Quantum dots with oriented light emission, their preparation methods, and applications

Abstract

This invention discloses a quantum dot with oriented luminescence, comprising: a core; and a shell covering the outer surface of the core. The core includes a wurtzite crystal structure, and the shell includes both a wurtzite crystal structure and a zincblende crystal structure, such that the quantum dot's crystal structure forms a polymorphic crystal structure along the c-axis of the wurtzite crystal. The polymorphic crystal structure includes two layers of zincblende crystal structure and a wurtzite crystal structure located between the two layers of zincblende crystal structure. By forming the quantum dot with a polymorphic crystal structure along the c-axis of the wurtzite crystal, the orientation of the quantum dot's transition dipole moment is controlled, thereby controlling the orientation of the quantum dot's luminescence. This invention also discloses a quantum dot thin film prepared using the above-mentioned quantum dot. The dipole-dipole interactions between the quantum dots cause the c-axis of the wurtzite crystals of the quantum dots to be antiparallel to each other and perpendicular to the substrate, making the preferred orientation of the quantum dot thin film's transition dipole moment parallel to the substrate.

Description

Technical Field

[0001] At least one embodiment of the present invention relates to a quantum dot, and more particularly to a quantum dot with oriented light emission, a method for preparing the same, and its application in quantum dot light-emitting diodes. Background Technology

[0002] Quantum dots, as novel luminescent materials, possess advantages such as narrow emission linewidth, tunable emission wavelength, simple synthesis methods, and high stability, making them a research hotspot in recent years. Typically, the light emitted by quantum dots is isotropic, meaning that the transition dipole moments of quantum dots do not have a specific orientation. This limits device performance in applications requiring control over the orientation of quantum dot transition dipole moments. Existing research has achieved control over the orientation of quantum dot transition dipole moments in nanorods, nanosheets, or quantum dots with large aspect ratios. However, due to the less overlap of wavefunctions and slower recombination rates of electrons and holes in nanorods, nanosheets, or quantum dots with large aspect ratios, their internal quantum efficiency is generally low, failing to meet the requirements of high-performance device applications. Therefore, it is necessary to find a new type of quantum dot that can achieve control over the orientation of transition dipole moments while maintaining high quantum yield.

[0003] Quantum dot light-emitting diodes (QD-LEDs) are considered the best solution for next-generation display technology due to their narrow emission linewidth, wide tunable emission wavelength range, long lifespan, and high stability. After more than 20 years of development, the internal quantum efficiency of QD-LEDs has been improved to nearly 100%. However, since the light emitted by quantum dots is usually isotropic, only about 30% is directly coupled out in QD-LEDs, meaning the external coupling efficiency (external quantum efficiency) is low. The rest is trapped or lost in the device, for example, in the substrate, in other layers as waveguides, or absorbed or lost as surface plasmons. The current low external coupling efficiency limits the improvement of QD-LED device efficiency (the product of internal and external quantum efficiency), which to some extent hinders the development and commercialization of QD-LEDs. Summary of the Invention

[0004] In view of this, the present invention provides a quantum dot with oriented light emission, a method for its preparation, and its application, so as to realize the oriented light emission of quantum dots and thereby effectively improve the external coupling efficiency of quantum dot light-emitting diodes.

[0005] As one aspect of the present invention, the present invention provides a quantum dot with oriented luminescence, comprising: a core; a shell covering the outer surface of the core; wherein the core comprises a wurtzite crystal structure, and the shell comprises a wurtzite crystal structure and a zincblende crystal structure, such that the crystal structure of the quantum dot forms a polymorphic crystal structure along the c-axis direction of the wurtzite crystal, the polymorphic crystal structure comprising two layers of zincblende crystal structure and a wurtzite crystal structure located between the two layers of zincblende crystal structure.

[0006] As another aspect of the present invention, the present invention provides a quantum dot film with oriented light emission, which is prepared by the above-mentioned quantum dots with oriented light emission; the preparation method of the quantum dot film with oriented light emission includes: dissolving quantum dots in n-octane to obtain a quantum dot n-octane solution; spin-coating the quantum dot n-octane solution to obtain a quantum dot film, wherein the spin-coating rate is 1000-4000 rpm.

[0007] As another aspect of the present invention, the present invention provides a quantum dot light-emitting diode, comprising: a substrate; a bottom electrode, a hole injection layer, a hole transport layer, a quantum dot layer, an electron transport layer, and a top electrode sequentially formed on the substrate; wherein the quantum dot layer is formed using the above-described quantum dot thin film with oriented light emission.

[0008] According to the above embodiments of the present invention, the quantum dot with oriented light emission is formed by forming a quantum dot with a polymorphic crystal structure, that is, the crystal structure of the quantum dot includes two layers of zincblende crystal structure and a zincblende crystal structure located between the two layers of zincblende crystal structure along the c-axis direction of the zincblende crystal. The first exciton absorption peak of the quantum dot is split into a heavy hole peak with a first peak energy and a light hole peak with a second peak energy, so that the preferred orientation of the quantum dot's transition dipole moment is perpendicular to the c-axis, thereby realizing the regulation of the quantum dot's transition dipole moment orientation, and thus realizing the regulation of the quantum dot's light emission orientation.

[0009] According to the above embodiments of the present invention, a quantum dot film with oriented light emission is prepared by using quantum dots with oriented light emission. The dipole-dipole interaction between the quantum dots causes the c-axis of the wurtzite crystals of the quantum dots with oriented light emission to be antiparallel to each other and perpendicular to the substrate, thereby making the preferred orientation of the transition dipole moment of the prepared quantum dot film parallel to the substrate.

[0010] According to the above embodiments of the present invention, the quantum dots with oriented light emission have a spherical shape. Compared with nanorods, nanosheets, or quantum dots with a large aspect ratio that achieve high transition dipole moment horizontal orientation rate through shape control, spherical quantum dots do not reduce electron-hole wave function overlap, and thus do not reduce internal quantum efficiency, so that the internal quantum efficiency of spherical quantum dots can reach close to 100%. Attached Figure Description

[0011] Figure 1 This is a front view of a quantum dot with oriented light emission according to an embodiment of the present invention;

[0012] Figure 2 A flowchart illustrating a method for preparing quantum dots with oriented light emission according to an embodiment of the present invention;

[0013] Figure 3 A cross-sectional view of a quantum dot light-emitting diode formed from quantum dots with oriented light emission according to an embodiment of the present invention;

[0014] Figure 4 X-ray diffraction patterns of quantum dot powder with oriented luminescence and quantum dot thin films made from quantum dot powder with oriented luminescence according to embodiments of the present invention.

[0015] Figure 5 A high-resolution transmission electron microscope image of quantum dots with oriented luminescence according to an embodiment of the present invention;

[0016] Figure 6 The transient absorption spectrum and second derivative plot of a quantum dot with oriented luminescence according to an embodiment of the present invention;

[0017] Figure 7 The dielectric spectrum test results of quantum dots with oriented luminescence according to an embodiment of the present invention are shown in the figure.

[0018] Figure 8 A back focal plane imaging test result image of a thin film made from quantum dots with oriented light emission according to an embodiment of the present invention; and

[0019] Figure 9 This is a performance test diagram of a quantum dot light-emitting diode formed from oriented quantum dots according to an embodiment of the present invention.

[0020] [Explanation of Labels in the Attached Image]

[0021] 1-Nucleosome;

[0022] 2-shell;

[0023] 21-First shell;

[0024] 22-Second shell;

[0025] 10-Substrate;

[0026] 20 - Bottom electrode;

[0027] 30-hole injection layer;

[0028] 40 - Hole transport layer;

[0029] 50-Quantum dot layer;

[0030] 60 - Electron transport layer;

[0031] 70 - Top electrode. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. However, this invention can be implemented in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to make the invention thorough and complete, and to fully convey the scope of the invention to those skilled in the art. In the accompanying drawings, for clarity, the dimensions and relative dimensions of layers and regions may be exaggerated, and the same reference numerals denote the same elements throughout.

[0033] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0034] In view of this, in order to solve the problem of low external coupling efficiency caused by the isotropic emission of quantum dots in the prior art, the present invention provides a quantum dot with oriented emission, its preparation method and its application in quantum dot light-emitting diodes, so as to realize the oriented emission of quantum dots and thereby improve the external coupling efficiency of quantum dots.

[0035] Figure 1 This is a front view of a quantum dot with oriented light emission according to an embodiment of the present invention.

[0036] According to an exemplary embodiment of the present invention, the present invention provides a quantum dot with oriented light emission, referenced to... Figure 1 As shown, it includes:

[0037] Nucleus 1;

[0038] Shell 2, which covers the outer surface of core 1;

[0039] The core 1 includes a wurtzite crystal structure, and the shell 2 includes a wurtzite crystal structure and a zincblende crystal structure, so that the quantum dot crystal structure forms a polymorphic crystal structure along the c-axis of the wurtzite crystal. The polymorphic crystal structure includes two zincblende crystal structures and a wurtzite crystal structure located between the two zincblende crystal structures.

[0040] According to an embodiment of the present invention, by forming a quantum dot with a polymorphic crystal structure, namely, the crystal structure of the quantum dot includes two layers of zincblende crystal structure and a zincblende crystal structure located between the two layers of zincblende crystal structure along the c-axis direction of the zincblende crystal, the first exciton absorption peak of the quantum dot is split into a heavy hole peak with a first peak energy and a light hole peak with a second peak energy, so that the preferred orientation of the quantum dot's transition dipole moment is perpendicular to the c-axis, thereby realizing the regulation of the quantum dot's transition dipole moment orientation, and thus realizing the regulation of the quantum dot's luminescence orientation.

[0041] According to embodiments of the present invention, the quantum dots with oriented luminescence obtained are quasi-spherical in shape when observed from any direction, with an aspect ratio of (0.5–2):1, preferably (0.8–1.2):1. Compared to nanorods, nanosheets, or quantum dots with larger aspect ratios that achieve high transition dipole moment horizontal orientation rates through shape manipulation, quasi-spherical quantum dots do not reduce electron-hole wavefunction overlap, and therefore do not reduce internal quantum efficiency. The internal quantum efficiency of quasi-spherical quantum dots can reach close to 100%.

[0042] In other words, by forming spherical quantum dots with polymorphic crystal structures, the quantum dots can achieve high quantum yield while controlling the orientation of the transition dipole moment, thus realizing oriented luminescence of quantum dots and solving the problem that the existing quantum dot luminescence can only be isotropic.

[0043] According to an embodiment of the present invention, the core 1 further includes a zincblende crystal structure. That is, the core 1 may simultaneously include a wurtzite crystal structure and a zincblende crystal structure.

[0044] refer to Figure 1 As shown, quantum dots exhibiting oriented luminescence possess polymorphic crystal structures, including wurtzite crystal structures along the c-axis of the wurtzite crystal, and wurtzite crystal structures of different types. The volume ratio of the portion with the wurtzite crystal structure to the quantum dot is k, where 0.5 < k < 1. For example, k can be 0.6, 0.7, 0.8, or 0.9. Figure 1 The dashed lines in the diagram represent the interfaces between different layers, and the c-axis of the wurtzite crystal structure is perpendicular to the interfaces between different layers.

[0045] According to an embodiment of the present invention, the material of the core 1 includes at least one of the following: CdS, CdSe, CdTe, ZnS, ZnSe, InP, InAs, InN, GaAs, GaP, GaN, Cd x Zn 1-x Se, where 0 < x < 1.

[0046] According to an embodiment of the present invention, the shell 2 includes a first shell 21 and a second shell 22. The first shell 21 covers the outer surface of the core 1, and the second shell 22 covers the outer surface of the first shell 21. The crystal structure of the first shell 21 includes both wurtzite and zincblende crystal structures, and the crystal structure of the second shell 21 also includes both wurtzite and zincblende crystal structures. Furthermore, the materials of the first shell 21 and the second shell 22 may be different.

[0047] According to an embodiment of the present invention, the material of the first shell layer 21 includes at least one of the following: CdS, CdSe, CdTe, ZnS, ZnSe, InP, InAs, InN, GaAs, GaP, GaN, ZnSe y S 1-y , where 0 < y < 1.

[0048] According to an embodiment of the present invention, the material of the second shell layer 22 includes at least one of the following: CdS, CdSe, CdTe, ZnS, ZnSe, InP, InAs, InN, GaAs, GaP, GaN.

[0049] According to an embodiment of the present invention, the second shell 22 may include ZnS having a wurtzite crystal structure and / or ZnS having a zincblende crystal structure.

[0050] According to an embodiment of the present invention, the quantum dots with oriented light emission are preferably Cd. x Zn 1-x Se / ZnSe y S 1-y / ZnS core-shell quantum dots; Cd x Zn 1-x Se / ZnSe y S 1-y The core of the ZnS core-shell quantum dot is Cd. x Zn 1-x Se, where 0 < x < 1; the first shell 21 is ZnSe. y S 1-y , where 0 < y < 1; the second shell 22 is ZnS.

[0051] According to an embodiment of the present invention, the particle size of the core 1 is 5nm to 25nm, for example, the particle size can be 5nm, 10nm, 15nm, 20nm, or 25nm; the thickness of the first shell 21 is 1nm to 3nm, for example, the thickness can be 1nm, 2nm, or 3nm; and the thickness of the second shell 22 is 0.1nm to 2nm, for example, the thickness can be 0.1nm, 0.5nm, 1nm, 1.5nm, or 2nm.

[0052] Figure 2This is a flowchart of a method for preparing quantum dots with oriented light emission according to an embodiment of the present invention.

[0053] According to an exemplary embodiment of the present invention, the present invention provides a Cd quantum dot with oriented luminescence. x Zn 1-x Se / ZnSe y S 1-y For the preparation method of / ZnS, refer to Figure 1 and Figure 2 As shown, it includes steps S01 to S03.

[0054] In step S01, cadmium oxide (CdO), zinc acetate (Zn(OAc)2), 1-octadecene (ODE), and oleic acid (OA) are mixed, heated, and kept at a specific temperature. At the nucleation temperature, a Se precursor is injected, and Cd grows through the nucleation reaction. x Zn 1-x Se nucleosome 1.

[0055] According to embodiments of the present invention, the molar mixing ratio of cadmium oxide and zinc acetate is (0.5–1):1, preferably (0.7–0.8):1; the volume ratio of 1-octadecene and oleic acid is (1–3):1, more preferably (1.8–2.2):1. The mixing ratio of zinc acetate and oleic acid is (1.5–3) mmol:10 mL, preferably (1.6–2) mmol:10 mL.

[0056] According to an embodiment of the present invention, the heat preservation temperature is 90℃ to 150℃, for example, 90℃, 100℃, 120℃, 140℃, or 150℃. The heat preservation time under a protective atmosphere is 5 min to 15 min; for example, it can be heat preservation for 10 min under a nitrogen atmosphere.

[0057] According to an embodiment of the present invention, the nucleation temperature is 280℃~340℃, for example, it can be 280℃, 300℃, 310℃, 320℃, or 340℃.

[0058] According to an embodiment of the present invention, the preparation method of the Se precursor includes: mixing selenium powder with trioctylphosphine (TOP) and stirring to obtain a clear liquid, thereby forming the Se precursor; wherein the ratio of selenium powder to trioctylphosphine is (0.5-1.5) mmol:2 mL, for example, it can be 0.5 mmol:2 mL, 0.8 mmol:2 mL, 1 mmol:2 mL, 1.2 mmol:2 mL, 1.5 mmol:2 mL, preferably 1 mmol:2 mL.

[0059] According to an embodiment of the present invention, the injection rate of the Se precursor is 1 to 20 mL / h; the ratio of the injected Se precursor to zinc acetate is (2 to 4) mL: 1 mmol, preferably (3.2 to 3.4) mL: 1 mmol.

[0060] According to an embodiment of the present invention, the nucleation reaction time is 30 min to 90 min, more preferably 60 min.

[0061] In step S02, at the first shell-forming temperature, Zn precursor and Se-S precursor are added, and after the first shell-forming reaction time, Cd... x Zn 1-x ZnSe is grown on the outer surface of Se nucleus 1. y S 1-y First shell 21.

[0062] According to an embodiment of the present invention, the preparation method of the Se-S precursor includes: mixing and stirring selenium powder, sulfur powder, and trioctylphosphine (TOP) to obtain a clear liquid, thereby forming the Se-S precursor; wherein the ratio of selenium powder, sulfur powder, and trioctylphosphine is (0.5-1.5) mmol:(0.5-1.5) mmol:4 mL, for example, it can be 0.5 mmol:0.5 mmol:4 mL, 0.5 mmol:1 mmol:4 mL, 0.5 mmol:1.5 mmol:4 mL, 1 mmol:0.5 mmol:4 mL, 1 mmol:1 mmol:4 mL, 1 mmol:1.5 mmol:4 mL, 1.5 mmol:0.5 mmol:4 mL, 1.5 mmol:1 mmol:4 mL, 1.5 mmol:1.5 mmol:4 mL; preferably 1 mmol:1 mmol:4 mL.

[0063] According to an embodiment of the present invention, the first shell-forming temperature is preferably 260°C to 320°C, for example, it can be 260°C, 280°C, 300°C, 310°C, or 320°C.

[0064] According to an embodiment of the present invention, the time for the first shell-forming reaction is 10 min to 30 min, more preferably 20 min.

[0065] According to an embodiment of the present invention, the preparation method of the Zn precursor is as follows: zinc acetate, oleic acid, and 1-octadecene are mixed and placed in a container; the mixed solution in the container is heated to 90°C to 150°C, preferably 120°C, and maintained for 5 to 15 minutes, preferably 10 minutes; then the temperature is raised to 280°C to 340°C, preferably 310°C, and maintained at this temperature for 10 to 30 minutes, preferably 20 minutes; wherein the ratio of zinc acetate, oleic acid, and 1-octadecene is (1 to 3) mmol:(0.5 to 1.5) mL:4 mL, preferably (1.8 to 2.2) mmol:(0.9 to 1.1) mL:4 mL.

[0066] According to an embodiment of the present invention, the process of adding the Zn precursor and the Se-S precursor includes: firstly, adding the Zn precursor dropwise at a rate of 1 to 20 mL / h; then, adding the Se-S precursor dropwise at a rate of 1 to 20 mL / h, wherein the volume ratio of the added Zn precursor to the Se-S precursor is (0.5 to 1.5):1, more preferably (0.8 to 1.2):1; and wherein the volume ratio of the added Zn precursor to oleic acid is (3 to 5):10, more preferably (3.5 to 4.5):10.

[0067] In step S03, at the second shell-forming temperature, Zn precursor and S precursor are added to form ZnSe. y S 1-y ZnS and a second shell 22 are grown on the outer surface of the first shell 21.

[0068] According to an embodiment of the present invention, the second shell-forming temperature is 280°C to 340°C, for example, it can be 280°C, 290°C, 300°C, 320°C, or 340°C.

[0069] According to an embodiment of the present invention, the preparation method of the S precursor includes: mixing sulfur powder with trioctylphosphine to obtain a clear liquid, which is the S precursor; wherein the ratio of sulfur powder to trioctylphosphine is (0.5-1.5) mmol:2 mL, for example, the ratio can be 0.5 mmol:2 mL, 0.8 mmol:2 mL, 1 mmol:2 mL, 1.2 mmol:2 mL, or 1.5 mmol:2 mL; preferably 1 mmol:2 mL.

[0070] According to an embodiment of the present invention, the process of adding Zn precursor and S precursor to grow a ZnS shell includes: firstly, adding Zn precursor dropwise at a rate of 1-20 mL / h; then adding S precursor dropwise at a rate of 1-20 mL / h, wherein the volume ratio of Zn precursor to S precursor is (0.5-1.5):1, more preferably (0.8-1.2):1; wherein the volume ratio of Zn precursor to oleic acid in step 1 is (3-5):10, more preferably (3.5-4.5):10; and then rapidly cooling the temperature to room temperature after completion.

[0071] It should be noted that the materials used in the above preparation method are preferably as follows: the purity of cadmium oxide (CdO) is preferably 99.99%; the purity of zinc acetate (Zn(OAc)2) is preferably 99.99%; the purity of sulfur powder (S, powder) is preferably 99.99%; the purity of 1-octadecene (ODE) is preferably 90%; the purity of oleic acid (OA) is preferably 90%; the purity of trioctylphosphine (TOP) is preferably 97%; and the purity of selenium powder (Se, powder) is preferably 99.99%.

[0072] According to an exemplary embodiment of the present invention, the present invention provides a quantum dot thin film with oriented light emission, which is prepared using the above-described quantum dots with oriented light emission.

[0073] According to an embodiment of the present invention, a method for preparing a quantum dot film with oriented light emission includes: dissolving quantum dots with oriented light emission in n-octane to obtain a quantum dot n-octane solution; spin-coating the quantum dot n-octane solution to obtain a quantum dot film with oriented light emission; wherein the spin-coating rate is 1000-4000 rpm.

[0074] According to an exemplary embodiment of the present invention, the present invention provides a quantum dot light-emitting diode, comprising: a substrate 10; a bottom electrode 20, a hole injection layer 30, a hole transport layer 40, a quantum dot layer 50, an electron transport layer 60, and a top electrode 70 sequentially formed on the substrate 10; wherein the quantum dot layer 50 is formed using the above-described quantum dot thin film with oriented light emission.

[0075] According to embodiments of the present invention, the substrate 10 can be made of transparent glass or ITO glass. The bottom electrode 20 can be made of indium tin oxide, and its thickness can be 90 nm to 110 nm. The hole injection layer 30 can be made of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) (PEDOT:PSS), and its thickness can be 20 nm to 50 nm. The hole transport layer 40 can be made of 1,2,4,5-tetra(trifluoromethyl)benzene (TFB), and its thickness can be 10 nm to 50 nm.

[0076] According to an embodiment of the present invention, the quantum dot film is prepared by spin-coating a solution of oriented luminescent quantum dots in n-octane at a rotation speed of 1000 to 4000 rpm; the rotation speed is further preferably 2500 rpm, and the thickness of the oriented luminescent quantum dot film is preferably 10 nm to 30 nm.

[0077] According to an embodiment of the present invention, the material of the electron transport layer 60 can be ZnMgO, and the thickness of the electron transport layer 60 is 40nm to 80nm.

[0078] According to an embodiment of the present invention, the material of the top electrode 70 is Al, and the thickness of the top electrode 70 is preferably 90 nm to 110 nm.

[0079] It should be noted that, compared with methods that enhance the external coupling efficiency of quantum dot light-emitting diodes by introducing structures such as microcavities, microlenses, or microprisms, the quantum dot light-emitting diodes provided by this invention have simpler fabrication steps, lower costs, and are easier to commercialize.

[0080] Figure 3 This is a cross-sectional view of a quantum dot light-emitting diode formed from quantum dots with oriented light emission according to an embodiment of the present invention.

[0081] According to an exemplary embodiment of the present invention, the present invention provides a method for fabricating a quantum dot light-emitting diode with oriented light emission, referring to... Figure 3 As shown, the process includes: sequentially spin-coating a hole injection layer 30, a hole transport layer 40, a quantum dot layer 50, and an electron transport layer 60 on a substrate 10 on which a bottom electrode 20 is formed; depositing a top electrode 70 on the electron transport layer 60 to obtain a quantum dot light-emitting diode with oriented light emission. The quantum dot layer 50 is formed using a quantum dot thin film with oriented light emission.

[0082] It should be noted that electrons and holes are injected into the quantum dot layer 50 with oriented light emission through the top electrode 70 and the bottom electrode 20, respectively. The electrons and holes recombine in the quantum dot layer 50, and the quantum dot layer 50 achieves oriented light emission.

[0083] According to an embodiment of the present invention, before spin-coating the hole injection layer 30 on the substrate 10 on which the bottom electrode 20 is formed, the substrate 10 on which the bottom electrode 20 is formed is pretreated. The pretreatment process includes cleaning the substrate 10 on which the bottom electrode 20 is formed and ultraviolet-ozone treatment, wherein the ultraviolet-ozone treatment time is 10 min to 20 min, preferably 15 min.

[0084] According to an embodiment of the present invention, the spin coating rate for forming the hole transport layer 40 is 2500-5000 rpm, preferably 4000 rpm; the spin coating time is 30-60 seconds, preferably 40 seconds; and then annealing is performed at 100-200°C for 10-20 minutes, with the annealing temperature further preferably 150°C and the annealing time further preferably 15 minutes.

[0085] According to an embodiment of the present invention, the spin coating rate for forming the hole injection layer 30 is 2000-4000 rpm, preferably 3000 rpm, and the spin coating time is 20-40 seconds, preferably 30 seconds; then, it is annealed at 90°C-130°C for 20-40 minutes, preferably 110°C, and preferably for 30 minutes.

[0086] According to an embodiment of the present invention, the spin coating rate of the spin-coated quantum dot layer 50 is 1000-3000 rpm, preferably 2000 rpm, and the spin coating time is 30-60 seconds, preferably 40 seconds.

[0087] According to an embodiment of the present invention, the spin coating rate of the electron transport layer 60 on the quantum dot layer 50 is 1000-3000 rpm, preferably 2000 rpm, and the spin coating time is 20-40 seconds, preferably 30 seconds; then, it is annealed at 120°C-160°C for 20-40 minutes, the annealing temperature is further preferably 145°C, and the annealing time is further preferably 30 minutes.

[0088] According to an embodiment of the present invention, a top electrode 70 is deposited under vacuum conditions, and the deposition rate of the top electrode 70 is... Preferred

[0089] The following illustration depicts a quantum dot with oriented light emission, its fabrication method, and its application in quantum dot light-emitting diodes. It should be noted that this illustration is merely a specific embodiment of the present invention and does not limit the scope of protection of the present invention.

[0090] Example 1

[0091] The specific method for preparing quantum dots with oriented luminescence is as follows:

[0092] (1) Preparation of precursors:

[0093] Preparation of Zn precursor: A mixture of 12 mmol Zn(OAc)2, 6 mL oleic acid (OA) and 24 mL 1-octadecene (ODE) was placed in a 100 mL flask, heated to 120 °C and held for 10 minutes, then the temperature was increased to 310 °C and held for 20 minutes.

[0094] Preparation of Se precursor: 5 mmol of selenium powder was mixed with 10 mL of trioctylphosphine (TOP) and stirred to obtain a clear solution.

[0095] Preparation of Se-S precursor: 2.5 mmol selenium powder, 2.5 mmol sulfur powder and 10 mL trioctylphosphine (TOP) were mixed and stirred to obtain a clear solution.

[0096] Preparation of S precursor: 5 mmol sulfur powder was mixed with 10 mL trioctylphosphine (TOP) and stirred to obtain a clear solution.

[0097] (2) Preparation of quantum dots with oriented light emission:

[0098] In a 100 mL three-necked flask, 1.4 mmol of CdO, 1.8 mmol of Zn(OAc)2, 20 mL of ODE, and 10 mL of OA were mixed and heated to 120 °C and maintained under a nitrogen atmosphere for 10 minutes. The temperature was then raised to 310 °C, and 6 mL of Se precursor was rapidly injected. The reaction was allowed to proceed for 60 minutes to grow the ZnCdSe core. The temperature was then lowered to 290 °C, and 4 mL of Zn precursor was added dropwise over 10 minutes, followed by 4 mL of Se-S precursor. The reaction was allowed to proceed for 20 minutes to grow the ZnSeS shell. The temperature was then raised to 310 °C, and 4 mL of Zn precursor was added dropwise over 10 minutes, followed by 4 mL of S precursor over 10 minutes to grow the ZnS shell. After the reaction was completed, the temperature was rapidly lowered to room temperature to prepare oriented luminescent quantum dots ZnCdSe / ZnSeS / ZnS.

[0099] (3) Preparation of quantum dot thin films with oriented luminescence:

[0100] A method for preparing oriented luminescent quantum dot films using the prepared oriented luminescent quantum dots ZnCdSe / ZnSeS / ZnS includes: dissolving the oriented luminescent quantum dots in n-octane; and spin-coating the 15 mg / mL n-octane solution of the oriented luminescent quantum dots at 2000 rpm for 40 seconds to obtain the oriented luminescent quantum dot film.

[0101] (4) Fabrication of quantum dot light-emitting diodes with oriented light emission:

[0102] The ITO glass substrate was ultrasonically cleaned for 15 minutes each with detergent, deionized water, acetone, and isopropanol, then dried and treated with ultraviolet ozone for 15 minutes.

[0103] Indium tin oxide is deposited as the bottom electrode on an ITO glass substrate. Then, the ITO glass substrate with the bottom electrode is transferred to a glove box under a nitrogen atmosphere and hole injection layer, hole transport layer, quantum dot layer and electron transport layer are spin-coated in sequence.

[0104] Specifically, poly(p-phenylene sulfonic acid) (PEDOT:PSS) was spin-coated onto the bottom electrode at 4000 rpm for 40 seconds, followed by annealing at 150°C for 15 minutes to form a hole injection layer. A chlorobenzene solution of 1,2,4,5-tetra(trifluoromethyl) (a chlorobenzene solution of TFB) at a concentration of 8 mg / mL was then spin-coated onto the hole injection layer for 30 seconds. After spin-coating with TFB, the solution was heated to 110°C and annealed for 30 minutes to prepare a hole transport layer on top of the hole injection layer. Finally, a n-octane solution of oriented luminescent quantum dots at a concentration of 15 mg / mL was spin-coated onto the hole transport layer for 40 seconds at 2000 rpm to prepare a quantum dot layer on top of the hole transport layer. An ethanol solution of ZnMgO with a concentration of 25 mg / mL was spin-coated onto the quantum dot layer at a speed of 2000 rpm for 30 seconds. After spin-coating ZnMgO, the solution was heated to 145 °C and annealed for 30 minutes to prepare an electron transport layer on the quantum dot layer with oriented luminescence.

[0105] Finally, under high vacuum (5×10 -6 An aluminum top electrode (mbar) is thermally deposited on the electron transport layer, with a thickness of 100 nm.

[0106] Figure 4 X-ray diffraction patterns of quantum dot powder with oriented luminescence and quantum dot films made from quantum dot powder with oriented luminescence according to embodiments of the present invention.

[0107] refer to Figure 4 As shown, the XRD pattern of the quantum dot film changes compared to the XRD pattern of the quantum dot powder with oriented luminescence. The (002) pattern of the quantum dot film with oriented luminescence... 纤锌矿 The relative intensity of its diffraction is compared to that of quantum dot powder with oriented luminescence (002). 纤锌矿 The relative intensity of the diffraction is significantly enhanced, indicating

[002] 纤锌矿 The crystal axis (that is, the c-axis of the wurtzite crystal) is perfectly perpendicular to the substrate.

[0108] In addition, the (002) in the XRD pattern of the quantum dot film 纤锌矿 The highest diffraction intensity on the crystal plane indicates that the quantum dots in the prepared quantum dot film are

[002] . 纤锌矿 Crystal orientation has a specific orientation.

[0109] Figure 5 This is a high-resolution transmission electron microscope image of quantum dots with oriented luminescence according to an embodiment of the present invention.

[0110] refer to Figure 5 As shown, the arrow indicates the c-axis direction of the wurtzite crystal. According to... Figure 5The spacing and angle of the diffraction fringes indicate that the crystal structure of the prepared quantum dots is along the c-axis direction of the wurtzite crystal (i.e.,

[002] ). 纤锌矿 The crystal orientations are, in order, zincblende, wurtzite, and zincblende crystal structures, respectively. Figure 1 The description is consistent with that in the text.

[0111] Figure 6 The transient absorption spectrum and second derivative plot of a quantum dot with oriented luminescence according to an embodiment of the present invention are shown.

[0112] refer to Figure 6 As shown, the first exciton absorption peak of the quantum dot with oriented luminescence is split into a heavy hole peak with a first peak energy and a light hole peak with a second peak energy, with the first peak energy and the second peak energy separated by 40 meV.

[0113] It should be noted that the light hole peak and heavy hole peak of a single wurtzite crystal structure quantum dot coincide, but after the introduction of a polymorphic crystal structure, the light hole peak and heavy hole peak separate.

[0114] Since the heavy hole state is the ground state, the greater the energy gap between the heavy hole peak (with the first peak energy) and the light hole peak (with the second peak energy), the lower the exciton transition probability corresponding to the light hole peak and the higher the exciton transition probability corresponding to the heavy hole peak. The transition dipole moments corresponding to the heavy hole peak and the light hole peak are oriented. The preferred orientation of the transition dipole moment corresponding to the heavy hole peak is perpendicular to the c-axis of the wurtzite crystal, while the transition dipole moment corresponding to the light hole peak has an orientation parallel to the c-axis of the wurtzite crystal. To control the orientation of the transition dipole moment to be perpendicular to the c-axis of the wurtzite crystal, it is necessary to reduce the exciton transition probability corresponding to the light hole peak, which means increasing the energy gap between the heavy hole peak and the light hole peak.

[0115] refer to Figure 6 As shown, the transient absorption spectrum and second derivative plot of the oriented luminescent quantum dot reveal the splitting between the heavy hole peak and the light hole peak. The energy difference between the first and second peaks is 40 meV, which decreases the exciton transition probability corresponding to the light hole peak and increases the exciton transition probability corresponding to the heavy hole peak. Since the preferred orientation of the exciton transition dipole moment corresponding to the heavy hole peak is perpendicular to the c-axis of the wurtzite crystal, the change in the exciton transition probabilities corresponding to the heavy and light hole peaks increases the probability that the transition dipole moment of the oriented luminescent quantum dot is perpendicular to the c-axis of the wurtzite crystal. In other words, the luminescence of a single oriented luminescent quantum dot is no longer isotropic.

[0116] Figure 7 The dielectric spectrum test results of quantum dots with oriented luminescence according to an embodiment of the present invention are shown in the figure.

[0117] refer to Figure 7As shown, by fitting the dielectric spectrum test results with the Debye relaxation relation, it can be seen that the electric dipole moment of the quantum dot prepared above is 320D.

[0118] See Figure 6 and Figure 7 It is known that the first exciton absorption peak of the prepared quantum dot is split into a heavy hole peak with a first peak energy and a light hole peak with a second peak energy. Furthermore, the fitted electric dipole moment of the quantum dot is greater than 300D, indicating that the preferred orientation of the transition dipole moment of the prepared quantum dot is parallel to the substrate. Specifically, the splitting of the first exciton absorption peak of the prepared quantum dot into a heavy hole peak with a first peak energy and a light hole peak with a second peak energy indicates that the preferred orientation of the transition dipole moment of the quantum dot is perpendicular to the c-axis; the fitted electric dipole moment (320D) of the quantum dot is greater than 300D, indicating that the c-axis of the wurtzite crystal is perpendicular to the substrate, meaning that the preferred orientation of the transition dipole moment of the quantum dot is parallel to the substrate.

[0119] According to an embodiment of the present invention, the preferred orientation of the quantum dot's transition dipole moment is parallel to the substrate. Since the quantum dot's luminescence orientation is perpendicular to the preferred orientation of the quantum dot's transition dipole moment, the quantum dot's luminescence orientation is parallel to the c-axis of the wurtzite crystal, thus realizing the quantum dot's oriented luminescence.

[0120] According to an embodiment of the present invention, the preferred orientation of the transition dipole moment of the quantum dot film prepared using oriented luminescent quantum dots is parallel to the substrate. Specifically, the oriented luminescent quantum dots prepared above contain a strongly ionic material with a wurtzite crystal structure (e.g., ZnS as the material of the second shell). Dielectric spectroscopy measurements of the oriented luminescent quantum dots, followed by Debye relaxation relation fitting, show that the oriented luminescent quantum dots prepared above have an electric dipole moment exceeding 300 D (Debye). Due to the spontaneous polarization characteristic of the wurtzite crystal structure, the direction of the electric dipole moment is parallel to the c-axis of the wurtzite crystal. When using oriented luminescent quantum dots to prepare oriented luminescent quantum dot films, the dipole-dipole interaction causes the wurtzite crystal c-axis of each oriented luminescent quantum dot to be antiparallel to each other and perpendicular to the substrate where the quantum dot film is located. Figure 4 and Figure 7 As shown, the relative diffraction intensity of (002) wurtzite in the quantum dot film with oriented luminescence is significantly enhanced compared to that of (002) wurtzite in the quantum dot powder with oriented luminescence, indicating that the

[002] wurtzite crystal axis (i.e., the c-axis of the wurtzite crystal) is very perpendicular to the substrate; therefore, the preferred orientation of the transition dipole moment of the quantum dot film with oriented luminescence is parallel to the substrate.

[0121] Figure 8The image shows the back focal plane imaging test results after the quantum dots with oriented light emission are made into a thin film according to an embodiment of the present invention.

[0122] refer to Figure 8 As shown, the experimental results of the back focal plane imaging test after the quantum dots with oriented light emission were made into thin films were obtained by fitting based on the transfer matrix method, and the horizontal orientation rate of the transition dipole moment of the quantum dot thin film with oriented light emission was 79%.

[0123] According to embodiments of the present invention, quantum dot films made of quantum dots with oriented light emission can achieve a horizontal orientation rate of over 79% for transition dipole moments, which can effectively improve the external coupling efficiency of quantum dot light-emitting diodes.

[0124] Figure 9 This is a performance test diagram of a quantum dot light-emitting diode formed from quantum dots with oriented light emission according to an embodiment of the present invention.

[0125] refer to Figure 9 As shown, the maximum external quantum efficiency of the prepared quantum dot light-emitting diode is 35.6%, indicating that the quantum dot prepared has a high quantum yield.

[0126] The use of ordinal numbers such as "first," "second," "third," etc., in the specification and claims to modify the corresponding elements does not imply that the element has any ordinal number, nor does it represent the order of one element with another element, or the order of manufacturing methods. The use of these ordinal numbers is only to enable a named element to be clearly distinguished from another element with the same name.

[0127] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A quantum dot with oriented luminescence, characterized in that, include: Nucleus (1); Shell (2), which covers the outer surface of the core (1); Wherein, the core (1) includes a wurtzite crystal structure, and the shell (2) includes a wurtzite crystal structure and a zincblende crystal structure, such that the crystal structure of the quantum dot forms a polymorphic crystal structure along the c-axis of the wurtzite crystal, wherein the polymorphic crystal structure is a two-layer zincblende crystal structure and a wurtzite crystal structure located between the two-layer zincblende crystal structures; The quantum dot with oriented light emission is spherical, and the aspect ratio of the quantum dot is (0.5~2):1; The shell (2) includes a first shell (21) and a second shell (22), with the second shell (22) covering the outer surface of the first shell (21); The first shell layer (21) and the second shell layer (22) are made of different materials; The quantum dots are Cd. x Zn 1-x Se / ZnSe y S 1-y / ZnS; Among them, 0 <x<1,0<y<1。 2. The quantum dot according to claim 1, characterized in that, The core (1) also includes a zincblende crystal structure.

3. The quantum dot according to claim 1, characterized in that, The volume ratio of the portion of the quantum dot with a wurtzite crystal structure to the quantum dot is k = 0.

5. <k<1。 4. A method for preparing quantum dots as described in claim 1, characterized in that, include: Cadmium oxide, zinc acetate, 1-octadecene, and oleic acid were mixed, heated, and held at the nucleation temperature. A Se precursor was then injected, and Cd was grown through the nucleation reaction. x Zn 1-x Se nucleosome (1); At the first shell-forming temperature, Zn precursor and Se-S precursor are added to Cd x Zn 1-x ZnSe is grown on the outer surface of the Se nucleus (1). y S 1-y First shell (21); At the second shell-forming temperature, Zn precursor and S precursor are added to form ZnSe. y S 1-y A second ZnS shell (22) is grown on the outer surface of the first shell (21).

5. A quantum dot thin film with oriented luminescence, characterized in that, It is prepared using quantum dots with oriented light emission as described in any one of claims 1 to 3; The method for preparing the quantum dot thin film with oriented light emission includes: Quantum dots are dissolved in n-octane to obtain a quantum dot n-octane solution; A solution of quantum dots in n-octane is spin-coated to obtain the quantum dot film, wherein the spin-coating rate is 1000~4000 rpm.

6. A quantum dot light-emitting diode, characterized in that, include: Substrate (10); A bottom electrode (20), a hole injection layer (30), a hole transport layer (40), a quantum dot layer (50), an electron transport layer (60), and a top electrode (70) are sequentially formed on the substrate (10). The quantum dot layer (50) is formed using a quantum dot thin film with oriented light emission as described in claim 5.

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