A high aperture ratio quantum dot electrophoretic display device based on a three-electrode pixel structure and a driving method thereof

Abstract

The application discloses a high-opening quantum dot electrophoretic display device based on a three-electrode pixel structure and a driving method thereof, and relates to the technical field of display devices.The pixel structure of the device comprises an upper substrate, a lower substrate and electrophoretic ink filled between the two, the upper substrate is provided with a first electrode on one side, and the lower substrate is provided with a second electrode and a third electrode arranged at intervals;the electrophoretic particles comprise first particles, second particles and third particles with different optical characteristics, the first particles and the second particles have opposite charges, the third particles have the same charge polarity as the first particles or the second particles, and the charge amount of the third particles is smaller than that of the particles with the same charge polarity;the application can efficiently and selectively separate multi-color electrophoretic particles in space through the design of the charge difference of the electrophoretic particles and the selective driving of the electric field of the three-electrode system, realizes dynamic adjustment and multiplexing of the light-emitting color of the pixel, and greatly improves the effective opening rate of the quantum dot display device when presenting quantum dot monochrome display.

Description

Technical Field

[0001] This invention relates to the field of display device technology, and in particular to a high aperture ratio quantum dot electrophoretic display device based on a three-electrode pixel structure and its driving method. Background Technology

[0002] Quantum dot materials have the characteristics of tunable emission wavelength, high color purity, excellent luminous efficiency, and can be processed by solution method. They are the core functional materials for the next generation of high color gamut display technology and have broad application prospects in the display industry.

[0003] Currently, printed quantum dot display technology is the main technological path for the industrialization of quantum dot displays. Its core logic relies on high-precision inkjet printing equipment to directly deposit quantum dot luminescent ink onto a preset area of ​​the substrate, forming a pixelated luminescent layer in situ. The current mainstream printed quantum dot color display solutions generally adopt a red, green, and blue sub-pixel spatial segmentation architecture. By depositing quantum dots of the three luminescent colors separately into independent sub-pixel units, full-color display is achieved through spatial color mixing. This architecture has inherent shortcomings that are difficult to avoid: First, in monochrome display mode, only about one-third of the sub-pixels participate in luminescence, naturally limiting the effective luminescent aperture ratio of the panel; Second, once the quantum dot layer is printed and deposited, the luminescent color of each sub-pixel is permanently fixed, making it impossible to dynamically adjust and reuse the luminescent color of the pixels according to the display content, which is difficult to adapt to advanced display requirements such as dynamic color gamut optimization and ultra-high resolution pixel reuse. Therefore, the field of quantum dot displays urgently needs a new technological route to achieve a higher effective monochrome aperture ratio and meet the needs of dynamic adjustment of pixel colors. Summary of the Invention

[0004] This invention provides a high aperture ratio quantum dot electrophoretic display device and its driving method based on a three-electrode pixel structure. It aims to replace the traditional printed quantum dot technology with the electrophoretic display technology route, and achieve high aperture ratio and dynamically adjustable pixel color quantum dot display by selectively driving different color particles through an electric field within a single pixel structure.

[0005] The quantum dot electrophoretic display device provided by the present invention includes a pixel structure, wherein the pixel structure includes an upper substrate, a lower substrate, and an electrophoretic ink filled between the upper substrate and the lower substrate. The upper substrate is the display side, and the electrophoretic ink includes an electrophoretic medium and electrophoretic particles dispersed in the electrophoretic medium. A first electrode is provided on the side of the upper substrate facing the electrophoretic ink, and a second electrode and a third electrode are arranged on the lower substrate. The electrophoretic particles include a first particle, a second particle, and at least one third particle with different optical properties. The first particle and the second particle have opposite charges, and the third particle has the same charge polarity as the first particle or the second particle, and the charge of the third particle is less than that of the first particle or the second particle with the same charge polarity. At least one of the first particle, the second particle, and the third particle is a quantum dot fluorescent particle, and the quantum dot fluorescent particle is composited with luminescent quantum dots.

[0006] Optionally, the charge of the third particle is 33% to 50% of the charge of the first or second particle with the same polarity.

[0007] Optionally, at least one of the first particle, the second particle, and the third particle is a reflective pigment particle or an upconversion luminescent particle.

[0008] Optionally, the quantum dot fluorescent particles are prepared by the following steps: A silane coupling agent and a dispersant are added to the carrier particle dispersion to obtain a first mixed solution. Then, a silane hydrolysis catalyst is added to the first mixed solution to carry out the reaction. The reactants are washed and dried to obtain functionalized oxide particles. The functionalized oxide particles are dissolved in a nonpolar solvent to obtain a second mixed solution. Then, polymer monomers and initiators are added to the second mixed solution under an inert atmosphere to carry out the reaction. The reactants are washed and dried to obtain composite particles with a polymer coating. The composite particles are dissolved in a nonpolar solvent to obtain a third mixed solution. A quantum dot precursor solution is added to the third mixed solution to carry out the reaction. The centrifuged precipitate after the reaction is washed to obtain quantum dot functionalized particles. The quantum dot functionalized particles are mixed with a charge control agent and a dispersion medium, and then subjected to ultrasonication and washing to obtain quantum dot fluorescent particles.

[0009] Optionally, the quantum dot precursor solution is prepared by the following steps: The metal halide precursor was dissolved in N,N-dimethylformamide, and then oleylamine and methacrylic acid were added to the N,N-dimethylformamide. After stirring, a quantum dot precursor solution was obtained.

[0010] Optionally, the optical characteristic is the color state displayed under preset display conditions.

[0011] The driving method for the quantum dot electrophoretic display device provided by the present invention includes the following steps: S1, apply an oscillating activation voltage to the first electrode, second electrode and third electrode of the quantum dot electrophoretic display device respectively; S2, apply migration driving voltages to the first electrode, the second electrode and the third electrode respectively, so that the display side of the quantum dot electrophoretic display device exhibits the optical properties of the first particle, the second particle or the third particle; The process of revealing the optical properties of the first particle includes the following steps: A first driving voltage is applied to the first electrode, and a second driving voltage is applied to the second and third electrodes to form a longitudinal driving electric field in a first direction between the upper and lower substrates, so that the first particle migrates to the surface of the first electrode. Presenting the optical properties of the second particle includes the following steps: A third driving voltage is applied to the first electrode, and a fourth driving voltage is applied to the second and third electrodes to form a longitudinal driving electric field in a second direction between the upper and lower substrates, so that the second particles migrate to the surface of the first electrode. The optical properties of a third particle are presented through the following steps: A zero-volt voltage is applied to the first electrode, a fifth driving voltage is applied to the second electrode, and a sixth driving voltage is applied to the third electrode. A transverse sorting electric field is formed between the second and third electrodes, causing the first and second particles to migrate to the surfaces of different electrodes in the second and third electrodes, respectively. The third particle migrates to the adjacent area of ​​the corresponding electrode along with the particles of the same polarity, and the spatial position of the third particle relative to the lower substrate is higher than that of the first or second particle with the same polarity. Maintaining the transverse sorting electric field, a seventh driving voltage is applied to the first electrode, so that the longitudinal electric field force on the third particle is less than the repulsive force generated by the first or second particle of the same polarity. The third particle migrates to the surface of the first electrode, while the first and second particles maintain their original adsorption state under the action of the transverse sorting electric field.

[0012] Optionally, in step S1, a first oscillation activation voltage is applied to the first electrode, and a second oscillation activation voltage is applied to the second and third electrodes, wherein the first oscillation activation voltage and the second oscillation activation voltage are alternating voltages with opposite phases.

[0013] Optionally, the absolute value of the seventh driving voltage is less than the absolute value of the fifth driving voltage or the sixth driving voltage, which have the same polarity.

[0014] Optionally, presenting the optical properties of the first particle, the second particle, or the third particle includes the following steps: The display side of the quantum dot electrophoretic display device is illuminated with light of a preset wavelength.

[0015] The present invention has the following beneficial effects: This invention allows multiple electrophoretic particles with different optical properties to coexist within the same pixel structure unit, with at least one of the particles being quantum dot fluorescent particles. Based on a three-electrode structure including one top electrode and two bottom electrodes, the invention enables electrophoretic particles with specific optical properties to appear on the display side of the device through differentiated charge design of the electrophoretic particles and selective electric field driving of the three-electrode system. This achieves dynamic adjustment and reuse of pixel emission colors in multi-color (more than two optical properties) quantum dot display devices. At the same time, when quantum dot electrophoretic particles migrate to the display side, they can occupy the entire pixel aperture, which greatly improves the effective aperture ratio of the quantum dot display device when presenting a quantum dot monochrome display. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 These are schematic diagrams of the pixel structure of some embodiments of the quantum dot electrophoretic display device of the present invention; Figure 2 A flowchart illustrating the driving method for some embodiments of the quantum dot electrophoretic display device of the present invention to present the optical properties of a third particle; Figure 3 The red driving voltage timing diagram is shown for the quantum dot electrophoretic display device of Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the electrophoretic particle distribution when the quantum dot electrophoretic display device displays red, according to Embodiment 1 of the present invention. Figure 5 This is a timing diagram of the driving voltage for displaying green in the quantum dot electrophoretic display device of Embodiment 1 of the present invention; Figure 6 This is a schematic diagram of the electrophoretic particle distribution when the quantum dot electrophoretic display device displays green according to Embodiment 1 of the present invention; Figure 7 This is a timing diagram of the driving voltage for displaying blue in the quantum dot electrophoretic display device of Embodiment 1 of the present invention; Figure 8This is a schematic diagram of the electrophoretic particle distribution in the first stage when the quantum dot electrophoretic display device displays blue, according to Embodiment 1 of the present invention. Figure 9 This is a schematic diagram of the electrophoretic particle distribution in the second stage when the quantum dot electrophoretic display device displays blue, according to Embodiment 1 of the present invention. Figure 10 This is a simulation diagram of the electric field distribution of the quantum dot electrophoretic display device after applying a red state driving voltage in Embodiment 2 of the present invention; Figure 11 This is a simulation diagram of the electric field distribution of the quantum dot electrophoretic display device after applying a green state driving voltage in Embodiment 2 of the present invention; Figure 12 This is a simulation diagram of the electric field distribution of the quantum dot electrophoretic display device after the first stage of applying the blue state driving voltage in Embodiment 2 of the present invention; Figure 13 This is a simulation diagram of the electric field distribution of the quantum dot electrophoretic display device after the second stage of applying the blue state driving voltage in Embodiment 2 of the present invention; Figure 14 This is a schematic diagram of the process flow for preparing quantum dot fluorescent particles in Example 3 of the present invention; Figure 15 This is a photograph of the quantum dot electrophoretic display device sample prepared in Example 3 of the present invention, showing green fluorescence. Figure 16 The image shows the quantum dot electrophoretic display device sample prepared in Example 4 of this invention, displaying red and blue colors.

[0018] Explanation of reference numerals in the attached figures: 1. Upper substrate; 2. Lower substrate; 3. First electrode; 4. Second electrode; 5. Third electrode; 6. Electrophoretic medium; 7. First particle; 8. Second particle; 9. Third particle. Detailed Implementation

[0019] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0020] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such process, method, product, or apparatus.

[0021] Experimental methods in the embodiments of this invention that do not specify specific conditions are generally performed under conventional conditions and conditions described in the manual, or under conditions recommended by the manufacturer; the general equipment, materials, reagents, etc. used are commercially available unless otherwise specified.

[0022] This invention provides a quantum dot electrophoretic display device and its driving method.

[0023] See Figure 1 In this embodiment of the invention, the quantum dot electrophoretic display device includes a pixel structure. Each pixel structure includes an upper substrate 1, a lower substrate 2, and electrophoretic ink filled between the upper substrate 1 and the lower substrate 2. The upper substrate 1 is the display side, and the electrophoretic ink includes an electrophoretic medium 6 and electrophoretic particles dispersed in the electrophoretic medium 6. A first electrode 3 is provided on the side of the upper substrate 1 facing the electrophoretic ink, and a second electrode 4 and a third electrode 5 are arranged on the lower substrate 2. The electrophoretic particles include a first particle 7, a second particle 8, and at least one third particle 9 with different optical properties. The first particle 7 and the second particle 8 have opposite charges, and the charge of the third particle 9 is the same as that of the first particle 7 or the second particle 8, and the charge of the third particle 9 is less than that of the first particle 7 or the second particle 8 with the same charge. At least one of the first particle 7, the second particle 8, and the third particle 9 is a quantum dot fluorescent particle, and the quantum dot fluorescent particle is composited with luminescent quantum dots.

[0024] For example, if both the first and third particles carry positive charges, the charge of the third particle must be less than the charge of the first particle, and the second particle carries negative charges; if both the second and third particles carry negative charges, the charge of the third particle must be less than the charge of the second particle, and the first particle carries positive charges.

[0025] In this embodiment of the invention, the optical properties of electrophoretic particles refer to the specific colors displayed by the electrophoretic particles under preset display conditions. Quantum dot fluorescent particles are composited with luminescent quantum dots. After the quantum dots absorb high-energy excitation photons (such as ultraviolet light), the valence band electrons jump to the conduction band. When the electrons fall back to the valence band, they release energy in the form of photons and emit visible light of a characteristic wavelength. The emission wavelength can be precisely controlled by the size and composition of the quantum dots. The color purity of quantum dot emission is much higher than that of conventional pigment particles.

[0026] In some embodiments, if one or two of the first, second, and third particles are not quantum dot fluorescent particles, the non-quantum dot fluorescent electrophoretic particles can be selected as reflective pigment particles or upconversion luminescent particles. Among them, reflective pigment particles selectively absorb specific wavelengths of incident white light through intrinsic material properties, and reflect the remaining wavelengths of light to the human eye, thereby presenting the corresponding colors. Upconversion luminescent particles continuously absorb low-energy near-infrared photons through intermediate metastable energy levels, and finally release energy in the form of high-energy visible light photons to achieve visible light display.

[0027] For example, the first particle, the second particle, and the third particle are all selected as quantum dot fluorescent particles; for example, one of the first particle, the second particle, and the third particle is selected as a quantum dot fluorescent particle, and the other two particles are selected as reflective pigment particles; for example, two of the first particle, the second particle, and the third particle are selected as quantum dot fluorescent particles, and the other is selected as a reflective pigment particle; for example, the first particle, the second particle, and the third particle are respectively selected as quantum dot fluorescent particles, reflective pigment particles, and upconversion luminescent particles; for example, one of the first particle, the second particle, and the third particle is selected as a quantum dot fluorescent particle, and the other two particles are selected as upconversion luminescent particles; for example, two of the first particle, the second particle, and the third particle are selected as quantum dot fluorescent particles, and the other is selected as an upconversion luminescent particle; those skilled in the art will understand that the present invention achieves selective spatial separation of multiple electrophoretic particles with different optical properties within the same pixel structure through the design of a three-electrode structure and a time-sequential electric field driven, and the above-example combinations of electrophoretic particles are all applicable to the technical solutions of the present invention.

[0028] In this embodiment of the invention, the electrophoretic medium is the main continuous phase of the electrophoretic ink, which is used to provide a liquid phase environment for the migration and dispersion of electrophoretic particles. The electrophoretic medium typically includes a main solvent (a single solvent or a compound solvent among organic solvents such as aliphatic hydrocarbons, aromatic hydrocarbons, and halogenated hydrocarbons), a charge control agent (polyisobutylene succinimide, fluorinated surfactants, ionic surfactants, etc.), and a dispersion stabilizer (sorbitan fatty acid esters, such as Span80, Span85, or polyoxyethylene ethers).

[0029] The quantum dot electrophoretic display device provided in this embodiment of the invention is driven by the following method: S1, apply oscillation activation voltages to the first, second, and third electrodes of the quantum dot electrophoretic display device, respectively.

[0030] Specifically, a first oscillation activation voltage is applied to the first electrode, and a second oscillation activation voltage is applied to the second and third electrodes. The first and second oscillation activation voltages are alternating voltages with opposite phases. The waveforms of the alternating voltages include, but are not limited to, periodic square waves, sine waves, triangular waves, intermittent pulses, etc. The opposite phases mean that the change steps of the first and second oscillation activation voltages differ by π radians, that is, when one is at the rising edge / high level, the other is synchronously at the falling edge / low level, ultimately forming an electric field with periodically reversed direction between the first electrode and the second / third electrode.

[0031] When electrophoretic particles are left to stand still or remain in a bistable state for a long time, they will agglomerate and settle due to van der Waals forces and gravitational sedimentation. In particular, small-diameter quantum dot modified particles are prone to forming aggregates. An alternating electric field can make the particles repeatedly perform small-amplitude reciprocating motions in the direction of the electric field. Through mechanical shearing force, the aggregates are broken up and the particles are uniformly dispersed in the dispersion medium. This avoids uneven display and color crosstalk caused by particle agglomeration and migration during subsequent driving. At the same time, the alternating electric field can promote the re-adsorption and equilibrium of charge control agents on the particle surface, restore the stable net surface charge of the particles, reduce the difference in migration rate between particles, and improve the consistency of response speed in subsequent sorting and driving.

[0032] S2, apply migration driving voltages to the first electrode, second electrode and third electrode respectively, so that the display side of the quantum dot electrophoretic display device exhibits the optical properties of the first particle, second particle or third particle; for quantum dot fluorescent particles, fluorescence display can be excited by irradiating the display side of the device with ultraviolet light of a specific wavelength range; for reflective pigment particles, reflective natural display can be achieved under sunlight or artificial visible light source; for upconversion luminescent particles, luminescence display can be achieved by irradiating with near-infrared light of a specific wavelength range.

[0033] The process of revealing the optical properties of the first particle includes the following steps: A first driving voltage is applied to the first electrode, and a second driving voltage is applied to the second and third electrodes to form a longitudinal driving electric field in a first direction between the upper and lower substrates, so as to cause the first particle to migrate to the surface of the first electrode.

[0034] Presenting the optical properties of the second particle includes the following steps: A third driving voltage is applied to the first electrode, and a fourth driving voltage is applied to the second and third electrodes to form a longitudinal driving electric field in a second direction between the upper and lower substrates, so that the second particles migrate to the surface of the first electrode; the absolute value of the seventh driving voltage is less than the absolute value of the fifth or sixth driving voltage with the same polarity.

[0035] See Figure 2 The optical properties of the third particle are exhibited through two voltage application stages: In the first stage (S2-1), a zero-volt voltage is applied to the first electrode, a fifth driving voltage is applied to the second electrode, and a sixth driving voltage is applied to the third electrode. A transverse sorting electric field is formed between the second and third electrodes, causing the first and second particles to migrate to the surfaces of different electrodes in the second and third electrodes, respectively. The third particle migrates to the adjacent area of ​​the corresponding electrode along with the particles of the same polarity. Since the third particle has a lower charge, the spatial position of the third particle relative to the lower substrate is higher than that of the first or second particle with the same polarity.

[0036] In the second stage (S2-2), the transverse sorting electric field is maintained, and the seventh driving voltage is applied to the first electrode so that the longitudinal electric field force on the third particle is less than the repulsive force generated by the first or second particles of the same polarity. The third particle migrates to the surface of the first electrode, while the first and second particles maintain their original adsorption state under the action of the transverse sorting electric field.

[0037] For example, the first particle carries a high positive charge, the second particle carries a negative charge, and the third particle carries a low positive charge. To display the optical properties of the first particle, a -15V voltage is applied to the first electrode, and a +15V voltage is applied to both the second and third electrodes. Under the influence of an upward vertical electric field, the first particle preferentially moves to the surface of the first electrode. The third particle, due to its low charge, has a slower migration rate and ultimately ends up positioned lower than the first particle, thus being blocked by it. To display the optical properties of the second particle, a +15V voltage is applied to the first electrode, and a -15V voltage is applied to both the second and third electrodes. Under the influence of a downward vertical electric field, the second particle moves to the surface of the first electrode, and both the first and third particles are adsorbed onto the surfaces / near the second and third electrodes. To display the optical properties of the third particle, in the first stage, a zero-volt voltage is applied to the first electrode, a +15V voltage is applied to the second electrode, and a -30V voltage is applied to the third electrode. At this point, the second particle is adsorbed on the surface of the second electrode, while the first particle preferentially adsorbs on the surface of the third electrode. Although the third particle, due to its low charge, also migrates towards the third electrode, its migration rate is slower, causing it to be positioned higher than the first particle. In the second stage, the voltages of the second and third electrodes remain unchanged, and a voltage of -15V is applied to the first electrode. At this time, the second particle is still adsorbed on the surface of the second electrode. Since the electric field direction between the first and third electrodes is still downward (the electric field strength decreases), the first particle is still adsorbed on the surface of the third electrode. The electric field attraction (downward) experienced by the third particle at this time is less than the repulsive force (upward) of the same charge generated by the first particle. Therefore, the third particle moves towards the first electrode until it is distributed on the surface of the first electrode to achieve display. In the second stage of driving the display of the third particle, the first electrode can be 0~-15V, and the third electrode can be -25~-40V. The difference between the two electrodes can be 10~40V.

[0038] The embodiments of the present invention do not impose specific limitations on the specific charge values ​​of each electrophoretic particle. Under the guidance of the above driving scheme, those skilled in the art can adaptively adjust the surface charge of each electrophoretic particle according to the driving electric field strength, dispersion medium system characteristics, target response speed and display performance requirements in the actual application scenario.

[0039] In some preferred embodiments, the charge of the third particle is 33% to 50% of the charge of the first or second particle with the same polarity; for example, if the first particle has a positive charge of 89 meV and the second particle has a negative charge of -36 meV, the third particle may be selected to have a positive charge of 30.9 meV.

[0040] If the charge of the third particle is too high, its migration behavior will become similar to that of the first particle; if it is too low, its migration response speed will be too slow. Both situations where the charge of the third particle is too high or too low can easily lead to color crosstalk and poor spatial separation between different types of particles.

[0041] This invention allows multiple electrophoretic particles with different optical properties to coexist within the same pixel structure unit, with at least one particle being a quantum dot fluorescent particle. Based on a three-electrode structure including one top electrode and two bottom electrodes, the electrophoretic particles are selectively driven by differentiated charge design and electric field, enabling electrophoretic particles with specific optical properties to appear on the display side of the device. This achieves dynamic adjustment and reuse of pixel emission colors in multi-color (more than two optical properties) quantum dot display devices. Simultaneously, when quantum dot electrophoretic particles migrate to the display side, they can occupy the entire pixel aperture, significantly improving the effective aperture ratio of the quantum dot display device when presenting a quantum dot monochrome display.

[0042] In this embodiment of the invention, the first particle, the second particle, and the third particle can display different colors from each other. Any combination of colors can be selected according to the needs of the display scene. The selectable colors include, but are not limited to, high-saturation colors (red, orange, yellow, green, cyan, blue, purple and other primary colors and their derivative colors), low-saturation colors (white, gray and other colors), black and other colors.

[0043] In some specific embodiments, the first particle, the second particle, and the third particle respectively display one of red, green, and blue under preset color display conditions. Red, green, and blue are the three primary colors of the additive color mixing system. By mixing them in different proportions, they can cover most of the color gamut visible to the human eye, thereby achieving full-color display.

[0044] It should be noted that the quantum dot electrophoretic display device provided by the present invention can also realize four-color display, that is, the third particle can include two types. One type has the same polarity as the first particle but has a lower charge than the first particle, and the other type has the same polarity as the second particle but has a lower charge than the second particle. The two types of third particles can coexist in the same pixel structure. The optical characteristics of the two types of third particles are different. For ease of description, the first type of third particle is called the first type particle, and the second type of third particle is called the second type particle.

[0045] In the scenario of a four-color electrophoretic display device, the color presentation of the first and second particles is consistent with the driving scheme described in the aforementioned embodiment, while the color presentation of the third particle can be distinguished into two cases: the first type of particle and the second type of particle. In the first stage, the first and second particles migrate to the surfaces of different electrodes in the second and third electrodes respectively under the action of the lateral sorting electric field. The first type of particle and the second type of particle also migrate to the adjacent area of ​​the corresponding electrode. Among them, the spatial position of the first type of particle relative to the lower substrate is higher than that of the first particle with the same polarity, and the spatial position of the second type of particle relative to the lower substrate is higher than that of the second particle with the same polarity.

[0046] In the second stage, the lateral sorting electric field is maintained. If the device is to display the color of the first type of particle, a preset voltage is applied to the first electrode so that the longitudinal electric field force on the first type of particle is less than the repulsive force generated by the first particle. The first type of particle migrates to the surface of the first electrode. The first particle, the second particle, and the second type of particle maintain their original adsorption state under the action of the lateral sorting electric field. If the device is to display the color of the second type of particle, a preset voltage is applied to the first electrode so that the longitudinal electric field force on the second type of particle is less than the repulsive force generated by the second particle. The second type of particle migrates to the surface of the first electrode. The first particle, the second particle, and the first type of particle maintain their original adsorption state under the action of the lateral sorting electric field.

[0047] In some specific embodiments, quantum dot fluorescent particles can be prepared by the following methods: Step 1: Add silane coupling agent and dispersant to the carrier particle dispersion to obtain a first mixed solution. Then add silane hydrolysis catalyst to the first mixed solution to carry out the reaction. After washing and drying, functionalized oxide particles are obtained.

[0048] The carrier particles, serving as the rigid supporting core, can be selected from high-whiteness, chemically stable nanoparticles such as titanium dioxide, silicon dioxide, zinc oxide, aluminum oxide, and zirconium dioxide; alternatively, black, chemically stable nanoparticles with hydroxyl active sites on their surface, such as iron-manganese black, copper-chromium black, iron oxide, silica-coated carbon black, and colloidal carbon microspheres, can be selected. The dispersant, used to inhibit oxide particle aggregation, can be selected from alcohol / water-soluble dispersants such as polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), ammonium polyacrylate, and trisodium citrate. A silane coupling agent is used to connect... For grafting onto the surface of oxide particles, γ-methacryloxypropyltrimethoxysilane (KH570), vinyltrimethoxysilane (VTMS), vinyltriethoxysilane (VTES), and γ-methacryloxypropyltriethoxysilane can be selected; common silane coupling agents such as γ-aminopropyltriethoxysilane (KH550) and γ-glycidoxypropyltrimethoxysilane (KH560) can also be selected according to grafting requirements; silane hydrolysis catalysts are used to catalyze the hydrolysis and condensation of siloxane bonds, and acetic acid, dilute hydrochloric acid, oxalic acid, nitric acid, etc. can be selected.

[0049] Step 2: Dissolve the functionalized oxide particles in a nonpolar solvent to obtain a second mixed solution. Then, add polymer monomers and initiators to the second mixed solution under an inert atmosphere to carry out the reaction. After washing and drying, the reactants are used to obtain composite particles with a polymer coating.

[0050] Among them, non-polar solvents are suitable for polymerization systems of oil-soluble monomers and initiators, and common non-polar solvents such as toluene, xylene, n-hexane, n-heptane, n-decane, dodecane, and chloroform can be selected; polymer monomers such as lauryl methacrylate, methyl methacrylate, butyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, vinyl acetate, and maleate can be selected; initiators such as azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), benzoyl peroxide (BPO), di-tert-butyl peroxide, and tert-butyl peroxypentanoate can be selected.

[0051] Step 3: Dissolve the composite particles in a nonpolar solvent to obtain a third mixed solution. Add a quantum dot precursor solution to the third mixed solution to react. Wash the centrifuged precipitate after the reaction to obtain quantum dot functionalized particles. Mix the quantum dot functionalized particles with a charge control agent and a dispersion medium, and then perform ultrasonic and washing treatments to obtain quantum dot fluorescent particles.

[0052] The dispersion medium can be a single or compound solvent from organic solvents such as aliphatic hydrocarbons, aromatic hydrocarbons, and halogenated hydrocarbons, for example, n-dodecane, tetradecane, isoalkanes, and perfluoroalkanes; the charge control agent can be polyisobutylene succinimide, fluorinated surfactants, ionic surfactants, etc.

[0053] In the above embodiments, the quantum dot precursor solution can be prepared by the following method: dissolving a metal halide precursor in N,N-dimethylformamide, then adding oleylamine and methacrylic acid to N,N-dimethylformamide, and stirring to obtain the quantum dot precursor solution; the metal halide typically includes at least one of cesium bromide, lead bromide, cesium iodide, lead iodide, and lead chloride. For example, the metal halide precursor for green quantum dots can be selected from cesium bromide and lead bromide, the metal halide precursor for red quantum dots can be selected from cesium iodide, lead iodide, and lead bromide, and the metal halide precursor for blue quantum dots can be selected from cesium bromide, lead bromide, and lead chloride.

[0054] Based on the above embodiments, the present invention also proposes the following specific embodiments. It should be noted that the following specific embodiments are merely exemplary and are not intended to limit the scope of protection of the present invention in any way.

[0055] Example 1

[0056] This embodiment provides a quantum dot electrophoretic display device, the pixel structure of which is as follows: Figure 1 As shown, the surfaces of the first, second, and third particles are respectively composited with quantum dots that can be excited by ultraviolet light to emit red, green, and blue light, and are named red fluorescent particles, green fluorescent particles, and blue fluorescent particles, respectively. The red fluorescent particles are strongly positively charged, the green fluorescent particles are negatively charged, and the blue fluorescent particles are weakly positively charged. The three colors of fluorescent particles coexist in the same pixel structure unit.

[0057] Showing in red: When a pixel needs to display red, apply an application such as... Figure 3 The driving waveform shown is as follows: The first, second, and third electrodes first oscillate in opposite phases, activating the charge activity of the electrophoretic particles. Then, the first electrode is applied to -15V, and the second and third electrodes are applied to +15V, generating a vertical electric field within the pixel space. Strongly positively charged red fluorescent particles, due to their higher mobility in the electric field, preferentially occupy the first electrode located on the display side. Weakly positively charged blue fluorescent particles also migrate towards the first electrode, but due to their slower mobility, they are blocked by the red fluorescent particles at the top and cannot be excited to fluoresce. Negatively charged green fluorescent particles are attracted to the bottom of the pixel space by the second and third electrodes. The final state of the particles within the pixel structure is as follows. Figure 4 As shown, after being excited by an ultraviolet light source, the pixel exhibits a red state with a high aperture ratio.

[0058] Showing green: When a pixel needs to display green, apply an application such as Figure 5 The driving waveform shown is as follows: The first, second, and third electrodes first oscillate in opposite phases, activating the charge activity of the particles. Then, +15V is applied to the first electrode, and -15V is applied to the second and third electrodes, generating a vertical electric field within the pixel space. Negatively charged green fluorescent particles are driven to the first electrode located on the display side, while positively charged red and blue fluorescent particles are attracted to the bottom of the pixel space by the second and third electrodes. The final state of the particles within the pixel structure is as follows. Figure 6 As shown, after being excited by an ultraviolet light source, the pixels exhibit a green state with a high aperture ratio.

[0059] Displayed in blue: When a pixel needs to display blue, apply an application such as... Figure 7 The driving waveform shown is as follows: The first, second, and third electrodes first oscillate in opposite phases, activating the charge activity of the particles. Then, the first electrode is applied at 0V, the second electrode at +15V, and the third electrode at -30V, generating a transverse electric field within the pixel space. Negatively charged green fluorescent particles are driven to the second electrode, while strongly positively charged red fluorescent particles, due to their higher mobility in the electric field, preferentially occupy the third electrode located at the bottom. At this point, the state of the particles within the pixel structure is as follows. Figure 8 As shown.

[0060] Subsequently, the first electrode is applied to -15V (not limited to -15V; the third electrode can be selected from -25V to -40V, the first electrode from 0V to -15V, and the potential difference between the two electrodes is preferably 10V to 40V). At this time, the weakly positively charged blue fluorescent particles experience a greater repulsive force from the strongly positively charged red fluorescent particles than the downward electric field force, driving the blue fluorescent particles to the surface of the first electrode on the display side, thus forming effective spatial separation from other fluorescent particles; the final state of the particles within the pixel structure is as follows: Figure 9 As shown, when excited by an ultraviolet light source, the pixel exhibits a blue state with a high aperture ratio.

[0061] Example 2

[0062] This embodiment performs electric field simulation on the quantum dot electrophoretic display device and its driving scheme provided in Embodiment 1 to verify whether the scheme provided in Embodiment 1 can generate the electric field distribution required to drive red, green and blue quantum dot composite electrophoretic particles.

[0063] This embodiment uses finite element electric field simulation software to establish a simulation relationship with... Figure 1 The two-dimensional electrostatic field model with consistent pixel structure is shown. The model parameters include: the length of the first electrode is 200 μm, the lengths of the second and third electrodes are both 66 μm, the interval between the second and third electrodes is 66 μm, and the cavity height is 30 μm.

[0064] Simulation results: Red state: like Figure 10 As shown, -15V is applied to the first electrode, and +15V is applied to both the second and third electrodes. Simulation results show that a vertical electric field is formed in the pixel space, with the electric field direction pointing from the bottom to the top, and the electric field intensity is uniformly distributed in the vertical direction. According to the principle of electrophoresis, positively charged particles will migrate to the first electrode (display side) along the direction of the electric field, and negatively charged particles will migrate to the bottom electrode. Therefore, strongly positively charged red fluorescent particles will quickly reach the display side and cover the display side opening. Although weakly positively charged blue fluorescent particles also migrate to the top, their speed is slower and they can be blocked by the red fluorescent particle layer.

[0065] Green state: like Figure 11 As shown, +15V is applied to the first electrode, and -15V is applied to the second and third electrodes. The simulation results show that the electric field direction is from top to bottom. Negatively charged green fluorescent particles are driven to the first electrode to appear green, while positively charged red and blue fluorescent particles migrate to the bottom. Since the red fluorescent particles have a larger charge than the blue fluorescent particles, the red fluorescent particles move faster and accumulate on the surface of the second and third electrodes in a short time. The blue fluorescent particles move slower and can only accumulate slowly outside the red fluorescent particles.

[0066] Blue state: Phase 1: As Figure 12 As shown, 0V is applied to the first electrode, +15V to the second electrode, and -30V to the third electrode. The simulation results show that a lateral electric field is generated at the bottom of the pixel, with the direction pointing from the second electrode to the third electrode. Negatively charged green fluorescent particles are pulled towards the second electrode, while strongly positively charged red fluorescent particles and weakly positively charged blue fluorescent particles are pulled towards the third electrode, with red fluorescent particles preferentially attaching to the surface of the third electrode.

[0067] Phase Two: As Figure 13 As shown, -15V is applied to the first electrode, +15V to the second electrode, and -30V to the third electrode. At this time, there is still a strong transverse electric field at the bottom of the pixel pointing from the second electrode to the third electrode to maintain the stable adsorption of green and red fluorescent particles on the second and third electrodes, respectively. For the weakly positively charged blue particles, they are attracted by the third electrode (downward), repelled by the red fluorescent particles (upward), and attracted by the first electrode (upward). At this time, the repulsive force of the red fluorescent particles (strongly positive) on the blue fluorescent particles (weakly positive) is greater than the electric field attraction of the third electrode on the blue fluorescent particles. Therefore, the repulsive force on the blue fluorescent particles is dominant, that is, the blue fluorescent particles move upward to occupy the surface of the first electrode under the action of the electric field.

[0068] The above electric field simulation results demonstrate that the three-electrode pixel structure proposed in this embodiment can generate longitudinal and transverse electric fields as needed, and the direction of the electric field can be flexibly controlled by switching the timing voltage. According to the basic principle of electrophoretic display, charged particles will migrate in the electric field due to electric force and electrostatic interaction. The migration direction depends on the polarity of the particle charge and the direction of the electric field. The driving waveform design of this invention can fully realize the selective driving of red, green and blue quantum dot composite electrophoretic particles, so that the target color particles occupy the entire pixel opening.

[0069] Example 3

[0070] This embodiment prepared R / G / B quantum dot fluorescent particles suitable for Example 1.

[0071] See Figure 14 The preparation of quantum dot fluorescent particles includes the following steps: Step 1: Disperse 10g of TiO2 powder in 100mL of ethanol and stir at 300rpm for 10min to obtain a TiO2 powder dispersion. Then, add 1g of silane coupling agent (γ-methacryloyloxypropyltrimethoxysilane, abbreviated as MPS) and 0.5g of dispersant to the TiO2 powder dispersion and continue stirring for 30min. Then, add 1mL of acetic acid dropwise to the TiO2 powder dispersion and stir for another 4h. The reaction product is washed twice by centrifugation with ethanol. Finally, the washed reaction product is dried at 60℃ to obtain particle 1 (functionalized oxide particles).

[0072] Step 2: Dissolve particle 1 in 50 mL of toluene and stir at 350 rpm for 10 min. Then add 10 g of lauryl methacrylate (LMA) to the solution and stir at 70 °C for 1 h under nitrogen protection. Subsequently, add 0.1 g of initiator AIBN to the solution and continue stirring for 16 h. After the solution reaction is complete, wash the centrifuged precipitate with toluene and dry the washed centrifuged precipitate at 60 °C to obtain particle 2 (polymer-coated composite particles).

[0073] Step 3: Dissolve 0.1g of particle 2 in 10ml of toluene and stir at 550rpm for 0.5h to obtain solution A. Slowly add 100~600μL of quantum dot precursor solution to solution A and stir the mixture at 550rpm for 0.5h to obtain solution C. Centrifuge solution C and discard the supernatant. Wash the centrifuged precipitate with toluene to obtain particle 3 (quantum dot functionalized particles). Then add charge control agent and dispersion medium to particle 3. Sonicate the mixture for 1h and wash it twice with dispersion medium. Finally, blend the washed particles with dispersion medium and store them to form quantum dot fluorescent particles.

[0074] The precursor solution for green quantum dots was prepared as follows: 20-70 mg of cesium bromide and 30-120 mg of lead bromide were dissolved in 4-6 mL of N,N-dimethylformamide (DMF). Then, 50-300 μL of oleylamine (OAM) and 140-160 μL of methacrylic acid (MAA) were added to the solution and stirred thoroughly (40-60℃) to obtain the precursor solution for green quantum dots. The luminescence performance of the finally prepared green quantum dot fluorescent particles in the electrophoretic display device is as follows: Figure 15 As shown.

[0075] The precursor solution of red quantum dots was prepared by the following method: 20-70 mg of cesium iodide, 20-70 mg of lead iodide, and 20-70 mg of lead bromide were dissolved in 4-6 mL of N,N-dimethylformamide. 50-300 μL of oleylamine and 140-160 μL of methacrylic acid were added to the solution and stirred evenly (40-60 °C) to obtain the precursor solution of red quantum dots.

[0076] The precursor solution of blue quantum dots was prepared by the following method: 20-70 mg of cesium bromide, 30-120 mg of lead bromide, and 10-180 mg of lead chloride were dissolved in 4-6 mL of N,N-dimethylformamide, and 50-300 μL of oleylamine and 140-160 μL of methacrylic acid were added and stirred evenly (40-60 °C) to obtain the precursor solution of blue quantum dots.

[0077] Example 4

[0078] This embodiment provides a quantum dot electrophoretic display device, the pixel structure of which is as follows: Figure 1 As shown, the electrophoretic particles include green fluorescent particles, red modified particles, and blue modified particles. The green fluorescent particles are prepared by the quantum dot fluorescent particle preparation method provided in Example 3, and the red and blue modified particles are reflective pigment particles.

[0079] The preparation method of modified particles includes the following steps: Step 1: Disperse 99.5 mg sodium silicate in 50 mL of deionized water, then add 10 g of pigment particles to the deionized water. Sonicate the mixture for 30 min and stir at 400 rpm for 10 min. Heat the mixture to 95 °C, then slowly add a solution prepared by dissolving 2.415 g of sodium silicate in 25 mL of deionized water. Adjust the pH of the mixture to 5-6 and continue stirring for 2 h. The reactants are washed with deionized water and dried at 60 °C to obtain particles 4 (inorganic pigments coated with SiO2 shells).

[0080] Step 2: Disperse 10g of particles 4 in 100mL of ethanol and stir at 300rpm for 10min. Then add 10g of silane coupling agent and 0.5g of dispersant to the solution and continue stirring for 30min. Then add 1mL of acetic acid dropwise to the mixed solution and stir for another 4h. The reaction product is washed twice by centrifugation with ethanol and finally dried at 60℃ to obtain particles 5 (surface-functionalized pigment particles).

[0081] Step 3: Dissolve particle 5 in 50 mL of toluene and stir at 350 rpm for 10 min. Then add 10 g of lauryl methacrylate to the dispersion and stir the mixture at 70 °C for 1 h under nitrogen protection. Subsequently, add 0.1 g of initiator AIBN (2,2'-azobisisobutyronitrile) to the mixture and continue stirring for 16 h to carry out the reaction. After the reaction is completed, wash the reactants with toluene and centrifuge. Dry the centrifuged precipitate at 60 °C to obtain particle 6 (polymer shell-coated pigment particles).

[0082] The red modified particles used iron oxide red pigment, and the blue modified particles used phthalocyanine blue or inorganic blue pigment. The final red and blue modified particles exhibit reflective color characteristics in the electrophoretic display device as follows: Figure 16 As shown.

[0083] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A high aperture ratio quantum dot electrophoretic display device based on a three-electrode pixel structure, comprising a pixel structure, wherein the pixel structure includes an upper substrate, a lower substrate, and an electrophoretic ink filled between the upper substrate and the lower substrate, the upper substrate being the display side, and the electrophoretic ink comprising an electrophoretic medium and electrophoretic particles dispersed in the electrophoretic medium, characterized in that, The upper substrate has a first electrode on the side facing the electrophoretic ink, and the lower substrate has a second electrode and a third electrode arranged at intervals. The electrophoretic particles include a first particle, a second particle, and at least one third particle with different optical properties. The first particle and the second particle have opposite charges, the third particle has the same charge polarity as the first particle or the second particle, and the charge of the third particle is less than that of the first particle or the second particle with the same charge polarity. At least one of the first particle, the second particle, and the third particle is a quantum dot fluorescent particle, and the quantum dot fluorescent particle is composited with luminescent quantum dots.

2. The high aperture ratio quantum dot electrophoretic display device based on a three-electrode pixel structure according to claim 1, characterized in that, The charge of the third particle is 33% to 50% of the charge of the first or second particle with the same polarity.

3. The high aperture ratio quantum dot electrophoretic display device based on a three-electrode pixel structure according to claim 1, characterized in that, At least one of the first particle, the second particle, and the third particle is a reflective pigment particle or an upconversion luminescent particle.

4. The high aperture ratio quantum dot electrophoretic display device based on a three-electrode pixel structure according to claim 1, characterized in that, The quantum dot fluorescent particles are prepared by the following steps: A silane coupling agent and a dispersant are added to the carrier particle dispersion to obtain a first mixed solution. Then, a silane hydrolysis catalyst is added to the first mixed solution to carry out the reaction. The reactants are washed and dried to obtain functionalized oxide particles. The functionalized oxide particles are dissolved in a nonpolar solvent to obtain a second mixed solution. Then, polymer monomers and initiators are added to the second mixed solution under an inert atmosphere to carry out the reaction. The reactants are washed and dried to obtain composite particles with a polymer coating. The composite particles are dissolved in a nonpolar solvent to obtain a third mixed solution. A quantum dot precursor solution is added to the third mixed solution to carry out the reaction. The centrifuged precipitate after the reaction is washed to obtain quantum dot functionalized particles. The quantum dot functionalized particles are mixed with a charge control agent and a dispersion medium, and then subjected to ultrasonication and washing to obtain quantum dot fluorescent particles.

5. The high aperture ratio quantum dot electrophoretic display device based on a three-electrode pixel structure according to claim 4, characterized in that, The quantum dot precursor solution is prepared by the following steps: The metal halide precursor was dissolved in N,N-dimethylformamide, and then oleylamine and methacrylic acid were added to the N,N-dimethylformamide. After stirring, a quantum dot precursor solution was obtained.

6. The high aperture ratio quantum dot electrophoretic display device based on a three-electrode pixel structure according to claim 1, characterized in that, The optical properties refer to the color state displayed under preset display conditions.

7. A driving method for a high aperture ratio quantum dot electrophoretic display device based on a three-electrode pixel structure according to any one of claims 1-6, characterized in that, Including the following steps: S1, apply an oscillating activation voltage to the first electrode, second electrode and third electrode of the quantum dot electrophoretic display device respectively; S2, apply migration driving voltages to the first electrode, the second electrode and the third electrode respectively, so that the display side of the quantum dot electrophoretic display device exhibits the optical properties of the first particle, the second particle or the third particle; In step S2, presenting the optical properties of the first particle includes the following steps: A first driving voltage is applied to the first electrode, and a second driving voltage is applied to the second and third electrodes to form a longitudinal driving electric field in a first direction between the upper and lower substrates, so that the first particle migrates to the surface of the first electrode. Presenting the optical properties of the second particle includes the following steps: A third driving voltage is applied to the first electrode, and a fourth driving voltage is applied to the second and third electrodes to form a longitudinal driving electric field in a second direction between the upper and lower substrates, so that the second particles migrate to the surface of the first electrode. The optical properties of a third particle are presented through the following steps: A zero-volt voltage is applied to the first electrode, a fifth driving voltage is applied to the second electrode, and a sixth driving voltage is applied to the third electrode. A transverse sorting electric field is formed between the second and third electrodes, causing the first and second particles to migrate to the surfaces of different electrodes in the second and third electrodes, respectively. The third particle migrates to the adjacent area of ​​the corresponding electrode along with the particles of the same polarity, and the spatial position of the third particle relative to the lower substrate is higher than that of the first or second particle with the same polarity. Maintaining the transverse sorting electric field, a seventh driving voltage is applied to the first electrode, so that the longitudinal electric field force on the third particle is less than the repulsive force generated by the first or second particle of the same polarity. The third particle migrates to the surface of the first electrode, while the first and second particles maintain their original adsorption state under the action of the transverse sorting electric field.

8. The driving method according to claim 7, characterized in that, In step S1, a first oscillation activation voltage is applied to the first electrode, and a second oscillation activation voltage is applied to the second and third electrodes. The first oscillation activation voltage and the second oscillation activation voltage are alternating voltages with opposite phases.

9. The driving method according to claim 7, characterized in that, The absolute value of the seventh driving voltage is less than the absolute value of the fifth driving voltage or the sixth driving voltage, which have the same polarity.

10. The driving method according to claim 7, characterized in that, Presenting the optical properties of the first, second, or third particle includes the following steps: The display side of the quantum dot electrophoretic display device is illuminated with light of a preset wavelength.

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