Filters for Micro LED Displays

Abstract

1. A method of forming a light emitting diode array including a plurality of light emitting pixels, at least one of the light emitting pixels including: a light emitting diode configured to emit light at a first dominant peak wavelength; a first region including a first down-conversion material configured to receive and convert input light from the light emitting diode at the first dominant peak wavelength to provide output light at a second dominant peak wavelength and unconverted light at the first dominant peak wavelength; and a second region including an organic semiconductor material dispersed in a medium, the organic semiconductor material configured to absorb the input light at the first dominant peak wavelength, the second region configured to transmit output light at the second dominant peak wavelength from the first region and absorb unconverted light at the first dominant peak wavelength that passes through the second region from the light emitting diode, thereby increasing the color purity of light emitted by the at least one light emitting pixel.

Description

[Technical Field]

[0001] The present invention relates to an array of light-emitting pixels and a method for forming an array of light-emitting pixels, particularly, but not exclusively, to an array of multicolor light-emitting devices having improved color purity and a method for forming an array of multicolor light-emitting devices having improved color purity. [Background technology]

[0002] Light emitting diode (LED) devices are known to provide efficient light sources for a wide range of applications. Increased LED light generation efficiency and extraction, combined with the production of smaller LEDs (with smaller emitting areas) and the integration of LED emitters of different wavelengths into arrays, have led to the provision of high quality color arrays with numerous applications, particularly in display technology.

[0003] It is known that highly efficient light emitting diodes can be formed from III-V compound semiconductor structures. For example, highly efficient blue light emitting LED devices can be formed from nitride-based materials. Because such efficient LEDs can be formed from such materials, in some cases it can be highly advantageous to use a blue light LED to pump a down-conversion material to provide light of a different wavelength, rather than procuring an LED that emits light of a different wavelength, e.g., for use in a multicolor display.

[0004] However, to provide higher resolution arrays, the pixel pitch within such arrays is reduced to very small pitches (e.g., less than 5 μm), which presents many challenges. For example, quantum dots (QDs) are typically used as color conversion layers to achieve full-color red-green-blue (RGB) displays, where blue LEDs are typically used as the input light source. Such QDs are typically used to convert blue input light into red and green light using suitable QDs. However, such QD layers are generally required to be on the order of 20 μm to 30 μm thick to achieve maximum color saturation. Therefore, at these thicknesses, the smallest pixels that can be produced are limited to widths greater than 20 μm.

[0005] Further difficulties are known to arise when processing QDs for light wavelength color conversion in micro-LED arrays, such as degradation of the efficiency and lifetime of wavelength-converting QDs when forming layers of materials containing QDs using photolithography and inkjet printing. Thus, there are significant challenges in the pursuit of high-resolution micro-LED arrays, where it would be beneficial to have a pixel pitch of less than 10 μm. Summary of the Invention [Means for solving the problem]

[0006] To alleviate at least some of the above-mentioned problems, a method of forming a light emitting diode array including a plurality of light emitting pixels, at least one of the light emitting pixels including: a light emitting diode configured to emit light at a first dominant peak wavelength; a first region including a first down-conversion material configured to receive and convert input light at the first dominant peak wavelength from the light emitting diode to provide output light at a second dominant peak wavelength and unconverted light at the first dominant peak wavelength; and a second region including an organic semiconductor material dispersed in a medium, the organic semiconductor material configured to absorb input light at the first dominant peak wavelength, the second region transmitting output light at the second dominant peak wavelength from the light emitting diode through the second region. a second region configured to absorb unconverted light of the one dominant peak wavelength, thereby increasing the color purity of light emitted by the at least one light-emitting pixel.

[0007] Also provided is a light emitting diode array formed according to this method.

[0008] Advantageously, the organic semiconductor material dispersed in the medium can be processed using well-known semiconductor fabrication techniques to provide a thin layer that selectively filters unconverted light in a color-converting LED array. Advantageously, because the organic semiconductor material dispersed in the medium increases color purity (reducing or eliminating selected wavelengths), thinner layers of color-converting material can be used, which counters the color saturation that can be achieved with thicker layers of color-converting material.

[0009] Preferably, the method includes forming at least one further light-emitting pixel, the at least one further light-emitting pixel including a further light-emitting diode configured to emit light at a first dominant peak wavelength, and a third region including a second down-conversion material configured to receive and convert input light at the first dominant peak wavelength from the further light-emitting diode and output light at a third dominant peak wavelength and unconverted light at the first dominant peak wavelength, the second region configured to transmit output light at the third dominant peak wavelength from the third region and absorb unconverted light at the first dominant peak wavelength from the further light-emitting diode that passes through the third region, thereby increasing the color purity of light emitted by the at least one further light-emitting pixel. Advantageously, the method provides a multicolor array of light-emitting pixels with higher color purity in an efficient and scalable manner, in which the same organic semiconductor material dispersed in a medium is used to absorb unconverted light from color conversion materials that emit different wavelengths of light.

[0010] Preferably, the second region is configured to absorb light at wavelengths associated with curing the medium that the organic semiconductor material is dispersed in. Advantageously, the second region is photosensitive, allowing for improved processing while increasing the purity of the color output from the light-emitting array.

[0011] Preferably, the method comprises depositing a second region on the light emitting diode array, and preferably depositing the second region comprises slit coating or spin coating the medium and / or further medium. Advantageously, the second region can be deposited in an efficient and scalable manner and integrated into a semiconductor fabrication process flow.

[0012] Preferably, the method includes selectively coating one or more light emitting diodes in the light emitting diode array with a material before depositing the second region, thereby enabling selective deposition of the second region. Advantageously, the second region is used to selectively filter wavelengths in a multicolor light emitting array.

[0013] Preferably, the material is at least one of a fugitive material that is removable, thereby allowing further deposition of further material on the selectively coated one or more light emitting diodes in a further separate step after deposition of the second region on the light emitting diode array, and an optically transparent material that allows light emission from the selectively coated one or more light emitting diodes, the one or more light emitting diodes being configured to emit light having a dominant peak wavelength. Advantageously, the selected light emitting diodes are consistent in their wavelength output.

[0014] Preferably, the medium comprises at least one of a resin and a polymer medium. Advantageously, such a medium allows for the fabrication of multicolor arrays in an efficient manner to improve color purity.

[0015] Preferably, the method includes forming a passivation layer over the light emitting diode array, thereby protecting the light emitting diode array. Advantageously, the passivation layer protects underlying layers while allowing light emission at specific wavelengths associated with different colored light emitting pixels.

[0016] Preferably, the organic semiconductor comprises a conjugated organic semiconductor having a plurality of conjugated structures, preferably the plurality of conjugated structures comprises a core and arms, and even more preferably at least two of the plurality of conjugated structures have different functional properties. Advantageously, such structures are tunable to provide absorption properties when integrated into semiconductor fabrication techniques.

[0017] Preferably, the organic semiconductor is deposited in a solvent, typically an organic solvent such as an alkene or alkane or mixtures thereof, preferably the concentration of the organic semiconductor in the solvent is 1-5%, more typically 2.5% by weight, more preferably the solvent comprises toluene and heptane.

[0018] Preferably, one functional property is absorption at a first dominant peak wavelength, and / or one functional property is absorption of light having a dominant peak wavelength that enables curing of the medium. Advantageously, absorption at the first dominant peak wavelength reduces the amount of unconverted light emitted from the color conversion region, and absorption at the dominant peak wavelength that enables curing of the medium provides an effective way to fabricate improved color purity arrays.

[0019] Preferably, the light emitting diode array is a high-resolution monolithic micro LED array, and preferably, the method includes forming a reflective layer between at least two of the light emitting diodes in the high-resolution monolithic micro LED array, and more preferably, the high-resolution monolithic LED has a pixel pitch of less than 10 μm, preferably less than 4 μm. Advantageously, high-resolution, high-efficiency arrays emitting at specific wavelengths can be used to provide multicolor arrays by light wavelength conversion materials while reducing the amount of unconverted light from the high-resolution monolithic micro LED array.

[0020] Preferably, the plurality of light-emitting pixels are 100 μm 2 Less than or equal to 16 μm, preferably 2 Advantageously, such an array enables high resolution, multicolor light emitting displays.

[0021] Preferably, the second region is a layer, preferably the layer has a thickness of less than 2 microns, more preferably the layer has a thickness of less than 0.5 microns. Advantageously, a thin layer of color conversion material allows for smaller emitting pixels and therefore a display with improved resolution.

[0022] Further aspects of the invention will become apparent from the description and the appended claims.

[0023] A detailed description of embodiments of the present invention will now be given, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 shows a cross-sectional view of a multicolor light-emitting array. [Figure 2] FIG. 2 shows the light spectra corresponding to different portions of the multicolored light-emitting array of FIG. [Figure 3] FIG. 3 shows a cross-sectional view of a multicolor light-emitting array. [Figure 4] FIG. 4 shows the light spectra corresponding to different portions of the multicolored light-emitting array of FIG. [Figure 5] Figure 5 shows the absorption characteristics of the organic semiconducting polymer domain. [Figure 6] FIG. 6 shows a sequence of steps for providing an organic semiconductor material. DETAILED DESCRIPTION OF THE INVENTION

[0025] Advantageously, methods are described for providing maximum color saturation using very thin films. For example, to provide a multicolor light-emitting array, a monolithic light-emitting diode (LED) array having LED devices emitting dominant peak wavelengths can be selectively colorized using color conversion regions that absorb light having a dominant peak wavelength and emit light having a different dominant peak wavelength. For example, a monolithic array of LED devices emitting light having a dominant wavelength corresponding to blue light (approximately 450 nm) can be selectively down-converted to provide light emission having dominant peak wavelengths corresponding to green light (approximately 540 nm) and / or red light (approximately 630 nm).

[0026] There are associated advantages when the thickness of the color conversion region is reduced to maximize color saturation with a thin film. For example, such a thin film allows for the use of thinner down-conversion regions with reduced absorption and therefore increased light emission compared to known techniques. Furthermore, advantageously, the use of thinner films allows for smaller light-emitting pixels to be provided, thereby facilitating high-resolution light-emitting arrays, such as high-resolution microLED arrays. Advantageously, the method is integrated within standard semiconductor processing techniques, meaning that multicolor arrays of light-emitting devices can be produced on a large scale in an economically efficient manner.

[0027] The color conversion materials described herein are materials that can be used to down-convert light having a shorter (higher energy) wavelength to provide light having a longer (lower energy) wavelength. For example, blue or UV light can be down-converted by absorption and emission by the color conversion material to provide light having a green and / or red wavelength. Advantageously, color conversion materials can be used to provide light emission at a wavelength different from that of an array of light-emitting devices emitting at one wavelength (e.g., a blue-emitting array of LED devices), thereby taking advantage of well-known methods for producing high-quality, high-efficiency light-emitting arrays using, for example, nitride-based III-V epitaxial crystalline compound semiconductor structures. Color conversion can be achieved using organic and inorganic materials. For example, inorganic quantum dot (QD) materials, such as compound semiconductor QD materials, can be used to provide color conversion from light having a shorter wavelength to provide light emission at a relatively longer wavelength.

[0028] Color conversion materials containing a medium in which an organic semiconductor is dispersed are also known to enable the down-conversion of shorter wavelength light to provide light with longer wavelengths. It is known that down-conversion organic semiconductors can be tailored to achieve targeted physical properties. Specifically, organic semiconductors can advantageously achieve specific values ​​for ionization potential or electron affinity, absorption and emission properties, charge transport properties, phase behavior, solubility, and processability. Typically, organic semiconductors are conjugated organic semiconductors containing multiple conjugated structures. In one example, such conjugated structures include a core and an arm. The functionality of these components of the organic semiconductor is tailored to provide specific properties.

[0029] Polymers are described, for example, in Acc. Chem. Res 2019, 52, 1665 to 1674 and J. Mater. Chem. C, 2016, 4, 11499, the contents of which are incorporated in their entirety. Tunable polymers include conjugated organic semiconductors containing multiple conjugated structures. Typically, these are organic semiconductors. Such structures can be formed to include a core and arms. The multiple conjugated structures can be formed to have different functional properties, for example, different absorption and / or emission properties. In one example, an organic semiconductor material that provides color conversion functionality is the synthetic TPA-BDI (triphenylamine-benzodiimidazole) molecular species, an organic system with a benzodiimidazole core. Such materials can be prepared from commercially available starting materials. benzodiimidazole The hydroxyl groups and their derivatives are push-pull donor-acceptor It has tunable optical properties by using donor-acceptor components. In one example, TPA-BDI in a down-conversion hybrid LED device is incorporated into an optically transparent material, such as a poly(urethane) resin, as a host and encapsulant.

[0030] FIG. 6 shows a sequence 600 illustrating how, in one example, TPA-BDI is synthesized in four steps from 1,5-difluoro-2,4-dinitrobenzene, shown as the first compound 602 in FIG. 6 . The SNAr reaction of the first compound 602 with isobutylamine is shown, yielding the second compound 604 in high yield (e.g., 90%). Subsequent reduction of the nitro group of the second compound 604 yields the third compound 606, and condensation of the third compound with 5-bromo-2-thiophenecarbaldehyde yields the key intermediate, the fourth compound 608, in approximately 47% yield over two steps. Suzuki-Miyaura cross-coupling of the fourth compound 608 with 4-(diphenylamino)phenylboronic acid pinacol ester affords the final material, TPA-BDI 610, in moderate yield (e.g., 55%), thereby affording TPA-BDI 610. In one example, the organic semiconductor material is benzodiimidazole and its derivatives, but in further examples, alternative and / or additional organic semiconductor materials that provide light conversion functionality are used within the color conversion regions described herein. Advantageously, such polymers containing organic semiconductor materials can be tailored to absorb light of specific wavelengths while remaining transparent to light of different wavelengths. Advantageously, such materials can be used to provide absorption at multiple distinct wavelengths. Furthermore, as described below, the use of organic semiconductor materials dispersed in a photosensitive medium allows for efficient and effective processing of materials for colorization of arrays of light-emitting devices, such as monolithic microLED arrays.

[0031] FIG. 1 illustrates a cross-sectional view of a multicolor light-emitting array 100. A monolithic array of light-emitting diode (LED) devices 104, 106, and 108 configured to emit light having a dominant peak wavelength corresponding to blue light is shown. The LED devices 104, 106, and 108 are formed on a layer 102. The layer 102 is a gallium nitride (GaN) layer. While the LED devices 104, 106, and 108 are shown as being encapsulated by the layer 102, those skilled in the art will appreciate that the arrangement of the LED devices 104, 106, and 108 relative to the layer 102 may be configured in any suitable manner. The individual LED devices 104, 106, and 108 are shown separated by a material 105 between each of the devices 104, 106, and 108. The material 105 is configured to prevent optical crosstalk between pixels. In further examples, additional and / or alternative layers and materials are used. In further examples, the material 105 is not used. Each of the LED devices 104, 106, and 108 has a color conversion region associated therewith. The first LED device 104 is associated with a first color conversion region 114. The second LED device 106 is associated with a second color conversion region 116. The third LED device 108 is associated with a region 118 that does not convert the light emitted by the corresponding third LED device 108. The region 118 associated with the third LED device 108 is substantially transparent to blue light. Thus, the region 118 defines an emitting surface associated with the pixel that emits light having a dominant peak wavelength corresponding to blue light. The use of the region 118 associated with the third LED device 108 in combination with the first color conversion region 114 and the second color conversion region 116 results in a uniform, planar layer. The region 118 associated with the third LED device 108 is an optically transparent resin. In a further example, alternative and / or additional materials form the region 118 associated with the third LED device 108 such that input light from the third LED device 108 passes through the region 118 and is emitted from the light emitting array 100 structure.

[0032] The first color conversion region 114 is configured to absorb light having a dominant peak wavelength corresponding to blue light from the first LED device 104 and emit light having a dominant peak wavelength corresponding to green light. Color conversion region 114 is configured to down-convert light to green. Color conversion region 114 therefore defines a light emitting surface associated with a pixel that emits light having a dominant peak wavelength corresponding to green light.

[0033] The second color conversion region 116 is configured to absorb light having a dominant peak wavelength corresponding to blue light from the first LED device 106 and downconvert the light to emit light having a dominant peak wavelength corresponding to red light. Thus, the color conversion region 116 defines an emitting surface associated with a pixel that emits light having a dominant peak wavelength corresponding to red light.

[0034] The color conversion regions are separated by regions 110 with additional reflective regions 112 to enable the formation of separate pixels. In one example, regions 110 are formed from a dielectric material, and reflective regions 112 are advantageously formed from a metal that is formed by patterning and depositing a suitable material prior to the formation of the color conversion regions. In further examples, alternative and / or additional materials and / or techniques are used. In a further example, additional reflective regions 112 replace light absorbing regions to better define pixels.

[0035] The LED devices 104, 106, 108 and their corresponding regions 114, 116, 118 provide a multicolor light-emitting array. A passivation layer 120 is shown over the regions 114, 116, 118. The LED devices 104, 106, 108 are nitride-based epitaxially grown compound crystalline semiconductor LEDs 104, 106, 108. In further examples, other LEDs, such as other III-V or II-VI-based compound semiconductor materials, are used. Advantageously, the LED devices 104, 106, 108 are monolithically grown, which results in high-quality material with excellent uniformity and efficiency without the need to transfer individual LED devices. Advantageously, the monolithic LED array is coupled to a backplane (not shown) to enable control of the individual LED devices 104, 106, 108 within the monolithic array. The LED devices 104, 106, 108 are grown as part of a monolithic array of LEDs using metal organic chemical vapor deposition (MOCVD). In further examples, alternative and / or additional techniques, such as molecular beam epitaxy (MBE) and other suitable deposition / growth techniques, are used to form the LED devices 104, 106, 108 as part of the monolithic array. In further examples, other additional and / or alternative semiconductor fabrication and processing techniques are used to provide a monolithic array of the LED devices 104, 108, 108. In further examples, alternatively and / or additionally, the array 100 is formed from individual LED devices that do not form part of a monolithic array.

[0036] Although the three LED devices 104, 106, 108 are shown without electrical connections to facilitate injection of carriers through the p-type and n-type regions to provide radiative recombination, those skilled in the art will appreciate that such electrical connections for injection of carriers through the p-type and n-type regions in the LED devices can be implemented in different ways. For example, the array 100 can be coupled with a complementary metal oxide semiconductor (CMOS) backplane to control the emission from the individual LED devices.

[0037] Although the LED devices 104, 106, 108 are shown in a particular configuration within the array 100, those skilled in the art will understand that alternative and / or additional configurations and implementations of the LED devices may be used in combination with the further features described herein. Although only three LED devices 104, 106, 108 are shown in cross section, in further examples, any suitable number of LED devices may be used to form the array 100.

[0038] FIG. 2 shows emission spectra corresponding to different portions of the multicolored light-emitting array of FIG.

[0039] The first spectrum 200A shows a plot of light intensity on a vertical scale 204 versus wavelength on a horizontal scale 202. Two significant peaks are present, a first peak 206 of which corresponds to blue light and a second peak 208 of which corresponds to green light. The blue light of the first peak 206 is light from the first LED device 104 that was not downconverted by the color conversion region 114, and the green light of the second peak 208 is light from the first LED device 104 that was downconverted by the color conversion region 114.

[0040] The second spectrum 200B shows a plot of light intensity on the vertical scale 204 versus wavelength on the horizontal scale 202. Two significant peaks are present, a first peak 210 of which corresponds to blue light and a second peak 212 of which corresponds to red light. The blue light of the first peak 210 is light from the second LED device 106 that was not downconverted by the color conversion region 116, and the red light of the second peak 212 is light from the second LED device 106 that was downconverted by the color conversion region 116.

[0041] The third spectrum 200C shows a plot of light intensity on the vertical scale 204 versus wavelength on the horizontal scale 202. There is one significant peak, peak 214, which corresponds to blue light. The blue light at peak 214 is light from the third LED device 108 that has passed through region 118.

[0042] To reduce the intensity of the peaks 206, 210 associated with unconverted blue light in the green and red pixels, the thickness of their associated color conversion regions 114, 116 can be increased. However, such an increase in thickness increases the absorption of light within the color conversion regions, resulting in a reduction in the intensity of the output (converted) light. Furthermore, thicker color conversion regions generally preclude the production of smaller emissive pixels for use in high-resolution displays.

[0043] Figure 3 shows a cross-sectional view of a multicolor light-emitting array 300. The multicolor light-emitting array 300 corresponds to the multicolor light-emitting array 100 of Figure 1 with an additional layer 302 formed on the color conversion regions 114, 116 associated with the first and second LED devices 104, 106. The additional layer 302 provides a region configured to absorb light at selected wavelengths, thereby improving the light output of the multicolor light-emitting array 300.

[0044] The additional layer 302 includes an organic semiconductor material dispersed in a resin and configured to absorb blue light. The additional layer 302 is formed by patterning and forming the additional layer 302 over the areas associated with the first and second LED devices 104, 106 of the multicolor light-emitting array 100 of FIG. 1 before forming the passivation layer. The multicolor light-emitting array 100 is patterned using well-known semiconductor fabrication techniques, such as photolithography, to selectively cover areas where the additional layer 302 should not be formed. The additional layer 302 is formed using spin coating or slit coating. In a further example, different methods and / or materials are used to form the additional layer 302 in appropriate locations on the multicolor light-emitting array 100 to provide a blue-light blocking layer for absorbing unconverted light from the LEDs 104, 106 associated with pixels that emit converted light in the associated color conversion regions 114, 116.

[0045] The absorption characteristics of the additional layer 302 are shown in Figure 5. Figure 5 shows an absorption spectrum 500, where the vertical scale 504 relates to absorption and the horizontal scale 502 relates to wavelength. The additional layer 302, which includes an organic semiconductor material, is shown to have two distinct absorption peaks. A first absorption peak 506 is associated with the absorption of ultraviolet (UV) light at approximately 350 nm. A second peak 508 is associated with the absorption of blue light at approximately 450 nm. This Away from these peaks, light is transmitted through the additional layer 302. For example, red and green light is transmitted through the additional layer 302. The first absorption peak 506 is associated with a resin in which an organic semiconductor material is dispersed. In a further example, the organic semiconductor material is configured to absorb light at the first absorption peak 506, thereby enhancing UV absorption by the additional layer 302 and enabling improved processing of the photosensitive additional layer 302. In one example, the organic semiconductor material providing the targeted absorption functionality is the synthetic TPA-BDI molecular species, a benzodiimidazole-cored organic system. Such materials can be prepared from commercially available starting materials. Benzodiimidazoles and their derivatives have tunable optical properties through the use of push-pull donor-acceptor components. In one example, TPA-BDI is incorporated into an optically transparent poly(urethane) resin as a host and encapsulant. In a further example, different media are used as hosts and encapsulants for TPA-BDI. The organic semiconductor is deposited in a solvent, typically an organic solvent such as an alkene or alkane or mixtures thereof, preferably the concentration of the organic semiconductor in the solvent is 1-5%, more typically 2.5% by weight, more preferably the solvent comprises toluene and heptane.

[0046] FIG. 6 shows how, in one example, TPA-BDI is synthesized in four steps from 1,5-difluoro-2,4-dinitrobenzene, shown as the first compound 502 in FIG. 6 . The SNAr reaction of the first compound 502 with isobutylamine is shown, yielding the second compound 504 in high yield (e.g., 90%). Subsequent reduction of the nitro group of the second compound 504 yields the third compound 506, and condensation of the third compound with 5-bromo-2-thiophenecarbaldehyde yields the key intermediate, the fourth compound 508, in approximately 47% yield over two steps. Suzuki-Miyaura cross-coupling of the fourth compound 508 with 4-(diphenylamino)phenylboronic acid pinacol ester affords the final material, TPA-BDI 510, in moderate yield (e.g., 55%), thereby affording TPA-BDI 510. In one example, the organic semiconductor material is benzodiimidazole and its derivatives, but in a further example, alternative and / or additional organic semiconductor materials that provide photoconversion functionality are used within the color conversion region. In a further example, the organic semiconductor polymer is based on 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY), e.g., the polymer comprises a BODIPY core. In yet a further example, the polymer is based on a 2,1,3-benzothiadiazole (BT) core.

[0047] While the additional layer 302 has been described as a region configured to absorb light having dominant peak wavelengths corresponding to blue light and ultraviolet light, in a further example, the additional layer 302 is a region configured to selectively absorb light having different wavelengths of light, for example, green light. Absorbing different wavelengths of light corresponding to input light from an array of light emitting devices that uses input light for the color conversion region to provide a converted light output results in increased color purity for the color converted light from a thin film of tunable organic semiconductor dispersed in a photosensitive medium by reducing or eliminating one or more unwanted wavelengths of light emitted from the array.

[0048] FIG. 4 shows light spectra corresponding to different portions of the multi-color light-emitting array 300 of FIG.

[0049] The first spectrum 400A shows a plot of light intensity on the vertical scale 204 versus wavelength on the horizontal scale 202. There is one significant peak, corresponding to the second peak 208, which corresponds to green light as described with reference to Figure 2. The blue light of the first peak 206 seen in Figure 2 is suppressed, and there is an insignificant peak 402, which corresponds to light from the first LED device 104 that was not downconverted by the color conversion region 114.

[0050] The second spectrum 400B shows a plot of light intensity on the vertical scale 204 versus wavelength on the horizontal scale 202. There is one significant peak, corresponding to the second peak 212, which corresponds to red light as described with reference to FIG. 2. The first peak seen in FIG. The blue light of peak 206 is suppressed and there is an insignificant peak 404 corresponding to light from second LED device 106 that was not downconverted by color conversion region 114 .

[0051] The third spectrum 400C shows a plot of light intensity on the vertical scale 204 versus wavelength on the horizontal scale 202. There is one significant peak, peak 214, which corresponds to blue light. The blue light at peak 214 is light from the third LED device 108 that has passed through region 118.

[0052] Thus, the use of the blue filter layer improves the color purity of the two light-emitting surfaces associated with the non-blue light of the first and second color conversion regions 114, 116, which downconvert light from the first and second LED devices 104, 106 by reducing or eliminating one or more unwanted wavelengths of light emitted from the array. An insignificant peak corresponds to the absence or near absence of emitted light at the corresponding wavelength. For example, the measured emitted light intensity is below a threshold. The threshold can relate to, for example, an acceptable color purity of the light emitted by the pixel relative to the intensity of the main peak output (e.g., red light for a red-emitting pixel, green light for a green-emitting pixel).

[0053] Advantageously, the use of the additional layer 302 acting as a blue-absorbing color filter means that the first and second color conversion regions 114, 118 can be thinner than typically used to achieve maximum color saturation with adequate color purity (e.g., appropriate levels of intensity reduction and / or removal of one or more unwanted wavelengths). Typically, for micro LED displays with a pitch of less than 5 microns, the ratio of color conversion region thickness to emitting area size is on the order of 1:4 to provide acceptable down-conversion efficiency of input light. For short-pitch arrays with an LED pitch of 3 microns square, the emitting area is on the order of 2 square microns. Therefore, ideally, the thickness of the down-conversion region is on the order of 0.4 microns. Typically, when such a thin layer of color conversion material (such as quantum dots) is used, not enough input pump light is converted, and therefore good color saturation is usually not achieved. The use of the additional layer 302 means that maximum color saturation can be achieved using color conversion regions on the order of 0.5 microns when the color conversion region includes an organic semiconductor material, and on the order of 2 microns when the color conversion region includes quantum dots. Thus, the combination of an organic semiconductor in a medium (such as TPA-BDI in a resin tailored to absorb unconverted light) with a color conversion region (such as one formed from TPA-BDI in a resin tailored to downconvert light) reduces the overall thickness of the region required to produce a particular color purity of light output. This enables shorter-pitch arrays with a higher density of LED devices that convert high-quality input light, such as light from a monolithic blue-emitting nitride-based array. Advantageously, high-efficiency, high-resolution arrays of light-emitting devices can be provided using well-known techniques, for example, by epitaxial growth of compound semiconductor materials, which are then processed to provide light at different wavelengths without compromising the color purity of the light output by individual pixels.

Claims

1. 1. A method of forming a light emitting diode array comprising a plurality of light emitting pixels, at least one of the light emitting pixels comprising: a first light emitting diode configured to emit light at a first dominant peak wavelength; a second light emitting diode configured to emit light at the first dominant peak wavelength; and The method comprises: depositing a first region comprising a first down-conversion material on the first light-emitting diode, the first down-conversion material comprising a conjugated organic semiconductor dispersed in a medium, the conjugated organic semiconductor of the first down-conversion material configured to receive and convert input light at the first dominant peak wavelength from the first light-emitting diode and provide output light at a second dominant peak wavelength and unconverted light at the first dominant peak wavelength; depositing a second region comprising a second down-conversion material on the second light-emitting diode, the second down-conversion material comprising an organic semiconductor material dispersed in a medium, the conjugated organic semiconductor of the second down-conversion material configured to receive and convert input light at the first dominant peak wavelength from the second light-emitting diode and provide output light at a third dominant peak wavelength and unconverted light at the first dominant peak wavelength; depositing a third region over the first region and the second region, the third region comprising a conjugated organic semiconductor dispersed in a medium, the third region configured to transmit output light at the second dominant peak wavelength from the first region and output light at the third dominant peak wavelength from the second region and to absorb unconverted light at the first dominant peak wavelength from the first light emitting diode and the second light emitting diode that passes through the first region and the second region, respectively, thereby increasing color purity of light emitted by the at least one light emitting pixel; A method comprising:

2. The method of claim 1 , wherein the third region is configured to absorb light at a wavelength capable of curing the medium in which the conjugated organic semiconductor is dispersed.

3. depositing the third region on a light emitting diode array; 3. The method of claim 1 or 2, wherein depositing comprises slit coating or spin coating the medium and / or the further medium.

4. 4. The method of claim 3, comprising selectively coating one or more light emitting diodes in the light emitting diode array with a material before depositing the third region, thereby enabling selective deposition of the third region.

5. The material is a fugitive material that is removable to allow further deposition of additional materials on the selectively coated one or more light emitting diodes in a further separate step after deposition of the third region on the light emitting diode array; and an optically transparent material that permits light emission from the selectively coated one or more light emitting diodes, the one or more light emitting diodes being configured to emit light having the dominant peak wavelength; The method of claim 4, wherein at least one of

6. The method of any one of claims 1 to 5, wherein the medium comprises at least one of a resin and a polymer medium.

7. The method of any one of claims 1 to 6, comprising forming a passivation layer on the light emitting diode array, thereby protecting the light emitting diode array.

8. 8. The method of claim 1, wherein the conjugated organic semiconductor has a plurality of conjugated structures, the plurality of conjugated structures comprising a core and an arm, and at least two of the plurality of conjugated structures have different functional properties.

9. 9. The method of claim 8, wherein one functional property is absorption at the first dominant peak wavelength and / or one functional property is absorption of light having a dominant peak wavelength that enables hardening of the medium.

10. 10. The method of any one of claims 1 to 9, wherein the light emitting diode array is a high resolution monolithic micro LED array, the method comprising forming a reflective layer between at least two of the light emitting diodes in the high resolution monolithic micro LED array, and the high resolution monolithic micro LED array has a pixel pitch of less than 10 μm, preferably less than 4 μm.

11. The plurality of light-emitting pixels are 100 μm ２ Preferably, 16 μm or less ２ The method of any one of claims 1 to 10, wherein each of the light emitting surfaces is less than 1000 nm.

12. A method according to any preceding claim, wherein the third region is a layer, the layer having a thickness of less than 2 microns, more preferably the layer having a thickness of less than 0.5 microns.

13. A light emitting diode array formed according to the method of any one of claims 1 to 12.

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