WO2014167758A1 - 発光装置 - Google Patents
発光装置 Download PDFInfo
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- WO2014167758A1 WO2014167758A1 PCT/JP2014/000220 JP2014000220W WO2014167758A1 WO 2014167758 A1 WO2014167758 A1 WO 2014167758A1 JP 2014000220 W JP2014000220 W JP 2014000220W WO 2014167758 A1 WO2014167758 A1 WO 2014167758A1
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- Prior art keywords
- refractive index
- light
- layer
- index layer
- light emitting
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Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
- H01L33/58—Optical field-shaping elements
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/02—Diffusing elements; Afocal elements
- G02B5/0205—Diffusing elements; Afocal elements characterised by the diffusing properties
- G02B5/021—Diffusing elements; Afocal elements characterised by the diffusing properties the diffusion taking place at the element's surface, e.g. by means of surface roughening or microprismatic structures
- G02B5/0221—Diffusing elements; Afocal elements characterised by the diffusing properties the diffusion taking place at the element's surface, e.g. by means of surface roughening or microprismatic structures the surface having an irregular structure
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/20—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular shape, e.g. curved or truncated substrate
- H01L33/22—Roughened surfaces, e.g. at the interface between epitaxial layers
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/80—Constructional details
- H10K50/85—Arrangements for extracting light from the devices
- H10K50/858—Arrangements for extracting light from the devices comprising refractive means, e.g. lenses
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K2102/00—Constructional details relating to the organic devices covered by this subclass
- H10K2102/301—Details of OLEDs
- H10K2102/302—Details of OLEDs of OLED structures
- H10K2102/3023—Direction of light emission
- H10K2102/3026—Top emission
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K2102/00—Constructional details relating to the organic devices covered by this subclass
- H10K2102/301—Details of OLEDs
- H10K2102/331—Nanoparticles used in non-emissive layers, e.g. in packaging layer
Definitions
- the present application relates to a light emitting device.
- organic electroluminescence element As an organic electroluminescence element (hereinafter referred to as “organic EL element”), a hole transport layer, an organic light emitting layer, an electron transport layer, and a cathode are sequentially laminated on a transparent electrode (anode) formed on the surface of a transparent substrate.
- organic EL element As an organic electroluminescence element (hereinafter referred to as “organic EL element”), a hole transport layer, an organic light emitting layer, an electron transport layer, and a cathode are sequentially laminated on a transparent electrode (anode) formed on the surface of a transparent substrate.
- anode anode
- Organic EL elements are self-luminous elements, have relatively high efficiency light emission characteristics, and can emit light in various colors. For this reason, it is expected to be used for a light emitter in a display device (for example, a flat panel display) and a light source (for example, a backlight or illumination for a liquid crystal display device), and some of them are already put into practical use. In order to apply the organic EL element to these uses, it is desired to develop an organic EL element having superior characteristics such as higher efficiency, longer life, and higher luminance.
- the driving voltage it is becoming possible to obtain an element that emits light with relatively high luminance at a voltage of about 10 to 20% higher than the voltage corresponding to the energy gap. In other words, there is not much room for improving the efficiency of the organic EL element by reducing the drive voltage.
- the light extraction efficiency of the organic EL element varies somewhat depending on the light emission pattern and the internal layer structure, but is generally about 20 to 30%, and there is much room for improvement.
- the reason why the light extraction efficiency is lowered in this way is that the material forming the portion where light is generated and the peripheral portion thereof have characteristics such as high refractive index and light absorption. For this reason, total reflection at interfaces having different refractive indexes and absorption of light by materials occur, and there arises a problem that light cannot effectively propagate to the outside where light emission is observed.
- the organic EL element light that cannot be used accounts for 70 to 80% of the total light emission amount. For this reason, the expectation for the efficiency improvement of the organic EL element by improvement of light extraction efficiency is very large.
- Patent Document 1 discloses an organic EL element provided with a diffraction grating in order to suppress total reflection at the interface.
- Patent Document 2 discloses an organic EL element in which a microlens array is provided on the surface of a transparent substrate.
- Patent Document 3 discloses an organic EL element provided with an optical sheet having an optical layer in which beads are dispersed in a binder.
- One non-limiting exemplary embodiment of the present application provides a light-emitting device that can increase light extraction efficiency.
- a light extraction sheet which is one embodiment of the present invention includes a light-transmitting substrate having a first main surface and a second main surface, and the first main surface of the light-transmitting substrate.
- a first light extraction structure provided on the surface side comprising: a low refractive index layer having a refractive index lower than that of the translucent substrate; and a high refractive index layer having a refractive index higher than that of the low refractive index layer.
- the low refractive index layer is formed between the translucent substrate and the high refractive index layer, and an interface between the high refractive index layer and the low refractive index layer has an uneven shape.
- the light extraction efficiency can be increased.
- FIG. 5B is a sectional view taken along line A-A ′ in FIG. 5A. It is a figure which shows the incident angle dependence of the transmittance
- FIG. 4 is a graph showing the dependence of light transmittance at an incident angle of 40 to 60 degrees on the aspect ratio of a microlens. It is a graph which shows the dependence of the light intensity with respect to an incident angle when an aspect ratio is changed. It is a figure which shows the modification of a micro lens array. It is a graph which shows the change of the dependence of the light intensity with respect to an incident angle when the structure of an external light extraction layer is changed. It is a top view which shows the example which employ
- FIG. 20B is a sectional view taken along line B-B ′ in FIG. 20A.
- FIG. 6 is a graph showing the dependence of the transmittance of light with an incident angle of 40 to 60 degrees on the apex angle when a pyramid structure is adopted. It is a graph which shows the change of the light intensity when changing the apex angle of a pyramid structure. It is a figure for demonstrating the period of an uneven structure. It is another figure for demonstrating the period of an uneven structure.
- (A) is a figure which shows the 1st example of an uneven structure
- (b) is a figure which shows the 2nd example of an uneven structure
- (c) is a figure which shows the 3rd example of an uneven structure. . It is a graph which shows the dependence of the light extraction efficiency with respect to the uneven
- the refractive index of the organic light emitting layer is 1.7 to 2.0, and the refractive index of the transparent substrate is about 1.5. Reflection occurs. According to the analysis by the present inventors, the loss of light due to the total reflection reaches about 50% or more of the total emitted light. Furthermore, since the refractive index of the transparent substrate is about 1.5 and the refractive index of air is about 1.0, light loss due to total reflection occurring at the interface between the transparent substrate and air also reaches the interface of the transparent substrate. Of about 50%. Thus, the total reflection loss at these two interfaces is very large.
- the present inventors have found a novel configuration that can reduce the total reflection loss at these two interfaces. Specifically, a first light extraction structure that causes light diffraction is provided between the light emitting layer and the transparent substrate, and a second lens such as a microlens array is provided on the opposite side of the transparent substrate from the light emitting layer. It has been found that the light extraction efficiency can be improved by providing the light extraction structure.
- a first light extraction structure that causes light diffraction is provided between the light emitting layer and the transparent substrate
- a second lens such as a microlens array
- a light-emitting device which is one embodiment of the present invention includes a light-emitting element that generates light having an average wavelength ⁇ , and a light extraction sheet that transmits light generated from the light-emitting element.
- the light emitting element includes a first electrode having light transparency, a second electrode, and a light emitting layer provided between the first and second electrodes.
- the light extraction sheet includes a light-transmitting substrate having a first main surface and a second main surface, and a first light extraction structure provided on the first main surface side of the light-transmitting substrate.
- the uneven shape is a shape in which a plurality of concave portions and a plurality of convex portions are randomly arranged two-dimensionally.
- the concavo-convex structure is a structure in which a plurality of concave portions and a plurality of convex portions are periodically arranged in a two-dimensional manner.
- the uneven shape is a shape in which a plurality of concave portions and a plurality of convex portions are two-dimensionally arranged, and an ellipse inscribed in each of the plurality of concave portions and the plurality of convex portions.
- a component smaller than 1 / (2w) among the spatial frequency components of the concavo-convex pattern randomly divides the plurality of concave portions and the plurality of convex portions. It is suppressed compared with the case where they are arranged in the.
- the concavo-convex shape is configured such that a predetermined number or more of recesses or protrusions do not continue in one direction.
- each of the plurality of concave portions and the plurality of convex portions has a quadrangular cross section, and the concave / convex shape is such that three or more concave portions or convex portions do not continue in one direction. It is configured as follows.
- each of the plurality of concave portions and the plurality of convex portions has a hexagonal cross section, and the concave / convex shape is such that four or more concave portions or convex portions do not continue in one direction. It is configured as follows.
- a minimum value of a short side length of an ellipse inscribed in each of the plurality of concave portions and the plurality of convex portions is 0.73 ⁇ or more.
- each of the plurality of concave portions and the plurality of convex portions has the same cross-sectional shape and the same size.
- an average period of each of the plurality of concave portions and the plurality of convex portions is 14.5 ⁇ or less.
- the refractive index of the low refractive index layer is not more than 0.98 times the refractive index of the translucent substrate.
- the distance between the light emitting point in the light emitting layer and the surface of the second electrode is 0.17 ⁇ or more.
- the refractive index of the low refractive index layer is 1.47 or less.
- the thickness of the low refractive index layer is (1/2) ⁇ or more.
- the refractive index of the translucent substrate is 1.5 or more.
- the refractive index of the high refractive index layer is 1.73 or more.
- the second light extraction structure is formed by a microlens array.
- the aspect ratio of the microlens array is 0.5 or more.
- the second light extraction structure has a pyramid structure, and an apex angle of the pyramid structure is set in a range of 30 degrees to 120 degrees.
- a light extraction sheet includes a translucent substrate having a first main surface and a second main surface, and the first main surface side of the translucent substrate.
- a first light extraction structure provided, having a low refractive index layer having a refractive index lower than that of the translucent substrate, and a high refractive index layer having a refractive index higher than that of the low refractive index layer, The low refractive index layer is formed between the translucent substrate and the high refractive index layer, and the interface between the high refractive index layer and the low refractive index layer has an uneven shape.
- a second light extraction structure provided on the second main surface side of the translucent substrate, which is transmitted through the translucent substrate and incident at an incident angle of 40 degrees to 60 degrees
- a second light extraction structure configured to have an average transmittance of light of 42% or more.
- FIG. 1 is a cross-sectional view showing a schematic configuration of an organic EL element 100 in the present embodiment.
- the organic EL element 100 of the present embodiment includes a light emitting element 110 and a light extraction sheet 120 that transmits light generated from the light emitting element 110.
- the light emitting element 110 includes a reflective electrode 11 having light reflectivity, a transparent electrode 13 having light transmittance, and an organic light emitting layer 12 formed therebetween.
- the light extraction sheet 120 includes a transparent substrate 14, an internal light extraction layer 15 provided on the first main surface side (lower side in FIG. 1) of the transparent substrate 14, and a second main surface side of the transparent substrate 14 ( And an external light extraction layer 16 provided on the upper side in FIG. As shown in FIG.
- the internal light extraction layer 15 includes a low refractive index layer 15a having a relatively low refractive index and a high refractive index layer 15b having a relatively high refractive index.
- the interface between the low refractive index layer 15a and the high refractive index layer 15b has an uneven shape, and is configured to diffract incident light.
- the reflective electrode 11 is an electrode (cathode) for injecting electrons into the light emitting layer 12. When a predetermined voltage is applied between the reflective electrode 11 and the transparent electrode 13, electrons are injected from the reflective electrode 11 into the light emitting layer 12.
- a material of the reflective electrode 11 for example, silver (Ag), aluminum (Al), copper (Cu), magnesium (Mg), lithium (Li), sodium (Na), or an alloy containing these as main components is used. be able to.
- the reflective electrode 11 may be formed by combining and laminating these metals, or indium tin oxide (ITO) or PEDOT: PSS (mixture of polythiophene and polystyrene sulfonic acid) so as to be in contact with these metals.
- the reflective electrode 11 may be configured by laminating a transparent conductive material such as.
- the transparent electrode 13 is an electrode (anode) for injecting holes into the light emitting layer 12.
- the transparent electrode 13 can be made of a material such as a metal, an alloy, an electrically conductive compound, or a mixture thereof having a relatively high work function.
- the material of the transparent electrode 13 include ITO, tin oxide, zinc oxide, IZO (registered trademark), inorganic compounds such as copper iodide, conductive polymers such as PEDOT and polyaniline, and conductivity doped with any acceptor.
- examples thereof include conductive light transmissive materials such as polymers and carbon nanotubes.
- the transparent electrode 13 can be formed as a thin film by sputtering, vacuum deposition, coating, or the like after the internal light extraction layer 15 is formed on the transparent substrate 14.
- the sheet resistance of the transparent electrode 13 is set to, for example, several hundred ⁇ / ⁇ or less, and in an example, can be set to 100 ⁇ / ⁇ or less.
- the film thickness of the transparent electrode 13 is, for example, 500 nm or less, and can be set in the range of 10-200 nm in an example. As the transparent electrode 13 is made thinner, the light transmittance is improved, but the sheet resistance increases in inverse proportion to the film thickness, so that the sheet resistance increases.
- auxiliary wiring such as metal may be formed on the transparent electrode 13.
- a material having excellent conductivity can be used.
- Ag, Cu, Au, Al, Rh, Ru, Ni, Mo, Cr, Pd and alloys thereof MoAlMo, AlMo, AgPdCu, etc.
- an insulation process may be performed to prevent current from flowing through the grid portion so that the metal grid does not function as a light shielding material.
- a metal having a high reflectance may be used for the grid.
- the transparent electrode 13 is used as an anode and the reflective electrode 11 is used as a cathode.
- the polarities of these electrodes may be reversed.
- the transparent electrode 13 and the reflective electrode 11 can be made of the same material as described above.
- the light emitting layer 12 is formed of a material that generates light by recombination of electrons and holes injected from the transparent electrode 13 and the reflective electrode 11.
- the light emitting layer 12 can be formed of, for example, any known light emitting material such as a low molecular or high molecular light emitting material or a metal complex.
- an electron transport layer and a hole transport layer may be provided on both sides of the light emitting layer 12.
- the electron transport layer is disposed on the reflective electrode 11 (cathode) side, and the hole transport layer is disposed on the transparent electrode 13 (anode) side.
- the electron transport layer is disposed on the transparent electrode 13 side, and the hole transport layer is disposed on the electrode 11 side.
- the electron transport layer can be appropriately selected from the group of compounds having electron transport properties.
- a metal complex such as Alq3 known as an electron transporting material
- a compound having a heterocycle such as a phenanthroline derivative, a pyridine derivative, a tetrazine derivative, or an oxadiazole derivative can be given.
- the hole transport layer can be appropriately selected from the group of compounds having hole transport properties.
- Examples of this type of compound include 4,4′-bis [N- (naphthyl) -N-phenyl-amino] biphenyl ( ⁇ -NPD), N, N′-bis (3-methylphenyl)-(1 , 1′-biphenyl) -4,4′-diamine (TPD), 2-TNATA, 4,4 ′, 4 ′′ -tris (N- (3-methylphenyl) N-phenylamino) triphenylamine (MTDATA) , 4,4'-N, N'-dicarbazole biphenyl (CBP), spiro-NPD, spiro-TPD, spiro-TAD, or a triarylamine compound typically represented by TNB, an amine containing a carbazole group Compounds, amine compounds containing fluorene derivatives, etc.
- TNB 4,4′-bis [N- (naphthyl) -N-phenyl-amino] biphen
- the present invention is not limited to these materials, and any generally known hole transporting material may be used.
- other layers such as an electron transport layer and a hole transport layer can be provided between the reflective electrode 11 and the transparent electrode 13 in addition to the light emitting layer 12.
- the entire layer between the reflective electrode 11 and the transparent electrode 13 may be collectively referred to as an “organic EL layer”.
- the structure of the organic EL layer is not limited to the above example, and various structures can be employed.
- a laminated structure of the hole transport layer and the light emitting layer 12 or a laminated structure of the light emitting layer 12 and the electron transport layer may be adopted.
- a hole injection layer may be interposed between the anode and the hole transport layer, or an electron injection layer may be interposed between the cathode and the electron transport layer.
- the light emitting layer 12 is not limited to a single layer structure, and may have a multilayer structure. For example, when the desired emission color is white, the light emitting layer 12 may be doped with three types of dopant dyes of red, green, and blue.
- a laminated structure of a blue hole transporting light emitting layer, a green electron transporting light emitting layer and a red electron transporting light emitting layer may be adopted, or a blue electron transporting light emitting layer, a green electron transporting light emitting layer and a red color may be adopted.
- a laminated structure with an electron transporting light emitting layer may be adopted.
- a layer composed of elements that emit light when a voltage is applied between an anode and a cathode is used as one light-emitting unit, and a plurality of light-emitting units are stacked via an intermediate layer having optical transparency and conductivity (electricity).
- a multi-unit structure connected in series may be employed.
- the transparent substrate 14 is a member for supporting the internal light extraction layer 15, the transparent electrode 13, the light emitting layer 12, and the reflective electrode 11.
- a material of the transparent substrate 14 for example, a transparent material such as glass or resin can be used.
- the refractive index of the transparent substrate 14 is, for example, about 1.45 to 1.65. However, a high refractive index substrate with a refractive index of 1.65 or more may be used, or a low refractive index lower than 1.45. A refractive index substrate may be used.
- the internal light extraction layer 15 is a translucent layer provided between the transparent substrate 14 and the transparent electrode 13.
- the internal light extraction layer 15 has a low refractive index layer 15a formed on the transparent substrate 14 side and a high refractive index layer 15b formed on the transparent electrode 13 side. These interfaces form a concavo-convex structure.
- the low refractive index layer 15 a in this embodiment is formed of a light transmissive material having a refractive index lower than that of the transparent substrate 14.
- the high refractive index layer 15 b is formed of a translucent material having a refractive index higher than that of the transparent substrate 14.
- the high refractive index layer 15b may be formed of a material having a refractive index higher than that of the transparent substrate 14 as long as the refractive index is lower than that of the low refractive index layer 15a.
- FIG. 2A is a plan view schematically showing an example of the concavo-convex structure in the present embodiment.
- FIG. 2B is a cross-sectional view schematically showing a part of the concavo-convex structure.
- the black and white regions in FIG. 2A represent a portion where the high refractive index layer 15b is formed relatively thick (convex portion) and a portion where the high refractive index layer 15b is formed relatively thin (concave portion), respectively.
- This uneven structure corresponds to a structure in which two types of unit structures (height difference h) each having a length (width) w of one side are randomly arranged in two dimensions.
- each unit structure may be referred to as a “block”.
- the pattern of the concavo-convex structure is not made completely random, but a structure in which randomness is suppressed is employed so that the same type of unit structure does not appear more than a predetermined number of times in one direction. May be.
- light diffraction may be generated by injecting particles with a high refractive index near the interface between the low refractive index layer 15a and the high refractive index layer 15b. . The light extraction efficiency in the case of employing each of these configurations will be described later.
- Part of the light generated in the light emitting layer 12 enters the internal light extraction layer 15 through the transparent electrode 13. At this time, the light incident at an incident angle exceeding the critical angle is totally totally totally reflected, but a part thereof is extracted to the transparent substrate 14 side by the diffractive action of the internal light extraction layer 15.
- the light that has not been extracted by the internal light extraction layer 15 is directed toward the light emitting layer 12 at a different angle due to reflection, but is then reflected by the reflective electrode 11 and is incident on the internal light extraction layer 15 again.
- part of the light generated in the light emitting layer 12 is reflected by the electrode 11, then passes through the transparent electrode 13 and enters the internal light extraction layer 15.
- the external light extraction layer 16 is provided on the surface of the transparent substrate 14 (the surface opposite to the surface on which the internal light extraction layer 15 is provided).
- the external light extraction layer 16 can be formed by, for example, a microlens array.
- the external light extraction layer 16 is configured to have an average transmittance of 42% or more of light transmitted through the transparent substrate 14 and incident at an incident angle of 40 degrees to 60 degrees. A specific configuration of the external light extraction layer 16 will be described later.
- the reflective electrode 11, the light emitting layer 12, the transparent electrode 13, and the internal light extraction layer 15 in this embodiment have a low light absorption property. Can be used.
- the light generated in the light emitting layer 12 reaches the external light extraction layer 16 after passing through the transparent electrode 13, the internal light extraction layer 15, and the transparent substrate 14.
- the external light extraction layer 16 may be formed by directly processing the transparent substrate 14, but can also be formed by sticking a film provided with a light extraction structure.
- the inventors first analyzed the light extraction structure using a microlens array film as shown in FIG. 3A and a diffusion film as shown in FIG. 3B as an example of the external light extraction layer 16. Went. In order to verify the total reflection suppression effect of these light extraction structures, the light transmittance of each film was measured. A method for measuring the light transmittance will be described with reference to FIG.
- a hemispherical lens having the same refractive index as that of the transparent substrate 14 is attached to each film (or substrate), and each film is detected by detecting light incident from the hemispherical lens side with an integrating sphere provided with minute holes.
- the transmittance of was measured.
- the angle dependency of the transmittance was measured by changing the incident angle of the incident light.
- calculation by ray tracing was performed with the same configuration as this experiment.
- FIG. 5A is a plan view showing the arrangement of microlens arrays used for experiments and calculations.
- 5B is a cross-sectional view taken along line A-A ′ in FIG. 5A.
- the microlens array on the surface of the external light extraction layer 16 has a close-packed structure by arranging in the honeycomb arrangement shown in FIG. 5A, so that the light extraction efficiency is the highest.
- r is the radius of each microlens
- h is the protruding amount (height) of the sphere
- FIG. 6A and FIG. 6B are graphs showing the results of the above experiments and calculations.
- FIG. 6A shows the results for the microlens array film
- FIG. 6B shows the results for the diffusion film.
- the solid line in the graph of each figure shows the result measured in the experiment, and the broken line shows the result of calculation by ray tracing. In either case, the experimental results and the calculation results are in good agreement.
- the transmittance peak is at an incident angle of 40 degrees to 60 degrees, and the transmittance sharply decreases from 60 degrees to 90 degrees.
- FIG. 6B in the diffusion film, the transmittance gradually decreases from 0 degrees to 90 degrees. Comparing the two, the transmittance at 0 to 40 degrees is almost equal, the transmittance at 40 to 60 degrees is higher in the micro lens array, and the transmittance at 60 to 80 degrees is a diffusion film. Is higher.
- FIG. 6C is a graph showing the results of measuring the transmittance at each incident angle for six types of diffusion films with various design conditions. As shown in this graph, when the external light extraction layer 16 of the diffusion system is used, the transmittance peak occurs in a region where the incident angle is small, and the transmittance of light incident at an incident angle of 40 to 60 degrees is not so much. You can see that it is not expensive.
- the inventors of the present invention have noted that the transmittance of 40 to 60 degrees is specifically high when a microlens array is used.
- the internal light extraction layer 15 When light from the light emitting layer 12 is extracted by the internal light extraction layer 15, if a large amount of light is collected in an incident angle range of 40 degrees to 60 degrees and the light of 60 degrees to 80 degrees is suppressed, the organic EL element 100 We thought that the light extraction efficiency could be improved as a whole.
- the configuration shown in FIG. 7 is a configuration in which a hemispherical lens that is sufficiently larger than the organic EL element 100 is attached instead of the external light extraction layer 16 of the organic EL element 100 of FIG.
- the refractive index of the hemispherical lens is substantially the same as the refractive index of the transparent substrate 14.
- a spectroradiometer was used for light distribution measurement, and was arranged so as to receive light from a light spot in a sufficiently small region of the light emitting layer 12.
- FIG. 8A The above measurements were performed on several samples of organic EL elements that were prototyped. The results are shown in FIG. 8A.
- the horizontal axis represents the incident angle
- the vertical axis represents the measured light intensity (arbitrary unit) per unit area.
- FIG. 8B and the following Table 1 As a sample configuration, the configuration shown in FIG. 8B and the following Table 1 was adopted.
- the transparent substrate 14 glass having a refractive index of 1.51 was used as the transparent substrate 14, and ITO was used as the transparent electrode 13.
- the average wavelength is defined such that, in the emission spectrum, the sum of the intensities of light having a wavelength larger than the average wavelength is equal to the sum of intensities of light having a wavelength smaller than the average wavelength.
- the positions of the two light emitting layers in each sample are as shown in Table 1.
- the distance from the reflective electrode 11 to the layer that emits light of the average wavelength ⁇ 1 is d1
- the distance from this layer to the transparent electrode 13 is d1 ′
- the distance from the reflective electrode 11 to the layer that emits light of the wavelength ⁇ 2 is d2
- this layer Is the distance from the transparent electrode 13 to d2 ′.
- a resin having a refractive index of 1.52 is used as a material for the low refractive index layer 15a
- a resin having a refractive index of 1.76 is used as a material for the high refractive index layer 15b.
- An uneven structure was formed.
- two types of patterns shown in FIGS. 9A and 9B were employed.
- Samples 1, 2, and 3 are obtained by changing the positional relationship between the two light emitting layers and the two electrodes, and the concavo-convex structure has a random structure (random 1) shown in FIG.
- the positions of the two light-emitting layers are the same as those in Sample 2, and the uneven structure is changed to the structure (random 2) shown in FIG. 9B.
- the structure of random 1 corresponds to a random arrangement of two types of blocks having a width of 0.6 ⁇ m and a height difference of 0.6 ⁇ m.
- the random 2 structure corresponds to a random arrangement of two types of blocks having a width of 1.2 ⁇ m and a height difference of 0.6 ⁇ m.
- the randomness is suppressed so that three or more blocks of the same kind do not appear continuously in each of the horizontal direction and the vertical direction in FIG. 9B.
- measurement was also performed on sample 2_0 obtained by removing the internal light extraction layer 15 from the configuration of sample 2 and sample 2_1 using a scattering internal light extraction layer instead of the uneven structure in the configuration of sample 2.
- the internal light extraction layer of the scattering system refers to an element formed by injecting particles with a high refractive index near the boundary between the low refractive index layer 15a and the high refractive index layer 15b.
- the light intensity does not change much with respect to the incident angle.
- the light intensity on the high angle side mainly increases, including the sample 2_1 (diffusion) using the diffusion type internal light extraction layer. It can be seen that the light intensity has a peak in the range of 80 to 80 degrees. Since such a tendency is seen regardless of the structure of the light emitting layer 12, it can be said that the internal light extraction layer 15 has the effect of extracting light mainly on the high angle side. As shown in FIG.
- FIG. 11 is a graph showing the measurement results.
- the thick solid line, dotted line, and broken line in FIG. 11 indicate the incident angle of light intensity per unit area when the refractive index of the low refractive index layer 15a in the internal light extraction layer 15 is 1.35, 1.45, and 1.52, respectively. Shows dependency.
- the refractive index of the low refractive index layer 15a is 1.52 (equivalent to the refractive index 1.51 of the transparent substrate), the light exists at all angles from 0 degree to 85 degrees, and particularly concentrates around 70 degrees. ing.
- the refractive index of the low refractive index layer 15a is 1.35 (smaller than the refractive index of the transparent substrate 1.51), it can be seen that there is no light at 64 degrees or more. Further, the light is bent to a low angle side due to refraction from the low refractive index layer 15a to the transparent substrate 14, so that a large amount of light is transmitted through the external light extraction layer 16 (microlens array) having a high transmittance of 40 to 60 degrees. (See FIG. 6A). In this way, by reducing the refractive index of the low refractive index layer 15a in the internal light extraction layer 15 and collecting light in the angular region of high transmittance in the external light extraction layer 16, the overall extraction efficiency can be increased. It is considered possible.
- the organic EL element 100 was prototyped to demonstrate the effect of the combination of the external light extraction layer 16 (microlens array) and the internal light extraction layer 15.
- the configuration of the sample is the same as that in FIG. Glass with a refractive index of 1.51 was used as the transparent substrate 14, a resin with a refractive index of 1.76 was used as the material for the high refractive index layer 15b, and ITO was used as the transparent electrode 13.
- the organic light emitting layer 12 was configured to emit light (white light) of 440 nm to 700 nm.
- the uneven structure at the interface between the low refractive index layer 15a and the high refractive index layer 15b has two types of square unit structures (blocks) having a height difference (height) h and a width w as shown in FIGS. 2A and 2B. Were arranged at random.
- the case where a film provided with a light diffusion layer was used as the external light extraction layer 16 was also measured.
- the thicknesses of the low refractive index layer 15a and the high refractive index layer 15b are 1.5 ⁇ m and 2 ⁇ m, respectively.
- the measurement result of the light extraction efficiency is shown in FIG. In the graph of FIG. 12, the horizontal axis represents the refractive index of the low refractive index layer 15a, and the vertical axis represents the light extraction efficiency.
- the light extraction efficiency was calculated.
- the calculation was divided into an example using a microlens array as the external light extraction layer 16 and a comparative example using a diffusion film.
- the refractive index of the transparent substrate 14 is 1.5
- the refractive index of the low refractive index layer 15a is 1.0 to 1.6
- the refractive index of the high refractive index layer 15b is 1.76
- their thicknesses are 0.7 mm, respectively. 2 ⁇ m and 2 ⁇ m.
- the distribution shown in FIG. 13 was applied as the angular distribution of light in the light emitting layer 12.
- the concavo-convex structure was a diffraction grating having a period of 2 ⁇ m and a height of 0.6 ⁇ m.
- a diffraction modal method (RCWA method) is applied to the diffraction grating portion, and the calculation result and the result of ray tracing are linked to calculate the light extraction efficiency of the organic EL element 100 as a whole. went.
- FIG. 14 shows the calculation result indicating the dependence of the light extraction efficiency on the refractive index of the low refractive index layer 15a.
- the refractive index of the low refractive index layer 15a is lower than 1.47, it can be seen that the efficiency is higher when the microlens array is used as the external light extraction layer 16 than the diffusion film. This is almost the same behavior as the experimental result of FIG. From these results, it can be seen that it is effective to adopt a configuration in which the refractive index of the low refractive index layer 15 a is lower than 1.47 and the microlens is used as the external light extraction layer 16.
- the refractive index n2 of the low refractive index layer 15a is set to a value smaller than 0.98 times the refractive index n1 of the transparent substrate 14.
- the present invention is not limited to this example, and a certain degree of effect can be obtained if the refractive index n2 of the low refractive index layer 15a is smaller than the refractive index n1 of the transparent substrate 4.
- the refractive index of the low refractive index layer 15a is set to 1.45, and other calculation conditions are the same as those in the calculation of FIG.
- the refractive index of the low refractive index layer 15a used in the experiment shown in FIG. 12 is 1.45
- the external light extraction layer 16 has the same configuration as that of the microlens array
- the high refractive index layer 15b Two types of elements with different refractive indexes of 1.75 and 1.80 were used. As shown in FIG. 15, it was found that the higher the refractive index of the high refractive index layer 15b, the greater the light extraction efficiency.
- the refractive index of the high refractive index layer 15b may be set to 1.73 or more.
- the uneven structure at the boundary between the low refractive index layer 15a and the high refractive index layer 15b can be formed, for example, by forming an uneven shape on the low refractive index layer 15a and then embedding the unevenness with a material having a high refractive index. . Thereafter, the transparent electrode 13, the organic light emitting layer 12, and the reflective electrode 11 are formed. If the flatness of the surface of the high refractive index layer 15b is poor, a short circuit is likely to occur between the transparent electrode 13 and the reflective electrode 11. In that case, there is a possibility that the element does not shine, and there is a possibility that the yield at the time of manufacture will deteriorate.
- a configuration is adopted in which the height of the concavo-convex shape is made as low as possible to ensure flatness after the high refractive index layer 15b is embedded. Further, by reducing the height of the concavo-convex structure in this way, the amount of material used for the low refractive index layer 15a and the high refractive index layer 15b can be suppressed, leading to cost reduction.
- the order of the height (size) of the concavo-convex structure needs to be at least about 1/4 of the wavelength of light. Thereby, a sufficient phase difference of light can be secured and light can be diffracted, so that the efficiency of extracting light can be improved.
- a diffraction grating such as a random structure or a periodic structure having a height (size) of around 1 ⁇ m is used as an example of the uneven structure.
- the light after passing through the concavo-convex structure is incident on the low refractive index layer 15a. If the thickness of the low-refractive index layer 15a is 1 ⁇ 2 or less of the wavelength of light, the light does not propagate through the low-refractive index layer 15a, and the light is transmitted to the transparent substrate 14 side through the evanescent field. Therefore, the effect of bending light in the low angle direction by the low refractive index layer 15a cannot be expected. Therefore, the thickness of the low refractive index layer 15a in this embodiment can be set to 1/2 or more of the average emission wavelength.
- the refractive index of the high refractive index layer 15b is set to 1.73 or more as described above, examples of materials used for the high refractive index layer 15b include ITO (indium tin oxide), TiO 2 (titanium oxide), and SiN (nitriding).
- ITO indium tin oxide
- TiO 2 titanium oxide
- SiN nitriding
- a relatively high refractive index inorganic material such as silicon), Ta 2 O 5 (tantalum pentoxide), or ZrO 2 (zirconia), or a high refractive index resin can be used.
- the transparent substrate 14 glass or resin is generally used, and the refractive index thereof is about 1.5 to 1.65. Therefore, as a material used for the low refractive index layer 15a, for example, an inorganic material such as glass or SiO 2 (quartz), a resin, or the like can be used.
- an inorganic material such as glass or SiO 2 (quartz), a resin, or the like can be used.
- a low refractive index layer 15a having a concavo-convex surface is formed on a transparent substrate 14, and a concavo-convex structure is buried with a high refractive index material thereon, on which There is a method of forming the transparent electrode 13, the organic light emitting layer 12, and the reflective electrode 11.
- the reflective electrode 11 is formed on the substrate, the organic light emitting layer 12, the transparent electrode 13, and the high refractive index layer 15 b having a concavo-convex shape on the surface are formed.
- a transparent substrate 14 is formed thereon.
- the internal light extraction layer 15 can be formed by a relatively low cost method such as coating, nanoimprinting, or spin coating. it can.
- FIG. 16 shows the change in the transmittance of incident light with an incident angle of 40 degrees to 60 degrees when the protrusion amount (height h) of each microlens sphere is changed in this arrangement.
- the vertical axis represents the average transmittance of light having an incident angle of 40 degrees to 60 degrees.
- FIG. 17 is a graph showing the incident angle dependence of the light intensity per unit area when the aspect ratio is 0.33, 0.5, 0.67, 0.8, and 1.0. As shown in this figure, it can be seen that the light intensity peak at an incident angle of 40 to 60 degrees becomes more prominent as the aspect ratio is closer to 1.0.
- FIG. 19 is a graph showing these comparison results.
- the horizontal axis represents the incident angle
- the vertical axis represents the light intensity per unit area.
- the solid line represents the result in the close-packed state shown in FIG. 5A
- the dotted line represents the result in the square arrangement shown in FIG. 18, and the broken line represents the result in the case without the microlens array.
- the transmittance of light having an incident angle of 40 degrees to 60 degrees is specifically increased only when a close-packed microlens is provided.
- the external light extraction layer 16 has been described by taking a microlens array as an example.
- the microlens array in this embodiment has a transmittance peak with respect to light having an incident angle in the range of 40 degrees to 60 degrees. Therefore, by combining the microlens array and the internal light extraction layer 15 including the low refractive index layer 15a having a relatively low refractive index, the efficiency can be increased as compared with other configurations. This effect is not limited to the microlens array, and can be similarly realized if the external light extraction layer 16 is configured so that the transmittance of light incident at an incident angle of 40 degrees to 60 degrees reaches a peak. . Accordingly, a modification of the external light extraction layer 16 will be described below.
- FIG. 20A is a plan view showing a pyramid structure which is a similar shape of a microlens array.
- 20B is a cross-sectional view taken along line B-B ′ in FIG. 20A.
- FIG. 21 is a graph showing the dependence of the average value of the transmittance of light having an incident angle of 40 degrees to 60 degrees with respect to the apex angle of the pyramid structure.
- FIG. 22 is a graph showing the incident angle dependence of the light intensity per unit area when the apex angle of the pyramid structure is 30 degrees, 50 degrees, 70 degrees, 90 degrees, 110 degrees, 130 degrees, and 150 degrees. . Also from this result, it can be seen that if the apex angle is in the range of 30 degrees to 120 degrees, the average transmittance of light with an incident angle of 40 degrees to 60 degrees is relatively high. Therefore, when an array having a pyramid structure is employed as the external light extraction layer 16, the apex angle may be set within a range of 30 degrees to 120 degrees.
- the average period in the arrangement direction is 4w.
- the average period in the arrangement direction is 2w. Note that the average period pexp when the blocks are arranged at random is obtained by the calculation shown in the balloon of FIG.
- a structure in which the randomness of the concavo-convex structure is controlled can be employed.
- “a structure in which randomness is controlled” means not a completely random structure but a structure in which randomness is suppressed so that the same type of block does not appear more than a predetermined number of times in one direction. To do.
- the light extraction efficiency can be further improved by adopting the concavo-convex structure in which the randomness is controlled.
- FIG. 24 shows a method for obtaining the average period from the structure pattern.
- an ellipse inscribed in a region composed of a group of continuous unit structures of the same type is considered.
- the average value of the size of the white portion in the lower diagram of FIG. 24 can be obtained by calculating the average value of the lengths of the ellipse axes inscribed in the white portion.
- the “axis length” refers to either the short axis length a or the long axis length b shown in the upper diagram of FIG. The same applies to the black part.
- a value obtained by adding these average values is defined as an average period.
- the concavo-convex structure may be a structure in which blocks having other shapes such as hexagons are arranged instead of squares.
- FIG. 26 is a graph showing the result of calculating the dependence of the light extraction efficiency on the width w of the concavo-convex shape.
- the height h of the structure is 1.0 ⁇ m.
- the refractive index of the transparent substrate 14 was 1.5
- the refractive index of the low refractive index layer 15a was 1.35
- the refractive index of the high refractive index layer 15b was 2.0.
- ( ⁇ ) indicates the result of adopting an uneven shape in which the blocks shown in FIG. 23 (a) are randomly arranged
- ( ⁇ ) indicates the result when the uneven shape in which the blocks shown in FIG. 23 (b) are periodically arranged is adopted. Show.
- the light extraction efficiency can be increased to 69% or more if w is in the range of 0.4 to 2 ⁇ m.
- the light extraction efficiency can be 69% or more if w is in the range of 0.4 to 4 ⁇ m.
- the average period of the random structure is 4w and the average period of the periodic structure is 2w, it can be seen that the light extraction efficiency is determined by the average period regardless of the structure pattern.
- p can be set to 8 ⁇ m or less, for example.
- the periodic structure is considered to have a large wavelength dependency due to the properties of the diffraction grating, and thus the color unevenness with respect to the viewing angle is increased. Therefore, in order to reduce color unevenness with respect to the viewing angle, a shape in which structures are arranged at random may be adopted as the uneven shape.
- FIG. 28 is a graph showing the results. ( ⁇ ), ( ⁇ ), and ( ⁇ ) in FIG. 28 show the results of calculation regarding the corresponding random structure in FIG.
- the refractive index of the transparent substrate 14 is 1.51
- the refractive index of the low refractive index layer 15a is 1.45
- the refractive index of the high refractive index layer 15b is 1.76.
- the structure ( ⁇ ) is a structure in which rectangular parallelepipeds having a structure size of 0.6 ⁇ m and a height of 0.2 to 0.8 ⁇ m are arranged at random.
- rectangular parallelepipeds having a structure size of 1.2 ⁇ m and a height of 0.6 ⁇ m are randomly arranged.
- the randomness is controlled so that three or more blocks do not appear continuously in the same direction.
- the structure of ( ⁇ ) is a structure in which hexagonal columns with a structure size (diameter of a hexagonal inscribed circle) of 1.2 ⁇ m and a height of 0.6 to 1.2 ⁇ m are randomly arranged.
- the randomness is controlled so that four or more blocks do not appear continuously in the same direction.
- FIG. 30 is a diagram showing the amplitude of the spatial frequency component by subjecting the random pattern to Fourier transform.
- the center of the distribution diagram on the right side of FIG. 30 represents a component having a spatial frequency of 0 (DC component).
- the spatial frequency is displayed so as to increase from the center toward the outside.
- the low-frequency component is suppressed in the spatial frequency of the controlled random pattern shown in FIG. 30A compared to the random pattern shown in FIG. .
- a component smaller than 1 / (2w) among the spatial frequency components is suppressed.
- w becomes a value within the range of 0.4 to 2 ⁇ m.
- the light extraction efficiency is increased. For this reason, a plurality of blocks whose sizes are appropriately changed within this range may be arranged at random.
- each block height gives a phase difference to the light, and the light is extracted by diffracting the light. Therefore, the block height h may not be constant. For example, a plurality of height levels may be provided. Moreover, the height in each block can also be made random.
- FIG. 31 is a perspective view showing an example of a configuration in which the block height is random.
- the illustrated relief structure 166 includes a first unit structure 166a having a first height, a second unit structure 166b having a second height, a third unit structure 166c having a third height,
- the fourth unit structure 166d having the fourth height has a structure that is randomly arranged in a two-dimensional manner.
- each block is filled with a high refractive index material and a low refractive index material, a difference occurs in the phase of light passing through these portions. Therefore, even if the height is random, the average phase difference of the transmitted light is determined by the average height of the plurality of unit structures. Accordingly, even in this case, a sufficient average phase difference can be given to the transmitted light, and therefore the height may be random.
- each cross-sectional shape can be configured in a round shape.
- a corner portion may be processed into a round shape, or a step portion may be processed into a slope shape. Even when these factors occur when processing the concavo-convex structure of the internal light extraction layer 15, as long as the properties of the random pattern described above are not lost, a structure in which corner portions are processed into rounded shapes is also possible. Included in this configuration.
- noise such as a small structure of 0.73 ⁇ or less (which can be caused by dust) that is unintentionally generated during manufacturing or a large structure (scratch etc.) of 4 ⁇ m or more, these are all If it is about 10% with respect to the area, sufficient effect is obtained. Therefore, even if these noises are intentionally added at about 10%, they are included in the scope of the present invention as long as the effect is obtained.
- the refractive index of the high refractive index layer 15b and the high refractive index hemispherical lens was 1.77.
- a simulation was also performed for comparison. Calculation was performed using a model in which the distance from the surface of the reflective electrode 11 was 50, 70, 90, 120, 160, 200, 240, and 290 nm, respectively, and the emission point was 580 nm. Measurement results and calculation results are shown in FIGS. 33A and 33B.
- FIG. 33A shows the result when the distance from the surface of the reflective electrode 11 is 160 nm or less
- FIG. 33B shows the result when the distance is 200 nm or more.
- the experimental results and measurement results are in good agreement.
- the position of the light emitting point is 90 nm or less, there is almost no light of 60 degrees or more. This is because when the distance between the transparent electrode 13 and the surface of the reflective electrode 11 is small, the light on the high angle side is combined with the surface plasmon of the reflective electrode and lost.
- the refractive index of the light emitting layer 12 is 1.75 and the refractive index of the transparent substrate 14 is 1.5, the critical angle of light propagating from the light emitting layer 12 to the transparent substrate 14 is approximately 60 degrees. Therefore, when there is no light of 60 degrees or more, it is not necessary to provide a light extraction structure inside.
- FIG. 34 shows the result of calculating the dependence of the luminous efficiency on the distance between the luminous point and the reflective electrode 11.
- the light emission efficiency is 60% or less, and it can be seen that 40% or more of the light is combined with the surface plasmon and lost. In such a situation, no matter how much the extraction efficiency is increased, there is a limit to increasing the efficiency because the proportion of the propagating light generated is small in the first place.
- the internal light extraction layer 15 was introduced into three models in which emission points with emission wavelengths of 580 nm were respectively provided at positions of 70, 160, and 290 nm from the surface of the reflective electrode 11.
- the angular distribution of the light intensity in the transparent substrate 14 after passing through the internal light extraction layer 15 was calculated.
- the calculation results are shown in FIG.
- the refractive index of the transparent substrate 14 is 1.51
- the refractive index of the low refractive index layer 15a is 1.45
- the refractive index of the high refractive index layer 15b is 1.76
- the uneven structure is a random structure.
- the light intensity distribution with respect to the incident angle in the transparent substrate 14 was calculated when the distance from the light emitting layer 12 to the surface of the reflective electrode 11 was in the range of 50 to 290 nm.
- the total amount of light included in each of the incident angles of 0 to 20 °, 20 to 40 °, and 40 to 60 ° is plotted against the distance between the light emitting point and the surface of the reflective electrode 11. Is shown in FIG. From the result, it can be seen that the total amount of light in the angle range of 40 to 60 ° is the largest in the element whose distance from the surface of the reflective electrode 11 to the light emitting point is 100 nm or more. Therefore, high efficiency can be obtained by combining such a light emitting element 110 with the external light extraction layer 16 having high transmittance of light incident at an incident angle of 40 degrees to 60 degrees.
- the light emitting element 110 in said embodiment light-emits by organic EL
- the configuration of the light emitting element 110 is arbitrary.
- the light-emitting device of the present disclosure can be applied to, for example, a flat panel display, a backlight for a liquid crystal display device, a light source for illumination, and the like. Further, the light extraction sheet of the present disclosure can be applied to the above light emitting device.
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Abstract
Description
以下、より具体的な実施の形態を説明する。本実施の形態では、一例として、有機EL素子を用いた発光装置を説明する。
図1は、本実施の形態における有機EL素子100の概略構成を示す断面図である。本実施の形態の有機EL素子100は、発光素子110と、発光素子110から生じた光を透過させる光取り出しシート120とを備える。発光素子110は、光反射性を有する反射電極11と、光透過性を有する透明電極13と、これらの間に形成された有機発光層12とを有している。光取り出しシート120は、透明基板14と、透明基板14の第1の主面側(図1における下側)に設けられた内部光取り出し層15と、透明基板14の第2の主面側(図1における上側)に設けられた外部光取り出し層16とを有している。図1に示すように、反射電極11、有機発光層12、透明電極13、内部光取り出し層15、透明基板14、外部光取り出し層16は、この順に積層されている。内部光取り出し層15は、相対的に屈折率の低い低屈折率層15aと、相対的に屈折率の高い高屈折率層15bとを含む。低屈折率層15aと高屈折率層15bとの界面は、凹凸形状を有しており、入射した光を回折させるように構成されている。
以下、有機EL素子100の各構成要素の詳細および本実施形態の構成に至るまでの分析結果を説明する。
発光層12で発生した光は、透明電極13、内部光取り出し層15、透明基板14を通過した後、外部光取り出し層16に到達する。外部光取り出し層16は、透明基板14を直接加工することで形成してもよいが、光取り出し構造が設けられたフィルムを貼ることによって形成することもできる。
しかしながら、このような考えで外部光取り出し層16への光の入射方向を調整するためには、そもそも外部光取り出し層16へ光がどのような角度分布で入射するかを明らかにする必要がある。そこで、本発明者らは、図7に示すような構成で光の角度分布の測定を行った。図7に示す構成は、図1の有機EL素子100の外部光取り出し層16の代わりに、有機EL素子100よりも十分大きい半球のレンズを貼り付けた構成である。ここで、半球レンズの屈折率は、透明基板14の屈折率とほぼ同一である。このような構成により、透明基板14から半球レンズを介して空気層まで光が屈折することなく取り出されるので、透明基板14から出射する光の角度分布の測定が可能となる。なお、光の分布測定には分光放射計を用い、発光層12における十分小さい領域の光のスポットからの光を受光するように配置した。
[2-3-1.低屈折率層15aの構成の検討]
そこで、本発明者らは、内部光取り出し層15の構成に工夫を加えることにより、透明基板14から出射する光の強度がピークとなる入射角度をシフトさせることを検討した。具体的には、低屈折率層15aとして、透明基板14に用いられる材料よりも低屈折率の材料を用いることにより、透明基板14への入射角度をシフトさせることを検討した。このような構成にすれば、図10に示すように、低屈折率層15aから透明基板14に光が伝播する際に、屈折により光が曲げられ、より低い入射角で外部光取り出し層16に入射するようにできる。この屈折による光の角度の変化はスネルの法則により決まる。透明基板14の屈折率をn1、低屈折率層15aの屈折率をn2、屈折角をθ1、入射角をθ2とすれば、スネルの法則は、n1sinθ1=n2sinθ2で表される。
上記と同様の計算により、高屈折率層15bの屈折率に対する光取り出し効率の依存性を求めた。また、高屈折率層15bの屈折率の異なる2種類の素子を作製し、それらの光取り出し効率を計測する実験を行った。それらの結果を図15に示す。図15のグラフにおいて、横軸は高屈折率層15bの屈折率、縦軸は光取り出し効率を表している。破線は計算結果を表し、四角形のマーカーは実験結果を表している。この計算では、低屈折率層15aの屈折率を1.45に設定し、その他の計算条件は図14の計算における条件と同じである。一方、実験については、図12に示す実験で用いた低屈折率層15aの屈折率が1.45、外部光取り出し層16がマイクロレンズアレイのものと同様の構成で、高屈折率層15bの屈折率を1.75、1.80と変えた2種類の素子を使用した。図15に示されているように、高屈折率層15bの屈折率が高いほど、光取り出し効率が大きくなることがわかった。
低屈折率層15aと高屈折率層15bとの境界における凹凸構造は、例えば低屈折率層15a上に凹凸形状を形成した後、高屈折率の材料で凹凸を埋め込むことによって形成することができる。その後、透明電極13、有機発光層12、反射電極11を形成するが、もし高屈折率層15bの表面の平坦性が悪いと、透明電極13-反射電極11間でショートが起きやすくなる。その場合、素子が光らなくなる可能性があり、製造時の歩留まりが悪くなるおそれがある。よって、本実施形態では、凹凸形状の高さをできるだけ低くし、高屈折率層15bの埋め込み後の平坦性を確保できる構成を採用する。また、このように凹凸構造の高さを低くすることにより、低屈折率層15aや高屈折率層15bの材料の使用量も抑えることができるため、低コスト化にもつながる。
高屈折率層15bの屈折率を上記のように1.73以上に設定する場合、高屈折率層15bに用いる材料として、例えばITO(酸化インジウム錫)、TiO2(酸化チタン)、SiN(窒化シリコン)、Ta2O5(五酸化タンタル)、ZrO2(ジルコニア)などの比較的高い屈折率の無機材料または高屈折率樹脂などを使用することができる。
上述のように、本実施形態では、図5A、5Bに示すようなマイクロレンズアレイを外部光取り出し層16として用いている。図5Aに示す蜂の巣状の配列を採用することにより、最密充填の構造となるため、光取り出し効率が最も高くなる。この配列において、各マイクロレンズの球の飛び出し量(高さh)を変化させたときの入射角40度~60度の入射光の透過率の変化を図16に示す。図16のグラフにおいて、横軸はアスペクト比(=高さh/球の半径r)、縦軸は40度~60度の入射角の光の平均透過率を表している。アスペクト比が高いほど平均透過率が高くなり、アスペクト比が1の構造(半球が並んでいる構造)が最も透過率が高くなることがわかる。なお、破線で示した透過率(=42%)は、図6Bに示した拡散系のフィルムに入射角40度~60度で入射する光の平均透過率の値である。図16の結果から、透過率42%を越えるのは、アスペクト比が0.5以上の場合であることがわかる。
[3-1.外部光取り出し層16の変形例]
外部光取り出し層16について、本実施の形態ではマイクロレンズアレイを例に挙げて説明した。本実施形態におけるマイクロレンズアレイは、入射角が40度~60度の範囲の光に対して透過率のピークを有する。このため、マイクロレンズアレイと比較的低い屈折率を有する低屈折率層15aを含む内部光取り出し層15とを組み合わせることにより、その他の構成に比べて効率を高めることができる。この効果は、マイクロレンズアレイに限らず、40度~60度の入射角で入射する光の透過率がピークになるように構成された外部光取り出し層16であれば同様に実現することができる。そこで、以下、外部光取り出し層16の変形例を説明する。
続いて、凹凸構造の変形例を説明する。
次に、発光素子110の変形例を説明する。図32に示すように、有機EL素子100の高屈折率層15b上に高屈折率の半球レンズを配置することにより、発光層12の発光強度の角度分布の測定を行った。ここで、発光波長が580nmの発光層12を積層した3種類の有機EL素子を試作した。それらの素子の発光点の位置は、反射電極11の表面からそれぞれ70,90,290nmの位置に設定した。高屈折率層15bおよび高屈折率半球レンズの屈折率は1.77とした。また、比較のために、シミュレーションも行った。反射電極11の表面からの距離がそれぞれ50,70,90,120,160,200,240,290nmの位置に、発光波長580nmの発光点があるモデルで計算を行った。測定結果及び計算結果を図33Aおよび図33Bに示す。ここで、反射電極11の表面からの距離が160nm以下の場合の結果を図33Aに示し、当該距離が200nm以上の場合の結果を図33Bに示している。実験結果と測定結果がよく合っている。
12 発光層
13 透明電極
14 透明基板
15 内部光取り出し層
15a 低屈折率層
15b 高屈折率層
16 外部光取り出し層
100 有機EL素子
110 発光素子
120 光取り出しシート
Claims (20)
- 平均波長λの光を発生する発光素子と、
前記発光素子から生じた光を透過させる光取り出しシートと、
を備える発光装置であって、
前記発光素子は、
光透過性を有する第1の電極と、
第2の電極と、
前記第1および第2の電極の間に設けられた発光層と、
を有し、
前記光取り出しシートは、
第1の主面および第2の主面を有する透光性基板と、
前記透光性基板の前記第1の主面の側に設けられた第1の光取り出し構造であって、前記透光性基板よりも屈折率の低い低屈折率層、および前記低屈折率層よりも屈折率の高い高屈折率層を有し、前記低屈折率層は前記透光性基板および前記高屈折率層の間に形成されており、前記高屈折率層および前記低屈折率層の界面は凹凸形状を有している第1の光取り出し構造と、
前記透光性基板の前記第2の主面の側に設けられた第2の光取り出し構造であって、前記透光性基板を透過して40度から60度の入射角で入射する光の平均透過率が42%以上になるように構成された第2の光取り出し構造と、
を有する、発光装置。 - 前記凹凸形状は、複数の凹部と複数の凸部とが2次元的にランダムに配列された形状である、請求項1に記載の発光装置。
- 前記凹凸構造は、複数の凹部と複数の凸部とが2次元的に周期的に配列された構造である、請求項1に記載の発光装置。
- 前記凹凸形状は、複数の凹部と複数の凸部とが2次元的に配列された形状であり、前記複数の凹部および前記複数の凸部の各々に内接する楕円の短辺の長さの最小値をwとするとき、前記凹凸形状のパターンの空間周波数成分のうち、1/(2w)よりも小さい成分が、前記複数の凹部および前記複数の凸部をランダムに並べた場合と比較して抑制されている、請求項1に記載の発光装置。
- 前記凹凸形状は、予め定められた個数以上の凹部または凸部が1つの方向に連続しないように構成されている、請求項4に記載の発光装置。
- 前記複数の凹部および前記複数の凸部の各々は、四角形状の断面を有し、前記凹凸形状は、3つ以上の凹部または凸部が1つの方向に連続しないように構成されている、請求項5に記載の発光装置。
- 前記複数の凹部および前記複数の凸部の各々は、六角形状の断面を有し、前記凹凸形状は、4つ以上の凹部または凸部が1つの方向に連続しないように構成されている、請求項5に記載の発光装置。
- 前記複数の凹部および前記複数の凸部の各々に内接する楕円の短辺の長さの最小値は、0.73λ以上である、請求項2から7のいずれかに記載の発光装置。
- 前記複数の凹部および前記複数の凸部の各々は、同一の断面形状および同一のサイズを有している、請求項2から8のいずれかに記載の発光装置。
- 前記複数の凹部および前記複数の凸部の各々の平均周期は14.5λ以下である、請求項9に記載の発光装置。
- 前記低屈折率層の屈折率は、前記透光性基板の屈折率の0.98倍以下である、請求項1から10のいずれかに記載の発光装置。
- 前記発光層における発光点と前記第2の電極の表面との距離は、0.17λ以上である、請求項1から11のいずれかに記載の発光装置。
- 前記低屈折率層の屈折率は、1.47以下である、請求項1から12のいずれかに記載の発光装置。
- 前記低屈折率層の厚さは(1/2)λ以上である、請求項1から13のいずれかに記載の発光装置。
- 前記透光性基板の屈折率は、1.5以上である、請求項1から14のいずれかに記載の発光装置。
- 前記高屈折率層の屈折率は、1.73以上である、請求項1から15のいずれかに記載の発光装置。
- 前記第2の光取り出し構造はマイクロレンズアレイによって形成されている、請求項1から16のいずれかに記載の発光装置。
- 前記マイクロレンズアレイのアスペクト比は0.5以上である、請求項17に記載の発光装置。
- 前記第2の光取り出し構造はピラミッド構造を有し、前記ピラミッド構造の頂角は30度から120度の範囲に設定されている、請求項1から18のいずれかに記載の発光装置。
- 第1の主面および第2の主面を有する透光性基板と、
前記透光性基板の前記第1の主面の側に設けられた第1の光取り出し構造であって、前記透光性基板よりも屈折率の低い低屈折率層、および前記低屈折率層よりも屈折率の高い高屈折率層を有し、前記低屈折率層は前記透光性基板および前記高屈折率層の間に形成されており、前記高屈折率層および前記低屈折率層の界面は凹凸形状を有している第1の光取り出し構造と、
前記透光性基板の前記第2の主面の側に設けられた第2の光取り出し構造であって、前記透光性基板を透過して40度から60度の入射角で入射する光の平均透過率が42%以上になるように構成された第2の光取り出し構造と、
を備える光取り出しシート。
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CN (1) | CN105027671B (ja) |
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US20220197041A1 (en) * | 2019-05-14 | 2022-06-23 | Osram Opto Semiconductors Gmbh | Illumination unit, method for producing an illumination unit, converter element for an optoelectronic component, radiation source inlcuding an led and a converter element, outcoupling structure, and optoelectronic device |
JP7349393B2 (ja) * | 2020-03-10 | 2023-09-22 | シャープ福山レーザー株式会社 | 画像表示素子 |
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CN114335389B (zh) * | 2021-12-30 | 2024-01-26 | 湖北长江新型显示产业创新中心有限公司 | 显示面板及显示装置 |
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Also Published As
Publication number | Publication date |
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US9595648B2 (en) | 2017-03-14 |
JPWO2014167758A1 (ja) | 2017-02-16 |
EP2986082A4 (en) | 2016-05-11 |
KR20150141955A (ko) | 2015-12-21 |
US20160049562A1 (en) | 2016-02-18 |
EP2986082A1 (en) | 2016-02-17 |
JP6471905B2 (ja) | 2019-02-20 |
CN105027671B (zh) | 2017-09-22 |
CN105027671A (zh) | 2015-11-04 |
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