JP2007157753A - Light emitting element, light emitting device and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting element in which malfunction resulting from crystallization of a compound can be reduced, a light emitting device in which poor display resulting from a defect in the light emitting element is suppressed, and an electronic apparatus which can transmit correct information to a user through a display image by suppressing misconception resulting from poor display in the light emitting device. <P>SOLUTION: The light emitting element has a layer generating electrons between first and second electrodes. The layer generating electrons contains a phenanthroline derivative represented by general formula (1), and a substance exhibiting electron donation properties to the phenanthroline derivative. A metal oxide exhibits electron donation properties to a phenanthroline derivative represented by general formula (1). In the general formula (1), R<SP>1</SP>-R<SP>5</SP>represent an alkyl group of 1-4C or a halogen group, respectively, and at least one of them represents a halogen group. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light-emitting element having a layer containing a light-emitting substance between a pair of electrodes, a light-emitting device using the same, and an electronic device.

  A light-emitting element having a layer containing a light-emitting substance between a pair of electrodes is used as a pixel, a light source, or the like, and is provided in a light-emitting device such as a display device or a lighting device. In such a light emitting device, the reliability of the light emitting element is closely related to the performance of the light emitting device. For example, when a short circuit occurs between the electrodes of the light emitting element, the display image is disturbed or a sufficient amount of light cannot be illuminated.

Therefore, in recent years, development of a light emitting element that has few element defects and can stably emit light for a long period of time has been advanced. For example, Patent Document 1 discloses a technique for manufacturing a light-emitting element that operates at a low driving voltage by using a metal oxide having a high work function such as molybdenum oxide for an anode. In addition, the effect of extending the life is obtained.
JP-A-9-63771

  It is an object of the present invention to provide a light-emitting element that can reduce malfunction caused by crystallization of a compound.

  The phenanthroline derivative used in the practice of the present invention is represented by the following general formula (1).

In the general formula (1), R ^{1 to} R ⁵ each represent an alkyl group having 1 to 4 carbon atoms or a halogen group, and at least one of R ^{1 to} R ⁵ represents a halogen group.

  One light-emitting element of the present invention includes a layer that generates electrons between a first electrode and a second electrode. The layer which generates electrons includes a phenanthroline derivative represented by the general formula (1) and a metal oxide. The metal oxide exhibits an electron donating property with respect to the phenanthroline derivative represented by the general formula (1).

  One light-emitting element of the present invention includes a layer that generates electrons between the first electrode and the second electrode, and a layer containing a light-emitting substance. Here, the layer which generates electrons includes a phenanthroline derivative represented by the general formula (1) and a metal oxide. The metal oxide exhibits an electron donating property with respect to the phenanthroline derivative represented by the general formula (1). The layer containing a light-emitting substance may be a single layer or a multilayer. In the case of multiple layers, it is sufficient that at least one layer contains a light-emitting substance.

  One light-emitting element of the present invention includes a layer that generates holes between a first electrode and a second electrode, a layer that contains a light-emitting substance, and a layer that generates electrons. The layer that generates holes is provided between the layer containing a light-emitting substance and the first electrode. The layer for generating electrons is provided between the layer containing a light-emitting substance and the second electrode. Here, the layer which generates electrons includes a phenanthroline derivative represented by the general formula (1) and a metal oxide. The metal oxide exhibits an electron donating property with respect to the phenanthroline derivative represented by the general formula (1). The layer containing a light-emitting substance may be a single layer or a multilayer. In the case of multiple layers, it is sufficient that at least one layer contains a light-emitting substance.

  One of the light-emitting elements of the present invention includes a first layer, a second layer, and a third layer between a first electrode and a second electrode. The first layer is a layer that generates holes, and the second layer is a layer that generates electrons. The third layer is a layer containing a light emitting substance. The first layer is provided closer to the first electrode than the second layer, and the third layer is provided closer to the second electrode than the second layer. The second layer includes a phenanthroline derivative represented by the general formula (1) and a metal oxide. The metal oxide exhibits an electron donating property with respect to the phenanthroline derivative represented by the general formula (1). The second layer and the third layer have electrons from the second layer to the third layer when a voltage is applied so that the potential at the first electrode is lower than the potential at the second electrode. Are joined so as to be injected. The layer containing a light-emitting substance may be a single layer or a multilayer. In the case of multiple layers, it is sufficient that at least one layer contains a light-emitting substance.

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

  One electronic device of the present invention uses a light-emitting device using any of the light-emitting elements described above as a pixel for a display portion.

  One of the electronic devices of the present invention uses a light-emitting device using any of the light-emitting elements described above as a light source for an illumination unit.

  Since the phenanthroline derivative used in the practice of the present invention easily receives electrons, by implementing the present invention, a light-emitting element that easily generates electrons and can stably supply electrons to the light-emitting layer can be obtained. By implementing the present invention, it is possible to obtain a light-emitting element that has higher conductivity than a layer made of only a phenanthroline derivative and has a small change in driving voltage accompanying an increase in the thickness of the layer. In addition, since a layer in which a phenanthroline derivative and a metal oxide used in the practice of the present invention are mixed is difficult to crystallize, a light-emitting element with less malfunction due to crystallization of the electron generating layer is obtained by implementing the present invention. be able to.

  Since the light-emitting element used for implementing the present invention has few malfunctions due to crystallization, a light-emitting device with few display defects caused by defects of the light-emitting element can be obtained by implementing the present invention.

  Since the light-emitting device used for carrying out the present invention uses a light-emitting element with few malfunctions due to crystallization, there are few display defects and the like. Therefore, by implementing the present invention, it is possible to obtain an electronic device in which there is little misidentification of an image due to display failure in the light emitting device and accurate information can be transmitted to the user through the display image.

  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 shows a light-emitting element having a hole-generating layer 111 between a first electrode 101 and a second electrode 102. Between the hole generating layer 111 and the second electrode 102, a hole transporting layer 112, a light emitting layer 113, an electron transporting layer 114, and an electron generating layer 115 are provided. When 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 has the first electrode Holes are injected from the 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.

  The electron generating layer 115 is a layer that generates electrons, and a phenanthroline derivative represented by the general formula (1) and a substance that exhibits an electron donating property with respect to the phenanthroline derivative represented by the general formula (1) are mixed. It consists of In the electron generating layer 115 having such a structure, the phenanthroline derivative represented by the general formula (1) receives electrons from a substance exhibiting an electron donating property. That is, the phenanthroline derivative represented by the general formula (1) is reduced, and electrons are generated.

In the general formula (1), R ^{1 to} R ⁵ each represents an alkyl group having 1 to 4 carbon atoms or a halogen group such as fluorine, chlorine, iodine, bromine, and at least one of R ^{1 to} R ⁵ is Represents a halogen group.

  Since the phenanthroline derivative represented by the general formula (1) has a halogen element such as fluorine as a substituent, it easily receives electrons. And by using such a phenanthroline derivative represented by the general formula (1), it becomes easy to generate electrons, and the supply of electrons to the light emitting layer can be stabilized. Further, by mixing a phenanthroline derivative and a substance that exhibits an electron donating property with respect to the phenanthroline derivative, the conductivity is improved as compared with a layer made of only the phenanthroline derivative. Therefore, by increasing the thickness of the electron generating layer 115, it is easy to adjust the optical path length and to reduce the unevenness of the electrode surface. In addition, since the electron generation layer 115 obtained by mixing a phenanthroline derivative and a substance that exhibits an electron donating property with respect to the phenanthroline derivative is difficult to crystallize, a device defect due to crystallization is unlikely to occur.

Of the phenanthroline derivatives represented by the general formula (1), a phenanthroline derivative having an electron mobility of 1 × 10 ⁻⁶ cm ² / Vs is particularly preferable. In addition, as a substance that exhibits an electron donating property with respect to the phenanthroline derivative represented by the general formula (1), 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. In addition, alkali metal oxide or alkaline earth metal oxide, alkali metal fluoride, alkaline earth metal fluoride, 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. By combining with these metal oxides and metal fluorides, crystallization of the electron generation layer 115 can be suppressed, and malfunction of the device due to crystallization can be reduced. Note that metal oxides and metal fluorides such as alkali metal oxides or alkaline earth metal oxides, alkali metal fluorides, and alkaline earth metal fluorides are preferable because they have low reactivity and are easy to handle.

The hole generating layer 111 is a layer that generates holes, and has at least one substance selected from a substance having a high hole transporting property and a bipolar substance, and has an electron accepting property for these substances. It is a layer formed by mixing with the substance shown. Here, among substances having a high hole-transport property and bipolar substances, a substance having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or more is particularly preferable. Note that a substance having a high hole-transport property has a higher hole mobility than an electron, and the ratio of the hole mobility to the electron mobility (= hole mobility / electron mobility) is 100. Larger than the substance. Specific examples of the substance having a high hole-transport property include 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (abbreviation: NPB), 4,4′-bis [N- ( 3-methylphenyl) -N-phenylamino] biphenyl (abbreviation: TPD), 4,4 ′, 4 ″ -tris (N, N-diphenylamino) 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), 1,3,5-tris [N, N-di (m-tolyl) amino] benzene (abbreviation: m-MTDAB), 4,4 ′ , 4 ″ -Tris (N-carbazolyl) trif Niruamin (abbreviation: TCTA), phthalocyanine _{(abbreviation:} H 2 Pc), copper phthalocyanine (abbreviation: CuPc), or vanadyl phthalocyanine (abbreviation: VOPc), and the like. In addition, a bipolar substance refers to the mobility of one carrier relative to the mobility of the other carrier when the mobility of one of the electrons or holes is compared with the mobility of the other carrier. A substance having a ratio value of 100 or less, preferably 10 or less. 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. There is no particular limitation on the substance exhibiting electron accepting properties, but it is preferable to use a metal oxide such as molybdenum oxide, vanadium oxide, ruthenium oxide, or rhenium oxide. However, other metal oxides such as titanium oxide, chromium oxide, zirconium oxide, hafnium oxide, tantalum oxide, tungsten oxide, and silver oxide may be used.

  The light emitting layer 113 includes 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, to obtain red light emission, 4-dicyanomethylene-2-isopropyl-6- [2- (1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] -4H-pyran ( Abbreviation: DCJTI), 4-dicyanomethylene-2-methyl-6- [2- (1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] -4H-pyran (abbreviation: DCJT), 4 -Dicyanomethylene-2-tert-butyl-6- [2- (1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] -4H-pyran (abbreviation: DCJTB), periflanthene, 2,5 -Dicyano-1,4-bis [2- (10-methoxy-1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] benzene, etc., emission spectrum from 600 nm to 680 nm Substance which exhibits emission with a peak can be used as a light-emitting substance. When green light emission is desired, N, N′-dimethylquinacridone (abbreviation: DMQd), coumarin 6, coumarin 545T, tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), etc., emits light from 500 nm to 550 nm. A substance that emits light having a spectral peak 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 at 420 nm to 500 nm, such as -8-quinolinolato) -4-phenylphenolato-aluminum (abbreviation: BAlq), can be used as the light-emitting substance. All of the light-emitting substances mentioned above emit fluorescent light. In addition, 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 ′} ) A substance that emits phosphorescence, such as iridium (abbreviation: Ir (ppy) 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 hole transport layer 112 has 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 hole generation layer 111 to the light-emitting layer 113. By providing the hole transport layer 112, the distance between the hole generation layer 111 and the light emitting layer 113 can be increased, and as a result, the light emission is quenched due to the metal contained in the hole generation layer 111. Can be prevented. The hole transport layer is preferably formed using a substance having a high hole transport property, and particularly preferably formed using a substance having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher. For specific examples of the substance having a high hole-transport property, the description of the specific examples of the substance having a high hole-transport property that can be used to form the hole-generating layer 111 is applied mutatis mutandis.

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 generation layer 115 to the light-emitting layer 113. By providing the electron transport layer 114, the distance between the electron generation layer 115 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 electron generation layer 115. be able to. The electron transport layer is preferably formed using a substance having a high electron transport property, and particularly preferably formed using a substance having an electron mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher. Note that a substance having a high electron-transport property has higher electron mobility than holes, and the ratio of the electron mobility to the hole mobility (= electron mobility / hole mobility) is 100 or more. Also refers to a large substance. Specific examples of a substance that can be used for forming the electron-transport layer 114 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- In addition to metal complexes such as (2-hydroxyphenyl) benzoxazolate] 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 (approximately) Name: 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), 4,4-bis (5-methylbenzoxa) Sol-2-yl) stilbene (BzOs) and the like.

Note that the hole transport layer 112 and the electron transport layer 114 may be formed using a bipolar substance in addition to the above substances. A bipolar substance is the ratio of the mobility of one carrier to the mobility of the other carrier when the mobility of one of the electrons or holes is compared with the mobility of the other carrier. A substance whose value is 100 or less, preferably 10 or less. 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. Alternatively, the hole transport layer 112 and the electron transport layer 114 may be formed using the same bipolar substance.

  The first electrode 101 is made of 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), or a material having a high work function such as tantalum nitride. Alternatively, it may be formed using a material having a low work function such as aluminum or magnesium. As described above, in the light-emitting element of this embodiment mode, the first electrode 101 can be formed without depending on the work function of the substance. This is because the hole generating layer 111 is provided between the first electrode 101 and the light emitting layer 113.

  For the second electrode 102, in addition to indium tin oxide, indium tin oxide containing silicon oxide, indium oxide containing zinc oxide, gold (Au), platinum (Pt), nickel (Ni), tungsten ( W, chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), tantalum nitride, or other high work function materials may be used. However, it may be formed using a material having a low work function such as aluminum or magnesium. As described above, in the light-emitting element of this embodiment mode, the second electrode 102 can be formed regardless of the work function of the substance. This is because the electron generating layer 115 is provided between the second electrode 102 and the light emitting layer 113.

Note that in this embodiment mode, a light-emitting element including the hole-transporting layer 112 and the electron-transporting layer 114 in addition to the hole-generating layer 111 and the light-emitting layer 113 has been described; however, the mode of the light-emitting element is not necessarily limited thereto. It is not a thing. For example, a light emitting element in which a hole injection layer 116 is provided instead of the hole generation layer 111 as shown in FIG. The hole injection layer 116 is a layer having a function of assisting injection of holes from the first electrode 101 to the hole transport layer 112. By providing the hole injection layer 116, the difference in ionization potential between the first electrode 101 and the hole transport layer 112 is reduced, and holes are easily injected. The hole injection layer 116 may be formed using a material having an ionization potential lower than that of the material forming the hole transport layer 112 and higher than that of the material forming the first electrode 101. preferable. Specific examples of a substance that can be used to form the hole-injection layer 116 include phthalocyanine-based compounds such as phthalocyanine (abbreviation: H ₂ Pc) and copper phthalocyanine (CuPC), or poly (ethylenedioxythiophene) / Examples thereof include a polymer such as a poly (styrenesulfonic acid) aqueous solution (PEDOT / PSS). Note that in the case where the hole injection layer 116 is provided, the first electrode 101 is preferably formed using a substance having a high work function such as indium tin oxide.

  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 material with a high ionization potential. That is, the hole blocking layer 117 may be formed 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 first electrode 101. .

  Note that whether or not the hole transport layer 112 and the electron transport layer 114 are provided may be appropriately selected by the practitioner of the invention. For example, the metal may be formed without the hole transport layer 112 and the electron transport layer 114. These layers are not necessarily provided when there is no problem such as quenching caused by extinction.

  The light emitting element of the present invention described above has little change in driving voltage depending on the thickness of the electron generating layer 115. Therefore, the distance between the light emitting layer 113 and the second electrode 102 can be easily adjusted by changing the thickness of the electron generating layer 115. 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 electron generating layer 115, unevenness on the surface of the second electrode 102 can be reduced, and a short circuit between the electrodes can be easily prevented.

  In addition, the light emitting element of the present invention has little change in driving voltage depending on the thickness of the hole generating layer 111. Therefore, it is easy to adjust the length of the optical path (optical path length) through which the emitted light passes by changing the thickness of the hole generating layer 111. In addition, by increasing the thickness of the hole generation layer 111, unevenness on the surface of the first electrode 101 can be reduced, and a short circuit between the electrodes can be easily prevented.

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

  FIG. 2 shows a light-emitting element having a first layer 211, a second layer 212, and a third layer 213 between the first electrode 201 and the second electrode 202. . The first layer 211 generates holes, and the second layer 212 generates electrons. The third layer 213 is formed by sequentially stacking an electron transport layer 221, a light emitting layer 222, a hole transport layer 223, and a hole generation layer 224. Here, the hole generation layer 224 is provided on the second electrode 202 side with respect to the light emitting layer 222, and the electron transport layer 221 is provided on the first electrode 201 side with respect to the light emitting layer 222. When voltage is applied to the first electrode 201 and the second electrode so that the potential of the first electrode 201 is lower than the potential of the second electrode 202, the first layer 211 moves to the first electrode 201. Holes are injected. Further, electrons from the second layer 212 and holes from the second electrode 202 are injected into the third layer 213, respectively. The electrons and holes injected into the third layer 213 are recombined in the light emitting layer 222. The light-emitting layer 222 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.

The first layer 211 and the hole generation layer 224 are layers that generate holes, respectively. It is a layer formed by mixing at least one substance selected from a substance having a high hole transporting property and a bipolar substance, and a substance showing an electron accepting property with respect to these substances. Here, among substances having a high hole-transport property and bipolar substances, a substance having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or more is particularly preferable. Note that a substance having a high hole-transport property has a higher hole mobility than an electron, and the ratio of the hole mobility to the electron mobility (= hole mobility / electron mobility) is 100. Larger than the substance. As for specific examples of the substance having a high hole-transport property and the bipolar substance, the description of the specific examples of the substance that can be used for forming the hole-transport layer 112 in Embodiment 1 is applied mutatis mutandis. There is no particular limitation on the substance exhibiting electron accepting properties, but it is preferable to use a metal oxide such as molybdenum oxide, vanadium oxide, ruthenium oxide, or rhenium oxide. However, other metal oxides such as titanium oxide, chromium oxide, zirconium oxide, hafnium oxide, tantalum oxide, tungsten oxide, and silver oxide may be used.

  The second layer 212 is a layer that generates electrons, and a phenanthroline derivative represented by the general formula (1) and a substance that exhibits an electron donating property with respect to the phenanthroline derivative represented by the general formula (1) are mixed. Made up. In the second layer 212 having such a structure, the phenanthroline derivative represented by the general formula (1) receives electrons from a substance exhibiting an electron donating property. That is, the phenanthroline derivative represented by the general formula (1) is reduced, and electrons are generated.

In the general formula (1), R ^{1 to} R ⁵ each represents an alkyl group having 1 to 4 carbon atoms or a halogen group such as fluorine, chlorine, iodine, bromine, and at least one of R ^{1 to} R ⁵ is Represents a halogen group.

  Since the phenanthroline derivative represented by the general formula (1) has a halogen element such as fluorine as a substituent, it easily receives electrons. And by using such a phenanthroline derivative represented by the general formula (1), it becomes easy to generate electrons, and the supply of electrons to the light emitting layer can be stabilized. Further, by mixing a phenanthroline derivative and a substance that exhibits an electron donating property with respect to the phenanthroline derivative, the conductivity is improved as compared with a layer made of only the phenanthroline derivative. Therefore, by increasing the thickness of the second layer 212, it is easy to adjust the optical path length and reduce the unevenness of the electrode surface. In addition, since the electron generation layer 115 obtained by mixing a phenanthroline derivative and a substance that exhibits an electron donating property with respect to the phenanthroline derivative is difficult to crystallize, a device defect due to crystallization is unlikely to occur.

Of the phenanthroline derivatives represented by the general formula (1), a phenanthroline derivative having an electron mobility of 1 × 10 ⁻⁶ cm ² / Vs is particularly preferable. In addition, as a substance that exhibits an electron donating property with respect to the phenanthroline derivative represented by the general formula (1), 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. Moreover, alkali metal oxides such as lithium oxide (Li ₂ O), sodium oxide (Na ₂ O), and potassium oxide (K ₂ O), calcium oxide (CaO), magnesium oxide (MgO), etc. Alkaline earth metal oxides and the like can also be used as a substance exhibiting electron donating properties. Further, alkali metal fluorides such as lithium fluoride (LiF) and cesium fluoride (CsF), alkaline earth metal fluorides such as calcium fluoride (CaF ₂ ), and alkaline earths such as calcium nitride (Ca ₃ N ₂ ) A metal nitride or the like can also be used as a substance exhibiting an electron donating property. At least one substance selected from alkali metals, alkaline earth metals, alkali metal oxides, alkaline earth metal oxides, alkali metal fluorides, alkaline earth metal fluorides, and alkaline earth metal nitrides; By combining (mixing) with the phenanthroline derivative represented by the general formula (1), crystallization of the electron generation layer 115 can be suppressed, and malfunction of the device due to crystallization can be reduced. Note that metal compounds such as alkali metal oxides, alkaline earth metal oxides, alkali metal nitrides, and alkaline earth metal nitrides are preferable because of low reactivity and easy handling.

The electron transport layer 221 is a layer having a function of transporting electrons. In the light-emitting element of this embodiment mode, the electron transport layer 221 has a function of transporting electrons from the second layer 212 to the light-emitting layer 222. By providing the electron transport layer 221, the distance between the second layer 212 and the light emitting layer 222 can be increased, and as a result, light emission is quenched due to the metal contained in the second layer 212. Can be prevented. The electron transport layer is preferably formed using a substance having a high electron transport property, and particularly preferably formed using a substance having an electron mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher. For specific examples of the substance that can be used for forming the electron-transport layer 221, the description of the specific examples of the substance that can be used for forming the electron-transport layer 114 in Embodiment 1 is applied mutatis mutandis.

  The light emitting layer 222 contains a light emitting substance. The light-emitting layer 222 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 made 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 222 in a dispersed manner, light emission can be prevented from being quenched due to concentration. Note that the description of the light-emitting substance in Embodiment 1 is applied to the light-emitting substance. Here, a substance that is included in the light-emitting layer 222 together with the light-emitting substance and is used for dispersing the light-emitting substance is included in the light-emitting layer 113 together with the light-emitting substance described in Embodiment 1 and the light-emitting substance is dispersed. The description of substances used for this purpose shall apply mutatis mutandis.

The hole transport layer 223 is a layer having a function of transporting holes. In the light-emitting element of this embodiment mode, the hole transport layer 223 has a function of transporting holes from the hole generation layer 224 to the light-emitting layer 222. By providing the hole-transporting layer 223, the distance between the hole-generating layer 224 and the light-emitting layer 222 can be increased. As a result, light emission is quenched due to the metal contained in the hole-generating layer 224. Can be prevented. The hole-transport layer 223 is preferably formed using a substance having a high hole-transport property, and particularly preferably formed using a substance having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher. . For specific examples of the substance that can be used for forming the hole-transport layer 223, the description of the specific examples of the substance that can be used for forming the hole-transport layer 112 in Embodiment 1 is applied mutatis mutandis. .

  The first electrode 201 is made of 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), or a material having a high work function such as tantalum nitride. Alternatively, it may be formed using a material having a low work function such as aluminum or magnesium. As described above, in the light-emitting element of this embodiment mode, the first electrode 201 can be formed without depending on the work function of the substance. This is because the first layer 211 and the second layer 212 are provided between the first electrode 201 and the light-emitting layer 222.

  Further, for the second electrode 202, in addition to indium tin oxide, indium tin oxide containing silicon oxide, indium oxide containing 2 to 20% zinc oxide, gold (Au), platinum (Pt), nickel ( Using a material having a high work function such as Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), and tantalum nitride. You may form using a substance with low work functions, such as aluminum and magnesium. As described above, in the light-emitting element of this embodiment mode, the second electrode 202 can be formed without depending on the work function of the substance. This is because the hole generating layer 224 is provided between the second electrode 202 and the light emitting layer 222.

Note that this embodiment mode shows a light-emitting element in which the third layer 213 that includes a light-emitting substance is a multilayer including an electron-transport layer 221, a light-emitting layer 222, a hole-transport layer 223, and a hole-generation layer 224. The mode of the light emitting element is not necessarily limited to this. For example, a light emitting element in which a hole injection layer 225 is provided instead of the hole generation layer 224 as shown in FIG. The hole injection layer 225 is a layer having a function of assisting injection of holes from the second electrode 202 to the hole transport layer 223. By providing the hole injection layer 225, the difference in ionization potential between the second electrode 202 and the hole transport layer 223 is reduced, and holes are easily injected. The hole injection layer 225 may be formed using a material having a lower ionization potential than the material forming the hole transport layer 223 and a higher ionization potential than the material forming the second electrode 202. preferable. That is, as a specific example of a substance that can be used to form the hole injection layer 225, a phthalocyanine-based compound such as phthalocyanine (abbreviation: H ₂ Pc) or copper phthalocyanine (CuPC), or poly (ethylenedioxythiophene) ) / Poly (styrenesulfonic acid) aqueous solution (PEDOT / PSS) and the like. Note that in the case where the hole injection layer 225 is provided, the second electrode 202 is preferably formed using a substance having a high work function such as indium tin oxide.

  Further, a hole blocking layer 226 may be provided between the light emitting layer 222 and the electron transporting layer 221 as shown in FIG. By providing the hole-blocking layer 226, holes can be prevented from penetrating the light-emitting layer 222 and flowing toward the first electrode 201, and the carrier recombination efficiency can be increased. In addition, the excitation energy generated in the light-emitting layer 222 can be prevented from moving to another layer such as the electron transport layer 221. The hole blocking layer 226 is formed of a material that can be used to form the electron transport layer 221 such as BAlq, OXD-7, TAZ, or BPhen, and more particularly than a material that is used to form the light emitting layer 222. It can be formed by selecting a material with a high ionization potential. That is, the hole blocking layer 117 may be formed so that the ionization potential in the hole blocking layer 226 is relatively larger than the ionization potential in the electron transport layer 221. Similarly, a layer may be provided between the light-emitting layer 222 and the hole transport layer 223 so as to prevent electrons from passing through the light-emitting layer 222 and flowing toward the second electrode 202. .

  Note that whether or not to provide the hole transport layer 223 and the electron transport layer 221 may be appropriately selected by the practitioner of the invention. For example, even if the hole transport layer 223 and the electron transport layer 221 are not provided, the metal may be used. These layers are not necessarily provided when there is no problem such as quenching caused by extinction.

  In the light-emitting element as described above, the electron affinity of the substance having a high electron-transport property included in the second layer 212 and the layer in contact with the second layer 212 among the layers included in the third layer 213 The difference from the electron affinity of the contained substance is preferably 2 eV or less, more preferably 1.5 eV or less. More specifically, when the second layer 212 and the electron transport layer 221 are in contact with each other as in the light-emitting element illustrated in FIG. 2, the electron transporting substance contained in the second layer 212 and the electron The difference in electron affinity from the substance having an electron transporting property contained in the transport layer 221 is preferably 2 eV or less, and more preferably 1.5 eV or less. In this manner, by bonding the second layer 212 and the third layer 213, electrons can be efficiently injected from the second layer 212 to the third layer 213.

  The light-emitting element of the present invention described above is an element in which a change in driving voltage depending on the thickness of the second layer 212 is small. Therefore, the distance between the light emitting layer 222 and the first electrode 201 can be easily adjusted by changing the thickness of the second layer 212. 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.

(Embodiment 3)
The light-emitting element of the present invention can reduce malfunction caused by crystallization of a compound. One of the light-emitting elements of the present invention can prevent a short circuit between electrodes by increasing the thickness of the electron generating layer. In the light-emitting element of the present invention, the optical path length can be adjusted by changing the thickness of the electron generation layer to increase the efficiency of external extraction 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 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 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, a current value supplied from the current supply line 917 to the light-emitting element 903 is determined by a signal input to the second transistor 902. Then, depending on the current value, 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, 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, a current input 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.

  The gate signal line 911 and the erasing gate signal line driving circuit 914 are immediately disconnected 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 switch 920 is switched to connect the source signal line 912 and the source signal line driver circuit 915. Then, the source signal line and the source signal line driver circuit 915 are connected, and the gate signal line 911 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 starts. For this purpose, the gate signal line 911 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 911 and the writing gate signal line driving circuit 913 are disconnected, and the gate signal line 911 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, immediately after the erasing period of the (n + 1) th row is completed, the writing period of the (m + 1) th row is started. 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 4)
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 is a light emitting element of the present invention having a layer 15 in which a hole generating layer, an electron generating layer, and a layer containing a light emitting substance are stacked between a first electrode 13 and a second electrode 14. . 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). Note that 21 is a gate electrode, 22 is a gate insulating film, 23 is a semiconductor layer, 24 is an n-type semiconductor layer, 25 is an electrode, and 26 is a protective film.

  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 in the range of approximately 0.1 Pa to 133 Pa, the power frequency is 1 MHz to 120 MHz, preferably 13 MHz to 60 MHz, and 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. 11A 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 a skeleton structure composed of a bond of acrylic or siloxane (silicon (Si) and oxygen (O), and has a substituent such as hydrogen or an alkyl group. And a compound having a self-flatness such as silicon oxide that can be formed by coating. 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. Thus, the 1st interlayer insulation film 16 may be formed using both an inorganic substance or an organic substance, or may be formed by either 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.

  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 self-flattening material such as acrylic, siloxane, or silicon oxide that can be coated and formed. 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 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; 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 in which a layer containing a light-emitting substance, an electron generation layer, and a hole generation layer are sequentially stacked is provided over a substrate 951 between an electrode 952 and an electrode 956. 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 (side facing the surface direction of the insulating layer 953 and in contact with the insulating layer 953) is the top side (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 5)
A light-emitting device using the light-emitting element of the present invention as a pixel has a good display operation with few display defects due to an operation failure of the light-emitting element. 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, such a light emitting device is used as an illumination unit such as a backlight, and by mounting the light emitting device of the present invention in this way, a dark portion is locally formed due to a defect of the light emitting element. Such malfunctions can be reduced and a good display can be achieved.

  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. A personal computer can be completed by incorporating a light-emitting device using the light-emitting element of the present invention as a pixel as shown in FIG. 7 as a display portion. 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 shown in FIG. 14, a liquid crystal device 5512 and a light-emitting device 5513 provided with at least one light-emitting element of the present invention are fitted in a display portion of a personal computer, as shown in FIG. Thus, a personal computer using the light emitting element of the present invention as a light source can be completed. 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. In the light emitting device, a plurality of the light emitting elements of the present invention may be arranged, or one light emitting element may be provided so as to cover most of the substrate. In the light-emitting device 5513, the color of light emitted from the light-emitting element is not particularly limited, and may be white, red, blue, green, or the like.

  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. 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. 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. 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 the electronic device is not limited to that described in this embodiment, and may be another electronic device such as a navigation device.

  5,8-bis [2- (3-fluorophenyl) ethenyl] -6,7-dihydrodibenzo [b, j] -1,10 represented by Structural Formula (2) and can be used in the practice of the present invention -The synthesis | combining method of phenanthroline is demonstrated.

[Step 1]
First, a compound represented by the structural formula (3), 5,8-dimethyl-6,7-dihydrodibenzo [b, j] -1,10-phenanthroline, is synthesized.

  A catalytic amount (about 5 mol%) of p-toluenesulfone in a solution of 2′-aminoacetophenone (24.6 g, 182 mmol) and 1,2-cyclohexadione (10.2 g, 91 mmol) in ethylene glycol monoethyl ether (100 mL). Acid monohydrate was added, and the mixture was heated to reflux for 48 hours (Synthesis scheme (a-1)). The reaction solution was cooled to room temperature, and the precipitated solid was filtered. The filtrate was recrystallized from tetrahydrofuran to obtain the compound in 38% yield. When the obtained compound was measured by NMR, it was confirmed that it was 5,8-dimethyl-6,7-dihydrodibenzo [b, j] -1,10-phenanthroline.

The NMR data of the obtained compound are shown below.
¹ H NMR (300 MHz, CDCl ₃ ) δ 8.43 (d, 2H, J = 8.4 Hz), 7.97 (d, 2H, J = 8.0 Hz), 7.66 (dd, 2H, J = 8) .4, 15 Hz), 7.53 (dd, 2H, J = 8.0, 15 Hz), 3.19 (s, 4H), 2.67 (s, 6H).

[Step 2]
A method for synthesizing the compound represented by the structural formula (2), 5,8-bis [2- (3-fluorophenyl) ethenyl] -6,7-dihydrodibenzo [b, j] -1,10-phenanthroline is described below. Shown in

  A compound represented by the structural formula (3), 5,8-dimethyl-6,7-dihydrodibenzo [b, j] -1,10-phenanthroline (7.7 g, 25 mmol), and 3-fluorobenzaldehyde (9.2 g). , 74 mmol) in acetic anhydride (about 50 mL) was heated to reflux for 36 hours (synthesis scheme (a-2)). The reaction solution was basified with 10% aqueous sodium hydroxide solution and extracted with ethyl acetate. The organic layer was dried over magnesium sulfate, filtered and concentrated, and the residue was purified twice by alumina chromatography (developing solvent, methylene chloride) to obtain a compound. Further, the obtained compound was purified using preparative liquid chromatography (manufactured by Nippon Analysis Co., Ltd., recycle preparative HPLC, LC-908W-C60 type, developing solvent chloroform), and then recrystallized with a hexane / ethyl acetate mixed solvent. As a result, the compound was obtained in a yield of 15%. The compound thus obtained was measured by NMR and found to be 5,8-bis [2- (3-fluorophenyl) ethenyl] -6,7-dihydrodibenzo [b, j] -1,10-phenanthroline. It was confirmed that.

NMR data is shown below.
¹ H NMR (300 MHz, CDCl ₃ ) δ 8.49 (d, 2H, J = 8.7 Hz), 6.08 (d, 2H, J = 8.4 Hz), 7.26-7.80 (m, 12H) ), Δ 7.07 (dd, 2H, J = 7.2, 17.0 Hz), 6.83 (d, 2H, J = 17.0 Hz), 3.28 (s, 4H).

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.

Explanation of symbols

101 1st electrode 102 2nd electrode 111 Hole generation layer 112 Hole transport layer 113 Light emitting layer 114 Electron transport layer 115 Electron generation layer 116 Hole injection layer 117 Hole blocking layer 201 1st electrode 202 2nd Electrode 211 First layer 212 Second layer 213 Third layer 221 Electron transport layer 222 Light emitting layer 223 Hole transport layer 224 Hole generation layer 225 Hole injection layer 226 Hole blocking layer 6500 Substrate 6503 FPC
6504 Printed wiring board 6511 Pixel portion 6512 Source signal line drive circuit 6513 Write gate signal line drive circuit 6514 Erase gate signal line drive circuit 901 Transistor 902 Transistor 903 Light emitting element 911 Gate signal line 912 Source signal line 913 Write gate Signal line drive circuit 914 Erase gate signal line drive circuit 915 Source signal line drive circuit 916 Power supply 917 Current supply line 918 Switch 919 Switch 920 Switch 1001 Transistor 1002 Transistor 1003 Gate signal line 1004 Source signal line 1005 Current supply line 1006 Electrode
501 subframe 502 subframe 503 subframe 504 subframe 501a period 501b holding period 502a period 502b holding period 503a period 503b holding period 504a period 504b holding period 504c erasing period 504d non-light emitting period 10 substrate 11 transistor 12 light emitting element 13 first Electrode 14 Second electrode 15 Layer 16 Interlayer insulating film 17 Wiring 18 Partition layer 19 Interlayer insulating film 951 Substrate 952 Electrode 956 Electrode 955 Layer 953 Insulating layer 954 Partition layer 953 Insulating layer 5521 Body 5522 Housing 5523 Display unit 5524 Keyboard 5511 Enclosure Body 5512 Liquid crystal device 5513 Light emitting device 5514 Housing 5515 External input terminal 5516 External input terminal 5551 Display unit 5552 Body 5553 Antenna 5554 Audio output unit 5555 Audio input 5556 Operation switch 5531 Display 5532 Housing 5533 Speaker

Claims (9)

Between the first electrode and the second electrode,
A layer containing a phenanthroline derivative represented by the general formula (1) and a substance exhibiting an electron donating property to the phenanthroline derivative;
A layer containing a luminescent material;
A light-emitting element including:

(Wherein R ^{1 to} R ⁵ each represent an alkyl group having 1 to 4 carbon atoms or a halogen group, and at least one of R ^{1 to} R ⁵ represents a halogen group.)   The electron-donating substance is at least one metal oxide selected from alkali metal oxides, alkaline earth metal oxides, alkali metal fluorides, and alkaline earth fluorides. Item 2. A light emitting device according to Item 1. Between the first electrode and the second electrode,
A first layer, a second layer, and a third layer;
The first layer includes a first substance having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher, and a second substance having an electron accepting property with respect to the first substance,
The second layer includes a layer containing a luminescent material;
The third layer includes a phenanthroline derivative represented by the general formula (1) and a third substance that exhibits an electron donating property to the phenanthroline derivative.

(Wherein R ^{1 to} R ⁵ each represent an alkyl group having 1 to 4 carbon atoms or a halogen group, and at least one of R ^{1 to} R ⁵ represents a halogen group.) The second substance is at least one substance selected from molybdenum oxide, vanadium oxide, and ruthenium oxide,
The third material is at least one material selected from an alkali metal oxide, an alkaline earth metal oxide, an alkali metal nitride, and an alkaline earth nitride. Light emitting element. Between the first electrode and the second electrode,
A first layer, a second layer, and a third layer;
The first layer includes a first substance having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher, and a second substance having an electron accepting property with respect to the first substance,
The second layer includes a phenanthroline derivative represented by the general formula (1) and a third substance that exhibits an electron donating property to the phenanthroline derivative.
The third layer includes a luminescent material;
The first layer is provided closer to the first electrode than the second layer;
The third layer is provided closer to the second electrode than the second layer;
The second layer and the third layer are formed from the second layer when the voltage is applied so that the potential of the first electrode is lower than the potential of the second electrode. A light-emitting element, which is bonded so that electrons are injected into the layer 3.

(Wherein R ^{1 to} R ⁵ each represent an alkyl group having 1 to 4 carbon atoms or a halogen group, and at least one of R ^{1 to} R ⁵ represents a halogen group.) Between the first electrode and the second electrode,
A first layer, a second layer, and a third layer;
The first layer includes a first substance having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher, and a second substance having an electron accepting property with respect to the first substance,
The second layer includes a phenanthroline derivative represented by the general formula (1) and a third substance that exhibits an electron donating property to the phenanthroline derivative.
The third layer includes an electron transport layer, a light emitting layer, a hole transport layer, and a hole generation layer,
The first layer is provided closer to the first electrode than the second layer;
The third layer is provided closer to the second electrode than the second layer;
The light emitting element, wherein the second layer and the electron transport layer are in contact with each other.

(Wherein R ^{1 to} R ⁵ each represent an alkyl group having 1 to 4 carbon atoms or a halogen group, and at least one of R ^{1 to} R ⁵ represents a halogen group.) The second substance is at least one substance selected from molybdenum oxide, vanadium oxide, and ruthenium oxide,
The third material is at least one material selected from an alkali metal oxide, an alkaline earth metal oxide, an alkali metal fluoride, and an alkaline earth fluoride. Item 7. A light emitting device according to Item 6.   A light-emitting device using the light-emitting element according to claim 1 as a pixel or a light source. An electronic apparatus using the light-emitting device according to claim 8 for a display portion.

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