JP2009070621A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device capable of improving the luminescent lifetime. <P>SOLUTION: The display device comprises: a display area 102 constituted by a plurality of pixels PX; a first electrode 60 disposed at the respective pixels PX on a substrate; an organic active layer 62 disposed on the first electrode 60; and a second electrode 64 formed by a mixture containing at least sliver and magnesium and disposed on the organic active layer 62. The second electrode 64 includes: a first region 641; and a second region 642 which is disposed on the side closer to the organic active layer 62 than the first region 641 and which has a silver concentration higher than that of the first region 641. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a display device, and more particularly to a display device including self-luminous elements.

  In recent years, organic electroluminescence (EL) display devices have attracted attention as flat display devices. Since this organic EL display device includes an organic EL element that is a self-luminous element, the viewing angle is wide, the backlight can be thinned, the power consumption can be reduced, and the response speed can be reduced. It has the feature of being fast.

  Because of these features, organic EL display devices are attracting attention as potential candidates for next-generation flat display devices that replace liquid crystal display devices. In such an organic EL display device, organic EL elements each holding an organic active layer containing an organic compound having a light emitting function are arranged in a matrix between a first electrode (anode) and a second electrode (cathode). The array substrate is provided.

  When a voltage is applied to the organic EL display device, holes are injected from the first electrode into the organic active layer, and electrons are injected from the second electrode into the organic active layer. These electrons and holes are recombined, and the electron-hole pair is excited. Light is emitted when the electron-hole pair transitions from the excited state to the ground state.

The second electrode is formed of a metal material having an electron injection function. For example, the structure which formed the 2nd electrode with the mixture of silver (Ag) and magnesium (Mg) is proposed (for example, refer patent document 1).
JP 2007-103303 A

  Magnesium is a metal with a relatively large ionization tendency. For this reason, in the structure which formed the 2nd electrode with the mixture of silver and magnesium, magnesium is easy to be oxidized. If magnesium is oxidized at the interface of the second electrode with the organic active layer, the electron injection efficiency may be reduced, leading to a reduction in the light emission lifetime of the display device.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a display device capable of improving the light emission lifetime.

A display device according to an aspect of the present invention includes:
A display device having a display area composed of a plurality of pixels,
A first electrode disposed in each pixel on the substrate;
An organic active layer disposed on the first electrode;
A second electrode formed by a mixture containing at least silver and magnesium and disposed on the organic active layer,
The second electrode includes a first region and a second region that is disposed closer to the organic active layer than the first region and has a silver concentration higher than that of the first region.

  According to the present invention, it is possible to provide a display device capable of improving the light emission lifetime.

  A display device according to an embodiment of the present invention will be described below with reference to the drawings. In this embodiment, a self-luminous display device, for example, an organic EL (electroluminescence) display device will be described as an example of the display device.

  As shown in FIG. 1, the organic EL display device 1 includes an array substrate 100 having a display area 102 for displaying an image. The display area 102 includes a plurality of pixels PX arranged in a matrix. Further, FIG. 1 illustrates a color display type organic EL display device 1 as an example, and a display area 102 includes a plurality of types of color pixels, for example, a red pixel PXR, a green pixel PXG, and a blue color corresponding to three primary colors. A pixel PXB is used.

  Each pixel PX (R, G, B) includes a pixel circuit 10 and a display element 40 that is driven and controlled by the pixel circuit 10. The pixel circuit 10 shown in FIG. 1 is an example, and it goes without saying that a pixel circuit having another configuration may be applied. In the example shown in FIG. 1, the pixel circuit 10 includes a drive transistor DRT, switches (first switch SW1, second switch SW2, third switch SW3), a storage capacitor element Cs, and the like. The drive transistor DRT has a function of controlling the amount of current supplied to the display element 40. The first switch SW1 and the second switch SW2 function as a sample / hold switch. The third switch element SW3 has a function of controlling driving current supply from the driving transistor DRT to the display element 40, that is, on / off of the display element 40. The storage capacitor element Cs has a function of holding the gate-source potential of the drive transistor DRT.

  The drive transistor DRT is connected between the high potential power supply line P1 and the third switch SW3. The display element 40 is connected between the third switch SW3 and the low potential power line P2. The gate electrodes of the first switch SW1 and the second switch SW2 are connected to the first gate line GL1. The gate electrode of the third switch SW3 is connected to the second gate line GL2. The source electrode of the first switch SW1 is connected to the video signal line SL. The drive transistor DRT, the first switch SW1, the second switch SW2, and the third switch element SW3 are configured by, for example, thin film transistors, and the semiconductor layer is formed of polysilicon here.

  In the case of such a circuit configuration, the first switch SW1 and the second switch SW2 are turned on based on the ON signal supplied from the first gate line GL1, and the high potential is set according to the amount of current flowing through the video signal line SL. A current flows from the power supply line P1 to the driving transistor DRT, and the storage capacitor element Cs is charged according to the current flowing through the driving transistor DRT. As a result, the drive transistor DRT can supply the same amount of current as that supplied from the video signal line SL to the display element 40 from the high potential power supply line P1.

  Then, the third switch SW3 is turned on based on the ON signal supplied from the second gate line GL2, and the driving transistor DRT is connected to the first potential from the high potential power supply line P1 according to the capacitance held in the storage capacitor element CS. A predetermined amount of current corresponding to a predetermined luminance is supplied to the display element 40 via the three switch SW3. Thereby, the display element 40 emits light with a predetermined luminance.

  The display element 40 includes an organic EL element 40 (R, G, B) that is a self-luminous display element. That is, the red pixel PXR includes an organic EL element 40R that mainly emits light corresponding to the red wavelength. The green pixel PXG includes an organic EL element 40G that mainly emits light corresponding to the green wavelength. The blue pixel PXB includes an organic EL element 40B that mainly emits light corresponding to the blue wavelength.

  The configurations of the various organic EL elements 40 (R, G, B) are basically the same. That is, as shown in FIG. 2, the array substrate 100 includes a plurality of organic EL elements 40 disposed on the wiring substrate 120. Note that the wiring substrate 120 is formed on an insulating support substrate such as a glass substrate or a plastic sheet, a switch SW, a driving transistor DRT, a storage capacitor element Cs, various wirings (gate line GL, video signal line SL, power supply line P, etc. ) And the like.

  The organic EL element 40 is arranged in a matrix and is arranged in an isolated island shape for each color pixel PX, and is opposed to the first electrode 60 and is arranged in common to the plurality of color pixels PX. The second electrode 64 and the organic active layer 62 held between the first electrode 60 and the second electrode 64 are configured.

  The first electrode 60 constituting the organic EL element 40 is disposed on the surface of the wiring board 120. The first electrode 60 functions as an anode. The first electrode 60 is in contact with the drain electrode of the third switch SW3 constituting the pixel circuit 10. The first electrode 60 is formed of a light-transmitting conductive material such as indium tin oxide (ITO) and a light-reflective conductive material such as aluminum (Al). Further, it may be constituted by a laminated body in which a reflective layer is laminated, or may be constituted by a single transmissive layer or a single reflective layer.

  The organic active layer 62 is disposed on the first electrode 60 and includes at least the light emitting layer 62A. The organic active layer 62 can include functional layers other than the light emitting layer 62A, and includes, for example, functional layers such as a hole injection layer, a hole transport layer, a blocking layer, an electron transport layer, an electron injection layer, and a buffer layer. Can do. The organic active layer 62 may be composed of a single layer in which a plurality of functional layers are combined, or may have a multilayer structure in which the functional layers are stacked. In the organic active layer 62, the light emitting layer 62A may be an organic material, and layers other than the light emitting layer 62A may be an inorganic material or an organic material.

  In the organic active layer 62, the functional layer other than the light emitting layer 62A may be a common layer. In the example shown in FIG. 2, the hole side shared layer 62H disposed on the first electrode 60 side of the light emitting layer 62A is The electron side common layer 62E that includes the hole injection layer and the hole transport layer and is disposed on the second electrode 64 side of the light emitting layer 62A includes a blocking layer, an electron transport layer, and an electron injection layer. The light emitting layer 62A is disposed between the hole side common layer 62H and the electron side common layer 62E. The light emitting layer 62A is formed of an organic compound having a light emitting function that emits red, green, or blue light.

  The second electrode 64 is disposed in common on the organic active layer 62 of each color pixel PX. The second electrode 64 functions as a cathode. The second electrode 64 is formed of a metal material having an electron injection function. Here, the second electrode 64 has a semi-transmissive layer formed of a mixture containing at least silver and magnesium. The second electrode 64 may include a transmission layer formed using a light-transmitting conductive material such as ITO.

  In addition, the array substrate 100 includes a partition wall 70 that separates the color pixels PX (R, G, B) at least for each adjacent color in the display area 102. The partition walls 70 are arranged in a lattice shape or a stripe shape along the periphery of each first electrode 60, for example. For example, the partition wall 70 is formed by patterning a resin material. The partition wall 70 is covered with the second electrode 64 together with the organic active layer 62.

  Further, the display area 102 of the array substrate 100 may be covered with a protective film (not shown). In this case, the second electrode 64 of each organic EL element 40 is covered with the protective film. Such a protective film includes a thin film formed of an inorganic material such as a silicon nitride film or a silicon oxide film. Further, this protective film may include a thin film formed of an organic material.

  In the array substrate 100 having such a configuration, at least the display area 102 is sealed by the sealing substrate 200. That is, the sealing substrate 200 is disposed so as to face the organic EL element 40 side of the array substrate 100. The array substrate 100 and the sealing substrate 200 are bonded together by a sealing material 300 arranged in a frame shape so as to surround the display area 102. The sealing material 300 may be a photosensitive resin (for example, an ultraviolet curable resin) or a frit.

  Here, the configuration of the second electrode 64 will be described in detail.

  As described above, the semi-transmissive layer of the second electrode 64 is formed using a mixture containing silver and magnesium. As shown in FIG. 3, in the present embodiment, the composition ratio of silver and magnesium is not uniform in the entire region of the second electrode 64. That is, the composition ratio of silver and magnesium is such that the interface 64A side of the second electrode 64 with the organic active layer 62 and the surface 64B side of the second electrode 64 (that is, the side facing the counter substrate 200 or the display area are protected). The structure covered with the film is different from the interface side with the protective film.

  In the present embodiment, the second electrode 64 is formed such that its silver concentration is higher in the second region 642 on the interface 64A side than in the first region 641 on the surface 64B side. Here, the concentration is the ratio (%) of silver atoms per unit volume. When the second electrode 64 is formed of two components of silver and magnesium, the concentration of magnesium decreases as the concentration of silver increases. That is, in the second electrode 64, the concentration of magnesium is lower in the second region 642 on the interface 64A side than in the first region 641 on the surface 64B side. That is, regarding the composition ratio between silver and magnesium, the proportion of magnesium is higher in the first region 641 than in the second region 642, and the proportion of silver is in the second region 642 than in the first region 641. high.

  According to such a second electrode 64, the magnesium concentration in the region near the interface 64A is low. For this reason, even if magnesium is oxidized, it is possible to prevent a decrease in electron injection efficiency at the interface 64A. Thereby, the light emission lifetime of the organic EL element can be improved.

  In this embodiment, particularly in the semi-transmissive layer containing silver and magnesium constituting the second electrode 64, the silver concentration of the second region 642 located on the interface 64A side with the organic active layer 62 is the second region 642. It is characterized by having a relationship higher than that of the first region 641 located on the surface 64B side (that is, the magnesium concentration of the second region 642 is lower than that of the first region 641). That is, the second electrode 64 may have a two-layer structure in which the first region 641 is stacked on the second region 642, or may have a stacked structure of three or more layers having the above-described relationship, and the organic active layer in the thickness direction thereof. It may be a structure formed so that the silver concentration gradually increases toward the interface 64A with 62 (that is, the silver concentration continuously changes).

  Here, in the semi-transmissive layer of the second electrode 64 as shown in FIG. 4, the silver concentration of the region W (that is, the region having the highest silver concentration in the second electrode 64) in contact with the interface 64 </ b> A with the organic active layer 62. The relationship between the emission lifetime and the emission lifetime was investigated. Here, the same number of samples of the organic EL elements in which the silver concentration in the region W is 90%, 80%, 70%, and 60%, respectively, were prepared, and the light emission lifetime of each sample was measured.

  The measurement results are shown in FIG. In FIG. 5, the light emission lifetimes of other samples are shown as relative values when the maximum light emission lifetime obtained for a sample having a silver concentration of 90% in the region W is 1.

  From the measurement results shown in FIG. 5, it was confirmed that in the region W, a sufficiently long light emission lifetime can be obtained by setting the silver concentration to 80% or more (that is, the magnesium concentration is less than 20%). Incidentally, the light emission lifetime of the sample having a silver concentration of 60% in the region W was only about half that of the sample having a silver concentration of 90%.

  As described above, in the region W in contact with the interface 64A of the second electrode 64, the higher the silver concentration, the lower the magnesium concentration, so that the light emission lifetime can be improved. In particular, in the region W, by setting the silver concentration to 80% or more, the light emission lifetime of the organic EL element can be sufficiently extended.

  On the other hand, the silver concentration contained in the semi-transmissive layer of the second electrode 64 has an upper limit. That is, when the semi-transmissive layer is formed only with silver (silver concentration is 100%), it is easily affected by the substrate temperature when silver is formed. For this reason, as in the embodiment described above, the semi-transmissive layer is formed of a mixture of silver and magnesium.

  Here, using the composition ratio of silver and magnesium as a parameter, the sheet resistance value (Ω / □) of the electrode with respect to the substrate temperature (° C.) during film formation was measured. When an electrode having a single silver layer is formed on a substrate, an electrode having a silver: magnesium composition ratio of 8: 2 is formed on the substrate, and a composition of silver and magnesium is formed on the substrate. The sheet resistance value at the substrate temperature at the time of film formation was measured for each sample when an electrode having a ratio of silver: magnesium = 6: 4 was formed. The measurement results are shown in FIG.

  From this measurement result, it can be seen that the sample in which the second electrode 64 is formed of a single silver layer is most affected by the substrate temperature. When the substrate temperature exceeds 45 ° C., the sheet resistance value of the electrode increases rapidly. That is, the margin of the substrate temperature that can suppress the increase in the sheet resistance value is narrow.

  On the other hand, it was confirmed that all the samples in which the electrodes were formed by a mixture of silver and magnesium were less affected by the substrate temperature and a stable sheet resistance value was obtained.

  Thus, it can be seen that when the ratio of silver increases in the composition ratio of silver and magnesium of the second electrode 64, the second electrode 64 is affected by the substrate temperature. That is, it can be seen that the greater the proportion of magnesium, the less affected by the substrate temperature. That is, it is effective to apply an electrode configuration in which magnesium is mixed with silver in order to suppress an increase in sheet resistance value even when the substrate temperature is significantly increased.

  In the present embodiment, the second electrode 64 is formed of a mixture of magnesium and silver, and is formed so that the concentration of magnesium is low and the concentration of silver is high in the region near the interface 64A. . Therefore, in the region near the interface of the second electrode 64, oxidation can be suppressed and the light emission lifetime can be improved, and the second electrode 64 formed is not easily affected by the substrate temperature in the process of forming the second electrode 64. An increase in the sheet resistance value of the two electrodes 64 can be suppressed.

  Next, in the present embodiment, an example of a specific method for manufacturing an organic EL element will be described.

  First, in the display area 102 on the wiring substrate 120, the independent island-shaped first electrode 60 is formed for each of a plurality of types of color pixels PX (R, G, B). That is, the first electrode 60 is formed by patterning a metal film functioning as an anode on one main surface side of the wiring board 120. The first electrode 60 may be generally formed by a photolithography process, or may correspond to a pattern corresponding to the color pixel PX (R, G, B) (that is, corresponding to the shape of the first electrode 60 of each color pixel PX). May be formed by a vapor deposition method in which a metal material source is vapor-deposited through a vapor deposition mask having an opening pattern.

  Subsequently, a partition wall 70 that separates the color pixels PX (R, G, B) is formed. That is, after a photosensitive resin material, for example, an acrylic positive tone resist is formed on the entire main surface of the wiring substrate 120 including the first electrode 60, a baking process is performed after patterning by a photolithography process or the like. I do. Thereby, a grid-like partition wall 70 is formed along the edge of the first electrode 60 so as to surround each color pixel PX (R, G, B).

  Subsequently, an organic active layer 62 is formed on the first electrode 60 in each color pixel PX (R, G, B). Here, the organic active layer 62 is formed by laminating a plurality of thin films, that is, a hole injection layer, a hole transport layer, a light emitting layer 62A, a blocking layer, and an electron transport layer.

  First, a hole injection layer and a hole transport layer that are common to a plurality of types of color pixels PX (R, G, B) are continuously formed by vapor deposition or the like to form a hole-side common layer 62H. Here, CuPc (copper phthalocyanine) was formed as the hole injection layer. As the hole transport layer, α-NPD (aromatic diamine) was formed.

Thereafter, individual light emitting layers 62A (R, G, B) are formed on the color pixels PX (R, G, B) by a mask vapor deposition method or the like. Here, as the light-emitting layer 62A disposed in the red pixel PXR, Alq ₃ (aluminum kilinol complex) is formed as a host material, and a DCM dye is formed as a dopant material. Further, as the light emitting layer 62A disposed in the green pixel PXG, Alq ₃ (aluminum kilinol complex) was formed as a host material, and a coumarin dielectric was formed as a dopant material. In addition, as the light emitting layer 62A disposed in the blue pixel PXB, Alq ₃ (aluminum kilinol complex) was formed as a host material, and perylene was formed as a dopant material.

Thereafter, a common blocking layer and an electron transport layer are successively formed on a plurality of types of color pixels PX (R, G, B) by vapor deposition or the like, thereby forming an electron side common layer 62E. Here, as a blocking layer, BAlq (kyrinol complex dielectric) was formed. Furthermore, Alq ₃ (aluminum kilinol complex) was formed as an electron transport layer.

  Subsequently, a second electrode 64 common to a plurality of types of color pixels PX (R, G, B) is formed on the organic active layer 62. That is, the second electrode 64 is a mask for depositing a metal material functioning as a cathode on one main surface side of the wiring substrate 120 on which the organic active layer 62 is disposed through a dry process, for example, a deposition mask having a predetermined opening pattern. It can be formed by vapor deposition.

  Here, the second electrode 64 is formed of a mixture of magnesium and silver. At this time, the deposition rate of silver is gradually changed from 0.8 angstrom / s to 0.4 angstrom / s, while the magnesium deposition rate is gradually changed from 0.2 angstrom / s to 0.6 angstrom / s. Magnesium is deposited at the same time. As a result, the second electrode 64 having a high silver concentration on the interface 64A side (low magnesium concentration) and a high magnesium concentration on the surface 64B side (low silver concentration) is formed.

  By such a process, the organic EL element 40 is formed.

  According to the organic EL element 40 thus formed, the second electrode 64 is formed such that the silver concentration gradually increases toward the interface 64A with the organic active layer 62 in the thickness direction thereof. In the region in contact with the interface 64A, the silver concentration was highest and the magnesium concentration was lowest. And according to this organic EL element, it has confirmed that a sufficiently long light emission lifetime was obtained.

  In addition, this invention is not limited to the said embodiment itself, In the stage of implementation, it can change and implement a component within the range which does not deviate from the summary. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

FIG. 1 is a diagram schematically showing a configuration of an organic EL display device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing the structure of one pixel of the organic EL display device shown in FIG. FIG. 3 is a cross-sectional view schematically showing the configuration of the second electrode of the organic EL display device shown in FIG. FIG. 4 is a view showing a region near the interface of the second electrode shown in FIG. FIG. 5 is a graph showing the relationship between the silver concentration in the vicinity of the interface of the second electrode and the light emission lifetime. FIG. 6 is a diagram showing the relationship between the substrate temperature and the sheet resistance value of the electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Organic EL display device PX (R, G, B) ... Color pixel 10 ... Pixel circuit DRT ... Drive transistor SW1 ... 1st switch SW2 ... 2nd switch SW3 ... 3rd switch Cs ... Storage capacitor element 40 ... Organic EL element DESCRIPTION OF SYMBOLS 60 ... 1st electrode 62 ... Organic active layer 64 ... 2nd electrode 64A ... Interface 64B ... Surface W ... Interface vicinity area 70 ... Partition 100 ... Array substrate 102 ... Display area 200 ... Sealing substrate

Claims (3)

A display device having a display area composed of a plurality of pixels,
A first electrode disposed in each pixel on the substrate;
An organic active layer disposed on the first electrode;
A second electrode formed by a mixture containing at least silver and magnesium and disposed on the organic active layer,
The display device, wherein the second electrode includes a first region and a second region that is disposed closer to the organic active layer than the first region and has a silver concentration higher than that of the first region.   The display device according to claim 1, wherein the second region is a region in contact with an interface with the organic active layer, and a silver concentration thereof is 80% or more.   The display device according to claim 1, wherein the second electrode is formed such that a silver concentration gradually increases in a thickness direction toward an interface with the organic active layer.

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