JP2005100789A - Spontaneous light emitting display device and organic el display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spontaneous light emitting display device, such as an organic EL display device, suppressing the deterioration of emission luminance of the display itself and achieving a bright display image, even if a polarizing plate is arranged on the screen for preventing outside light reflection. <P>SOLUTION: An organic EL light emitting part 6 is formed by laminating electrode layers 3, 5, and an organic layer 4 on a transparent substrate 1. A reflection polarizing plate 7 is arranged on a surface opposite to the surface on which the organic EL light emitting part 6 is formed. In other words, the organic EL display device has the reflection polarizing plate on the screen side. Over the reflection polarizing plate 7 on the screen side, an absorbing polarizing plate 8 is arranged with the polarizing axes aligned, which allows effective use of the light emitting part, while suppressing reflection light on the screen. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an organic EL display device constituting a display using organic electroluminescence (EL) and a self-luminous display device such as an organic EL display device. More specifically, a structure in which a polarizing plate is provided on the display surface side in order to prevent external light from being reflected inside the display device and preventing ambient light from being reflected and the back side of the display device (a hygroscopic agent or a reflection member) from being seen through. However, the present invention relates to a self-luminous display device such as an organic EL display device having a structure capable of suppressing a decrease in luminance of the display screen.

  For example, an EL element using an organic substance has been developed as an inexpensive display element of a solid light emitting type. A conventional organic EL display device has a structure as shown in FIG. That is, in FIG. 3A, a plurality of strip-like anode electrodes 33 made of ITO or the like are provided in parallel on one surface of a transparent substrate 32 such as glass, and the gap portion and the ITO film 33 formed in a strip shape. An insulating film 34 made of, for example, a positive type photoresist is formed in a region where light is not emitted (will not be a pixel) by using a photolithography technique, and further, for example, a negative type photoresist is applied on the surface thereof. By patterning, a plurality of partition walls 35 are formed in parallel in a direction perpendicular to the anode electrode 33 (in a direction perpendicular to the paper surface). Then, the organic layer 36 is formed in a vacuum deposition apparatus, and aluminum (Al) is deposited on the surface thereof to a thickness of about 0.1 μm by the vacuum deposition apparatus, whereby the cathode electrode 37 is an anode made of ITO. It is formed in a strip shape in a direction orthogonal to the electrode 33.

Note that the organic layer 36a (the organic layer 36a is not attached when a metal mask is used when forming the organic layer) and the electrode material layer 37a are stacked on the partition wall 35, but the partition wall 35 is high. The organic layer 36 and the cathode electrode 37 of each pixel column serving as the light emitting portion are electrically separated from the film on the partition, and the organic layer 36 and the cathode electrode 37 of the adjacent pixel column are also electrically connected by the partition 35. To be separated. As a result, a portion where the orthogonal anode electrode 33 and the cathode electrode 37 intersect becomes a pixel, a voltage is applied only to the pixel selected by both electrodes, and the desired pixel is lit, from the other surface side of the transparent substrate 32. An image is displayed by irradiation.

  In such a configuration, the light of the image formed by emitting light from the organic layer is irradiated from the other surface side of the transparent substrate 32, and as shown in FIG. Since the image is reflected by the metal film such as the electrode 37, the background becomes bright and the display image is difficult to see. In order to solve such a problem, as shown in FIG. 3B, a polarizing plate (circular polarizing plate) 40 is provided on the display surface side, and the polarization direction of the light reflected inside is changed. A structure is used in which light coming out through the plate is not so noticeable because a large amount of light that does not coincide with the polarization axis of the polarizing plate is attenuated (see Patent Document 1, for example).

That is, by inserting an ordinary polarizing plate, the light that enters the display device from outside is only light that vibrates in the direction along the polarizing axis of the polarizing plate, and other light is absorbed. Almost half of the light enters, and the direction of vibration of the light reflected inside becomes random, and the light reflected and passing through the polarizing plate is further reduced to half of the light entering inside. . Therefore, the ratio of the light that enters the display device, reflects inside, and exits to the outside is attenuated to approximately 25%, and is hardly affected by the external light.
Japanese Patent Laid-Open No. 8-321381 (FIG. 1)

  As described above, by providing the polarizing plate on the display surface of the display device, it is possible to solve the problem that the background becomes bright due to the reflection of external light or the display image is difficult to see. However, the polarizing plate transmits only a component of light that vibrates in one direction and blocks light that vibrates in a direction orthogonal to that direction, so that only about half of normal light that vibrates in any direction is blocked. The other half cannot pass through and is absorbed. As a result, only half of the light emitted from the organic EL light emitting part can contribute to the display, and the screen becomes darker. If the user tries to make it brighter, the input must be increased, resulting in increased power consumption and shorter life. There is a problem of becoming. Such a problem is not limited to organic EL display devices, but is common to self-luminous display devices that emit light themselves, such as inorganic EL display devices and display devices using LEDs.

  The present invention has been made in view of such circumstances, and in a self-luminous display device, even when a polarizing plate is provided on the display surface in order to prevent reflection of external light, the luminance of the display device itself is reduced. An object of the present invention is to provide a self-luminous display device such as an organic EL display device having a structure capable of suppressing a decrease and obtaining a bright display image.

  A self-luminous display device according to the present invention includes a light-emitting portion that constitutes a self-luminous display device, and a reflective polarizing plate provided on the display surface side of the light-emitting portion. The organic EL display device according to the present invention includes a transparent substrate, an organic EL light emitting unit having an electrode layer and an organic layer laminated on one surface of the transparent substrate, and the organic EL light emitting unit forming surface of the transparent substrate. It consists of a reflective polarizing plate provided on the opposite surface.

  Here, the self-luminous display device means a device that constitutes the display device while emitting light by itself, such as an organic or inorganic EL display device or LED display device. The reflective polarizing plate means a polarizing plate that transmits light that vibrates in a specific direction and reflects light that does not absorb light that vibrates in a direction crossing the specific direction.

  By providing an absorption polarizing plate having a polarization axis combined with the polarization axis of the reflective polarizing plate on the surface of the reflective polarizing plate, external light that cannot pass through the polarizing plate is absorbed without being reflected on the display surface. Therefore, the display light emitted from the light emitting portion is attenuated because the polarization axis is the same direction as that of the reflective polarizing plate, while reducing the influence of external light to almost the same as the structure in which the conventional polarizing plate is provided. Light that is transmitted without being transmitted through the reflective polarizing plate can be reflected repeatedly and transmitted with light whose polarization axis and vibration direction coincide with each other, so that most of the emitted light can be transmitted and the display screen is brightened. A very bright display can be achieved without too much. Here, the polarization axis means the vibration direction of light transmitted through the polarizing plate. The absorption variable plate means a variable plate that absorbs light that vibrates in a direction orthogonal to the polarization axis.

  A quarter-wave retardation plate with an optical axis set to form an angle of 45 ° with the polarization axis of the reflective polarizing plate is bonded to the reflective polarizing plate, thereby forming a circular polarizing plate. Since the circularly polarized light reflected by the metal film is inverted in polarization direction and cancels out as light having opposite phases, the reflected light does not pass through the circularly polarizing plate and return. As a result, even if there is a reflective polarizing plate, the light that has entered the interior is rapidly attenuated and the phenomenon that the inner surface of the display device is reflected is eliminated, and the visual characteristics are greatly improved.

  The reflective polarizing plate is configured as a birefringent dielectric multilayer film, for example.

  With this structure, about half of the external light that enters the light emitting portion from the display surface side is reflected by the surface of the reflective polarizing plate, and almost half of the light enters the light emitting portion. The light reflected on the surface of the reflective polarizing plate is visually recognized by the observer observing the display surface together with the display image, but only half of the external light is reflected and is reflected uniformly on the entire surface. Just looks bright, and the display screen is not glaring. In addition, the light transmitted through the display device is irregularly reflected and returns to the reflective polarizing plate, but the vibration direction of the irregularly reflected light is randomized by the reflection, so that the light transmitted through the reflective polarizing plate is almost halved. . The light reflected by the reflective polarizing plate is also diffusely reflected inside again and transmitted through the reflective polarizing plate, but the attenuation is larger than the light emitted from the light emitting unit. As a result, the light that enters the interior and is reflected is about 1/6 to 2/6 of the diplomacy, and there is almost no phenomenon that the internal electrodes and the like are reflected, and the visual characteristics are not deteriorated.

  On the other hand, the light emitted from the light emitting portion has a random vibration direction, and the light transmitted through the reflective polarizing plate is approximately ½. However, since the light emitted from the light emitting part is emitted between the very narrow reflective polarizing plate and the metal electrode, the light that cannot be transmitted and reflected is immediately reflected by the metal electrode such as an organic EL display device. Since the vibration direction changes and reaches the reflective polarizing plate, the vibration light that matches the direction of the polarization axis of the reflective polarizing plate is transmitted. That is, the light of the light emitting part reflected by the reflective polarizing plate is repeatedly reflected at a narrow interval, and the vibration direction coincides with the polarization axis of the reflective polarizing plate and passes through the reflective polarizing plate. Do not proceed to the direction of the screen, but proceed to the display screen side.

  As a result, the light reflected by the external light is brighter than the case where the conventional absorption polarizing plate is used, while the display screen is brighter than the case where the conventional absorption polarizing plate is used, and the light emitted from the light emitting portion is much brighter than the case where the conventional absorption polarizing plate is used. Therefore, a bright display image can be obtained while greatly reducing the influence of external light.

  That is, according to the present invention, by providing the polarizing plate on the display surface side, the light emitted from the light emitting portion can be used for a display image with almost no attenuation while being hardly affected by external light. A self-luminous display device such as an organic EL display device which can display very bright and has excellent visual characteristics can be obtained.

  Next, the self-luminous display device of the present invention will be described using an example of an organic EL display device with reference to the drawings. In the organic EL display device of the present invention, as shown in a partially perspective explanatory view of one embodiment of FIG. 1, electrode layers 3 and 5 and an organic layer 4 are laminated on one surface of a transparent substrate 1, and organic An EL light emitting unit 6 is formed, and a reflective polarizing plate 7 is provided on the surface opposite to the surface on which the organic EL light emitting unit 6 is formed. That is, the organic EL display device of the present invention is characterized in that the reflective polarizing plate 7 is provided on the display surface A side of the transparent substrate 1. In the example shown in FIG. 1, an absorption polarizing plate 8 is provided on the further surface side of the reflective polarizing plate 7, and a sealing plate 9 is provided so as to cover the light emitting unit 6 side.

  The reflective polarizing plate 7 transmits light oscillating in a specific direction (also referred to as a polarization axis), while reflecting light oscillating in a direction intersecting with the specific polarizing plate 7. For example, as shown in FIG. For example, an adhesive (not shown) such as an acrylic resin is joined to one surface of the transparent substrate 1 made of.

  The reflective polarizing plate 7 is configured as a birefringent dielectric multilayer film, for example. The dielectric multilayer film is formed by laminating a plurality of sets of two polymer layers having different photoelastic moduli, for example, PEN (2,6-polyethylene terephthalate) and coPEN (70-naphthalate / 30-terephthalate copolyester) alternately. This is stretched about 5 times, for example. While these polymer layers have different refractive indexes in the stretching direction, the refractive indexes in the direction orthogonal to the stretching direction are the same, and each pair has birefringence by stretching in one direction, While the light oscillating in the stretching direction can be reflected by the difference in refractive index, the light oscillating in the direction orthogonal to the stretching direction can be transmitted. And if the film thickness of the two polymer layers is half-wave, reflection occurs, so if multiple sets with different film thickness are stacked, the light that oscillates in the stretching direction is reflected over a wide wavelength range. can do.

  In the example shown in FIG. 1, an absorbing polarizing plate 8 having the polarizing axis aligned with the reflective polarizing plate 7 is provided on the outer side of the reflective polarizing plate 7. As shown in FIG. 3, the absorption polarizing plate 9 transmits only light that vibrates strongly in a specific direction in the same manner as a polarizing plate conventionally provided to suppress reflection of external light. It has the function of absorbing other components and is the same as the polarizing plate provided on both surfaces of the liquid crystal panel of the liquid crystal display device. That is, for example, a film-like film in which a polarizing film called an H film is sandwiched between support films such as cellulose acetate can be used. For example, the H film is stretched while heating a thin film of polyvinyl alcohol (PVA) and immersed in a solution called H ink containing a large amount of iodine, so that the PVA film absorbs iodine in the H ink. The film has a polarizing ability.

  Although not shown in FIG. 1, a linearly polarizing plate that makes light whose vibration direction is random, such as the reflective polarizing plate 7, light only in a certain vibration direction, and an optical axis that is the polarization axis of the linearly polarizing plate and 45. A circularly polarizing plate can be formed by bonding a quarter-wave retardation plate set to make an angle of °. By making such a circularly polarizing plate, the circularly polarized light reflected by the metal film is reversed in polarization direction and cancels out as light having opposite phases, so that the reflected light does not return to the display surface A side. be able to.

  As the transparent substrate 1, transparent substrates such as glass and various insulating plastics such as a polyimide film, a polyester film, a polyethylene film, a polyphenylene sulfide film, and a polyparaxylene film can be used.

  In the example shown in FIG. 1, the first electrode layer 3 is formed as an anode electrode, and in order to extract light on the surface side, it is necessary to use a transparent electrode. ITO (Indium Tin Oxide) provided by vapor deposition or the like, Indium oxide or the like is used.

  The organic EL light emitting unit 6 has a structure having a partition wall as shown in FIG. 3 described above, but has a structure in which an organic layer or an electrode layer is formed only on a necessary portion using a metal mask without a partition wall. For example, the first electrode layer 3, the organic layer 4, and the second electrode layer 5 are formed on the transparent substrate 1. When the first electrode layer 3 is an anode electrode, the organic layer 4 is formed in a structure including a hole transport layer 41, a light emitting layer 42, and an electron transport layer 43 as shown in FIG. The electron injection layer 5a is formed between the layer (cathode electrode) 5 and the organic layer 4 is not limited to this three-layer structure, and at least a light emitting layer may be formed. Each layer can also be made into multiple layers. Further, when the anode and the cathode are turned upside down, the laminated structure of the organic layer 4 is also reversed.

  The hole transport layer 41 generally has a small ionization energy to improve the hole injection property to the light emitting layer 42 and improve the stable transport of holes, and confine electrons (energy) to the light emitting layer 42. And an amine-based material such as a triphenyldiamine derivative, a styrylamine derivative, an amine derivative having an aromatic condensed ring, and the like is used, and it is 10 to 100 nm, preferably 20 to 50 nm. Provided to a thickness of about. Although not shown in the drawing, a hole injection layer is provided between the hole transport layer 41 and the anode electrode 3 to further improve the carrier injection property to the hole transport layer 41. . Also in this case, in order to improve the injectability of holes from the anode electrode 3, a material having good ionization energy consistency is used, and as a representative example, an amine or phthalocyanine is used. In the example shown in FIG. 2, NPB is provided as a hole transport layer 41 with a thickness of 35 nm.

  The light emitting layer 42 is selected according to the emission wavelength. For example, a DSA-based material is used as a blue material, and Alq is used as a green and red light-emitting material, and has a thickness of about 35 nm. Is provided. The light emitting layer 42 can obtain an emission color unique to the doping material by doping an organic fluorescent material, and can improve the light emission efficiency and stability. This doping is performed at about several weight (wt)% (0.1 to 20 wt%) with respect to the light emitting material.

  As the fluorescent substance, quinacridone, rubrene, styryl dyes and the like can be used. Alternatively, quinoline derivatives, tetraphenylbutadiene, anthracene, perylene, coronene, 12-phthaloperinone derivatives, phenylanthracene derivatives, tetraarylethene derivatives, and the like can be used. Further, it is preferably used in combination with a host material capable of emitting light by itself, and as the host material, a quinolinolato complex is preferable, an aluminum complex having 8-quinolinol or a derivative thereof as a ligand is preferable, A phenylanthracene derivative, a tetraarylethene derivative, or the like can be used.

  The electron transport layer 43 has a function of improving the injectability of electrons from the cathode electrode 5 and a function of stably transporting electrons. In the example shown in FIG. 2, Alq3 (tris (8-quinolinolato) aluminum) Is provided with a thickness of 25 nm. When this layer becomes too thick, light is emitted from this layer instead of the light emitting layer. Therefore, the layer is not excessively thick, and is usually provided in a thickness of about 10 to 80 nm, preferably about 20 to 50 nm. As the electron transport layer 43, in addition to the above materials, a quinoline derivative, a metal complex having 8-quinolinol or a derivative thereof as a ligand, a phenylanthracene derivative, a tetraarylethene derivative, or the like can be used. When the gap between the electron transport layer 43 and the cathode electrode 5 is large, an electron injection layer 5a made of LiF or the like is provided similarly to the hole side.

  As the second electrode layer 5 serving as a cathode electrode, a metal having a small work function is mainly used in order to improve the electron injection property. As typical examples, Mg, K, Li, Na, Ca, Sr, Ba, Al, Ag, In, Sn, Zn, Zr and the like are generally used. A transparent film such as indium oxide can also be used. In order to prevent oxidation of these metals and stabilize them, they are often alloyed with other metals. In the example shown in FIG. 2, an Al layer is formed to a thickness of about 110 nm through the LiF layer 5a. Thus, the cathode electrode 5 is formed.

The sealing plate 9 is provided on the transparent substrate 1 so as to cover the organic EL light emitting unit 6, and the inside thereof is filled with dry nitrogen or the like, or a hygroscopic agent (not shown) is enclosed. As the sealing plate 9, a cap pressed into a can type with stainless steel or the like may be attached to the transparent substrate 1. Is attached to the one surface side of the transparent substrate 1 so that the organic EL light emitting unit 6 and the like are accommodated in the counterbored hole. The sealing plate 9 is for blocking the organic EL light emitting unit 6 from the outside air. The sealing plate 9 may not be a cap or a glass plate but may have a structure in which a passivation film such as Si _x N _y is coated. .

  By adopting this structure, light from the outside does not enter the light emitting part, and the parts in the light emitting part are reflected, or glare reflected on the entire surface of the display screen. The luminance of the light emitted from the screen does not decrease, and the display screen does not become difficult to see.

  That is, since the reflective polarizing plate is provided on the display surface side, the light traveling from the outside to the organic EL light emitting unit has an irregular vibration direction, and the light that does not vibrate in the same direction as the polarization axis of the reflective polarizing plate is reflected. Only light that vibrates in the same direction enters. That is, approximately 1/2 of the light is reflected by the surface of the reflective polarizing plate, and the remaining approximately 1/2 of the light enters the organic EL light emitting unit. The light reflected on the surface is approximately 4/6 to 5/6 in total of approximately 1/2 light directly reflected and light reflected through the reflective polarizing plate and returned internally. As will be described later, since there is almost no internal reflection, only the display screen becomes bright, and the visual recognition characteristics hardly deteriorate. As shown in the example shown in FIG. 1, by providing an absorption polarizing plate on the surface, light that vibrates in a direction that cannot pass through the absorption polarizing plate is absorbed and not reflected, so that reflection on the surface is eliminated. Can do.

  The light entering the organic EL light emitting part is reflected by the metal electrode and returns to the reflective polarizing plate, but when reflected, the vibration direction changes and becomes random, so the same direction as the polarization axis of the reflective polarizing plate The light that vibrates in the light is transmitted and returns to the observer, but the other light is reflected by the reflective polarizing plate and returns to the organic EL light emitting unit again. This is repeated, but since it was originally incident in an oblique direction from the outer surface side, much light is reflected in the oblique direction, much light is attenuated and extinguished, and the light that passes through the reflective polarizing plate returns to the inside. Is about 1/3 to 2/3 of the light entering the light source, and is about 1/6 to 2/6 of the entire outside light directed to the display device, and the reflection inside the light emitting portion hardly appears.

  On the other hand, the light emitted from the organic EL light emitting unit 6 is similarly light having a random vibration direction, and only light that vibrates in the same direction as the polarization axis of the reflective polarizing plate is transmitted, but is reflected with a different vibration direction. The light is reflected again by the metal electrode (second electrode layer) 5 provided at a narrow interval and reaches the reflective polarizing plate 8. Since the direction of vibration also changes during this reflection, some of the light is transmitted with the direction of vibration coinciding with the direction of the polarization axis of the reflective polarizer, and the light that does not match is reflected again by the reflective polarizer, Eventually most of the light passes through the reflective polarizer. That is, although the light emitting layer 4 and the transparent substrate 1 are written thick in FIG. 1, the distance between the reflective polarizing plate 8 and the metal electrode 5 is actually very narrow, and the light emitted during this time is repeatedly reflected between them. Thus, it does not reflect toward the other pixels and passes through the reflective polarizing plate with almost no attenuation. As a result, 80% or more of the light emitted from the organic EL light emitting unit 6 is transmitted through the reflective polarizing plate, and a very bright display image can be exhibited even when the polarizing plate is provided.

  In the case where an absorption polarizing plate is provided on the surface side as in the example shown in FIG. 1, the light whose vibration direction does not coincide with the polarization axis of the polarizing plate is absorbed without reflection as described above, and the display surface Can be displayed without making it too bright. On the other hand, since the light emitted from the light emitting unit has the same polarization axis as the absorption polarizing plate and the reflection polarizing plate, the light transmitted through the reflection polarizing plate passes through the absorption polarizing plate as it is and cannot pass through the reflection polarizing plate. If the light can be transmitted through the reflective polarizing plate while repeating reflection with the metal electrode as described above, the light also passes through the absorbing polarizing plate as it is. Therefore, by providing the absorption polarizing plate, the light emitted from the organic EL light emitting part is used for the display image with almost no attenuation by the reflective polarizing plate, and the external light is hardly reflected, and the visual characteristic is very low. Can be improved.

  The above-described example is an example of an organic EL display device, but an inorganic EL display device is similar in that an inorganic layer is used instead of an organic layer, and in the case of an LED, the luminance of the light emitting unit is large. Although it is hardly affected by external light, a display device using LEDs can have the same structure, and can be applied not only to an organic EL display device but also to a self-luminous display device.

It is explanatory drawing which shows one Embodiment of the organic electroluminescent display apparatus by this invention. FIG. 2 is a cross-sectional explanatory diagram illustrating a structural example of the organic EL light emitting unit illustrated in FIG. 1. It is sectional explanatory drawing which shows the structural example of the conventional organic electroluminescence display.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent substrate 3 1st electrode layer 4 Organic layer 5 2nd electrode layer 6 Organic electroluminescent light emission part 7 Reflective polarizing plate 8 Absorbing polarizing plate 9 Sealing plate

Claims (5)

  A self-luminous display device comprising a light-emitting portion constituting a self-luminous display device and a reflective polarizing plate provided on a display surface side of the light-emitting portion.   From a transparent substrate, an organic EL light emitting unit having an electrode layer and an organic layer laminated on one surface of the transparent substrate, and a reflective polarizing plate provided on the surface opposite to the surface on which the organic EL light emitting unit is formed on the transparent substrate An organic EL display device.   The display device according to claim 1, wherein an absorption polarizing plate having a polarization axis combined with the polarization axis of the reflective polarizing plate is provided on a surface of the reflective polarizing plate.   A quarter-wave retardation plate whose optical axis is set to form an angle of 45 ° with the polarization axis of the reflective polarizing plate is bonded to the reflective polarizing plate to form a circularly polarizing plate. The display device according to 1, 2, or 3.   The display device according to claim 1, wherein the reflective polarizing plate is configured as a birefringent dielectric multilayer film.

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