JP2006128717A - Light emitting device, manufacturing method thereof, and light emitting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting device having a dopant which is easy to handle, and a manufacturing method thereof. <P>SOLUTION: The light emitting device has at least a pair of electrodes comprising a positive electrode and a negative electrode, and an organic compound layer prepared between the pair of electrodes. The organic compound layer, which is in substantially electrical contact with the negative electrode, is constituted of at least an organic compound and a carbonate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light-emitting element having at least one organic compound layer between an anode and a cathode, a method for manufacturing the same, and a light-emitting device having the light-emitting element.

  The light emitting element is a so-called organic electroluminescence element in which an organic compound existing between both electrodes emits light by a current flowing between a cathode and an anode.

  A general cross-sectional structure of the light-emitting element is shown in FIG. In the figure, 1 is a transparent substrate, 2 is a transparent electrode (anode), 3 is a hole transport layer, 4 is a light emitting layer, 5 is an electron transport layer, 6 is an electron injection layer, and 7 is a cathode.

  In this light emitting device, electrons injected from the cathode 7 into the light emitting layer 4 through the electron injection / transport layers 5 and 6 and holes injected from the transparent electrode 2 into the light emitting layer 4 through the hole transport layer 3. Exciton is generated by recombination with. It is an element that utilizes light emitted when the exciton returns to the ground state.

  For the cathode 7 of such a light emitting element, a material having a relatively small work function and good electron injection characteristics, for example, a single metal such as magnesium (Mg), or a metal alloy such as Ag—Mg, Al—Li, etc. Is used.

  Patent Document 1 discloses a configuration in which an organic layer having a metal functioning as a donor (electron donating) dopant is provided in contact with a cathode. As the metal used as the donor (electron donating) dopant, an alkali metal, an alkaline earth metal, a transition metal containing a rare earth, and the like are disclosed in Patent Document 1.

Patent Document 2 discloses a configuration in which an organic layer having a metal oxide or a metal salt as a dopant is provided in contact with a cathode.
Japanese Patent Laid-Open No. 10-270171 (page 2, lines 9-13, FIG. 1) Japanese Patent Laid-Open No. 10-270172 (2 pages, lines 2-7, FIG. 1)

  As these dopants, metals having a work function as small as possible, and oxides and metal salts containing these metals are desirable. Such metals are generally highly reactive and are very difficult to handle. In addition, when a metal oxide containing such a metal or a metal salt is used as a dopant, the stability is improved as compared with the case of handling a single metal, but still some metal oxides and metal salts are used. Are unstable and difficult to handle under normal atmospheric conditions. There are some metal oxides and metal salts that can be handled in the atmosphere, but they are still unstable, so it may be difficult to introduce them as dopants into the organic layer in contact with the cathode. is there. For this reason, the difficulty in handling these dopants can cause a low yield and a high manufacturing cost in the manufacture of light-emitting elements.

  The present invention provides a light emitting device having a dopant that is easy to handle and a method for manufacturing the same.

  Specifically, the present invention is a light-emitting element comprising at least a pair of electrodes composed of an anode and a cathode, and an organic compound layer provided between the pair of electrodes, and is electrically connected to the cathode electrode. The organic compound layer in substantial contact is composed of at least an organic compound and a carbonate, and the molar ratio of the organic compound to the carbonate in the organic compound layer is in the range of 1: 0.01 to 1: 100. Provided is a light-emitting element.

  The present invention also relates to a method for manufacturing a light emitting device having a pair of electrodes composed of an anode and a cathode, and an organic compound layer provided between the pair of electrodes, wherein the organic compound layer is formed on the cathode side. An organic compound layer forming step of providing at least an organic compound and a carbonate, and a step of providing a cathode in electrical contact with the organic compound layer, the organic compound layer forming step comprising: Provided is a method for manufacturing a light-emitting element, which is a step of forming the organic compound layer having a molar ratio with the carbonate of 1: 0.01 to 1: 100.

(First embodiment)
The light emitting device according to the first embodiment of the present invention is a light emitting device having at least a pair of electrodes (anode, cathode) and a light emitting layer disposed between the pair of electrodes, in an organic compound layer in contact with the cathode. The dopant is carbonate. In other words, it paid attention to the anion of the salt. Carbonate is easy to handle. Of these, alkali metal or alkaline earth metal carbonates are preferred because of their ease of handling. Of course, each organic carbonate (alkaline metal, alkaline earth metal) may be present in the organic compound layer, or the organic compound and the above carbonate for facilitating electron injection or transportation are separated. The additive may be mixed.
The reason why carbonate is preferable may be that the durability of the resulting element is improved. Durability is the lifetime of the element. This is because carbonate has a relatively large molecular weight, and thus it is considered difficult to move in the organic compound layer when the element is driven. Furthermore, the good affinity with the organic compound constituting the organic compound layer may be a reason why the carbonate is preferably used.

  The organic compound layer efficiently supplies electrons from the cathode to the light emitting layer. As a result, in this embodiment, when selecting a metal material to be used for the cathode, it is not limited in consideration of the work function of the material, that is, an electrode material having a relatively high work function, such as ITO, gold, silver, Even when these alloys are selected, good electron injection into the light emitting layer is possible.

In the present embodiment, the carbonate that can be particularly preferably used is at least one of cesium carbonate (Cs ₂ CO ₃ ) and lithium carbonate (Li ₂ CO ₃ ). Among them, a light-emitting element using ITO as a cathode and cesium carbonate or lithium carbonate as a dopant has good optical transmittance and can extract light from the cathode, which is suitable for a so-called top emission light-emitting element. . Of course, the light-emitting element of the present invention may be a light-emitting element in which light is extracted from the anode.
In addition, a well-known thing may be sufficient as an organic compound, for example, an aluminum chelate (Alq3) etc. can be mentioned. The optical transmittance of the organic compound layer in contact with the cathode is 80% or more and further 95% or more in the wavelength region of 450 nm to 700 nm (meaning 450 nm to 700 nm, the same applies hereinafter).

  The film thickness of the organic compound layer containing carbonate is in the range of 0.1 to 10,000 nm, preferably in the range of 1 to 500 nm. The light emitting layer may have any thickness. In order to obtain high luminous efficiency, it is desirable that the light emitting layer has a sufficient recombination region in the film thickness direction, and the thickness of the light emitting layer is generally about 15 to 20 nm. The light emitting element according to this embodiment may also have a light emitting layer of approximately that degree.

In the light-emitting element of this embodiment mode, the main organic compound constituting the organic compound layer is a low molecular compound.
The low molecular compound is defined in the present invention as an organic compound having a molecular weight of 2000 or less, preferably 1000 or less.
Specific types of organic compounds will be described later.
This organic compound is of course a non-insulator.

The amount ratio between the organic compound and the carbonate will be described.
The amount ratio between the organic compound and the carbonate is in the range of 1: 0.01 to 1: 100 in molar ratio. More preferably, it is in the range of 1: 0.1 to 1:10. The molar ratio here refers to the ratio of the number of moles of the organic compound and carbonate introduced as the organic compound layer. In particular, when a carbonate having a cation as an alkali metal is used, the molar ratio is 1: 0. 0.5, electrons can be efficiently supplied from the cathode to the light emitting layer.
Note that there may be a difference of about 20% before and after 1: 0.5, that is, a particularly preferred molar ratio is in the range of 1: 0.4 to 1: 0.6. The reason why the effect is best when the ratio is 1: 0.5 is not clear at present, but is considered to be a suitable quantitative ratio relationship for the interaction between the organic compound and the carbonate.
When a carbonate such as cesium carbonate is used for the organic compound layer, even if the cathode is aluminum or a transparent conductive oxide such as ITO, good electron injection from the cathode to the organic compound layer is realized. The luminous efficiency is very good. In particular, in the case of ITO, it can be suitably used for a top emission type light-emitting element that extracts light from the electrode that is not on the substrate side out of the pair of counter electrodes.
That is, the present invention can provide a light-emitting element characterized in that a transparent conductive oxide such as ITO or IZO is used as a cathode and a carbonate is contained in an organic compound layer. A top emission type light emitting element having such characteristics can be provided.
On the other hand, instead of the organic compound layer, in an element provided with a single layer of a material such as lithium fluoride that has been widely used in the past or an element including a material such as lithium fluoride in the organic compound layer, the cathode is aluminum, In any transparent conductive oxide, the electron injection is inferior. In particular, when a transparent conductive oxide was used as a cathode, electron injection was hardly performed, and electron injection of such a device was extremely bad.

  Further, another layer may be provided between the cathode and the organic compound layer. The other layer may be an organic layer, an inorganic layer, or a mixed organic / inorganic layer. More specifically, a LiF layer may be used. In addition, electron injection is further improved by providing such another layer. And even if this other layer is provided, it can be said that the cathode and the organic compound layer are in substantial electrical contact.

By the way, when forming the organic compound layer which consists of an organic compound and carbonate, it is preferable to co-evaporate both. In particular, the organic compound layer is preferably formed in a state where the carbonate is heated. By forming the organic compound layer while the carbonate is heated, the current density of the light emitting element reaches a practically preferable level. Also in the case of heating and using, carbonates such as cesium carbonate and lithium carbonate can be heated at about 150 ° C. or more and 700 ° C. or less. This temperature range is a relatively low temperature range. Furthermore, in such a temperature range, it can be handled with heating together with the organic compound. This temperature region (range) may be any of the melting point, decomposition point, and decomposition start point of carbonate. For example, the decomposition start point of cesium carbonate is preferably about 610 ° C. Moreover, since melting | fusing point of lithium carbonate is 615 degreeC, it is preferable.
The reason why it is preferable to heat the carbonate cannot be stated at present, but it is preferable to obtain the above-mentioned interaction.

  Alternatively, the carbonate may be heated and reduce the organic compound. And even if gold (Au), silver (Ag), which are stable metals, or transparent electrode ITO is used, the electron injection barrier from the cathode can be reduced, and the drive voltage of the element can be lowered. unknown.

In addition, carbonate (eg, Cs ₂ CO ₃ ) is preferable compared to simple metal (eg, cesium metal). This is probably because carbonate has a higher molecular weight (ie, is heavier) than a single metal, and cesium elements are less likely to move.

  The organic compound layer may be formed by any thin film forming method. For example, a vapor deposition method or a sputtering method can be used. These methods are preferable because the carbonate can be heated.

  This embodiment will be described in more detail and more specifically below.

  The inventors of the present invention can easily obtain a material for doping in the organic layer in contact with the cathode, and do not require a special working environment that excludes contact with the atmosphere or moisture for handling. The specific material which can be formed into a film by general methods, such as these, was discovered. That is carbonate.

  In addition, the light-emitting element of the present embodiment is used as a light-emitting element array having a plurality of light-emitting elements, a display element such as a display (regardless of monochromatic full color), and a photoconductor of an electrophotographic system (for example, a laser beam printer or a copier). It can be applied as an exposure light source.

  In the light emitting device of the embodiment of the present invention, as a material used for the cathode electrode, aluminum (Al), silver (Ag), gold (Au), indium tin oxide (ITO), or an alloy containing at least one of them is used. Etc. can be mentioned. In addition, magnesium (Mg), platinum (Pt), palladium (Pd), selenium (Se), iridium (Ir), tin oxide, and copper iodide or a mixed metal containing at least one of them (for example, an alloy) is used. I can do it.

  The light emitting element of the embodiment of the present invention is not limited to the order in which the cathode electrode and the organic compound layer in contact therewith are formed, and the film forming order can be freely selected.

(Second Embodiment)
FIG. 2 is a schematic diagram showing a second embodiment of the present invention. In the present embodiment, the description is extended to a layer structure including a part of the light emitting element according to the first embodiment including the anode. In the figure, a light emitting device of the present invention comprises an electrode 11 serving as an anode, a hole transporting layer 12 having a hole transporting property, a light emitting layer 13 and an organic compound layer composed of an organic compound and a carbonate on a substrate 10. 14 is configured by laminating an electrode 15 serving as a cathode.

  In addition, the organic compound layer is composed of an electrode (anode) / light-emitting layer / organic compound layer / electrode (cathode), electrode (anode) / hole transport layer / light-emitting layer / electron transport layer / organic compound layer / Electrode (cathode), electrode (anode) / hole injection layer / light emitting layer / organic compound layer / electrode (cathode), electrode (anode) / hole injection layer / hole transport layer / light emitting layer / organic compound layer / electrode (Cathode), electrode (anode) / hole injection layer / hole transport layer / light emitting layer / electron transport layer / organic compound layer / electrode (cathode), and the like. The light emitting device according to the present invention is an organic compound layer. Any device configuration may be used as long as 14 is provided at the interface with the cathode 15. More specifically, the layer structure should preferably be in the order of the cathode, the organic compound layer, and the electron transport layer (of course, from the order of production, the organic compound layer and then the cathode after the electron transport layer) Each layer may be manufactured in order). In particular, in the case of this layer structure, it is preferable to use at least one of metal complex compounds such as Alq3 and PBO, heterocyclic compounds such as oxazole, quinoxaline, triazine, triazole and silole, and heterocyclic condensed ring compounds as the electron transport layer. I can do it. By further providing such an electron transport layer, the efficiency of supplying electrons from the cathode to the light emitting layer is further improved. In this case, the material for the electron transport layer and the main organic compound constituting the organic compound layer may be separate compounds, but are preferably the same compound.

  The organic compound that can be used as the hole transport layer 12 and the hole injection layer is not particularly limited, and for example, a triphenyldiamine derivative, an oxadiazole derivative, a polyphylyl derivative, a stilbene derivative, and the like can be used. It is not limited.

  Examples of organic compounds that can be used as the material of the light emitting layer 13 include triarylamine derivatives, stilbene derivatives, polyarylenes, aromatic condensed polycyclic compounds, aromatic heterocyclic compounds, aromatic heterocyclic condensed ring compounds, metal complex compounds, and the like. These can be employed from single oligo compounds or composite oligo compounds. One or more of these light emitting materials can be doped into the hole injection layer, the hole transport layer, or the electron electron transport layer. These materials and configurations are not limited to these.

  As the electrode 11 serving as the anode, one having a large work function is desirable. For example, indium tin oxide (ITO), tin oxide, gold (Au), platinum (Pt) chromium (Cr), palladium (Pd), selenium (Se) ), Iridium (Ir), copper iodide, or an alloy thereof.

  The hole transport layer 12, the hole injection layer, the light emitting layer 13, and the electron transport layer may be any thin film forming method. For example, a vapor deposition method, a sputtering method, a CVD method, a molecular beam vapor deposition method (MBE method). ), Dipping method, spin coating method, casting method, bar coating method, roll coating method, ink jet method and the like can be used.

  In addition, in the light-emitting element described in this embodiment of the present invention, a protective layer made of an organic material or an inorganic material can be provided to protect the element from oxygen or moisture, which obstructs the characteristics of the present invention. It is not something to do. It is also possible to improve the environmental resistance of the element by sealing the element with an inert gas.

(Third embodiment)
The light emitting element according to the third embodiment of the present invention is a form in which another layer is provided between the organic compound layer and the light emitting layer. The rest is the same as the second embodiment. This embodiment is an electrode (anode) / hole transport layer / light-emitting layer / electron transport layer / organic compound layer / electrode (cathode), electrode (anode) / positive electrode in the layer configuration described in the second embodiment. Layer configurations such as a hole injection layer / hole transport layer / light emitting layer / electron transport layer / organic compound layer / electrode (cathode) are included in the category of the present embodiment, but in addition, a light emitting layer, an organic compound layer, A layer having a function as a block layer, more specifically as a hole blocking layer, may be provided between them. The hole blocking layer may have the above-described electron transport ability or electron injection ability.
When this block layer is described in the itemized list, it may be any of the following A to F.
A. As a material constituting the block layer, a metal complex compound can be mentioned.
B. Examples of the material constituting the block layer include heterocyclic compounds.
C. Examples of the material constituting the block layer include hetero-fused ring compounds.
D. As a material constituting the block layer, an aluminum chelate complex (Alq3) can be mentioned.
E. An example of a material constituting the block layer is bathophenanthroline.
F. As a material constituting the block layer, bathocuproine can be mentioned.

  In the following, a preferred embodiment of the present invention will be described by exemplifying cesium carbonate as a carbonate based on the drawings. However, lithium carbonate is also applicable, that is, the present invention is not limited to this embodiment.

Example 1
FIG. 2 shows a first embodiment. In the figure, 10 is a transparent substrate on the anode side, 11 is an ITO layer as an anode electrode for hole injection, 12 is a hole transport layer, 13 is a light emitting layer, 14 is an organic compound layer, and 15 is a cathode. Electrode.

  A transparent anode 10 was obtained by depositing indium tin oxide (ITO) with a thickness of 120 nm on the transparent substrate 10 by sputtering. Thereafter, the substrate was successively subjected to ultrasonic cleaning with acetone and isopropyl alcohol (IPA), then boiled with IPA and dried. Further, UV / ozone cleaning was performed.

で表されるαＮＰＤを真空蒸着法により３５ｎｍの膜厚で成膜し正孔輸送層１３を形成した。蒸着時の真空度は、１．０×１０−６Ｔｏｒｒ、成膜速度は、成膜速度は０．２〜０．３ｎｍ／ｓｅｃの条件で成膜した。次に、前記正孔輸送層１３の上に、下記化学式２：

で表される、アルミキレート錯体（以下Ａｌｑ３という）を真空着法により１５ｎｍの膜厚で成膜し発光層１４を、正孔輸送層１３を成膜するときと同じ条件で形成した。次に、前記発光層１４の上に、有機化合物層１５として、Ａｌｑ３と炭酸セシウム（Ｃｓ_２ＣＯ_３）を膜厚比９：１の割合で混合されるよう、各々の蒸着速度を調整して３５ｎｍの厚さに成膜した。最後に、前記有機化合物層１５の上に陰極電極１６として、アルミニウム（Ａｌ）を蒸着速度１ｎｍ／ｓｅｃの条件で１５０ｎｍ蒸着した。この有機化合物層におけるＡｌｑ３とＣｓ_２ＣＯ_３とのモル比は１：０.５７である。モル比はとは、有機化合物層を構成する材料の分子量と比重及び、膜厚重量比とから算出される比である。 Then, using a vacuum deposition apparatus [manufactured by Vacuum Kiko Co., Ltd.], the following chemical formula 1 having hole transportability on the cleaned substrate is provided:

The hole transport layer 13 was formed by forming αNPD represented by the following formula with a film thickness of 35 nm by a vacuum deposition method. The degree of vacuum at the time of vapor deposition was 1.0 × 10 −6 Torr, and the film formation rate was 0.2 to 0.3 nm / sec. Next, on the hole transport layer 13, the following chemical formula 2:

An aluminum chelate complex (hereinafter referred to as Alq3) represented by the following formula was formed with a film thickness of 15 nm by a vacuum deposition method, and the light emitting layer 14 was formed under the same conditions as when the hole transport layer 13 was formed. Next, each vapor deposition rate is adjusted so that Alq3 and cesium carbonate (Cs ₂ CO ₃ ) are mixed on the light emitting layer 14 as the organic compound layer 15 at a film thickness ratio of 9: 1. A film was formed to a thickness of 35 nm. Finally, aluminum (Al) was deposited as a cathode electrode 16 on the organic compound layer 15 at a deposition rate of 1 nm / sec. The molar ratio of Alq3 to Cs ₂ CO ₃ in this organic compound layer is 1: 0.57. The molar ratio is a ratio calculated from the molecular weight and specific gravity of the material constituting the organic compound layer and the film thickness / weight ratio.

Thus, the anode electrode 11, the hole transport layer 12, the light emitting layer 13, the organic compound layer 14, and the cathode electrode 15 were provided on the transparent substrate 10, and the light emitting element was obtained. Subsequently, in this light emitting device, ITO was used as the anode electrode 11 and aluminum was used as the cathode electrode 15, and a direct current voltage was applied to examine the light emitting characteristics of the device. As a result, this device showed a maximum luminance of 41200 cd / m ² and a current density of 3200 mA / cm ² at an applied voltage of 15V. The maximum efficiency of 0.91 lm / W was exhibited at an applied voltage of 5V. The voltage-luminance characteristics of this light emitting element are shown in FIGS.

(Comparative Example 1)
This comparative example is an example using no carbonate as compared with Example 1.
Under the same conditions as in Example 1, first, α-NPD having a thickness of 35 nm was formed as a hole transport layer 13 on ITO serving as the anode electrode 12, and then Alq3 was formed as a light emitting layer 14 with a thickness of 50 nm. The film was formed with a film thickness. Finally, 150 nm of aluminum (Al) was deposited as the cathode electrode 16.

Thus, the anode electrode 11, the hole transport layer 12, the light emitting layer 13, the organic compound layer 14, and the cathode electrode 15 were provided on the transparent substrate 10, and the light emitting element was obtained. Subsequently, in this light emitting device, ITO was used as the anode electrode 11 and aluminum was used as the cathode electrode 15, and a direct current voltage was applied to examine the light emitting characteristics of the device. As a result, this device showed a maximum luminance of 1926 cd / m ² and a current density of 350 mA / cm ² at an applied voltage of 20V. The maximum efficiency of 0.17 lm / W was exhibited at an applied voltage of 12V. The voltage-luminance characteristics of this light emitting element are shown in FIGS.

  From the comparison of the voltage-luminance characteristics of Example 1 and Comparative Example 1 shown in FIG. 1, the light-emitting element using cesium carbonate in the organic compound layer shown in Example 1 is compared with the element of Comparative Example 1, It can be seen that the drive voltage is greatly reduced. Therefore, it can be seen that the organic compound layer is effective in reducing the driving voltage of the element.

(Comparative Example 2)
In this comparative example, an attempt was made to form a cesium metal, which is difficult to handle, in the same process as in Example 1, but the film could not be formed.
Under the same conditions as in Example 1, first, α-NPD having a film thickness of 35 nm was formed as a hole transport layer 13 on ITO serving as the anode electrode 12, and then Alq3 was formed as a light emitting layer 14 with a thickness of 15 nm. The film was formed with a film thickness. Next, Alq3 and cesium (Cs) were tried to be mixed at a film thickness ratio of 9: 1 as the organic compound layer 15, but highly reactive metal cesium was introduced into the film forming apparatus in an atmospheric environment. The film could not be formed. Therefore, in order to manufacture an element in which an alkali metal such as cesium (Cs) is introduced into the organic compound layer 15, a special working environment in which an alkali metal is handled and deposited under conditions that do not come into contact with air or moisture is required. Necessary. The construction of such a working environment is costly and the time required for device fabrication is longer than in a normal environment, and the device fabrication throughput is low.

(Comparative Example 3)
This comparative example is an example using a special apparatus for using cesium metal which is difficult to handle.
Under the same conditions as in Example 1, first, α-NPD having a film thickness of 35 nm was formed as a hole transport layer 13 on ITO serving as the anode electrode 12, and then Alq3 was formed as a light emitting layer 14 with a thickness of 15 nm. The film was formed with a film thickness. Next, an attempt was made to form a 35 nm mixed film of Alq3 and cesium (Cs) as the organic compound layer 15. In this comparative example 3, the introduction of cesium into the organic compound layer 15 was performed using an alkali metal dispenser (SAES Getters) capable of generating high-purity alkali metal vapor under vacuum. . The organic compound layer 15 was formed to a thickness of 35 nm by adjusting the deposition rate so that Alq3 and cesium (Cs) were mixed at a film thickness ratio of 9: 1. Finally, aluminum (Al) was deposited as a cathode electrode 16 on the organic compound layer 15 at a deposition rate of 1 nm / sec.

Thus, the anode electrode 11, the hole transport layer 12, the light emitting layer 13, the organic compound layer 14, and the cathode electrode 15 were provided on the transparent substrate 10, and the light emitting element was obtained. Subsequently, in this light emitting device, ITO was used as the anode electrode 11 and aluminum was used as the cathode electrode 15, and a direct current voltage was applied to examine the light emitting characteristics of the device. As a result, this device showed a maximum luminance of 11000 cd / m ² and a current density of 3085 mA / cm ² at an applied voltage of 12V. The maximum efficiency of 0.47 lm / W was exhibited at an applied voltage of 5V. FIG. 3 shows voltage-luminance characteristics of this light emitting element.

(Comparative Example 4)
This comparative example is an example using a salt other than carbonate.
Under the same conditions as in Example 1, first, α-NPD having a film thickness of 35 nm was formed as a hole transport layer 13 on ITO serving as the anode electrode 12, and then Alq3 was formed as a light emitting layer 14 with a thickness of 15 nm. The film was formed with a film thickness. Next, the organic compound layer 15 was formed to a thickness of 35 nm by adjusting the deposition rate so that Alq3 and lithium fluoride (LiF) were mixed at a film thickness ratio of 9: 1. Finally, aluminum (Al) was deposited as a cathode electrode 16 on the organic compound layer 15 at a deposition rate of 1 nm / sec.

Thus, the anode electrode 11, the hole transport layer 12, the light emitting layer 13, the organic compound layer 14, and the cathode electrode 15 were provided on the transparent substrate 10, and the light emitting element was obtained. Subsequently, in this light emitting device, ITO was used as the anode electrode 11 and aluminum was used as the cathode electrode 15, and a direct current voltage was applied to examine the light emitting characteristics of the device. As a result, this device showed a maximum luminance of 23900 cd / m ² and a current density of 2450 mA / cm ² at an applied voltage of 18V. The maximum efficiency of 0.78 lm / W was exhibited at an applied voltage of 5V. The voltage-luminance characteristics of this light emitting element are shown in FIGS.

(Comparative Example 5)
This comparative example is an example in which lithium fluoride (LiF) is used in place of the organic compound layer made of the carbonate and organic compound of Example 1.
Under the same conditions as in Example 1, first, α-NPD having a film thickness of 35 nm is formed as a hole transport layer on ITO which is an anode electrode, and Alq3 is continuously formed as a light emitting layer by 50 nm thereon. did. Next, lithium fluoride (LiF) was deposited to a thickness of 1 nm. Finally, aluminum (Al) was deposited as a cathode electrode at a thickness of 150 nm at a deposition rate of 1 nm / sec.
In this manner, an anode electrode, a hole transport layer, a light emitting layer, lithium fluoride (LiF), and a cathode electrode were provided on the transparent substrate to obtain a light emitting element. Subsequently, a direct current voltage was applied to the light emitting device using ITO as an anode electrode and aluminum as a cathode electrode, and the light emission characteristics of the device were examined. As a result, this device showed a maximum luminance of 26790 cd / m ² and a current density of 2188 mA / cm ² at an applied voltage of 18V. The maximum efficiency was 0.861lm / W at an applied voltage of 5V. The voltage-luminance characteristics of this light emitting element are shown in FIGS.

(Example 2)
In this embodiment, gold is used as the cathode as compared with the first embodiment.
Under the same conditions as in Example 1, first, α-NPD having a film thickness of 35 nm was formed as a hole transport layer 13 on ITO serving as the anode electrode 12, and then Alq3 was formed as a light emitting layer 14 with a thickness of 15 nm. The film was formed with a film thickness. Next, the organic compound layer 15 was formed to a thickness of 35 nm by adjusting the deposition rate so that Alq3 and cesium carbonate (Cs ₂ CO ₃ ) were mixed at a film thickness ratio of 9: 1. Finally, gold (Au) was deposited as a cathode electrode 16 on the organic compound layer 15 at a deposition rate of 1 nm / sec.

Thus, the anode electrode 11, the hole transport layer 12, the light emitting layer 13, the organic compound layer 14, and the cathode electrode 15 were provided on the transparent substrate 10, and the light emitting element was obtained. Subsequently, in this light emitting device, ITO was used as the anode electrode 11 and gold (Au) was used as the cathode electrode 15, and a direct current voltage was applied to examine the light emission characteristics of the device. As a result, this device showed a maximum luminance of 29700 cd / m ² and a current density of 3000 mA / cm ² at an applied voltage of 15V. The maximum efficiency was 0.79 lm / W at an applied voltage of 6V. FIG. 4 shows voltage-luminance characteristics of the light emitting element.

(Comparative Example 6)
This comparative example is an example using lithium fluoride (LiF) instead of carbonate as compared with Example 2.
Under the same conditions as in Example 2, first, α-NPD having a thickness of 35 nm was formed as a hole transport layer 13 on ITO serving as the anode electrode 12, and then Alq3 was formed as a light emitting layer 14 with a thickness of 15 nm. The film was formed with a film thickness. Next, the organic compound layer 15 was formed to a thickness of 35 nm by adjusting the deposition rate so that Alq3 and lithium fluoride (LiF) were mixed at a film thickness ratio of 9: 1. Finally, gold (Au) was deposited as a cathode electrode 16 on the organic compound layer 15 at a deposition rate of 1 nm / sec.

Thus, the anode electrode 11, the hole transport layer 12, the light emitting layer 13, the organic compound layer 14, and the cathode electrode 15 were provided on the transparent substrate 10, and the light emitting element was obtained. Subsequently, in this light emitting device, ITO was used as the anode electrode 11 and gold (Au) was used as the cathode electrode 15, and a direct current voltage was applied to examine the light emission characteristics of the device. As a result, this device showed a maximum luminance of 93 cd / m ² and a current density of 26 mA / cm ² at an applied voltage of 25V.
The maximum efficiency of 0.047 lm / W was exhibited at an applied voltage of 24V. FIG. 4 shows voltage-luminance characteristics of the light emitting element.
When lithium fluoride is used in the organic compound layer, if the cathode is aluminum, the electron injection characteristics are good, but if the cathode is gold, the electron injection characteristics deteriorate. On the other hand, when carbonate is used, good electron injection characteristics can be obtained regardless of whether the cathode is aluminum or gold. That is, the degree of freedom in selecting the cathode material is increased.

(Example 3)
FIG. 5 shows a third embodiment of the present invention. In FIG. 5, 20 is a substrate, 21 is a bottom electrode, 22 is an organic compound layer, and 23 is a top electrode.

The substrate 20 was ultrasonically washed successively with acetone and isopropyl alcohol (IPA), then boiled and washed with IPA, and then dried. Next, using a vacuum vapor deposition apparatus [manufactured by Vacuum Kiko Co., Ltd.], the bottom electrode 21 was formed by depositing aluminum (Al) with a film thickness of 50 nm on the cleaned substrate by a vacuum vapor deposition method. The degree of vacuum during the deposition was 1.0 × 10 ⁻⁶ Torr and a deposition rate of 1 nm / sec. Next, as the organic compound layer 22, each of the deposition rates was adjusted so that Alq3 and cesium carbonate (Cs ₂ CO ₃ ) were mixed at a film thickness ratio of 9: 1 to form a film having a thickness of 50 nm. Finally, aluminum (Al), which is the same material as the lower electrode, was deposited on the organic compound layer 22 as the upper electrode 23 at a deposition rate of 1 nm / sec. The molar ratio of Alq3 to Cs ₂ CO ₃ in this organic compound layer is 1: 0.57.

Thus, the element which provided the lower surface electrode 21, the organic compound layer 22, and the upper surface electrode 23 on the board | substrate 20 was obtained. A DC voltage was applied to the device using the lower electrode 21 of the device as the anode, the upper electrode 23 as the cathode, the lower electrode 21 as the cathode, and the upper electrode 23 as the anode, and the voltage-current characteristics at that time were examined. As a result, at the applied voltage 10V, current density at that time, when the upper electrode 23 and the cathode, 2250mA / cm ^2, when the lower electrode 21 as a cathode, shown 1960mA / cm ^2, respectively.

(Comparative Example 7)
This comparative example is an example using lithium fluoride instead of carbonate as compared with Example 3.
Under the same conditions as in Example 3, aluminum (Al) was formed as the lower electrode 21 with a film thickness of 50 nm, and Alq3 and lithium fluoride (LiF) as the organic compound layer 22 were formed thereon with a film thickness ratio of 9 Each film was formed to a thickness of 50 nm by adjusting the deposition rate so that the mixture was mixed at a ratio of 1: 2. Finally, 150 nm of aluminum (Al) was deposited on the organic compound layer 22 as the upper electrode 23 under the condition of a deposition rate of 1 nm / sec.

Thus, the element which provided the lower surface electrode 21, the organic compound layer 22, and the upper surface electrode 23 on the transparent substrate 20 was obtained. A DC voltage was applied to the device using the lower electrode 21 of the device as the anode, the upper electrode 23 as the cathode, the lower electrode 21 as the cathode, and the upper electrode 23 as the anode, and the voltage-current characteristics at that time were examined. As a result, at the applied voltage 10V, current density at that time, when the upper electrode 23 and the cathode, 935mA / cm ^2, when the lower electrode 21 as a cathode, indicated 11 mA / cm ^2, respectively.

  From the result of Comparative Example 7, in the element using lithium fluoride (LiF) for the organic compound layer, an electric current flows when electrons are injected from the side of the top electrode 23 formed after the organic compound layer is formed. It can be seen that almost no electrons are injected from the lower electrode 21 side. When the electrode is formed in a heated state on the organic compound layer having a salt, a current flows better.

On the other hand, in the element using cesium carbonate (Cs ₂ CO ₃ ) for the organic compound layer 22 according to the present invention, the electrons from the cathode are not subject to any particular restrictions on the film formation order of the organic compound layer 22 and the electrodes in contact therewith. It is possible to reduce the injection barrier and lower the drive voltage of the element.

で表される、バソフェナントロリン（以下B-phenという）を10nmの膜厚で成膜した。続いて、前記ブロック層34の上に、有機化合物層35として、B-phenと炭酸セシウム（Cs₂CO₃）を膜厚比8.8：1.2の割合で混合されるよう、各々の蒸着速度を調整して25nmの厚さに成膜した。最後に前記有機化合物層35の上に陰極電極36として、アルミニウム（Al）を蒸着速度1nm/secの条件で150nm蒸着した。この有機化合物層35におけるB-phenとCs₂CO₃のモル比は、1：0.5である。
このようにして、透明基板30上に、陽極電極31、正孔輸送層32、発光層33、ブロック層34、有機化合物層35、および陰極電極36を設け、発光素子を得た。続いて、この発光素子において、ITOを陽極電極31、アルミニウムを陰極電極36として、直流電圧を印加し、素子の発光特性を調べた。その結果この素子は、印加電圧9Vにて最高輝度44105cd/m²、電流密度1760mA/cm²を示した。また、印加電圧5Vにて最高効率2.3lm/Wを示した。この発光素子の電圧−輝度特性を図７に示す。 Example 4
This example is an example of a light-emitting element in which another layer (block layer) is provided between an organic compound layer and a light-emitting layer.
FIG. 6 shows a fourth embodiment. In the figure, 30 is a transparent substrate on the anode side, 31 is an ITO layer as an anode electrode for hole injection, 32 is a hole transport layer, 33 is a light emitting layer, 34 is a block layer, 35 is an organic compound layer , 36 are cathode electrodes.
Under the same conditions as in Example 1, first, an α-NPD film having a thickness of 35 nm was formed as a hole transport layer 32 on ITO serving as an anode electrode 31, and then Alq3 was formed as a light emitting layer 33 with a thickness of 15 nm. The film was formed with a film thickness of. Next, the block layer 34 has the following chemical formula 3:

As shown, a bathophenanthroline (hereinafter referred to as B-phen) film having a thickness of 10 nm was formed. Subsequently, each vapor deposition rate is adjusted so that B-phen and cesium carbonate (Cs ₂ CO ₃ ) are mixed at a ratio of 8.8: 1.2 as an organic compound layer 35 on the block layer 34. The film was formed to a thickness of 25 nm. Finally, 150 nm of aluminum (Al) was deposited on the organic compound layer 35 as a cathode electrode 36 at a deposition rate of 1 nm / sec. The molar ratio of B-phen and Cs ₂ CO ₃ in the organic compound layer 35 is 1: 0.5.
Thus, the anode electrode 31, the hole transport layer 32, the light emitting layer 33, the block layer 34, the organic compound layer 35, and the cathode electrode 36 were provided on the transparent substrate 30 to obtain a light emitting element. Subsequently, in this light emitting device, ITO was used as the anode electrode 31 and aluminum was used as the cathode electrode 36, and a direct current voltage was applied to examine the light emission characteristics of the device. As a result, this device showed a maximum luminance of 44105 cd / m ² and a current density of 1760 mA / cm ² at an applied voltage of 9 V. The maximum efficiency was 2.3 lm / W at an applied voltage of 5V. FIG. 7 shows voltage-luminance characteristics of this light-emitting element.

(Comparative Example 8)
This comparative example does not use the block layer 34 as compared with the fourth embodiment.
Under the same conditions as in Example 4, first, α-NPD having a film thickness of 35 nm was formed as the hole transport layer 32 on the ITO serving as the anode electrode 31, and then Alq3 was formed as the light emitting layer 33 with a thickness of 15 nm. The film was formed with a film thickness of. Subsequently, the deposition rate was adjusted so that B-phen and cesium carbonate (Cs ₂ CO ₃ ) were mixed as the organic compound layer 35 on the light emitting layer 33 at a film thickness ratio of 8.8: 1.2. A film was formed to a thickness of 35 nm. Finally, 150 nm of aluminum (Al) was deposited on the organic compound layer 35 as the cathode electrode 36.
Thus, the anode electrode 31, the hole transport layer 32, the light emitting layer 33, the organic compound layer 35, and the cathode electrode 36 were provided on the transparent substrate 30 to obtain a light emitting element. Subsequently, in this light emitting device, ITO was used as the anode electrode 31 and aluminum was used as the cathode electrode 36, and a direct current voltage was applied to examine the light emission characteristics of the device. As a result, this device showed a luminance of 33651 cd / m ² and a current density of 3223 mA / cm ² at an applied voltage of 11 V. The efficiency was 1.01 lm / W at an applied voltage of 5V. FIG. 7 shows voltage-luminance characteristics of this light-emitting element.

The light emitting element using cesium carbonate for the block layer and the organic compound layer shown in Example 4 has significantly improved luminous efficiency as compared with Comparative Example 8 that does not include the block layer. The block layer has a function of preventing holes injected from the anode electrode from passing through the light emitting layer, and prevents the carbonate contained in the organic compound layer on the block layer from entering the light emitting layer. Is a layer. When carbonate enters the light emitting layer, the region does not emit light, and the light emission efficiency decreases. Although the reason why the carbonate contained in the organic compound layer enters the light emitting layer is not clear, the present inventors presume that the carbonate penetrates into the light emitting layer by the energy during film formation.
A block layer that is provided between the light emitting layer and the organic compound layer to prevent the passage of holes from the light emitting layer and prevent the carbonate used in the organic compound layer from entering the light emitting layer has a luminous efficiency. It turns out that it is effective for improvement.

  As described above with reference to the respective embodiments and examples, the present invention can provide a light-emitting element in which an organic compound layer composed of a carbonate and an organic compound that are easy to handle is in contact with the cathode.

It is a schematic diagram which shows the example of laminated structure of a general light emitting element. It is a schematic diagram which shows the laminated structure example of the light emitting element of this embodiment. It is a figure which shows the voltage-luminance characteristic of the light emitting element of a present Example, and the light emitting element of a comparative example. It is a figure which shows the voltage-luminance characteristic of the light emitting element of a present Example, and the light emitting element of a comparative example. It is a schematic diagram which shows a 3rd Example. It is a schematic diagram which shows the layer structure of the light emitting element which concerns on a 4th Example. It is a figure which shows the voltage-luminance characteristic of a 4th Example and an 8th comparative example.

Claims (16)

  A light-emitting element comprising at least a pair of electrodes comprising an anode and a cathode and an organic compound layer provided between the pair of electrodes, wherein the organic compound is in electrical contact with the cathode electrode. A light-emitting element, wherein the layer is composed of at least an organic compound and a carbonate.   The light emitting device according to claim 1, wherein the carbonate has a cation of an alkali metal ion or an alkaline earth metal ion.   The light emitting device according to claim 1, wherein the carbonate is cesium carbonate.   The light emitting device according to claim 1, wherein the carbonate is lithium carbonate.   The light emitting device according to claim 1, wherein the cathode is transparent to visible light.   The light emitting device according to claim 1, wherein the cathode is an ITO electrode.   The light emitting device according to claim 1, wherein the cathode is an electrode of at least one of gold, silver, and aluminum.   The light emitting device according to claim 1, further comprising a light emitting layer different from the organic compound layer between the organic compound layer and the anode.   The light-emitting element according to claim 8, further comprising an electron transport layer between the organic compound layer and the light-emitting layer.   The light emitting device according to claim 1, wherein light is extracted from the cathode.   A light-emitting device comprising a plurality of the light-emitting elements according to claim 1 in a plane.   The light emitting device according to claim 11, wherein the light emitting device is used in an information display unit of a display.   The light emitting device according to claim 11, wherein the light emitting device is used as an exposure device that exposes a photosensitive member in an electrophotographic image forming apparatus.   A method of manufacturing a light-emitting device having a pair of electrodes composed of an anode and a cathode and an organic compound layer provided between the pair of electrodes, wherein at least the organic compound and carbonic acid constituting the organic compound layer are formed on the cathode side. A method for producing a light-emitting element, comprising: an organic compound layer forming step of providing a salt; and a step of providing a cathode in electrical contact with the organic compound layer.   The method of manufacturing a light emitting device according to claim 14, wherein the organic compound layer forming step is a step of forming the organic compound layer and carbonate by co-evaporation.   The method according to claim 15, wherein the organic compound layer forming step co-deposits the carbonate with the organic compound in a temperature range of 700 ° C. or less.

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