JP5020423B1 - Organic light emitting device - Google Patents

Abstract

An organic light emitting device comprising a transparent conductive film formed on a transparent substrate, an organic light emitting functional layer formed on the transparent conductive film, and a reflective metal film formed on the organic light emitting functional layer, The transparent conductive film has a refractive index that increases from one surface on the transparent substrate side of the transparent conductive film toward the other surface on the organic light emitting functional layer side.
[Selection] Figure 14

Description

  The present invention relates to an organic light emitting device such as an organic EL (Electro Luminescence) device.

  An illumination device using an organic EL (Electro Luminescence) element as a light source has been proposed. An organic EL element illumination device (organic EL illumination device) has a feature that there is no restriction in shape due to surface emission, and such a feature cannot be obtained by other illumination devices such as an LED (light emitting diode) illumination device. Therefore, further development for future practical use is expected.

  Generally, an organic EL element as a light emitting source is an organic multilayer structure sandwiched between an anode made of a transparent conductive film such as ITO formed on a transparent substrate, a cathode made of a metal such as Al, and the anode and the cathode. And an organic light emitting functional layer. The organic light emitting functional layer is made of an organic material, and is composed of, for example, a hole injection / transport layer, a light emitting layer, an electron transport layer, and an electron injection layer in order from the anode side. Can be formed.

  The light generated in the organic light emitting functional layer is emitted from the organic light emitting functional layer to the outside through the anode and the transparent substrate. However, a part of the light that has passed through the anode is reflected by the transparent substrate surface, and a part is reflected by the interface between the anode and the transparent substrate. There is also light emitted from the organic light emitting functional layer to the cathode side and reflected at the interface between the organic light emitting functional layer and the cathode. In particular, the refractive index difference between the anode and the transparent substrate is large, and therefore, it is not extracted from the substrate surface of the organic light emitting device by reflecting at the interface between the anode and the transparent function, and thus is effectively used out of the generated light. There is not much light. That is, only a part of the light generated in the organic light emitting functional layer is extracted by reflection between the respective layers in the organic light emitting element, and efficient light extraction is not performed.

  In order to cope with this, conventionally, a configuration in which an antireflection film is formed between the anode and the transparent substrate to prevent reflection of light generated in the organic light emitting functional layer in the organic light emitting element has been proposed. (Patent Document 1).

Special table 2006-12726 gazette

  However, in the conventional configuration shown in Patent Document 1, the number of manufacturing steps is increased in order to form an antireflection film between the anode and the transparent substrate. Therefore, the organic light emitting functional layer is formed without forming the antireflection film. It is desired to extract the light from the substrate surface more efficiently.

  Thus, the problem to be solved by the present invention is to provide an organic light-emitting device capable of efficiently extracting light generated in the organic light-emitting functional layer from the substrate surface. Is the purpose.

An organic light-emitting device according to claim 1 is a transparent substrate, a transparent conductive film formed on the transparent substrate, and formed on the transparent conductive film, injecting holes sequentially from the transparent conductive film side. An organic light emitting device comprising an organic light emitting functional layer having a transport layer, a light emitting layer, and an electron injection transport layer, and a reflective metal film formed on the organic light emitting functional layer, wherein the transparent conductive film is refraction of the refractive index possess becomes higher toward the one surface of the transparent substrate side on the other surface of the organic luminescent functional layer side, the refractive index of the transparent substrate is the transparent conductive film of the transparent conductive film The refractive index of the organic light emitting functional layer is higher than the refractive index of the transparent conductive film, and the refractive index of the hole injection transport layer is lower than the refractive index of the electron injection transport layer .

  According to the organic light emitting device of the invention according to claim 1, the transparent conductive film has a refractive index that increases from one surface on the transparent substrate side toward the other surface on the organic light emitting functional layer side. The multi-reflection effect in the film is enhanced, so that the light generated in the organic light emitting functional layer can be efficiently extracted from the surface of the transparent substrate without forming an antireflection film between the anode and the transparent substrate as in the past. Can do.

It is sectional drawing which shows the structure of an organic EL element as an Example of this invention. It is a flowchart which shows the manufacturing process of the organic EL element of FIG. Luminescent colors R (red), O (orange), G (green), and B (blue) for each organic EL element, the luminance on the surface of the glass substrate is determined without laser annealing and with laser annealing. It is a figure shown by. Regarding the case where the organic light emitting functional layer of the organic EL element of emission color R (red) includes a hole injection layer and the case where the hole injection layer is not included, the brightness on the surface of the glass substrate is determined without laser annealing and with laser annealing. It is a figure shown by. It is a figure which shows the brightness | luminance on the surface of the glass substrate about each time length of a laser annealing process with the organic EL element of luminescent color R (red). It is a figure which shows the transmittance | permeability of the glass substrate containing an anode about the case with and without laser annealing treatment. It is a figure which shows the contrast of a wide-angle X-ray-diffraction pattern and standard data as a X-ray-diffraction (XRD) measurement result of the glass substrate containing the anode which consists of ITO about the case where a laser annealing process is and is not. It is a figure which shows a crystallite size as a X-ray-diffraction measurement result of the glass substrate containing the anode which consists of ITO about the case where a laser annealing process is and is not. It is a figure which shows the XRD peak data in the case of not performing laser annealing treatment. It is a figure which shows the XRD peak data in case a laser annealing process exists. It is a figure which shows the wavelength dependence of the refractive index n and the extinction coefficient k in the case of not performing laser annealing treatment. It is a figure which shows the wavelength dependence of the refractive index n and the extinction coefficient k in the case of laser annealing treatment. It is a figure which shows the depth direction (film thickness direction) dependence from the interface with the glass substrate of the refractive index n and the extinction coefficient k in the case of no laser annealing treatment. It is a figure which shows the depth direction dependence from the interface with the glass substrate of the refractive index n and the extinction coefficient k in the case of laser annealing treatment. It is sectional drawing of the organic EL element which has a molybdenum oxide layer between an anode and an organic light emitting functional layer.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a cross section of an organic EL element which is an embodiment of the present invention, and FIG. 2 shows a flowchart showing a manufacturing method thereof.

  For example, as shown in FIG. 2, the organic EL element is formed by forming an anode (transparent conductive film) 12 on a glass substrate (transparent substrate) 11 (step S1), laser annealing treatment for the anode 12 (step S2), The organic light emitting functional layer 13 is manufactured (step S3) and the cathode (reflective metal film) 14 is formed (step S4) in this order.

  In this organic EL element, a transparent anode 12 is formed on a transparent (including translucent) glass substrate 11. The thickness of the glass substrate 11 is 0.7 mm, for example. The anode 12 is formed by adhering and forming a transparent conductive film on the glass substrate 11 with a light-transmitting material such as ITO and patterning using a photolithography technique.

  Further, the anode 12 formed on the glass substrate 11 is subjected to laser annealing in step S2, and as a result, the chemical composition of the anode 12 is thermally changed. By this laser annealing treatment, the anode 12 has a refractive index that increases (increases) from one surface on the glass substrate 11 side toward the other surface on the opposite side. The laser specifications for laser annealing are laser model number: LS-2132U, Pulsed Nd: YAG laser, wavelength (variable): 1064nm, 532nm, 355nm, 266nm, laser output (variable): 1-180mj, laser annealing The treatment was carried out with a laser power of about 10 mj.

An organic light emitting functional layer 13 is formed on the anode 12 after the laser annealing treatment. The organic light emitting functional layer 13 has a multilayered structure of a hole transport layer, a light emitting layer, and an electron transport layer in order from the anode 12 side, and can be formed by a dry method such as a vacuum evaporation method, as well as an ink jet method or a printing method. It can also be formed by a wet method such as. The hole transport layer is made of NPB and has a thickness of 40 nm. As the material of the light emitting layer, host CBP and dopant Ir (phq) ₂ tpy can be used in the red light emitting layer, host CBP and dopant HexIr (phq) ₃ can be used in the orange light emitting layer, and host CBP in the green light emitting layer. The dopant Ir (ppy) ₃ can be used, and the host PAND and the dopant DPAV can be used in the blue light emitting layer. As the material for the electron transport layer, NBphen doped with CsxMoOx can be used.

  A cathode 14 is formed on the organic light emitting functional layer 13. The cathode 14 can be formed by a vacuum deposition method, and it is preferable to use a light reflective metal such as Al or Ag as the metal material.

  FIG. 3 shows the organic EL of each of the emission colors R (red), O (orange), G (green), and B (blue) when ITO is used as the anode 12 and the thicknesses are 70 nm and 155 nm. The luminance of the element on the surface of the glass substrate 11 is shown when the laser annealing process is not performed on the ITO and when the laser annealing process is performed. In the organic EL element used for the measurement shown in FIG. 3, the thickness of the hole transport layer of the organic light emitting functional layer 13 is 40 nm, the thickness of the electron transport layer is 30 nm, and the blue light emitting layer is 40 nm thick. Except for having a thickness of 60 nm. The cathode 14 is formed to 5 to 10 nm at a deposition rate of 0.1 to 0.5 nm / sec, and further to 65 to 100 nm at a deposition rate of 0.5 nm / sec, and the total thickness is 70 to 100 nm. The film formation was performed at In addition, it is preferable that a vapor deposition rate is a rate (for example, 0.5-1 nm / sec) of the grade which a cathode material does not oxidize with oxygen within the chamber for vapor deposition. The thickness of the cathode 14 is preferably 50 nm or more in order to obtain sufficient reflection.

  In the case of laser annealing treatment, the laser annealing treatment time is the same time (for example, 1 hour). In addition, after the organic EL element is manufactured, the laminated portions 12 to 14 on the glass substrate 11 are made of metal or glass including a desiccant (not shown) in a glove box in an inert gas atmosphere from a vacuum vapor deposition machine. Sealing with a sealing can (not shown) was performed.

In luminance measurement, a driving current of ^2.5 mA / cm ² (7.5 mA / cm ² for a device having a blue light emitting layer) was passed between the anode 12 and the cathode 14 to cause the organic EL device to emit light. From the measurement results shown in FIG. 3, it can be seen that the brightness is improved when the thickness of the anode 12 is 70 nm than when the thickness is 155 nm. This is considered to be because it is easily affected by optical interference due to the film thickness when the thickness is 70 nm.

FIG. 4 does not include the case where ITO is used as the anode 12 and the thickness of the organic light emitting functional layer 13 of the organic EL element of the emission color R (red) is 70 nm and 155 nm, respectively, and the hole injection layer is included. The brightness on the surface of the glass substrate 11 is shown for the case without laser annealing and with laser annealing. In the organic EL element used for the measurement shown in FIG. 4, the organic light emitting functional layer 13 has a laminated structure including a hole injection layer, a hole transport layer, a light emitting layer, and an electron transport layer in this order from the anode 12 side. . The hole injection layer is made of MoOx, which is a molybdenum oxide, with a thickness of 5 nm. The hole transport layer has a thickness of 40 nm, the electron transport layer has a thickness of 30 nm, and the red light emitting layer has a thickness of 60 nm. The cathode 14 is formed to 5 to 10 nm at a deposition rate of 0.1 to 0.5 nm / sec, and further to 65 to 100 nm at a deposition rate of 0.5 nm / sec, and the total thickness is 70 to 100 nm. The film formation was performed at In the case of laser annealing treatment, the laser annealing treatment time is the same time (for example, 1 hour). In addition, after the organic EL element is manufactured, the laminated portions 12 to 14 on the glass substrate 11 are made of metal or glass including a desiccant (not shown) in a glove box in an inert gas atmosphere from a vacuum vapor deposition machine. Sealing with a sealing can (not shown) was performed. In the luminance measurement, a driving current of ^2.5 mA / cm ² was passed between the anode 12 and the cathode 14 to cause the organic EL element to emit light.

  From the measurement results shown in FIG. 4, it was confirmed that the luminance was improved by including a hole injection layer having a high refractive index of 2.3 in the organic light emitting functional layer 13. In the case of the laser annealing treatment and the hole injection layer, compared to the case of no laser annealing treatment and the case of no hole injection layer, the ITO anode 12 has a thickness of 1.12 times and 1.11 times at a thickness of 70 nm. Increased brightness.

  FIG. 5 shows the surface of the glass substrate 11 for each of the organic EL elements of the emission color R (red), in which the time length of the laser annealing treatment is 0 (no laser annealing treatment), 10, 30, 60, 120, 180, 240 minutes. The brightness is shown. In the organic EL element used for the measurement shown in FIG. 5, ITO is used as the anode 12 and the thickness thereof is 155 nm. The thickness of the hole transport layer of the organic light emitting functional layer 13 is 40 nm. The thickness is 30 nm, and the red light emitting layer has a thickness of 60 nm. The cathode 14 is formed to 5 to 10 nm at a deposition rate of 0.1 to 0.5 nm / sec, and further to 65 to 100 nm at a deposition rate of 0.5 nm / sec, and the total thickness is 70 to 100 nm. The film formation was performed at In addition, after the organic EL element is manufactured, the laminated portions 12 to 14 on the glass substrate 11 are made of metal or glass including a desiccant (not shown) in a glove box in an inert gas atmosphere from a vacuum vapor deposition machine. Sealing with a sealing can (not shown) was performed.

In the luminance measurement, a driving current of ^2.5 mA / cm ² was passed between the anode 12 and the cathode 14 to cause the organic EL element to emit light. From the measurement results shown in FIG. 5, it can be seen that there is no particular change in luminance when the laser annealing treatment is 10 minutes or longer.

  FIG. 6 shows the transmittance of the glass substrate 11 including the anode 12 made of ITO with and without the laser annealing treatment. The transmittance in the wavelength range of 250 to 900 nm is measured. From the measurement results shown in FIG. 4, it was confirmed that the anode 12 was reduced by about 3% by laser annealing. This is considered that oxygen injected into ITO is deficient by laser annealing.

7 and 8 show X-ray diffraction (XRD: RU-200R (rotary anti-cathode type)) measurement results of glass substrate 11 including anode 12 made of ITO with and without laser annealing. ing. Irrespective of the treatment, ITO diffraction peaks showing a diffraction pattern similar to In ₂ O ₃ were observed. In addition, amorphous scattering, which seems to be a glass substrate, was observed. Amorphous ITO showed diffuse scattering near a diffraction angle of 30 °, but no scattering that was considered to be amorphous ITO was detected in the two samples measured this time (FIG. 7). Moreover, although the diffraction pattern of ITO is substantially the same, the relative intensity of a few 400 peaks is strong by laser annealing treatment. Therefore, it is considered that the laser annealing treatment has a slightly stronger orientation of 400 compared to the case without the treatment. There is no significant difference in the half width of the diffraction peak. Therefore, although there is no great difference in the crystallite size, the crystallite size is slightly increased by the laser annealing treatment, and the crystallinity is high (FIG. 8). The crystallite size was calculated using the following formula.

Here, λ (0.15418 nm), βe: half width of diffraction peak, βo: correction value of half width (0.12 °).
FIG. 9 shows XRD peak data without laser annealing, and FIG. 10 shows XRD peak data with laser annealing. Note that hkl is a lattice plane, d is a surface interval, and cps is an abbreviation for count per second.

  FIGS. 11 to 14 show the results of measuring the refractive index n and extinction coefficient k of ITO as the anode 12 using a high-speed spectroscopic ellipsometer M-2000 (manufactured by J.A. Woollam). FIG. 11 shows the wavelength dependence of the refractive index n and the extinction coefficient k without laser annealing, and FIG. 12 shows the wavelength dependence of the refractive index n and the extinction coefficient k with laser annealing. Yes. FIG. 13 shows the dependence of the refractive index n and extinction coefficient k without laser annealing on the depth direction (film thickness direction) from the interface with the glass substrate, and FIG. 14 shows the refractive index with laser annealing. The dependence of n and extinction coefficient k on the depth direction from the interface with the glass substrate is shown. As measurement conditions, incident angles were 60 degrees, 65 degrees, 70 degrees, and 75 degrees, measurement wavelengths were 195 nm to 1680 nm, and analysis software used WVASE32. In the measurement, the back surface of the sample was roughed and the back surface reflection was eliminated as much as possible.

  In calculating the refractive index n and the extinction coefficient k from the measurement results, the optical constant of the glass substrate was calculated from the reference of the glass substrate alone. The ITO layer assumed a change in dielectric constant in the depth direction, and the sample with laser annealing treatment assumed two ITO layers and assumed a dielectric constant distribution only on the surface side.

  The sample without laser annealing treatment is a layered structure of a rough surface layer, ITO layer (assuming a linear change in dielectric constant in the film thickness direction) and glass substrate, and the sample with laser annealing treatment is rough surface A layered structure of an ITO layer, an ITO layer (assuming a linear change in dielectric constant in the film thickness direction), an ITO layer, and a glass substrate was used.

  In the calculation of the refractive index n and the extinction coefficient k, the spectrum of Δ (phase difference) and ψ (amplitude reflectance) measured in the sample is compared with (Δ, ψ) calculated from the calculation model, and the measured value ( Fitting was performed by changing the dielectric function so as to approach (Δ, ψ). The fitting result shown here is the result of the best fit (mean square error converges to the minimum) between the measured value and the theoretical value.

  In the case of no laser annealing treatment, as can be seen from FIGS. 11 and 13, the change in the refractive index n is small in both wavelength dependency and depth direction dependency. On the other hand, in the case of the laser annealing treatment, as can be seen from FIGS. 12 and 14, the refractive index n at the interface between the glass substrate and ITO is not different between the laser annealing treatment and the laser annealing treatment. Refractive index n is increased by processing on the surface of ITO opposite to the glass substrate side surface. The refractive index n increases with a gradient of 0.1 with respect to the depth direction of 85 nm, and changes linearly. This means that the refractive index decreases in the depth direction (glass substrate side direction) from the ITO surface. For this reason, when a hole injection layer having a high refractive index of 2.3 described with reference to FIG. 4 is inserted, it is presumed that a result of further improving the output was obtained. The extinction coefficient k tends to be contrary to the increase and decrease of the refractive index n. However, the change of the extinction coefficient k is small.

  From these analyses, by applying laser annealing to the anode ITO, oxygen on the ITO surface is lost, the refractive index n of the ITO surface is improved, and the multiple reflection effect in the ITO layer is enhanced, thereby increasing the brightness. It is thought that it improved.

  Thus, in the organic EL element of the embodiment of the present invention, the anode 12 has a refractive index that increases from one surface (interface) on the glass substrate 11 side toward the other surface on the organic light emitting functional layer 13 side. The multiple reflection effect in the anode 12 is enhanced, whereby the light generated by the organic light emitting functional layer 13 can be efficiently extracted from the surface of the glass substrate 11. In addition, since it is not necessary to form an antireflection film between the anode and the transparent substrate as in the prior art, the film manufacturing process can be reduced by that much.

  In the above embodiment, each refractive index from the glass substrate 11 to the organic light emitting functional layer 13 may be increased from the surface of the glass substrate 11 toward the interface between the organic light emitting functional layer 13 and the cathode 14. That is, the refractive index of the glass substrate 11 may be lower than the refractive index of the anode 12, and the refractive index of the organic light emitting functional layer 13 may be higher than the refractive index of the anode 12. For example, the refractive index of the glass substrate 11 is set to a value between 1.4 and 1.5, the refractive index of the anode 12 is changed between 1.7 and 2.3, and the organic light emitting functional layer 13 has a low refractive index of 1. A layer portion (hole injection transport layer portion) of .5 to 1.8 and a layer portion (electron injection transport layer portion) of a high refractive index of 1.8 to 2.3 can be formed. By doing so, the multiple reflection effect in the element is enhanced, so that it can be efficiently taken out from the surface of the glass substrate 11. In addition, in order that the layer part (electron injection transport layer part) with a high refractive index of the organic light emitting functional layer 13 may raise a refractive index more, a metal acid salt compound may be mixed. Moreover, the low refractive index layer portion of the organic light emitting functional layer 13 has a thickness of 1 to 180 nm, for example, and the high refractive index layer portion has a thickness of 1 to 70 nm, for example. The layer portion having a high refractive index is formed to have a thickness that prevents an increase in the waveguide mode of the organic layer and does not cause a light emission loss. The hole injection / transport layer is a hole injection layer and / or a hole transport layer, and the electron injection / transport layer is an electron injection layer and / or an electron transport layer.

  Furthermore, as shown in FIG. 15, the molybdenum oxide layer 21 may be formed between the anode 12 and the organic light emitting functional layer 13 by, for example, vacuum deposition. The molybdenum oxide layer 21 is conductive and has a refractive index higher than that of the anode 12, for example, 2.2. By including the molybdenum oxide layer 21 in this way, the light generated in the organic light emitting functional layer 13 can be extracted from the surface of the glass substrate 11 more efficiently. The molybdenum oxide layer 21 may be provided as a hole injection layer of the organic light emitting functional layer 13 as described above. In addition to the molybdenum oxide layer 21, other conductive inorganic oxide layers such as titanium oxide may be used.

  Further, the transparent substrate is not limited to the glass substrate 11 shown in the embodiment, and a resin substrate may be used. The anode 12 which is a transparent conductive film is not limited to ITO, and IZO may be used. Furthermore, the structure and material of the organic light emitting functional layer 13 are not limited to the above-described embodiments.

  Further, in the above-described embodiment, the laser annealing process is performed on the anode 12 in step S2. As a result, the chemical composition of the anode 12 is thermally changed, but the chemical composition of the anode 12 is thermally changed. If it is a technique, the process of step S2 is not limited to the laser annealing process.

  The organic light emitting device of the present invention can be used in an organic light emitting panel for a lighting device.

11 Glass substrate 12 Anode 13 Organic light emitting functional layer 14 Cathode 21 Molybdenum oxide layer

Claims (6)

A transparent substrate;
A transparent conductive film formed on the transparent substrate;
An organic light emitting functional layer formed on the transparent conductive film and having a hole injecting and transporting layer, a light emitting layer, and an electron injecting and transporting layer in order from the transparent conductive film side ;
A reflective metal film formed on the organic light emitting functional layer, and an organic light emitting device comprising:
The transparent conductive film is perforated the organic light-emitting functional layer side refractive index becomes higher toward the other side from the one surface of the transparent substrate side of the transparent conductive film,
The refractive index of the transparent substrate is lower than the refractive index of the transparent conductive film, the refractive index of the organic light emitting functional layer is higher than the refractive index of the transparent conductive film,
The organic light emitting device, wherein a refractive index of the hole injection transport layer is lower than a refractive index of the electron injection transport layer . The organic light emitting device according to claim 1, wherein the refractive index of the transparent conductive film is characterized in that it varies linearly. 3. The organic light emitting device according to claim 1, wherein a refractive index of the transparent conductive film increases with a gradient of 0.1 with respect to a film thickness of 85 nm of the transparent conductive film. Of claim 1 to 3, characterized in that the formation of the inorganic oxide layer of the conductive having a refractive index greater than the refractive index of the transparent conductive film between the transparent conductive film and the organic luminescent functional layer The organic light emitting element of any one. 5. The organic light emitting device according to claim 4, wherein the inorganic oxide layer acts as a hole injection layer of the organic light emitting functional layer. The inorganic oxide layer is an organic light emitting device according to claim 4 or 5, wherein the molybdenum oxide.

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