Quantum dot color filter ink compositions and devices utilizing the same

Abstract

To provide liquid ink compositions containing quantum dots for optoelectronic display applications, solid films formed by drying the ink compositions, optical elements incorporating the solid films, display devices incorporating the optical elements, and methods of forming the solid films, the optical elements, and the devices.SOLUTION: Liquid ink compositions and solid films formed by drying the liquid ink compositions include one or more blue light-absorbing materials in combination with red light-emitting QDs or green light-emitting QDs.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Patent Application No. 62 / 737,790, filed Sep. 27, 2018, the contents of which are incorporated herein by reference in their entirety. [Background technology]

[0002] Display technology is constantly evolving in terms of improving the end-user experience. One aspect of improving the end-user experience is to increase the color gamut of liquid crystal display (LCD) devices and to improve the efficiency of these devices. For this reason, quantum dot (QD) technology has been considered in terms of increasing the color gamut and improving the efficiency of the above devices.

[0003] One way to improve the efficiency, color gamut, and viewing angle of LCD panels is to use quantum dot color filters (QDCFs) instead of traditional color filters. In this configuration, the QDs "filter" at least a portion of the incident light having a first wavelength or range of wavelengths (e.g., blue light) by converting it to light of a different wavelength or range of wavelengths (e.g., red and / or green light).

[0004] In a typical red-green-blue (RGB) pixelated display device having a backlight unit (BLU), a QDCF layer is disposed in the light path between the BLU and a viewer. For a standard blue light emitting diode (LED) BLU, the QDCF layer absorbs all or a portion of the incident blue photons from the BLU and converts at least a portion of the absorbed photons into green photons in the green subpixel regions and red photons in the red subpixel regions.

[0005] However, at least some of the blue light from the BLU is often transmitted through the red and green subpixels of the display device, resulting in color contamination and poor color gamut. This is particularly problematic when implementing QDCFs that use certain types of QDs that have low optical density (OD) due to their small absorption cross-section in the blue region of the visible spectrum. Additionally, QDCFs with poor forward light extraction can limit the external quantum efficiency (EQE) of the display device.

[0006] One way to reduce blue light leakage through QDCFs is to increase the concentration of QDs to increase blue light absorption and OD. To increase blue light absorption, the layer containing QDs can be made thicker, more QDs can be dispersed in the layer, or both. However, thicker layers can cause parallax issues and worsen the viewing angle of the display. Also, at very high QD concentrations, emitted photons can be reabsorbed, which can lead to a large overlap between QD absorption and QD emission, decreasing the EQE. Furthermore, multiple reabsorptions can cause red shifts, leading to color distortion. Summary of the Invention

[0007] Optoelectronic display devices are provided that utilize blue light absorbing materials in combination with QDs to improve optical performance, as well as QD-containing liquid ink compositions for optoelectronic display applications, solid films formed from the ink compositions, and optical elements incorporating the solid films.

[0008] One embodiment of an optoelectronic display device comprises a blue-emitting backlight unit BLU, a pixel array disposed in an optical path of the BLU, the pixel array including at least one red subpixel, at least one green subpixel, and at least one blue subpixel, and a solid film including red-emitting QDs and a blue light-absorbing material in the red subpixels and / or a solid film including green-emitting QDs and a blue light-absorbing material in the green subpixels, the blue light-absorbing material being characterized by preferential absorption of blue light relative to red or green light.

[0009] One embodiment of the liquid ink composition contains 10% to 94.99% by weight of a di(meth)acrylate monomer or a combination of di(meth)acrylate monomers and mono(meth)acrylate monomers, 4% to 10% by weight of a multifunctional (meth)acrylate crosslinker, 1% to 50% by weight of red-emitting quantum dots or green-emitting quantum dots, and 0.01% to 85% by weight of a blue light absorbing material, wherein the blue light absorbing material is characterized by preferential absorption of blue light relative to red light or green light.

[0010] One embodiment of the cured film is comprised of the polymerized product of the liquid ink composition described above.One embodiment of an optoelectronic device includes a blue light source and the cured film described above disposed within the optical path of the blue light source. [Brief description of the drawings]

[0011] Exemplary embodiments of the present invention are described below with reference to the accompanying drawings, in which like reference numerals denote like elements, and in which:

[0012] [Figure 1] FIG. 1 is a schematic diagram of a basic embodiment of an RGB pixel with an organic light emitting diode (OLED) BLU.

[0013] [Diagram 2] FIG. 1 is a schematic diagram showing RGB pixels of an LCD device.

[0014] [Diagram 3] FIG. 2 is a diagram showing an optical property evaluation setup used in the examples.

[0015] [Figure 4] FIG. 1 shows a reference spectrum of a blue LED through a bare glass substrate ("Blue LED") and an actual spectrum through QDCF Film A in an embodiment.

[0016] [Diagram 5] FIG. 1 shows a reference spectrum of a blue LED through a bare glass substrate ("Blue LED") and an actual spectrum through QDCF Film B in an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] QD-containing liquid ink compositions for optoelectronic display applications are provided, as well as solid films formed by drying and / or curing the ink compositions, optical elements incorporating the solid films, display devices incorporating the optical elements, and methods of forming the solid films, optical elements, and devices.

[0018] The liquid ink compositions and the solid films formed by drying the liquid ink compositions contain one or more blue light absorbing materials in combination with red-emitting or green-emitting QDs. As used herein, the term "blue light absorbing material" refers to a material that has higher absorption in the blue region of the electromagnetic spectrum than in the red and / or green regions of the electromagnetic spectrum. Thus, the ink compositions and films can be used in a variety of optoelectronic devices where it is desirable to filter (i.e., absorb) blue light.

[0019] One application of the ink compositions and films is as QD color filters to reduce or eliminate blue light leakage from the red and / or green subpixels of optoelectronic display devices and improve their external quantum efficiency.

[0020] The color filters can be incorporated into the red and / or green subpixels of an RGB pixel, which includes a red (R), green (G), and blue (B) subpixel. A basic embodiment of an RGB pixel is shown in FIG. 1. Although only a single pixel is shown in this figure, the pixel can be part of a larger array of multiple pixels. In this embodiment, the pixel 100 includes an optically transparent substrate 102, a red (R) subpixel 103, a green (G) subpixel 104, and a blue (B) subpixel 105. Each subpixel is defined by a subpixel well (106, 107, 108). The subpixel wells can be provided in a black matrix material using photolithography. The black matrix material separates and defines each subpixel and prevents light leakage between the subpixels. Suitable substrates onto which the black matrix material can be deposited to create the subpixels include glass, polymer, and gallium nitride (GaN). However, other substrates can be used. Optionally, the substrate may be surface coated, such as with silicon nitride or a polymer coating.

[0021] The optically transparent substrate is illuminated from the back with a blue light emitting BLU 109. The BLU may be, for example, a blue LED with a diffuser or a blue OLED. Alternatively, the BLU may be a GaN-based LED grown on a GaN substrate. In this case, the subpixel wells may be formed directly on the GaN substrate. As shown in FIG. 1, a single diffuse backlight may be used to illuminate all the subpixels. However, multiple separate micro LEDs may be integrated with the substrate below each subpixel. In this case, each subpixel would have its own blue light source. The red subpixel 103 includes a red-emitting QDCF layer 110 that includes red-emitting QDs (represented by solid circles) and a blue light absorbing material (represented by open circles). Similarly, the green subpixel 104 includes a green-emitting QDCF layer 111 that includes green-emitting QDs (represented by solid circles) and a blue light absorbing material (represented by open circles). 1, BLU 109 and substrate 102 are in direct contact, however, there may be intervening layers, provided that QDCF layers 110, 111 are in the optical path of the blue light emitted from BLU 109. Examples of intervening layers include capping layers, thin encapsulation layers, buffer layers, and / or simply air spaces between adjacent layers.

[0022] One embodiment of an LCD incorporating a QDCF layer is shown in Figure 2. In this device, red subpixels 103, green subpixels 104, and blue subpixels 105 are illuminated by one or more blue light sources 109 (e.g., blue OLEDs) through a liquid crystal layer 112. Although not shown, the LCD display may include intervening layers between the BLU 109 and the liquid crystal layer 112, or between the liquid crystal layer 112 and the pixels 100. Such intervening layers may include, for example, polarizers, thin film transistors, and / or air gaps.

[0023] As shown in Figures 1 and 2, the QDCF layer can be patterned by inkjet printing an ink composition containing QDs and emissive material into the subpixel wells and sealing the ink composition within the subpixel wells. However, the use of subpixel wells is not required. Patterning of the QDCF layer can also be achieved by processing a QD-containing photoresist with conventional photolithography. Also, while Figures 1 and 2 show the blue light absorbing material as being uniformly dispersed throughout the QDCF layer, the blue light absorbing material can be gradient in concentration, such that there is a higher concentration of blue light absorbing material on the light output side of the subpixel than on the BLU light input side of the subpixel.

[0024] QDs are small crystalline inorganic particles that absorb blue light from a BLU and convert the energy of that radiation into light having a different wavelength or range of wavelengths. The converted light is emitted from the QDs in a very narrow optical spectral range. The wavelength of radiation that the QDs absorb and emit depends on the size of the QDs. Thus, by incorporating QDs of appropriate size and material in the QDCF layer in the appropriate concentration and ratio, the QDCF layer can be designed to absorb blue light and convert at least a portion of it into radiation of another wavelength. In this disclosure, QDs that absorb blue light and convert it to red light are referred to as red-emitting QDs, and QDs that absorb blue light and convert it to green light are referred to as green-emitting QDs. Quantum dots may be composed of various semiconductors, such as II (e.g., Zn, Cd)-VI (e.g., Se, S) semiconductors, III-V semiconductors, and IV-VI semiconductors.

[0025] The light absorbing material may be a single material or multiple materials that function to reduce blue light leakage from the QDCF and / or improve the EQE of the QDCF. The blue light absorbing material is characterized by absorbing ("blocking") light having wavelengths in the blue region of the visible spectrum (i.e., light from about 380 nm to about 500 nm) but transmitting light having wavelengths outside the blue region. For example, the light absorbing material may have an absorption peak at wavelengths from 400 nm to 500 nm (such as 420 nm to 480 nm or even 430 nm to 460 nm). The blue light absorbing material does not need to absorb 100% of the blue light in the red or green subpixels, and does not need to transmit 100% of the red or green light in the red or green subpixels. However, the transmittance of blue light should be significantly lower than the transmittance of red or green light in the blue light absorbing material.

[0026] Examples of light absorbing materials that aid in absorbing blue light include blue light absorbing organic dye molecules. These organic dye molecules may have narrow or broad absorption bands in the blue region of the visible spectrum. It is desirable for the organic dye molecules to have strong absorption in the blue region of the visible spectrum and a narrow absorption spectrum so as not to quench the red or green light from the red and green emitting QDs in the red and green subpixels. One example of such a dye is ABS454 (visible narrow band absorber), an absorption dye available from Exciton. This dye has a peak absorption at 453±1 nm and a narrow absorption peak from 400 nm to 480 nm (in methylene chloride). Examples of blue light absorbing organic dye molecules include azo dyes, although some embodiments of the ink composition do not include azo dyes.

[0027] In some embodiments of the QDCF, the light absorbing material is an emissive material that contains a luminophore. These materials increase the EQE of the QDCF and aid in the absorption of blue light. The emissive material is characterized by its efficient absorption in the blue region of the visible spectrum and re-emit radiation at another wavelength shifted by the Stokes shift. A luminophore is an atom or functional group in the emissive material that is responsible for its luminescent properties. When an emissive material absorbs light, an exciton is formed. The energy of the exciton can be transferred to the QDs in the QDCF to improve the overall efficiency of the display device while reducing blue light leakage. The emissive material can be organic, inorganic, or a combination thereof. Examples of emissive blue light absorbing materials that can transfer energy to the QDs include organic molecules such as coumarin, rhodamine, fluorescein, acridine, perylene; tris[2-phenylpyridinate-C 2 ,N]Iridium(III) (Ir(ppy) 3 ), bis[2-(4,6-difluorophenyl)pyridinate-C 2phosphorescent and fluorescent dopants, including those commonly used in OLED materials, such as [N](picolinato)iridium(III) (Firpic), platinum octaethylporphyrin (PtOEP), tris-(8-hydroxyquinoline)aluminum (Alq), 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB), coumarin C545, and rubrene; emissive blue-light absorbing polymers, such as polyfluorenes; materials incorporating lanthanide-containing luminophores, such as ZnS:Eu and ZnS:Tb; emissive blue-light absorbing polycyclic aromatic hydrocarbons (PAHs), such as tetracene, perylene, and derivatives of these molecules with one or more side chains added or chemically modified; and QDs that, when acting as emissive materials, behave differently than the red- and green-emitting QDs in the red and green subpixels. Examples of commercially available coumarins that can be used in the ink composition include coumarin 334, coumarin 314, and coumarin 6. These have absorption peaks in the wavelength range of 430 nm to 460 nm. Organic molecules such as coumarins are also organic laser molecules. Organic laser molecules are commonly used as laser dyes because they can exhibit laser action.

[0028] The exciton energy transfer process from the donor (light-emitting material) to the acceptor (QD) can be long-range radiative transfer (typically longer than 10 nm) or short-range non-radiative transfer (typically shorter than 10 nm).

[0029] Long-range radiative energy transfer is a process of photon reabsorption. Such energy transfer can occur in principle with unlimited range as long as the emission spectrum of the donor and the absorption spectrum of the acceptor overlap. Energy transfer is initiated by exciton recombination in the emissive material, which emits a photon. This photon may be absorbed by the QD due to the spectral overlap. The rate of energy transfer is determined by the quantum yield of emission from the emissive material and the absorption coefficient of the QD.

[0030] Short-range non-radiative energy transfer includes a) Förster type and b) Dexter type energy transfer. Förster type energy transfer occurs through dipole-dipole bonds between molecules. Initially, the emissive material is in an excited state and the QDs are in a ground state. The interaction of the two wave functions of the emissive material and the QDs causes a photon transfer from the emissive material to the QDs, which causes the wave function of the QDs to oscillate at a frequency equal to that of the emissive material. After the transfer, the QDs move to an excited state and the emissive material returns to its ground state.

[0031] Förster transfer requires a spectral overlap between the emission of the donor and the absorption of the acceptor. The efficiency of energy transfer is highly dependent on the transfer distance and scales as the inverse sixth power of the intermolecular distance. The main conditions for enabling Förster energy transfer are a), b), and c): a) the emitter and the QDs must be in close proximity (usually about 1 nm to about 10 nm); b) the absorption spectrum of the QDs overlaps with the emission spectrum of the emitter; and c) the transition dipoles of the emitter and the QDs must be approximately parallel.

[0032] As an example, in a typical QD color filter film, the intermolecular distance between QDs at nominal QD loading conditions (e.g., about 30 wt%) is about 10 nm. If the luminophores of the blue light absorbing material are in close proximity to the QDs (about 1 nm to 10 nm) and other key conditions for Förster-type transfer are met, Förster-type energy transfer will occur as long as the energy transfer proceeds faster than the natural decay time of the excitons in the emitting material. For example, the decay time of the fluorescent dye coumarin is on the order of nanoseconds, so the energy transfer will proceed faster than that time scale.

[0033] The efficiency improvement of the QDCF will depend on the quantum yield of the emissive material at the wavelength of blue light from the BLU (e.g., 450 nm), the area of ​​spectral overlap between the emission by the emissive material and the absorption by the QDs, and the intermolecular distance and lifetime decay of the emissive material. Using these criteria as a guide, we can select the appropriate emissive material for the red-emitting QDs and the green-emitting QDs, as well as identify the appropriate concentration of the emissive material in the QDCF.

[0034] The performance efficiency of the QDCFs used for the red and green subpixels can be characterized by the blue light transmission and EQE of these pixels. The blue light transmission is a measure of the amount of blue light from the source that is transmitted through the QDCF, or the OD of the QDCF in the blue region of the spectrum. If the QDCF layer is high performance, most of the blue light from the source will not be transmitted through the red and green subpixels. If the blue light leaks through these subpixels, color contamination will occur and the color gamut of the device will be reduced. For example, to achieve a wide color gamut, it is desirable for less than 1% of the blue light from the BLU to be transmitted through the red and green subpixels. In terms of OD, this corresponds to an OD of 2 at the blue peak wavelength of 450 nm. This is a practical criterion, since 450 nm corresponds to the peak wavelength of standard blue LEDs used as BLUs in optoelectronic displays. In various embodiments of the red and / or green subpixels, the OD at 450 nm is 0.3 or greater. The above includes red and / or green subpixel OD at 450 nm of 1.0 or more, 1.1 or more, 1.2 or more, and 1.3 or more. Methods for measuring blue light transmittance and OD are described in the Examples.

[0035] EQE is an index that indicates the number of photons emitted by a QD in a subpixel that leave the display device in the forward / viewing direction. EQE is defined as follows: QD photons emitted in the positive direction / source photons incident in the positive direction Various embodiments of films containing blue light absorbing materials can achieve subpixel EQEs of 4% to 40%, although EQEs outside these ranges can also be achieved.

[0036] QDCFs can be formed by applying a liquid ink composition comprising QDs and a blue light absorbing material onto a substrate and drying the application to a solid film. The drying step can include simply removing volatile components from the composition, such as water and / or organic solvents, by evaporating them. However, for embodiments in which the ink composition includes a crosslinkable monomer and, optionally, a crosslinker, the drying step can include curing the ink composition such that the cured film is a polymerization product of the ink composition. The film thickness of the final film can be very thin (e.g., 5 μm to 20 μm). However, film thicknesses outside these ranges can also be used.

[0037] In various embodiments, the liquid ink composition comprises one or more curable di(meth)acrylate monomers or a mixture of one or more curable di(meth)acrylate monomers and one or more mono(meth)acrylate monomers; one or more multifunctional (meth)acrylate crosslinkers; red- or green-emitting QDs; and one or more blue light absorbing materials. As used herein, "(meth)acrylate monomer" indicates that the monomer described may be an acrylate or a methacrylate.

[0038] As an example, in an embodiment, the ink composition includes (a) 10% to 94.99% by weight of a di(meth)acrylate monomer or a combination of a di(meth)acrylate monomer and a mono(meth)acrylate monomer, (b) 4% to 10% by weight of a multifunctional (meth)acrylate crosslinker, (c) 1% to 50% by weight of QDs, (d) 0.01% to 85% by weight of a blue light absorbing material, and optionally (e) 0.1% to 30% by weight of scattering particles. However, concentrations outside these ranges can also be used. For example, an ink composition can be used in which the content of the blue light absorbing material is 0.05% to 5.0% by weight. The above includes a content of the blue light absorbing material in the ink composition of 0.1% to 1.0% by weight, or even 0.1% to 0.5% by weight. In such ink compositions, the balance of the ink composition can be adjusted by varying the amount of one or more of the other components in the ink composition (i.e., components (a), (b), (c), and / or (e)). In some embodiments of the ink composition, a curing initiator, such as a photoinitiator or a thermal initiator, is included. By way of example, the curing initiator can be included in an amount of about 0.1% to about 20% by weight.

[0039] A scattering particle (abbreviated SP) may be a geometric scattering particle (abbreviated GSP), a plasmonic scattering nanoparticle (abbreviated PSNP), or a combination thereof. It is noted that PSNPs typically have at least one nanoscale dimension (i.e., at least one dimension of about 1000 nm or less), but the nanoparticles need not be spherical. For example, nanoparticles can be elongated particles such as nanowires or irregularly shaped particles. GSPs can be nanoparticles, but are not required to be nanoparticles. Scattering by GSPs is achieved by reflection, refraction, and diffraction at the particle surface. Examples of GSPs include metal oxide particles such as zirconium oxide (i.e. zirconia), titanium oxide (i.e. titania), and aluminum oxide (i.e. alumina) particles. PSNPs are characterized by incident light exciting electron density waves within the nanoparticle, forming a localized oscillating electric field that extends outward from the nanoparticle surface. Examples of PSNPs include metal nanoparticles such as silver nanoparticles.

[0040] The ink composition can include two or more SPs. For example, various embodiments of the ink composition include a mixture of QDs and PSNPs, a mixture of QDs and GSPs, or a mixture of QDs, GSPs, and PSNPs. A QD-containing ink composition used to form a QDCF for a subpixel of a particular color (e.g., red or green) will include a QD that converts light from a BLU to that color.

[0041] A GSP-containing ink composition can include two or more GSPs, where the different GSPs differ in nominal particle size and / or shape, particle material, or both. Similarly, a PSNP-containing ink composition can include two or more PSNPs, where the different PSNPs differ in nominal particle size and / or shape, particle material, or both.

[0042] Mono(meth)acrylate and di(meth)acrylate monomers are ether and / or ester compounds with film-forming properties that function as binder materials upon curing. As components of liquid ink compositions, these monomers can form jettable compositions at a range of inkjet printing temperatures, including room temperature. However, liquid ink compositions can also be applied by other methods, such as slot-die coating or spin coating. In general, for ink compositions to be useful for inkjet printing applications, the surface tension, viscosity, and wetting properties of the ink composition must be tailored to allow the ink composition to be ejected through an inkjet printing nozzle at printing temperatures (e.g., room temperature, about 22° C., or higher, such as up to about 70° C.) without drying on the nozzle or clogging the nozzle. In various embodiments, the ink composition can be formulated to have a viscosity of, for example, about 2 cps to about 30 cps (e.g., a viscosity of about 10 cps to about 27 cps, a viscosity of about 14 cps to about 25 cps) at a temperature of 22° C. to 70° C., and a surface tension of about 25 dynes / cm to about 45 dynes / cm (e.g., a surface tension of about 30 dynes / cm to about 42 dynes / cm, a surface tension of about 28 dynes / cm to about 38 dynes / cm) at a temperature of 22° C. to 70° C. Methods for measuring viscosity and surface tension are well known and include the use of commercially available flow meters (e.g., a DV-I Prime Brookfield flow meter) and tensiometers (e.g., a SITA bubble pressure tensiometer).

[0043] The mono(meth)acrylate and di(meth)acrylate monomers may be, for example, linear aliphatic mono(meth)acrylates and di(meth)acrylates, or may contain cyclic and / or aromatic groups. In various embodiments of the inkjet printable ink composition, the mono(meth)acrylate and / or di(meth)acrylate monomers are polyethers. The monomers are preferably polar, low vapor pressure monomers with relatively high boiling points.

[0044] Suitable (meth)acrylate monomers include, but are not limited to, alkyl or aryl (meth)acrylates, such as methyl (meth)acrylate, ethyl (meth)acrylate, benzyl (meth)acrylate, and the like; cyclic trimethylolpropane formal (meth)acrylate; alkoxylated tetrahydrofurfuryl (meth)acrylate; phenoxyalkyl (meth)acrylates, such as 2-phenoxyethyl (meth)acrylate, phenoxymethyl (meth)acrylate, and the like; 2(2-ethoxyethoxy)ethyl (meth)acrylate. Other suitable di(meth)acrylate monomers include 1,6-hexanediol diacrylate, 1,12-dodecanediol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, di(ethylene glycol) methyl ether methacrylate, polyethylene glycol di(meth)acrylate monomers, such as ethylene glycol di(meth)acrylate monomers and polyethylene glycol di(meth)acrylate monomers having a number average molecular weight of about 230 g / mol to about 440 g / mol. In various embodiments of the ink composition, other mono- and di(meth)acrylate monomers include dicyclopentenyloxyethyl acrylate (DCPOEA), isobornyl acrylate (ISOBA), dicyclopentenyloxyethyl methacrylate (DCPOEMA), isobornyl methacrylate (ISOBMA), and N-octadecyl methacrylate (OctaM), which may be used alone or in combination. Also usable are homologs of ISOBA and ISOBMA in which one or more of the methyl groups on the ring are replaced with hydrogen (collectively referred to as "ISOB(M)A" homologs).

[0045] In various embodiments of the inkjet printable ink composition, the di(meth)acrylate monomer is an alkoxylated aliphatic di(meth)acrylate monomer. These include neopentyl glycol group-containing di(meth)acrylates such as alkoxylated neopentyl glycol diacrylates such as neopentyl glycol propoxylate di(meth)acrylate and neopentyl glycol ethoxylate di(meth)acrylate. In various embodiments, the neopentyl glycol group-containing di(meth)acrylate has a molecular weight of about 200 g / mol to about 400 g / mol. These include neopentyl glycol group-containing di(meth)acrylates having a molecular weight of about 280 g / mol to about 350 g / mol, as well as neopentyl glycol group-containing di(meth)acrylates having a molecular weight of about 300 g / mol to about 330 g / mol. Various neopentyl glycol group-containing di(meth)acrylate monomers are commercially available. For example, neopentyl glycol propoxylate diacrylate is sold by Sartomer Corporation under the trade name SR9003B and by Sigma Aldrich Corporation under the trade name Aldrich-412147 (approximately 330 g / mole; viscosity of approximately 18 cps at 24° C.; surface tension of approximately 34 dynes / cm at 24° C.). Neopentyl glycol diacrylate is also sold by Sigma Aldrich Corporation under the trade name Aldrich-408255 (approximately 212 g / mole; viscosity of approximately 7 cps; surface tension of approximately 33 dynes / cm).

[0046] The multifunctional (meth)acrylate crosslinker desirably has at least three reactive (meth)acrylate groups. Thus, the multifunctional (meth)acrylate crosslinker may be, for example, a tri(meth)acrylate, a tetra(meth)acrylate, and / or a higher multifunctional (meth)acrylate. Pentaerythritol tetraacrylate or pentaerythritol tetramethacrylate, di(trimethylolpropane) tetraacrylate, di(trimethylolpropane) tetramethacrylate are examples of multifunctional (meth)acrylates that can be used as primary crosslinkers. In this specification, the term "primary" indicates that other components of the ink composition may also contribute to crosslinking, but crosslinking is not the primary functional purpose of those components.

[0047] When the ink composition includes a photoinitiator, the particular photoinitiator used in a given ink composition is desirably selected to activate at a wavelength that will not damage the materials used to fabricate the device. Acylphosphine oxide photoinitiators can be used, but it will be understood that a wide variety of photoinitiators can be used. For example, but not limited to, α-hydroxyketone, phenylglyoxylate, and α-aminoketone photoinitiators can also be considered. To initiate polymerization using free radicals, various photoinitiators can have an absorption profile from about 200 nm to about 400 nm. In various embodiments of the ink compositions and printing methods disclosed herein, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) and 2,4,6-trimethylbenzoyl-diphenylphosphinate salts have preferred properties. Examples of acylphosphine photoinitiators include the UV-curable initiator Irgacure® TPO (previously sold under the trade name Lucirin® TPO), which is a type I hemolytic initiator that absorbs at 380 nm; the type I photoinitiators Irgacure® TPO-L, which absorbs at 380 nm; Irgacure® 819, which absorbs at 370 nm; and Irgacure® 907. Examples include acylphosphine photoinitiators with a maximum output of 1.5 J / cm at nominal wavelengths of 350 nm to 395 nm. 2 The ink composition containing the TPO photoinitiator can be cured using a light source emitting radiation at a radiant energy density of about 0.1% to about 20% by weight, such as about 0.1% to about 8% by weight.

[0048] Although various embodiments of the ink compositions described herein include a photoinitiator, other types of initiators can be used instead of or in addition to a photoinitiator. For example, other suitable curing initiators include thermal initiators and initiators that use other types of energy to induce polymerization, such as electron beam initiators.

[0049] The ink composition will further comprise red- or green-emitting QDs and, optionally, SPs dispersed in an organic binder material. The QDs optionally comprise a surface film of coating ligands. These coating ligands, which passivate the QDs and help stabilize them from agglomeration, often result from the solution-phase growth of the QDs. The QD-containing ink composition may also include another type of ligand, referred to herein as a crosslinking ligand. The crosslinking ligands attach to the QDs, usually by forming hydrogen bonds, and covalently crosslink to the polymeric components in the ink composition upon curing. The crosslinking ligands are monomers characterized by having one or more functional groups (e.g., acrylate or methacrylate groups) with polymerizable double bonds and functional groups that specifically attach to the surface of the QDs in the ink composition. The monomer may further comprise a spacer chain separating these functional groups. The dual functionality of these crosslinking ligands keeps the QDs dispersed in the curable ink composition and prevents re-aggregation of the QDs during the curing process. 2 Monomers containing thiol groups (-SH), where R is an H atom or an alkyl group, have strong binding affinity to QDs composed of II-VI elements. 2-Carboxyethyl acrylate (2CEA) is an example of a crosslinking ligand used for octadecylamine-coated core-shell CdSe / ZnS QDs.

[0050] In some embodiments of the ink composition, an organic solvent can be added to adjust the viscosity and / or surface tension of the ink composition and / or to allow for higher concentration of QDs. Suitable organic solvents include esters and ethers. Examples of organic solvents that can be included in the ink composition include high boiling organic solvents, such as those with a boiling point of 200° C. or higher. These include organic solvents with a boiling point of 230° C. or higher, 250° C. or higher, or even 280° C. or higher. Examples of high boiling organic solvents that can be used include diols and glycols, such as propanediol, pentanediol, diethylene glycol, and triethylene glycol. High boiling aprotic solvents, such as those with a boiling point of 240° C. or higher, can also be used. Sulfolane, 2,3,4,5-tetrahydrothiophene-1,1-dioxide (also known as tetramethylene sulfone), is an example of a relatively high boiling aprotic solvent. Non-limiting examples of other organic solvents include xylene, mesitylene, propylene glycol methyl ether, methylnaphthalene, methyl benzoate, tetrahydronaphthalene, dimethylformamide, terpineol, phenoxyethanol, and butyrophenone. When an organic solvent is included in the ink composition, the aforementioned QD and monomer concentrations are based on the solids content of the ink composition.

[0051] The types of jettable ink compositions that can be used to print one or more polymer layers with the addition of QDs and emissive materials are described in U.S. Patent Application Publication No. 2016 / 0024322, filed July 22, 2015, U.S. Patent Application Publication No. 2017 / 0062762, filed July 19, 2016, U.S. Patent Application Publication No. 2018 / 0102449, and PCT International Patent Application Publication No. 2018 / 017541, filed July 18, 2017, each of which is incorporated herein by reference in its entirety.

[0052] The ink composition can be printed in air or in an inert environment, such as with the printing system described in U.S. Patent No. 8,714,719, the contents of which are incorporated herein in their entirety. The film can be cured in air or in an inert environment using UV radiation, thermal energy, or other forms of energy (e.g., electron beam). During curing, volatile components (e.g., solvents) in the ink composition are removed and the curable monomers polymerize into polymer chains to form the cured film. EXAMPLES

[0053] Example 1: Ink composition containing a perylene dye and a film formed therefrom

[0054] To illustrate the improvement realized by including light-absorbing material in the red subpixel, two QDCF ink compositions (Ink A and Ink B) were formulated. Ink A was used as a control and is an ultraviolet (UV) curable ink containing red-emitting QDs. Ink B had a similar composition to Ink A but contained 1 wt % of a perylene derivative dye (Lumogen F Yellow 083) as a blue light absorber.

[0055] QD: The red-emitting QDs were InP / ZnS QDs functionalized with hydrophilic ligands, sold by Nanosys.

[0056] Luminescent material: Lumogen F Yellow 083 was sold by BASF. Lumogen F Yellow 083 absorbs in the blue wavelength region of the visible spectrum with an absorption maximum in dichloromethane at about 476 nm. The dye has multiple emission peaks with a peak maximum at 496 nm in dichloromethane.

[0057] UV-curable ink composition:A UV-curable ink composition was prepared by mixing 90% by weight of benzyl methacrylate monomer, 7% by weight of pentaerythritol tetraacrylate (PET) crosslinker, and 3% by weight of photopolymerization initiator TPO. A stock solution of this composition was prepared and stored.

[0058] Base Red Ink Composition: 170 mg of the dried red QD concentrate was added to 1 ml of a UV-curable ink composition and left on a roller overnight. The composition was then filtered using a 0.45 μm nylon membrane. The final concentration of red QDs in the base red ink composition was 15 wt%.

[0059] Base luminophore ink composition: To 10 ml of the UV-curable ink composition, 200 mg of Lumogen F Yellow 083 yellow dye powder was added. The resulting solution was stirred with a magnetic stirrer for 4 hours until the dye was completely dissolved. The final concentration of the dye was about 2% by weight.

[0060] Ink A (comparative example): In a separate vial, 0.2 ml of the base red ink composition was diluted with 0.2 ml of the UV-curable ink composition. The final composition of Ink A was about 7.8 wt% ligand-coated InP / ZnSQDs, about 83 wt% benzyl methacrylate monomer, 6.5 wt% PET, and 2.7 wt% TPO.

[0061] Ink B (Example): In a separate vial, 0.2 ml of the base luminophore ink composition was mixed with 0.2 ml of the base red ink composition. The resulting solution was stirred with a magnetic stirrer for 4 hours to ensure thorough mixing. The final composition of Ink B was about 7.8 wt% ligand-coated InP / ZnSQDs, 1 wt% Lumogen F Yellow 083, about 82 wt% benzyl methacrylate, 6.5 wt% PET, and 2.7 wt% L-TPO.

[0062] QDCF film:A QDCF film was formed on a glass slide measuring 50 mm x 50 mm. The substrate was UV ozone treated for 15 minutes, after which Ink A or Ink B was doctor-bladed onto the substrate. Ink A was used to make QDCF film A, and Ink B was used to make QDCF film B. The target film thickness in wet state was about 12 μm. The wet film was then cured for 2 minutes with a 395 nm LED excited under nitrogen environment. The film appeared to be sufficiently cured.

[0063] Optical characterization: A schematic diagram of the in-house optical characterization setup is shown in Figure 3. An array of blue LEDs with a diffuser was used as the BLU. A substrate coated with QDCF film was placed on the LED BLU, and an Ocean Optics integrating sphere (FOIS-1) was placed over the sample to capture all the forward light. The captured light included both the blue light transmitted through the glass substrate and the QDCF film, and the emission from the QDs. The integrating sphere was coupled to an Ocean Optics JAZ series spectrometer (with a fiber optic cable) connected to a PC with SpectraSuite software. The EQE was the spectral integral of the QD emission region relative to the spectral integral of the blue LED reference spectrum measured in the forward direction. The OD at 450 nm was calculated from the film transmittance value of blue light as follows: OD=2-log(100x(%T QDCF ) / (%T 基板 )), where %T QDCF is the percentage of light transmitted through the QDCF film, and %T 基板 is the percentage of light transmitted through the substrate.

[0064] Experimental Results

[0065] QDCF Film A (Comparative Example): The reference spectrum of a blue LED through a bare glass substrate ("Blue LED") and the actual spectrum through QDCF Film A ("Blue LED+QDCF") are shown in FIG.

[0066] Ink B (Example): The reference spectrum of a blue LED through a bare glass substrate ("Blue LED") and the actual spectrum through QDCF Film B ("Blue LED+QDCF") are shown in FIG.

[0067] 4 and 5, the amount of blue light transmitted through QDCF film B is approximately 50% of the amount of blue light transmitted through QDCF film A. The results are shown in Table 1 below. [Table 1]

[0068] Because the comparative films (7 μm) were thinner than the inventive films (10 μm), the ODs of the comparative films shown in Table 1 were normalized to a thickness of 10 μm and shown in the table. As shown in Table 1, the normalized OD of QDCF Film A was 0.18, while the normalized OD of QDCF Film B was 0.36.

[0069] Example 2: Ink composition containing a coumarin dye and a film formed from the ink composition

[0070] To illustrate the improvement achieved by including a light-absorbing material in the green subpixel, four QDCF ink compositions (Ink A2, Ink B2, Ink C2, and Ink D2) were formulated. Ink A2 was used as a control and is a UV-curable ink containing green-emitting QDs. Inks B2, C2, and D2 have the same composition as Ink A but contain 0.15% to 0.24% by weight of coumarin as a blue-light absorbing material.

[0071] QD: Green-emitting QDs were sold by Nanosys.

[0072] Blue light absorbing material:Coumarin 334 for ink composition B2, Coumarin 314 for ink composition C2, and Coumarin 6 for ink composition D2 were each commercially available from Sigma-Aldrich Co. Coumarin absorbs in the blue wavelength region of the visible spectrum and has an absorption maximum in the wavelength range of 430 nm to 460 nm.

[0073] The formulations of ink composition A2 (comparative example), ink composition B2, ink composition C2, and ink composition D2 are shown in Table 2. [Table 2]

[0074] QDCF film: A QDCF film was formed according to the procedure described in Example 1.

[0075] Optical characterization: The optical properties of the QDCF films were evaluated as described in Example 1. The results are shown in Table 3. [Table 3]

[0076] As used herein, the term "exemplary" means serving as an example, illustration, or illustration. Any aspect or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, in this disclosure, "a" or "an" means "one or more" unless expressly stated otherwise.

[0077] The foregoing description of the exemplary embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the present invention to the precise form disclosed. Modifications and variations of the exemplary embodiments are possible in light of the above teachings or by practice of the present invention. The above embodiments have been chosen and described in order to explain the principles of the present invention and as practical applications thereof. Thus, those skilled in the art will be able to utilize the present invention in its various embodiments and to make various modifications as suited to the particular use contemplated. It is intended that the scope of the present invention be defined by the appended claims and their equivalents.

Claims

1. 1. An optoelectronic display device, comprising: a pixel array including at least one red subpixel and at least one green subpixel, the red subpixel including red light-emitting quantum dots and blue light-absorbing material, and the green subpixel including green light-emitting quantum dots and blue light-absorbing material; 1. An optoelectronic display device, wherein the blue light absorbing material of each subpixel preferentially absorbs blue light relative to red or green light and transfers energy to a red-emitting quantum dot and a green-emitting quantum dot, respectively, and at least one of the red and green subpixels further comprises scattering particles.

2. 10. The optoelectronic display device of claim 1 wherein one or both of the blue light absorbing materials comprises an organic molecule.

3. 3. The optoelectronic display device of claim 2 wherein the organic molecules comprise coumarin molecules.

4. 10. The optoelectronic display device of claim 1 wherein one or both of the blue light absorbing materials comprises an inorganic material.

5. 10. The optoelectronic display device of claim 1 wherein one or both of the blue light absorbing materials comprises a luminophore.

6. 6. The optoelectronic display device of claim 5, wherein one or both of the blue light absorbing materials are selected from phosphorescent dopant molecules, fluorescent dopant molecules, phosphorescent polymer molecules, fluorescent polymer molecules, semiconductor quantum dots, lanthanide-containing compounds, polycyclic aromatic hydrocarbons, and combinations of two or more thereof.

7. 2. An optoelectronic display device as claimed in claim 1 , wherein the blue light absorbing material is present in each or both of the red and green subpixels in a concentration gradient such that the blue light absorbing material is more concentrated on a light output side of the subpixel than on a light input side of the subpixel.

8. 1. An optoelectronic display device, comprising: a pixel array including at least one red subpixel and at least one green subpixel, the red subpixel including red light-emitting quantum dots and blue light-absorbing material, and the green subpixel including green light-emitting quantum dots and blue light-absorbing material; a blue light absorbing material of each subpixel that preferentially absorbs blue light relative to red or green light and transfers energy to the red-emitting quantum dots and the green-emitting quantum dots, the blue light absorbing material being selected from phosphorescent dopant molecules, fluorescent dopant molecules, phosphorescent polymer molecules, fluorescent polymer molecules, semiconductor quantum dots, lanthanide-containing compounds, polycyclic aromatic hydrocarbons, and combinations thereof; At least one of the red and green sub-pixels further comprises scattering particles.

9. The blue light absorbing materials are coumarin, rhodamine, fluorescein, acridine, rubrene, polyfluorene, ZnS:Eu, ZnS:Tb, tetracene, perylene, tris[2-phenylpyridinato-C2,N]iridium(III), bis[2-(4,6-difluorophenyl)pyridinato-C 2 10. The optoelectronic display device of claim 8, wherein the organic emissive group is selected from the group consisting of [,N](picolinato)iridium(III), platinum octaethylporphyrin, tris-(8-hydroxyquinoline)aluminum (Alq), 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran, and combinations thereof.

10. 10. The optoelectronic display device of claim 8, wherein each blue light absorbing material comprises an organic molecule.

11. 10. The optoelectronic display device of claim 8 wherein each blue light absorbing material comprises a di(meth)acrylate polymer.

12. 10. The optoelectronic display device of claim 8 wherein each blue light absorbing material comprises a coumarin.

13. 9. An optoelectronic display device according to claim 8, wherein the material of the red and green subpixels has an optical density of at least 0.3 at a wavelength of 450 nm.

14. 1. An optoelectronic display device, comprising: a pixel array including at least one red subpixel and at least one green subpixel, the red subpixel including red light-emitting quantum dots, scattering particles, and blue light-absorbing material, and the green subpixel including green light-emitting quantum dots, scattering particles, and blue light-absorbing material; 1. An optoelectronic display device, wherein the blue light absorbing material of each subpixel preferentially absorbs blue light relative to red or green light and transfers energy to the red-emitting quantum dots and the green-emitting quantum dots, the blue light absorbing material being selected from the group consisting of coumarin, rhodamine, fluorescein, acridine, rubrene, polyfluorene, tetracene, perylene, and combinations thereof.

15. 15. The optoelectronic display device of claim 1, 8, or 14, further comprising the blue light emitting backlight unit, the blue light emitting backlight unit comprising a blue LED, a blue OLED, or a GaN-based LED unit.

16. 15. The optoelectronic display device of claim 1, 8, or 14, further comprising the blue light emitting backlight unit, the blue light emitting backlight unit including a plurality of micro LEDs disposed adjacent each of the subpixels.

17. 15. An optoelectronic display device according to claim 1, 8 or 14, wherein the blue light absorbing material of the red sub-pixel is different from the blue light absorbing material of the green sub-pixel.

18. 15. An optoelectronic display device as claimed in claim 1, 8 or 14, wherein at least some of the scattering particles are nanoparticles.

19. 20. An optoelectronic display device as claimed in claim 18, wherein the nanoparticles are metallic nanoparticles.

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