JP5314834B2 - LIGHT EMITTING ELEMENT, LIGHT EMITTING DEVICE, LIGHTING DEVICE, AND ELECTRONIC DEVICE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting element capable of reducing malfunction due to the crystallization of compounds contained in the layer provided between electrodes. <P>SOLUTION: A light emitting element has a layer containing an aromatic hydrocarbon and a metal oxide between electrodes. Although there are no special limitations on the aromatic hydrocarbon, it preferably has the hole mobility of 1&times;10<SP>-6</SP>cm<SP>2</SP>/Vs or more. As such aromatic hydrocarbon, there are mentioned, for example, 2-tert-butyl-9,10-di(2-naphthyl)anthracene, anthracene, 9,10-diphenyl anthracene, tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, etc. Moreover, the metal oxide preferably shows electron-accepting property to the aromatic hydrocarbon. As such metal oxide, there are mentioned, for example, a molybdenum oxide, vanadium oxide, ruthenium oxide, rhenium oxide, etc. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a light emitting element having a layer containing a light emitting substance between electrodes, a light emitting device having the light emitting element, and an electronic apparatus.

  In recent years, a light-emitting element that has attracted attention as a pixel of a display device or a light source of a lighting device has a light-emitting layer between electrodes and is included in the light-emitting layer when a current flows between the electrodes. The luminescent material emits light.

  In such a light emitting element development field, extending the life of the light emitting element is one of important issues. In order to be able to use a light emitting device such as a display device or a lighting device in a good state for a long period of time, it is necessary to operate the light emitting element provided in the light emitting device for a long period of time. It is.

  As one of techniques for realizing a long lifetime of the light emitting element, for example, a technique related to a light emitting element using molybdenum oxide or the like as an anode as described in Patent Document 1 can be cited.

Although it is considered that the technique as described in Patent Document 1 is also effective, however, molybdenum oxide is easily crystallized, and the technique described in Patent Document 1 tends to cause malfunction of the light-emitting element due to crystallization. There is a problem. In addition, since molybdenum oxide has low conductivity, if the thickness of the molybdenum oxide layer is excessively increased, current may be difficult to flow.
JP-A-9-63771

  It is an object of the present invention to provide a light-emitting element that can reduce malfunction due to crystallization of a compound contained in a layer provided between electrodes.

One embodiment of the present invention is a light-emitting element having a layer containing an aromatic hydrocarbon and a metal oxide between electrodes. Although there is no limitation in particular about aromatic hydrocarbon, what has a hole mobility of 1 * 10 < ^-6 > cm < ² > / Vs or more is preferable. Examples of such aromatic hydrocarbons include 2-tert-butyl-9,10-di (2-naphthyl) anthracene, anthracene, 9,10-diphenylanthracene, tetracene, rubrene, perylene, 2,5,8, Examples include 11-tetra (tert-butyl) perylene. Moreover, as a metal oxide, what shows an electron accepting property with respect to an aromatic hydrocarbon is preferable. Examples of such metal oxides include molybdenum oxide, vanadium oxide, ruthenium oxide, and rhenium oxide.

According to one embodiment of the present invention, a light-emitting layer is provided between a first electrode and a second electrode, and a layer containing an aromatic hydrocarbon and a metal oxide is provided between the light-emitting layer and the first electrode. It is a light emitting element characterized by having. When a voltage is applied to each electrode so that the potential of the first electrode is higher than the potential of the second electrode, the light-emitting substance contained in the light-emitting layer emits light. Although there is no limitation in particular about aromatic hydrocarbon, what has a hole mobility of 1 * 10 < ^-6 > cm < ² > / Vs or more is preferable. Examples of such aromatic hydrocarbons include 2-tert-butyl-9,10-di (2-naphthyl) anthracene, anthracene, 9,10-diphenylanthracene, tetracene, rubrene, perylene, 2,5,8, Examples include 11-tetra (tert-butyl) perylene. Moreover, as a metal oxide, what shows an electron accepting property with respect to an aromatic hydrocarbon is preferable. Examples of such metal oxides include molybdenum oxide, vanadium oxide, ruthenium oxide, and rhenium oxide.

One embodiment of the present invention includes a light-emitting layer, a first mixed layer, and a second mixed layer between a first electrode and a second electrode, and the potential of the first electrode is greater A light-emitting element in which a light-emitting substance contained in a light-emitting layer emits light when a voltage is applied to each electrode so as to be higher than a potential of a second electrode. In such a light emitting element, the light emitting layer is provided closer to the first electrode than the first mixed layer, and the second mixed layer is provided closer to the second electrode than the first mixed layer. The first mixed layer includes a material selected from alkali metals and alkaline earth metals, alkali metal oxides, alkaline earth metal oxides, alkali metal fluorides, alkaline earth metal fluorides, and electron transport. It is a layer containing a sex substance. Here, as an alkali metal, lithium (Li), sodium (Na), potassium (K) etc. are mentioned, for example. Examples of the alkaline earth metal include magnesium (Mg) and calcium (Ca). Examples of the alkali metal oxide include lithium oxide (Li ₂ O), sodium oxide (Na ₂ O), and potassium oxide (K ₂ O). Examples of alkaline earth metal oxides include magnesium oxide (MgO) and calcium oxide (CaO). Examples of the alkali metal fluoride include lithium fluoride (LiF) and cesium fluoride (CsF). Examples of the alkaline earth metal fluoride include magnesium fluoride (MgF ₂ ) and calcium fluoride (CaF ₂ ). Further, the second mixed layer is a layer containing an aromatic hydrocarbon and a metal oxide. Here, although there is no limitation in particular about an aromatic hydrocarbon, what has a hole mobility of 1 * 10 < ^-6 > cm < ² > / Vs or more is preferable. Examples of such aromatic hydrocarbons include 2-tert-butyl-9,10-di (2-naphthyl) anthracene, anthracene, 9,10-diphenylanthracene, tetracene, rubrene, perylene, 2,5,8, Examples include 11-tetra (tert-butyl) perylene. Moreover, as a metal oxide, what shows an electron accepting property with respect to an aromatic hydrocarbon is preferable. Examples of such metal oxides include molybdenum oxide, vanadium oxide, ruthenium oxide, and rhenium oxide.

One embodiment of the present invention includes n (n is an arbitrary natural number of 2 or more) light-emitting layers between a first electrode and a second electrode, and m (m is an arbitrary natural number, and 1 ≦ A first mixed layer and a second mixed layer are provided between the light emitting layer of the first layer (m ≦ n−1) and the light emitting layer of the (m + 1) th layer, and the potential of the first electrode Is a light-emitting element in which a light-emitting substance contained in the light-emitting layer emits light when a voltage is applied to each electrode so that becomes higher than the potential of the second electrode. Here, the first mixed layer is provided closer to the first electrode than the second mixed layer. The first mixed layer includes a material selected from alkali metals and alkaline earth metals, alkali metal oxides, alkaline earth metal oxides, alkali metal fluorides, alkaline earth metal fluorides, and electron transport. It is a layer containing a sex substance. Here, as an alkali metal, lithium (Li), sodium (Na), potassium (K) etc. are mentioned, for example. Examples of the alkaline earth metal include magnesium (Mg) and calcium (Ca). Examples of the alkali metal oxide include lithium oxide (Li ₂ O), sodium oxide (Na ₂ O), and potassium oxide (K ₂ O). Examples of alkaline earth metal oxides include magnesium oxide (MgO) and calcium oxide (CaO). Examples of the alkali metal fluoride include lithium fluoride (LiF) and cesium fluoride (CsF). Examples of the alkaline earth metal fluoride include magnesium fluoride (MgF ₂ ) and calcium fluoride (CaF ₂ ). Further, the second mixed layer is a layer containing an aromatic hydrocarbon and a metal oxide. Here, although there is no limitation in particular about an aromatic hydrocarbon, what has a hole mobility of 1 * 10 < ^-6 > cm < ² > / Vs or more is preferable. Examples of such aromatic hydrocarbons include 2-tert-butyl-9,10-di (2-naphthyl) anthracene, anthracene, 9,10-diphenylanthracene, tetracene, rubrene, perylene, 2,5,8, Examples include 11-tetra (tert-butyl) perylene. Moreover, as a metal oxide, what shows an electron accepting property with respect to an aromatic hydrocarbon is preferable. Examples of such metal oxides include molybdenum oxide, vanadium oxide, ruthenium oxide, and rhenium oxide.

  One embodiment of the present invention is a light-emitting device using any of the light-emitting elements described above as a pixel or a light source.

  One embodiment of the present invention is an electronic device in which a light-emitting device using any of the light-emitting elements described above as a pixel is used for a display portion.

  One embodiment of the present invention is an electronic device in which a light-emitting device using any of the light-emitting elements described above as a light source is used for a lighting portion.

  By implementing the present invention, a light-emitting element in which malfunction of the light-emitting element due to crystallization of a compound contained in a layer provided between electrodes is reduced can be obtained. This is because by mixing aromatic hydrocarbons and metal oxides, the aromatic hydrocarbons and metal oxides inhibit each other from crystallizing, so that a layer that is difficult to crystallize can be formed. .

  By implementing the present invention, a light emitting element capable of easily changing the length of an optical path through which emitted light passes can be obtained. This is because, by providing a mixed layer containing an aromatic hydrocarbon and a metal oxide between the electrodes, a light emitting element in which an increase in driving voltage depending on an increase in the thickness of the mixed layer can be obtained can be obtained. As a result, the distance from the light emitting layer to the electrode can be easily changed.

  By implementing the present invention, a light-emitting element in which a short circuit between electrodes is less likely to occur can be obtained. This is because, by providing a mixed layer containing an aromatic hydrocarbon and a metal oxide between the electrodes, a light emitting element in which an increase in driving voltage depending on an increase in the thickness of the mixed layer can be obtained can be obtained. As a result, it is easy to relieve the unevenness of the electrode by a method of increasing the thickness of the mixed layer.

  By implementing the present invention, a light-emitting element that emits light with high color purity can be obtained, and as a result, a light-emitting device that can provide an image with excellent color can be obtained. This is because the light emitting device of the present invention can easily adjust the optical path length suitable for the wavelength of the emitted light by changing the length of the optical path through which the emitted light passes without worrying about the increase in driving voltage. Because of that.

  Hereinafter, one embodiment of the present invention will be described. However, the present invention can be implemented in many different modes, and those skilled in the art can easily understand that the modes and details can be variously changed without departing from the spirit and scope of the present invention. Is done. Therefore, the present invention is not construed as being limited to the description of the embodiment.

(Embodiment 1)
One mode of a light-emitting element of the present invention will be described with reference to FIG.

  FIG. 1 illustrates a light-emitting element having a light-emitting layer 113 between a first electrode 101 and a second electrode 102. In the light-emitting element illustrated in FIG. 1, a mixed layer 111 is provided between the light-emitting layer 113 and the first electrode 101. In addition, a hole transport layer 112 is provided between the light-emitting layer 113 and the mixed layer 111, and an electron transport layer 114 and an electron injection layer 115 are provided between the light-emitting layer 113 and the second electrode 102. ing. In such a light-emitting element, when a voltage is applied to the first electrode 101 and the second electrode 102 so that the potential of the first electrode 101 is higher than the potential of the second electrode 102, the light-emitting layer 113 is used. Then, holes are injected from the first electrode 101 side, and electrons are injected from the second electrode 102 side. Then, the holes and electrons injected into the light emitting layer 113 are recombined. The light-emitting layer 113 contains a light-emitting substance, and the light-emitting substance is excited by excitation energy generated by recombination. The luminescent material in the excited state emits light when returning to the ground state.

  Hereinafter, the first electrode 101, the second electrode 102, and each layer provided between the first electrode 101 and the second electrode 102 will be specifically described.

  There is no particular limitation on the substance forming the first electrode 101. Indium tin oxide, indium tin oxide containing silicon oxide, indium oxide containing 2 to 20% zinc oxide, gold (Au), platinum (Pt) , Nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), tantalum nitride, etc. In addition, a substance having a low work function such as aluminum or magnesium can be used. This is because, in the light emitting element of the present invention, holes are generated from the mixed layer 111 when a voltage is applied.

  The substance forming the second electrode 102 is preferably a substance having a low work function such as aluminum or magnesium; however, a layer that generates electrons is provided between the second electrode 102 and the light-emitting layer 113. Indium tin oxide, indium tin oxide containing silicon oxide, indium oxide containing 2 to 20% zinc oxide, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), A substance having a high work function such as chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), tantalum nitride, or the like can also be used. Therefore, which substance is used as a substance for forming the second electrode 102 may be selected as appropriate in accordance with the properties of the layer provided between the second electrode 102 and the light-emitting layer 113.

  Note that the first electrode 101 and the second electrode 102 are preferably formed so that one or both of the electrodes can transmit light emitted.

The mixed layer 111 is a layer containing an aromatic hydrocarbon and a metal oxide. Although there is no limitation in particular about aromatic hydrocarbon, what has a hole mobility of 1 * 10 < ^-6 > cm < ² > / Vs or more is preferable. By having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher, holes injected from the metal oxide can be efficiently transported. As an aromatic hydrocarbon having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher, for example, 2-tert-butyl-9,10-di (2-naphthyl) anthracene (abbreviation: t-BuDNA), Anthracene, 9,10-diphenylanthracene, tetracene, rubrene, perylene, 2,5,8,11-tetra (tert-butyl) perylene and the like can be mentioned. In addition, pentacene, coronene, and the like can also be used. Thus, it is more preferable to use an aromatic hydrocarbon having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or more and having 14 to 42 carbon atoms. Moreover, as a metal oxide, what shows an electron accepting property with respect to an aromatic hydrocarbon is preferable. Examples of such metal oxides include molybdenum oxide, vanadium oxide, ruthenium oxide, and rhenium oxide. In addition, metal oxides such as titanium oxide, chromium oxide, zirconium oxide, hafnium oxide, tantalum oxide, tungsten oxide, and silver oxide can also be used. In the mixed layer 111, the metal oxide is included so that the mass ratio is 0.5 to 2 or the molar ratio is 1 to 4 (= metal oxide / aromatic hydrocarbon) with respect to the aromatic hydrocarbon. Preferably it is. Aromatic hydrocarbons generally have the property of being easily crystallized, but are difficult to crystallize when mixed with a metal oxide as in this embodiment. Among metal oxides, molybdenum oxide, in particular, is easily crystallized when it is made of a layer made of only it, but is difficult to crystallize by mixing with an aromatic hydrocarbon as in this embodiment. In this way, by mixing the aromatic hydrocarbon and the metal oxide, the aromatic hydrocarbon and the metal oxide inhibit crystallization from each other, and a layer that is difficult to crystallize can be formed. Moreover, since aromatic hydrocarbon has a high glass transition temperature, 4,4 ′, 4 ″ -tris (N, N-diphenylamino) can be obtained by using a structure containing aromatic hydrocarbon such as mixed layer 111. Triphenylamine (abbreviation: TDATA), 4,4 ′, 4 ″ -tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine (abbreviation: MTDATA), 4,4′-bis { N- [4- (N, N-di-m-tolylamino) phenyl] -N-phenylamino} biphenyl (abbreviation: DNTPD) or the like is superior in heat resistance and more positive. A layer having a function of injecting holes into the hole transport layer 112 can be obtained.

The hole transport layer 112 is a layer having a function of transporting holes. In the light-emitting element of this embodiment mode, the hole transport layer 112 has a function of transporting holes from the mixed layer 111 to the light-emitting layer 113. By providing the hole transport layer 112, the distance between the mixed layer 111 and the light emitting layer 113 can be increased, and as a result, the light emission is prevented from being quenched due to the metal contained in the mixed layer 111. Can do. The hole transport layer 112 is preferably formed using a hole transport material, and in particular, a hole transport material having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher, or 1 × 10 ^−6. It is preferable to use a bipolar substance having a hole mobility of cm ² / Vs or higher. Note that the hole transporting substance is a substance having a hole mobility higher than that of electrons, and is preferably a value of a ratio of hole mobility to electron mobility (= hole mobility / electron mobility). ) Refers to a substance greater than 100. Specific examples of the hole transporting substance include 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (abbreviation: NPB), 4,4′-bis [N- (3- Methylphenyl) -N-phenylamino] biphenyl (abbreviation: TPD), 1,3,5-tris [N, N-di (m-tolyl) amino] benzene (abbreviation: m-MTDAB), 4,4 ′, 4 ″ -tris (N-carbazolyl) triphenylamine (abbreviation: TCTA), and the like. In addition, the bipolar substance means that the ratio of the mobility of one carrier to the mobility of the other carrier is 100 or less, preferably 10 or less when the mobility of electrons and the mobility of holes are compared. Is a substance. As a bipolar substance, for example, 2,3-bis (4-diphenylaminophenyl) quinoxaline (abbreviation: TPAQn), 2,3-bis {4- [N- (1-naphthyl) -N-phenylamino] phenyl } -Dibenzo [f, h] quinoxaline (abbreviation: NPDiBzQn) and the like. Among bipolar substances, it is particularly preferable to use a substance having a hole and electron mobility of 1 × 10 ⁻⁶ cm ² / Vs or more.

  The light emitting layer 113 is a layer containing a light emitting substance. Here, the light-emitting substance is a substance that has good emission efficiency and can emit light of a desired wavelength. The light-emitting layer 113 may be a layer formed only of a light-emitting substance, but when concentration quenching occurs, the light-emitting substance is contained in a layer formed of a substance having an energy gap larger than that of the light-emitting substance. A layer mixed so as to be dispersed is preferable. By including a light-emitting substance in the light-emitting layer 113 in a dispersed manner, light emission can be prevented from being quenched due to concentration. Here, the energy gap refers to an energy gap between the LUMO level and the HOMO level.

There is no particular limitation on the light-emitting substance, and a substance that has favorable emission efficiency and can emit light with a desired emission wavelength may be used. For example, when red light emission is desired, 4-dicyanomethylene-2-isopropyl-6- [2- (1,1,7,7-tetramethyl-9-julolidyl) ethenyl] -4H-pyran (abbreviation: DCJTI), 4-dicyanomethylene-2-methyl-6- [2- (1,1,7,7-tetramethyl-9-julolidyl) ethenyl] -4H-pyran (abbreviation: DCJT), 4-dicyanomethylene- 2-tert-butyl-6- [2- (1,1,7,7-tetramethyl-9-julolidyl) ethenyl] -4H-pyran (abbreviation: DCJTB), perifuranthene, 2,5-dicyano-1,4 Such as bis [2- (10-methoxy-1,1,7,7-tetramethyl-9-julolidyl) ethenyl] benzene, and the like. It can be used and a substance which exhibits emission with a click as a luminous material. When green light emission is desired, N, N′-dimethylquinacridone (abbreviation: DMQd), coumarin 6, coumarin 545T, tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), etc., a wavelength of 500 nm to 550 nm A substance that emits light having an emission spectrum peak in a band can be used as the light-emitting substance. When blue light emission is desired, 9,10-bis (2-naphthyl) -tert-butylanthracene (abbreviation: t-BuDNA), 9,9′-bianthryl, 9,10-diphenylanthracene (abbreviation) : DPA), 9,10-bis (2-naphthyl) anthracene (abbreviation: DNA), bis (2-methyl-8-quinolinolato) -4-phenylphenolato-gallium (abbreviation: BGaq), bis (2-methyl) A substance exhibiting light emission having an emission spectrum peak in the wavelength band of 420 nm to 500 nm, such as -8-quinolinolato) -4-phenylphenolato-aluminum (abbreviation: BAlq), can be used as the light-emitting substance. As described above, in addition to a substance that emits fluorescence, bis [2- (3,5-bis (trifluoromethyl) phenyl) pyridinato-N, C ^{2 ′} ] iridium (III) picolinate (abbreviation: Ir (CF ₃ ppy) ₂ (pic)), bis [2- (4,6-difluorophenyl) pyridinato-N, C ^{2 ′} ] iridium (III) acetylacetonate (abbreviation: FIr (acac)), bis [2- (4 , 6-Difluorophenyl) pyridinato-N, C ^{2 ′} ] iridium (III) picolinate (abbreviation: FIr (pic)), tris (2-phenylpyridinato-N, C ^{2 ′} ) iridium (abbreviation: Ir (ppy) ₃ ) A phosphorescent substance such as ₃ ) can also be used as the light emitting substance.

There is no particular limitation on a substance that is included in the light-emitting layer 113 together with the light-emitting substance and is used for dispersing the light-emitting substance, and may be appropriately selected in consideration of an energy gap of the substance used as the light-emitting substance. For example, anthracene derivatives such as 9,10-di (2-naphthyl) -2-tert-butylanthracene (abbreviation: t-BuDNA), or 4,4′-bis (N-carbazolyl) biphenyl (abbreviation: CBP) Carbazole derivatives of 2,3-bis (4-diphenylaminophenyl) quinoxaline (abbreviation: TPAQn), 2,3-bis {4- [N- (1-naphthyl) -N-phenylamino] phenyl} -dibenzo [ In addition to quinoxaline derivatives such as f, h] quinoxaline (abbreviation: NPDiBzQn), bis [2- (2-hydroxyphenyl) pyridinato] zinc (abbreviation: Znpp ₂ ), bis [2- (2-hydroxyphenyl) benzoxazola G] A metal complex such as zinc (abbreviation: ZnBOX) or the like can be used together with a light-emitting substance.

The electron transport layer 114 is a layer having a function of transporting electrons. In the light emitting element of this embodiment mode, the electron transport layer 114 has a function of transporting electrons from the electron injection layer 115 to the light emitting layer 113. By providing the electron transport layer 114, the distance between the second electrode 102 and the light-emitting layer 113 can be increased, and as a result, light emission is quenched due to the metal contained in the second electrode 102. Can be prevented. The electron transporting layer is preferably formed using an electron transporting substance, particularly 1 × ¹⁰ -6 ^cm 2 / Vs or more electron-transport property having an electron mobility substance or 1 × ¹⁰ -6 ^cm 2 / Vs or more It is preferable to form using a bipolar substance having the electron mobility. Here, the electron transporting substance is a substance having electron mobility higher than that of holes, and is preferably a value of a ratio of electron mobility to hole mobility (= electron mobility / hole mobility). Refers to a substance having a degree greater than 100. Specific examples of the electron-transporting substance include tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), tris (4-methyl-8-quinolinolato) aluminum (abbreviation: Almq ₃ ), bis (10-hydroxybenzo [h ] - quinolinato) beryllium (abbreviation: BeBq _2), bis (2-methyl-8-quinolinolato) -4-phenylphenolato - aluminum (abbreviation: BAlq), bis [2- (2-hydroxyphenyl) benzoxazolato ] In addition to metal complexes such as zinc (abbreviation: Zn (BOX) ₂ ), bis [2- (2-hydroxyphenyl) benzothiazolate] zinc (abbreviation: Zn (BTZ) ₂ ), 2- (4-biphenylyl) -5 -(4-tert-butylphenyl) -1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis [5- (p- tert-butylphenyl) -1,3,4-oxadiazol-2-yl] benzene (abbreviation: OXD-7), TAZ, p-EtTAZ, BPhen, BCP, 4,4-bis (5-methylbenzoxa) Zolyl-2-yl) stilbene (abbreviation: BzOs) and the like. The bipolar substance is as described above. Note that the electron transport layer 114 and the hole transport layer 112 may be formed using the same bipolar substance.

The electron injection layer 115 is a layer having a function of assisting injection of electrons from the second electrode 102 to the electron transport layer 114. By providing the electron injection layer 115, the difference in electron affinity between the second electrode 102 and the electron transport layer 114 is reduced, and electrons are easily injected. The electron injection layer 115 is a substance having a higher electron affinity than the substance forming the electron transport layer 114 and a lower electron affinity than the substance forming the second electrode 102, or the electron transport layer 114 and the second transport layer 114. It is preferable to use a substance having such a property that an energy band bends when it is provided as a thin film of about 1 to 2 nm between the electrode 102. Specific examples of a substance that can be used to form the electron injection layer 115 include alkali metals such as lithium (Li), alkaline earth metals such as magnesium (Mg), and alkali metals such as cesium fluoride (CsF). Fluorides of alkaline earth metals such as calcium fluoride (CaF ₂ ), alkalis such as lithium oxide (Li ₂ O), sodium oxide (Na ₂ O), potassium oxide (K ₂ O) Examples thereof include inorganic substances such as metal oxides, oxides of alkaline earth metals such as calcium oxide (CaO) and magnesium oxide (MgO). These materials are preferable because the energy band bends when provided as a thin film. In addition to inorganic substances, bathophenanthroline (abbreviation: BPhen), bathocuproin (abbreviation: BCP), 3- (4-tert-butylphenyl) -4- (4-ethylphenyl) -5- (4-biphenylyl) -1 2,4-triazole (abbreviation: p-EtTAZ), 3- (4-tert-butylphenyl) -4-phenyl-5- (4-biphenylyl) -1,2,4-triazole (abbreviation: TAZ), etc. The organic material that can be used to form the electron transport layer 114 is selected from those materials having a higher electron affinity than the material used to form the electron transport layer 114. It can be used as a substance that forms That is, the electron injection layer 115 may be formed by selecting a substance so that the electron affinity in the electron injection layer 115 is relatively larger than the electron affinity in the electron transport layer 114. Note that in the case where the electron-injecting layer 115 is provided, the second electrode 102 is preferably formed using a substance having a low work function such as aluminum.

  In the light-emitting element described above, when the mobility of the electron-transporting substance used for forming the electron-transport layer 114 is compared with the mobility of aromatic hydrocarbons included in the mixed layer 111, the movement of one substance is compared. It is preferable to select each of the electron transporting substance and the aromatic hydrocarbon so that the ratio of the mobility of the other substance to the degree is 1000 or less. Thus, by selecting each substance, the recombination efficiency in the light emitting layer can be increased.

Note that in this embodiment mode, a light-emitting element including the hole transport layer 112, the electron transport layer 114, the electron injection layer 115, and the like in addition to the mixed layer 111 and the light-emitting layer 113 is described; It is not limited. For example, as shown in FIG. 3, the electron generation layer 116 may be provided instead of the electron injection layer 115. The electron generating layer 116 is a layer that generates electrons, and is formed by mixing at least one substance selected from an electron transporting substance and a bipolar substance and a substance that exhibits an electron donating property with respect to these substances. Can do. Here, among electron transporting substances and bipolar substances, a substance having an electron mobility of 1 × 10 ⁻⁶ cm ² / Vs or more is particularly preferable. As the electron transporting substance and the bipolar substance, those described above can be used. Moreover, as the substance exhibiting electron donating property, a substance selected from alkali metals and alkaline earth metals, specifically, lithium (Li), calcium (Ca), sodium (Na), potassium (K), Magnesium (Mg) or the like can be used. Further, alkali metal oxides and alkaline earth metal oxides, alkali metal fluorides, alkaline earth metal fluorides, etc., specifically lithium oxide (Li ₂ O), calcium oxide (CaO), sodium oxide At least one selected from (Na ₂ O), potassium oxide (K ₂ O), magnesium oxide (MgO), lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF ₂ ) and the like. Substances can also be used as substances exhibiting electron donating properties.

  Further, a hole blocking layer 117 may be provided between the light emitting layer 113 and the electron transporting layer 114 as shown in FIG. By providing the hole blocking layer 117, holes can be prevented from penetrating through the light emitting layer 113 and flowing toward the second electrode 102, and the carrier recombination efficiency can be increased. In addition, the excitation energy generated in the light emitting layer 113 can be prevented from moving to another layer such as the electron transport layer 114. The hole blocking layer 117 is formed of a material that can be used to form the electron transport layer 114 such as BAlq, OXD-7, TAZ, or BPhen, and more particularly than a material that is used to form the light emitting layer 113. It can be formed by selecting a substance having a large ionization potential and excitation energy. That is, the hole blocking layer 117 may be formed by selecting a material so that the ionization potential in the hole blocking layer 117 is relatively larger than the ionization potential in the electron transport layer 114. Similarly, a layer may be provided between the light emitting layer 113 and the hole transporting layer 112 to prevent electrons from passing through the light emitting layer 113 and flowing toward the second electrode 102. .

  Note that whether or not to provide the electron injection layer 115, the electron transport layer 114, and the hole transport layer 112 may be appropriately selected by the practitioner of the invention. For example, the hole transport layer 112, the electron transport layer 114, and the like If there is no problem such as quenching due to metal even if it is not provided, or if electron injection from the electrode can be satisfactorily performed without providing the electron injection layer 115, these layers are not necessarily provided.

  As described above, the light emitting element having the mixed layer 111 containing the aromatic hydrocarbon and the metal oxide makes the crystal of the layer more than the light emitting element provided with the layer made of only the aromatic hydrocarbon or the metal oxide. It is possible to reduce defects due to crystallization, for example, a short circuit between electrodes resulting from the occurrence of unevenness due to crystallization. In addition, since the mixed layer 111 can generate holes, by providing the mixed layer 111 containing an aromatic hydrocarbon and a metal oxide, a change in driving voltage depending on the thickness of the mixed layer 111 is small. A light emitting element can be obtained. Therefore, the distance between the light emitting layer 113 and the first electrode 101 can be easily adjusted by changing the thickness of the mixed layer 111. In other words, the length of the optical path (optical path length) through which the emitted light passes is set so that the length of the emitted light can be efficiently extracted to the outside or the color purity of the emitted light extracted to the outside is improved. Easy to adjust. Further, by increasing the thickness of the mixed layer 111, unevenness on the surface of the first electrode 101 can be relaxed, and a short circuit between the electrodes can be reduced.

  In the light-emitting element described above, the mixed layer 111, the hole transport layer 112, the light-emitting layer 113, the electron transport layer 114, the electron injection layer 115, and the like are stacked over the first electrode 101 in this order, Alternatively, the electron injection layer 115, the electron transport layer 114, the light emitting layer 113, the hole transport layer 112, and the mixed layer 111 may be sequentially formed over the second electrode 102. After stacking, the first electrode 101 may be formed by a method. By forming the mixed layer 111 after forming the light emitting layer 113 as in the latter method, the mixed layer 111 functions as a protective layer even when the first electrode 101 is formed by a sputtering method. A favorable light-emitting element which is unlikely to be damaged due to sputtering of a layer formed using an organic compound such as 113 can be manufactured.

(Embodiment 2)
One mode of the light-emitting element of the present invention will be described with reference to FIG.

  In FIG. 2, a light emitting layer 213, a first mixed layer 215, and a second mixed layer 216 are provided between the first electrode 201 and the second electrode 202. The light-emitting element is shown in which the first mixed layer 215 is provided on the first electrode 201 side, and the second mixed layer 216 is provided on the second electrode 202 side with respect to the first mixed layer 215. In this light-emitting element, a hole injection layer 211 and a hole transport layer 212 are provided between the light-emitting layer and the first electrode 201, and between the light-emitting layer 213 and the first mixed layer 215. Is provided with an electron transport layer 214. The first mixed layer 215 includes a substance selected from an alkali metal, an alkaline earth metal, an alkali metal oxide, an alkaline earth metal oxide, an alkali metal fluoride, and an alkaline earth metal fluoride, and an electron. A layer containing a transporting substance. The second mixed layer 216 is a layer containing an aromatic hydrocarbon and a metal oxide. The light-emitting layer 213 contains a light-emitting substance. When a voltage is applied to each electrode so that the potential of the first electrode 201 is higher than the potential of the second electrode 202, the first mixing is performed. Electrons are injected from the layer 215 to the electron transport layer 214, holes are injected from the second mixed layer 216 to the second electrode 202, and holes are further injected from the first electrode 201 to the hole injection layer 211. Injected. Then, holes injected from the first electrode 201 side to the light-emitting layer 213 and electrons injected from the second electrode 202 side to the light-emitting layer 213 are recombined, and excited energy generated by the recombination is generated. The luminescent material contained in the luminescent layer 213 is excited. The excited luminescent material emits light when returning to the ground state.

  Hereinafter, the first electrode 201, the second electrode 202, and each layer provided between the first electrode 201 and the second electrode 202 will be specifically described.

  The material forming the first electrode 201 is indium tin oxide, indium tin oxide containing silicon oxide, indium oxide containing 2 to 20% zinc oxide, gold (Au), platinum (Pt), nickel (Ni ), Tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), tantalum nitride and the like. preferable.

  The substance forming the second electrode 202 is preferably a substance having a low work function such as aluminum or magnesium; however, a layer that generates electrons is provided between the second electrode 202 and the light-emitting layer 213. Indium tin oxide, indium tin oxide containing silicon oxide, indium oxide containing 2 to 20% zinc oxide, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), A substance having a high work function such as chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), tantalum nitride, or the like can also be used. Accordingly, which material is used as the material for forming the second electrode 202 may be selected as appropriate in accordance with the properties of the layer provided between the second electrode 202 and the light-emitting layer 213.

  Note that the first electrode 201 and the second electrode 202 are preferably formed so that one or both of the electrodes can transmit light emitted.

The hole injection layer 211 is a layer having a function of assisting injection of holes from the first electrode 201 to the hole transport layer 212 in the light-emitting element of this embodiment. By providing the hole injection layer 211, the difference in ionization potential between the first electrode 201 and the hole transport layer 212 is reduced, and holes are easily injected. The hole injection layer 211 may be formed using a material having a lower ionization potential than the material forming the hole transport layer 212 and a higher ionization potential than the material forming the first electrode 201. preferable. Specific examples of a substance that can be used to form the hole-injecting layer 211 include low molecules such as phthalocyanine (abbreviation: H ₂ Pc) and copper phthalocyanine (abbreviation: CuPC), or poly (ethylenedioxythiophene) / And a polymer such as a poly (styrenesulfonic acid) aqueous solution (abbreviation: PEDOT / PSS).

The hole transport layer 212 is a layer having a function of transporting holes. In the light-emitting element of this embodiment mode, the hole transport layer 212 has a function of transporting holes from the hole injection layer 211 to the light-emitting layer 213. By providing the hole transport layer 212, the distance between the first electrode 201 and the light emitting layer 213 can be increased, and as a result, light emission is quenched due to the metal contained in the first electrode 201. Can be prevented. The hole transport layer 212 is preferably formed using a hole transport material, and in particular, a hole transport material having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher, or 1 × 10 ^−6. It is preferable to use a bipolar substance having a hole mobility of cm ² / Vs or higher. Note that for the hole-transporting substance and the bipolar substance, the description about the hole-transporting substance and the bipolar substance in Embodiment 1 is applied mutatis mutandis, and description thereof is omitted in this embodiment.

  The light emitting layer 213 is a layer containing a light emitting substance. The light emitting layer 213 may be a layer formed only of a light emitting material. However, when concentration quenching occurs, the light emitting material is contained in a layer made of a material having an energy gap larger than that of the light emitting material. A layer mixed so as to be dispersed is preferable. By including a light-emitting substance in the light-emitting layer 213 in a dispersed manner, light emission can be prevented from being quenched due to concentration. Here, the energy gap refers to an energy gap between the LUMO level and the HOMO level. For the light-emitting substance and the substance used for bringing the light-emitting substance into a dispersed state, the description relating to the light-emitting substance and the substance used for bringing the light-emitting substance into a dispersed state in Embodiment 1 is applied mutatis mutandis, and description thereof is omitted in this embodiment. To do.

The electron-transport layer 214 is a layer having a function of transporting electrons. In the light-emitting element of this embodiment mode, the electron-transport layer 214 has a function of transporting electrons injected from the first mixed layer 215 to the light-emitting layer 213. By providing the electron transport layer 214, the distance between the second mixed layer 216 and the light emitting layer 213 can be increased. As a result, the first mixed layer 216 is caused by the metal contained in the second mixed layer 216 (first In the case where the mixed layer 215 contains a metal, it is possible to prevent the light emission from being quenched. The electron transport layer 214 is preferably formed using an electron transport material, and in particular, an electron transport material having an electron mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher or 1 × 10 ⁻⁶ cm ² / Vs. It is preferable to use a bipolar substance having the above electron mobility. Note that for the electron-transporting substance and the bipolar substance, the description about the electron-transporting substance and the bipolar substance in Embodiment 1 is applied mutatis mutandis, and description thereof is omitted in this embodiment.

The first mixed layer 215 is a layer that generates electrons, and is formed by mixing at least one substance selected from an electron transporting substance and a bipolar substance and a substance that exhibits an electron donating property with respect to these substances. can do. Here, among electron transporting substances and bipolar substances, a substance having an electron mobility of 1 × 10 ⁻⁶ cm ² / Vs or more is particularly preferable. For the electron transporting substance and the bipolar substance, the description about the electron transporting substance and the bipolar substance in Embodiment 1 is applied mutatis mutandis, and description thereof is omitted here. In addition, as for the electron-transporting substance and the substance showing an electron-donating property with respect to the bipolar substance, the description relating to the substance showing the electron-donating property in Embodiment Mode 1 is applied mutatis mutandis, and the description thereof is omitted here.

The second mixed layer 216 is a layer containing an aromatic hydrocarbon and a metal oxide. Although there is no limitation in particular about aromatic hydrocarbon, what has a hole mobility of 1 * 10 < ^-6 > cm < ² > / Vs or more is preferable. By having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher, holes injected from the metal oxide can be efficiently transported. As an aromatic hydrocarbon having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher, for example, 2-tert-butyl-9,10-di (2-naphthyl) anthracene (abbreviation: t-BuDNA), Anthracene, 9,10-diphenylanthracene, tetracene, rubrene, perylene, 2,5,8,11-tetra (tert-butyl) perylene and the like can be mentioned. In addition, pentacene, coronene, and the like can also be used. Thus, it is more preferable to use an aromatic hydrocarbon having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or more and having 14 to 42 carbon atoms. Moreover, as a metal oxide, what shows an electron accepting property with respect to an aromatic hydrocarbon is preferable. Examples of such metal oxides include molybdenum oxide, vanadium oxide, ruthenium oxide, and rhenium oxide. In addition, metal oxides such as titanium oxide, chromium oxide, zirconium oxide, hafnium oxide, tantalum oxide, tungsten oxide, and silver oxide can also be used. In the second mixed layer 216, the metal oxide has a mass ratio of 0.5 to 2 or a molar ratio of 1 to 4 (= metal oxide / aromatic hydrocarbon) with respect to the aromatic hydrocarbon. It is preferably included. Aromatic hydrocarbons generally have the property of being easily crystallized, but are difficult to crystallize when mixed with a metal oxide as in this embodiment. Among metal oxides, molybdenum oxide, in particular, is easily crystallized when it is made of a layer made of only it, but is difficult to crystallize by mixing with an aromatic hydrocarbon as in this embodiment. In this way, by mixing the aromatic hydrocarbon and the metal oxide, the aromatic hydrocarbon and the metal oxide inhibit crystallization from each other, and a layer that is difficult to crystallize can be formed.

  Note that in this embodiment, a light-emitting element including a hole-injection layer 211, a hole-transport layer 212, an electron-transport layer 214, and the like in addition to the light-emitting layer 213, the first mixed layer 215, and the second mixed layer 216 is described. However, the mode of the light emitting element is not necessarily limited to this. For example, as illustrated in FIG. 5, a configuration in which a layer 217 including the same aromatic hydrocarbon and metal oxide as the second mixed layer is provided instead of the hole injection layer 211 may be employed. By providing the layer 217 including an aromatic hydrocarbon and a metal oxide, the light-emitting element can be favorably operated even when the first electrode 201 is formed using a material having a low work function such as aluminum or magnesium. Can do. In addition, as illustrated in FIG. 6, a hole blocking layer 218 may be provided between the electron transport layer 214 and the light emitting layer 213. The hole blocking layer 218 is similar to the hole blocking layer 117 described in Embodiment 1, and description thereof is omitted here.

  Note that whether or not to provide the hole injection layer 211, the hole transport layer 212, and the electron transport layer 214 may be appropriately selected by the practitioner of the invention. For example, the hole transport layer 212, the electron transport layer 214, etc. If there is no problem such as quenching due to the metal without providing the hole, and if the hole injection from the electrode can be satisfactorily performed without providing the hole injection layer 211, it is necessary to provide these layers. Absent.

  As described above, by using the light-emitting element having the second mixed layer 216 containing the aromatic hydrocarbon and the metal oxide, the light-emitting element provided with the layer made of only the aromatic hydrocarbon or the metal oxide is used. Defects caused by layer crystallization, for example, short-circuiting between electrodes resulting from the occurrence of unevenness due to crystallization can be reduced. In addition, since the second mixed layer 216 can generate holes, the thickness of the second mixed layer 216 is provided by providing the second mixed layer 216 containing an aromatic hydrocarbon and a metal oxide. Thus, a light-emitting element with little change in driving voltage depending on the above can be obtained. Therefore, the distance between the light emitting layer 213 and the second electrode 202 can be easily adjusted by changing the thickness of the second mixed layer 216. In other words, the length of the optical path (optical path length) through which the emitted light passes is set so that the length of the emitted light can be efficiently extracted to the outside or the color purity of the emitted light extracted to the outside is improved. Easy to adjust. In addition, by increasing the thickness of the second mixed layer 216, unevenness on the surface of the second electrode 202 can be reduced, and a short circuit between the electrodes can be reduced.

  Further, the distance between the first electrode 201 and the light-emitting layer 213 is adjusted by providing a layer containing an aromatic hydrocarbon and a metal oxide on the first electrode 201 side instead of the hole injection layer 211. In addition, the unevenness of the surface of the first electrode 201 can be eased, and a short circuit between the electrodes can be reduced.

  The light-emitting element described above may be manufactured by a method in which the first electrode 201 is first formed and each layer such as the light-emitting layer 213 is formed, and then the second electrode 202 is formed. The second electrode 202 may be formed first, and after forming each layer such as the light emitting layer 213, the first electrode 201 may be formed. In any method, after the light emitting layer 213 is formed, a layer containing an aromatic hydrocarbon and a metal oxide is formed, so that the electrode (the first electrode 201 or the second electrode 202) is formed by a sputtering method. Even when formed, a layer containing an aromatic hydrocarbon and a metal oxide functions as a protective layer, and a layer formed using an organic compound such as the light-emitting layer 213 is less likely to be damaged due to sputtering and has excellent light emission. An element can be manufactured.

(Embodiment 3)
One mode of the light-emitting element of the present invention will be described with reference to FIGS.
In FIG. 20, a plurality of light-emitting layers, specifically, a first light-emitting layer 413a, a second light-emitting layer 413b, and a third light-emitting layer 413c are provided between the first electrode 401 and the second electrode 402. A light emitting device is shown. This light-emitting element includes a first mixed layer 421a and a second mixed layer 422a between the first light-emitting layer 413a and the second light-emitting layer 413b, and the second light-emitting layer 413b and the third light-emitting layer 413c. 1st mixed layer 421b and second mixed layer 422b. The first mixed layers 421a and 421b are made of a substance selected from an alkali metal, an alkaline earth metal, an alkali metal oxide, an alkaline earth metal oxide, an alkali metal fluoride, and an alkaline earth metal fluoride. And a layer containing an electron transporting substance. The second mixed layers 422a and 422b are layers containing an aromatic hydrocarbon and a metal oxide. Note that the first mixed layer 421a is provided closer to the first electrode 401 than the second mixed layer 422a, and the first mixed layer 421b is provided closer to the first electrode 401 than the second mixed layer 422b. It has been. Between the first electrode 401 and the first light emitting layer 413a, between the second mixed layer 422a and the second light emitting layer 413b, and between the second mixed layer 422b and the third light emitting layer 413c, respectively. , Hole transport layers 412a, 412b, and 412c are provided. Further, between the first light emitting layer 413a and the first mixed layer 421a, between the second light emitting layer 413b and the first mixed layer 421b, and between the third light emitting layer 413c and the second electrode 402, Electron transport layers 414a, 414b, and 414c are provided, respectively. A hole injection layer 411 is provided between the first electrode 401 and the hole transport layer 412a, and an electron injection layer 415 is provided between the second electrode 402 and the electron transport layer 414c. Yes. The first light-emitting layer 413a, the second light-emitting layer 413b, and the third light-emitting layer 413c contain a light-emitting substance, so that the potential of the first electrode 401 is higher than the potential of the second electrode 402. When a voltage is applied to the electrodes, holes and electrons recombine in each light-emitting layer, and the light-emitting substance contained in each light-emitting layer is excited by the excitation energy generated by the recombination. . The excited luminescent material emits light when returning to the ground state. Note that the light-emitting substances contained in each light-emitting layer may be the same or different.

  The materials forming the first electrode 401 are indium tin oxide, indium tin oxide containing silicon oxide, indium oxide containing 2 to 20% zinc oxide, gold (Au), platinum (Pt), nickel (Ni ), Tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), tantalum nitride and the like. preferable. Note that in the case where a layer containing an aromatic hydrocarbon and a metal oxide is provided instead of the hole injecting layer 411, the first electrode 401 is formed using a substance having a low work function such as aluminum or magnesium. You can also.

  The substance forming the second electrode 402 is preferably a substance having a low work function, such as aluminum and magnesium, but a layer that generates electrons between the second electrode 402 and the third light-emitting layer 413c. Indium tin oxide, indium tin oxide containing silicon oxide, indium oxide containing 2 to 20% zinc oxide, gold (Au), platinum (Pt), nickel (Ni), tungsten (W ), Chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), tantalum nitride and other high work function materials can also be used. Accordingly, which material is used as the material for forming the second electrode 402 may be selected as appropriate in accordance with the properties of the layer provided between the second electrode 402 and the third light-emitting layer 413c.

  In the light-emitting element of this embodiment as described above, the first mixed layers 421a and 421b are similar to the first mixed layer 215 described in Embodiment 2. The second mixed layers 422a and 422b are similar to the second mixed layer 216 described in Embodiment 2. The first light-emitting layer 413a, the second light-emitting layer 413b, and the third light-emitting layer 413c are each the same as the light-emitting layer 213 in Embodiment 2. The hole injection layer 411, the hole transport layers 412a, 412b, 412c, the electron transport layers 414a, 414b, 414c, and the electron injection layer 415 are also the same as the layers described with the same names in Embodiment 2. It is.

  As described above, by using the light-emitting element having the second mixed layers 422a and 422b containing the aromatic hydrocarbon and the metal oxide, the light-emitting element provided with the layer made of only the aromatic hydrocarbon or the metal oxide In addition, it is possible to reduce defects due to crystallization of layers, for example, short-circuiting between electrodes resulting from the occurrence of unevenness due to crystallization. Further, as described above, the second mixed layers 422a and 422b containing the aromatic hydrocarbon and the metal oxide are provided, so that the layer is formed using a sputtering method such as a layer made of indium tin oxide. A light-emitting element in which damage caused by sputtering of a layer formed using an organic compound such as a light-emitting layer is less likely to occur than in a light-emitting element having a structure in which the formed layers are provided between the light-emitting layers can be obtained.

(Embodiment 4)
The light-emitting element of the present invention can reduce malfunction caused by crystallization of a layer provided between electrodes. Moreover, the short circuit between electrodes can be prevented by thickening the thickness of the mixed layer provided between electrodes and containing an aromatic hydrocarbon and a metal oxide. In addition, by changing the thickness of the mixed layer, the optical path length can be adjusted to increase the external extraction efficiency of light emission or to obtain light emission with good color purity. Therefore, by using the light-emitting element of the present invention as a pixel, a favorable light-emitting device with few display defects due to malfunction of the light-emitting element can be obtained. In addition, by using the light-emitting element of the present invention as a pixel, a light-emitting device that can provide an image with favorable display color can be obtained. In addition, by using the light-emitting element of the present invention as a light source, a light-emitting device that can be favorably illuminated with few defects due to malfunction of the light-emitting element can be obtained.

  In this embodiment, a circuit configuration and a driving method of a light-emitting device having a display function will be described with reference to FIGS.

  FIG. 7 is a schematic view of a light emitting device to which the present invention is applied as viewed from above. In FIG. 7, a pixel portion 6511, a source signal line driver circuit 6512, a writing gate signal line driver circuit 6513, and an erasing gate signal line driver circuit 6514 are provided over a substrate 6500. The source signal line drive circuit 6512, the write gate signal line drive circuit 6513, and the erase gate signal line drive circuit 6514 are each an FPC (flexible printed circuit) 6503 which is an external input terminal via a wiring group. Connected. The source signal line driver circuit 6512, the writing gate signal line driver circuit 6513, and the erasing gate signal line driver circuit 6514 receive a video signal, a clock signal, a start signal, a reset signal, and the like from the FPC 6503, respectively. . A printed wiring board (PWB) 6504 is attached to the FPC 6503. Note that the driver circuit portion is not necessarily provided over the same substrate as the pixel portion 6511 as described above. For example, an IC chip mounted on an FPC on which a wiring pattern is formed (TCP) or the like is used. It may be used and provided outside the substrate.

  In the pixel portion 6511, a plurality of source signal lines extending in the column direction are arranged side by side in the row direction. In addition, current supply lines are arranged side by side in the row direction. In the pixel portion 6511, a plurality of gate signal lines extending in the row direction are arranged side by side in the column direction. In the pixel portion 6511, a plurality of sets of circuits including light-emitting elements are arranged.

  FIG. 8 is a diagram illustrating a circuit for operating one pixel. The circuit illustrated in FIG. 8 includes a first transistor 901, a second transistor 902, and a light-emitting element 903.

  Each of the first transistor 901 and the second transistor 902 is a three-terminal element including a gate electrode, a drain region, and a source region, and has a channel region between the drain region and the source region. Here, since the source region and the drain region vary depending on the structure and operating conditions of the transistor, it is difficult to limit which is the source region or the drain region. Therefore, in this embodiment, regions functioning as a source or a drain are referred to as a first electrode and a second electrode, respectively.

  The gate signal line 911 and the writing gate signal line driving circuit 913 are provided so as to be electrically connected or disconnected by a switch 918. The gate signal line 911 and the erasing gate signal line driver circuit 914 are provided so as to be electrically connected or disconnected by a switch 919. The source signal line 912 is provided so as to be electrically connected to either the source signal line driver circuit 915 or the power source 916 by the switch 920. The gate of the first transistor 901 is electrically connected to the gate signal line 911. The first electrode of the first transistor is electrically connected to the source signal line 912, and the second electrode is electrically connected to the gate electrode of the second transistor 902. The first electrode of the second transistor 902 is electrically connected to the current supply line 917, and the second electrode is electrically connected to one electrode included in the light-emitting element 903. Note that the switch 918 may be included in the write gate signal line driver circuit 913. The switch 919 may also be included in the erase gate signal line driver circuit 914. Further, the switch 920 may also be included in the source signal line driver circuit 915.

  There is no particular limitation on the arrangement of transistors, light-emitting elements, and the like in the pixel portion. For example, they can be arranged as shown in the top view of FIG. In FIG. 9, the first electrode of the first transistor 1001 is connected to the source signal line 1004, and the second electrode is connected to the gate electrode of the second transistor 1002. The first electrode of the second transistor is connected to the current supply line 1005, and the second electrode is connected to the electrode 1006 of the light emitting element. Part of the gate signal line 1003 functions as a gate electrode of the first transistor 1001.

  Next, a driving method will be described. FIG. 10 is a diagram for explaining the operation of a frame over time. In FIG. 10, the horizontal direction represents the passage of time, and the vertical direction represents the number of scanning stages of the gate signal line.

  When image display is performed using the light emitting device of the present invention, the screen rewriting operation and the display operation are repeatedly performed during the display period. The number of rewrites is not particularly limited, but is preferably at least about 60 times per second so that a person viewing the image does not feel flicker. Here, a period during which one screen (one frame) is rewritten and displayed is referred to as one frame period.

As shown in FIG. 10, one frame is time-divided into four subframes 501, 502, 503, and 504 including a writing period 501a, 502a, 503a, and 504a and a holding period 501b, 502b, 503b, and 504b. . A light emitting element to which a signal for emitting light is given is in a light emitting state in the holding period. The ratio of the length of the holding period in each subframe is as follows: first subframe 501: second subframe 502: third subframe 503: fourth subframe 504 = 2 ³ : 2 ² : 2 ¹ : 2 ⁰ = 8: 4: 2: 1. As a result, 4-bit gradation can be expressed. However, the number of bits and the number of gradations are not limited to those described here. For example, eight subframes may be provided so that 8-bit gradation can be performed.

  An operation in one frame will be described. First, in the subframe 501, the write operation is performed in order from the first row to the last row. Therefore, the start time of the writing period differs depending on the row. From the row in which the writing period 501a ends, the storage period 501b is started in order. In the holding period, the light-emitting element to which a signal for emitting light is given is in a light-emitting state. Further, the processing proceeds to the next subframe 502 in order from the row in which the holding period 501b ends, and the writing operation is performed in order from the first row to the last row as in the case of the subframe 501. The operation as described above is repeated until the holding period 504b of the subframe 504 ends. When the operation in the subframe 504 is completed, the process proceeds to the next frame. Thus, the accumulated time of the light emission in each subframe is the light emission time of each light emitting element in one frame. Various display colors having different brightness and chromaticity can be formed by changing the light emission time for each light emitting element and combining them in various ways within one pixel.

  When it is desired to forcibly end the holding period in the row that has already finished writing and has shifted to the holding period before the writing up to the last row is completed as in the subframe 504, after the holding period 504b. It is preferable to provide an erasing period 504c and control to forcibly enter a non-light emitting state. Then, the row that is forcibly set to the non-light-emitting state is kept in the non-light-emitting state for a certain period (this period is referred to as a non-light-emitting period 504d). Then, as soon as the writing period of the last row ends, the next (or frame) writing period starts in order from the first row. Accordingly, it is possible to prevent the writing period of the subframe 504 and the writing period of the next subframe from overlapping.

  In this embodiment, the subframes 501 to 504 are arranged in order from the longest holding period. However, the subframes 501 to 504 are not necessarily arranged as in the present embodiment. For example, the subframes 501 to 504 may be arranged in order from the shortest holding period. Alternatively, a long holding period and a short holding period may be arranged at random. In addition, the subframe may be further divided into a plurality of frames. That is, the gate signal line may be scanned a plurality of times during the period when the same video signal is applied.

  Here, the operation of the circuit shown in FIG. 8 in the writing period and the erasing period will be described.

  First, the operation in the writing period will be described. In the writing period, the gate signal line 911 in the n-th row (n is a natural number) is electrically connected to the writing gate signal line driving circuit 913 via the switch 918 and is connected to the erasing gate signal line driving circuit 914. Is disconnected. The source signal line 912 is electrically connected to the source signal line driver circuit through the switch 920. Here, a signal is input to the gate of the first transistor 901 connected to the gate signal line 911 in the n-th row (n is a natural number), and the first transistor 901 is turned on. At this time, video signals are simultaneously input to the source signal lines from the first column to the last column. Note that the video signals input from the source signal lines 912 in each column are independent from each other. A video signal input from the source signal line 912 is input to the gate electrode of the second transistor 902 through the first transistor 901 connected to each source signal line. At this time, the light-emitting element 903 determines whether to emit light or not according to a signal input to the second transistor 902. For example, in the case where the second transistor 902 is a p-channel transistor, the light-emitting element 903 emits light by inputting a low level signal to the gate electrode of the second transistor 902. On the other hand, in the case where the second transistor 902 is an n-channel transistor, the light-emitting element 903 emits light when a high level signal is input to the gate electrode of the second transistor 902.

  Next, the operation in the erasing period will be described. In the erasing period, the gate signal line 911 in the n-th row (n is a natural number) is electrically connected to the erasing gate signal line driving circuit 914 via the switch 919, and is connected to the writing gate signal line driving circuit 913. Not connected. The source signal line 912 is electrically connected to the power source 916 through the switch 920. Here, a signal is input to the gate of the first transistor 901 connected to the gate signal line 911 in the n-th row, and the first transistor 901 is turned on. At this time, the erase signal is simultaneously input to the source signal lines from the first column to the last column. The erase signal input from the source signal line 912 is input to the gate electrode of the second transistor 902 through the first transistor 901 connected to each source signal line. At this time, current supplied from the current supply line 917 to the light-emitting element 903 is blocked by a signal input to the second transistor 902. Then, the light emitting element 903 is forced to emit no light. For example, in the case where the second transistor 902 is a p-channel transistor, the light-emitting element 903 does not emit light when a high level signal is input to the gate electrode of the second transistor 902. On the other hand, in the case where the second transistor 902 is an n-channel transistor, the light emitting element 903 does not emit light by inputting a low level signal to the gate electrode of the second transistor 902.

  In the erasing period, for the nth row (n is a natural number), a signal for erasing is input by the operation as described above. However, as described above, the nth row may be an erasing period and the other row (mth row (m is a natural number)) may be a writing period. In such a case, it is necessary to input a signal for erasure to the n-th row and a signal for writing to the m-th row using the source signal line in the same column. It is preferable to operate as described above.

  Immediately after the light emitting element 903 in the n-th row does not emit light by the operation in the erasing period described above, the gate signal line and the erasing gate signal line driving circuit 914 are immediately disconnected, and the switch The source signal line and the source signal line driver circuit 915 are connected by switching 918. Then, the source signal line and the source signal line driver circuit 915 are connected, and the gate signal line and the writing gate signal line driver circuit 913 are connected. Then, a signal is selectively input from the writing gate signal line driving circuit 913 to the m-th signal line, the first transistor is turned on, and the source signal line driving circuit 915 receives the final signal from the first column. A signal for writing is input to the source signal lines up to the column. By this signal, the m-th row light emitting element emits light or does not emit light.

  Immediately after the writing period for the m-th row is completed as described above, the erasing period for the (n + 1) -th row is started. For this purpose, the gate signal line and the writing gate signal line drive circuit 913 are disconnected, and the switch 918 is switched to connect the source signal line to the power source 916. Further, the gate signal line and the writing gate signal line driving circuit 913 are disconnected, and the gate signal line is connected to the erasing gate signal line driving circuit 914. Then, a signal is selectively input from the erasing gate signal line driving circuit 914 to the gate signal line of the (n + 1) th row to turn on the signal to the first transistor, and an erasing signal is input from the power supply 916. In this way, when the erasing period of the (n + 1) th row is finished, the writing period immediately proceeds to the mth row. Thereafter, similarly, the erasing period and the writing period may be repeated until the erasing period of the last row is operated.

  In this embodiment, the mode in which the m-th writing period is provided between the n-th erasing period and the (n + 1) -th erasing period has been described. An m-th writing period may be provided between the period and the n-th erasing period.

  In this embodiment, when the non-light emission period 504d is provided as in the subframe 504, the erasing gate signal line driver circuit 914 and one gate signal line are disconnected from each other, and the write gate The operation of connecting the signal line driver circuit 913 and the other gate signal lines is repeated. Such an operation may be performed particularly in a frame in which a non-light emitting period is not provided.

(Embodiment 5)
One mode of a light-emitting device including the light-emitting element of the present invention is described with reference to a cross-sectional view of FIG.

  In FIG. 11, what is surrounded by a dotted line is a transistor 11 provided to drive the light emitting element 12 of the present invention. The light-emitting element 12 has a layer including an aromatic hydrocarbon and a metal oxide between the first electrode 13 and the second electrode 14 as described in Embodiments 1 to 3. It is a light emitting element. The drain of the transistor 11 and the first electrode 13 are electrically connected by a wiring 17 penetrating the first interlayer insulating film 16 (16a, 16b, 16c). The light emitting element 12 is separated from another light emitting element provided adjacent thereto by a partition wall layer 18. The light-emitting device of the present invention having such a structure is provided over the substrate 10 in this embodiment.

  Note that the transistor 11 illustrated in FIG. 11 is a top-gate transistor in which a gate electrode is provided on the side opposite to a substrate with a semiconductor layer as a center. However, the structure of the transistor 11 is not particularly limited, and may be, for example, a bottom gate type. In the case of a bottom gate, the semiconductor layer forming a channel may be formed with a protective film (channel protection type), or the semiconductor layer forming the channel may be partially concave ( Channel etch type).

  Further, the semiconductor layer included in the transistor 11 may be either crystalline or non-crystalline. Moreover, a semi-amorphous etc. may be sufficient.

The semi-amorphous semiconductor is as follows. A semiconductor having an intermediate structure between amorphous and crystalline (including single crystal and polycrystal) and having a third state that is stable in terms of free energy, has a short-range order, and has a lattice distortion. It contains a crystalline region. Further, at least a part of the region in the film contains crystal grains of 0.5 to 20 nm. The Raman spectrum is shifted to the lower wavenumber side than 520 cm ⁻¹ . In X-ray diffraction, diffraction peaks of (111) and (220) that are derived from the Si crystal lattice are observed. In order to terminate dangling bonds (dangling bonds), hydrogen or halogen is contained at least 1 atomic% or more. It is also called a so-called microcrystalline semiconductor (microcrystal semiconductor). A gas selected from SiH ₄ , Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , and SiF ₄ is formed by glow discharge decomposition (plasma CVD). These gases may be diluted with H ₂ , or H ₂ and one or more kinds of rare gas elements selected from He, Ar, Kr, and Ne. The dilution rate is in the range of 2 to 1000 times. The pressure is generally in the range of 0.1 Pa to 133 Pa, and the power supply frequency is 1 MHz to 120 MHz, preferably 13 MHz to 60 MHz. The substrate heating temperature may be 300 ° C. or less, preferably 100 to 250 ° C. As an impurity element in the film, impurities of atmospheric components such as oxygen, nitrogen, and carbon are desirably 1 × 10 ²⁰ / cm ³ or less, and in particular, the oxygen concentration is 5 × 10 ¹⁹ / cm ³ or less, preferably 1 × 10 ¹⁹ / cm ³ or less.

  Further, specific examples of the crystalline semiconductor layer include those made of single crystal or polycrystalline silicon, silicon germanium, or the like. These may be formed by laser crystallization, or may be formed by crystallization by a solid phase growth method using nickel or the like, for example.

  Note that in the case where the semiconductor layer is formed of an amorphous material, for example, amorphous silicon, the transistor 11 and other transistors (transistors constituting a circuit for driving a light emitting element) are all configured by N-channel transistors. It is preferable that the light-emitting device have a structured circuit. Other than that, a light-emitting device having a circuit including any one of an N-channel transistor and a P-channel transistor, or a light-emitting device including a circuit including both transistors may be used.

  Further, the first interlayer insulating film 16 may be a multilayer as shown in FIGS. 11A, 11B, and 11C, or may be a single layer. Note that 16a is made of an inorganic material such as silicon oxide or silicon nitride, and 16b is acrylic or siloxane (siloxane has a skeletal structure formed by a bond of silicon (Si) and oxygen (O). Group or hydrogen or an organic group (for example, an alkyl group or an aromatic hydrocarbon) or a substance such as silicon oxide that can be coated. Further, 16c is made of a silicon nitride film containing argon (Ar). In addition, there is no limitation in particular about the substance which comprises each layer, You may use things other than what was described here. Moreover, you may further combine the layer which consists of substances other than these. As described above, the first interlayer insulating film 16 may be formed using both an inorganic material and an organic material, or may be formed of any one of an inorganic material and an organic material.

  The partition layer 18 preferably has a shape in which the radius of curvature continuously changes at the edge portion. The partition layer 18 is formed using acrylic, siloxane, resist, silicon oxide, or the like. The partition wall layer 18 may be formed of any one of an inorganic film and an organic film, or may be formed using both.

  Note that in FIGS. 11A and 11C, only the first interlayer insulating film 16 is provided between the transistor 11 and the light emitting element 12, but as shown in FIG. 11B, the first interlayer insulating film 16 is provided. In addition to the insulating film 16 (16a, 16b), the second interlayer insulating film 19 (19a, 19b) may be provided. In the light emitting device shown in FIG. 11B, the first electrode 13 penetrates through the second interlayer insulating film 19 and is connected to the wiring 17.

  Similar to the first interlayer insulating film 16, the second interlayer insulating film 19 may be a multilayer or a single layer. 19a is made of a material such as acrylic, siloxane, or silicon oxide capable of being coated. Further, 19b is made of a silicon nitride film containing argon (Ar). In addition, there is no limitation in particular about the substance which comprises each layer, You may use things other than what was described here. Moreover, you may further combine the layer which consists of substances other than these. As described above, the second interlayer insulating film 19 may be formed using both an inorganic material and an organic material, or may be formed of any one of an inorganic material and an organic material.

  In the light-emitting element 12, when both the first electrode and the second electrode are formed using a light-transmitting substance, the first electrode and the second electrode are represented by the white arrows in FIG. Light emission can be extracted from both the electrode 13 side and the second electrode 14 side. In addition, in the case where only the second electrode 14 is formed using a light-transmitting substance, light emission is extracted only from the second electrode 14 side as represented by a white arrow in FIG. be able to. In this case, it is preferable that the first electrode 13 is made of a material having a high reflectivity, or a film (reflective film) made of a material having a high reflectivity is provided below the first electrode 13. In addition, in the case where only the first electrode 13 is formed using a light-transmitting substance, light emission is extracted only from the first electrode 13 side as represented by a white arrow in FIG. be able to. In this case, it is preferable that the second electrode 14 is made of a highly reflective material, or a reflective film is provided above the second electrode 14.

  In addition, the light emitting element 12 may be one in which the layer 15 is stacked so as to operate when a voltage is applied so that the potential of the second electrode 14 is higher than the potential of the first electrode 13. Alternatively, the layer 15 may be stacked so as to operate when a voltage is applied so that the potential of the second electrode 14 is lower than the potential of the first electrode 13. In the former case, the transistor 11 is an N-channel transistor, and in the latter case, the transistor 11 is a P-channel transistor.

  As described above, in this embodiment mode, an active light-emitting device that controls driving of a light-emitting element using a transistor has been described. In addition to this, a light-emitting element is driven without particularly providing a driving element such as a transistor. A passive light emitting device may be used. FIG. 12 is a perspective view of a passive light emitting device manufactured by applying the present invention. In FIG. 12, a layer 955 having a multilayer structure including a layer including an aromatic hydrocarbon and a metal oxide, a light emitting layer, and the like is provided between an electrode 952 and an electrode 956 over a substrate 951. An end portion of the electrode 952 is covered with an insulating layer 953. A partition layer 954 is provided over the insulating layer 953. The side wall of the partition wall layer 954 has an inclination such that the distance between one side wall and the other side wall becomes narrower as it approaches the substrate surface. That is, the cross section in the short side direction of the partition wall layer 954 has a trapezoidal shape, and the bottom side (the side facing the insulating layer 953 in the same direction as the surface direction of the insulating layer 953) is the top side (the surface of the insulating layer 953). The direction is the same as the direction and is shorter than the side not in contact with the insulating layer 953. In this manner, by providing the partition layer 954, defects in the light-emitting element due to static electricity or the like can be prevented. A passive light emitting device can also be driven with low power consumption by including the light emitting element of the present invention that operates at a low driving voltage.

(Embodiment 6)
A light-emitting element provided with a layer having an aromatic hydrocarbon and a metal oxide provided between electrodes is caused by unevenness formed by crystallization of the layer provided between the electrodes or unevenness of the electrode surface. Since the operation failure due to the short circuit between the electrodes is reduced, a light emitting device using such a light emitting element as a pixel has a good display operation with few display defects. Therefore, by applying such a light-emitting device to a display portion, an electronic device with few misperceptions of a display image due to display defects can be obtained. In addition, a light-emitting device using the light-emitting element of the present invention as a light source can be favorably illuminated with few defects due to malfunction of the light-emitting element. Therefore, by using such a light emitting device as an illuminating unit such as a backlight, by mounting the light emitting device of the present invention in this way, a dark part is locally formed due to a defect of the light emitting element. Such malfunctions can be reduced and a good display can be achieved. In addition, in a light-emitting element in which the distance between the light-emitting layer and the electrode is adjusted by changing the thickness of the layer including the aromatic hydrocarbon and the metal oxide, a change in driving voltage due to the layer thickness is small. In addition, a light emitting device that operates with a low driving voltage and emits a color with high color purity can be obtained. Therefore, by applying such a light-emitting device to a display portion, an electronic device that can provide an image with low power consumption and excellent color can be obtained.

  An example of an electronic device in which the light-emitting device to which the present invention is applied is shown in FIG.

  FIG. 13A illustrates a personal computer manufactured by applying the present invention, which includes a main body 5521, a housing 5522, a display portion 5523, a keyboard 5524, and the like. By incorporating a light-emitting device using the light-emitting element of the present invention as a pixel as described in Embodiments 1 and 2 as a pixel (for example, a light-emitting device including the structure described in Embodiments 3 and 4) as a display portion A personal computer that can provide a display image with few defects in the portion and no misrecognition of the display image and excellent color can be completed. Further, a personal computer can be completed even if a light emitting device using the light emitting element of the present invention as a light source is incorporated as a backlight. Specifically, as illustrated in FIG. 14, a lighting device in which a liquid crystal device 5512 and a light-emitting device 5513 are fitted in a housing 5511 and a housing 5514 may be incorporated as a display portion. In FIG. 14, an external input terminal 5515 is attached to the liquid crystal device 5512, and an external input terminal 5516 is attached to the light emitting device 5513.

  FIG. 13B illustrates a telephone manufactured by applying the present invention. The main body 5552 includes a display portion 5551, an audio output portion 5554, an audio input portion 5555, operation switches 5556 and 5557, an antenna 5553, and the like. ing. By incorporating the light-emitting device having the light-emitting element of the present invention as a display portion, a telephone that can display a display image with few defects in the display portion and no misrecognition of a display image and excellent color can be completed.

  FIG. 13C illustrates a television set manufactured by applying the present invention, which includes a display portion 5531, a housing 5532, a speaker 5533, and the like. By incorporating a light-emitting device having the light-emitting element of the present invention as a display portion, a television receiver that can provide a display image with few defects in the display portion and no misrecognition of a display image and excellent color can be completed.

  As described above, the light-emitting device of the present invention is very suitable for use as a display portion of various electronic devices. Note that the electronic device is not limited to that described in this embodiment, and may be another electronic device such as a navigation device.

  A method for manufacturing a light-emitting element having a layer containing an aromatic hydrocarbon and a metal oxide between electrodes, and operation characteristics thereof will be described below. Note that in this example, two light-emitting elements (light-emitting element (1) and light-emitting element (2)) having different molar ratios of aromatic hydrocarbon and metal oxide and having the same structure are manufactured. did.

  As shown in FIG. 15, indium tin oxide containing silicon oxide was formed to a thickness of 110 nm over the substrate 300, whereby the first electrode 301 was formed. Note that a sputtering method was used for film formation.

  Next, a first layer 311 containing t-BuDNA and molybdenum oxide (VI) was formed over the first electrode 301 by a co-evaporation method. The thickness of the first layer 311 was set to 120 nm. The weight ratio of t-BuDNA and molybdenum oxide contained in the light-emitting element (1) is 1: 0.5 (molar ratio is 1: 1.7) (= t-BuDNA: molybdenum oxide). Thus, the weight ratio of t-BuDNA and molybdenum oxide contained in the light-emitting element (2) is 1: 0.75 (molar ratio is 1: 2.5) (= t-BuDNA: molybdenum oxide). It was made to become. Note that co-evaporation is vapor deposition in which a raw material is vaporized from a plurality of vapor deposition sources provided in one processing chamber, and the vaporized raw material is deposited on a workpiece to form a layer in which a plurality of substances are mixed. Say the law.

  Next, a second layer 312 made of NPB was formed on the first layer 311 by vapor deposition. The thickness of the second layer 312 was set to 10 nm. The second layer 312 functions as a hole transport layer when the light emitting element is driven.

Next, a third layer 313 containing Alq ₃ and coumarin 6 was formed on the second layer 312 by a co-evaporation method. The thickness of the third layer 313 was set to 37.5 nm. The weight ratio of Alq ₃ to coumarin 6 was 1: 0.01 (molar ratio was 1: 0.013) (= Alq ₃ : coumarin 6). As a result, the coumarin 6 is dispersed and contained in the Alq ₃ layer. The third layer 313 formed in this manner functions as a light emitting layer when the light emitting element is driven.

Next, a fourth layer 314 made of Alq ₃ was formed on the third layer 313 by an evaporation method. The thickness of the fourth layer 314 was set to 37.5 nm. The fourth layer 314 functions as an electron transport layer when the light emitting element is driven.

  Next, a fifth layer 315 made of lithium fluoride was formed on the fourth layer 314 by vapor deposition. The thickness of the fifth layer 315 was set to 1 nm. The fifth layer 315 functions as an electron injection layer when the light emitting element is driven.

  Next, an aluminum film was formed to a thickness of 200 nm on the fifth layer 315 by an evaporation method, whereby the second electrode 302 was formed.

As described above, a voltage was applied to the manufactured light-emitting element so that the potential of the first electrode 301 was higher than the potential of the second electrode 302, and the operating characteristics of the light-emitting element were examined. Shown in FIGS. FIG. 16 illustrates voltage-luminance characteristics of the light-emitting element, in which the horizontal axis represents voltage (V) and the vertical axis represents luminance (cd / m ² ). FIG. 17 is a graph showing voltage-current characteristics of the light-emitting element, in which the horizontal axis represents voltage (V) and the vertical axis represents current (mA). FIG. 18 illustrates luminance-current efficiency characteristics of the light-emitting element, in which the horizontal axis represents luminance (cd / m ² ) and the vertical axis represents current efficiency (cd / A). 16-18, the plot represented by ● is for the light emitting element (1), and the plot represented by ◯ is for the light emitting element (2).

(Comparative example)
As a comparative example for the light-emitting element manufactured in Example 1, a light-emitting element in which a layer composed only of t-BuDNA is provided between electrodes will be described. The light-emitting element of the comparative example is different from the light-emitting elements (1) and (2) described in Example 1 in that a layer made only of t-BuDNA is provided instead of the mixed layer 111. Is the same as the light-emitting elements (1) and (2) described in Example 1. Therefore, description of a method for manufacturing the light-emitting element of the comparative example is omitted. When the light emitting device of the comparative example was operated, results as plotted with Δ in FIGS. 16 to 18 were obtained.

From Example 1 and the comparative example, by providing a layer containing an aromatic hydrocarbon and a metal oxide between the electrodes, the light emission start voltage (when light emission starts at a luminance of 1 cd / m ² is set as the light emission start). The voltage applied at that time is referred to as a light emission start voltage), and the applied voltage required for light emission at an arbitrary luminance is also low, so that a good light-emitting element operating at a low driving voltage can be obtained. . It can also be seen that by providing a layer containing an aromatic hydrocarbon and a metal oxide between the electrodes, current efficiency is high when light is emitted at an arbitrary luminance, and a favorable light-emitting element can be obtained.

  Voltage is applied to three samples (1) to (3) having a layer containing an aromatic hydrocarbon and a metal oxide between the electrodes and a sample (4) having a layer consisting only of the aromatic hydrocarbon between the electrodes. -Current characteristics were examined. As a result, it was found that the layer in which the aromatic hydrocarbon and the metal oxide were mixed was easier to inject carriers from the electrode and the conductivity was higher than the layer made only of the aromatic hydrocarbon.

  FIG. 19 shows the results of examining the voltage-current characteristics. In FIG. 19, the horizontal axis represents voltage (V) and the vertical axis represents current (mA). In FIG. 19, ● is a plot for sample (1), ■ is a sample (2), □ is a sample (3), and Δ is a plot for sample (4).

  The samples (1) to (3) used for the measurement were an aromatic hydrocarbon and a metal between an electrode (110 nm) made of indium tin oxide containing silicon oxide and an electrode (200 nm) made of aluminum. The sample (4) has a structure including an oxide and a layer (200 nm). The sample (4) has an fragrance between an electrode (110 nm) made of indium tin oxide containing silicon oxide and an electrode (200 nm) made of aluminum. This is a structure having a layer (200 nm) consisting only of a group hydrocarbon. Samples (1) to (3) have different weight ratios between the aromatic hydrocarbon and the metal oxide contained in the layer provided between the electrodes. In the sample (1), the weight ratio is 1: 0.5 (= t-BuDNA: molybdenum oxide), and in the sample (2), the weight ratio is 2: 0.75 (= t-BuDNA: molybdenum oxide). In the sample (3), the weight ratio is 1: 1 (= t-BuDNA: molybdenum oxide).

4A and 4B illustrate one embodiment of a light-emitting element of the present invention. 4A and 4B illustrate one embodiment of a light-emitting element of the present invention. 4A and 4B illustrate one embodiment of a light-emitting element of the present invention. 4A and 4B illustrate one embodiment of a light-emitting element of the present invention. 4A and 4B illustrate one embodiment of a light-emitting element of the present invention. 4A and 4B illustrate one embodiment of a light-emitting element of the present invention. FIG. 6 is a top view illustrating one embodiment of a light-emitting device of the present invention. 4A and 4B each illustrate one embodiment of a circuit for driving pixels provided in a light-emitting device of the present invention. 4A and 4B illustrate one embodiment of a pixel portion included in a light-emitting device of the present invention. 4 is a frame diagram illustrating a driving method for driving pixels included in the light-emitting device of the present invention. FIG. 3A and 3B each illustrate one embodiment of a cross section of a light-emitting device of the present invention. 4A and 4B illustrate one embodiment of a light-emitting device of the present invention. 6A and 6B illustrate one embodiment of an electronic device to which the present invention is applied. The figure explaining the illuminating device to which this invention is applied. 4A and 4B illustrate a method for manufacturing the light-emitting element of Example 1. FIG. FIG. 6 shows voltage-luminance characteristics of the light-emitting element of Example 1. FIG. 6 shows voltage-current characteristics of the light-emitting element of Example 1. FIG. 6 shows luminance-current efficiency characteristics of the light-emitting element of Example 1. FIG. 10 is a diagram illustrating voltage-current characteristics of the element of Example 2. 4A and 4B illustrate one embodiment of a light-emitting device of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substrate 11 Transistor 12 Light emitting element 13 1st electrode 14 2nd electrode 15 Layer 16 Interlayer insulation film 17 Wiring 18 Partition layer 19 Interlayer insulation film 101 1st electrode 102 2nd electrode 111 Mixed layer 112 Hole transport layer 113 light emitting layer 114 electron transport layer 115 electron injection layer 116 electron generation layer 117 hole blocking layer 201 first electrode 202 second electrode 211 hole injection layer 212 hole transport layer 213 light emission layer 214 electron transport layer 215 first Mixed layer 216 Second mixed layer 217 Layer 218 Hole blocking layer 223 Hole transport layer 300 Substrate 301 First electrode 302 Second electrode 311 First layer 312 Second layer 313 Third layer 314 Second 4 layer 315 5th layer 401 1st electrode 402 2nd electrode 411 Hole injection layer 412a Hole transport layer 412b Hole transport layer 412c Hole transport layer 4 3a First light emitting layer 413b Second light emitting layer 413c Third light emitting layer 414a Electron transport layer 414b Electron transport layer 414c Electron transport layer 415 Electron injection layer 421a First mixed layer 421b First mixed layer 422a Second mixed layer 422b Second mixed layer 501 Subframe 502 Subframe 503 Subframe 504 Subframe 901 First transistor 902 Second transistor 903 Light emitting element 911 Gate signal line 912 Source signal line 913 Writing gate signal line driving circuit 914 Erasing Gate signal line driver circuit 915 Source signal line driver circuit 916 Power source 917 Current supply line 918 Switch 919 Switch 920 Switch 951 Substrate 952 Electrode 953 Insulating layer 954 Partition layer 955 Layer 956 Electrode 1001 First transistor 1002 Second transistor 1003 Gate signal line 1004 Source signal line 1005 Current supply line 1006 Electrode 501a Writing period 501b Holding period 502a Writing period 502b Holding period 503a Writing period 503b Holding period 504a Writing period 504b Holding period 504b Holding period 504c Erasing period 504d Non-light emitting period 5511 Body 5512 Liquid crystal device 5513 Light emitting device 5514 Case 5515 External input terminal 5516 External input terminal 5521 Body 5522 Case 5523 Display portion 5524 Keyboard 5551 Display portion 5532 Case 5533 Speaker 5551 Display portion 5552 Body 5553 Antenna 5554 Audio output portion 5555 Sound input 5556 Operation switch 6500 Substrate 6503 FPC
6504 Printed Wiring Board (PWB)
6511 Pixel portion 6512 Source signal line drive circuit 6513 Write gate signal line drive circuit 6514 Erase gate signal line drive circuit

Claims (9)

A light emitting layer and a mixed layer between the anode and the cathode ;
The mixed layer, seen containing an aromatic hydrocarbon, and a metal oxide, a,
The light emitting element , wherein the mixed layer is provided between the anode and the light emitting layer . A light emitting layer and a mixed layer between the anode and the cathode ;
The mixed layer, seen containing an aromatic hydrocarbon, and a metal oxide, a,
The light-emitting element , wherein the mixed layer is in contact with the anode . In claim 1 or 2,
The light-emitting element, wherein the metal oxide is a metal oxide that exhibits an electron accepting property with respect to the aromatic hydrocarbon. In claim 1 or 2,
The light-emitting element, wherein the metal oxide is molybdenum oxide. In claim 1 or 2,
The metal oxide is any one selected from vanadium oxide, ruthenium oxide, rhenium oxide, titanium oxide, chromium oxide, zirconium oxide, hafnium oxide, tantalum oxide, tungsten oxide, and silver oxide. Or a light-emitting element. In any one of Claims 1 thru | or 5 ,
The aromatic hydrocarbon is 2-tert-butyl-9,10-di (2-naphthyl) anthracene , anthracene, 9,10-diphenylanthracene, tetracene, rubrene, perylene, 2,5,8,11-tetra ( A light-emitting element, which is any one selected from tert-butyl) perylene, pentacene, and coronene . A light emitting device comprising the light emitting element according to claim 1. The illuminating device which has a light emitting element as described in any one of Claims 1 thru | or 6. An electronic apparatus having the light emitting element according to claim 1.

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