JP6287848B2 - Electroluminescent device and lighting device using the electroluminescent device - Google Patents

Description

  The present invention relates to an electroluminescent element and an illumination device using the electroluminescent element.

  In recent years, surface light sources with high luminous efficiency using electroluminescent elements such as organic EL (Electro-Luminescence) and inorganic EL have attracted attention. The electroluminescent element is composed of an electroluminescent layer sandwiched between a planar cathode and an anode. In general, the anode is often a transparent electrode, and the cathode is often a metal light reflecting electrode. When one of them is composed of a metal light reflecting electrode, light is extracted from the anode side of the transparent electrode and used as a single-sided light emitting device.

  For example, in a conventional organic light emitting device, substrate loss, waveguide loss, and plasmon loss occur, and it is a problem to reduce these losses and extract more light.

  The substrate loss means a loss of light that is totally reflected at the interface between the transparent substrate and air and cannot be extracted to the light extraction side, and usually has a loss of about 20%.

  The waveguide loss means a loss of light that is totally reflected at the interface between the transparent electrode and the transparent substrate to generate a waveguide mode and is confined in the organic light emitting layer and the transparent electrode, and is usually about 20 to 25%. There is a loss.

  Plasmon loss is a type of guided mode, where light enters a metal electrode and interacts with free electrons in the metal electrode, generating a plasmon mode and reducing the loss of light confined near the surface of the metal electrode. Meaning, there is usually a loss of about 30-40%.

  Japanese Patent Application Laid-Open No. 2011-233288 (Patent Document 1) discloses an organic light-emitting element in which light use efficiency is improved by reducing waveguide loss and plasmon loss.

JP 2011-233288 A

  In Patent Document 1, the portion that is normally a metal electrode is configured as a transparent electrode + optical buffer layer + reflecting mirror, and the refractive index of the optical buffer layer is made higher than that of the other layers to reduce plasmon loss. A structure that reduces and improves light utilization efficiency is disclosed. However, further improvement in light utilization efficiency has been desired.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an electroluminescent element and an illumination device using the electroluminescent element that can further improve the light utilization efficiency.

  In the electroluminescent element based on this invention, the first transparent electrode layer, the second transparent electrode layer, the electroluminescent layer sandwiched between the first transparent electrode layer and the second transparent electrode layer, and the first An optical buffer layer provided on the opposite side of the two transparent electrode layers from the side on which the electroluminescent layer is provided, and a light reflecting layer provided on the opposite side of the optical buffer layer from the side on which the second transparent electrode layer is provided. The optical buffer layer has a refractive index different between the light reflecting layer side and the second transparent electrode layer side, and the refractive index of the light reflecting layer side is the refractive index of the second transparent electrode layer side. Greater than rate.

  The illumination device according to the present invention has the above-described electroluminescent element.

  According to the present invention, it is possible to further improve the light use efficiency in the electroluminescent element and the illumination device using the electroluminescent element.

FIG. 3 is a plan view of the organic electroluminescent element in the first embodiment. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1 of the organic electroluminescent element in the first embodiment. It is a figure which shows the material, film thickness, and refractive index of each layer of the organic electroluminescent element shown in FIG. FIG. 6 is a diagram showing the result of calculating the plasmon mode light intensity distribution of the organic electroluminescent element in the first embodiment. It is the figure which expanded the organic light emitting layer vicinity of FIG. It is sectional drawing which shows the structure of the organic electroluminescent element in the background art 1. FIG. It is a figure which shows the material, film thickness, and refractive index of each layer of the organic electroluminescent element shown in FIG. It is a figure which shows the result of having calculated the light intensity distribution of the plasmon mode of the organic electroluminescent element in the background art 1. FIG. It is sectional drawing which shows the structure of the organic electroluminescent element in the background art 2. FIG. It is a figure which shows the material, film thickness, and refractive index of each layer of the organic electroluminescent element shown in FIG. It is a figure which shows the result of having calculated the light intensity distribution of the plasmon mode of the organic electroluminescent element in the background art 2. FIG. FIG. 5 is a cross-sectional view showing the structure of an organic electroluminescent element in a second embodiment. It is a figure which shows the result of having calculated the light intensity distribution of the plasmon mode of the organic electroluminescent element in Embodiment 2. FIG. FIG. 6 is a cross-sectional view showing a structure of an organic electroluminescent element in a fourth embodiment. FIG. 6 is a cross-sectional view showing the structure of an organic electroluminescent element in a fifth embodiment. It is a figure which shows the material, film thickness, and refractive index of each layer of the organic electroluminescent element shown in FIG. It is a figure which shows the result of having calculated the light intensity distribution of the plasmon mode of the organic electroluminescent element in Embodiment 5. FIG. It is sectional drawing which shows the structure of the organic electroluminescent element in Embodiment 6. It is a figure which shows the material, film thickness, and refractive index of each layer of the organic electroluminescent element shown in FIG. It is a figure which shows the result of having calculated the light intensity distribution of the plasmon mode of the organic electroluminescent element in Embodiment 6. FIG. FIG. 10 is a diagram illustrating a schematic configuration of a lighting device in a seventh embodiment. FIG. 20 is a diagram illustrating a schematic configuration of a lighting device according to an eighth embodiment.

  An electroluminescent element and an illumination device using the electroluminescent element in each embodiment based on the present invention will be described below with reference to the drawings. In each embodiment described below, when referring to the number, amount, and the like, the scope of the present invention is not necessarily limited to the number, amount, and the like unless otherwise specified. The same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated. In addition, it is planned from the beginning to use the structures in the embodiments in appropriate combinations.

(Embodiment 1)
With reference to FIG. 1 to FIG. 5, the organic electroluminescent element 1 in the first embodiment will be described. 1 is a plan view of the organic electroluminescent element 1 in the present embodiment, FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1 of the organic electroluminescent element 1 in the present embodiment, and FIG. 2 is a diagram showing the material, film thickness, and refractive index of each layer of the organic electroluminescent device 1 shown in FIG. 2, FIG. 4 is a diagram showing the result of calculating the plasmon mode light intensity distribution of the organic electroluminescent device 1, and FIG. FIG. 5 is an enlarged view of the vicinity of the organic light emitting layer in FIG. 4. In addition, sectional drawing in each embodiment shown below is a cross section equivalent to the II-II arrow line in FIG.

  With reference to FIGS. 1 and 2, the organic electroluminescent element 1 in the present embodiment includes a transparent substrate 10, a first transparent electrode layer 11 provided on one side of the transparent substrate 10, and a first transparent electrode layer 11. The organic electroluminescent layer 20 provided on the opposite side to the side on which the transparent substrate 10 is provided, and the second transparent electrode layer provided on the opposite side of the organic electroluminescent layer 20 from the side on which the first transparent electrode layer 11 is provided. 15. The organic electroluminescent layer 20 is sandwiched between the first transparent electrode layer 11 and the second transparent electrode layer 15.

  In the present embodiment, the organic electroluminescent layer 20 includes a hole transport layer 12 located on the first transparent electrode layer 11 side, an electron transport layer 14 located on the second transparent electrode layer 15 side, and a hole transport. An organic light emitting layer 13 sandwiched between the layer 12 and the electron transport layer 14 is included.

  An optical buffer layer 16 is provided on the side of the second transparent electrode layer 15 opposite to the side on which the organic electroluminescent layer 20 is provided, and the side of the optical buffer layer 16 opposite to the side on which the second transparent electrode layer 15 is provided. Is provided with a light reflecting layer 30.

  In the present embodiment, the refractive index of the optical buffer layer 16 is larger on the light reflecting layer 30 side than on the second transparent electrode layer 15 side. Specifically, the optical buffer layer 16 includes a first optical buffer layer 16a provided on the second transparent electrode layer 15 side, and a second optical buffer layer 16b provided on the light reflecting layer 30 side, and the second optical buffer layer 16b is provided. The refractive index n2 of the buffer layer 16b is larger than the refractive index n1 of the first optical buffer layer 16a (n2> n1).

  With reference to FIG. 3, an example of the material of each layer which comprises the organic electroluminescent element 1 of the said structure, a film thickness, and a refractive index is demonstrated. Glass is used for the transparent substrate 10. The refractive index is 1.50. For the first transparent electrode layer 11 as the anode, 150 nm-thick ITO (mixture of indium oxide and tin oxide) is used. The refractive index is 1.83 + 0.007i.

  For the hole transport layer 12, α-NPD having a film thickness of 40 nm is used. α-NPD is 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl. The refractive index is 1.78. For the organic light emitting layer 13, Alq3 having a film thickness of 30 nm is used. Alq3 is tris (8-quinolinolato) aluminum. The refractive index is 1.72 + 0.005i. For the electron transport layer 14, Alq3 having a film thickness of 40 nm is used. The refractive index is 1.72 + 0.005i. For the second transparent electrode layer 15 as the cathode, Ag having a thickness of 9 nm is used. The refractive index is 0.128 + 3.17i.

For the first optical buffer layer 16a, Ta ₂ O ₅ having a thickness of 50 nm is used as a dielectric film. The refractive index is 1.81. For the second optical buffer layer 16b, the following three types of films were used in order to cause a refractive index difference with the first optical buffer layer 16a. Ta ₂ O _{5 having} a refractive index of 1.81, HfO ₂ having a refractive index of 1.93, and Si ₃ N ₄ having a refractive index of 2.03 were used. The refractive index difference (Δn) with Ta ₂ O ₅ is 0.00, the refractive index difference (Δn) with HfO ₂ is 0.12, and the refractive index difference (Δn) with Si ₃ N ₄ is 0.22. .

  The light reflecting layer 30 is made of Ag having a thickness of 100 nm. The refractive index is 0.128 + 3.17i.

  The results of calculating the plasmon mode light intensity distribution in the organic electroluminescent device 1 having the above-described film configuration are shown in FIGS. In the calculation, 530 nm was used as the emission wavelength. The calculation results in the other embodiments described below are the same, and the wavelength is used. In the figure, the horizontal axis indicates the relative distance based on the back surface of the organic electroluminescent element 1, and the left vertical axis indicates the normalized light intensity.

  4 and 5, the refractive index difference (Δn) between the first optical buffer layer 16a and the second optical buffer layer 16b is changed from 0.00 to 0.22 using the above-described materials. It is a calculation result of the light intensity distribution of the plasmon mode. However, the refractive index n2 of the second optical buffer layer 16b is larger than the refractive index n1 of the first optical buffer layer 16a. The refractive index n1 of the first optical buffer layer 16a is fixed at 1.81, and the refractive index n2 of the second optical buffer layer 16b is 2.03, 1.93, and 1.81, using the above-described film materials. Changed.

  As apparent from FIGS. 4 and 5, the plasmon mode is generated at the interface between the electron transport layer 14 and the second transparent electrode layer 15 which is the metal surface, so that the light intensity distribution thereof is the second transparent which is the metal electrode surface. The electrode layer 15 is strongest.

  By making the refractive index difference larger than 0.00, the plasmon mode distributed in the second transparent electrode layer 15 constituting the organic electroluminescent layer 20 is decreased, and the intensity of the plasmon mode distributed in the organic light emitting layer 13 is decreased. I understand that As a result, the ratio of the light generated in the organic light emitting layer 13 to be coupled to the plasmon mode is reduced, so that the plasmon loss can be reduced. As a result, the use efficiency of light in the organic electroluminescent element 1 can be improved.

  The material used for each layer of the organic electroluminescent element 1 is not limited to the above, and the following materials can be used.

  For the transparent substrate 10, a transparent material suitable for the emission wavelength of the organic electroluminescent element 1, such as quartz, sapphire, and plastic, can be used in addition to glass. If a flexible material such as very thin glass or resin film is used, the light source can be curved.

  The organic electroluminescent device 1 shown in FIGS. 1 and 2 has a bottom emission configuration in which each layer is stacked on the transparent substrate 10 and light is extracted from the transparent substrate 10 side. However, the light reflecting layer 30 is a substrate for stacking. And a top emission configuration in which light is extracted from the side opposite to the substrate.

For the first transparent electrode layer 11 and the second transparent electrode layer 15, ITO (mixture of indium oxide and tin oxide), IZO (mixture of indium oxide and zinc oxide), IGZO (indium (In) Oxidize gallium (Ga) and zinc (Zn) to give crystallinity), conductive metal oxide material (transparent oxide semiconductor) such as ZnO, SnO ₂ , CuI, thin translucent Metal thin film (As a metal material, a metal material such as Ag, Al, Au, Sn, Ti, Ni, Na, Ca, Zn, or an alloy containing any of them can be used, and there is conductivity. Any film may be used, or a combination of them, for example, an MIM (metal / ITO / metal) electrode may be used.

  Furthermore, a conductive resin (PEDOT / PSS, etc.) is used, and a film in which conductive wires and conductive fine particles such as carbon nanotubes, metal nanowires such as Ag, and nanoparticles of Ag and Cu are dispersed in the conductive resin is used. It may be used.

  In addition, a metal thin film may be used for one of the first transparent electrode layer 11 and the second transparent electrode layer 15, and a film made of a conductive metal oxide may be used for the other. In particular, the second transparent electrode layer 15 on the cathode side has a metal thin film having a work function suitable for electron injection, and the first transparent electrode layer 11 on the anode side has a work function suitable for hole injection. It is preferable to use a conductive metal oxide.

  In particular, it is preferable to use ITO for the first transparent electrode layer 11 and a silver thin film for the second transparent electrode layer 15. ITO has the advantage of high light transmittance, and the metal thin film has the advantage that it can be formed at a low temperature. Further, when the metal thin film is used as a transparent electrode, a film thickness of several nm to several tens of nm is suitable for increasing the light transmittance. In addition, the conductive metal oxide has a thickness of 10 nm to 200 nm suitable for reducing the surface resistance.

  As the hole transport layer 12, the organic light emitting layer 13, and the electron transport layer 14 constituting the organic electroluminescent layer 20, various materials generally used in organic EL elements can be used. In addition, an electron injection layer, a hole injection layer, a carrier block layer, and the like may be combined.

As the optical buffer layer 16, in addition to various organic materials that are transparent at the emission wavelength of the organic EL, TiO ₂ , SiO ₂ , ZnO, Al ₂ O ₃ , Ta ₂ O ₅ , HfO ₂ , ZrO ₂ , KTaO ₃ , MgO A material such as Si ₃ N ₄ , AlN, GaN, SiC, or Y ₂ O ₃ can be used. Furthermore, a material whose refractive index is adjusted by mixing fine particles having a diameter of 100 nm or less, such as TiO ₂ and ZrO ₂ , with an organic resin may be used.

As the light reflection layer 30, a metal material such as Ag, Al, Au, Sn, Ti, Ni, Na, Ca, Zn, an alloy containing any of them can be used, and light may be reflected. Further, a dielectric mirror in which dielectric films such as TiO ₂ / SiO ₂ are laminated in multiple layers may be used.

  The organic electroluminescent element 1 shown in FIG. 2 has a bottom emission configuration, but may have a top emission configuration in which the layer configuration is reversed. Furthermore, the cathode and the anode may be reversed. That is, in order from the substrate side, substrate 10 / first transparent electrode layer 11 (cathode) / electron transport layer 14 / organic light emitting layer 13 / hole transport layer 12 / second transparent electrode layer 15 (anode) / first optical buffer. The layer 16a / second optical buffer layer 16b / light reflecting layer 30 may be arranged in this order.

  An organic material is deteriorated by oxygen or moisture, and is used by being sealed with a gas barrier layer. However, the layer and structure for sealing are not shown.

  In order to clarify the effect obtained by the organic electroluminescent element 1 in the present embodiment shown in FIGS. 4 and 5, in the case of the organic electroluminescent element in the background art 1 and the organic electroluminescent element in the background technique 2, The results of calculating the light intensity distribution in the plasmon mode are shown in FIGS.

  6 is a cross-sectional view showing the structure of the organic electroluminescent element 2 in the background art 1, FIG. 7 is a diagram showing the material, film thickness, and refractive index of each layer of the organic electroluminescent element 2 shown in FIG. 6, and FIG. It is a figure which shows the result of having calculated the light intensity distribution of the plasmon mode of the organic electroluminescent element in the background art 1. FIG. 9 is a cross-sectional view showing the structure of the organic electroluminescent element 3 in Background Art 2, FIG. 10 is a diagram showing the material, film thickness, and refractive index of each layer of the organic electroluminescent element 3 shown in FIG. It is a figure which shows the result of having calculated the light intensity distribution of the plasmon mode of the organic electroluminescent element in the background art 2. FIG.

(Organic electroluminescent element 2 (background art 1))
With reference to FIG. 6, the organic electroluminescent element 2 in the background art 1 includes a transparent substrate 10, a first transparent electrode layer 11 provided on one surface side of the transparent substrate 10, and a transparent substrate of the first transparent electrode layer 11. 10 is provided with an organic electroluminescent layer 20 provided on the opposite side to the side on which 10 is provided, and a metal electrode layer 15A provided on the opposite side of the organic electroluminescent layer 20 from the side on which the first transparent electrode layer 11 is provided. The organic electroluminescent layer 20 is sandwiched between the first transparent electrode layer 11 and the metal electrode layer 15A.

  The organic electroluminescent layer 20 includes a hole transport layer 12 located on the first transparent electrode layer 11 side, an electron transport layer 14 located on the metal electrode layer 15A side, a hole transport layer 12 and an electron transport layer 14. And an organic light emitting layer 13 sandwiched therebetween.

  With reference to FIG. 7, the material of each layer which comprises the organic electroluminescent element 2 of the said structure, a film thickness, and a refractive index are demonstrated. Glass is used for the transparent substrate 10. The refractive index is 1.50. For the first transparent electrode layer 11 as the anode, 150 nm-thick ITO (mixture of indium oxide and tin oxide) is used. The refractive index is 1.83 + 0.007i.

  For the hole transport layer 12, α-NPD having a film thickness of 40 nm is used. The refractive index is 1.78. For the organic light emitting layer 13, Alq3 having a film thickness of 30 nm is used. For the electron transport layer 14, Alq3 having a film thickness of 40 nm is used. The refractive index is 1.72 + 0.005i. For the metal electrode layer 15A as the cathode, Ag with a film thickness of 100 nm is used. The refractive index is 0.128 + 3.17i. In the organic electroluminescent element 2, the buffer layer is not provided, and it can be considered that the metal electrode layer 15A also serves as the light reflecting layer.

  FIG. 8 shows the result of calculating the plasmon mode light intensity distribution in the organic electroluminescent device 2 having the above-described configuration. In the figure, the horizontal axis indicates the relative distance based on the back surface of the organic electroluminescent element 2, and the left vertical axis indicates the normalized light intensity.

  As can be seen from FIG. 8, the plasmon mode has the strongest intensity on the metal surface and decreases exponentially with increasing distance from the metal surface, but the organic luminescent layer 13 has a strong plasmon mode of about 0.4 to 0.5. Is present. A part of the light emitted from the organic light emitting layer 13 is coupled to the plasmon mode, and is eventually lost as a plasmon loss. Therefore, in order to reduce the plasmon loss, it is important to reduce the light intensity of the plasmon mode existing in the organic light emitting layer 13 as much as possible.

(Organic electroluminescent element 3 (background art 2))
With reference to FIG. 9, the organic electroluminescent element 3 in the background art 2 includes a transparent substrate 10, a first transparent electrode layer 11 provided on one surface side of the transparent substrate 10, and a transparent substrate of the first transparent electrode layer 11. An organic electroluminescent layer 20 provided on the side opposite to the side on which 10 is provided, and a second transparent electrode layer 15 provided on the side opposite to the side on which the first transparent electrode layer 11 of the organic electroluminescent layer 20 is provided. Prepare. The organic electroluminescent layer 20 is sandwiched between the first transparent electrode layer 11 and the second transparent electrode layer 15.

  The organic electroluminescent layer 20 includes a hole transport layer 12 located on the first transparent electrode layer 11 side, an electron transport layer 14 located on the second transparent electrode layer 15 side, a hole transport layer 12 and an electron transport layer 14. And an organic light emitting layer 13 sandwiched between.

  An optical buffer layer 16 is provided on the side of the second transparent electrode layer 15 opposite to the side on which the organic electroluminescent layer 20 is provided, and the side of the optical buffer layer 16 opposite to the side on which the second transparent electrode layer 15 is provided. Is provided with a light reflecting layer 30.

  With reference to FIG. 10, the material of each layer which comprises the organic electroluminescent element 3 of the said structure, a film thickness, and a refractive index are demonstrated. Glass is used for the transparent substrate 10. The refractive index is 1.50. For the first transparent electrode layer 11 as the anode, 150 nm-thick ITO (mixture of indium oxide and tin oxide) is used. The refractive index is 1.83 + 0.007i.

For the hole transport layer 12, α-NPD having a film thickness of 40 nm is used. The refractive index is 1.78. For the organic light emitting layer 13, Alq3 having a film thickness of 30 nm is used. For the electron transport layer 14, Alq3 having a film thickness of 40 nm is used. The refractive index is 1.72 + 0.005i. For the second transparent electrode layer 15 as the cathode, Ag with a film thickness of 100 nm is used. The refractive index is 0.128 + 3.17i. The first optical buffer layer 16 uses Ta ₂ O ₅ having a thickness of 100 nm as a dielectric film. The refractive index is 1.81. The light reflecting layer 30 is made of Ag having a thickness of 100 nm. The refractive index is 0.128 + 3.17i.

  FIG. 11 shows the result of calculating the plasmon mode light intensity distribution in the organic electroluminescent element 3 having the above-described configuration. In the figure, the horizontal axis indicates the relative distance based on the back surface of the organic electroluminescent element 3, and the left vertical axis indicates the normalized light intensity.

  As can be seen from FIG. 11, compared to the calculation result shown in FIG. 8, the second transparent electrode layer 15 is a thin film metal electrode, and the side on which the organic electroluminescent layer 20 is provided of the second transparent electrode layer 15. By providing the optical buffer layer 16 (refractive index 1.81) and the light reflecting layer 30 on the opposite side, the distance between the organic electroluminescent layer 20 and the light reflecting layer 30 is as shown in FIG. It is possible to be farther than in the case of 2. As a result, compared to the calculation result shown in FIG. 8, the intensity of the plasmon mode distributed in the organic light emitting layer 13 can be reduced to 0.2 or less.

  Furthermore, in the organic electroluminescent element 1 according to the present embodiment, the optical buffer layer 16 has different refractive indexes on the light reflection layer 30 side and the second transparent electrode layer 15 side, and the refraction on the light reflection layer 30 side. The refractive index is larger than the refractive index on the second transparent electrode layer 15 side. Specifically, the optical buffer layer 16 includes a first optical buffer layer 16a provided on the second transparent electrode layer 15 side, and a second optical buffer layer 16b provided on the light reflecting layer 30 side, and the second optical buffer layer 16b is provided. A configuration is adopted in which the refractive index n2 of the buffer layer 16b is larger than the refractive index n1 of the first optical buffer layer 16a.

  By adopting this configuration, as shown in FIGS. 4 and 5, the intensity of the plasmon mode distributed in the organic light emitting layer 13 is 0.15 or less when the refractive index difference (Δn) is 0.12. In the case where the refractive index difference (Δn) is 0.22, the intensity of the plasmon mode distributed in the organic light emitting layer 13 is reduced to 0.125 or less.

  As a result, according to the organic electroluminescent element 1 in the present embodiment, as described above, the refractive index difference (n1) between the refractive index n1 of the first optical buffer layer 16a and the refractive index n2 of the second optical buffer layer 16b. By making <n2) larger than 0.00, the ratio of the light generated in the organic light emitting layer 13 to be coupled to the plasmon mode is reduced, and the plasmon loss can be reduced. As a result, it is possible to improve the light use efficiency in the organic electroluminescent element 1.

(Embodiment 2)
An organic electroluminescent element 1A according to Embodiment 2 will be described with reference to FIGS. FIG. 12 is a cross-sectional view showing the structure of the organic electroluminescent element 1A in the present embodiment, and FIG. 13 is a diagram showing the result of calculating the plasmon mode light intensity distribution of the organic electroluminescent element 1A.

  In the organic electroluminescent element 1 in the first embodiment, the optical buffer layer 16 has different refractive indexes on the light reflecting layer 30 side and the second transparent electrode layer 15 side, and the refractive index on the light reflecting layer 30 side. This has a configuration in which the refractive index is larger than the refractive index on the second transparent electrode layer 15 side. Specifically, the optical buffer layer 16 includes a first optical buffer layer 16a provided on the second transparent electrode layer 15 side, and a second optical buffer layer 16b provided on the light reflecting layer 30 side, and the second optical buffer layer 16b is provided. A configuration in which the refractive index n2 of the buffer layer 16b is larger than the refractive index n1 of the first optical buffer layer 16a is adopted.

  In the organic electroluminescent element 1A in the present embodiment, as shown in FIG. 12, the optical buffer layer 16A has a single-layer structure. In the optical buffer layer 16A, light is reflected from the second transparent electrode layer 15 side so that the refractive index of the optical buffer layer 16 is larger on the light reflecting layer 30 side than on the second transparent electrode layer 15 side. A structure that changes gradually toward the layer 30 side is adopted. Other configurations are the same as those of the organic electroluminescent element 1 in the first embodiment.

  In the optical buffer layer 16A in the present embodiment, when the refractive index immediately above the second transparent electrode layer 15 is n1, and the refractive index in front of the light reflecting layer 30 is n2, the refractive index between them is n1. The plasmon mode normalized light intensity distribution was calculated for the case of gradually changing from n to n2. Specifically, the refractive index of the optical buffer layer 16A is gradually changed from 1.82 to 1.93 and 2.03 from the second transparent electrode layer 15 side toward the light reflecting layer 30 side. I let you.

  The optical buffer layer 16A is made of, for example, a material in which a material 1 having a refractive index n1 and a material 2 having a refractive index n2 are mixed, and the ratio of the material 1 and the material 2 is the second transparent electrode layer 15. A mixing method that gradually changes from the side toward the light reflecting layer 30 side can be considered.

  As shown in FIG. 13, it can be seen that as Δn = n2−n1 increases as in FIG. 5, the intensity of the plasmon mode distributed in the organic light emitting layer 13 decreases and the plasmon mode is reduced.

(Embodiment 3)
In the organic electroluminescent elements 1 and 1A shown in the first and second embodiments, a conductive material may be used for the optical buffer layer 16. By using the conductive material, the second transparent electrode 15, the optical buffer layer 16 (the first optical buffer layer 16 a and the second optical buffer layer 16 b), and the light reflecting layer 30 as a whole contribute to conduction. The resistance value of the light emitting element can be reduced.

  As a result, it is possible to avoid an increase in driving voltage when the organic electroluminescent elements 1 and 1A are increased in area. In addition, it is possible to suppress unevenness of the in-plane distribution of luminance of the organic electroluminescent elements 1 and 1A. This configuration can also be adopted in the following embodiments.

(Embodiment 4)
FIG. 14 shows a cross-sectional structure of organic electroluminescent element 1B in the fourth embodiment. In the organic electroluminescent elements 1 and 1A shown in the first to third embodiments, the optical buffer layer 16 (at least one of the first optical buffer layer 16a and the second optical buffer layer 16b) has fine particles 16c having a light scattering effect. May be added. By adopting this configuration, light (waveguide mode or glass mode) guided inside the organic electroluminescent device 1B can be extracted to the outside of the organic electroluminescent device 1B by scattering, and the light utilization efficiency is further improved. improves.

  In the organic electroluminescent element 1B shown in FIG. 14, as the optical buffer layer 16B, fine particles 16c having a light scattering effect are added to both the first optical buffer layer 16a and the second optical buffer layer 16b. At least one of the first optical buffer layer 16a and the second optical buffer layer 16b may be used. Moreover, you may make it add the microparticles | fine-particles which have a light-scattering effect to a part of layer instead of the whole layer of the 1st optical buffer layer 16a and the 2nd optical buffer layer 16b.

  It is also possible to adjust the refractive index of the optical buffer layer 16B by appropriately controlling the material and amount of fine particles added to the optical buffer layer 16B. The size of the fine particles 16c is preferably 100 nm or less if only the refractive index adjustment is performed, and 100 nm or more if the scattering effect is expected.

As the material of the fine particles 16c, inorganic materials such as SiO ₂ , ZrO ₂ and TiO ₂ , organic materials such as PMMA (Poly methyl methacrylate), etc. can be used in combination. In order to obtain this, the addition amount is preferably 1 wt% (deposition percentage) or more, and this configuration can also be adopted in each embodiment described below.

(Embodiment 5)
With reference to FIG. 15 to FIG. 17, the organic electroluminescent element 1 </ b> C in the present embodiment will be described. 15 is a cross-sectional view showing the structure of the organic electroluminescent element 1C in the present embodiment, FIG. 16 is a diagram showing the material, film thickness, and refractive index of each layer of the organic electroluminescent element 1C shown in FIG. These are figures which show the result of having calculated the light intensity distribution of the plasmon mode of the organic electroluminescent element in this Embodiment.

  In each of Embodiments 1 to 4, the refractive index of the optical buffer layers 16 and 16A (the refractive index on the second transparent electrode layer side) is higher than the refractive index of the organic light emitting layer 13. . If the refractive index of the optical buffer layers 16 and 16A is higher than the refractive index of the organic light emitting layer 13, the optical distance can be increased, which is advantageous in reducing the plasmon mode. Therefore, in the present embodiment, it will be described that the same effect can be obtained even when the refractive indexes of the optical buffer layers 16 and 16A are 1.65 + Δn and are lower than those of other layers. As the optical buffer layer, the optical buffer layer 16 having the two-layer structure of the first optical buffer layer 16a and the second optical buffer layer 16b, which is employed in the first embodiment, is employed.

  FIG. 15 shows an organic electroluminescent element 1C in the present embodiment. Except for the first optical buffer layer 16a and the second optical buffer layer 16b constituting the optical buffer layer 16, the other configurations are the same as those of the organic electroluminescent element 1 in the first embodiment shown in FIGS.

  In the organic electroluminescent element 1C, TYZ65 having a film thickness of 50 nm is used for the first optical buffer layer 16a. The refractive index is 1.65. TYZ65 is a product number of a high refractive type hard coating agent “LIODURAS (registered trademark)” manufactured by Toyo Ink Co., Ltd.

For the second optical buffer layer 16b, the following five types of films were used in order to cause a refractive index difference with the first optical buffer layer 16a. TYZ65 with a refractive index of 1.65, MgO with a refractive index of 1.74, Ta ₂ O _{5 with} a refractive index of 1.81, HfO _{2 with} a refractive index of 1.93, and Si ₃ N ₄ with a refractive index of 2.03 were used. . The refractive index difference (Δn) from TYZ65 is 0.00, the refractive index difference (Δn) from MgO having a refractive index of 1.74 is 0.09, and the refractive index difference (Δn) from Ta ₂ O ₅ is 0.16. The difference in refractive index (Δn) from HfO ₂ is 0.28, and the difference in refractive index (Δn) from Si ₃ N ₄ is 0.38.

  FIG. 17 shows the result of calculating the light intensity distribution in the plasmon mode in the organic electroluminescent element 1C having the above film configuration. In the calculation, 530 nm was used as the emission wavelength. In the figure, the horizontal axis indicates the relative distance based on the back surface of the organic electroluminescent element 1, and the left vertical axis indicates the normalized light intensity.

  Even if the refractive index of the optical buffer layer 16 is 1.65 + Δn and is lower than the other layers, the optical buffer layer 16 has a two-layer structure of the first optical buffer layer 16a and the second optical buffer layer 16b. In the relationship between the refractive index n1 of the first optical buffer layer 16a and the refractive index n2 of the second optical buffer layer 16b, the intensity of the plasmon mode distributed in the organic light emitting layer 13 decreases as Δn = n2-n1 increases. It can be seen that the plasmon mode is reduced.

  The above-described effects are not limited to the case where the optical buffer layer 16 has a two-layer structure of the first optical buffer layer 16a and the second optical buffer layer 16b, and the same applies to the organic electroluminescent element 1A according to the second embodiment. The effect of this can be obtained.

(Embodiment 6)
With reference to FIG. 18 to FIG. 20, the organic electroluminescent element 1D in the present embodiment will be described. 18 is a cross-sectional view showing the structure of the organic electroluminescent element 1D in the present embodiment, FIG. 19 is a diagram showing the material, film thickness, and refractive index of each layer of the organic electroluminescent element 1D shown in FIG. These are figures which show the result of having calculated the light intensity distribution of the plasmon mode of the organic electroluminescent element in this Embodiment.

  In the present embodiment, when the optical buffer layer 16 has a two-layer structure of the first optical buffer layer 16a and the second optical buffer layer 16b, the first optical buffer layer 16a and the second optical buffer layer 16b are the same. Comparison was made between a case where the refractive index is present (case 1) and a case where the relationship between the refractive index n1 of the first optical buffer layer 16a and the refractive index n2 of the second optical buffer layer 16b is n1 <n2 (case 2). Is. In case 2, the refractive index is different from that of the first and fifth embodiments in the material of the first optical buffer layer 16a. Other configurations are the same as those of the organic electroluminescent element 1 according to the first embodiment shown in FIGS.

As shown in FIG. 19, in case 1, Ta ₂ O ₅ having a thickness of 50 nm is used for the first optical buffer layer 16a and the second optical buffer layer 16b. The refractive index is 1.81. In Case 2, TYZ69 having a thickness of 50 nm is used for the first optical buffer layer 16a. The refractive index is 1.69. For the second optical buffer layer 16b, HfO2 having a thickness of 50 nm is used. The refractive index is 1.93. Note that TYZ69 is a product number of a high refractive type hard coat agent “LIODURAS (registered trademark)” manufactured by Toyo Ink Co., Ltd.

  FIG. 20 shows the result of calculating the plasmon mode light intensity distribution in the organic electroluminescent element 1D having the above film configuration. In the calculation, 530 nm was used as the emission wavelength. In the figure, the horizontal axis indicates the relative distance based on the back surface of the organic electroluminescent element 1, and the left vertical axis indicates the normalized light intensity.

  When the two-layer structure is adopted for the optical buffer layer 16, the high refractive index layer (second optical buffer layer 16 b) / low refractive index layer (first optical buffer) compared to Case 1 consisting of a single refractive index layer. It can be seen that in the case 2 consisting of two layers 16a), the plasmon mode distributed in the organic light emitting layer 13 is reduced, and the plasmon loss reduction effect is obtained.

(Embodiment 7)
A lighting apparatus 1000 using an organic electroluminescent element having the configuration shown in each of the above embodiments will be described below. FIG. 21 shows a schematic configuration of lighting apparatus 1000 in the present embodiment. The lighting device 1000 in the present embodiment is a ceiling lighting device using the organic electroluminescent element 1100 in each of the above embodiments on a ceiling 1200 of a room.

(Embodiment 8)
Hereinafter, another lighting device using the organic electroluminescence element having the configuration described in each of the above embodiments will be described. FIG. 22 shows a schematic configuration of lighting apparatus 2000 in the present embodiment. The lighting device 2000 in the present embodiment is a lighting stand, and the organic electroluminescent element 2200 in each of the above embodiments is used for the head 2100 portion.

  As described above, according to the electroluminescent element and the illuminating device using the electroluminescent element in the present embodiment, the electroluminescent element and the illuminating device using the electroluminescent element that can further improve the utilization efficiency of light. It is possible to provide.

  In addition, although the electroluminescent element in each embodiment of this invention and the illuminating device using the electroluminescent element were demonstrated, embodiment disclosed this time is an illustration and restrictive at no points. Should be considered. Therefore, the scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1, 1A, 1B, 1C, 1D, 1000, 2000 Organic electroluminescent device, 10 Transparent substrate, 11 First transparent electrode layer, 12 Hole transport layer, 13 Organic light emitting layer, 14 Electron transport layer, 15 Second transparent electrode Layer, 15A metal electrode layer, 16, 16A, 16B optical buffer layer, 16a first optical buffer layer, 16b second optical buffer layer, 16c fine particles, 20 organic electroluminescent layer, 30 light reflecting layer, 1000 illumination device, 1200 ceiling 2000 Illuminator, 2100 heads.

Claims (11)

A first transparent electrode layer;
A second transparent electrode layer;
An electroluminescent layer sandwiched between the first transparent electrode layer and the second transparent electrode layer;
An optical buffer layer provided on the opposite side of the second transparent electrode layer from the side on which the electroluminescent layer is provided;
A light reflecting layer provided on the opposite side of the optical buffer layer from the side on which the second transparent electrode layer is provided,
The optical buffer layer has different refractive indexes on the light reflecting layer side and the second transparent electrode layer side, and the refractive index on the light reflecting layer side is larger than the refractive index on the second transparent electrode layer side. An electroluminescent element which reduces plasmon loss of light from the electroluminescent layer by being provided . The optical buffer layer is
A first optical buffer layer provided on the second transparent electrode layer side;
A second optical buffer layer provided on the light reflecting layer side,
The electroluminescent element according to claim 1, wherein a refractive index of the second optical buffer layer is larger than a refractive index of the first optical buffer layer.   2. The electroluminescent element according to claim 1, wherein a refractive index of the optical buffer layer changes so as to gradually increase from the second transparent electrode layer side toward the light reflecting layer side.   The electroluminescent element according to claim 1, wherein a conductive film is used for the optical buffer layer.   The electroluminescent element according to claim 1, wherein fine particles having a light scattering effect are dispersed in the optical buffer layer.   The electroluminescent element according to claim 1, wherein a refractive index of the optical buffer layer on the second transparent electrode layer side is larger than a refractive index of the electroluminescent layer.   The electroluminescent element according to any one of claims 1 to 6, wherein a metal thin film is used for at least one of the first transparent electrode layer and the second transparent electrode layer.   The electroluminescent element according to claim 7, wherein a metal thin film is used for the second transparent electrode layer, and a film made of a conductive metal oxide is used for the first transparent electrode layer.   The electroluminescent element according to claim 8, wherein a silver thin film is used for the second transparent electrode layer, and ITO is used for the first transparent electrode layer.   The electroluminescent element according to claim 1, wherein a metal material is used for the light reflecting layer.   The illuminating device which has an electroluminescent element of any one of Claim 1 to 10.

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