Display element and display device

Abstract

To provide a display element and a display device capable of enhancing both of macro light utilization efficiency of a wavelength conversion layer and color purity.SOLUTION: A display element comprises: a light emission layer array which has a plurality of light emission layers being two-dimensionally arranged and emitting light of a first wavelength; and a conversion layer array having a first coupling part which is optically coupled to parts of the plurality of light emission layers, and a first extraction part and a first reflection part which are arranged to face each other so as to alternately reflect the light of the first wavelength collected through the first coupling part, and guide the light toward a direction separating from the first coupling part, and includes a plurality of first conversion layers which emit light of a second wavelength obtained by wavelength conversion of the light of the first wavelength through the first extraction part.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a display element and a display device.

Background Art

[0002] In a display element and a display device for displaying an image, as a technique for realizing high color purity and high luminous efficiency, a technique using a light-emitting layer containing quantum dots is known. When the light-emitting layer uses primary light as excitation light, such a light-emitting layer may be referred to as a color conversion layer because it performs wavelength conversion.

[0003] Patent Document 1 discloses a high-resolution display device that monolithically constitutes an inorganic micro LED array that emits blue light and a color conversion layer array corresponding to sub-pixels of each of RGB colors, thereby reducing manufacturing costs and improving macro light utilization efficiency. Patent Document 1 further discloses a rear optical arrangement in which blue light is incident as excitation light from behind the color conversion layer array corresponding to sub-pixels of each of RGB colors, and the light converted in color is emitted toward the front of the color conversion layer array. With such an arrangement of the rear optical system, the display device described in Patent Document 1 secures an optical coupling area between the light-emitting element and the color conversion layer, and secures a macro light utilization efficiency, which is the light propagation efficiency from the light-emitting element to the wavelength conversion layer. Patent Document 1 discloses a form in which the color conversion layer includes quantum dots and a light-scattering material. Also, the color conversion layer may be referred to as a wavelength conversion layer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the pixel configuration of the back-facing optical system described in Patent Document 1, the amount of light emitted after wavelength conversion is ensured by making the optical density of quantum dots present in the thickness direction of the wavelength conversion layer equal to or greater than a predetermined value. In such a pixel configuration of the back-facing optical system, the optical paths used by the primary light (excitation light) and the secondary light (light after wavelength conversion) are arranged in the same direction. Furthermore, in such a pixel configuration of the back-facing optical system, the first window, which is a coupling region for guiding the primary light to the wavelength conversion layer, and the second window, which corresponds to the light emission surface from which the wavelength conversion layer emits light toward the viewer, have a superimposed arrangement where they overlap when viewed in the thickness direction of the wavelength conversion layer. In other words, in the pixel configuration of the back-facing optical system described in Patent Document 1, the primary light (excitation light) and the secondary light (light after wavelength conversion) are coaxially arranged.

[0006] In the pixel configuration of the back-facing optical system described in Patent Document 1, the optical density of quantum dots can be increased by adjusting any of the following: quantum dot density, absorption coefficient, or thickness of the wavelength conversion layer. This increases the emission intensity per unit depth at the penetration depth of primary light. On the other hand, according to the Lambert-Beer law, absorption per unit depth of at least one of the primary and secondary light also increases. Due to the tension between the emission and absorption effects, the increase in macroscopic light utilization efficiency with respect to the increase in the optical density of quantum dots plateaus. In other words, in the pixel configuration of the back-facing optical system adopted in Patent Document 1, there was a limit to the improvement in macroscopic light utilization efficiency by adjusting the optical density.

[0007] Similarly, if the optical density of quantum dots in the wavelength conversion layer is reduced, the absorption of primary and secondary light per unit depth decreases, but the primary light reaches the light-emitting side of the color conversion layer, reducing the color purity of the extracted emitted light. To address this reduction in color purity, an optical filter is placed on the light-emitting side of the wavelength conversion layer, but the macroscopic light utilization efficiency of the emitted light after color conversion is limited by the optical filter.

[0008] In other words, the methods for adjusting the optical density in the thickness direction of these wavelength conversion layers resulted in at least one of two conflicting problems: an upper limit on brightness and a decrease in color purity. Therefore, improvements were needed because these methods did not lead to a fundamental improvement in the macroscopic light utilization efficiency of the wavelength conversion layers.

[0009] This invention has been made in view of the above-mentioned problems, and aims to provide a display element and a display device in which both the macroscopic light utilization efficiency and color purity of the wavelength conversion layer are improved. [Means for solving the problem]

[0010] A display element according to an embodiment of the present invention includes: an emissive layer array comprising a plurality of emissive layers arranged in two dimensions and emitting light of a first wavelength; a first coupling portion optically coupled to a part of the plurality of emissive layers; a first extraction portion and a first reflecting portion arranged opposite each other to alternately reflect the light of the first wavelength collected through the first coupling portion and guide it toward a direction away from the first coupling portion; and a conversion layer array comprising a plurality of first conversion layers that emit light of a second wavelength obtained by wavelength conversion of the light of the first wavelength through the first extraction portion. [Effects of the Invention]

[0011] The display element according to the present invention provides a display element and a display device in which both the macroscopic light utilization efficiency and color purity of the wavelength conversion layer are improved. [Brief explanation of the drawing]

[0012] [Figure 1] These are cross-sectional pixel views of the green (a), red (d), and blue (e) display elements according to the first embodiment, a plan view of the partially unfolded green display element (b), and a plan view of the array-like display element (c). [Figure 2] This figure shows the cross-sectional structure of the display element according to the first embodiment (a) and the conventional form (b), and the in-layer structure of the wavelength conversion layer according to the first embodiment (c) and the conventional form (d). [Figure 3] These are cross-sectional views (a) and (b) showing the conventional pixel arrangement. [Figure 4] This figure shows the waveguide characteristics of the conversion layer applicable to each embodiment. [Figure 5]Pixel cross-sectional views of display elements (a) to (f) according to the second to seventh embodiments. [Figure 6] Pixel cross-sectional views of display elements according to the eighth to twelfth embodiments (a), (c), (e), (g), (i), pixel planes (h), (j) of display elements according to the eleventh and twelfth embodiments, and luminance distribution profiles of display elements (b), (d), (f) according to the eighth to tenth embodiments. [Figure 7] Pixel plan view (a), array plan view (c), and pixel cross-sectional view (b) of a display element according to the thirteenth embodiment. [Figure 8] Pixel plan view (a), array plan view (c), and pixel cross-sectional view (b) of a display element according to the fourteenth embodiment. MODE FOR CARRYING OUT THE INVENTION

[0013] Hereinafter, a display element according to an embodiment of the present invention will be described in detail, but the present invention is not limited thereto.

[0014] <First Embodiment> The display element 100 according to the first embodiment will be described with reference to FIGS. 1(a) to (e) and FIGS. 2(a) and (c).

[0015] 1(a) and 1(b) are cross-sectional views showing the pixel structure of the green display element 100G according to the present embodiment and a plan view showing the pixel structure of a part of the green display element 100G developed, respectively. 1(c) is a plan view of the matrix-arranged array display element 100 of the present embodiment. 1(d) and 1(e) are cross-sectional views showing the pixel structures of the blue display element 100B and the blue display element 100B according to the present embodiment, respectively. The two-dimensional arrangement of the display elements may include a delta array (Δ array) and can be appropriately changed according to the display performance targeted.

[0016] In the specification of the present application, green, red, and blue are each treated as having a maximum value in a wavelength band of at least 515 nm or more and 545 nm or less, 615 nm or more and 645 nm or less, and 445 nm or more and 475 nm or less, respectively. More preferably, green, red, and blue are those in which the wavelengths at which they take their maximum values are within the respective bands of 528 nm or more and 532 nm or less, 628 nm or more and 632 nm or less, and 458 nm or more and 462 nm or less. Further, in each of the embodiments described later, green, red, and blue, which are secondary light of the light of the second to fourth wavelengths, are preferably those in which the upper limit of the bandwidth (full width at half maximum FWHM) is 10 nm.

[0017] (First display element array) Next, the green display element 100G for displaying green will be described using FIGS. 1(a) to (c), FIGS. 2(a) and (c). As shown in FIG. 1(c), the green display element 100G is a 100-1 two-dimensional array arranged in a matrix along the first direction D1 and the third direction D3. The green display element 100G may be replaced with each of the two-dimensional arrays 100-2 and 100-3, or may be arranged in part or all of the display element arrays 100-1, 100-2, and 100-3. Note that FIG. 1(a) is a cross-sectional view showing the cross-sectional structure of the display element 100 in which the plan view is shown in FIG. 1(b) on the plane A-A'. Further, FIG. 1(b) partially trims and shows the light shielding portion 10s, a part of the first extraction portion 24, and a part of the first conversion portion 26 for understanding the elements arranged overlapping in the layer direction.

[0018] (Light-emitting layer array) As shown in Figures 1(a) and 1(b), the green display element 100G according to this embodiment includes a light-emitting layer array 10A comprising a plurality of light-emitting layers 10 arranged in two dimensions, each emitting light L1 of a first wavelength. The light-emitting layer array 10A employs self-emissive elements such as inorganic semiconductor light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), and semiconductor laser elements. The light-emitting elements constituting the first light-emitting layer 10 employ micro-light-emitting diodes (LEDs) or micro-organic light-emitting diodes (OLEDs) having a microcavity structure. Since such light-emitting elements are directional light sources, they can guide light L1 of the first wavelength to the first conversion unit 20 in a waveguide mode.

[0019] The light-emitting layer array 10A includes a light-shielding portion 10s that shields the area around the light-emitting layer 10, leaving a region that connects with the first connection portion 22, in order to guide light L1 of the first wavelength to the first coupling portion 22 of the first conversion layer 20, as described later, and to prevent light leakage to the periphery of the light-emitting layer 10.

[0020] (Conversion layer array) Furthermore, the green display element 100G has a conversion layer array 20A comprising a plurality of first conversion layers 20 that convert light L1 of a first wavelength guided from the light-emitting layer array 10A into light L2 of a second wavelength, and change the propagation direction of the light L1 of the first wavelength and the light L2 of the second wavelength. As shown in Figures 1(a) and (b), the propagation direction of light changes the propagation direction of light within the layers of the first conversion layer 20, and can be rephrased as the light transport direction or the direction in which light is utilized.

[0021] As shown in Figures 1(a) and 1(b), the first conversion layer 20 includes a first coupling portion 22 that optically couples with a portion of the plurality of light-emitting layers 10. The first conversion layer 20 also has a waveguide-like optical structure that alternately reflects light L1 of a first wavelength (λ1) collected through the first coupling portion 22 and guides light L1 of the first wavelength by multiple reflections in a direction D1 away from the first coupling portion 22. This waveguide-like optical structure includes a first extraction portion 24 and a first reflection portion 28 that are arranged opposite each other.

[0022] (Conversion section) Furthermore, as shown in Figures 1(a) and 2(c), the first conversion layer 20 includes a first conversion section 26 containing a plurality of photoresponsive nanoparticles 30 that form quantum dots. It emits light L2 at a first wavelength (λ2) that is wavelength-shifted to a longer wavelength than light L1 at a first wavelength (λ1). In other words, the second wavelength λ2 is longer than the first wavelength λ1.

[0023] Furthermore, the first conversion layer 20 can be rephrased as an emission layer that reduces the bandwidth Δλ1 of the central wavelength of the first wavelength light L1 to a bandwidth Δλ2, thereby generating secondary light L2 with higher color purity than primary light L1. The first conversion layer 20 can be replaced with a configuration that performs wavelength conversion using a band filter (color filter) instead of quantum dots.

[0024] The first conversion layer 20-1 and the second conversion layer 20-2 are designed to convert light L1 of a first wavelength into light of a different wavelength. The conversion layer array 20A includes the first conversion layer 20-1 which converts light L1 of a first wavelength into light L2 of a second wavelength, and the second conversion layer 20-2 which converts light L1 of a first wavelength into light L3 of a third wavelength. The light L2 of the second wavelength is green, and the light L3 of the third wavelength is red. In this embodiment, the thickness of the first conversion layer and the second conversion layer 20-2 is preferably 4 μm or more and 20 μm or less, and more preferably 6 μm or more and 10 μm or less.

[0025] The device comprises a conversion layer in which phosphor particles are dispersed in a resin. The phosphor particles can be inorganic or organic, but quantum dots are particularly preferred. This is because quantum dots exhibit emission with a narrow full width at half maximum of the emission spectrum and excellent color purity.

[0026] Inorganic particles used in quantum dots are sometimes called nanoparticles due to their size. Examples of materials for quantum dots include semiconductor crystals, such as nanoparticles of group IV semiconductors, group III-V and group II-VI compound semiconductors, and compound semiconductors composed of three or more combinations of group II, III, IV, V, and group VI elements. Specific examples of materials that exhibit light emission in the wavelength range suitable for display elements include CsS, CdSe, CdZnSe, CdSeTe, ZnSe, ZnTeSe, ZnTeS, InP, CuInS2, AgInS2, and Pb-based perovskites. These can be used as the core of the quantum dot, and the quantum dot material may be covered with a coating compound to form a core-shell structure. In this case, ligands are provided in the shell portion.

[0027] The average particle size of quantum dots is preferably between 2 nm and 15 nm. When the particle size of quantum dots is reduced to a size smaller than the bore radius of the intrinsic excitons, a phenomenon occurs where the band gap of the quantum dot changes due to the quantum size effect. For example, in InP, a III-V semiconductor, the bore radius is said to be around 10 nm to 14 nm. In other words, if the average particle size of quantum dots is 15 nm or less, it becomes possible to control the band gap due to the quantum size effect. By setting the average particle size of quantum dots to 2 nm or more, it becomes easier to control the crystal growth of quantum dots during synthesis.

[0028] Quantum dots have ligands on their surface. When there are first and second quantum dots, the ligands may have a crosslinking structure that bridges the two. Crosslinking means that one molecule bonds to both the first and second quantum dots. When crosslinking is done with organic ligands, the distance between quantum dots can be controlled by the molecular length of the organic ligand. Specifically, the crosslinking structure may be a hydroxyl group, a thiol group, or a carboxyl group. It is preferable to have at least one organic molecule between quantum dots. When there are many organic ligands, both ends of the organic molecules bond strongly to the quantum dot surface, improving heat resistance and environmental resistance, and increasing the stability of the luminescence properties.

[0029] As phosphor particles used in the first and second conversion layers of this embodiment, quantum dots having a full width at half maximum of less than 50 nm can preferably be used. For example, as quantum dots, generally available quantum dots, such as InP / ZnS quantum dots product numbers 776769, 776750, 776793, 776777, and 776785 from Sigma-Aldrich can be used. Product number 776750 is preferred as the first conversion layer, and product number 776777 is preferred as the second conversion layer 20-2. Also, as perovskite quantum dots, product numbers 905062, 900746, 900747, and 900748 can be used. Product number 905062 or 900746 is preferred as the first conversion layer, and product number 900748 is preferred as the second conversion layer 20-2.

[0030] In the first to third conversion units 26 of this embodiment, monofunctional monomers and bifunctional monomers are used as polymer matrix materials, and examples include acrylic resins, polyester resins, polyurethane resins, and polyamide resins. By mixing these together with photoresponsive nanoparticles, viscosity and surface tension suitable for film formation by photolithography and inkjet methods (inkjet printing) can be obtained. Furthermore, a concentration of 2 to 5 wt% of the photopolymerization initiator is used for a monomer concentration of 85 to 98 wt%. Titanium dioxide is not contained. The resin unit 17 contains a light scattering material such as titanium dioxide that scatters blue light (L3), but it is desirable that the concentration be 5 wt% or less so that multiple scattering does not occur.

[0031] (Removal section) The first extraction section 24 employs a structure in which the spectral reflectance of the first wavelength light L1 propagating along the first direction D1 away from the first coupling section 22 is higher than that of the second wavelength light L2 that is wavelength-converted within the first conversion layer 20 and propagates radially. By employing such a first extraction section 24, along with the first reflecting section 28 described later, the propagation of the first wavelength light L1, which serves as the source of the second wavelength light L2, within the layer is ensured, thereby ensuring the generation range of the second wavelength light L2.

[0032] The first extraction section 24 employs a structure in which the spectral transmittance for light of the second wavelength L2 is higher than that for light of the first wavelength L1. This limits the emission of light of the first wavelength L1, which is mixed within the first conversion layer 20, from the display surface, while allowing the emission of light of the second wavelength L2 from the display surface, thereby ensuring high color purity.

[0033] The spectral reflectance or spectral transmission characteristics of the first extraction section 24 are obtained by the difference in refractive index n between the first conversion section 26 and an optical member (not shown) in contact with both sides in the layer thickness direction (z direction). In this embodiment, as shown in Figure 1(a), the refractive index n1 of the first conversion section 26 is higher than the refractive index n2 of the optical structure on the interface side of the first extraction section 24.

[0034] The first extraction section 24 may employ a dielectric multilayer film, or it may be a core / cladding configuration that utilizes the refractive index difference, as in the first extraction section 24.

[0035] The waveguide-like optical structure between the first extraction unit 24 and the first conversion unit 26 will be described in detail using Figure 5, which shows the display element 200 of the 13th embodiment.

[0036] (Reflector) The first reflecting section 28 employs a structure that has a higher spectral reflectance for light L2 of the second wavelength than the first extraction section 24. By employing such a first reflecting section 28, along with the aforementioned first extraction section 24, the propagation of light L1 of the first wavelength, which serves as the source of light L2 of the second wavelength, within the layer is ensured, thereby ensuring the generation range of light L2 of the second wavelength.

[0037] The spectral reflectance characteristics of the first reflecting portion 28 are obtained by the difference in refractive index n between the first transforming portion 26 and an optical member (not shown) in contact with both sides in the layer thickness direction (z direction). In this embodiment, as shown in Figure 1(a), the display element 100 has a refractive index n1 of the first transforming portion 26 that is higher than the refractive index n2 of the optical structure (not shown) on the interface side of the first reflecting portion 28.

[0038] The first reflective section 28 employs a metal reflective member with low wavelength dependence that utilizes plasmon reflection, but a dielectric multilayer film may also be used, or a core / cladding configuration utilizing refractive index difference may be used, similar to the first extraction section 24.

[0039] The first conversion layer 20 has a terminal light-shielding portion 20s at the end opposite to the first coupling portion 22 in the first direction D1.

[0040] [Optical components] The optical element forms an interface with the conversion section 26 and constitutes either the extraction section 24 or the reflection section 28. The optical element constituting the extraction section 24 is made of a translucent material that transmits the secondary light transmitted through the extraction section 24, and may be an organic resin, an inorganic glass material, or the like. As the optical element, a transparent resin with a transmittance of 85% or more, more preferably 90% or more, for blue light, green light, and red light can be used. The refractive index of the resin used as the optical element can be 1.45 or more and 1.5.

[0041] Here, the refractive index of the optical element is set so that the conversion layer 20 functions as a waveguide. The refractive index (n1) of the conversion layer varies depending on the type and concentration of quantum dots, but when the concentration is 0.01 to 5 wt%, n1 is generally in the range of 1.45 to 1.50. The refractive index (n2) of the optical element is preferably set so that Δ = 0.3 to 2.0% in the relative refractive index difference Δ = (n1 - n2) / 2n1. For example, if the refractive index n1 of the conversion layer is 1.50, then n2 = 1.490 when Δ = 0.35%, and n2 = 1.455 when Δ = 1.5%.

[0042] (Second display element array) Next, the red display element 100R, which displays the color red, will be explained using Figures 1(c) and (d). As shown in Figure 1(c), the red display element 100R is a 100-2 two-dimensional array arranged in a matrix along the first direction D1 and the third direction D3. The red display element 100R may replace the 100-1 and 100-3 two-dimensional arrays, or it may be arranged in part or all of the 100-1, 100-2, and 100-3 display element arrays.

[0043] In this embodiment, the red display element 100R is a second display element array 100A, and its cross-sectional structure is shown in Figure 1(d).

[0044] The red display element 100R of this embodiment, similar to the green display element 100G, has an emissive layer array 10A comprising a plurality of emissive layers 10 and a conversion layer array 20A comprising a plurality of second conversion layers 40. The second conversion layer 40, similar to the first conversion layer 20, includes a configuration in which it wavelength-converts first wavelength light L1 (primary light) containing blue or ultraviolet light to the longer wavelength side to produce red secondary light as third wavelength light L3, which is emitted from the second output section 44. The second conversion layer 40, similar to the first conversion layer 20, also includes a configuration in which it narrows the bandwidth of first wavelength light L1 (primary light) containing blue or ultraviolet light to produce second wavelength light L3, which is red secondary light, and emits it from the second output section 44.

[0045] The second conversion layer 40, in the same manner as the first conversion layer 20, includes a second coupling section 42, a second extraction section 44, a second reflecting section 48, and a second conversion section 46. By adopting this configuration, the second conversion layer 40 wavelength-converts the light L1 of the first wavelength collected through the second coupling section 42 to generate light L3 of the third wavelength, and emits the light L3 of the third wavelength through the second extraction section 44 as the display surface.

[0046] In other words, the conversion layer array 20A has a second conversion layer 40 which has a plurality of second coupling portions 42 which optically couple with a plurality of light-emitting layers 10 in areas other than the portion in which the light-emitting layer array 10A is optically coupled with a plurality of first conversion layers 20. The second conversion layer 40 further has a second extraction portion and a second reflection portion which are arranged opposite each other to alternately reflect the light L1 of a first wavelength collected through the plurality of second coupling portions 42 and guide it in a direction D1 away from the second coupling portions 42. The second conversion layer 40 emits light L3 of a third wavelength obtained by wavelength conversion of the light L1 of the first wavelength through the second extraction portion 44.

[0047] The second conversion layer 40, like the first conversion layer 20, contains a second photoresponsive nanoparticle that converts light L1 of a first wavelength to light L3 of a third wavelength.

[0048] The second extraction section 44 employs a structure similar to the first extraction section 24, in which the spectral reflectance for light L1 of the first wavelength is higher than that for light L3 of the third wavelength. Furthermore, the second extraction section 44 employs a structure similar to the first extraction section 24, in which the spectral transmittance for light L3 of the third wavelength is higher than that for light L1 of the first wavelength.

[0049] The second reflecting section 48, like the first reflecting section 28, employs a structure that provides a higher spectral reflectance for light L3 of the third wavelength than the second extraction section 44.

[0050] (Third display element array) Next, the blue display element 100B, which displays blue, will be explained using Figures 1(c) and (e). As shown in Figure 1(c), the blue display element 100B is a 100-3 two-dimensional array arranged in a matrix along the first direction D1 and the third direction D3. The blue display element 100B may replace the 100-1 and 100-2 two-dimensional arrays, or it may be arranged in part or all of the 100-1, 100-2, and 100-3 display element arrays.

[0051] In this embodiment, the blue display element 100B is shown as a second display element array 100A, and its cross-sectional structure is shown in Figure 1(d).

[0052] The blue display element 100B of this embodiment, similar to the green display element 100G and the red display element 100R, has an emissive layer array 10A comprising a plurality of emissive layers 10 and a conversion layer array 20A comprising a plurality of third conversion layers 50. The third conversion layer 50, similar to the green display element 100G, collects light L1 (primary light) of a first wavelength including blue or ultraviolet light, generates light L4 of a fourth wavelength which is a blue secondary light with a narrower bandwidth than the first wavelength light L1, and emits it from the third extraction unit 54. That is, the third conversion layer 50 changes the propagation direction in the propagation optical path from the third coupling unit 52 to the third extraction unit 54, but does not perform wavelength conversion of the first wavelength light L1.

[0053] The third conversion layer 50, similar to the first conversion layer 20, includes a third coupling section 52, a third extraction section 54, a third reflecting section 58, and a third conversion section 56. By adopting this configuration, the third conversion layer 50 wavelength-converts the light L1 of the first wavelength collected through the third coupling section 52 to generate light L4 of the fourth wavelength, and emits the light L4 of the fourth wavelength through the third extraction section 54 as the display surface.

[0054] In other words, the conversion layer array 20A has a third conversion layer 50 which has a plurality of third coupling portions 52 which optically couple with a plurality of light-emitting layers 10 in areas other than the portion in which the light-emitting layer array 10A is optically coupled with a plurality of first conversion layers 20. The third conversion layer 50 further has a second extraction portion and a second reflection portion which are arranged opposite to each other to alternately reflect the light L1 of a first wavelength collected through the plurality of third coupling portions 52 and guide it in a direction D1 away from the third coupling portions 52. The third conversion layer 50 emits light L4 of a fourth wavelength obtained by wavelength conversion of the light L1 of the first wavelength through the third extraction portion 54.

[0055] The third conversion layer 50, like the first conversion layer 20, may contain a third photoresponsive nanoparticle that converts light L1 of a first wavelength into light L4 of a fourth wavelength that is closer to the first wavelength than the second and third wavelengths. The fourth wavelength includes forms that are longer than the first wavelength and shorter than either the second or third wavelength.

[0056] The third extraction section 54 employs a structure in which the spectral reflectance for light L1 of the first wavelength is higher than that for light L4 of the fourth wavelength. Furthermore, similar to the first extraction section 24, the third extraction section 54 employs a structure in which the spectral transmittance for light L4 of the fourth wavelength is higher than that for light L1 of the first wavelength.

[0057] The third reflecting section 58, like the first reflecting section 28, employs a structure that provides a higher spectral reflectance for light L4 of the fourth wavelength than the third extraction section 54. The first conversion unit 26, the second conversion unit 46, and the third conversion unit 56 may contain a light scattering material such as titanium dioxide that scatters light L1 of a first wavelength. The concentration of the light scattering material in the first conversion unit 26, the second conversion unit 46, and the third conversion unit 56 is preferably below a concentration that does not cause multiple scattering among the light scattering materials, and a concentration of 5 wt% or less is adopted.

[0058] <Technical significance> Next, using Figures 2(a) to (d) and Figures 3(a) and (b), the display element 100 according to this embodiment will be compared with a conventional display element 900, and the structural features of the display element 100 and the effects unique to this embodiment that result from these features will be explained.

[0059] Figure 2(a) shows the cross-sectional structure of the display element 100 according to the first embodiment, and Figure 2(c) shows the in-layer structure of the first conversion layer 20 according to the first embodiment. On the other hand, Figure 2(b) shows the cross-sectional structure of the conventional display element 900, and Figure 2(d) shows the in-layer structure of the conversion layer 920 of the conventional display element 900. In other words, Figures 2(c) and (d) show the dispersion state of the photoresponsive nanoparticles 30 provided in the first conversion section 26 of the display element 100 and the conversion section 926 of the display element 900, respectively.

[0060] Display element 100 and display element 900 differ in the following points A and C.

[0061] Difference A is whether the propagation path of the primary light and the propagation path using the secondary light are coaxial or non-coaxial in the light propagation path from the coupling part to the extraction part. Display element 100 has a non-coaxial arrangement in the light propagation path from the first coupling part 22 to the first extraction part 24, where the directions of the propagation paths of the primary light and the secondary light are different. In contrast, display element 900 has a coaxial arrangement in the light propagation path from the coupling part 922 to the extraction part 924, where the propagation paths of the primary light and the secondary light are in the same direction. That is, when viewed along an axis parallel to the thickness direction D2 of the conversion layer 20, the display element 100 is arranged so that the first coupling part 22 does not overlap with the first extraction part 24. The thickness direction D2 of the conversion layer 20 can be rephrased as the light extraction direction. Furthermore, in the first light propagation direction D1 of the conversion layer 20, the display element 100 is arranged such that the first coupling portion 22 does not overlap with the first extraction portion 24.

[0062] Difference B is whether or not the reflective section can be placed across the entire area in a position opposite the extraction section. The display element 100 has a non-coaxial arrangement of the light propagation path from the first coupling section 22 to the first extraction section 24, while the display element 900 has a coaxial arrangement of the light propagation path from the coupling section 922 to the extraction section 924.

[0063] Difference C is whether the optical density of the photoresponsive nanoparticles can be made sparse so that the absorption of the propagating primary and secondary light does not exceed the effect of emission.

[0064] The differences A through C mentioned above are explained below.

[0065] In this embodiment, the display element 100, due to differences A and B, allows the optical elements responsible for different functions, the first coupling portion 22 and the first reflecting portion 28, to be positioned appropriately. Therefore, the display element 100 can independently assign suitable optical characteristics to the light-gathering characteristics from the light-emitting layer 10 to the first conversion layer 20 and the reflection characteristics of the first reflecting portion 28, without mutual constraints. Specifically, the first coupling portion 22 can be set to have a high transmittance for light L1 of a first wavelength, which is primary light, and the first reflecting portion 28 can be set to have a high reflectance for both light L1 of a first wavelength (primary light) and light L2 of a second wavelength (secondary light). Furthermore, the display element 100 can construct the reflecting portion 28 with a metal layer that is robust to wavelength dependence, and the reflecting portion 28 can be provided over the entire area behind the extraction portion 24, thereby improving the macroscopic utilization efficiency of light from the first conversion layer 20.

[0066] In contrast, the conventional display element 900 does not have differences A and B, and therefore, at the position of reference numeral 922, it is necessary to use the same optical coupling element for collecting primary light from the light-emitting layer 910 and the reflective element for reflecting secondary light generated in the conversion layer 920. For this reason, the display element 900 will have constraints on at least one of the transmittance and reflectance of the interface of reference numeral 922, or it will be necessary to divide the region of reference numeral 922 and assign characteristics to it, and the macroscopic utilization efficiency of light from the conversion layer 920 will be limited.

[0067] In this embodiment, the display element 100 has a propagation path for light L1 of the first wavelength that changes from the layer thickness direction (z direction) of the display element 900 to the layer surface direction (in-plane xy direction) which is substantially parallel to the layer surface, resulting in an increase in propagation distance of about one order of magnitude. For this reason, the display element 100 can be made sparser than the display element 900 by reducing the optical density of the photoresponsive nanoparticles by about one order of magnitude, and thus has a difference C.

[0068] Therefore, in the display element 100 according to this embodiment, the generation of secondary light is less constrained by the absorption of primary and secondary light, and the macroscopic light utilization efficiency in the first conversion layer 20 is higher than that of the display element 900.

[0069] A more specific comparison between the display element 100 according to this embodiment and the display element 900 according to the prior art will be described below.

[0070] The display element 900 is constructed by laminating a light-emitting layer 910 that emits light L1 of a first wavelength (blue, primary light) and a conversion layer 920 containing photoresponsive nanoparticles that receive the primary light from the light-emitting layer 910 and emit light L2 of a second wavelength (green, secondary light) via a bonding portion 922. The thickness of the conversion layer 920 is typically several μm to 10 μm. The conversion layer 920 contains photoresponsive nanoparticles 30 at a concentration of 10-30 wt%, as shown in Figure 2(d), in order to completely absorb the light L1 of the first wavelength in the propagation path of this thickness. The conversion layer 920 also contains a light-scattering material 38, such as titanium dioxide, at a concentration of 10-30 wt%, for the purpose of improving the utilization efficiency of the light L1 of the first wavelength and reducing light leakage to the extraction surface 924. The conversion layer 920 increases the opportunity for the photoresponsive nanoparticles 30 to absorb the first wavelength of light L1 per unit thickness in the layer thickness direction (depth direction, z direction) by scattering light L1 of the first wavelength multiple times within the layer through the scattering of the light scattering material 38, thereby improving the wavelength conversion efficiency.

[0071] Here, the photoresponsive nanoparticles 30 (quantum dots) have a small Stokes shift, and since part of the emission band and excitation band overlap, self-absorption is likely to occur. Therefore, when the optical density of the photoresponsive nanoparticles 30 is high, a decrease in luminescence efficiency due to self-absorption is likely to occur. In addition, because the distance between the photoresponsive nanoparticles 30 is close, a decrease in luminescence efficiency due to fluorescence resonance energy transfer (FRET) is likely to occur. Furthermore, the light scattering material 38 also scatters the secondary light, which is wavelength-converted light, and the effective optical distance is extended, resulting in a decrease in light extraction efficiency.

[0072] In particular, among the secondary light that propagates in the opposite direction to the light extraction direction D1 and is emitted outside the conversion layer 920, the light that is recurrently incident on the conversion layer 920 is attenuated by self-absorption by the photoresponsive nanoparticles 30 and the shielding effect of the light scattering material 38, which is thought to easily reduce the light extraction efficiency.

[0073] The configuration of the RGB pixel array in the prior art will be explained using Figures 3(a) and 3(b).

[0074] The display element 909 shown in Figure 3(a) has a coupling portion 922 formed by providing an optical member 918 behind the conversion layers 920-1 to 3 (on the side of the light-emitting layer 910). The coupling portion 922 has the function of scattering primary light L1 forward (towards the side of the optical member 914) by utilizing the difference in refractive index between the conversion layers 920-1 to 3 and the optical member 918. From the viewpoint of balancing the light collection efficiency of primary light L1 from the light-emitting layers 910-1 to 3 and the forward reflection characteristics, at least one of the reflection characteristics and transmission characteristics of the coupling portion 922 is limited as described above.

[0075] The display element 990 shown in Figure 3(b) has a dielectric multilayer film 917 provided behind the conversion layers 920-1 to 920-3 (on the side of the light-emitting layer 910) to form a coupling portion 922. This allows the recurrence of secondary light L2 and L3 from the wavelength-converted light that propagates towards the light-emitting layers 910-1 to 910-3 to be utilized.

[0076] As stated above, in both display elements 909 and 990, the macroscopic light utilization efficiency is expected to decrease due to losses caused by the conversion layers 920-1 to 920-3 themselves and a decrease in the utilization efficiency of the secondary light (light after wavelength conversion) emitted backward. The losses caused by the conversion layers 920-1 to 920-3 themselves include self-absorption by quantum dots and the shielding effect of light scattering materials. The coupling portion 922 has its reflection and transmission characteristics limited in at least one aspect, as described above, from the viewpoint of balancing the light collection efficiency of the primary light L1 from the light-emitting layers 910-1 to 920-3 with forward reflection characteristics.

[0077] On the other hand, in the display element 100 according to this embodiment, the conversion layer 20 functions as a waveguide for light L1 (primary light) of a first wavelength propagating in the first direction D1. The conversion layer 20, which functions as a waveguide, guides the light L1 (blue light) of the first wavelength by total internal reflection along the plane direction of the layer, converting its wavelength to secondary light. According to the configuration of this embodiment, the optical path length over which the light L1 of the first wavelength, i.e., the primary light (blue light), propagates while undergoing wavelength conversion can be made longer than in the conventional configuration. For example, in the case of a 100 μm × 300 μm subpixel, the optical path length can be 100 μm in the short direction or 300 μm in the long direction. According to the Lambert-Beer law, as the optical path length of absorption increases, the quantum dot concentration (concentration of photoresponsive nanoparticles) contained in the conversion layer 20 can be reduced.

[0078] In other words, compared to the conventional display elements 900, 909, and 990, the display element 100 of this embodiment can have an optical path length for the first wavelength of light L1 that is about an order of magnitude larger, making it possible to reduce the quantum dot density by an order of magnitude. Furthermore, when the quantum dot density is low, the decrease in luminous efficiency due to self-absorption and FRET is suppressed, making it possible to increase the luminous efficiency. Therefore, the quantum dot density in the configuration of this embodiment can be 0.01 to 5 wt%. The quantum dot density is determined by the pixel size corresponding to the propagation optical path length of the primary light, as well as the required display performance, the driving conditions of the primary light, etc. Also, in the configuration of this embodiment, the reflective part 28 does not need to be a wavelength-selective mirror, and metal mirrors such as Al and Ag can be used. Alternatively, a wavelength-selective mirror composed of a dielectric multilayer film can be used.

[0079] (Waveguide mode and light emission mode) Next, the operating modes of the waveguide-like first to third conversion layers 20-1 to 20-3 will be explained using Figures 1 and 4.

[0080] In the configuration of the present invention, as shown in Figure 1(a), the refractive index (n2) of the optical material constituting the interface, which is the first extraction section 24, is lower than the refractive index (n1) of the first conversion layer 20, and the first conversion layer 20 functions as a waveguide. As a result, the light L1 of the first wavelength (primary light, blue light) propagates and is guided while repeatedly undergoing total internal reflection within the first conversion layer 20. In Figure 1(b), only a portion of the light L2 of the second wavelength, which is the light after wavelength conversion generated within the first conversion layer 20, is shown for illustrative purposes, and the path through the first reflection section 28, etc., is omitted. The light L2 of the second wavelength is actually generated on the propagation path of the light L1 of the first wavelength, which is composed of multiple optical paths, and around the propagation path by the light diffusing material. Secondary light generated within the first conversion layer 20 is either scattered by the light diffusing material, reflected by the reflecting section 28, or directly reaches the extraction section 24 from the light emission point (wavelength conversion point) and is extracted in front of the first conversion layer 20.

[0081] In a sandwich configuration where a layer with a high refractive index (core) is sandwiched between layers with a low refractive index (cladding), total internal reflection occurs when the angle of incidence of light propagating within the core layer to the cladding layer exceeds the critical angle. This repeated reflection at the core / cladding interface allows the system to function as a waveguide. Generally, among the total emission modes of light isotropically emitted from the core layer, the light that undergoes repeated total internal reflection within the core layer is called the waveguide mode, and the light extracted from the core layer is called the emission mode.

[0082] Here, the waveguide mode is employed for the first wavelength of light L1 (primary light, blue, violet), and from the viewpoint of light extraction, the emission mode component is set to be relatively small for the second wavelength of light L2 (green) and the third wavelength of light L3 (red). More preferably, for the second wavelength of light L2 and the third wavelength of light L3, a configuration is adopted in which the emission mode is more dominant than the waveguide mode.

[0083] In this specification, the waveguide mode and emission mode are treated using the waveguide parameter V used in optical waveguides.

[0084] V<2.405 (Equation 1)

[0085]

number

[0086] Here, d is the film thickness, λ0 is the wavelength of light, and n1 and n2 are the refractive indices of the core and cladding layers. When the waveguide parameter V < 2.405, it becomes a single-mode waveguide, and for any given wavelength, only the basic waveguide mode can be guided, while other radiation modes become emission modes. Furthermore, when the relative refractive index difference Δ = (n1 - n2) / 2n1 of the core and cladding is determined, it is possible to reduce the number of waveguide modes and increase the emission modes by reducing the film thickness, thereby improving the light extraction efficiency. When the film thickness is thick, such as 10 μm or more, it becomes a multi-mode waveguide, and since there are many waveguide modes, the light extraction efficiency decreases. In the configuration of the present invention, it is desirable that the thickness is 10 μm or less so that the wavelength conversion section functions sufficiently as a waveguide, but it is also applicable to thicker films.

[0087] Here, we assume that the blue, green, and red light that constitute the display colors are 460 nm, 530 nm, and 630 nm, respectively. Waveguide parameters become smaller as the wavelength increases, resulting in fewer waveguide modes. That is, the film thickness and specific refractive index difference can be set so that it is single-mode for green and red light, and multi-mode for blue light. In this way, the wavelength conversion section functions as a multi-mode waveguide for blue light, while for the wavelength-converted light, the radiation mode takes precedence, enabling a configuration in which light is extracted efficiently.

[0088] Figure 4 shows the boundary lines for the waveguide parameter V = 2.405 for blue, green, and red light, respectively, in relation to the relative refractive index difference Δ and film thickness. When plotting a specific relative refractive index difference Δ and film thickness, if the boundary line for each color is to the right of the plot point, that color is single-mode; if it is to the left, that color is multi-mode.

[0089] For example, if the film thickness is 3 μm and the relative refractive index difference Δ = 0.35, it will be multi-mode for blue light and single-mode for wavelength-converted light (green light, red light). In other words, it will function as a waveguide for blue light, and the emission mode will take precedence for wavelength-converted light. If the film thickness is 10 μm, a relative refractive index difference Δ = 0.03 is required to achieve a similar configuration, making it difficult to fabricate a single-mode configuration for wavelength-converted light. If the film thickness becomes even thicker, it becomes practically impossible to fabricate. However, even if it is not completely single-mode, there is an effect of reducing the waveguide mode by approaching the single-mode condition, so if the relative refractive index difference Δ is constant, the light extraction efficiency will increase as the film thickness decreases. Also, in the case of a single-mode waveguide, some of the guided light (blue light in this case) leaks into the cladding layer as evanescent waves, so the cladding layer may contain quantum dots and have wavelength conversion functionality.

[0090] (Transformation layer variant 1) Next, the display elements 110 to 160 according to the second to seventh embodiments will be described using Figures 5(a) to (f). The second to seventh embodiments are variations of the first embodiment, in which the optical arrangement of the conversion layer including the coupling portion differs from that of the first embodiment.

[0091] <Second Embodiment> The display element 110 according to the second embodiment shown in Figure 5(a) differs from the first embodiment in that it has a coupling portion 23 that is separated from the light-emitting layer 10 and the first conversion unit 26 with an air gap between them.

[0092] <Third Embodiment> The display element 120 according to the third embodiment shown in Figure 5(b) differs from the first and second embodiments in that it has a coupling portion 23 that is separated from the light-emitting layer 10 via a coupling member 15. The light-shielding portion 10s in this embodiment extends to the outer edge of the coupling member 15.

[0093] <Fourth Embodiment> The display element 130 according to the fourth embodiment shown in Figure 5(c) differs from the first to third embodiments in that it has a coupling portion 23 that is separated from the light-emitting layer 10 via a deflection member 15 that changes the propagation direction. The light-shielding portion 10s of this embodiment extends to the outer edge of the deflection member 15. The direction of emission of primary light from the light-emitting layer 10 in this embodiment coincides with the second direction D2 which is parallel to the thickness direction of the first conversion layer 20. However, the extraction region of secondary light L from the first extraction portion 24 and the emission region of primary light L1 from the light-emitting layer 10 are arranged in a non-coaxial configuration, offset from each other in the x-direction.

[0094] <Fifth Embodiment> The display element 140 according to the fifth embodiment shown in Figure 5(d) differs from the first to fourth embodiments in that it has a window 24d with low wavelength selectivity near the end of the first extraction section 24 opposite to the coupling section 20. The terminal side of the first light-emitting layer 20 does not need to propagate light L1 of the first wavelength in waveguide mode in a direction further away from the coupling section 20, and the window 24d is provided because the component of light L1 of the first wavelength is substantially absorbed at the position where the window 24d is provided.

[0095] <Sixth Embodiment> The display element 150 according to the sixth embodiment shown in Figure 5(e) differs from the first to fifth embodiments in that a front reflective portion 28p is provided in a specific location near the coupling portion 2 of the first extraction portion 4. This is to compensate for the fact that, upstream of the propagation path in the first light-emitting layer 20, the component ratio of light L1 of the first wavelength to light L2 of the second wavelength is high, and the wavelength selectivity of the extraction portion 24 is insufficient to reduce the forward leakage of the primary light L1.

[0096] <Seventh Embodiment> The display element 160 according to the seventh embodiment shown in Figure 5(f) differs from the first to sixth embodiments in that a light-shielding portion 24s is provided near the coupling portion 2 of the first extraction portion 4. The light-shielding portion 24s is an extension of the light-shielding portion 10s. The light-shielding portion 24s provides the same effect as the front reflective portion 28p of the sixth embodiment.

[0097] (Transformation layer variant 2) Next, the display elements 170 to 210 according to the 8th to 12th embodiments will be described using Figures 6(a) to 6(j). The 8th to 12th embodiments are variations of the first embodiment, differing from the first embodiment in that the optical density of the photoresponsive nanoparticles in the first conversion layer 20 has a specific intralayer distribution.

[0098] <Eighth Embodiment> The display element 170 according to the eighth embodiment shown in Figure 6(a) differs from the first embodiment in that it has a first conversion layer 20u having a first conversion section 26u containing photoresponsive nanoparticles at a constant optical density (dashed line) in the first direction D1, as shown in Figure 6(b).

[0099] In such a first conversion layer 20u, according to the Lambert-Beer law, the amount of light L2 of the second wavelength emitted from the first conversion layer 26u has a logarithmic distribution in the range from the coupling portion 22 to the terminal light-shielding portion 20s. In order to position the emission centroid of the pixel at the center of the pixel, the spectral characteristics of other optical elements such as the first extraction portion 24 and the first reflection portion 28 can be used to mitigate the brightness profile shown in Figure 6(b).

[0100] In Figures 6(b), (d), and (f), the amount of light emitted is shown as luminance, which is the amount of light emitted per unit area in the first extraction section 24.

[0101] <Ninth Embodiment> The display element 180 according to the ninth embodiment shown in Figure 6(c) differs from the first and eighth embodiments in that, as shown in Figure 6(d), it has an optical density distribution (dashed line) in which the optical density of photoresponsive nanoparticles increases in a stepwise manner as it moves away from the coupling portion 22 in the first direction D1.

[0102] As a result, the display element 180 smooths the distribution of the amount of light L2 of the second wavelength in the range from the coupling portion 22 to the terminal light-shielding portion 20s, according to the Lambert-Beer law, as shown in Figure 6(d), compared to the eighth embodiment.

[0103] <Tenth Embodiment> The display element 190 according to the tenth embodiment shown in Figure 6(e) differs from the first, eighth, and ninth embodiments in that, as shown in Figure 6(f), it has an optical density distribution (dashed line) in which the optical density of photoresponsive nanoparticles increases continuously as it moves away from the coupling portion 22 in the first direction D1. In other words, the first conversion layer 20 of this embodiment can be rephrased as having a first optical gradient such that the optical density of photoresponsive nanoparticles 38 increases with increasing distance from the first coupling portion 22 in the layer plane direction of the first conversion layer 20.

[0104] Figure 6(e) shows the configuration of a pixel that displays green as the display color, but the diagram of the configuration of a pixel that displays red as the display color is omitted. However, brightness smoothing is achieved with a configuration similar to that of the display element 190 that displays green as the display color. That is, the second conversion layer 20-2 has a configuration that has a second optical gradient such that the optical density of the photoresponsive nanoparticles 38 increases with increasing distance from the second bonding portion 22 in the layer plane direction of the second conversion layer 20-2.

[0105] As a result, the display element 180, as shown in Figure 6(d), further smooths the distribution of the amount of light L2 of the second wavelength in the range from the coupling portion 22 to the end light-shielding portion 20s according to the Lambert-Beer law, compared to the ninth embodiment.

[0106] <Embodiment 11> The display element 200 according to the eleventh embodiment shown in Figures 6(g) and (h) differs from the other embodiments in that it has a wedge-shaped inert region 25 such that the optical density of photoresponsive nanoparticles increases continuously in space as it moves away from the bonding portion 22, as shown in Figure 6(h).

[0107] The wedge-shaped inert region 25 can be composed of a region in the first conversion unit 26 that does not contain any photoresponsive nanoparticles among the components contained in the first conversion unit 26.

[0108] <Twelfth Embodiment> The display element 210 according to the twelfth embodiment shown in Figures 6(i) and (j) differs from the other embodiments in that the light-emitting layer 10 is provided in the center of the first coupling portion 20, as shown in Figures 6(i) and (j). The first conversion layer 20 of this embodiment, like the eighth embodiment, contains photoresponsive nanoparticles at a constant optical density in the xy plane away from the coupling portion 22. Therefore, microscopically, the display element 210 has a brightness distribution for the second wavelength light L2 (light after wavelength conversion) in the xy plane, but the light emission beam distribution within the pixel is a roughly concentric rectangular annular light emission distribution, making it possible to align the light emission centroid of each RGB color with the pixel center.

[0109] <13th Embodiment> Next, the display element 220 of the 13th embodiment, which is a modified form of the display element 100 of the first embodiment, will be described using Figures 7(a) to (c). Figure 7(b) is a cross-sectional view of the display element 220 of Figure 7(a) cut along cross section DD'.

[0110] As shown in Figures 7(a) and (c), the display element 220 of this embodiment has multiple display elements 130-G, 130-R, and 130-B arranged in a matrix as green, red, and blue subpixels. For simplicity, in this embodiment, the subscripts -G, -R, and -B representing the emission color of each pixel may be replaced with sub-numbers -1, -2, and -3 in the drawings.

[0111] As shown in Figure 7(b), the display element 220 has a black matrix 20s that defines the periphery of the pixels, and within each of the three regions enclosed by the black matrix 20s, it has a first light-emitting layer 10-1, a second light-emitting layer 10-2, and a third light-emitting layer 10-3. Furthermore, within each of the three regions enclosed by the black matrix 20s, the display element 220 is provided with first to third conversion layers 20-1 to 20-3 that are optically coupled to the first to third light-emitting layers 10-1 to 10-3. The display element 220 is further provided with optical members 124 in front of the first to third conversion layers 20-1 to 20-3, each having a refractive index lower than that of the conversion layers 20-1 to 20-3, forming extraction sections 24-1 to 24-3. The display element 220 further comprises reflective sections 28-1 to 28-3, each having an optical member 128 with a refractive index lower than that of the conversion layers 20-1 to 20-3, behind the first to third conversion layers 20-1 to 20-3. The black matrix 20s and the optical members 28 are bonded to the multilayer dielectric film 29. The display element 220 is arranged juxtaposed on the xy plane such that, when viewed along an axis parallel to the layer thickness direction, the first extraction section 24-G and the second extraction section 24-R have at least a portion that does not overlap. Similarly, the display element 220 is arranged juxtaposed on the xy plane such that, when viewed along an axis parallel to the layer thickness direction, the second extraction section 24-R and the third extraction section 24-B have at least a portion that does not overlap. Note that in Figure 7(b), the first extraction section 24-G and the second extraction section 24-R are omitted for simplicity. <14th Embodiment> Next, the display element 230 of the 14th embodiment, which is a modified form of the display element 230 of the 13th embodiment, will be described using Figures 8(a) to (c). Figure 8(b) is a cross-sectional view of the display element 230 of Figure 8(a) cut along cross section EE'.

[0112] The display element 230 in this embodiment differs from the display element 220 in that, as shown in Figures 8(a) and (c), the display elements 230-R, 230-G, and 230-B, which constitute the red, green, and blue pixels respectively, are stacked in the thickness direction of the conversion layer 20-R.

[0113] When viewed along an axis parallel to the layer thickness direction, the display element 230 is stacked in the z direction such that the first extraction section 24-G and the second extraction section 24-R have at least an overlapping portion. Similarly, when viewed along an axis parallel to the layer thickness direction, the display element 230 is stacked in the z direction such that the second extraction section 24-R and the third extraction section 24-B have at least an overlapping portion. Note that in Figure 8(b), the first extraction section 24-G and the second extraction section 24-R are omitted for simplicity. As shown in Figure 8(b), the display element 230 has a black matrix 20s that defines the periphery of a pixel, and within a single pixel region enclosed by the black matrix 20s, it has a first light-emitting layer 10-1, a second light-emitting layer 10-2, and a third light-emitting layer 10-3. Furthermore, the display element 230 has first to third conversion layers 20-1 to 20-3 that are optically coupled to the first to third light-emitting layers 10-1 to 10-3 in each of the three regions enclosed by the black matrix 20s. The display element 230 also has optical members 35 in front of the first to third conversion layers 20-1 to 20-3, each having a refractive index lower than that of the conversion layers 20-1 to 20-3, forming extraction sections 24-1 to 24-3. The display element 230 further comprises reflective sections 28-1 to 28-3, each having an optical element 35 with a refractive index lower than that of the conversion layers 20-1 to 20-3, behind the first to third conversion layers 20-1 to 20-3. The black matrix 20s and the bottom optical element 128 are bonded to the multilayer dielectric film 29.

[0114] As shown in Figure 8(b), the display element 230 consists of display elements 230-B, 230-R, and 230-G, which are stacked in the direction of light extraction and constitute subpixels, stacked in this order from the display surface.

[0115] Here, wavelength-selective optical layers 34 and 36 are provided between the conversion layers 20-B, 20-G, and 20-R. Optical layer 34 is positioned between the conversion layers 20-B and 20-G and is provided as a layer that reflects blue light and transmits green and red light, or absorbs blue light, or has wavelength selectivity for both. Optical layer 36 is positioned between the conversion layers 20-G and 20-R and is provided as a layer that reflects green light and transmits red light, or absorbs green light, or has wavelength selectivity for both. Wavelength selectivity can sometimes be rephrased as spectral characteristics.

[0116] The optical layer 34 and the optical layer 36 may be provided with a low refractive index layer having a lower refractive index than the optical member 35. When silicon dioxide SiO2 (refractive index = 1.45) is used as the skeletal material, the refractive index of the optical member 35 is preferably 1.10 to 1.30, and more preferably 1.10 to 1.15.

[0117] Now, let's consider the case where optical layers 34 and 36 are wavelength-selective reflective layers. Of the light emitted from conversion layer 230-B, the light emitted forward is extracted as is, and the light emitted backward is reflected by optical layer 34 and extracted. Of the light emitted from conversion layer 230-G, the light emitted forward is extracted by passing through optical layer 34 and conversion layer 230-B, and the light emitted backward is reflected by optical layer 36 and extracted in the same way. Of the light emitted from conversion layer 230-R, the light emitted forward is extracted by passing through optical layer 36 and conversion layer 230-G, and further through optical layer 34 and conversion layer 230-B, and the light emitted backward is reflected by reflective layer 20 and extracted in the same way.

[0118] In the display element 230 having stacked subpixels as shown in Figure 8(b), the area of ​​the conversion layer is three times that of the display element 220, provided that the resolution of the display pixels shown in Figure 7(b) is the same. This allows for an improvement in brightness even when considering light absorption due to stacking. Alternatively, if the stacking is performed with the same configuration as in Figure 8(b) and the same projected area of ​​the conversion layer viewed from the z direction, the pixel size becomes one-third of that of the display element 220, resulting in a threefold increase in resolution. [Examples]

[0119] The following describes in detail an embodiment of the present invention, but the present invention is not limited to the following embodiment.

[0120] [Example 1]

[0121] (Preparation of cladding layer) A 1 μm thick film containing 4.5 at% TiO2 in SiO2 was deposited on a quartz substrate by simultaneous sputtering of SiO2 and TiO2 (substrate A1). The refractive index was measured to be 1.477, and the specific refractive index difference Δ was 1.5. Similarly, after depositing a 100 nm thick film of Al as a reflective film on a quartz substrate by sputtering, a 1 μm thick optical film containing 4.5 at% TiO2 in SiO2 was deposited by simultaneous sputtering of SiO2 and TiO2 (substrate A2).

[0122] A 1 μm film containing 8.0 at% TiO2 in SiO2 was deposited on a quartz substrate by simultaneous sputtering of SiO2 and TiO2 (substrate B1). The refractive index was measured to be 1.495, and the specific refractive index difference Δ was 0.35. Similarly, after depositing a 100 nm film of Al as a reflective film on a quartz substrate by sputtering, a 1 μm film containing 8.0 at% TiO2 in SiO2 was deposited by simultaneous sputtering of SiO2 and TiO2 (substrate B2).

[0123] (Fabrication of the conversion layer) Ten parts of cesium carbonate, 27 parts of oleic acid, and 385 parts of 1-octadecene were placed in a flask, heated to 120°C, and degassed for 30 minutes using a vacuum pump. The mixture was then heated to 150°C under a stream of dry nitrogen and held for 30 minutes to obtain a cation raw material solution.

[0124] Separately, 10 parts of lead(II) bromide and 494 parts of 1-octadecene were placed in a flask, the liquid temperature was heated to 120°C, and the mixture was degassed for 1 hour using a vacuum pump. 89 parts of oleic acid and 31 parts of oleylamine were added, and the mixture was degassed again for 30 minutes using a vacuum pump. After that, the liquid temperature was raised to 185°C using a nitrogen flow.

[0125] Forty parts of the cation raw material solution were added, and the mixture was cooled with ice after 5 seconds. Two thousand parts of ethyl acetate were added, and centrifugation was performed, after which the supernatant was removed. The resulting residue was dispersed in toluene to adjust the solid content concentration to 1% by weight, obtaining a dispersion of luminescent nanocrystals having a perovskite-type crystalline structure of CsPbBr3.

[0126] The solvent was removed from the above CsPbBr3 dispersion by blowing a stream of dry nitrogen air onto it, and the mixture was prepared to contain 1 wt% CsPbBr3 nanocrystals, 94 wt% 3,3,5-trimethylcyclohexyl acrylate (TMCHA), and 5 wt% 1-hydroxycyclohexyl phenyl ketone (Omnirad184) to obtain ink composition A.

[0127] When the above ink composition was applied as a film to a glass substrate, the refractive index was calculated from the reflection spectrum to be 1.500.

[0128] Measuring the refractive index Using the above ink composition A, a material printer (DMP-2850, manufactured by Fujifilm Dimatix) was used to print a conversion layer onto the optical film deposited on substrate A2, with dimensions of 100 μm (width) x 300 μm (length) x 10 μm (thickness) from the edge of the substrate. Immediately after printing, the optical film deposited on substrate A1 was sandwiched between the two and cured by UV irradiation to create a display element that uses green light as the second wavelength, L2.

[0129] CsPbBr3 to CsPb(Br 0.35 I 0.65 A similar study was conducted with a composition of 3, and a display element was fabricated when the conversion layer emitted red light.

[0130] [Example 2] A display element was fabricated in the same manner as in Example 1, except that the thickness of the conversion layer was set to 3 μm.

[0131] [Example 3] A display element was fabricated in the same manner as in Example 1, except that the thickness of the conversion layer was set to 1.5 μm.

[0132] [Example 4] A display element was fabricated in the same manner as in Example 1, except that substrate A1 was designated as substrate B1, substrate A2 as substrate B2, and the thickness of the conversion layer was set to 3 μm.

[0133] [Example 5] A display element was fabricated in the same manner as in Example 1, except that the conversion layer was printed so that it measured 300 μm horizontally, 100 μm vertically, and 3 μm thick from the edge of the substrate.

[0134] [Example 6] Similar to Example 1, the solvent was removed from the CsPbBr3 dispersion by blowing a stream of dry nitrogen air onto it, and ink composition B was prepared to consist of 1 wt% CsPbBr3 nanocrystals, 89 wt% 3,3,5-trimethylcyclohexyl acrylate (TMCHA), 5 wt% 1-hydroxycyclohexyl phenyl ketone (Omnirad184), and 5 wt% titanium dioxide.

[0135] First, a conversion layer was printed in the same manner as in Example 1, with dimensions of 80 μm (horizontal) x 300 μm (vertical) x 10 μm (thickness) from the edge of the substrate. Next to this, ink composition B was used to print a display element with dimensions of 20 μm (horizontal) x 300 μm (vertical) x 10 μm (thickness). This configuration corresponds to Figure 7(b).

[0136] [Example 7] A display element was fabricated in the same manner as in Example 6, except that substrate A1 was replaced with substrate B1, substrate A2 with substrate B2, and the thickness of the conversion layer was set to 3 μm. This configuration corresponds to Figure 7(b).

[0137] [Example 8] This embodiment is an example in which subpixels are configured by stacking them in the light extraction direction shown in Figure 8.

[0138] First, substrates were fabricated on which optical layers 34 and 36 were formed on a quartz substrate. The optical layers 34 and 36 used here refer to wavelength-selective layers that selectively reflect or transmit specific wavelengths. Such wavelength-selective layers can be obtained by dielectric multilayer films. The dielectric material constituting the dielectric multilayer film may be an inorganic material, an organic material, or a combination thereof. Examples of organic materials include polyester resins, urethane resins, and acrylic resins. Examples of inorganic materials include fluoride materials and oxide materials. For example, AlF2 (1.36), MgF2 (1.38), and CaF2 (1.43) can be used as fluoride materials. Suitable oxide materials include SiO2 (1.45), Al2O3 (1.64), MgO (1.72), Y2O3 (1.88), HfO2 (2.05), SrTiO3 (2.44), and TiO2 (2.49). The values ​​in parentheses are reference values ​​for refractive index. The dielectric multilayer film is composed of a multilayer film in which low-refractive-index materials and high-refractive-index materials selected from these material types are alternately layered.

[0139] In this case, the thickness d of each layer is set to d = λ0 / 4n, where n is the refractive index of each layer at the central wavelength λ0 of the reflection band. This reduces the transmittance and forms a reflection band as the light reflected at the layer boundaries cancels out. The refractive index of the high refractive index material is n H , the refractive index of a low refractive index material n L Therefore, the width W = 2 / π × Sin[(n H -n L ) / (n H +n L A reflection band of ) × λ0 is formed.

[0140] Optical layer 34 is designed as a dielectric multilayer film that reflects blue light (460 nm) and transmits green light (530 nm) from the green subpixel and red light (630 nm) from the red subpixel, which are emitted from the conversion layer. Optical layer 36 is designed as a dielectric multilayer film that reflects green light (530 nm) from the green subpixel and transmits red light (630 nm) from the red subpixel.

[0141] The following explanation uses an example where SiO2 is used as the low refractive index material and TiO2 as the high refractive index material. We will describe an example where SiO2 and TiO2 are alternately stacked, and this is repeated 10 times to create a multilayer film. For optical layer 34, the thickness of SiO2 and TiO2 is determined according to the center wavelength of the reflection band for incident light at an incident angle of 0 degrees. As an example for optical layer 34, if the center wavelength of the reflection band is 400 nm, the thicknesses of SiO2 and TiO2 are 69 nm and 40 nm, respectively, and the total thickness is 1090 nm. In this case, the width of the reflection band is approximately 133 nm. As an example for optical layer 36, if the center wavelength of the reflection band is 470 nm, the thicknesses of SiO2 and TiO2 are 81 nm and 47 nm, respectively, and the total thickness is 1282 nm. In this case, the width of the reflection band is approximately 156 nm. The reflective layer can be fabricated by methods such as sputtering, ion beam deposition, or PLD (Pulsed Laser Deposition).

[0142] In the same manner as in Example 1, a green subpixel display element with a green light-emitting conversion layer was fabricated using a substrate on which an optical layer 34 was formed, and a red subpixel display element with a red light-emitting conversion layer was fabricated using a substrate on which an optical layer 36 was formed. The area of ​​the conversion layer was set to 300 μm × 300 μm. Using an ink composition obtained by removing CsPbBr3 nanocrystals from ink composition B, a resin portion containing a light-scattering material of 300 μm × 300 μm was fabricated in the same manner as in Example 1, and a blue subpixel display element was fabricated. The red subpixel display element, green subpixel display element, and blue subpixel display element were stacked in this order on an Al reflective film to fabricate a display element.

[0143] [Comparative Example 1] A dielectric multilayer mirror that transmits blue light and reflects green and red light was formed on a quartz substrate using ion beam deposition. This dielectric multilayer mirror transmits blue light (460 nm) at incident angles from 0 to 30 degrees and reflects light at angles greater than 30 degrees. It also reflects green light (530 nm) and red light (630 nm) at all incident angles. The mirror was constructed using a multilayer film composed of SiO2 and TiO2, with a reflective layer consisting of stacked multilayer films whose reflection band center wavelengths were 580 nm, 670 nm, and 760 nm, respectively. The film thicknesses of the SiO2 and TiO2 layers were 100 nm and 58 nm, 116 nm and 67 nm, and 131 nm and 76 nm, respectively. Each band had 5 repetitions, and the total thickness of the reflective layer was 2.7 μm.

[0144] Similar to Example 1, the solvent was removed from the CsPbBr3 dispersion by blowing a stream of dry nitrogen air onto it, and ink composition C was prepared to consist of 10 wt% CsPbBr3 nanocrystals, 75 wt% 3,3,5-trimethylcyclohexyl acrylate (TMCHA), 5 wt% 1-hydroxycyclohexyl phenyl ketone (Omnirad184), and 10 wt% titanium dioxide.

[0145] A display element was fabricated by printing ink composition C onto a dielectric multilayer film mirror formed on a quartz substrate, in the same manner as in Example 1, so that the conversion layer had dimensions of 100 μm (width) x 300 μm (height) x 10 μm (thickness). This configuration corresponds to Figure 3(b).

[0146] [Comparative Example 2] A display element was fabricated on a quartz substrate using the same ink composition C as in Comparative Example 1, in the same manner as in Example 1, so that the conversion layer had dimensions of 100 μm (width) x 300 μm (height) x 10 μm (thickness). This configuration corresponds to Figure 3(a).

[0147] [Comparative Example 3] Similar to Comparative Example 1, ink composition D was prepared to consist of 1 wt% CsPbBr3 nanocrystals, 84 wt% 3,3,5-trimethylcyclohexyl acrylate (TMCHA), 5 wt% 1-hydroxycyclohexyl phenyl ketone (Omnirad184), and 10 wt% titanium dioxide.

[0148] A display element was fabricated on a quartz substrate using the same ink composition D as in Comparative Example 1, in the same manner as in Example 1, so that the conversion layer had dimensions of 100 μm (width) x 300 μm (height) x 10 μm (thickness). This configuration corresponds to Figure 3(a).

[0149] <Brightness Evaluation> As excitation light, blue light with a peak emission wavelength of 460 nm was guided through an optical fiber, and the emitted light was imaged with a lens and incident on the conversion layer from the side. At this time, the amount of blue light irradiation (intensity × area) was kept constant. In other words, the blue light intensity per unit area increases as the film thickness decreases. Example 5 showed a higher intensity. An integrating sphere was placed directly above the conversion layer, and the integral values ​​of the emission spectra of green (530 nm ± 30 nm) and red (630 nm ± 30 nm) were measured as luminance using a multi-channel spectrometer C10027-01 (Hamamatsu Photonics).

[0150] Table 1 shows the brightness values ​​for green and red.

[0151] [Table 1] When the specific refractive index difference Δ of the waveguide was set to 1.5, the brightness of green and red improved as the film thickness decreased (Examples 1-3). This is thought to be because the waveguide mode decreases.

[0152] When the waveguide film thickness was kept constant at 3 μm, the brightness of green and red improved as the specific refractive index difference Δ decreased (Examples 2 and 4). This is thought to be due to a decrease in waveguide modes.

[0153] The brightness was almost the same regardless of whether the blue light incident direction was longitudinal or lateral (Examples 2 and 5).

[0154] Introducing a scattering section to the terminal improved the brightness of green and red light. This is thought to be because the light from the waveguide mode was scattered by the light scattering section and extracted as light from the emission mode (Examples 6 and 7).

[0155] By adopting a stacked configuration, the brightness of green and red was improved. This is because the area of ​​the conversion layer was tripled (Example 8).

[0156] In Example 1 and Comparative Example 1, the film thickness was 10 μm and the configuration with a reflective layer on the bottom surface was the same. In Comparative Example 1, the concentration of luminescent nanocrystals was 10 wt%, but the brightness of green and red light was relatively lower. This means that the light extraction efficiency of Example 1 is superior. When the concentration of luminescent nanocrystals was the same as in Comparative Example 2 (1 wt%), the brightness of green and red light decreased further. Also, when the reflective layer was not provided on the bottom surface, the brightness of green and red light decreased (Comparative Example 3). [Explanation of symbols]

[0157] 100 display elements 10A Light-emitting layer array 10. Emitting layer 20A Conversion Layer Array 20 First Conversion Layer 22 First joint 24 First removal section 26 First conversion section 28 First reflector

Claims

1. A light-emitting layer array comprising multiple light-emitting layers arranged in two dimensions and emitting light of a first wavelength, The device comprises a first coupling portion that optically couples with a portion of the plurality of light-emitting layers, and a first extraction portion and a first reflecting portion arranged opposite each other to alternately reflect the light of the first wavelength collected through the first coupling portion and guide it toward a direction away from the first coupling portion, and a conversion layer array comprising a plurality of first conversion layers that emit light of a second wavelength obtained by wavelength conversion of the light of the first wavelength through the first extraction portion, The conversion layer array further comprises a plurality of second coupling portions that optically couple with the plurality of first conversion layers in regions other than the portion where the light-emitting layer array is optically coupled with the plurality of first conversion layers, and a second extraction portion and a second reflecting portion arranged opposite each other to alternately reflect the light of the first wavelength collected through the plurality of second coupling portions and guide the light toward a direction away from the second coupling portions, and a plurality of second conversion layers that emit light of a third wavelength obtained by wavelength conversion of the light of the first wavelength through the second extraction portion. A display device in which, when viewed along an axis parallel to the layer thickness direction, the first extraction section and the second extraction section are arranged to have an overlapping portion.

2. The display device according to claim 1, wherein the plurality of first conversion layers contain first photoresponsive nanoparticles that convert light of a first wavelength into light of a second wavelength.

3. The display device according to claim 1, wherein the first extraction unit has a spectral reflectance for light of the first wavelength that is higher than that for light of the second wavelength.

4. The display device according to claim 1, wherein the first extraction unit has a spectral transmittance higher for light of the second wavelength than for light of the first wavelength.

5. The display device according to claim 1, wherein the second wavelength is longer than the first wavelength.

6. The display device according to claim 1, wherein the first reflective portion has a higher spectral reflectance for light of the second wavelength than the first extraction portion.

7. The display device according to claim 2, wherein the first conversion layer has a first optical gradient such that the optical density of the first photoresponsive nanoparticles increases with increasing distance from the first bonding portion in a direction perpendicular to the layer thickness direction.

8. The display device according to claim 1, wherein the plurality of second conversion layers contain second photoresponsive nanoparticles that convert light of the first wavelength into light of the third wavelength.

9. The display device according to claim 1, wherein the second extraction unit has a spectral reflectance for light of the first wavelength that is higher than that for light of the third wavelength.

10. The display device according to claim 1, wherein the second extraction unit has a spectral transmittance higher for light of the third wavelength than for light of the first wavelength.

11. The display device according to claim 1, wherein the third wavelength is longer than the first wavelength and the second wavelength.

12. The display device according to claim 1, wherein the second reflective portion has a higher spectral reflectance for light of the third wavelength than the second extraction portion.

13. The display device according to claim 8, wherein the second conversion layer has a second optical gradient such that the optical density of the second photoresponsive nanoparticles increases with increasing distance from the second bonding portion in a direction perpendicular to the layer thickness direction.

14. The display device according to claim 1, wherein the conversion layer array has a third coupling portion that optically couples with the plurality of light-emitting layers in a region other than the portion in which the light-emitting layer array is optically coupled with the plurality of first conversion layers or the plurality of second conversion layers, and a third extraction portion and a third reflecting portion that are arranged opposite to each other to alternately reflect the light of the first wavelength collected through the third coupling portion and guide the light toward a direction away from the third coupling portion, and further comprises a plurality of third conversion layers that emit at least one of the light of a fourth wavelength obtained by wavelength conversion of the light of the first wavelength or the light of the first wavelength through the third extraction portion.

15. The display device according to claim 14, wherein the plurality of third conversion layers contain third photoresponsive nanoparticles that convert light of the first wavelength into light of a fourth wavelength which is closer to the emission wavelength of light of the first wavelength than the emission wavelength of light of the second wavelength and the emission wavelength of light of the third wavelength.

16. The display device according to claim 14, wherein the third extraction unit has a spectral reflectance for light of the first wavelength that is higher than that for light of the fourth wavelength.

17. The display device according to claim 14, wherein the third extraction unit has a spectral reflectance for light of the first wavelength that is higher than that for light of the fourth wavelength.

18. The display device according to claim 14, wherein the fourth wavelength is longer than the first wavelength.

19. The display device according to claim 14, wherein the third reflective portion has a higher spectral reflectance for light of the fourth wavelength than the third extraction portion.

20. The display device according to claim 14, wherein the plurality of third conversion layers change the propagation direction in the propagation light path from the third coupling portion to the third extraction portion, but do not perform wavelength conversion of the light of the first wavelength.

21. The display device according to claim 1, wherein the first coupling portion is arranged such that it does not overlap with the first extraction portion when viewed along an axis parallel to the layer thickness direction.

22. The display device according to claim 1, wherein, when viewed along an axis parallel to the layer thickness direction, the first extraction portion and the second extraction portion are arranged such that they do not overlap.

23. A light-emitting layer array comprising multiple light-emitting layers arranged in two dimensions and emitting blue light, The layer array comprises a first coupling portion that optically couples with a portion of the plurality of light-emitting layers, and a first extraction portion and a first reflecting portion that are arranged opposite each other to alternately reflect the blue light collected through the first coupling portion and guide it toward a direction away from the first coupling portion, and a plurality of layers that emit blue light through the first extraction portion, The layer array includes a plurality of second coupling portions that optically couple with the plurality of light-emitting layers in regions other than the portion where the light-emitting layer array is optically coupled with the plurality of layers, and a second extraction portion and a second reflecting portion that are arranged opposite each other to alternately reflect the blue light collected through the plurality of second coupling portions and guide the light toward a direction away from the second coupling portions, and further comprises a plurality of second conversion layers that emit light of a third wavelength obtained by wavelength conversion of the blue light through the second extraction portions. A display device in which, when viewed along an axis parallel to the layer thickness direction, the first extraction section and the second extraction section are arranged to have an overlapping portion.

24. The display device according to claim 23, wherein the blue light emitted by the light-emitting layer array, the collected blue light, and the blue light emitted from the plurality of layers have a maximum value in the wavelength band of 445 nm to 475 nm.

25. The display device according to claim 23, wherein the third wavelength is longer than the wavelength of the blue light emitted from the plurality of layers.

26. The display device according to claim 23, wherein the second extraction unit has a spectral reflectance for the collected blue light that is higher than that of the third wavelength of light.

27. The display device according to claim 23, wherein the second extraction unit has a spectral transmittance higher for light of the third wavelength than for the collected blue light.

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