a polyvinyl alcohol substrate 8 or a polypropylene substrate 8.
In one embodiment of the present invention, when the substrate 8 is stretched, the substrate 8 may be heated to a temperature equal to or higher than the glass transition temperature of the substrate 8 in order to facilitate stretching and improve the stretching effect. That is, the temperature at which the base sheet 8 is stretched is a preset stretching temperature; the preset stretching temperature is equal to or higher than the glass transition temperature of the substrate 8. Wherein, the glass transition temperature of the substrate material is less than 120 ℃, the luminescent property of the quantum dots can be influenced because the heating temperature is too high, and the luminescent property of the quantum dots is not influenced when the heating temperature is not more than 120 ℃.
Referring to fig. 7, in one embodiment of the present invention, stretching the base sheet 8 includes: the base sheet 8 is stretched in a single direction, or the base sheet 8 is stretched in two perpendicular directions. The substrate 8 is stretched in a single direction (uniaxial stretching), so that the distance between the quantum dots on the substrate 8 in the direction is increased, and the distance between the quantum dots in the direction perpendicular to the direction is not changed, thereby forming the quantum dots arranged in rows, i.e. forming the grating (forming the quantum dot light emitting layer after the uniaxial stretching). The substrate 8 is stretched in two perpendicular directions (biaxially stretched), so that the distance between the quantum dots on the substrate 8 in the two perpendicular directions is increased, and the mutual interval distribution of the quantum dots is formed, i.e. a quantum dot interval lattice (a biaxially stretched quantum dot light-emitting layer is formed).
In one embodiment of the invention, the quantum dot spacing is controlled between 0.1 and 20nm by controlling the stretching of the substrate 8. For example, by determining the corresponding relationship between the stretch ratio of the substrate 8 and the quantum dot pitch, the purpose of controlling the quantum dot pitch by controlling the stretch ratio of the substrate 8 is achieved.
In the embodiment of the invention, the quantum dot light-emitting layer 5 is transferred to the anode 1 by means of transfer printing. Referring to fig. 8 to 10, in an embodiment of the present invention, the S300 includes:
s301, adsorbing quantum dots by a seal 9;
s302, the quantum dots adsorbed on the seal 9 are pressed on the anode 1.
Optionally, the stamp 9 is a PDMS (polydimethylsiloxane) stamp 9.
In one embodiment of the present invention, the thickness of the quantum dot light emitting layer 5 is 3 to 20 nm.
In one embodiment of the invention, the cathode 7 is an aluminum cathode 7.
In an embodiment of the present invention, after S100 and before S200, the method further includes:
and S500, forming a barrier layer 4 on the anode 1.
Wherein the barrier layer 4 is used to reduce leakage current. The band gap of the material of the barrier layer 4 is not less than 3eV, the LOMO is not less than-2 eV, and the material has a certain adsorption effect on the quantum dots, and optionally, the material of the barrier layer is one or more of polymethyl methacrylate (PMMA) and polyvinylpyrrolidone (PVP).
In order to improve the light emitting efficiency of the quantum dot light emitting diode, in an embodiment of the present invention, after S100 and before S500, the method further includes:
and S600, forming a hole functional layer on the anode 1.
Wherein, the S600 specifically includes:
s601, forming a hole injection layer 2 on the anode 1 layer;
and S602, forming a hole transport layer 3 on the hole injection layer 2.
Optionally, the hole injection layer 2 is a poly 3, 4-ethylenedioxythiophene: polystyrene sulfonate hole injection layer 2(PEDOT: PSS hole injection layer); the hole transport layer 3 is a poly (9, 9-dioctylfluorene-CO-N- (4-butylphenyl) diphenylamine) hole transport layer 3(TFB hole transport layer).
In order to improve the light emitting efficiency of the quantum dot light emitting diode, in an embodiment of the present invention, after S300 and before S400, the method further includes:
and S700, forming an electron transmission layer 6 on the quantum dot light-emitting layer 5.
Optionally, the electron transport layer 6 is a ZnO electron transport layer 6, and the thickness of the ZnO electron transport layer 6 is 60-150 nm.
In the preparation method of the quantum dot light-emitting diode provided by the embodiment of the invention, quantum dots are firstly coated on the substrate 8 in a spin mode, the substrate 8 is transversely and longitudinally stretched after being heated, so that the interval between the quantum dots on the substrate 8 is increased, and then the quantum dot film layer is transferred to a prepared device (such as an anode 1) in the previous process in a transfer mode to form the quantum dot light-emitting layer 5.
The technical solution of the present invention is explained below by specific examples.
Example (b): 1
The embodiment provides a quantum dot light-emitting diode, and the preparation method specifically comprises the following steps:
(1) providing an ITO anode 1, and pretreating the anode 1: sequentially performing ultrasonic treatment with alkaline washing solution (such as sodium hydroxide solution with pH of 10) for 15min, ultrasonic treatment with deionized water for 15min twice, ultrasonic cleaning with isopropanol for 15min, oven drying at 80 deg.C for 2 hr, and performing ozone ultraviolet treatment for 15 min;
(2) forming a hole injection layer 2 on the anode 1: spin-coating a PEDOT (PSS) solution on the anode 1, spin-coating at 5000rpm for 40s, and then carrying out annealing treatment at 150 ℃ for 15min to form a hole injection layer 2;
(3) forming a hole transport layer 3 on the hole injection layer 2: spin-coating a TFB solution (with concentration of 8mg/mL and solvent of chlorobenzene) on the hole injection layer 2, carrying out spin-coating at 3000rpm for 30s, and then carrying out annealing treatment at 80 ℃ for 30min to form a hole transport layer 3;
(4) forming a blocking layer 4 on the hole transport layer 3: taking a PMMA solution (the concentration is 0.5mg/mL, the solvent is acetone), and spin-coating the PMMA solution on the hole transport layer 3 in a glove box (the water oxygen content is less than 0.1ppm) at the rotating speed of 4000rpm to form a barrier layer 4;
(5) preparing a gap quantum dot light-emitting layer 5: taking a CdSe/ZnS quantum dot solution (the concentration is 10mg/mL, the solvent is n-octane), spin-coating the CdSe/ZnS quantum dot solution on a PVA substrate 8 in a glove box (the water oxygen content is less than 0.1ppm) at the rotating speed of 3000rpm, placing the substrate 8 on a stretcher, heating to the temperature above the PVA glass transition temperature (80 ℃) for transverse stretching, wherein the stretching ratio (stretching rate) is 0.5; heating to 100 ℃, and transferring the stretched quantum dot film onto the hole transport layer 3 through the PDMS stamp 9 to form a quantum dot light-emitting layer 5;
(6) forming an electron transport layer 6 on the quantum dot light emitting layer 5: in a glove box (the water oxygen content is less than 0.1ppm), ZnO solution (the concentration is 45mg/mL, the solvent is ethanol) is spin-coated on the quantum dot light-emitting layer 5, the quantum dot light-emitting layer is spin-coated at 3000rpm for 30s, and then annealing treatment is carried out at 80 ℃ for 30min, so as to form the electron transport layer 6.
(7) Forming a cathode 7 on the electron transport layer 6: al is deposited on the electron transport layer 6 by vapor deposition to form an Al electrode.
The quantum dot light-emitting diode with the gratings formed by arranging the quantum dots in rows can be prepared.
Example (b): 2
The embodiment provides a quantum dot light-emitting diode, and the preparation method specifically comprises the following steps:
(1) providing an ITO anode 1, and pretreating the anode 1: ultrasonic cleaning with alkaline cleaning solution (such as sodium hydroxide solution with pH of 10) for 15min, ultrasonic cleaning with deionized water for 15min twice, ultrasonic cleaning with isopropanol for 15min, oven drying at 80 deg.C for 2 hr, and treating with ozone for 15 min;
(2) forming a hole injection layer 2 on the anode 1: spin-coating a PEDOT (PSS) solution on an anode 1, spin-coating at 5000rpm for 40s, and then annealing at 150 ℃ for 15min to form a hole injection layer 2;
(3) forming a hole transport layer 3 on the hole injection layer 2: spin-coating a TFB solution (with concentration of 8mg/mL and solvent of chlorobenzene) on the hole injection layer 2, carrying out spin-coating at 3000rpm for 30s, and then carrying out annealing treatment at 80 ℃ for 30min to form a hole transport layer 3;
(4) forming a blocking layer 4 on the hole transport layer 3: a PMMA solution (with the concentration of 0.5mg/mL and the solvent of acetone) is taken and is spin-coated on the hole transport layer 3 in a glove box (the water oxygen content is less than 0.1ppm) at the rotating speed of 4000rpm to form the barrier layer 4.
(5) Preparing a gap quantum dot light-emitting layer 5: taking a CdSe/ZnS quantum dot solution (the concentration is 10mg/mL, the solvent is n-octane), spin-coating the CdSe/ZnS quantum dot solution on a PVA substrate 8 in a glove box (the water oxygen content is less than 0.1ppm) at the rotating speed of 3000rpm, placing the substrate 8 on a stretching machine, heating to the temperature higher than the PVA glass transition temperature (80 ℃) to respectively carry out transverse stretching and longitudinal stretching, wherein the stretching multiple is 0.5. And heating to 100 ℃, and transferring the stretched quantum dot film onto the hole transport layer 3 through the PDMS stamp 9 to form the quantum dot light-emitting layer 5.
(6) Forming an electron transport layer 6 on the quantum dot light emitting layer 5: in a glove box (the water oxygen content is less than 0.1ppm), ZnO solution (the concentration is 45mg/mL, the solvent is ethanol) is spin-coated on the quantum dot light-emitting layer 5, the quantum dot light-emitting layer is spin-coated at 3000rpm for 30s, and then annealing treatment is carried out at 80 ℃ for 30min, so as to form the electron transport layer 6.
(7) Forming a cathode 7 on the electron transport layer 6: al is deposited on the electron transport layer 6 by vapor deposition to form an Al electrode having a thickness of 60 to 150 nm.
The quantum dot light-emitting diode with quantum dots arranged at intervals to form the quantum dot interval lattice can be prepared.
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 and a quantum dot light-emitting layer arranged between the anode and the cathode, and is characterized in that the distance between quantum dots in the quantum dot light-emitting layer in a first direction is larger than the distance between the quantum dots in a second direction;
or the spacing of the quantum dots in the first direction is more than 0.1nm and less than or equal to 20nm, and the spacing of the quantum dots in the second direction is more than 0.1nm and less than or equal to 20 nm;
wherein the first direction and the second direction are perpendicular to each other.
2. The quantum dot light-emitting diode of claim 1, wherein when the pitch of the quantum dots in the quantum dot light-emitting layer in the first direction is greater than the pitch in the second direction, the pitch of the quantum dots in the first direction is 5nm to 20nm, and the pitch of the quantum dots in the second direction is 0.1nm to 1 nm.
3. The quantum dot light-emitting diode of claim 1, wherein when the pitch of the quantum dots in the first direction and the pitch of the quantum dots in the second direction are both greater than 0.1nm and 20nm or less, the pitch of the quantum dots in the first direction is equal to the pitch in the second direction.
4. The quantum dot light-emitting diode of claim 1, further comprising: a barrier layer disposed between the anode and the quantum dot light emitting layer for reducing leakage current.
5. The qd-led of claim 4, wherein the band gap of the barrier material is greater than or equal to 3 eV.
6. The qd-led of claim 4, wherein the barrier layer material is selected from one or more of polymethyl methacrylate and polyvinylpyrrolidone.
7. A preparation method of a quantum dot light-emitting diode is characterized by comprising the following steps:
providing an anode;
forming a quantum dot light emitting layer on the anode;
forming a cathode on the quantum dot light emitting layer;
alternatively, a cathode is provided;
forming a quantum dot light emitting layer on the cathode;
forming an anode on the quantum dot light emitting layer;
wherein the interval of the quantum dots in the quantum dot light-emitting layer in the first direction is larger than that in the second direction, or the interval of the quantum dots in the first direction is larger than 0.1nm and less than or equal to 20nm, and the interval of the quantum dots in the second direction is larger than 0.1nm and less than or equal to 20nm, wherein the first direction and the second direction are perpendicular to each other.
8. The method of claim 7, wherein the method of forming the quantum dot light emitting layer comprises:
depositing quantum dots on a substrate, and stretching the substrate to form a quantum dot light-emitting layer;
transferring the quantum dot light emitting layer onto the anode or the cathode.
9. The method of claim 8, wherein stretching the substrate comprises:
stretching the substrate in a first direction;
alternatively, the substrate is stretched in both the first direction and the second direction.
10. The method for manufacturing a quantum dot light-emitting diode according to claim 8, wherein the temperature for stretching the substrate is a preset stretching temperature;
the preset stretching temperature is greater than or equal to the glass transition temperature of the substrate.
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