Displays using quantum dot or quantum wafer converters

Abstract

The present invention relates to a display device including a pixel array, each pixel including at least three sub-pixels having an LED device that emits light having a blue dot, wherein a first sub-pixel is designed to emit red light having a first color dot, a second sub-pixel is designed to emit green light having a second color dot, characterized in that the LED device of the third sub-pixel is covered with a third wavelength conversion layer designed to emit light having a fourth color dot, the fourth color dot such that a combination of the light emitted by the LED device without being converted by the wavelength conversion layer and the light converted by the wavelength conversion layer produces light having a third color dot, wherein the first, second, and third color dots define a second color space including a preset color space.

Description

Technical Field

[0001] The present invention relates to improvements in LED displays having a conversion layer and methods of designing such displays, as well as pixel structures and methods for manufacturing and driving LED displays. Background Art

[0002] US9728687 “Quantum Platelet Converter” describes an exemplary LED device including a QPC downconverter that converts light emitted by an LED at an emission wavelength to light at a longer wavelength. As illustrated in Figure 1 which corresponds to Figure 8 of US9728687, such an LED device 100 includes an LED die or chip 102. A sealant 106 such as silicone may be disposed on the LED die or chip 102 that emits UV or blue light. The sealant 106 can serve as a substrate for holding one or more QPC downconverters 108 and 110. The sealant and the QPC downconverters form a wavelength conversion layer 104. The QPC downconverter 108 may include different QPC structures for downconverting blue light emitted by the LED chip 102 to different longer optical wavelengths (e.g., red, green, or yellow light). For example, the QPC downconverter 108 may include a red QPC structure (108) for converting blue light to red light, a green QPC structure (110) for converting blue light to green light, a yellow QPC structure for converting blue light to yellow light, or a combination of two or all three types of the above QPC structures. The various QPC structures can be embedded in the sealant 106 that may include an adhesive material such as silicone.

[0003] Additionally, as illustrated in Figure 2 corresponding to FIG. 11 of US9728687, a transparent layer 112 may be disposed between the wavelength conversion layer 104 embedded with QPCs and the LED chip 102. The transparent layer can act as a heat dissipation layer to reduce the negative impact of heat on the color conversion material 102, and can also act as an optical peak flux reduction layer by diffusing the LED light over a larger surface, commonly referred to as a “remote phosphor” application, as in high power lighting.

[0004] US9865577 “LED display with wavelength converting layer” describes a pixel in which R, G, and B sub-pixels use the same blue, dark blue, or UV LED for all red, green, and blue sub-pixels. The blue, dark blue, or UV LED 400 is bonded to a substrate 102 and covered with a wavelength conversion layer 310. A light / heat distribution layer 320 may be formed between the LED 400 and the conversion layer 310.

[0005] of the present invention Figure 3A is a schematic side view illustration of a pixel 106 according to the prior art. Figure 3A Corresponds to FIG. 11B of US9865577. As explained in Figure 3A , each micro-LED device 400 is designed to emit in the deep blue (DB) color spectrum. Different wavelength conversion layers 310 can be designed to emit red (R), green (G), and blue (B) in an RGB sub-pixel arrangement.

[0006] When using color conversion materials, generally, the lower the excitation spectrum compared to the emission spectrum, the better the absorbance of the color conversion material. The absorption cross-section of NPL (nanoplate) or QDOT depends on the excitation wavelength. For a specific conversion material, there may be a peak in absorbance. Figure 7 Shows the spectrum of Lumidot CdSe / ZnS 610nm red-emitting quantum dot particles from TM . Line 710 represents the absorption spectrum. As can be seen in this figure, there is a local absorption peak 730 (attributed to the first excitation level) near the emission peak, but for wavelengths below 500nm, the absorbance is much stronger. Different conversion materials and the same material with different emission peak wavelengths will show excitation peaks at different wavelengths, but all will exhibit an increase in absorption towards deeper blue.

[0007] The smaller the absorption cross-section, the more QDot / NPL is required to achieve full-color conversion. There are two advantages to using a deep blue / UV excitation source: (1) the absorption cross-section is significantly larger at lower wavelengths, thus significantly reducing the required concentration (by a factor of 4 to 10 or even more), and (2) because the required concentration is lower, the average path length of reabsorption will decrease. The second advantage is explained as follows: when a blue photon is absorbed and converted to red, the red photon can encounter another color QDOT / NPL and be reabsorbed. It then has two possibilities: the QDOT / NPL can re-emit the red photon, or it can be converted to heat. Of course, the higher the concentration of QDOT / NPL, the higher the probability that the absorbed red photon is converted to heat. Therefore, reducing the concentration of the color conversion material will increase the escape probability of the red photon.

[0008] A deep blue excitation source is needed to obtain good efficiency because (1) it provides higher absorption efficiency, and (2) it reduces the probability of reabsorption.

[0009] However, in RGB displays, the requirements for color dots are strict. For example, it is necessary to implement a specific color rectangle such as Rec709, DCI-P3, Rec2020, or any other. In this case, the native deep blue LED cannot be used as the blue dot of the display because it far exceeds these color triangles. The display will lose a large number of blue dots / cyan dots. One solution to this problem is to use another blue LED as the blue dot without using color conversion materials. However, this means that two LEDs should be used: deep blue for red and green conversion, and normal blue (about 465 nm) for blue.

[0010] From a manufacturing perspective, this means that two different blue LEDs need to be filled. High-resolution LED walls are usually filled using so-called mass transfer techniques because the pick-and-place single-component method becomes too expensive. Thus, using two different blue LEDs is less compatible with mass transfer techniques due to the need for two steps. Using the same blue LED will simplify / enable mass transfer techniques and also simplify logistics, thereby reducing the high cost of high-resolution LED displays. A solution needs to be found to avoid using two types of LEDs or using an LED similar to 465 nm to generate blue emission.

[0011] The Figure 3B is a schematic side view illustration of a pixel according to the prior art, corresponding to FIG. 11C of US9865577. As explained in Figure 3B , each micro-LED device is designed to emit light in the blue (B) color spectrum. In such embodiments, different wavelength conversion layers 310 can be designed to emit red (R) and green (G). The wavelength conversion layer 310 is not formed on the third light distribution layer 320. In this way, an RGB sub-pixel arrangement is achieved without having to convert the blue light from the blue-emitting sub-pixels. The blue light in US9865577 is defined as the spectrum whose range is between 450 nm and 495 nm.

[0012] Unfortunately, other problems arise in this case. When using a blue diode (peak wavelength greater than 455 nm) for exciting the R and G converter layers and for the blue sub-pixels, more converter material is needed to achieve the correct brightness required when using a shorter peak wavelength to excite light.

[0013] The Figure 3C is a schematic side view illustration of a pixel 106 according to the prior art (from FIG. 11D of US9865577). As explained in Figure 3C , each micro-LED device 400 is designed to emit an ultraviolet (UV) color spectrum. In such embodiments, different wavelength conversion layers 310 can be designed to emit red (R), green (G), and blue (B) light.

[0014] There are problems when using UV light in pixels. For example, the UV light must be prevented from leaking out of the conversion layer and reaching the eyes of viewers who are watching a display using these LEDs.

[0015] US9865577 “LED display with wavelength converting layer” also discloses using dyes or pigments dispersed in the wavelength conversion layer to absorb colors other than green (for green sub-pixels) or red (for red sub-pixels). Specifically, the dyes or pigments dispersed in the conversion layer can absorb the blue or deep blue light emission of the LED device, thereby reducing the leakage of unconverted blue or dark blue. This dye or pigment reduces the efficiency of the structure (input power to output brightness). In fact, before the blue or deep blue light can be down-converted into red or green light, at least some of the blue or deep blue light can be absorbed in the conversion layer. This may affect the overall power efficiency of an LED display using the pixels described in US9865577.

[0016] Pixels made of LEDs as described in US9865577 and US9728687 can be smaller than pixels that have been possible heretofore. Smaller pixels are a requirement for increasing the resolution of an LED display. In the art, the space between pixels is typically a black matrix that increases the contrast of an LED display. As the resolution increases, the ratio of the area occupied by the LEDs to the area of the black matrix also increases. This means that the optical properties of the LEDs or the encapsulation of the LEDs have a greater impact on the contrast of the LED display. In fact, more ambient light interacts with the LEDs or their encapsulation than with the black matrix between the LEDs. Solutions are needed to prevent a reduction in contrast.

[0017] Improvements to the prior art are needed. SUMMARY OF THE INVENTION

[0018] Some of the problems presented by LED displays with a conversion layer in the art are given below, and one or some or all of these problems can be solved by embodiments of the present invention:

[0019] - The contrast of an LED display is increasingly affected by the surface of the pixels and less by the black matrix between the pixels. When the deep blue diode used as the excitation light is the same as the blue diode used in the blue sub-pixels, the color space that can be achieved is not recommended in standards such as Rec709 or Rec2020, etc.

[0020] - Using deep blue + color converter allows the reproduction of the desired color space, but (1) too deep blue or UV limits the use of materials because many transparent materials have an absorption edge in UV, (2) the display may emit some UV, and (3) too deep blue or UV introduces greater Stokes shift loss.

[0021] - Using the same blue LED compatible with the color space for the blue subpixel and as the excitation for the red and green down-conversion materials requires a high concentration of color conversion materials, resulting in a lower energy conversion efficiency. This energy loss is converted into heat. However, the increase in temperature will also reduce the efficiency because the conversion layer relying on quantum dots or quantum wafers is (very) sensitive to temperature changes: as the temperature increases, the quantum yield is negatively affected.

[0022] In an embodiment of the present invention, a pixel structure and a display are respectively provided, in which a deep blue LED is used for the best efficiency. Q dots can be used as the conversion layer. The LED panel can be equipped with the same deep blue LED for all subpixels, and there is no need to classify the LEDs.

[0023] The deep blue dot may be disadvantageous to certain color standards. For example, it may be too deep in the spectral locus. By using a green conversion layer (such as quantum dots) with specific color coordinates (providing a blue wavelength difference of up to 45 nm from 25 nm) and the residual light from a deep blue LED with specific color coordinates, a new blue dot is created.

[0024] The object of the present invention is to provide a pixel structure including at least three subpixels, each subpixel including an LED device configured to emit a color spectrum with a light source color point, and the three LED devices are of the same type.

[0025] The LED device of the first subpixel is covered with a first wavelength conversion layer designed to emit red light with a first color point.

[0026] The LED device of the second subpixel is covered with a second wavelength conversion layer designed to emit green light with a second color point.

[0027] The light source color point, the first color point, and the second color point define a first color space different from the set color space.

[0028] It is characterized in that the LED device of the third subpixel is covered with a third wavelength conversion layer designed to emit light with a main wavelength having a fourth color point, and the fourth color point enables the combination of the light emitted by the LED device that is not converted by the wavelength conversion layer and the light converted by the wavelength conversion layer to produce light with a third color point, where the first, second, and third color points define a second color space including the set color space.

[0029] The three LED devices of the pixel structure are preferably from the same manufacturer. The three LED devices of the pixel structure preferably emit light of the same color. The light emitted by the LED devices of the first to third sub-pixels of the pixel structure is preferably the same and has a dominant wavelength equal to or less than 455 nm.

[0030] The light emitted by the LED devices of the first to third sub-pixels of the pixel structure is the same and has a dominant wavelength in the range of 420 nm to 455 nm, or has a dominant wavelength less than 455 nm and greater than 400 nm, or greater than 380 nm, or greater than the transparent absorption edge of the materials used in the pixel.

[0031] The wavelength of the light emitted by the LED device of the third sub-pixel and the light emitted by the third wavelength conversion layer differ by at least 25 nm, preferably up to 35 nm, and even more preferably up to 45 nm.

[0032] The predefined color space is not arbitrary. It is not controlled by the manufacturer of the display. In the present application, the term "predefined color space" is an exact technical term related to standards. The predefined color space can be any one of the color spaces defined by Rec 709, Rec 2020, sRGB, DCI-P3.

[0033] The object of the present invention is to provide a display, wherein for each pixel of the display, the pixel includes red, green, and blue sub-pixels, and each sub-pixel is driven by the same light source or the same type of light source, and the display can reproduce any color within a predefined color space or within a color space defined by standards (such as the Rec.2020 (ITU-R Recommendation BT.2020) color space, Rec.709 standard, DCI-P3 color space, etc.). The predefined color space is not arbitrary. It is not controlled by the manufacturer of the display. In the present application, the term "predefined color space" is an exact technical term related to standards.

[0034] In order to be able to reproduce these color spaces with red, green, and blue light sources, the color space must be within the triangle formed by the three color points associated with the red, green, and blue light sources. Using a deep blue LED as discussed in the prior art section, it is impossible to reproduce all the colors of color spaces such as Rec.2020, Rec.709 ( Figure 8 880 in Figure 8 ), or DCI-P3 ( Figure 8 870 in

[0035] For example, for the REC.709 color space (ITU-R Recommendation BT.709), the CIE coordinates of the red primary color are (xr = 0.64; yr = 0.33); the green primary color (xg = 0.30; yg = 0.60); the blue primary color (xb = 0.15; yb = 0.06). Colors within the color gamut will fall within the triangle connecting these primary colors. In the REC2020 color gamut, the CIE coordinates of the red primary color are (xr = 0.708; yr = 0.292); the green primary color (xg = 0.170; yg = 0.797); the blue primary color (xb = 0.131; yb = 0.046). The object of the present invention is to provide a display device including a pixel array, each pixel including at least three sub-pixels, each sub-pixel including an LED device configured to emit a color spectrum having a light source color point, wherein the LED device of the first sub-pixel is covered with a first wavelength conversion layer designed to emit red light having a first color point, the LED device of the second sub-pixel is covered with a second wavelength conversion layer designed to emit green light having a second color point, the light source color point, the first color point and the second color point define a first color space different from the set color space, characterized in that the LED device of the third sub-pixel is covered with a third wavelength conversion layer, the third wavelength conversion layer being designed to emit light having a main wavelength with a fourth color point, the fourth color point such that the combination of the light emitted by the LED device not converted by the wavelength conversion layer and the light converted by the wavelength conversion layer produces light having a third color point, wherein the first, second and third color points define a second color space including the set color space.

[0036] All the excited LED devices are preferably the same, for example, emitting the same color and preferably supplied by the same manufacturer. The excited LED devices can even be from the same manufacturing batch. If all the excited LED devices are the same, there is no need for re-alignment when the robot picks and places different excited LED devices. Also, less time may be lost between batches. This makes the sourcing and procurement issues much easier and can reduce costs.

[0037] The light emitted by the excited LED devices may be outside the set color space that the display device is to display. With these excited LED devices, the display device can display in a color space including the set color space. The set color space can be the minimum color space that the display must be able to display. The set color space is not arbitrary. It is not under the control of the display manufacturer. The term "set color space" is an exact technical term related to standards.

[0038] Advantages are that by three LEDs of the same type, emitting light not included in the set color space, it is possible to efficiently provide a color space including the set color space. Using LEDs of the same type or substantially the same LEDs, the manufacturing process of the display device according to the present invention is improved because it is compatible with the mass transfer technology as a pick-and-place single-component method. In addition, the required color space can be generated by the display in an efficient manner.

[0039] Advantageously, the wavelength emitted by the LED device of the third sub-pixel and the light emitted by the third wavelength conversion layer differ by at least 25 nm, preferably up to 35 nm, and even more preferably up to 45 nm.

[0040] Increasing the wavelength difference between the wavelength of light excitation and the light emission of the wavelength conversion layer improves the efficiency of the wavelength conversion layer.

[0041] Advantageously, the set color space is any one of Rec 709, Rec 2020, sRGB, DCI-P3. Such color spaces define the standards or recommendations that a display needs to meet. For the color points that an RGB light source must satisfy, many technologies cannot meet these strict requirements. The present invention provides a means to use LEDs of the same type for all red, green, and blue sub-pixels to achieve those target color spaces.

[0042] Advantageously, the fourth color point is located to the left of the line connecting the light source color point and the third color point in the chromaticity diagram color space and above the third color point.

[0043] To achieve the target color point or the third color point, using color mixing theory, the inventors have observed that any point to the left of the line connecting the light source color point and the third color point of the target color space in the CIE chromaticity diagram and above the light source color point can be selected.

[0044] Advantageously, the thickness of the third wavelength conversion layer and the density of the down-conversion material in the third wavelength conversion layer are selected such that when the converted light having the fourth color point and the unconverted light having the light source color point are combined, an appropriate amount of light emitted by the LED of the third sub-pixel is converted to obtain the third color point.

[0045] These parameters determine the amount of light converted by the wavelength conversion layer, which further determines the third color point of the light emitted by the third sub-pixel, which includes the converted light and the unconverted light passing through the wavelength conversion layer.

[0046] Advantageously, the thickness of the wavelength conversion layer and the density of the down-conversion material in the third wavelength conversion layer are such that the light flux of the light including the converted light and the unconverted light having the third color point is maximized.

[0047] Advantageously, the LED device is configured to emit a color spectrum having a peak wavelength less than 455 nm and / or greater than 420 nm, or greater than 400 nm, or greater than 380 nm, or greater than the transparent absorption edge of the material used in the pixel.

[0048] Advantageously, the light source color point is a blue point.

[0049] The advantage is that shifting the excitation wavelength towards the UV increases the absorption of the wavelength conversion layer and thus the efficiency. However, the lower limit is determined by the transparent absorption edge of the material used in the pixel.

[0050] Advantageously, the third wavelength conversion layer is configured to emit light having a wavelength greater than 480 nm and / or preferably less than 520 nm, and even more preferably a wavelength of 490 nm when excited by blue light emitted by the LED device of the third sub-pixel.

[0051] This wavelength has the advantage of providing the desired fourth color point such that when the converted light having this fourth color point is mixed with the unconverted light of the light source having the light source color point, light having the third color point is generated.

[0052] Advantageously, the third wavelength conversion layer is configured to absorb less than 50%, preferably less than 20%, and even more preferably less than 10% of the blue light emitted by the third LED device.

[0053] In an embodiment of the invention, a small portion of the light emitted by the light source of the third sub-pixel needs to be absorbed and thus converted in order to provide the third color point when mixing the converted light and the unconverted light.

[0054] Advantageously, the first wavelength conversion layer is configured to emit light at 620 nm when excited by the blue light of the first LED device.

[0055] These wavelengths need to be compatible with the intended color space. In the case of color spaces such as Rec 709, Rec 2020, sRGB, etc., emission at 620 nm is optimal for red. However, without departing from the spirit of the invention, if the display is to generate a different intended color space, the invention is not limited to using this wavelength.

[0056] Advantageously, the second wavelength conversion layer is configured to emit light at 532 nm when excited by the blue light of the second LED device. The blue light emitted by the second LED device is preferably the same blue as that emitted by the first and third LED devices.

[0057] These wavelengths need to be compatible with the set color space. In the case of color spaces such as Rec 709, Rec 2020, sRGB, etc., the emission at 532 nm is optimal for green. However, without departing from the spirit of the present invention, if the display is to generate a different set color space, the present invention is not limited to using this wavelength.

[0058] Advantageously, preferably less than 10% or preferably less than 5% or preferably less than 1% of the blue light emitted by the LED device of the first sub-pixel escapes through the first wavelength conversion layer, and / or preferably less than 10% or preferably less than 5% or preferably less than 1% of the blue light emitted by the LED device of the second sub-pixel escapes through the second wavelength conversion layer.

[0059] The advantage is that most of the light emitted by the LED is converted by the wavelength conversion layers of the first and second sub-pixels. Such high efficiency is generally achieved considering the wavelength difference between the excitation light and the emitted light.

[0060] Advantageously, the wavelength conversion layer includes quantum sheets or quantum dots.

[0061] Compared with, for example, phosphor particles, quantum dots and quantum sheets have the advantages of being very small and providing pure colors and light with a narrow bandwidth. The emission wavelength can also be selected by changing the size of the particles.

[0062] Advantageously, the first filter is positioned on the first wavelength conversion layer, and / or the second filter is positioned on the second wavelength conversion layer, and / or the third filter is positioned on the third wavelength conversion layer.

[0063] The filters can be the same or different.

[0064] Advantageously, the first, second and third filters are screen printed or inkjet printed on the sub-pixels.

[0065] Advantageously, the first and / or second filters filter out the blue light emitted by the corresponding LED device that passes through the corresponding wavelength conversion layer.

[0066] Filtering out the blue light that is not converted within the first and second sub-pixels has the advantages of improving the contrast of the display device and improving the image quality.

[0067] Advantageously, the first and / or second filters absorb the blue wavelength and optionally other wavelengths found in the spectrum of ambient light.

[0068] Advantageously, the first and / or second filter filters out the blue light emitted by the corresponding LED device that passes through the corresponding wavelength conversion layer, and / or wherein the first and / or second filter and / or the third filter absorbs at least a portion of the wavelengths found in the spectrum of the ambient light, excluding the wavelengths corresponding to the first color point for the first filter, excluding the wavelengths corresponding to the second color point for the second filter, and excluding the wavelengths corresponding to the blue point and the fourth color point for the third filter.

[0069] Another advantage is to provide a blue absorption layer on the third wavelength conversion layer configured to absorb ambient light.

[0070] Such filters have the advantage of increasing the contrast of the display device and being able to sharpen the desired emission spectrum of the sub-pixels of the display device according to the present invention.

[0071] Advantageously, the size of the pixel is less than 1 mm and the pixel pitch is at most 1 mm, such that the display device is a high-resolution display device.

[0072] The present invention also provides a method of manufacturing a display device, comprising:

[0073] - forming a pixel array, each pixel including at least three sub-pixels, each sub-pixel including an LED device configured to emit a color spectrum having a light source color point,

[0074] - covering the first LED device of the first sub-pixel with a first wavelength conversion layer designed to emit red light having a first color point,

[0075] - covering the second LED device of the second sub-pixel with a second wavelength conversion layer designed to emit green light having a second color point,

[0076] - the light source color point, the first color point, and the second color point define a first color space different from the set color space,

[0077] It is characterized in that a third LED device covering a third sub-pixel is covered with a third wavelength conversion layer, which is designed to emit light having a main wavelength with a fourth color point, and the fourth color point is such that the combination of the light emitted by the LED device that is not converted by the wavelength conversion layer and the light converted by the wavelength conversion layer produces light having a third color point, wherein the first, second, and third color points define a second color space including a preset color space. The blue light emitted by the LED device should be the same and may have a main wavelength equal to or less than 455 nm, preferably in the range of 420 nm to 455 nm. All the excited LED devices (i.e., the first to third LED devices) are preferably the same, for example, emitting the same color light and preferably supplied by the same manufacturer. The excited LED devices may even be from the same manufacturing batch. If all the excited LED devices are the same, there is no need for re-alignment when the robot picks and places different excited LED devices. Also, less time may be lost between batches. This makes the sourcing and procurement issues much easier and can reduce costs. The light emitted by the excited LED devices may be outside the preset color space that the display device is to display. Through these excited LED devices, the display device can display in a color space including the preset color space. The preset color space may be the minimum color space that the display must be able to display.

[0078] According to the present invention, there is provided a display device including a pixel array, each pixel including at least three LED devices configured to emit a blue spectrum, wherein a first LED device among the three LED devices is covered with a first wavelength conversion layer designed to emit red light, a second LED device among the three LED devices is covered with a second wavelength conversion layer designed to emit green light, and it is characterized in that a third LED device among the three LED devices is covered with a third wavelength conversion layer, which is designed to emit light having a main wavelength greater than the wavelength corresponding to a target blue point, such that the combination of the light emitted by the third LED device that is not converted by the wavelength conversion layer and the light converted by the wavelength conversion layer produces light having the target blue point, and the target blue point is compatible with a preset or predefined color space such as a standard color space.

[0079] To achieve the above object, the pixels of the display have at least three light sources, such as LED devices designed to emit in the blue (B) color spectrum. One of the light sources, such as an LED device, is covered with a first conversion layer designed to perform wavelength conversion on the blue light and emit red light (R). One of the light sources, such as an LED device, is covered with a second conversion layer designed to perform wavelength conversion on the blue light and emit green light (G). A third light source, such as an LED device, is covered with a third conversion layer designed to perform wavelength conversion on the blue light. This wavelength conversion can be designed to adjust the color gamut or color space that can be displayed. For example, the third wavelength converter can be adapted to emit a specific amount of cyan light (C). The third converter layer can be designed to absorb less blue light compared to the first and second conversion layers.

[0080] An advantage of this aspect of the invention is that it allows the same excitation light source, such as an LED device, to be used for the R, G, and B sub-pixels of a display, such as an LED display, without affecting the color space. This is achieved by selecting three wavelength conversion materials to emit red, green, and blue light.

[0081] Another advantage of this aspect of the invention is that it allows the same light source, such as an LED device, to be used for the R, G, and B sub-pixels of a display, such as an LED display, without increasing power dissipation.

[0082] Yet another advantage of this aspect of the invention is that it allows the same light source, such as an LED device, to be used for the R, G, and B sub-pixels of a display, such as an LED display, while reducing the amount of converter material required for the R and G sub-pixels. The light source, such as an LED device, designed to emit in the blue color spectrum preferably has a dominant wavelength of less than 455 nm.

[0083] When excited by blue light emitted by a light source such as an LED device, the red wavelength converter layer can emit light at 620 nm. When excited by blue light emitted by a light source such as an LED device, the green wavelength converter layer can emit light at 532 nm.

[0084] The third wavelength conversion layer can emit light with a wavelength greater than 480 nm when excited by blue light emitted by a light source such as an LED device to obtain a target blue point, and absorb less than 50% of the blue light emitted by the LED device, preferably less than 20% or more preferably less than 10% of the blue light emitted by the LED device. The third wavelength conversion layer can emit light with a wavelength of 490 nm when excited by the blue light emitted by the LED device, and absorb less than 15% of the blue light. Description of the Drawings

[0085] The following description of the drawings of specific embodiments of the present invention is exemplary in nature only and is not intended to limit the teachings of the present invention and its application or use. Throughout the drawings, corresponding reference numerals indicate the same or corresponding components or features.

[0086] Figure 1 is a schematic representation of an LED device with a QPC downconverter according to the prior art.

[0087] Figure 2 is a schematic representation of an LED device according to the prior art.

[0088] Figure 3A is a schematic representation according to the prior art.

[0089] Figure 3B is a schematic representation according to the prior art.

[0090] Figure 3C is a schematic representation according to the prior art.

[0091] Figure 4 is a schematic representation of a pixel structure according to an embodiment of the present invention.

[0092] Figure 5 is a schematic representation of a pixel structure according to another embodiment of the present invention.

[0093] Figure 6 is a graph showing the spectrum of a white LED, which shows the blue light directly emitted by a GaN-based LED for exciting a phosphor and the Stokes-shifted light emitted by a Ce3+:YAG phosphor.

[0094] Figure 7 illustrates from the Lumidot TM spectrum of CdSe / ZnS 610nm red-emitting quantum dot particles.

[0095] Figure 8 illustrates the CIE 1931 color space chromaticity diagram and the various color spaces that can be achieved according to embodiments of the present invention.

[0096] Figure 9 illustrates the color space and color points achieved with a third wavelength conversion layer when the blue light source emits at 440nm, and the third wavelength conversion layer can be selected to achieve a target blue point.

[0097] Figure 10 illustrates the color space and color points achieved with a third wavelength conversion layer when the blue light source emits at 445nm, and the third wavelength conversion layer can be selected to achieve a target blue point.

[0098] Acronyms and Definitions

[0099] Color points. The color points correspond to the coordinates of a color in a chromaticity diagram (such as the CIE 1931 color space).

[0100] Contrast ratio is a property of a display system, defined as the ratio of the luminance of the brightest color (white) that the system can produce to the luminance of the darkest color (black). A high contrast ratio is a desired aspect of any display.

[0101] Cyan is a blue - green color. It is caused by light with a dominant wavelength between 480 - 520 nm or in the range 490 - 520 (i.e., between the wavelengths of green and blue light).

[0102] Deep blue light refers to light having a wavelength included in the range from 380 to 455 nm.

[0103] Peak optical wavelength is the highest wavelength optically emitted from a light source such as an LED device, while the dominant optical wavelength refers to the color shade perceived by the human eye.

[0104] The dominant wavelength is defined as a single wavelength perceived by the human eye. Generally, a light source consists of a spectrum of multiple wavelengths from that source rather than a single wavelength. Our brain converts these multiple spectra into a monochromatic light consistent with a particular wavelength, which is what we see when we look at the light. This is the dominant wavelength of the light source.

[0105] High - resolution displays. For LED wall - mounted displays, the state - of - the - art in high resolution has been continuously improving. Some years ago, like the giant billboards in Times Square, USA, the pixel pitch was around 10 mm, and a few years ago 4 mm was the standard pitch. Today, a high - resolution LED wall means a pixel pitch in the order of 0.8 to 1.2 mm.

[0106] Same light sources refer to substantially the same light sources or the same type, i.e., within a given tolerance of their emission spectra or emission peak wavelengths. It can also refer to light sources from the same manufacturer and manufactured by the same process. They can belong to the same batch.

[0107] Peak wavelength. The peak wavelength is defined as the single wavelength at which the radiant emittance spectrum of a light source reaches its maximum. More simply, it does not represent any perceived emission by the human eye of the light source, but rather is through a photodetector.

[0108] A quantum sheet converter (QPC) is a two-dimensional semiconductor nanocrystal with unique optical properties, typically 4 to 7 layers of crystal unit cells (e.g., CdSe). These are two-dimensional structures where the excited electron-hole (= exciton) has degrees of freedom only in two dimensions, and one dimension is forbidden, called one-dimensional confinement. (The extreme case is an atom-thick layer, such as graphene). In contrast, a quantum dot is a spherical semiconductor nanocrystal with a radius typically of 50 to 200 unit cells. These are "zero-dimensional" structures; the exciton has no degrees of freedom, called three-dimensional confinement. There are also two-dimensional confinement cases where the exciton has only one degree of freedom; these are called nanorods (e.g., carbon nanotubes).

[0109] Both rely on the principle of bandgap tuning and thus result in emission wavelength tuning due to confinement effects.

[0110] Subpixel A subpixel is a component of a pixel designed to emit light of a specific color (e.g., red, green, or blue).

[0111] Wavelength conversion layer A wavelength conversion layer is a layer containing downconversion materials, such as quantum dots or quantum sheets (also called nanoplatelets). The density of the downconversion materials required for the most efficient conversion is determined by many factors. The most important factors are: (1) the absorption cross-section of deep blue photons; a high absorption cross-section of deep blue photons reduces the number of particles required for complete conversion, (2) the reabsorption cross-section of the converted photons, (3) the concentration of color conversion particles, and (4) the thickness of the layer.

[0112] The concentration and thickness are related to each other; the higher the concentration, the thinner the layer. The layer thickness can be made very small, which is limited by the manufacturing method.

[0113] The set color space or predefined color space is not arbitrary. They are not under the control of the display manufacturer. The terms "set color space" or "predefined color space" are both precise technical terms related to standards.

[0114] Detailed description of the illustrative embodiments

[0115] The present invention will be described with reference to specific embodiments, but the invention is not limited thereto and is only limited by the claims. Any reference signs in the claims should not be construed as limiting the scope.

[0116] When the term "comprising" is used in this specification and the claims, this term does not exclude other elements or steps. Where an indefinite or definite article (e.g., "a" or "the", "said") is used in reference to a singular noun, this includes the plural form of the noun, unless otherwise stated.

[0117] In addition, the terms first, second, third, etc. in the specification and in the claims are used to distinguish between similar elements and are not necessarily used to describe an order of sequence or temporal order, unless specified. It is understood that the terms so used are interchangeable under appropriate circumstances, and the embodiments of the invention described herein are capable of operating in an order different from that described or illustrated herein. The terms or definitions used herein are provided solely to assist in understanding the invention.

[0118] The terms "about" or "approximate", etc. are synonyms and are used to indicate that the value modified by the term has an associated range of understanding, where the range can be +20%, +15%, +10%, +5% or +1%. The term "substantially" is used to indicate that a result (e.g., a measured value) is close to a target value, where close can mean, for example, that the result is within 80% of the value, within 90% of the value, within 95% of the value, or within 99% of the value.

[0119] To avoid problems associated with the prior art, the inventors made the following observations. Using a deep blue light source (such as a deep blue LED, e.g., 450 nm) provides the advantage of significantly increasing the absorption cross-section of green and red wavelength converters. However, for the blue dot, the blue 450 nm light is not efficiently and fully converted into an optimal blue dot or a target blue dot (e.g., 465 nm). In fact, the difference between the excitation wavelength and the emission wavelength is too small; this would be very inefficient. The inventors have found that by depositing a small amount of cyan wavelength conversion material (e.g., 490 nm) on top of a blue light source such as a blue LED (e.g., 450 nm), a better blue color can be generated. This small amount of cyan, together with the blue 450 nm light from the blue light source (such as a blue LED), is sufficient to generate an optimized (target) blue dot, while the difference between the excitation spectrum and the emission spectrum is still large enough to obtain significant efficiency. The blue light emitted by the LED device should be the same and can have a dominant wavelength equal to or less than 455 nm, preferably in the range of 420 nm to 455 nm. All the excited LED devices (i.e., the first to the third LED devices) are preferably the same, e.g., emitting the same color light (e.g., 450 nm) and preferably supplied by the same manufacturer. The excited LED devices can even be from the same manufacturing batch. If all the excited LED devices are the same, no realignment is required when the robot picks and places different excited LED devices. Also, less time may be lost between batches. This makes the sourcing and procurement issues much easier and can reduce costs. The light emitted by the excited LED devices may be outside the set color space that the display device is to display. Through these excited LED devices, the display device can display in a color space that includes the set color space. The set color space can be the smallest color space that the display must be able to display.

[0120] Figure 4 Fig. Figure 4 shows a schematic representation of a pixel according to a first aspect of the invention. Pixel 406 has three sub-pixels. The first sub-pixel may be a red sub-pixel. The first blue LED 400 illuminates the first wavelength conversion layer 310, which is designed to emit red light (R) when excited by the light emitted by the first blue LED 400. The second sub-pixel may be a green sub-pixel. The second blue LED 401 illuminates the second wavelength conversion layer 311, which is designed to emit green light (G) when excited by the light emitted by the second blue LED 401. The third sub-pixel may be a blue sub-pixel. The third blue LED 402 illuminates the third wavelength conversion layer 312, which is designed to emit light having a color point such that the combination of the converted light and the non-converted light of the third blue LED produces emitted light having a target blue point. If the target blue point corresponds to light having a wavelength of 467 nm and the blue LED emits light having a main wavelength of 450 nm, then the third wavelength conversion element should emit light when excited by light having a wavelength of approximately 490 nm (which corresponds to cyan light (C)) emitted by the third blue LED 402. Those skilled in the art are well aware that the additive mixing theory in the CIE xy chromaticity diagram can be used to evaluate the color point corresponding to the wavelength of the converted light or the color point corresponding to the target blue point. For all sub-pixels, the blue light emitted by the LED device should be the same and may have a main wavelength equal to or less than 455 nm, preferably in the range of 420 nm to 455 nm.

[0121] Preferably, the blue LEDs 400, 401, and 402 are substantially the same, in particular they are designed to emit substantially the same spectrum. "Same" may mean, for example, that they are from the same manufacturer, have the same reference number, and exhibit the same or substantially the same properties (such as main wavelength, spectral half-width, radiant flux) within a predetermined tolerance within a predetermined range.

[0122] The blue light emitted by the LEDs 400, 401, and 402 has a main wavelength equal to or less than 455 nm, preferably in the range of 420 nm to 455 nm. In fact, as mentioned above, it is advantageous to use as deep a blue as possible because the absorption cross-section is larger and reabsorption is less for the red and green wavelength conversion layers. However, the lower limit is determined by the absorption edge of the materials used, and the use of harmful ultraviolet light poses a danger to the user.

[0123] The first wavelength conversion layer 310 is designed to emit red light having a main wavelength of 620 nm or substantially 620 nm. The tolerance regarding the wavelength emitted by the first wavelength conversion layer depends on the color space to be reproduced as defined above.

[0124] The thickness of layer 310 and the density of the down-converting material (e.g., quantum dots or quantum flakes) in the wavelength conversion layer are preferably such that the conversion obtained is maximized. For example, preferably less than 10% or preferably less than 5% or preferably less than 1% of the blue light emitted by a blue light source such as diode 400 will leak out of the wavelength conversion layer 310. This will result in some blue light leakage, which can be absorbed by the top layer.

[0125] The second wavelength conversion layer 311 is designed to emit green light with a main wavelength of 532 nm or substantially 532 nm. The tolerance with respect to the wavelength emitted by the first wavelength conversion layer depends on the color space to be reproduced as defined above. The thickness of layer 311 and the density of the down-converting material (e.g., quantum dots or quantum flakes) are such that the conversion obtained is maximized. For example, less than 10% or preferably less than 5% or preferably less than 1% of the blue light emitted by a blue light source such as diode 401 will leak out of the wavelength conversion layer 310. This will result in some blue light leakage, which can be absorbed by the additional top layer.

[0126] As described above, for primary colors, e.g., blue of 445 to 450 nm, green of 532 nm, red of 620 nm, it is not possible to generate the color space required for an LED display that complies with industry standards such as ITU-R Recommendation BT.709, also known as Rec709, because all the colors of this color space standard are not within the triangle formed by the three color points corresponding to these three wavelengths. In fact, the green-blue part of the color space cannot be reproduced.

[0127] To overcome these problems, the third wavelength conversion layer 312 is designed to emit a further color when excited by a light source, preferably having a spectrum with a wavelength higher than the required blue, such that the combination of this further color and the excitation wavelength provides the target blue point. Thus, the selection of the third wavelength conversion layer 312 is such that the pixels of the display can reach a specific color gamut or color space. Consequently, the wavelength conversion layer can be configured to emit, for example, cyan light. This is provided to generate a color space that can be covered by the pixels 406 and meet the requirements of, for example, Rec709. The spectrum of the light emitted by the third wavelength conversion layer preferably has a main wavelength as follows: it is preferably at least 480 nm, more preferably in the range of 480 nm to 520 nm, and even more preferably at, for example, 490 nm.

[0128] The thickness of layer 312 and the density of the down-converting material (e.g., quantum dots or quantum flakes) in the third wavelength conversion layer 312 can be such that the luminous flux obtained is maximized for the correct (or target) blue point. For example, as Figure 4As shown, 80% or more of the blue light emitted by a blue light source such as diode 402 will leave the wavelength conversion layer 312 without being converted. The non-converted blue light 403 (the light that has not been converted) leaving the wavelength conversion layer 312 and the cyan light 313 (converted light) emitted by the conversion layer are mixed by the wavelength conversion layer 312. Thus, the thickness of the layer and the density of the down-conversion material are selected such that an appropriate amount of the light emitted by the light source is converted in order to reach the target color point when the converted light and the non-converted light are combined. Thus, in order to achieve the desired effect, the following parameters must be considered simultaneously in the design: the wavelength of the light source (or blue LED), the target blue point (or wavelength), the wavelength of the light emitted by the third wavelength conversion layer after being excited by the light source, the thickness of the wavelength conversion layer, and the density of the down-conversion material in the wavelength conversion layer.

[0129] Figure 8 The CIE color space, spectral locus 890, and each color space defined by standards such as Rec.709(880), DCI P3(870) are illustrated. The red point 810, green point 820, and target blue point 860 form triangle 805, within which each color space is included. The color point corresponding to the deep blue light source is represented by 850. In order to reach the target blue point 860, the light emitted by the light source must be combined with the light having the color point 840 in the cyan region. For efficiency reasons (the wavelengths need to be further apart), the cyan point 840 should be further away from the target blue point 860 than the deep blue point 850. It can be seen that all three color points (840, 850, 860) are on the same line in the color space, and the target blue point can be calculated as the weighted arithmetic mean of the light source color point 850 and the cyan point 840 weighted by their intensities. In Figure 8 the example, the blue light source emits a wavelength of 440 nm, with an FWHM of 19 nm, and the wavelength conversion layer emits a wavelength of 490 nm, with an FWHM of 50 nm, after being excited by the blue light source. In order to reach the target blue point, the contribution of the non-converted blue light is 92%, while the contribution of the converted cyan light is 8%.

[0130] As outlined above, those skilled in the art know that the theory of additive color mixing can be used to evaluate the contributions of the non-converted light and the converted light required to reach the target blue point. In practice, the contributions of the non-converted light and the converted light to reaching the target blue point depend on many factors. A first guess can be made. This first guess can be made using the theory of additive color mixing and will be more accurate if the spectral bandwidth of the light source and the light emitted by the wavelength conversion layer are known. In order to obtain the correct value, in practice, the color point of the combined light beam is measured.

[0131] Thus, in order to reach the target blue point, the third wavelength conversion layer should emit light with a wavelength greater than 480 nm when excited by blue light emitted by a light source such as an LED device. The third wavelength conversion layer should also absorb less than 50% of the LED blue light, preferably less than 20% or more preferably less than 10% of the blue light emitted by the LED device in order to reach the target blue point.

[0132] Figure 9 and 10 shows which color points corresponding to the wavelengths emitted by the wavelength conversion layer can be selected theoretically with blue light sources emitting at 440 nm and 445 nm respectively. Figure 9 to the left of line 900 in Figure 10 and to the left of line 1000 in

[0133] All color points to the left of line 900 in

[0134] and to the left of line 1000 in can theoretically be selected with 440 nm and 445 nm light sources respectively to reach the target color point. However, the efficiency requirements as defined by the wavelength difference between the excitation wavelength of the light source and the emission wavelength of the wavelength conversion layer must not be forgotten. This wavelength difference should be at least 25 nm, preferably 35 nm, and even more preferably 45 nm.

[0135] Using a light source or LED emitting light at 405 nm as the excitation wavelength of the wavelength conversion material forms part of the scope of the present invention. However, depending on the depth of the blue color, the following effects may occur:

[0136] (1) The display may emit some UV light, but this should be avoided for safety reasons.

[0137] (2) Many optically transparent materials absorb UV light, and so choosing a UV LED already excludes many standard economic materials or off-the-shelf materials, and

[0138] (3) The greater the depth of the blue color, the greater the Stokes shift loss. For example, when 405 nm photons are absorbed and 620 nm red photons are emitted, due to the quantum nature of this problem, the upper limit of the achievable efficiency is determined by the ratio 405 / 620 = 65%.

[0139] Thus, for display applications, the wavelength of the blue light source should preferably be in the range of, for example, 420 nm to 455 nm, with the lower boundary determined by the transparent absorption edge of the materials used.

[0140] As discussed above, the deeper the wavelength of the blue light source, the higher the absorption of the down-conversion material (or wavelength conversion layer). This effect is illustrated in Figure 7 . Reducing the excitation wavelength has the effect of increasing absorption, which is shown by line 710 in Figure 7 . As discussed above, reducing the wavelength towards the ultraviolet spectrum increases absorption. As mentioned above, the lower limit in the UV spectrum is mainly defined based on the transparent absorption edge of the materials used, UV-related safety issues known to those skilled in the art, and the Stokes shift.

[0141] Therefore, the light source or LED light source can emit deep blue light or light with a wavelength in the range of 380 to 455 nm, or 400 to 455 nm, or 420 to 455 nm, where the lower boundary is determined by the transparent absorption edge of the materials used.

[0142] For the above wavelength ranges, by using a cyan conversion material deposited on a blue light source (such as a deep blue LED), the blue dots can be corrected and shifted towards the target blue dots, and thus the earlier mentioned problems can be solved.

[0143] The important properties of this structure are:

[0144] (1) The target color triangle (or color space) obtained due to the color dot shift,

[0145] (2) As high an energy efficiency as possible (which is achieved because the difference between the excitation spectrum and the emission spectrum of all three wavelength conversion elements is large enough to obtain a very high efficiency),

[0146] (3) According to the present invention, three identical light sources are used for each sub-pixel of the pixel to improve the manufacturing process of the display.

[0147] The effect that occurs when using the color conversion layer is that it would be imagined that as much blue as possible needs to be absorbed, which will be converted into, for example, red. But then the red needs to escape from the layer, and self-absorption needs to be minimized. These two requirements are competitive, i.e., a high concentration for blue absorption and a low concentration for red escape. As discussed earlier, a deeper blue color helps. It turns out that when aiming for the maximum color conversion efficiency, due to the competition between the two effects of conversion and self-absorption, some blue will leak through the structure. However, this leakage can be removed by providing a blue absorption layer after (i.e., above) the wavelength conversion layer. Mixing this blue absorption into the wavelength conversion layer itself will not help improve the efficiency, because if the absorbing material is mixed with the color conversion material, some blue photons will have been absorbed in the first part of the color conversion layer.

[0148] In a second aspect of the present invention, as Figure 5 shown, the filters are placed on the first and second wavelength conversion layers of the red and green sub-pixels. For these two sub-pixels, the filters can be the same, or the filter 500 on the red sub-pixel can be different from the filter 501 on the green sub-pixel.

[0149] The filters 500, 501 can be screen-printed on the sub-pixels, for example.

[0150] The filters 500 and 501 filter out the blue light emitted by the LEDs 400, 401 and that would otherwise pass through the wavelength conversion layers.

[0151] The filters 500, 501 can also be designed to absorb blue wavelengths and other wavelengths found in the spectrum of ambient light (e.g., sunlight or artificial light expected around an LED display). This will advantageously increase the contrast of an LED display using pixels according to embodiments of the present invention. All wavelengths other than the target emission wavelengths (to reach the target color point) will be absorbed; the red of the red pixels, the blue and cyan of the blue pixels, and the green of the green pixels. Such filters can also be printed on the blue pixels to remove some ambient light, in addition to the wavelengths that contribute to the target blue point.

[0152] Figure 6 The spectrum of a white LED is shown, which shows the blue light directly emitted by the GaN-based LED (peaking at approximately 465 nm) used to excite the phosphor and the broader band of Stokes-shifted light emitted by the Ce3+:YAG phosphor (which emits at approximately 500–700 nm).

[0153] For this particular phosphor, the absorption (excitation) peak is at approximately 465 nm. If it is assumed that it will peak at 450 nm, then for efficiency reasons, it is best to pump the phosphor at 450 nm.

[0154] Figure 7 Shown as an example is from Lumidot TMSpectrum of CdSe / ZnS 610nm red emitting quantum dot particles. Line 710 represents the absorption spectrum, while line 720 represents fluorescence. It is clear from the figure that absorption is most effective and increases rapidly at deep UV. An optical filter that attenuates the wavelength to below 500nm will not only attenuate the blue light reflected on the LED, it will also prevent the blue light present in the ambient light (i.e., light emitted by light sources other than LED devices 400, 401, 402) from exciting the wavelength conversion layer. The pigments dispersed in the wavelength conversion layer are expected to be less efficient than filters located on the wavelength conversion layer (i.e., farther away from the blue LEDs 400, 401, 402 than the wavelength conversion layer). In fact, such filters will not attenuate the blue light emitted by LEDs 400, 4001, 402 before it is able to interact with the wavelength conversion layer. Blue light emitted by an external source will first be attenuated before reaching the wavelength conversion layer.

[0155] from Figure 6 and 7 It can be seen that the difference between phosphor particles and quantum dots (and also quantum flakes) is the spectral bandwidth of the emitted light. The advantage of quantum dots / quantum flakes is that they produce pure and saturated emission colors with narrow bandwidths, characterized by a full width at half maximum in the range of 20-45nm. Their emission wavelength can be tuned by changing the size of the quantum dots.

[0156] In contrast, most phosphor particles have broadband emission spectra. The color point associated with the light emitted by phosphor particles will tend to be closer to the white point in color space than that of a quantum dot / quantum particle based wavelength conversion layer, and thus will not be as Figure 9 and 10 to the left of the line shown.

[0157] The core of the quantum dots / quantum sheets of the wavelength conversion layer according to an embodiment of the present invention may be indium phosphide based or cadmium selenide based.

[0158] Wavelength conversion layers comprising quantum dots and / or quantum flakes are particularly suitable for high-resolution displays, in particular due to the size of the quantum dots / quantum flakes. In fact, the size of pixels (each pixel comprising three sub-pixels) that can be achieved is less than 1 mm, with a pixel pitch of about 1 mm. Such sizes cannot be achieved using phosphors, as the phosphor particles are too large (of the order of 10 μm). Grinding the phosphor particles will reduce their size, but will also affect their efficiency.

[0159] Quantum dot / quantum flake LED displays will be mass produced using inkjet printing. (1) Inkjet printing of phosphor particles will take too much time. Since the size of the phosphor particles is much larger, much thicker conversions are required, and (2) the printer head should also be replaced frequently due to the abrasive nature of the phosphor particles and longer time.

[0160] Therefore, due to their size and broader spectral bandwidth, phosphors are not suitable for color conversion on high-resolution displays.

[0161] Although the embodiments of the present invention have been described with reference to LED light sources, the present invention is not limited thereto. Any light source suitable for exciting the wavelength conversion layer according to the embodiments of the present invention can be used. For example, OLEDs can also be used in conjunction with the embodiments of the present invention.

[0162] Although the present invention has been described above with reference to specific embodiments, this is for the purpose of illustration and not limitation. Those skilled in the art will understand that various modifications and different combinations of the disclosed features can be made without departing from the scope of the present invention.

Claims

1. A display device including a pixel array, each pixel including at least three sub-pixels, each sub-pixel including an LED device configured to emit a color spectrum having a light source color point, the three LED devices being of the same type, the LED devices emitting the same blue light, the blue light being deep blue light, wherein the LED device of the first sub-pixel is covered with a first wavelength conversion layer designed to emit red light having a first color point, the LED device of the second sub-pixel is designed to be covered with a second wavelength conversion layer emitting green light having a second color point, the light source color point, the first color point and the second color point define a first color space different from the set color space, It is characterized in that the LED device of the third sub-pixel is covered with a third wavelength conversion layer, the third wavelength conversion layer being designed to emit light having a dominant wavelength with a fourth color point, the fourth color point being a cyan point, wherein some light from the LED device of the third sub-pixel is not converted by the third wavelength conversion layer and some light from the LED device of the third sub-pixel is converted by the third wavelength conversion layer, the fourth color point causing the combination of the light emitted by the LED device that is not converted by the third wavelength conversion layer and the light converted by the third wavelength conversion layer to produce light having a third color point, the third color point being a combination of blue point light and cyan point light, wherein the first, second and third color points define a second color space including the set color space, wherein the third wavelength conversion layer is configured to absorb less than 20% of the blue light emitted by the LED device of the third sub-pixel when excited by the blue light emitted by the LED device of the third sub-pixel, and 80% or more of the blue light exits without being converted.

2. The display device according to claim 1, wherein The light emitted by the LED devices of the first to third sub-pixels has a dominant wavelength equal to or less than 455 nm.

3. The display device according to claim 1, wherein The light emitted by the LED devices of the first to third sub-pixels has a dominant wavelength in the range of 420 nm to 455 nm, or has a dominant wavelength less than 455 nm and greater than 400 nm, or greater than 380 nm, or greater than the transparent absorption edge of the materials used in the pixel.

4. The display device according to claim 1, characterized in that, The wavelength emitted by the LED device of the third sub-pixel and the light emitted from the third wavelength conversion layer differ by at least 25 nm.

5. The display device according to claim 4, wherein The wavelength emitted by the LED device of the third sub-pixel and the light emitted from the third wavelength conversion layer differ by up to 35 nm.

6. The display device according to claim 5, wherein The wavelength emitted by the LED device of the third sub-pixel and the light emitted from the third wavelength conversion layer differ by up to 45 nm.

7. The display device according to claim 1, wherein The set color space is any one of Rec 709, Rec 2020, sRGB, DCI-P3.

8. The display device according to claim 1, characterized in that, The fourth color point is such that it is located to the left of the line connecting the light source color point and the third color point in the chromaticity diagram color space and above the third color point.

9. The display device according to claim 1, wherein, The thickness of the third wavelength conversion layer and the density of the down-conversion material in the third wavelength conversion layer are selected such that when the converted light having the fourth color point and the unconverted light having the light source color point are combined, an appropriate amount of light emitted by the LED device of the third sub-pixel is converted to obtain the third color point.

10. The display device according to claim 1, wherein The LED devices have the same peak wavelength, spectral half-width, or radiant flux.

11. The display device according to claim 1, wherein The third wavelength conversion layer is configured to emit light having a wavelength less than 520 nm when excited by the blue light emitted by the LED device of the third sub-pixel.

12. The display device according to claim 11, wherein The third wavelength conversion layer is configured to emit light having a wavelength of 490 nm when excited by the blue light emitted by the LED device of the third sub-pixel.

13. The display device according to claim 1, characterized in that, The first wavelength conversion layer is configured to emit light having a wavelength of 620 nm when excited by the blue light of the LED device of the first sub-pixel.

14. The display device according to claim 1, wherein The second wavelength conversion layer is configured to emit light having a wavelength of 532 nm when excited by the blue light of the LED device of the second sub-pixel.

15. The display device according to claim 1, wherein Less than 10% of the blue light emitted by the LED device of the first sub-pixel escapes through the first wavelength conversion layer, and / or less than 10% of the blue light emitted by the LED device of the second sub-pixel escapes through the second wavelength conversion layer.

16. The display device according to claim 15, wherein Less than 5% of the blue light emitted by the LED device of the first sub-pixel escapes through the first wavelength conversion layer, and / or less than 5% of the blue light emitted by the LED device of the second sub-pixel escapes through the second wavelength conversion layer.

17. The display device according to claim 16, characterized in that, Less than 1% of the blue light emitted by the LED device of the first sub-pixel escapes through the first wavelength conversion layer, and / or less than 1% of the blue light emitted by the LED device of the second sub-pixel escapes through the second wavelength conversion layer.

18. The display device according to claim 1, wherein The wavelength conversion layers include quantum sheets or quantum dots.

19. The display device according to claim 1, characterized in that, A first filter is positioned on the first wavelength conversion layer, and / or a second filter is positioned on the second wavelength conversion layer, and / or a third filter is positioned on the third wavelength conversion layer.

20. The display device according to claim 19, wherein The first and / or second filter filters out the blue light emitted by the corresponding LED device that passes through the corresponding wavelength conversion layer.

21. The display device according to claim 19, wherein, The first and / or second filter and / or the third filter absorbs at least a portion of the wavelengths found in the spectrum of ambient light, excluding the wavelengths corresponding to the first color point for the first filter, excluding the wavelengths corresponding to the second color point for the second filter, and excluding the wavelengths corresponding to the blue point and the fourth color point for the third filter.

22. A method of manufacturing a display device, comprising: - forming a pixel array, each pixel including at least three sub-pixels, each sub-pixel including an LED device configured to emit a color spectrum having a light source color point, the LED devices of the at least three sub-pixels all being of the same type, the LED devices emitting the same blue light, the blue light being deep blue light, - covering the LED device of the first sub-pixel with a first wavelength conversion layer designed to emit red light having a first color point, - An LED device covering a second sub-pixel with a second wavelength conversion layer designed to emit green light having a second color point, - The light source color point, the first color point, and the second color point define a first color space different from the assumed color space, - Characterized in that an LED device covering a third sub-pixel with a third wavelength conversion layer, the third wavelength conversion layer being designed to emit light having a main wavelength with a fourth color point, the fourth color point being a cyan point, wherein some light from the LED device of the third sub-pixel is not converted by the third wavelength conversion layer and some light from the LED device of the third sub-pixel is converted by the third wavelength conversion layer, the fourth color point causing the combination of the light emitted by the LED device that is not converted by the third wavelength conversion layer and the light converted by the third wavelength conversion layer to produce light having a third color point, wherein the first, second, and third color points define a second color space including the assumed color space, the third color point being a combination of light of a blue point and light of a cyan point, Wherein the third wavelength conversion layer is configured to absorb less than 20% of the blue light emitted by the LED device of the third sub-pixel when excited by the blue light emitted by the LED device of the third sub-pixel, and 80% or more of the blue light exits without being converted.

23. The method according to claim 22, wherein The light emitted by the LED devices of the first to third sub-pixels has a main wavelength equal to or less than 455 nm.

24. The method according to claim 23, wherein The light emitted by the LED devices of the first to third sub-pixels has a main wavelength in the range of 420 nm to 455 nm, or has a main wavelength less than 455 nm and greater than 400 nm, or greater than 380 nm, or greater than the transparent absorption edge of the material used in the pixel.

25. The method according to claim 22, wherein, The wavelength emitted by the LED device of the third sub-pixel and the light emitted by the third wavelength conversion layer differ by at least 25 nm.

26. The method according to claim 25, wherein The wavelength emitted by the LED device of the third sub-pixel and the light emitted by the third wavelength conversion layer differ by up to 35 nm.

27. The method according to claim 26, wherein, The wavelength emitted by the LED device of the third sub-pixel and the light emitted by the third wavelength conversion layer differ by up to 45 nm.

28. The method according to claim 22, wherein The assumed color space is any one of Rec 709, Rec2020, sRGB, DCI-P3.

29. The method according to claim 22, wherein The fourth color point is such that it is located to the left of the line connecting the light source color point and the third color point in the chromaticity diagram color space and above the third color point.

30. The method according to claim 22, wherein, The thickness of the third wavelength conversion layer and the density of the down-conversion material in the third wavelength conversion layer are selected such that when the converted light having the fourth color point and the unconverted light having the light source color point are combined, an appropriate amount of the light emitted by the LED of the third sub-pixel is converted to obtain the third color point.

31. The method according to claim 22, wherein The LED devices have the same main wavelength, spectral half-width, or radiant flux.

32. The method according to claim 22, wherein The third wavelength conversion layer is configured to emit light having a wavelength greater than 480 nm and / or less than 520 nm when excited by the blue light emitted by the LED device of the third sub-pixel.

33. The method according to claim 32, wherein The third wavelength conversion layer is configured to emit light with a wavelength of 490 nm when excited by blue light emitted by the LED device of the third sub-pixel.

34. The method according to claim 22, wherein The first wavelength conversion layer is configured to emit light with a wavelength of 620 nm when excited by blue light of the LED device of the first sub-pixel.

35. The method according to claim 22, characterized in that, The second wavelength conversion layer is configured to emit light with a wavelength of 532 nm when excited by blue light of the LED device of the second sub-pixel.

36. The method according to claim 22, wherein Less than 10% of the blue light emitted by the LED device of the first sub-pixel escapes through the first wavelength conversion layer, and / or less than 10% of the blue light emitted by the LED device of the second sub-pixel escapes through the second wavelength conversion layer.

37. The method according to claim 36, wherein Less than 5% of the blue light emitted by the LED device of the first sub-pixel escapes through the first wavelength conversion layer, and / or less than 5% of the blue light emitted by the LED device of the second sub-pixel escapes through the second wavelength conversion layer.

38. The method according to claim 37, wherein Less than 1% of the blue light emitted by the LED device of the first sub-pixel escapes through the first wavelength conversion layer, and / or less than 1% of the blue light emitted by the LED device of the second sub-pixel escapes through the second wavelength conversion layer.

39. The method according to claim 22, wherein The wavelength conversion layers include quantum sheets or quantum dots.

40. The method according to claim 22, wherein The first filter is positioned on the first wavelength conversion layer, and / or the second filter is positioned on the second wavelength conversion layer, and / or the third filter is positioned on the third wavelength conversion layer.

41. The method according to claim 40, wherein The first and / or second filter filters out the blue light emitted by the corresponding LED device that passes through the corresponding wavelength conversion layer.

42. The method according to claim 40, wherein The first and / or second filter and / or the third filter absorbs at least a portion of the wavelengths found in the spectrum of ambient light, except for the wavelengths corresponding to the first color point for the first filter, except for the wavelengths corresponding to the second color point for the second filter, and except for the wavelengths corresponding to the blue point and the fourth color point for the third filter.

43. A pixel structure including at least three sub-pixels, each sub-pixel including an LED device configured to emit a color spectrum having a light source color point, the three LED devices being of the same type, the LED devices emitting the same blue light, the blue light being deep blue light, wherein the LED device of the first sub-pixel is covered with a first wavelength conversion layer designed to emit red light having a first color point, the LED device of the second sub-pixel is designed to be covered with a second wavelength conversion layer that emits green light having a second color point, the light source color point, the first color point, and the second color point define a first color space different from the set color space. It is characterized in that The LED device of the third sub-pixel is covered with a third wavelength conversion layer, and the third wavelength conversion layer is designed to emit light having a main wavelength with a fourth color point, and the fourth color point is a cyan point. Among them, some light from the LED device of the third sub-pixel is not converted by the third wavelength conversion layer and some light from the LED device of the third sub-pixel is converted by the third wavelength conversion layer. The fourth color point causes the combination of the light emitted by the LED device that is not converted by the third wavelength conversion layer and the light converted by the third wavelength conversion layer to produce light having a third color point. Among them, the first, second, and third color points define a second color space including a preset color space, and the third color point is a combination of light of a blue point and light of a cyan point. Among them, the third wavelength conversion layer is configured to absorb less than 20% of the blue light emitted by the LED device of the third sub-pixel when excited by the blue light emitted by the LED device of the third sub-pixel, and 80% or more of the blue light exits without being converted.

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