Light-emitting element, display device, and method for manufacturing light-emitting element

Abstract

The present invention comprises: a first electrode (E1) and a second electrode (E2); a light-emitting layer (EM) that is located between the first electrode and the second electrode; and a functional layer (F) that is located between the first electrode and the light-emitting layer. At least one of the first electrode (E1) and the functional layer (F) includes grain boundaries and is a light-reflecting member having an average roughness of 3-20nm on the surface thereof on the light-emitting layer (EM) side.

Description

[Technical Field]

[0001] The present invention relates to a light-emitting element, a display device, and a method for manufacturing a light-emitting element. [Background technology]

[0002] The organic light-emitting component disclosed in Patent Document 1 includes a semitransparent first electrode and a diffusely reflecting second electrode, the second electrode including an electrode layer including a number of crystals with boundaries for diffuse reflection. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US 2017 / 0047552 (released February 16, 2017) [Non-patent literature]

[0004] [Non-Patent Document 1] "High Rate Thick Film Growth" (Ann.Rev.Mater.Sci.,7(1997)239.) Summary of the Invention [Problem to be solved by the invention]

[0005] The conventional technology has a problem in that the light extraction efficiency from the light emitting element is low. [Means for solving the problem]

[0006] A light-emitting element according to one embodiment of the present disclosure comprises a first electrode and a second electrode, a light-emitting layer located between the first electrode and the second electrode, and a functional layer located between the first electrode and the light-emitting layer, wherein at least one of the first electrode and the functional layer has grain boundaries and is a light-reflecting portion having an average roughness of 3 nm to 20 nm on the surface facing the light-emitting layer. [Effects of the Invention]

[0007] According to one aspect of the present disclosure, the light extraction efficiency from the light-emitting element is improved. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing an example of the configuration of a light-emitting element according to Embodiment 1. FIG. [Figure 2] 3 is a cross-sectional view showing an example of the configuration of a reflecting section according to the first embodiment. FIG. [Figure 3] 3 is a cross-sectional view showing an example of the configuration of a reflecting section according to the first embodiment. FIG. [Figure 4] 3 is a cross-sectional view showing an example of the configuration of a reflecting section according to the first embodiment. FIG. [Figure 5] 1 is a photograph of a cross section of the light-emitting device according to the first embodiment. [Figure 6] 1 is a flowchart illustrating an example of a method for manufacturing a light-emitting element according to an embodiment. [Figure 7] This is a diagram quoting Thornton's zone model showing the structural changes in a sputtered thin film. [Figure 8] FIG. 2 is a diagram showing current-voltage (JV) characteristics of the light-emitting element according to the first embodiment and a light-emitting element according to a comparative example. [Figure 9] FIG. 10 is a diagram showing current-luminance (JL) characteristics of the light-emitting element according to the first embodiment and a light-emitting element according to a comparative example. [Figure 10] FIG. 2 is a diagram showing current luminous efficiency (J-EQE) characteristics of the light emitting device according to the first embodiment and a light emitting device according to a comparative example. [Figure 11] 10A and 10B are schematic diagrams illustrating light extraction from a light-emitting element according to a comparative example. [Figure 12] 1 is a schematic diagram showing light extraction from the light-emitting device according to Embodiment 1. FIG. [Figure 13] FIG. 10 is a cross-sectional view showing an example of the configuration of a light-emitting element according to a second embodiment. [Figure 14] FIG. 10 is a cross-sectional view showing an example of the configuration of a light-emitting element according to a second embodiment. [Figure 15] FIG. 10 is a cross-sectional view showing an example of the configuration of a light-emitting element according to a second embodiment. [Figure 16] FIG. 10 is a cross-sectional view showing an example of the configuration of a light-emitting element according to a third embodiment. [Figure 17] FIG. 10 is a plan view showing a configuration example of a display device according to a fourth embodiment. [Figure 18] FIG. 10 is a cross-sectional view showing an example of the configuration of a display device according to a fourth embodiment. [Figure 19] FIG. 10 is a cross-sectional view showing an example of the configuration of a display device according to a fourth embodiment. [Figure 20] FIG. 10 is a cross-sectional view showing an example of the configuration of a display device according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Embodiment 1] FIG. 1 is a cross-sectional view showing an example of the configuration of a light-emitting element according to an embodiment of the present disclosure. As shown in FIG. 1, the light-emitting element 10 may include a first electrode E1, a hole injection layer HJ, a hole transport layer HT, an emitting layer EM, an electron transport layer ET, and a second electrode E2, in this order. The light-emitting element 10 may be provided on a substrate BP and may be covered with a sealing film SL that prevents the intrusion of water, oxygen, and the like. The first electrode E1 may be an anode, and the second electrode E2 may be a cathode. The hole injection layer HJ and the hole transport layer HT may each be referred to as a functional layer F. The light-emitting element 10 may be a top-emission type in which the second electrode E2 is a translucent electrode.

[0010] The hole injection layer HJ may contain a hole transport material having a higher electrical resistivity than polyethylenedioxythiophene doped with polystyrene sulfonate (PEDOT:PSS). 6The hole transport material may have a resistivity of Ωcm or more. Examples include materials containing one or more selected from the group consisting of oxides, nitrides, and carbides containing one or more of Zn, Cr, Ni, Ti, Nb, Al, Si, Mg, Ta, Hf, Zr, Y, La, Sr, and W. Among these, inorganic hole transport materials are preferably oxides containing one or more of Zn, Cr, Ni, Ti, Nb, Al, Si, Mg, Ta, Hf, Zr, Y, La, and Sr, and more preferably at least one selected from NiO, MgO, MgNiO, LaNiO, CuO, and CuO. Furthermore, suitable hole transport materials include materials such as CuSCN in which a CN group, an SCN group, and a SeCN group are bonded to a metal.

[0011] The hole transport layer HT may comprise an organic hole transport material having an electrical resistivity higher than that of polystyrene sulfonate-doped polyethylenedioxythiophene (PEDOT:PSS). 6 The organic hole transport material may include an organic hole transport material having a resistivity of Ωcm or more. The organic hole transport material may be appropriately selected from materials commonly used in the field, such as 4,4',4''-tris(9-carbazolyl)triphenylamine (TCTA), 4,4'-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (NPB), zinc phthalocyanine (ZnPC), di[4-(N,N-ditolylamino)phenyl]cyclohexane (TAPC), 4,4'-bis(carbazol-9-yl)biphenyl (CBP), 2,3,6,7,10,11-hexacyano-1 Examples of suitable materials include 4,5,8,9,12-hexaazatriphenylene (HATCN), poly(N-vinylcarbazole) (PVK), poly(2,7-(9,9-di-n-octylfluorene)-(1,4-phenylene-((4-sec-butylphenyl)imino)-1,4-phenylene) (TFB), and poly(triphenylamine) derivatives (Poly-TPD). Among these, tetracyano compounds such as TFB, carbazole derivatives such as PVK, and triarylamine derivatives such as Poly-TPD are preferred.

[0012] 2 is a cross-sectional view showing an example of the configuration of the reflective section according to the first embodiment. As shown in FIG. 2, the first electrode E1 is a light-reflective section 3 having grain boundaries B and a surface S on the side of the light-emitting layer EM with an average roughness of 3 nm to 20 nm. The average roughness of the surface S may be 10 nm to 20 nm. In this way, the hole injection layer HJ bites into the irregularities of the surface S, and the adhesive strength between the first electrode E1 and the hole injection layer HJ increases due to an anchor effect. This makes it difficult for the hole injection layer HJ to peel off from the first electrode E1.

[0013] The light reflecting portion 3 includes a plurality of crystal grains C that form grain boundaries B. The crystal grains C may be crystals, which are components of a polycrystal, or may be nanoparticles. The average size of the crystal grains C may be 1 / 10 or less of the emission peak wavelength of the light emitting layer EM so as to cause Rayleigh scattering. A plurality of pits P may be formed on the surface S of the light reflecting portion 3. The pits P are portions where the grain boundaries B are exposed on the surface S and the surface S is recessed.

[0014] The pits P preferably increase the adhesive strength between the first electrode E1 and the hole injection layer HJ without deteriorating the electrical and light-emitting characteristics of the light-emitting element 10. The average depth of the pits P is preferably 3.0 to 50 nm. If the average depth of the pits P is less than 3.0 nm, the anchor effect will be reduced. If the average depth of the pits P is more than 50 nm, the electrical connectivity between the first electrode E1 and the hole injection layer HJ may be deteriorated.

[0015] The average pit distance (average value of the distances PT between adjacent pits) among the pits P may be 3 nm to 50 nm. The average pit distance may be equal to or greater than the average size of the crystal grains. If the average pit distance is less than 3 nm or less than the average size of the crystal grains C, the electrical connectivity between the first electrode E1 and the hole injection layer HJ may be deteriorated. If the average pit distance is more than 50 nm or greater than the average size of the crystal grains C, the anchor effect is low.

[0016] Because the first electrode E1 and the hole injection layer HJ are not soluble in each other, the adhesive strength between them depends on resistive adhesion due to the anchor effect. The pits P increase the area of ​​the surface S, enhancing the anchor effect. The configuration according to the present disclosure prevents peeling by improving adhesive strength, thereby improving the manufacturing yield of the light-emitting element 10. In conventional technology, resistive adhesion is weaker than welding, so there was a risk of the hole injection layer HJ peeling from the first electrode E1. Delamination leads to element destruction and reduces manufacturing yield.

[0017] On the other hand, if the roughness of the surface S is too large, the arrangement of the quantum dots will deteriorate in the light-emitting layer EM above the first electrode E1 (light-reflecting portion 3). The deterioration of the arrangement of the quantum dots will cause a decrease in carrier injection into the quantum dots, causing a deterioration in the electrical and light-emitting characteristics of the light-emitting element 10. The area and average roughness of the surface S are approximately inversely proportional to the average pit-to-pit distance, provided that the average depth of the pits P is constant. When the average pit-to-pit distance is 5 nm or more, the average roughness of the surface S is preferably 20 nm or less. When the average pit-to-pit distance is 20 nm or less, the average roughness of the surface S is preferably 5 nm or more. The product of the average pit-to-pit distance and the average roughness is 30 nm. 2 ~150nm 2 is preferred.

[0018] The average pit distance may be correlated to the average roughness of the surface S and the average depth of the pits P. For example, the average pit distance may be equal to or less than the greater of the average roughness of the surface S and the average depth of the pits P. For example, the average pit distance may be equal to or less than the geometric mean of the average roughness of the surface S and the average depth of the pits P.

[0019] The grain boundary B may be a crystal mismatch plane where at least one of the crystal lattice and the crystal orientation of the crystal grains C differs. In this case, light is scattered at the grain boundary B. The grain boundary B may be an internal fracture surface of the first electrode E1 (light reflecting portion 3). In this case, light is scattered at the grain boundary B.

[0020] 3 and 4 are cross-sectional views showing exemplary configurations of the reflective section according to the first embodiment. As shown in FIG. 3, the first electrode E1 may be accompanied by a lower conductive layer ES. For example, if the first electrode E1 is made of a light-transmitting metal film containing indium zinc oxide (InZnO) or indium gallium zinc oxide (InGaZnO), a conductive layer ES having higher light reflectivity than the first electrode E1 may be located below the first electrode E1. The conductive layer ES may have a lower work function than the first electrode E1 and may be composed of, for example, a light-reflective metal film containing aluminum (Al) or silver (Ag). As shown in FIG. 4, the first electrode E1 may be accompanied by an upper conductive layer EU. For example, if the first electrode E1 is made of a light-reflective metal film containing Al or Ag, a conductive layer EU having a higher work function than the first electrode E1 may be located above the first electrode E1. The conductive layer EU may have high optical transparency and may be made of an optically transparent metal film containing, for example, InZnO or InGaZnO.

[0021] The average roughness of the surface S, the average depth of the pits P, and the average size of the crystal grains C can be obtained from a micrograph of the cross section of the first electrode E1 (light reflecting portion 3). For simplicity of explanation, this section will explain an example of an image of the first electrode E1 taken with a transmission electron microscope (TEM).

[0022] FIG. 5 is a cross-sectional image of a light-emitting device according to this embodiment. As shown in FIG. 5, grain boundaries B and crystal grains C of the first electrode E1 can be seen. Here, the micrograph captures an area 500 nm or more wide in an in-plane direction (x or y direction) perpendicular to the thickness direction. First, multiple measurement points are defined on the surface S of the first electrode E1, and the position of each measurement point in the thickness direction (z direction) is measured. At least 20 measurement points may be defined per 100 nm width. The measurement points are defined at equal intervals. When a range 500 nm or wider is captured, at least 100 measurement points are defined in the imaging area, and the measurement points are defined at equal intervals. The average position of all measurement points in the thickness direction is then calculated, and the arithmetic mean value of the differences (absolute values) between the average position and the position in the thickness direction for all measurement points is defined as the average roughness of the surface S.

[0023] Next, grain boundaries B are extracted from the micrograph. This extraction may be performed by human visual inspection, by AI or computer image processing, or a combination of the two. For example, a human may specify the range of the first electrode E1 in the micrograph, and a computer may extract positions with a high contrast ratio between adjacent pixels from the specified range. Each region separated by grain boundaries B may then be treated as a cross-section of a crystal grain C. For each crystal grain C, the distance between opposing grain boundaries B in two or more directions may be measured, and the arithmetic mean value of the distances may be used as the size of the crystal grain C. The cross-sectional area of ​​each crystal grain C may be measured, and the diameter of a circle having the same area as the cross-sectional area may be used as the size of the crystal grain C. The arithmetic mean value of the sizes of multiple crystal grains C may be used as the average size of the crystal grains C. For each crystal grain C, the distance between opposing grain boundaries B in the layer thickness direction (z direction) may be measured, and the arithmetic mean value may be used as the average thickness of the crystal grain C. For each crystal grain C, the distance between opposing grain boundaries B in the in-plane directions (x direction and y direction) may be measured, and the arithmetic mean value may be used as the average width of the crystal grain C. The grain C to be measured has a cross-sectional area of ​​5000 nm 2 The number of crystal grains C is 100 or more per crystal grain. Hereinafter, the grain size, thickness, and width of the crystal grains C are collectively referred to as the size of the crystal grains C. The average size of the crystal grains C may be any of the average grain size, average thickness, and average width of the crystal grains C.

[0024] Next, pits P are extracted from the micrograph. This extraction may be performed by human visual inspection, image processing using AI or a computer, or a combination thereof. For example, first, the location where the surface S intersects with the grain boundary B is defined as a pit P. Alternatively, for example, a location where a grain boundary B is observed on the surface S within a range lower than the average position in the thickness direction of the surface S may be defined as a pit P. Then, the distance from the lowest position of each pit P in the thickness direction (z direction) to the average position in the thickness direction of the surface S is measured, and the arithmetic mean value of this distance is defined as the average depth of the pit P. Furthermore, the distance in the in-plane direction (x direction or y direction) between the lowest positions in the thickness direction of adjacent pits P is measured, and the average of these distances is defined as the average inter-pit distance. Among the locations defined as pit P, locations where an upper layer (e.g., a hole injection layer HJ) penetrates into the pit P and the material of the upper layer is observed within the pit P may be considered valid pit P. Then, the average depth and average inter-pit distance of the valid pit P may be calculated. Here, the number of pits P to be measured is 30 or more per 500 nm width.

[0025] (Manufacturing method) 6 is a flowchart illustrating an example of a method for manufacturing a light-emitting device according to this embodiment. As shown in FIG. 6, a substrate BP is prepared (Step S1), and a first electrode E1 (light-reflecting portion) is formed on the substrate BP (Step S2). Then, a hole injection layer HJ is formed on the first electrode E1 (Step S3), a hole transport layer HT is formed on the hole injection layer HJ (Step S4), an emitting layer EM is formed on the hole transport layer HT (Step S5), an electron transport layer ETL is formed on the emitting layer EM (Step S6), and a second electrode E2 is formed on the electron transport layer ETL (Step S7). Then, a sealing film SL is formed to cover the light-emitting element 10 (Step S8). The hole injection layer HJ and the hole transport layer HT can be formed using a hole transport layer material.

[0026] In step S2, the first electrode E1 is made into a light reflecting portion 3 having grain boundaries B and an average roughness of the surface S on the light emitting layer EM side of 3 nm to 20 nm. Various methods for forming a polycrystalline body can be applied to form the first electrode E1.

[0027] Figure 7 is a diagram quoting Thornton's zone model showing the structural changes of a sputtered thin film, taken from the paper "High Rate Thick Film Growth" by J.A. Thornton (Ann. Rev. Mater. Sci., 7 (1997) 239.) As shown in Figure 7, under the condition of low argon gas pressure in Zone 3, grain boundaries are generated inside the sputtered thin film, and the surface of the sputtered thin film is relatively flat and has fine pits.

[0028] For example, the first electrode E1 can be formed by sputtering under conditions where the argon gas pressure in zone 3 is low. Specifically, the first electrode E1 can be formed under conditions where the temperature (T) of the substrate BP is 80% or higher, in absolute temperature, than the melting point (Tm) of the first electrode E1 and the argon gas pressure is 20 mTorr or lower. Here, Torr is a unit of pressure, and 1 Torr = 133.32 Pa. Suitable materials (electrode materials) for the first electrode E1 include Al (aluminum), Ag (silver), and alloys thereof.

[0029] The first electrode E1 may be formed by sputtering under the following conditions: a glass substrate is used as the substrate BP, the temperature of the substrate BP is increased to a high temperature of about 200 degrees Celsius (i.e., 473K), argon gas is introduced into a chamber, and the pressure of the argon gas in the chamber is reduced to a low pressure of about 1 Pa or less. As a result, the average size of the crystal grains C in the first electrode E1 is 3 nm to 50 nm, and at the same time, pits P with an average depth of 3 nm to 50 nm are formed on the surface S of the first electrode E1. Here, the argon gas supply amount V Ar and the ratio V to the total supply of gases other than argon gas V ArThe product of argon gas pressure (V) and the pressure inside the chamber measured by a pressure gauge is the pressure of the argon gas. Gases other than argon gas, such as nitrogen and oxygen, may be supplied. For example, the average size of the crystal grains C may be within the range of 3 nm to 15 nm, 3 nm to 20 nm, 3 nm to 30 nm, 3 nm to 40 nm, 3 nm to 50 nm, 10 nm to 15 nm, 10 nm to 20 nm, 10 nm to 30 nm, 10 nm to 40 nm, or 10 nm to 50 nm. Here, the pits P are formed at the intersections where the surfaces S and the grain boundaries B intersect. The average depth of the pits P may be less than the average size of the crystal grains C. For example, the average depth of the pits P may be within the range of 3 nm to 15 nm, 3 nm to 20 nm, 3 nm to 30 nm, 3 nm to 40 nm, 3 nm to 50 nm, 10 nm to 15 nm, 10 nm to 20 nm, 10 nm to 30 nm, 10 nm to 40 nm, or 10 nm to 50 nm. According to Thornton's zone model, the size of the crystal grains C and the depth of the pits P can be controlled. By setting the argon gas pressure on the order of 10 Pa to 100 Pa, the average size of the crystal grains C can be reduced. Furthermore, by fixing the pressure and lowering the temperature of the substrate BP, columnar (or near-columnar) crystal grains C extending in the thickness direction of the first electrode E1 can be formed. Here, "on the order of 10 Pa to 100 Pa" refers to a pressure in units of 10 Pa or 100 Pa, i.e., a pressure of 10 Pa or greater but less than 1000 Pa.

[0030] For example, the first electrode E1 can be formed by sintering powder or by combining printing with an ink containing nanoparticles and heat treatment. Alternatively or additionally, various methods for generating internal fractures can be applied to form the first electrode E1. For example, a sudden temperature change can be applied to the first electrode E1, causing internal stress to generate internal fractures in the first electrode E1. The average size of the crystal grains C can be affected by the mechanical properties, such as elasticity and brittleness, of the material of the first electrode E1. The harder the material of the first electrode E1, the more likely the first electrode E1 is to crack and the smaller the crystal grains C.

[0031] Fig. 8 is a diagram showing current-voltage (JV) characteristics of the light-emitting element according to embodiment 1 and a light-emitting element according to a comparative example. Fig. 9 is a diagram showing current-luminance (JL) characteristics of the light-emitting element according to embodiment 1 and a light-emitting element according to a comparative example. Fig. 10 is a diagram showing current-luminous efficiency (J-EQE) characteristics of the light-emitting element according to embodiment 1 and a light-emitting element according to a comparative example. In each diagram, the measured values ​​according to embodiment 1 are shown by solid lines, and the measured values ​​according to the comparative example are shown by dashed lines.

[0032] The first electrode E1 according to the first embodiment was formed by sputtering under low gas pressure conditions in zone 3 (see FIG. 7). On the other hand, the first electrode EA according to the first embodiment was formed by vacuum deposition. The materials and thicknesses of the other layers were the same between the first embodiment and the comparative example.

[0033] As shown in Fig. 8, the voltage to current is smaller in the first embodiment than in the comparative example. Therefore, the first electrode E1 is the light-reflecting portion 3, which reduces the electrical resistance of the light-emitting element 10 according to the first embodiment. This is presumably because the improved mechanical adhesion between the first electrode E1 and the hole injection layer HJ improves the electrical connection, thereby improving the hole injection efficiency. Additionally, or alternatively, it is presumed that the electric field concentration in the pits P improves the hole injection efficiency.

[0034] As shown in Fig. 9, the luminance relative to the current is higher in the first embodiment than in the comparative example. Furthermore, as shown in Fig. 10, the external quantum efficiency (EQE) is higher in the first embodiment than in the comparative example. This is presumably because the grain boundaries B of the first electrode E1 (light reflecting portion 3) scatter and reflect light, improving the light extraction efficiency from the light emitting element 10.

[0035] FIG. 11 is a diagram showing light extraction from a light-emitting device according to a comparative example. FIG. 12 is a diagram showing light extraction from a light-emitting device according to embodiment 1. For simplicity of explanation, a configuration in which the upper electrode is in contact with the atmosphere will be described. As shown in FIG. 11, in the light-emitting device according to the comparative example, light is emitted obliquely from the light-emitting layer (at a large angle relative to the normal), and the light reflected by the lower electrode EA is incident on the upper electrode EC at a large incident angle and is totally reflected. If a typical critical angle is 15°, only light that enters a cone with a tip angle of 30° can be extracted from the light-emitting device, and the theoretical limit of light extraction efficiency is 25%.

[0036] 12, in the light-emitting element 10 according to embodiment 1, light emitted obliquely (at a large angle relative to the normal) from the light-emitting layer EM is more likely to enter the second electrode E2 at a smaller angle of incidence than in the comparative example due to the optical properties (at least one of light scattering and diffuse reflection) of the first electrode E1 (light-reflecting portion 3), and is more likely to exit to the outside. Therefore, in embodiment 1, the light extraction efficiency is higher than in the comparative example.

[0037] To improve the light extraction efficiency, the scattering by the light reflecting portion 3 is preferably Rayleigh scattering. While Mie scattering strongly scatters incident light in the direction of travel, Rayleigh scattering scatters light isotropically. A condition for Rayleigh scattering is that the size of the crystal grains C is 1 / 10 or less of the wavelength of the incident light. Therefore, the average size of the crystal grains C is preferably 1 / 10 or less of the emission peak wavelength of the light-emitting layer EM. The average size of the crystal grains C may be the average particle size, average thickness, or average width.

[0038] [Embodiment 2] 13 to 15 are cross-sectional views showing examples of the configuration of a light-emitting device according to embodiment 2. As shown in FIG. 13, the hole injection layer HJ (functional layer F) may be a light-reflecting portion 3 having grain boundaries B and a surface S on the light-emitting layer EM side having an average roughness of 3 nm to 20 nm. As shown in FIG. 14, the hole transport layer HT (functional layer F) may be a light-reflecting portion 3 having grain boundaries B and a surface S on the light-emitting layer EM side having an average roughness of 3 nm to 20 nm. As shown in FIG. 15, the hole injection layer HJ (functional layer F) and the hole transport layer HT (functional layer F) may each be a light-reflecting portion 3 having grain boundaries B and a surface S on the light-emitting layer EM side having an average roughness of 3 nm to 20 nm. When the light-reflecting portion 3 is formed of, for example, an organic hole-transporting material, the grain boundaries B of the light-reflecting portion 3 may be an internal fracture surface of the organic layer.

[0039] In embodiment 2, the light reflecting portion 3 is located between the first electrode E1 and the light emitting layer EM, and therefore, the same effects as in embodiment 1 are achieved. At least one of the hole injection layer HJ (light reflecting portion 3) and the hole transport layer HT (light reflecting portion 3) may be a layer containing metal oxide nanoparticles (coating layer).

[0040] [Embodiment 3] Fig. 16 is a cross-sectional view showing an example of the configuration of a light-emitting device according to embodiment 3. As shown in Fig. 16, in embodiment 3, the first electrode E1 and the hole injection layer HJ (functional layer) each serve as a light reflecting portion 3. The first electrode E1 includes a plurality of crystal grains C1 that form a grain boundary B1, and a plurality of pits P1 are formed on a surface S1 of the first electrode E1 that faces the light-emitting layer EM. The hole injection layer HJ includes a plurality of crystal grains C2 that form a grain boundary B2, and a plurality of pits P2 are formed on a surface S2 of the hole injection layer HJ that faces the light-emitting layer EM.

[0041] The average size of the crystal grains C1 and C2 across the first electrode E1 and the hole injection layer HJ is calculated by weighting the average size of the crystal grains C1 and C2 with the thicknesses of the first electrode E1 and the hole injection layer HJ. If the thickness of the first electrode E1 is t1, the average size of the crystal grains C1 in the first electrode E1 is N1, the thickness of the hole injection layer HJ is t2, and the average size of the crystal grains C2 in the hole injection layer HJ is N2, then the average size of the crystal grains C(C1 and C2) across the first electrode E1 and the hole injection layer HJ is (t1N1+t2N2) / (t1+t2). The average size of the crystal grains C(C1 and C2) across the first electrode E1 and the hole injection layer HJ is preferably 1 / 10 or less of the emission peak wavelength of the light-emitting layer EM. The average size may be the average particle diameter, average thickness, or average width.

[0042] For the first electrode E1, the average depth of the pits P1 on the surface S1 on the side of the light-emitting layer EM may be 3 nm to 50 nm, and for the hole injection layer HJ, the average depth of the pits P2 on the surface S2 on the side of the light-emitting layer EM may be 3 nm to 50 nm. For the first electrode E1, the average pit-to-pit distance among the plurality of pits P1 may be equal to or greater than the average size of the plurality of crystal grains C1, and for the hole injection layer HJ, the average pit-to-pit distance among the plurality of pits P2 may be equal to or greater than the average size of the plurality of crystal grains C2.

[0043] The average pit-to-pit distance among the pits P1 is preferably 3 nm to 50 nm. The average pit-to-pit distance among the pits P1 may correlate with the average roughness of the surface S1 and the average depth of the pits P1. For example, the average pit-to-pit distance among the pits P1 may be equal to or less than the larger of the average roughness of the surface S1 and the average depth of the pits P1. The average pit-to-pit distance among the pits P1 may be equal to or less than the geometric mean of the average roughness of the surface S1 and the average depth of the pits P1.

[0044] Similarly, the average pit-to-pit distance in the plurality of pits P2 may be 3 nm to 50 nm. The average pit-to-pit distance in the plurality of pits P2 may be correlated with the average roughness of the surface S2 and the average depth of the plurality of pits P2. For example, the average pit-to-pit distance in the plurality of pits P2 may be equal to or less than the larger of the average roughness of the surface S2 and the average depth of the plurality of pits P2. The average pit-to-pit distance in the plurality of pits P2 may be equal to or less than the geometric mean of the average roughness of the surface S2 and the average depth of the plurality of pits P2.

[0045] [Embodiment 4] Fig. 17 is a plan view showing an example of the configuration of a display device according to embodiment 4. Figs. 18 and 19 are cross-sectional views showing examples of the configuration of a display device according to embodiment 4. As shown in Fig. 17, a display device 50 according to embodiment 4 includes a display unit DA, a driver circuit DR that drives the display unit DA, and a control unit DC that controls the driver circuit DR. The display unit DA includes a first sub-pixel X1, a second sub-pixel X2, and a third sub-pixel X3 that emit light of different colors (having different emission peak wavelengths). Each of the first sub-pixel X1, the second sub-pixel X2, and the third sub-pixel X3 includes a light-emitting element 10 and a pixel circuit PC connected to the light-emitting element 10.

[0046] As shown in FIG. 18, the display device 50 may include an edge cover BK that covers the edge of the first electrode E1 and a sealing film SL that covers the light-emitting element 10. The light-emitting element 10 included in each of the first sub-pixel X1 and the second sub-pixel X2 includes a first electrode E1, which is a light-reflecting portion 3, and a hole-injection layer HJ, which is also a light-reflecting portion 3. It is preferable that the external quantum efficiency (EQE) of each light-emitting element 10 is approximately the same, regardless of the color of light emitted by the light-emitting element 10 of the first sub-pixel X1 and the second sub-pixel X2. In other words, it is preferable that the theoretical limits of light extraction efficiency are approximately the same. Having the same EQE allows the first sub-pixel X1 and the second sub-pixel X2 to be driven and controlled in the same way. Simplifying the drive control reduces the costs of the substrate BP and the control algorithm.

[0047] The light extraction efficiency depends on the layer thickness T1 (the total thickness of the first electrode E1 and the hole injection layer HJ in the first subpixel X1), the layer thickness T2 (the total thickness of the first electrode E1 and the hole injection layer HJ in the second subpixel X2), and the Rayleigh scattering intensity I in each subpixel. The intensity I is expressed by the following equation:

[0048] I=4.5×I0×K×(1+cos 2 θ)×(π 2 V 2 ) / (λ 4 ×R 2 ) K=(n 2 -1) 2 / (n 2 +2) 2 I0: Incident light intensity R: Distance to the scatterer λ: wavelength of incident light V: Volume of the scatterer n: refractive index of the scatterer θ: Incident angle "×" is the symbol for multiplication. " / " is the symbol for division.

[0049] From the above equation, it can be seen that when the peak emission wavelengths of the first sub-pixel X1 and the second sub-pixel X2 are different, the scattering intensity can be made equal by making the size of the crystal grains C, which are scatterers, proportional to the 2 / 3 power of the peak emission wavelength. In other words, when the average size d1·d2 of the crystal grains C is proportional to the 2 / 3 power of the peak emission wavelengths L1·L2, the light extraction efficiency becomes approximately constant regardless of the emission color of the light-emitting element 10. This proportional relationship allows for a difference of 20%, 10%, or 5%. For example, when a difference of 10% is allowed, 0.9×d1 3 / L1 2 ≦d2 3 / L2 2 ≦1.1×d1 3 / L1 2 Meet the following.

[0050] When the first subpixel X1 and the second subpixel X2 each include a plurality of light reflecting portions 3, the average sizes of the crystal grains C in the first subpixel X1 and the second subpixel X2 may be substantially the same for one or more of the plurality of layers. For example, as shown in Fig. 18, when the peak emission wavelength of the second subpixel X2 is greater than the peak emission wavelength of the first subpixel X1, the average size of the crystal grains C1 in the first electrode E1 of the first subpixel X1 may be substantially the same as the average size of the crystal grains C1 in the first electrode E1 of the second subpixel X2, and the average size of the crystal grains C2 in the hole injection layer HJ (functional layer) of the second subpixel X2 may be greater than the average size of the crystal grains C2 in the hole injection layer HJ (functional layer) of the first subpixel X1.

[0051] 19, when the emission peak wavelength of the second subpixel X2 is longer than that of the first subpixel X1, the average size of the crystal grains C2 in the hole injection layer HJ (functional layer) of the first subpixel X1 may be substantially equal to the average size of the crystal grains C2 in the hole injection layer HJ (functional layer) of the second subpixel X2, and the average size of the crystal grains C1 in the first electrode E1 of the second subpixel X2 may be larger than the average size of the crystal grains C1 in the first electrode E1 of the first subpixel X1. Because the layers in which the average sizes of the crystal grains in the first subpixel X1 and the second subpixel X2 are substantially equal can be formed in the same process, the production efficiency of the display device 50 can be improved.

[0052] [Embodiment 5] 20 is a cross-sectional view showing an example of the configuration of a display device according to embodiment 5. In embodiment 5, the layer thicknesses Tf·Ts of the light-reflecting portions 3 of the first subpixel X1 and the second subpixel X2 are different (Tf>Ts), and the average sizes of the crystal grains C in the light-reflecting portions 3 of the first subpixel X1 and the second subpixel X2 are equivalent. The peak emission wavelength L1 of the first subpixel X1 is greater than the peak emission wavelength L2 of the second subpixel X2.

[0053] In the configuration according to the fifth embodiment, when the layer thicknesses Tf and Ts of the light reflecting section 3 are proportional to the 2 / 3 power of the emission peak wavelengths L1 and L2 of the emission layers EM of the first sub-pixel X1 and the second sub-pixel X2, the light extraction efficiency is approximately constant regardless of the emission color of the light emitting element 10. This proportional relationship allows for a difference of 20%, 10%, or 5%. For example, when a difference of 10% is allowed, 0.9×Tf 3 / L1 2 ≦Ts 3 / L2 2 ≦1.1×Tf 3 / L1 2 Meet the following.

[0054] When the emission peak wavelengths of the first subpixel X1 and the second subpixel X2 are different, the light extraction efficiency can be made approximately constant regardless of the light emitted by the light-emitting element 10 by optimizing both the layer thickness of the light-reflecting portion 3 and the average size of the crystal grains C.

[0055] The above disclosure is intended for purposes of illustration and description, not for purposes of limitation. Based on these examples and descriptions, many variations will be obvious to those skilled in the art, and it should be noted that these variations are also included in the embodiments. [Explanation of symbols]

[0056] 3 Light reflecting part 10 Light-emitting element 50 Display device B grain boundary C grain F Functional Layer E1 1st electrode E2 2nd electrode EM light-emitting layer P Pit S surface X1 First sub-pixel X2 Second sub-pixel

Claims

1. a first electrode and a second electrode, a light-emitting layer located between the first electrode and the second electrode, and a functional layer located between the first electrode and the light-emitting layer; At least one of the first electrode and the functional layer is a light reflecting portion having a grain boundary and an average roughness of a surface on the light emitting layer side of 3 nm to 20 nm, the light reflecting portion includes a plurality of crystal grains that form the grain boundary and has a plurality of pits on the surface; an average pit distance among the plurality of pits is equal to or greater than an average size of the plurality of crystal grains.

2. The light-emitting element described in Claim 1, wherein the average depth of the plurality of pits is 3 nm to 50 nm.

3. A light-emitting element as described in claim 1, wherein the average pit-to-pit distance among the plurality of pits is less than or equal to the greater of the average roughness and the average depth of the plurality of pits.

4. A semiconductor device comprising: a first electrode and a second electrode; a light-emitting layer located between the first electrode and the second electrode; and a functional layer located between the first electrode and the light-emitting layer; At least one of the first electrode and the functional layer is a light reflecting portion having a grain boundary and an average roughness of a surface on the light emitting layer side of 3 nm to 20 nm, the light reflecting portion has a plurality of pits on the surface, the average depth of the pits is between 3 nm and 50 nm; and the first electrode and the functional layer each constitute the light reflecting portion including a plurality of crystal grains that form the grain boundary, and an average size of the plurality of crystal grains across the first electrode and the functional layer is 1 / 10 or less of the emission peak wavelength of the light emitting layer; or The first electrode and the functional layer each are the light reflecting portion having a plurality of pits on the surface, and an average pit distance among the plurality of pits is 3 nm to 50 nm for each of the first electrode and the functional layer, or the first electrode and the functional layer each include a plurality of crystal grains that form the grain boundaries and are the light reflecting portion having a plurality of pits on the surface, and an average pit distance among the plurality of pits is equal to or greater than an average size of the plurality of crystal grains for each of the first electrode and the functional layer; Light-emitting element.

5. A semiconductor device comprising: a first electrode and a second electrode; a light-emitting layer located between the first electrode and the second electrode; and a functional layer located between the first electrode and the light-emitting layer; At least one of the first electrode and the functional layer is a light reflecting portion having a grain boundary and an average roughness of a surface on the light emitting layer side of 3 nm to 20 nm, the light reflecting portion has a plurality of pits on the surface, an average pit distance among the plurality of pits is equal to or less than a larger value of the average roughness and an average depth of the plurality of pits; and the first electrode and the functional layer each constitute the light reflecting portion including a plurality of crystal grains that form the grain boundary, and an average size of the plurality of crystal grains across the first electrode and the functional layer is 1 / 10 or less of the emission peak wavelength of the light emitting layer; or The first electrode and the functional layer each are the light reflecting portion having a plurality of pits on the surface, and an average pit distance among the plurality of pits is 3 nm to 50 nm for each of the first electrode and the functional layer, or the first electrode and the functional layer each include a plurality of crystal grains that form the grain boundaries and are the light reflecting portion having a plurality of pits on the surface, and an average pit distance among the plurality of pits is equal to or greater than an average size of the plurality of crystal grains for each of the first electrode and the functional layer; Light-emitting element.

6. A semiconductor device comprising: a first electrode and a second electrode; a light-emitting layer located between the first electrode and the second electrode; and a functional layer located between the first electrode and the light-emitting layer; At least one of the first electrode and the functional layer is a light reflecting portion having a grain boundary and an average roughness of a surface on the light emitting layer side of 3 nm to 20 nm, the light reflecting portion has a plurality of pits on the surface, the average depth of the plurality of pits is 3 nm to 50 nm; a plurality of functional layers positioned between the first electrode and the light-emitting layer; each of the plurality of functional layers is a light-reflecting portion having a grain boundary and an average roughness of a surface on the light-emitting layer side of 3 nm to 20 nm; Light-emitting element.

7. A semiconductor device comprising: a first electrode and a second electrode; a light-emitting layer located between the first electrode and the second electrode; and a functional layer located between the first electrode and the light-emitting layer; At least one of the first electrode and the functional layer is a light reflecting portion having a grain boundary and an average roughness of a surface on the light emitting layer side of 3 nm to 20 nm, the light reflecting portion has a plurality of pits on the surface, an average pit distance among the plurality of pits is equal to or less than a larger value of the average roughness and an average depth of the plurality of pits; a plurality of functional layers positioned between the first electrode and the light-emitting layer; each of the plurality of functional layers is a light-reflecting portion having a grain boundary and an average roughness of a surface on the light-emitting layer side of 3 nm to 20 nm; Light-emitting element.

8. A light-emitting element described in any one of claims 1 to 7, wherein the average pit-to-pit distance among the plurality of pits is less than or equal to the geometric mean value of the average roughness and the average depth of the plurality of pits.

9. the first electrode and the functional layer each constitute the light reflecting portion having a plurality of pits on the surface, 8. The light-emitting device according to claim 1, wherein the average depth of the plurality of pits in each of the first electrode and the functional layer is 3 nm to 50 nm.

10. 8. The light-emitting device according to claim 1, wherein the functional layer is a hole injection layer or a hole transport layer.

11. 8. The light-emitting device according to claim 1, wherein the grain boundary is a crystal mismatch plane or an internal fracture plane.

12. a first sub-pixel and a second sub-pixel that emits light of a different color from the first sub-pixel; A display device, wherein each of a first sub-pixel and a second sub-pixel includes the light-emitting element according to any one of claims 1 to 7.

13. For the first sub-pixel, the average size of the plurality of crystal grains forming the grain boundary of the light reflecting portion is d １ , the emission peak wavelength of the light-emitting layer is L １ and For the second sub-pixel, the average size of the plurality of crystal grains forming the grain boundary of the light reflecting portion is d ２ , the emission peak wavelength of the light-emitting layer is L ２ and L ２ >L １ and d ２ >d １ The display device according to claim 12 , wherein the following relationship is satisfied: or 0.9×d 1 3 / L 1 2 ≦d 2 3 / L 2 2 ≦1.1×d 1 3 / L 1 2 .

14. For the first sub-pixel, the first electrode and the functional layer each have a light reflecting portion including a plurality of crystal grains that form the grain boundary, and an average size of the plurality of crystal grains extending from the first electrode to the functional layer is d １ , the emission peak wavelength of the light-emitting layer is L １ and For the second sub-pixel, the first electrode and the functional layer each have a light reflecting portion including a plurality of crystal grains that form the grain boundary, and an average size of the plurality of crystal grains extending from the first electrode to the functional layer is d ２ , the emission peak wavelength of the light-emitting layer is L ２ and 0.9×d １ ３ / L １ ２ ≦d ２ ３ / L ２ ２ ≦1.1×d １ ３ / L １ ２ The display device according to claim 12 , wherein

15. an average size of the plurality of crystal grains in the first electrode of the first subpixel is equal to an average size of the plurality of crystal grains in the first electrode of the second subpixel; or an average size of the plurality of crystal grains in the functional layer of the first sub-pixel is equal to an average size of the plurality of crystal grains in the functional layer of the second sub-pixel; The display device according to claim 14.

16. The display device according to claim 13 , wherein the average size is an average grain diameter or an average thickness of a plurality of crystal grains.

17. For the first sub-pixel, the thickness of the light reflecting portion is Tf, and the emission peak wavelength of the light emitting layer is L １ and For the second sub-pixel, the thickness of the light reflecting portion is Ts, and the emission peak wavelength of the light emitting layer is L ２ and L １ >L ２ The display device according to claim 12 , wherein Tf>Ts or 0.9×Tf 3 / L 1 2 ≦Ts 3 / L 2 2 ≦1.1×Tf 3 / L 1 2 is satisfied.

Images