JP2009054710A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device in which film thickness controllability can be improved and variations in light emission efficiency and driving voltages can be suppressed. <P>SOLUTION: The display device having a self light-emitting display element includes: a first electrode 60 disposed on a substrate; a second electrode 66 disposed opposite to the first electrode 60; an optical active layer 64 disposed between the first electrode 60 and second electrode 66; and an electron injection layer EI disposed between the optical active layer 64 and second electrode 66 and formed of a non-deliquescent material. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  In recent years, organic electroluminescence (EL) display devices have attracted attention as flat display devices. Since this organic EL display device includes a self-luminous display element, it has a wide viewing angle, can be thinned without requiring a backlight, can reduce power consumption, and can respond quickly. 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. Such an organic EL display device includes, as a display element, an organic EL element that holds a photoactive layer containing an organic compound having a light emitting function between an anode and a cathode on a substrate.

  According to Patent Document 1, a substrate, a positive electrode between the substrates, an organic layer involved in at least a light emitting function, and a negative electrode are sequentially formed, and the negative electrode is formed of a low work function material. The first electrode layer and the second electrode layer formed of a low-resistance material, and the constituent material of the first electrode layer is within a range of 10 nm from the electron injection electrode interface of the organic layer. There has been proposed an organic EL element that is present in a larger amount than the constituent material of the second electrode layer.

According to this, the film thickness of the first electrode layer is 0.5 to 10 nm, and the first electrode layer is composed of lithium oxide (Li ₂ O), rubidium oxide (Rb ₂ O), potassium oxide (K ₂ O), sodium oxide (Na ₂ O), cesium oxide (Cs ₂ O), strontium oxide (SrO), magnesium oxide (MgO), and calcium oxide (CaO) are contained in one or more types. It is disclosed.
JP 2001-060498 A

  An object of the present invention is to provide a display device capable of improving film thickness controllability and suppressing variations in light emission efficiency and driving voltage.

A display device according to an aspect of the present invention includes:
A display device including a self-luminous display element,
The display element is
A first electrode disposed on the substrate;
A second electrode disposed opposite the first electrode;
A photoactive layer disposed between the first electrode and the second electrode;
An electron injection layer disposed between the photoactive layer and the second electrode and formed of a non-deliquescent material;
It is provided with.

  According to the present invention, it is possible to provide a display device capable of improving film thickness controllability and suppressing variations in light emission efficiency and drive voltage.

  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 such as 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. The organic EL display device 1 has a substantially rectangular display area 101 for displaying an image. In the color display type organic EL display device 1, the display area 101 includes a plurality of types of color pixels PX (R, G, B) arranged in a matrix. Further, in this embodiment, the organic EL display device 1 includes a sealing substrate 200 disposed to face the main surface side of the array substrate 100. The sealing substrate 200 is bonded to the array substrate 100 via a sealing material 400 so as to seal at least the display area 101.

  On the array substrate 100, each color pixel PX (R, G, B) includes a pixel circuit and a display element that is driven and controlled by the pixel circuit. The pixel circuit 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 illustrated in FIG. 1, the pixel circuit includes a pixel switch 10, a drive transistor 20 that supplies a desired drive current to the display element based on a video signal supplied via the pixel switch 10, and a gate of the drive transistor 20. -It has a storage capacitor 30 or the like that holds the source-to-source potential for a predetermined period. The pixel switch 10 and the driving transistor 20 are constituted by, for example, thin film transistors, and here, thin film transistors including a semiconductor layer made of polysilicon are applied.

  The display element 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.

  In addition, the array substrate 100 includes a plurality of scanning lines Ym (m = 1, 2,...) Extending along the row direction of the color pixels PX (that is, the Y direction in FIG. 1), and columns substantially orthogonal to the scanning lines Ym. A plurality of signal lines Xn (n = 1, 2,...) Extending along a direction (that is, the X direction in FIG. 1), a power supply line P for supplying power to the organic EL element 40, and the like. .

  Further, the array substrate 100 supplies a video signal to each of the signal lines Xn and at least a part of the scanning line driving circuit 107 that supplies a scanning signal to each of the scanning lines Ym in the peripheral area 104 located outside the display area 101. At least part of the signal line driver circuit 108 to be supplied is provided. All the scanning lines Ym are connected to the scanning line driving circuit 107. All signal lines Xn are connected to the signal line driving circuit 108.

  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 an organic EL element 40 disposed on the main surface side of the wiring substrate 120. The wiring substrate 120 is formed on an insulating support substrate such as a glass substrate or a plastic sheet on the pixel switch 10, the driving transistor 20, the storage capacitor element 30, the scanning line driving circuit 107, the signal line driving circuit 108, and various wirings ( Scanning lines, signal lines, power supply lines, etc.).

  The organic EL element 40 is disposed on the wiring substrate 120 so as to face the first electrode 60 (that is, disposed closer to the sealing substrate 200 than the first electrode 60), and has a plurality of colors. A second electrode 66 common to the pixels PX and a photoactive layer 64 disposed between the first electrode 60 and the second electrode 66 are configured.

  More specifically, the first electrode 60 is arranged in an independent island shape for each color pixel PX on the wiring board 120. In the configuration employing the top emission type, the first electrode 60 may include a reflective layer having light reflectivity. That is, as shown in FIG. 2, the first electrode 60 may be formed as a single layer having a function as an electrode and a function as a reflection layer using a conductive material having light reflectivity. In the case where the electrode is formed using a light-transmitting conductive material, a two-layer structure in which a reflective layer formed using a light-reflecting material is stacked on the electrode may be used.

  The photoactive layer 64 is disposed on the first electrode 60 and includes at least the light emitting layer 64A. The photoactive layer 64 can include functional layers other than the light emitting layer 64A, and can include functional layers such as a hole injection layer, a hole transport layer, a blocking layer, an electron transport layer, and a buffer layer. The photoactive layer 64 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 photoactive layer 64, the light emitting layer 64A may be an organic material, and layers other than the light emitting layer 64A may be an inorganic material or an organic material. In the photoactive layer 64, the functional layers other than the light emitting layer 64A may be a common layer. In the example shown in FIG. 2, there are common layers on the first electrode 60 side and the second electrode 66 side of the light emitting layer 64A, respectively. Is arranged. One common layer includes a hole injection layer 64HI and a hole transport layer 64HT, and the other common layer includes an electron transport layer 64ET. The light emitting layer 64A is formed of an organic compound having a light emitting function that emits red, green, or blue light.

  The second electrode 66 is disposed on the photoactive layer 64 of each color pixel PX. The second electrode 66 includes a semi-transmissive layer 66A in order to realize a microcavity configuration. That is, as shown in FIG. 2, the second electrode 66 is formed of a transmissive layer 66B formed using a light-transmissive conductive material, and a half layer disposed between the transmissive layer 66B and the photoactive layer 64. It may be a two-layer structure with the transmissive layer 66A, or may be configured as a semi-transmissive layer single-layer electrode. In this embodiment, the semi-transmissive layer 66A is formed of a mixture of silver (Ag) and magnesium (Mg), and the transmissive layer 66B is formed of indium tin oxide (ITO).

  In this embodiment, the organic EL element 40 further includes an electron injection layer EI disposed between the photoactive layer 64 and the second electrode 66. This electron injection layer EI is formed of a non-deliquescent material.

  Further, the array substrate 100 includes a partition wall 70 that separates at least adjacent color pixels PX (R, G, B) in the display area 101. For example, the partition walls 70 are arranged in a grid pattern or a stripe pattern along the edge of each first electrode 60. The partition wall 70 is made of, for example, a resin material.

  The above-described electron injection layer EI will be described in more detail.

  As the electron injection layer EI, cesium (Cs) having a relatively high electron injection performance may be applied. In this case, for example, cesium fluoride (CsF) can be selected as the vapor deposition material. That is, the electron injection layer EI can be formed by vapor deposition using cesium fluoride as a material source. However, cesium fluoride has deliquescence that absorbs and dissolves moisture in the atmosphere. For this reason, the film thickness measurement at the time of tooling is difficult, and the film thickness management at the time of film formation is difficult.

  Therefore, in this embodiment, when cesium is applied to the electron injection layer, a non-deliquescent cesium-based material is applied. Specifically, an alloy made of cesium, fluorine (F), and aluminum (Al) is applicable. Such an alloy of cesium, fluorine, and aluminum has a feature that it becomes non-deliquescent by loosely bonding these three elements. Therefore, it is possible to improve the film thickness controllability in forming the electron injection layer.

  Next, more specific examples will be described.

  First, as shown in FIG. 3A, the first electrode 60 is formed on the wiring board 120. That is, the first electrode 60 in which the reflective layer 60A made of aluminum and the transmissive layer 60B made of ITO are stacked is formed for each pixel by film formation and patterning of a conductive material.

  Thereafter, the photoactive layer 64 is formed on the first electrode 60. That is, amorphous carbon is formed as the hole injection layer 64HI and αNPD is formed as the hole transport layer 64HT on the transmission layer 60B by vapor deposition. Then, for the red pixel, the green pixel, and the blue pixel, using a fine mask, the Red light emitting layer material (host: Alq3, dopant: DCM), the Green light emitting layer material (host: Alq, dopant: coumarin), Blue light emission. Layer materials (host: BH120, dopant: BD-102) are vapor-deposited to form respective light emitting layers 64A. Then, an electron transport layer (PyPySPyPy) 64ET is formed on each of the light emitting layers 64A.

  Subsequently, as shown in FIG. 3B, an electron injection layer EI is formed on the electron transport layer 64ET by depositing an alloy A containing cesium, fluorine, and aluminum to a thickness of 10 angstroms. At this time, the cesium contained in the alloy A was 60% by weight.

  Subsequently, magnesium and silver are deposited as shown in FIG. 3C. Thereby, a semi-transmissive layer 66A in which magnesium and silver are mixed and formed is formed on the electron injection layer EI. And ITO is vapor-deposited and the transmissive layer 66B is formed. Through these steps, a display device provided with a top emission type organic EL element was produced.

  As described above, the alloy A forming the electron injection layer EI is characterized by non-deliquescent properties due to the presence of aluminum. Since cesium fluoride is deliquescent in the atmosphere, it was extremely difficult to measure the film thickness during tooling, but the alloy A was non-deliquescent, so that normal film thickness evaluation was possible. For this reason, in the alloy A, the film thickness controllability is remarkably improved as compared with the case where cesium fluoride is applied.

  Specifically, when an electron injection layer EI having a thickness of 10 angstroms is to be obtained, when cesium fluoride is applied, a lot-to-lot variation of ± 40% is present, but when alloy A is applied. The film can be formed with a variation of ± 20%. For this reason, it is possible to suppress the variation in the light emission efficiency and the driving voltage, and the process stability is improved.

  As described above, according to this embodiment, when cesium is applied as the electron injection layer, it is possible to improve the film thickness controllability of the electron injection layer by using a non-deliquescent cesium-based material. It becomes. For this reason, variation in the thickness of the electron injection layer can be suppressed, and variation in light emission efficiency and driving voltage can be suppressed.

  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 view for explaining a manufacturing process of the organic EL element, and is a view for explaining a manufacturing process of the first electrode and the photoactive layer. FIG. 3B is a diagram for explaining a manufacturing process of the organic EL element and is a diagram for explaining a manufacturing process of the electron injection layer. FIG. 3C is a diagram for explaining a manufacturing process of the organic EL element, and is a diagram for explaining a manufacturing process of the second electrode.

Explanation of symbols

PX ... Color pixel 1 ... Organic EL display device 40 ... Organic EL element (display element)
60 ... first electrode 60A ... reflective layer 60B ... transmissive layer 64 ... photoactive layer 64A ... light emitting layer 64HI ... hole injection layer 64HT ... hole transport layer 64ET ... electron transport layer 66 ... second electrode 66A ... semi-transmissive layer 66B ... transmissive Layer EI ... Electron injection layer 70 ... Partition 100 ... Array substrate

Claims (3)

A display device including a self-luminous display element,
The display element is
A first electrode disposed on the substrate;
A second electrode disposed opposite the first electrode;
A photoactive layer disposed between the first electrode and the second electrode;
An electron injection layer formed between the photoactive layer and the second electrode and formed of a non-deliquescent material including cesium (Cs);
A display device comprising:   The display device according to claim 1, wherein the electron injection layer is formed of an alloy containing cesium (Cs), fluorine (F), and aluminum (Al). The first electrode has a reflective layer;
The display device according to claim 1, wherein the second electrode has a semi-transmissive layer formed of a mixture of silver (Ag) and magnesium (Mg).

Images