JP2006261653A - Light emitting element and light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting element having low driving voltage, long life, and high production yield. <P>SOLUTION: A light emitting element has a layer containing an organic material and a nonorganic material, wherein activation energy of electric conductivity is 0.01 eV to 0.3 eV in the layer containing the organic material and the nonorganic material. Preferably, the activation energy of electric conductivity of the layer is 0.01 eV to 0.26 eV, and more preferably 0.01 eV to 0.20 eV. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light emitting element having a configuration in which a plurality of layers are sandwiched between a pair of electrodes. Further, the present invention relates to a light emitting device having a light emitting element.

  A light-emitting device using light emitted from an electroluminescence element (light-emitting element) has attracted attention as a display or illumination device.

  As a light-emitting element used in a light-emitting device, one having a structure in which a layer containing a light-emitting compound is sandwiched between a pair of electrodes is well known.

  In such a light-emitting element, one electrode functions as an anode and the other electrode functions as a cathode, and holes injected from the anode side and electrons injected from the cathode side are recombined to be in an excited state. It forms a molecule and emits light when it returns to the ground state.

  By the way, display devices to be incorporated into various information processing devices that have been rapidly developed in recent years have a particularly high demand for low power consumption. In order to achieve this, attempts have been made to reduce the driving voltage of light-emitting elements. Yes. In view of commercialization, it is important not only to lower the driving voltage but also to extend the life of the light emitting element, and the development of light emitting elements to achieve this is underway.

  For example, in Patent Document 1, a low driving voltage of a light-emitting element is achieved by using a metal oxide having a high work function such as molybdenum oxide for an anode (see Patent Document 1).

  However, in particular, regarding the extension of the lifetime, it cannot be said that the means disclosed in Patent Document 1 alone is sufficient, and it is necessary to develop a technology for achieving a longer lifetime.

Further, since the light emitting element is formed of an organic thin film having a thickness of, for example, about 0.1 μm, there is a problem that a short circuit easily occurs between the upper and lower electrodes. In particular, low yield due to dust generated in the manufacturing process of the light-emitting element is a problem.
JP-A-9-63771

  In view of the above problems, the present invention provides a light-emitting element with low driving voltage. In addition, a light-emitting element having a long element lifetime is provided. In addition, a light-emitting element with high manufacturing yield is provided. In addition, a light-emitting device including the light-emitting element is provided.

  The present inventors have found that the above-described problems can be solved by using a layer having a low activation energy of electrical conductivity for a light-emitting element.

  Therefore, one of the light-emitting elements of the present invention has a layer containing an organic material and an inorganic material between a pair of electrodes, and the activation energy of the electrical conductivity of the layer containing the organic material and the inorganic material is 0. It is 01 eV or more and less than 0.3 eV. More preferably, the activation energy of the electric conductivity of the layer containing the organic material and the inorganic material is 0.01 eV or more and less than 0.26 eV. More preferably, it is 0.01 eV or more and less than 0.20 eV.

  One of the light-emitting elements of the present invention includes a layer containing an organic material and an inorganic material between a pair of electrodes. In the above structure, the layer containing an organic material and an inorganic material absorbs in the visible light region. There is no peak, and the concentration of the inorganic material is 30 to 95 wt%.

  In the above structure, the activation energy of the electric conductivity of the layer including the organic material and the inorganic material is 0.01 eV or more and less than 0.20 eV.

  As the organic material in the case where the layer containing an organic material and an inorganic material does not have an absorption peak in the visible light region, 4,4′-bis (N- {4- [N, N′-bis (3-methyl) is used. Phenyl) amino] phenyl} -N-phenylamino) biphenyl (abbreviation: DNTPD), 4,4′-bis [N- (4-diphenylaminophenyl) -N-phenylamino] biphenyl (abbreviation: DPAB), and the like. It is done.

  One of the light-emitting elements of the present invention has a layer containing an organic material and an inorganic material between a pair of electrodes, and the layer containing an organic material and an inorganic material has an absorption peak in the visible light region, The inorganic material has a concentration of 5 to 95 wt%.

  In the above structure, the activation energy of the electric conductivity of the layer including the organic material and the inorganic material is 0.01 eV or more and less than 0.3 eV. More preferably, the activation energy of the electric conductivity of the layer containing the organic material and the inorganic material is 0.01 eV or more and less than 0.26 eV. More preferably, it is 0.01 eV or more and less than 0.20 eV.

  As an organic material in a case where a layer containing an organic material and an inorganic material has an absorption peak in the visible light region, N, N′-bis (3-methylphenyl) -N, N′-diphenyl- [1,1 ′ -Biphenyl] -4,4'-diamine (abbreviation: TPD), 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (abbreviation: α-NPD), N, N'- Bis (spiro-9,9′-bifluoren-2-yl) -N, N′-diphenylbenzidine (abbreviation: BSPB), 4,4′-bis [N- (9,9-dimethylfluoren-2-yl) -N-phenylamino] biphenyl (abbreviation: DFLDPBi), 4,4′-bis [N- (4-biphenylyl) -N-phenylamino] biphenyl (abbreviation: BBPB), and the like.

  In the above structure, the inorganic material is a metal oxide. Specifically, it is possible to use one or more of molybdenum oxide, vanadium oxide, ruthenium oxide, and tungsten oxide as the inorganic material.

  In the above structure, the layer including an organic material and an inorganic material is provided so as to be in contact with one electrode between the pair of electrodes.

  The present invention also includes a light emitting device having the above-described light emitting element. Note that a light-emitting device in this specification includes an image display device, a light-emitting device, or a light source (including a lighting device) in its category. In addition, a module in which a connector such as an FPC (Flexible Printed Circuit) or TAB (Tape Automated Bonding) tape or TCP (Tape Carrier Package) is attached to the panel, a TAB tape or a module having a printed wiring board at the end of TCP, Alternatively, a module in which an IC (integrated circuit) is directly mounted on a light emitting element by a COG (Chip On Glass) method is included in the light emitting device.

  In the light-emitting element of the present invention, the driving voltage can be reduced by providing a layer with low activation energy of electrical conductivity. In addition, a light-emitting element having a long element lifetime can be provided.

  In addition, since a layer having a small activation energy can suppress an increase in driving voltage even if it is thickened, a layer having a small activation energy can be thickened to suppress a short circuit between the upper and lower electrodes. . Therefore, it is possible to suppress a decrease in yield due to dust generated in the manufacturing process.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that modes and details can be variously changed without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments below.

(Embodiment 1)
The light-emitting element of the present invention has a plurality of layers between a pair of electrodes. The plurality of layers have a high carrier injection property and carrier transport so that a light emitting region is formed at a position away from the electrode, that is, a carrier (carrier) is recombined at a position away from the electrode. The layers are formed by combining layers made of highly specific materials.

  One embodiment of a light-emitting element of the present invention is described below with reference to FIG.

  In this embodiment, the light-emitting element includes a first electrode 102, a first layer 103, a second layer 104, a third layer 105, and a fourth layer 106 that are sequentially stacked over the first electrode 102. And a second electrode 107 provided thereon. Note that in this embodiment mode, the first electrode 102 functions as an anode and the second electrode 107 functions as a cathode.

  The substrate 101 is used as a support for the light emitting element. As the substrate 101, for example, glass or plastic can be used. Note that other materials may be used as long as the light-emitting element functions as a support in the manufacturing process.

  As the first electrode 102, various metals, alloys, and electrically conductive compounds can be used. For example, indium tin oxide (ITO), indium tin oxide containing silicon or silicon oxide, indium oxide-zinc oxide (IZO), indium oxide containing tungsten oxide and zinc oxide- A tin oxide (IWZO) etc. are mentioned. These conductive metal oxide films are usually formed by sputtering. For example, indium oxide-zinc oxide (IZO) can be formed by a sputtering method using a target in which 1 to 20 wt% of zinc oxide is added to indium oxide. Indium oxide-tin oxide (IWZO) containing tungsten oxide and zinc oxide is sputtered using a target containing 0.5 to 5 wt% tungsten oxide and 0.1 to 1 wt% zinc oxide with respect to indium oxide. It can be formed by the method. In addition, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), titanium (Ti), Copper (Cu), palladium (Pd), aluminum (Al), aluminum-silicon (Al-Si), aluminum-titanium (Al-Ti), aluminum-silicon-copper (Al-Si-Cu) or nitridation of metallic materials A material (TiN) or the like can be used, but when the first electrode is used as an anode, it is preferably formed of a material having a high work function (work function of 4.0 eV or more).

  Note that in the light-emitting element of the present invention, the first electrode 102 is not limited to a material having a high work function, and a material having a low work function can also be used.

  The first layer 103 is a layer that includes an organic material and an inorganic material, and has a conductivity activation energy of 0.01 eV or more and less than 0.30 eV. More preferably, the layer is 0.01 eV or more and less than 0.26 eV. More preferably, the layer is 0.01 eV or more and less than 0.20 eV. Hereinafter, in this specification, it describes as a layer with small activation energy of electrical conductivity.

  The light-emitting element of the present invention has a layer with low activation energy of electrical conductivity, and thus has a high carrier density and can make ohmic contact with the electrode. Therefore, the driving voltage of the light emitting element can be reduced. In addition, since the carrier density is high, the carrier transportability is also excellent. In order to obtain a sufficient carrier density, the activation energy of electrical conductivity is preferably 0.01 eV or more and less than 0.30 eV. Moreover, it is more preferable that the activation energy of electrical conductivity is 0.01 eV or more and less than 0.26 eV. Further, when used for a light-emitting element, it is more preferable that the activation energy of electrical conductivity is 0.01 eV or more and less than 0.20 eV because the current-voltage characteristics do not change even on the high voltage side.

  The inorganic material contained in the first layer 103 which is a layer having a small activation energy for electrical conductivity is preferably a metal oxide. Specific examples include molybdenum oxide (MoOx), vanadium oxide (VOx), ruthenium oxide (RuOx), tungsten oxide (WOx), and the like. In addition, indium tin oxide (ITO) or zinc oxide (ZnO) can be used. However, it is not limited to those shown here, and other substances may be used. The organic material is preferably an organic material having an arylamine skeleton, for example, 4,4′-bis (N- {4- [N, N′-bis (3-methylphenyl) amino] phenyl}. -N-phenylamino) biphenyl (abbreviation: DNTPD), 4,4'-bis [N- (4-diphenylaminophenyl) -N-phenylamino] biphenyl (abbreviation: DPAB), N, N'-bis (3 -Methylphenyl) -N, N'-diphenyl- [1,1'-biphenyl] -4,4'-diamine (abbreviation: TPD), 4,4'-bis [N- (1-naphthyl) -N- Phenylamino] biphenyl (abbreviation: α-NPD), N, N′-bis (spiro-9,9′-bifluoren-2-yl) -N, N′-diphenylbenzidine (abbreviation: BSPB), 4,4 ′ -Screw [N (9,9-dimethylfluoren-2-yl) -N-phenylamino] biphenyl (abbreviation: DFLDPBi), 4,4′-bis [N- (4-biphenylyl) -N-phenylamino] biphenyl (abbreviation: BBPB) ), 1,5-bis (diphenylamino) naphthalene (abbreviation: DPAN), 4,4 ′, 4 ″ -tris (N, N-diphenylamino) triphenylamine (abbreviation: TDATA), 4,4 ′, 4 ″ -tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine (abbreviation: MTDATA), etc., an aromatic amine-based compound (that is, having a benzene ring-nitrogen bond) Can be used. Note that other than these substances, any substance that has a property of transporting more holes than electrons may be used.

Note that the first layer 103 is not limited to a single layer as described above, and may have a structure in which two or more layers are stacked.

The second layer 104 is a layer made of a substance having a high hole transporting property, for example, an aromatic amine-based compound such as α-NPD, TPD, TDATA, MTDATA, or BSPB (ie, having a benzene ring-nitrogen bond). It is. The substances described here are mainly substances having a hole mobility of 10 ⁻⁶ cm ² / Vs or higher. Note that other than these substances, any substance that has a property of transporting more holes than electrons may be used. Note that the second layer 104 is not limited to a single layer, and may be a stack of two or more layers including any of the above substances.

The third layer 105 is a layer including a substance having a high light-emitting property. For example, a highly luminescent substance such as N, N′-dimethylquinacridone (abbreviation: DMQd) or 3- (2-benzothiazoyl) -7-diethylaminocoumarin (abbreviation: coumarin 6) and tris (8-quinolinolato) aluminum (Abbreviation: Alq ₃ ) and 9,10-di (2-naphthyl) anthracene (abbreviation: DNA), etc., which can be freely combined with substances having high carrier transport properties and good film quality (that is, difficult to crystallize). Configured. However, since Alq ₃ and DNA are highly luminescent materials, these materials may be used alone, and the third layer 105 may be used.

The fourth layer 106 is formed using a substance having a high electron-transport property, such as tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), tris (5-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), etc., having a quinoline skeleton or a benzoquinoline skeleton It is a layer made of a metal complex or the like. In addition, bis [2- (2-hydroxyphenyl) -benzoxazolate] zinc (abbreviation: Zn (BOX) ₂ ), bis [2- (2-hydroxyphenyl) -benzothiazolate] zinc (abbreviation: Zn ( A metal complex having an oxazole-based or thiazole-based ligand such as BTZ) ₂ ) can also be used. In addition to metal complexes, 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), 3- (4-tert-butylphenyl) -4-phenyl-5 (4-Biphenylyl) -1,2,4-triazole (abbreviation: TAZ), 3- (4-tert-butylphenyl) -4- (4-ethylphenyl) -5- (4-biphenylyl) -1,2 , 4-triazole (abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen), bathocuproin (abbreviation: BCP), and the like can also be used. The substances mentioned here are mainly substances having an electron mobility of 10 ⁻⁶ cm ² / Vs or higher. Note that a substance other than the above substances may be used for the fourth layer 106 as long as it has a property of transporting more electrons than holes. The fourth layer 106 is not limited to a single layer, and may be a stack of two or more layers formed using the above substances.

  As a material for forming the second electrode 107, a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like having a low work function (a work function of 3.8 eV or less) can be used. Specific examples of such a cathode material include elements belonging to Group 1 or Group 2 of the periodic table of elements, that is, alkali metals such as lithium (Li) and cesium (Cs), and magnesium (Mg), calcium (Ca), Examples thereof include alkaline earth metals such as strontium (Sr) and alloys containing them (Mg: Ag, Al: Li). However, by providing a layer having a function of accelerating electron injection between the second electrode 107 and the light-emitting layer by stacking with the second electrode, regardless of the work function, Al, Ag, Various conductive materials such as indium tin oxide containing ITO and silicon can be used for the second electrode 107.

Note that as a layer having a function of promoting electron injection, an alkali metal or alkaline earth metal compound such as lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF ₂ ), or the like is used. Can do. In addition, a layer made of a substance having an electron transporting property containing an alkali metal or an alkaline earth metal, for example, a layer containing magnesium (Mg) in Alq ₃ can be used.

  In addition, the first layer 103, the second layer 104, the third layer 105, and the fourth layer 106 may be formed by an evaporation method. In addition to the above evaporation method, for example, an ink jet method or a spin coating method may be used. Moreover, you may form using the different film-forming method for each electrode or each layer.

  The light-emitting element of the present invention having the above structure is a third layer that contains a highly light-emitting substance because a current flows due to a potential difference generated between the first electrode 102 and the second electrode 107. In the layer 105, holes and electrons recombine to emit light. That is, a light emitting region is formed in the third layer 105. However, it is not necessary that all of the third layer 105 functions as a light emitting region. For example, the light emitting region is formed only on the second layer 104 side or the fourth layer 106 side of the third layer 105. It may be anything.

  Light emission is extracted outside through one or both of the first electrode 102 and the second electrode 107. Therefore, one or both of the first electrode 102 and the second electrode 107 is formed using a light-transmitting substance. In the case where only the first electrode 102 is formed using a light-transmitting substance, light emission is extracted from the substrate side through the first electrode 102 as illustrated in FIG. In the case where only the second electrode 107 is formed using a light-transmitting substance, light emission is extracted from the side opposite to the substrate through the second electrode 107 as illustrated in FIG. In the case where both the first electrode 102 and the second electrode 107 are made of a light-transmitting substance, light is emitted from the first electrode 102 and the second electrode 107 as shown in FIG. And is taken out from both the substrate side and the opposite side of the substrate.

Note that the structure of the layers provided between the first electrode 102 and the second electrode 107 is not limited to the above. A structure in which holes and electrons are recombined in a portion away from the first electrode 102 and the second electrode 107 so that quenching caused by the proximity of the light emitting region and the metal is suppressed. As long as it has a layer with a small activation energy of electrical conductivity, other than the above may be used.
In other words, the layered structure of the layers is not particularly limited, and a substance having a high electron transporting property or a substance having a high hole transporting property, a substance having a high electron injecting property, a substance having a high hole injecting property, or a bipolar property (electron and hole) A layer made of a material having a high transportability) may be freely combined with a layer having a low activation energy of electrical conductivity. Alternatively, a carrier recombination site may be controlled by providing a layer made of a silicon oxide film or the like over the first electrode 102.

  A light-emitting element illustrated in FIG. 2 includes a first layer 303 formed using a substance having a high electron-transport property, a second layer 304 containing a substance having a high light-emitting property, and a hole transport over the first electrode 302 functioning as a cathode. A third layer 305 made of a highly conductive material, a fourth layer 306 that is a layer with low activation energy of electrical conductivity, and a second electrode 307 that functions as an anode are sequentially stacked. . Reference numeral 301 denotes a substrate.

  In this embodiment mode, a light-emitting element is manufactured over a substrate made of glass, plastic, or the like. A passive light-emitting device can be manufactured by manufacturing a plurality of such light-emitting elements over one substrate. In addition to a substrate made of glass, plastic, or the like, a light emitting element may be manufactured on a thin film transistor (TFT) array substrate, for example. Thus, an active matrix light-emitting device in which driving of the light-emitting element is controlled by the TFT can be manufactured. Note that the structure of the TFT is not particularly limited. A staggered TFT or an inverted staggered TFT may be used. Also, the driving circuit formed on the TFT array substrate may be composed of N-type and P-type TFTs, or may be composed of only one of N-type and P-type.

  The light-emitting element of the present invention has a layer with a small activation energy of electrical conductivity, thereby realizing a low driving voltage. That is, the layer with low activation energy of the electrical conductivity of the present invention has high carrier density, and can make ohmic contact with the electrode. Therefore, the driving voltage of the light emitting element can be reduced. In addition, since the carrier density is high, the carrier transportability is also excellent. In order to obtain a sufficient carrier density, the activation energy of electrical conductivity is preferably 0.01 eV or more and less than 0.30 eV. Moreover, it is more preferable that the activation energy of electrical conductivity is 0.01 eV or more and less than 0.26 eV. Further, when used for a light-emitting element, it is more preferable that the activation energy of electrical conductivity is 0.01 eV or more and less than 0.20 eV because current-voltage characteristics do not change.

  In addition, since the layer with low activation energy of electric conductivity has a high carrier density, the increase in driving voltage can be suppressed even if the film thickness is increased. Therefore, the layer with low activation energy of electric conductivity is thick. And short circuit between the upper and lower electrodes can be suppressed. Therefore, defects due to dust generated in the manufacturing process can be suppressed and yield can be improved.

  Further, by increasing the thickness of the layer having a low activation energy for electrical conductivity, a short circuit due to impact or the like can be prevented, so that a highly reliable light-emitting element can be obtained. For example, while the film thickness between the electrodes of a normal light emitting element is 100 nm to 150 nm, the film thickness between the electrodes of the light emitting element using a layer with low activation energy of electrical conductivity is preferably 100 to 500 nm. Can be 200-500 nm.

  In addition, since the layer with low activation energy for electrical conductivity used in the light-emitting element of the present invention has high carrier density, it can be in ohmic contact with the electrode. That is, the contact resistance with the electrode is small. Therefore, the electrode material can be selected without considering the work function or the like. That is, the choice of electrode material is expanded.

  In addition, since the layer having a small activation energy for electrical conductivity according to the present invention can be formed by vacuum deposition, when a layer containing a light emitting material is formed by vacuum deposition, both layers are in the same vacuum apparatus. It is possible to form a film without using the atmosphere. That is, the film can be formed in a consistent vacuum. Therefore, it is possible to prevent dust from adhering in the manufacturing process and improve yield.

  In addition, since the layer with low activation energy of electrical conductivity according to the present invention includes an organic material and an inorganic material, stress generated between the electrode and the layer including a light-emitting substance can be reduced.

(Embodiment 2)
In this embodiment mode, the layer having a small electrical conductivity activation energy shown in Embodiment Mode 1 is a layer containing an organic material and an inorganic material, and the electrical conductivity activation energy is 0.01 eV or more and 0.0. A layer that is less than 30 eV, more preferably a layer that is 0.01 eV or more and less than 0.26 eV, and still more preferably a layer that is 0.01 eV or more and less than 0.20 eV) will be described in more detail.

  In this embodiment, the case where a layer including an organic material and an inorganic material does not have an absorption peak in the visible light region will be described. In this embodiment, description is made using a layer containing DNTPD and molybdenum oxide which does not have an absorption peak in the visible light region. FIG. 11 shows an absorption spectrum of a layer formed by co-evaporation of DNTPD and molybdenum oxide so that the weight ratio is 1: 1. FIG. 11 shows that the layer containing DNTPD and molybdenum oxide has no absorption peak in the visible light region. In addition to DNTPD, a layer containing an organic material such as DPAB and molybdenum oxide does not have an absorption peak in the visible light region. Note that, in this specification, the visible light region indicates a wavelength region of 400 nm to 800 nm.

An ITO film having a thickness of 110 nm was formed on the first glass substrate to produce an anode having an area of 4 mm ² . After the first glass substrate having the ITO anode was washed with water and dried, the first glass substrate was set in a vapor deposition machine, and the vacuum chamber was evacuated until the pressure became 1 × 10 ⁻³ Pa or less. .

Next, DNTPD as an organic material and molybdenum oxide as an inorganic material were formed by co-evaporation. Here, the co-evaporation was controlled so that the molybdenum oxide concentration became the level shown in Table 1. The film was formed so that the film thickness was 200 nm. The element 1 was formed only by DNTPD so as to have a film thickness of 200 nm by vapor deposition.

Thereafter, Al was deposited as a cathode in a thickness of 200 nm, and the second glass substrate on which the desiccant was pasted was bonded to the first glass substrate with an epoxy-based adhesive in an N ₂ atmosphere, and elements 1 to 9 were formed. Obtained.

  FIG. 13 shows current-voltage characteristics of the elements 1 to 9 at 25 ° C. It can be seen that the elements 2 to 9 containing molybdenum oxide have a lower resistance than the element 1 not containing molybdenum oxide. Note that, as the molybdenum oxide concentration increases, the resistance decreases, but it can be seen that when the molybdenum oxide concentration exceeds 80 wt%, the resistance increases.

  Next, FIG. 14 shows a graph in which current-voltage characteristics are displayed in logarithm. It can be seen that the current-voltage characteristics in the low voltage region of the elements 2 to 9 are proportional to the square of the voltage. On the other hand, it can be seen that the element 1 is proportional to the voltage with a larger power. This is because the contact with the ITO anode in the element 1 is a Schottky contact, while the contact in the elements 2 to 9 is an ohmic contact. Therefore, it is considered that the ohm current is dominant in the elements 2 to 9.

  Therefore, assuming that the current flowing in the elements 2 to 9 in the low voltage region is an ohmic current and the layer containing DNTPD and molybdenum oxide is a semiconductor, it is expressed by the Arrhenius equation.

  From this equation, the following equation can be derived in the case of a certain voltage.

  Therefore, activation energy can be obtained from an Arrhenius plot in which ln (I) and 1 / T are plotted.

  An Arrhenius plot at 1V for elements 2-9 is shown in FIG. It can be seen that all the elements are on a substantially straight line. The activation energy is obtained from the slope of this straight line, and the change in activation energy with respect to the molybdenum oxide concentration is shown in FIG. It can be seen that the graph is convex downward. In addition, when the same analysis was performed in the element (henceforth the element 10) which vapor-deposited only 50 nm of molybdenum oxide on the ITO anode, and was made into Al cathode, activation energy was calculated | required with 0.26 eV. The activation energy of the element 2 is larger than that of the element 10. This is probably because the molybdenum oxide concentration is too low. On the other hand, the elements 3 to 9 are lower than the activation energy value of the element 10, and by containing a certain amount of molybdenum oxide, activation energy that cannot be obtained by a molybdenum oxide single film can be obtained.

  Note that in the case where a layer having no absorption peak in the visible light region described in this embodiment is used for a light-emitting element, it is preferable that the activation energy be 0.01 eV or more and less than 0.30 eV. More preferably, it is preferably 0.01 eV or more and less than 0.26 eV. More preferably, it is less than 0.20 eV. Further, it is preferable to use a layer having a molybdenum oxide concentration of 30 wt% or more and 95 wt% or less.

(Embodiment 3)
In this embodiment, unlike Embodiment 2, a case where a layer containing an organic material and an inorganic material has an absorption peak in the visible light region will be described. In this embodiment, a layer containing an absorption peak in the visible light region and including BSPB and molybdenum oxide is described. FIG. 12 shows an absorption spectrum of a layer formed by co-evaporation so that the weight ratio of BSPB and molybdenum oxide is 1: 1. FIG. 12 shows that the layer containing BSPB and molybdenum oxide has an absorption peak in the visible light region. In addition to BSPB, a layer containing an organic material such as TPD, α-NPD, DFLDPBi, or BBPB and molybdenum oxide has an absorption peak in the visible light region.

An ITO film having a thickness of 110 nm was formed on the first glass substrate to produce an anode having an area of 4 mm ² . The first glass substrate having the ITO anode is washed with water and dried, then the first glass substrate is set in a vapor deposition machine, and the vacuum chamber is evacuated until the pressure becomes 1 × 10 ⁻³ Pa or less. did.

Next, BSPB as an organic material and molybdenum oxide as an inorganic material were formed by co-evaporation. Here, the co-evaporation was controlled so that the molybdenum oxide concentration was at the level shown in the table below. The film was formed so that the film thickness was 200 nm. The element 11 was formed by vapor deposition so that the film thickness was 200 nm only with BSPB.

Thereafter, Al was deposited as a cathode at a thickness of 200 nm, and the second glass substrate on which the desiccant was pasted was bonded to the first glass substrate with an epoxy-based adhesive in an N ₂ atmosphere, and the elements 11 to 15 were assembled. Obtained.

  FIG. 17 shows current-voltage characteristics at 25 ° C. in the elements 11 to 15. It can be seen that the elements 12 to 15 containing molybdenum oxide have a lower resistance than the element 11 not containing molybdenum oxide.

  Next, a graph in which the current-voltage characteristics are displayed in logarithm is shown in FIG. It can be seen that the current-voltage characteristics in the low voltage region of the elements 12 to 15 are proportional to the voltage between the first power and the second power. On the other hand, it can be seen that the element 11 is proportional to the voltage with a larger power. This is because the contact with the ITO anode in the element 11 is a Schottky contact, whereas the contact in the elements 12 to 15 is an ohmic contact. Therefore, it is considered that the ohm current is dominant in the elements 12 to 15.

  Therefore, similarly to the second embodiment, assuming that the current flowing in the elements 12 to 15 in the low voltage region is an ohmic current and the layer containing BSPB and molybdenum oxide is a semiconductor, the activation energy is obtained from the Arrhenius plot. It was. FIG. 19 shows an Arrhenius plot at 1 V for elements 12-15. It can be seen that all the elements are on a substantially straight line. The activation energy is obtained from the slope of this straight line, and the change in activation energy with respect to the molybdenum oxide concentration is shown in FIG. In addition, considering that the activation energy of the element 10 on which only molybdenum oxide is deposited is 0.26 eV, it can be said that FIG. 20 is a downwardly convex graph. Further, the activation energy of the element 12 is larger than that of the element 10. This is probably because the molybdenum oxide concentration is too low. On the other hand, the elements 13 to 15 were lower than the activation energy value of the element 10, and by containing a certain amount of molybdenum oxide, activation energy that could not be obtained with a molybdenum oxide single film could be obtained.

  Note that in the case where the layer having an absorption peak in the visible light region described in this embodiment is used for a light-emitting element, the activation energy is preferably 0.01 eV or more and less than 0.30 eV. More preferably, it is preferably 0.01 eV or more and less than 0.26 eV. More preferably, it is less than 0.20 eV. It is preferable to use a layer having a molybdenum oxide concentration of 5 wt% or more and 95 wt% or less.

(Embodiment 4)
In this embodiment, a light-emitting element having a structure different from that described in Embodiment 1 will be described with reference to FIGS.

  FIG. 3A shows an example of the structure of the light-emitting element of the present invention. A first layer 211, a second layer 212, a third layer 213, and a fourth layer 214 are stacked between the first electrode 201 and the second electrode 202. In this embodiment, the case where the first electrode 201 functions as an anode and the second electrode 202 functions as a cathode is described.

  The first electrode 201 and the second electrode 202 can have the same structure as that in Embodiment 1. In addition, the first layer 211 is a layer with low activation energy described in Embodiments 2 and 3, and the second layer 212 is a layer containing a substance having a high light-emitting property. The third layer 213 includes one compound selected from metal oxides and a compound having a high electron-transport property, and the fourth layer 214 is described in Embodiment Modes 2 and 3. It is a layer with a small activation energy. The metal oxide contained in the third layer 213 is preferably an alkali metal oxide or an alkaline earth metal oxide. Specific examples include lithium oxide, calcium oxide, and barium oxide.

  With such a configuration, as shown in FIG. 3A, by applying a voltage to the light-emitting element, electrons are exchanged near the interface between the third layer 213 and the fourth layer 214. Electrons and holes are generated, and the third layer 213 transports electrons to the second layer 212, and the fourth layer 214 transports holes to the second electrode 202. That is, the third layer 213 and the fourth layer 214 together serve as a carrier generation layer. In addition, it can be said that the fourth layer 214 has a function of transporting holes to the second electrode 202. Note that a tandem light-emitting element can be obtained by stacking the second layer and the third layer again between the fourth layer 214 and the second electrode 202.

  In addition, the first layer 211 and the fourth layer 214 exhibit extremely high hole injecting property and hole transporting property. Therefore, the light emitting element of this embodiment can make the both sides of the second layer responsible for the light emitting function very thick, and can effectively prevent a short circuit of the light emitting element. Further, taking FIG. 3A as an example, when the second electrode 202 is formed by sputtering, damage to the second layer 212 containing a light-emitting substance can be reduced. Further, by forming the first layer 211 and the fourth layer 214 with the same material, the first electrode side of the layer 203 containing a light-emitting substance and the second electrode side of the layer 203 containing a light-emitting substance are made of the same material. Since it is comprised, the effect which suppresses stress distortion can also be anticipated.

  Note that the light-emitting element of this embodiment also has various variations by changing the types of the first electrode 201 and the second electrode 202. The schematic diagram is shown in FIG. 3 (b), FIG. 3 (c) and FIG. In FIGS. 3B, 3C, and 4, the reference numerals in FIG. 3A are cited. Reference numeral 200 denotes a substrate carrying the light emitting element of the present invention.

  FIG. 3 shows an example in which the first layer 211, the second layer 212, the third layer 213, and the fourth layer 214 are configured in this order from the substrate 200 side. At this time, the first electrode 201 is light-transmitting and the second electrode 202 is light-shielding (particularly reflective) so that light is emitted from the substrate 200 side as shown in FIG. Become. Further, the first electrode 201 is made light-shielding (particularly reflective), and the second electrode 202 is made light-transmissive so that light is emitted from the opposite side of the substrate 200 as shown in FIG. It becomes. Further, by making both the first electrode 201 and the second electrode 202 light transmissive, light is emitted to both the substrate 200 side and the opposite side of the substrate 200 as shown in FIG. Configuration is also possible.

  FIG. 4 shows an example in which the fourth layer 214, the third layer 213, the second layer 212, and the first layer 211 are configured in this order from the substrate 200 side. At this time, the first electrode 201 is made light-shielding (particularly reflective), and the second electrode 202 is made light-transmissive so that light is extracted from the substrate 200 side as shown in FIG. . Further, the first electrode 201 is made light-transmitting and the second electrode 202 is made light-shielding (particularly reflective), whereby light is extracted from the opposite side of the substrate 200 as shown in FIG. Become. Furthermore, by making both the first electrode 201 and the second electrode 202 light transmissive, light is emitted to both the substrate 200 side and the opposite side of the substrate 200 as shown in FIG. Configuration is also possible.

  Note that the first layer 211 includes one compound selected from metal oxides and a compound having a high electron-transport property, the second layer 212 includes a light-emitting substance, and the third layer 213. Is a layer with a small activation energy shown in Embodiment Mode 2 and Embodiment Mode 3, and the fourth layer 214 includes one compound selected from metal oxides and a compound having a high electron-transport property. It is also possible to have a configuration including this.

  Note that in the case of manufacturing the light-emitting element in this embodiment, a known method can be used regardless of a wet method or a dry method.

  Alternatively, after the first electrode 201 is formed, the first layer 211, the second layer 212, the third layer 213, and the fourth layer 214 are sequentially stacked to form the second electrode 202. Alternatively, after the second electrode 202 is formed, the fourth layer 214, the third layer 213, the second layer 212, and the first layer 211 may be sequentially stacked to form the first electrode. Good.

(Embodiment 5)
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. 5 is a schematic view of a light emitting device to which the present invention is applied as viewed from above. In FIG. 5, a pixel portion 6511, a source signal line driver circuit 6512, a write gate signal line driver circuit 6513, and an erase gate signal line driver circuit 6514 are provided over a substrate 6500. The source signal line driver circuit 6512, the writing gate signal line driver circuit 6513, and the erasing gate signal line driver circuit 6514 are respectively FPC (flexible printed circuit) 6503 which is an external input terminal through 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. 6 is a diagram illustrating a circuit for operating one pixel. The circuit illustrated in FIG. 6 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 of a transistor and a second electrode of the transistor, 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 of the first transistor is electrically connected to the gate electrode of the second transistor 902. A first electrode of the second transistor 902 is electrically connected to the current supply line 917, and a second electrode of the second transistor 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, but they can be arranged as shown in the top view of FIG. In FIG. 7, the first electrode of the first transistor 1001 is connected to the source signal line 1004, and the second electrode of the first transistor 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 of the second transistor 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. 8 is a diagram for explaining an operation in one frame as time elapses. In FIG. 8, 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. 8, 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 the pixel portion.

  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, immediately after the writing period of the last row is completed, the writing period of the next subframe (or the next frame) is started 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. 6 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. The 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, conduction or non-conduction between the current supply line 917 and the light-emitting element 903 is determined by a signal input to the second transistor 902, and the light-emitting element 903 determines light emission or non-light emission. 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, when 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, the current supply line 917 and the light-emitting element 903 are turned off 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 920. 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 driving circuit 913 are disconnected, and the switch 920 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.

  Further, 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 a certain gate signal line are brought into a non-connected state, and writing is performed. The operation of connecting the gate signal line driving 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 6)
One mode of a cross-sectional view of a light-emitting device including the light-emitting element of the present invention is described with reference to FIGS.

  In FIG. 9, the transistor 11 provided for driving the light emitting element 12 of the present invention is surrounded by a dotted line. The light-emitting element 12 is a light-emitting element of the present invention having a layer 15 in which a layer containing a light-emitting substance and a layer having low activation energy of electrical conductivity are stacked between a first electrode 13 and a second electrode 14. is there. The drain of the transistor 11 and the first electrode 13 are electrically connected by a wiring 17 penetrating the first interlayer insulating layer 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. 9 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 containing silicon is formed by glow discharge decomposition (plasma CVD). As a gas containing silicon, SiH ₄ , Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , SiF _4, or the like can be used. The gas containing silicon 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. Note that the mobility of a TFT (thin film transistor) using a semi-amorphous semiconductor is approximately 1 to 10 m ² / Vsec.

  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. 9A, 9B, or 9C, or may be a single layer. The first interlayer insulating layer 16a is made of an inorganic material such as silicon oxide or silicon nitride, and the first interlayer insulating film 16b has a skeleton structure formed of a bond of acrylic or siloxane (silicon (Si) and oxygen (O). , A substance containing at least hydrogen as a substituent), and a self-flattening substance such as silicon oxide that can be coated and formed. Further, the first interlayer insulating film 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 film and an organic film.

  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.

  In FIGS. 9A and 9C, only the first interlayer insulating film 16 is provided between the transistor 11 and the light emitting element 12. However, as shown in FIG. 9B, the first interlayer insulating film 16 is provided. In addition to the insulating film 16 (first interlayer insulating films 16a and 16b), a structure in which a second interlayer insulating film 19 (second interlayer insulating films 19a and 19b) is provided may be used. In the light emitting device shown in FIG. 9B, 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 a substance having self-flatness such as acrylic or siloxane (a substance having a skeletal structure composed of a bond of silicon (Si) and oxygen (O) and having at least hydrogen as a substituent), silicon oxide capable of being coated and formed. Consists of. 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 film and an organic film.

  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 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. 9B. 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. 9C. 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. 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 drive voltage.

(Embodiment 7)
Since a light-emitting device including the light-emitting element of the present invention can display a good image, an electronic device that can provide excellent images can be obtained by applying the light-emitting device of the present invention to a display portion of an electronic device. it can. In addition, since a light-emitting device including a light-emitting element of the present invention is driven with low power consumption, an electronic device with low power consumption can be obtained by applying the light-emitting device of the present invention to a display portion of an electronic device. A telephone with a long standby time can be obtained.

  One embodiment of an electronic device mounted with a light emitting device to which the present invention is applied is shown in FIG.

  FIG. 10A illustrates a 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. A computer can be completed by incorporating a light-emitting device having the light-emitting element of the present invention as a display portion.

  FIG. 10B illustrates a telephone manufactured by applying the present invention. The main body 5552 includes a display portion 5551, a sound output portion 5554, a sound input portion 5555, operation switches 5556 and 5557, an antenna 5553, and the like. ing. A telephone can be completed by incorporating a light-emitting device having the light-emitting element of the present invention as a display portion.

  FIG. 10C 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. A television receiver can be completed by incorporating a light-emitting device having the light-emitting element of the present invention as a display portion.

  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 although a computer, a telephone set, and a television receiver are described in this embodiment mode, a light-emitting device having the light-emitting element of the present invention may be mounted on a telephone, a navigation device, a lighting device, or the like. Absent.

(Synthesis example)
In this example, N, N′-bis (spiro-9,9′-bifluoren-2-yl) -N, N′-diphenylbenzidine represented by the structural formula (1) used in Embodiment 3 ( A method for synthesizing (abbreviation: BSPB) will be described.

[Step 1]
A method for synthesizing 2-bromo-spiro-9,9′-bifluorene will be described.

  Into a 100 ml three-necked flask, 1.26 g (0.052 mol) of magnesium was put, the inside of the system was put under vacuum, and the mixture was heated and stirred for 30 minutes to activate. After cooling to room temperature, the system is placed under a nitrogen stream, 5 ml of diethyl ether and a few drops of dibromoethane are added, and 11.65 g (0.050 mol) of 2-bromobiphenyl dissolved in 15 ml of diethyl ether is slowly added dropwise to complete the addition. Thereafter, the mixture was refluxed for 3 hours to obtain a Grignard reagent. In a 200 ml three-necked flask, 11.7 g (0.045 mol) of 2-bromofluorenone and 40 ml of diethyl ether were placed. The synthesized Grignard reagent was slowly added dropwise to the reaction solution, refluxed for 2 hours after completion of the addition, and further stirred overnight at room temperature. After completion of the reaction, the reaction solution was washed twice with a saturated aqueous ammonium chloride solution, the aqueous layer was extracted twice with ethyl acetate, and the organic layer was washed with saturated brine. After drying with magnesium sulfate, suction filtration and concentration were performed to obtain 18.76 g of solid 9- (2-biphenylyl) -2-bromo-9-fluorenol in a yield of 90%.

Next, the synthesized 9- (2-biphenylyl) -2-bromo-9-fluorenol (18.76 g, 0.045 mol) and glacial acetic acid (100 ml) were placed in a 200 ml three-necked flask, and a few drops of concentrated hydrochloric acid were added and refluxed for 2 hours. did. After completion of the reaction, the precipitate was collected by suction filtration, and washed by filtration with a saturated aqueous sodium hydrogen carbonate solution and water. The obtained brown solid was recrystallized with ethanol to obtain 10.24 g of a light brown powdery solid in a yield of 57%. This light brown powdery solid was confirmed to be 2-bromo-spiro-9,9′-bifluorene by nuclear magnetic resonance ( ¹ H-NMR). ¹ H-NMR of this compound was as follows.

¹ H-NMR of this compound is shown below.
¹ H-NMR (300 MHz, CDCl ₃ ) δ ppm: 7.86-7.79 (m, 3H), 7.70 (d, 1H, J = 8.4 Hz), 7.47-7.50 (m , 1H), 7.41-7.34 (m, 3H), 7.12 (t, 3H, J = 7.7 Hz), 6.85 (d, 1H, J = 2.1 Hz), 6.74. -6.70 (m, 3H)

  Moreover, the synthesis scheme (b-1) of the synthesis method described above is shown below.

[Step 2]
A method for synthesizing N, N′-bis (spiro-9,9′-bifluoren-2-yl) -N, N′-diphenylbenzidine (abbreviation: BSPB) will be described.

  In a 100 ml three-necked flask, 1.00 g (0.0030 mol) of N, N′-diphenylbenzidine, 2.49 g (0.0062 mol) of 2-bromo-spiro-9,9′-bifluorene synthesized by the synthesis method of Step 1 , 170 mg (0.30 mmol) of bis (dibenzylideneacetone) palladium and 1.08 g (0.011 mol) of tert-butoxy sodium were added, and the system was purged with nitrogen, and then 20 ml of dehydrated toluene and tri-tert-butyl were added. 0.6 ml of 10% phosphine hexane solution was added and stirred at 80 ° C. for 6 hours. After completion of the reaction, the reaction solution was cooled to room temperature, water was added, and the precipitated solid was collected by suction filtration and washed with dichloromethane. The obtained white solid was purified by alumina column chromatography (chloroform) and recrystallized with dichloromethane. As a result, 2.66 g of white powdery solid was obtained in a yield of 93%.

  A synthesis scheme (b-2) of the synthesis method described above is shown below. Thus, the compound of the present invention can be synthesized by a coupling reaction of N, N'-diphenylbenzidine and 2-bromo-spiro-9,9'-bifluorene.

  Further, the glass transition temperature, crystallization temperature, and melting point of the obtained compound were examined using a differential scanning calorimeter (DSC: Differential Scanning Calorimetry, manufactured by PerkinElmer, model number: Pyris1 DSC). Here, the measurement by DSC was performed according to the following procedure. First, after heating the sample (the obtained compound) to 450 ° C. at a temperature rising rate of 40 ° C./min, the sample was cooled to a glass state by cooling at a temperature decreasing rate of 40 ° C./min. And the sample which became a glass state was heated at the temperature increase rate of 10 degree-C / min, and the measurement result as shown in FIG. 21 was obtained. In FIG. 21, the horizontal axis represents temperature (° C.), and the vertical axis represents heat flow (upward is endothermic) (mW). From the measurement results, it was found that the obtained compound had a glass transition temperature of 172 ° C. and a crystallization temperature of 268 ° C. Moreover, it turned out that melting | fusing point is 323 to 324 degreeC from the intersection of the tangent line at 312 degreeC and the tangent line at 327 to 328 degreeC. That is, the BSPB synthesized in this example has high heat resistance because it has a glass transition temperature of 150 ° C. or higher, preferably 160 ° C. to 300 ° C. and a melting point of 180 ° C. to 400 ° C. It is preferable.

Thus, the obtained compound has a high glass transition temperature of 172 ° C. and has good heat resistance. Further, in FIG. 21, the peak representing crystallization of the obtained compound is broad, and it was found that the obtained compound is a substance that is difficult to crystallize.

  In this example, a light-emitting element having a layer with low activation energy according to the present invention will be described.

  First, indium tin oxide containing silicon is formed as the first electrode. On top of that, a layer having a small activation energy of the present invention was formed. In this example, the film was formed by co-evaporating DNTPD, molybdenum oxide, and rubrene. Here, the co-evaporation was controlled so that the molybdenum oxide concentration became the level shown in Table 3. The film formation was performed so that the film thickness was 120 nm.

  On this low activation energy layer, 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (abbreviation: α-NPD) is formed to a thickness of 10 nm as a hole transport layer. A film was formed by vacuum evaporation.

On this α-NPD film, Alq ₃ and coumarin 6 were formed by co-evaporation. This film is a light emitting layer, and the film thickness is 40 nm. Further, the co-evaporation was controlled so that Alq ₃ and coumarin 6 were in a weight ratio of 1: 0.015.

On this light-emitting layer, Alq ₃ is formed to a thickness of 15 nm as an electron transport layer, and lithium fluoride is formed to a thickness of 1 nm as an electron injection layer, and finally, 200 nm of Al functioning as a second electrode is formed. Was made.

  The current-voltage characteristics of the fabricated elements 21 to 24 are shown in FIG. As shown in FIG. 22, it can be seen that the concentration of molybdenum oxide increases and current easily flows.

  The luminance-voltage characteristics of the elements 21 to 24 are shown in FIG. From FIG. 23, it can be seen that the molybdenum oxide concentration increases and high luminance is obtained. That is, it can be seen that when the current efficiency of each element is constant, the current flows easily.

  In this example, a light-emitting element having a layer with low activation energy according to the present invention will be described.

  First, indium tin oxide containing silicon is formed as the first electrode. On top of that, a layer having a small activation energy of the present invention was formed. In this example, the film was formed by co-evaporating DNTPD, molybdenum oxide, and rubrene. Here, the co-evaporation was controlled so that the molybdenum oxide concentration became the level shown in Table 3. The film formation was performed so that the film thickness was 120 nm.

  On this low activation energy layer, α-NPD was deposited as a hole transport layer with a thickness of 10 nm by vacuum deposition.

On this α-NPD film, Alq ₃ and coumarin 6 were formed by co-evaporation. This film is a light emitting layer, and the film thickness is 37.5 nm. Further, the co-evaporation was controlled so that Alq ₃ and coumarin 6 were 1: 0.005 in weight ratio.

On this light-emitting layer, Alq ₃ is formed with a thickness of 37.5 nm as an electron transport layer, and lithium fluoride is formed with a thickness of 1 nm as an electron injection layer, and finally, Al that functions as a second electrode is formed to emit light. An element was produced.

  The current-voltage characteristics of the fabricated elements 31 to 34 are shown in FIG. FIG. 24 shows that the current tends to flow as the concentration of molybdenum oxide increases, but the current-voltage characteristics hardly change when the molybdenum oxide concentration of the element 32 is 40 wt% or more. Therefore, it can be seen that when DNTPD is used as a layer having a small activation energy, a molybdenum oxide concentration of 40 wt% is sufficiently effective for lowering the voltage of the light-emitting element.

  In addition, FIG. 25 shows luminance-voltage characteristics of the elements 31 to 34. From FIG. 25, it can be seen that although there is almost no difference in luminance-voltage characteristics in any of the elements, the element 31 is slightly shifted to the high voltage side.

4A and 4B illustrate a light-emitting element of the present invention. 4A and 4B illustrate a light-emitting element of the present invention. 4A and 4B illustrate a light-emitting element of the present invention. 4A and 4B illustrate a light-emitting element of the present invention. 4A and 4B illustrate a light-emitting device to which the present invention is applied. 6A and 6B illustrate a circuit included in a light-emitting device to which the present invention is applied. The top view of the light-emitting device to which this invention is applied. 4A and 4B illustrate an operation in one frame of a light-emitting device to which the present invention is applied. Sectional drawing of the light-emitting device to which this invention is applied. The figure of the electronic device to which this invention is applied. The figure which shows the absorption spectrum of the layer containing DNTPD and molybdenum oxide. The figure which shows the absorption spectrum of the layer containing BSPB and molybdenum oxide. The figure which shows the current-voltage characteristic of the layer containing DNTPD and molybdenum oxide. The figure which shows the logarithm display of the electric current-voltage characteristic of the layer containing DNTPD and molybdenum oxide. The figure which shows the Arrhenius plot in 1V of the layer containing DNTPD and molybdenum oxide. The figure which shows the activation energy of the layer containing DNTPD and molybdenum oxide. The figure which shows the current-voltage characteristic of the layer containing BSPB and molybdenum oxide. The figure which shows the logarithm display of the electric current-voltage characteristic of the layer containing BSPB and molybdenum oxide. The figure which shows the Arrhenius plot in 1V of the layer containing BSPB and molybdenum oxide. The figure which shows the activation energy of the layer containing BSPB and molybdenum oxide. The figure of the measurement result which carried out the differential scanning calorimetry analysis of N, N'-bis (spiro-9,9'-bifluoren-2-yl) -N, N'-diphenylbenzidine. FIG. 13 shows current-voltage characteristics of a light-emitting element having a layer containing DNTPD and molybdenum oxide. The figure which shows the luminance-voltage characteristic of the light emitting element which has a layer containing DNTPD and molybdenum oxide FIG. 13 shows current-voltage characteristics of a light-emitting element having a layer containing DNTPD and molybdenum oxide. FIG. 11 shows luminance-voltage characteristics of a light-emitting element having a layer containing DNTPD and molybdenum oxide.

Explanation of symbols

101 Substrate 102 First Electrode 103 First Layer 104 Second Layer 105 Third Layer 106 Fourth Layer 107 Second Electrode 200 Substrate 201 First Electrode 202 Second Electrode 203 A Layer Containing a Luminescent Material 211 1st layer 212 2nd layer 213 3rd layer 214 4th layer 302 1st electrode 303 1st layer 304 2nd layer 305 3rd layer 306 4th layer 307 2nd electrode 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 driving circuit 915 Source signal line drive circuit 916 Power supply 917 Current supply line 918 Switch 919 Switch 920 Switch 100 1st transistor 1002 2nd transistor 1003 Gate signal line 1004 Source signal line 1005 Current supply line 1006 Electrode 501a Period 501b Retention period 504b Retention period 504c Erase period 504d Non-light emission period 5521 Body 5522 Housing 5523 Display portion 5524 Keyboard 5531 Display Unit 5532 Housing 5533 Speaker 5551 Display unit 5552 Main body 5553 Antenna 5554 Audio output unit 5555 Audio input unit 5556 Operation switch 6500 Substrate 6503 FPC (flexible printed circuit)
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 10 Substrate 11 Transistor 12 Light emitting element 13 First electrode 14 Second electrode 15 Layer 16a First interlayer insulation Film 16b First interlayer insulating film 16c First interlayer insulating film 17 Wiring 18 Partition layer 19a Second interlayer insulating film 19b Second interlayer insulating film

Claims (11)

Having a layer containing an organic material and an inorganic material between a pair of electrodes;
An activation energy of electric conductivity of the layer containing the organic material and the inorganic material is 0.01 eV or more and less than 0.3 eV. Having a layer containing an organic material and an inorganic material between a pair of electrodes;
An activation energy of electric conductivity of the layer including the organic material and the inorganic material is 0.01 eV or more and less than 0.26 eV. Having a layer containing an organic material and an inorganic material between a pair of electrodes;
An activation energy of electric conductivity of the layer containing the organic material and the inorganic material is 0.01 eV or more and less than 0.20 eV. The layer containing the organic material and the inorganic material according to any one of claims 1 to 3, wherein the layer containing no organic material has no absorption peak in a visible light region, and the concentration of the inorganic material is 30 to 95 wt%. Light emitting element. 5. The organic material according to claim 4, wherein the organic material is 4,4′-bis (N- {4- [N, N′-bis (3-methylphenyl) amino] phenyl} -N-phenylamino) biphenyl, 4,4 A light-emitting element which is any one of '-bis [N- (4-diphenylaminophenyl) -N-phenylamino] biphenyl. The layer containing the organic material and the inorganic material according to any one of claims 1 to 3, has an absorption peak in a visible light region, and a concentration of the inorganic material is 5 to 95 wt%. Light emitting element. 7. The organic material according to claim 6, wherein the organic material is N, N′-bis (3-methylphenyl) -N, N′-diphenyl- [1,1′-biphenyl] -4,4′-diamine, 4,4 ′. -Bis [N- (1-naphthyl) -N-phenylamino] biphenyl, N, N'-bis (spiro-9,9'-bifluoren-2-yl) -N, N'-diphenylbenzidine, 4,4 One of '-bis [N- (9,9-dimethylfluoren-2-yl) -N-phenylamino] biphenyl and 4,4'-bis [N- (4-biphenylyl) -N-phenylamino] biphenyl A light emitting element characterized by the above. 8. The light-emitting element according to claim 1, wherein the inorganic material is a metal oxide. 8. The light-emitting element according to claim 1, wherein the inorganic material is one or more of molybdenum oxide, vanadium oxide, ruthenium oxide, and tungsten oxide. . 10. The light-emitting element according to claim 1, wherein the layer including the organic material and the inorganic material is provided in contact with one electrode of the pair of electrodes. The light-emitting device which has a light emitting element as described in any one of Claims 1 thru | or 10.

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