JP2001291592A - Light emission device and electric fixture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means to enhance a recombination efficiency of a carrier, and provide a light emission device of a high luminous efficiency. SOLUTION: An electron capture region 106 and a hole capture region 107 are formed on the inside of a luminous layer 103. The electron capture region 107 has an action of confining electrons, that have been transported on the lowest unoccupied molecular orbital(LUMO) level of luminous layer 103 in the luminous layer, and the hole capture region 107 has the action of confining holes that have been transported on the highest occupied molecular orbital(HOMO) level of luminous layer 103 in the luminous layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light emitting device using a light emitting organic film. Further, the present invention relates to an electric appliance using the light emitting device as a display portion or a light source. Note that the light-emitting organic film that can be used in the present invention includes all organic films that emit light (phosphorescence and / or fluorescence) via singlet excitation or triplet excitation or both excitations.

[0002]

2. Description of the Related Art In recent years, a light-emitting device (hereinafter, referred to as an EL device) using a light-emitting element (hereinafter, referred to as an EL element) using a light-emitting organic film (hereinafter, referred to as an organic EL film) capable of obtaining EL (Electro Luminescence). Is being developed. An EL light emitting device has an EL element having a structure in which an organic EL film is sandwiched between an anode and a cathode, and emits light by applying a voltage between the anode and the cathode.

At this time, holes (holes) from the anode are E
Injected into the L material and electrons (electrons) from the cathode
Is injected into the organic EL film. Charges (carriers) injected from the electrodes move inside the organic EL film and recombine. Recombination produces excited states, some of which are converted to photons. When this photon is taken out, it can be visually recognized as light emission.

[0004] Such a conventional light emitting mechanism is shown in FIG.
It is shown in (B). FIG. 2A shows a conventional EL element junction structure, in which 201 is a cathode, 202 is an electron transport layer, and 203 is a light emitting layer (Emi).
ssion layer), 204 is a hole transport layer (Hole Transfer L)
ayer) and 205 are anodes. FIG.
(B) shows the carrier injection process. When a voltage is applied between the cathode 201 and the anode 205, electrons 206 and holes 207 are injected and recombined, and light emission 208 is obtained.

Considering such a light emission mechanism, the efficiency of light emitted from the EL element, that is, the light emission efficiency (expressed as η (light emission)) is expressed by the following equation. η (emission) = η (injection) × η (recombination) × η (excitation) ×
η (quantum) where η (injection) is the efficiency when carriers are injected from the electrode, η (recombination) is the efficiency at which electrons and holes recombine,
η (excitation) is the efficiency at which singlet excitons are generated by recombination, and η (quantum) is the efficiency at which singlet excitons are converted to photons.

[0006] η (injection) is the cathode (or anode) and EL
It changes due to the potential barrier at the interface with the material, and the lower the potential barrier, the higher the efficiency. Further, η (recombination) changes depending on the carrier injection balance (balance of the ratio of injected electrons and holes), and is affected by the carrier transport characteristics of the light emitting layer (the organic EL film that actually emits light). Also, η
(Excitation) is the generation efficiency of singlet excitons that contribute to light emission, and is theoretically determined to be about 0.25. Further, η (quantum) changes depending on whether the light emitting layer is crystalline or amorphous, and a higher value is generally obtained for crystalline.

Further, most of the photons generated in the light emitting layer are lost by scattering or heat deactivation (about 80% is lost) before being extracted to the outside. This includes losses. As described above, EL
In the process of the light emitting mechanism of the device, the luminous efficiency is reduced by various factors. The only way to obtain high luminous efficiency is to increase the various efficiencies described above and seek a comprehensively high luminous efficiency.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide means for increasing the recombination efficiency of carriers in an EL element, and to provide a light emitting device having high luminous efficiency. Another object is to provide an electric appliance using such a light-emitting device as a display portion or a light source.

[0009]

SUMMARY OF THE INVENTION The present invention focuses on the band structure of an EL element in order to improve the recombination efficiency of electrons and holes (expressed as η (recombination)). By confining holes, the probability of recombination is increased, and the recombination efficiency is enhanced. Therefore, FIG.
An EL element having a band structure as shown in FIG.

In FIG. 1A, reference numeral 101 denotes a cathode, 10
2 is an electron transport layer, 103 is a light emitting layer, 104 is a hole transport layer, and 105 is an anode. An electron trapping region (Electron Trap Region) 106 and a hole trapping region (Hole Trap Region) 107 are formed inside the light emitting layer 103.
Note that a structure in which one of the electron capture region 106 and the hole capture region 107 is provided may be employed.

Here, the electron capture region 106 is formed in the light emitting layer 1
03 is a region having an effect of confining electrons transported to the lowest unoccupied molecular orbital (LUMO) level of the light-emitting layer 103 in the light-emitting layer, and a LUMO level lower than the LUMO level of the light-emitting layer 103.
Refers to a region indicating a level. Further, the hole capture region 107 is
This region has a function of confining holes transported to the highest occupied molecular orbital (HOMO) level of the light-emitting layer 103 in the light-emitting layer, and has a higher H than the HOMO level of the light-emitting layer 103.
Refers to a region showing the OMO level.

The electron capture region 106 can be formed by a structure in which an organic film or an organic cluster acting to lower the LUMO level is interposed between the light emitting layers 103. Further, the hole-trapping region 107 can be formed by a structure in which an organic film or a cluster of organic substances acting to increase the HOMO level is sandwiched between the light-emitting layers 103.

The electron transport layer 102 and the hole transport region 107 are provided at the same time as the electron transport layer 102 is provided.
A hole blocking layer may be provided between the light emitting layer 103 and
An electron blocking layer may be provided between the light emitting layer 103 and the hole transport layer 104. Of course, a structure in which both the hole blocking layer and the electron blocking layer are provided may be employed.

With the band structure as shown in FIG. 1A, a carrier injection process as shown in FIG. 1B is performed. That is, the electrons 108 transported at the LUMO level are confined in the electron capture region 106 provided inside the light emitting layer 103. On the other hand, the holes 109 transported at the HOMO level are confined in the hole capture region 107. As a result, recombination of the electrons 108 and the holes 109 occurs between the electron capturing region 106 and the hole capturing region 107, and light emission is obtained.

At this time, in the present invention, recombination is performed in a state where electrons or holes are confined in the trapping region, so that recombination efficiency (η (recombination)) can be improved as compared with the conventional example. The idea of forming a level well inside the light emitting layer to confine carriers can be said to be an idea that has not existed in the past.

As described above, by implementing the present invention, among several parameters contributing to the luminous efficiency, the efficiency due to recombination (η (recombination)) is improved, and the luminous efficiency of the EL element is improved. I do. Therefore, the driving voltage of the EL element can be set low to obtain the same luminance as in the related art.
Low power consumption of the light emitting device can be achieved. Further, by lowering the driving voltage, the deterioration of the organic EL film is suppressed and the reliability is improved.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In this embodiment, a structure of an EL element for obtaining a band structure shown in FIG. 1A will be described with reference to FIG. FIG. 3A schematically illustrates a cross-sectional structure of a pixel of an active matrix light-emitting device.

In FIG. 3A, reference numeral 301 denotes a substrate;
2 is a TFT (thin film transistor), 303 is a pixel electrode, and the pixel electrode 303 functions as an anode of an EL element. As the substrate 301, a glass substrate or a plastic substrate (including a plastic film) may be used. Also, TF
For T302, a TFT having any structure may be used, and a planar TFT or an inverted staggered TFT can be used. The pixel electrode 303 may be formed using a transparent conductive film having a large work function, typically, a compound film of indium oxide and tin oxide or a compound film of indium oxide and zinc oxide.

Reference numeral 304 denotes an insulating film for preventing the EL material from being formed on the steps of the pixel electrode, and includes an insulating film containing silicon (a silicon oxide film, a silicon oxynitride film, or a silicon nitride film) or an organic resin. It is possible to use a membrane.

The organic EL layer 305 may be a single layer or a stacked organic EL film. That is, the organic EL film may be used as a single layer to form a light emitting layer, or various organic films may be combined and stacked, each of which may be a hole transport layer (including a hole injection layer), a hole blocking layer, and a light emitting layer. It can also function as either an electron blocking layer or an electron transporting layer (including an electron injection layer).

The cathode 306 is preferably made of a material having a small work function, and is made of a material containing an element belonging to Group 1 or 2 of the periodic table. Typically, an alloy film of aluminum and lithium or an alloy film of magnesium and silver may be used. Of course, any other combination of conductive films may be used.

Here, FIG. 3B shows an enlarged structure of a region indicated by 307 in FIG. In this embodiment mode, the organic EL layer 305 includes a hole transport layer 308,
The light emitting layer 309 and the electron transport layer 310 are formed. Further, the light-emitting layer 309 includes a light-emitting layer 309a, a light-emitting layer 309b,
The light emitting layer 309c has a three-layer structure. Of course, the light emitting layer 309a, the light emitting layer 309b, and the light emitting layer 309c are all the same organic EL film. Further, an organic cluster 311 is formed at the interface between the light emitting layer 309a and the light emitting layer 309b, and an organic cluster 312 is formed at the interface between the light emitting layer 309b and the light emitting layer 309c.

Here, the organic material cluster 311 forms a hole capturing region, and the organic material cluster 312 forms an electron capturing region. However, by changing the material, it is also possible to form an electron capture region with the organic material cluster 311 and to form a hole capture region with the organic material cluster 312.

The organic EL layer 305 shown here is formed by an evaporation method,
It may be formed by a coating method (spin coating method, dip method, LB method or knife edge method) or a printing method. However, it is desirable that the organic clusters 311 and 312 be formed by an evaporation method. Further, the clusters of the organic substance may be provided regularly or irregularly. Further, the shape may be a flat shape or a granular shape. Needless to say, the present invention is not limited to the above film formation method, and any film formation method may be used as long as the structure shown in FIG. 3B can be formed.

The organic E having the structure as in this embodiment
In the EL device having the L layer, holes injected from the anode 304 are trapped by the organic cluster 311 and the holes are injected into the cathode 30.
The electrons injected from 6 are captured by the organic cluster 312. This is the HOM in the organic cluster 311
This is because the O level is high and the LUMO level is low in the organic substance cluster 312.

Therefore, the electrons and holes confined in the well of the local potential (energy level) are recombined with high efficiency, and the luminous efficiency of the entire EL element is improved. As a result, a light-emitting device with low power consumption and high reliability can be obtained.

It is to be noted that a fluorescent substance may be added to the light emitting layer 309 to shift the emission center to the fluorescent substance. In the case of color development, three types of light-emitting layers of R (red), G (green), and B (blue) may be formed side by side for each pixel, or a white light-emitting layer may be formed of a color. Filters may be combined. Further, a color conversion layer (CCM) and a color filter may be combined with the blue light emitting layer. It is also possible to use a technique called a photobleaching technique (a technique utilizing a phenomenon in which a fluorescent dye is deteriorated by light irradiation).

In this embodiment mode, an active matrix type light emitting device in which a TFT and an EL element are electrically connected has been described as an example. However, the present invention may be applied to a passive matrix type light emitting device. Further, it can be used as a light source serving as a backlight of a liquid crystal display or a backlight of a fluorescent display lamp.

[0029]

Embodiment 1 In this embodiment, FIG. 4 shows an example in which an organic film is used instead of the organic clusters 311 and 312 shown in FIG. Note that the structure of the light-emitting device is similar to that of FIG.

In the present embodiment, the organic film 4 acting to lower the LUMO level to form an electron capture region is formed.
01 or a structure in which an organic film 402 acting to increase the HOMO level in order to form a hole trapping region is provided. Both of the organic films 401 and 402 may be provided, or one of them may be provided. The thickness of the organic films 401 and 402 may be set to 10 to 50 nm (preferably, 20 to 30 nm).

Also in the structure of this embodiment, holes are captured by the organic film 401 and electrons are captured by the organic film 402, so that the recombination efficiency can be improved,
The drive voltage of the L element can be reduced. That is, a light-emitting device with low power consumption and high reliability can be obtained.

[Embodiment 2] In the structure shown in FIG. 3B, an organic material cluster 311 serving as a hole-capturing region is provided on the anode 303 side, and an organic material cluster 312 serving as an electron-capturing region is provided on the cathode 306 side. , But this arrangement may be reversed. That is, the organic substance cluster 311 serving as a hole capture region may be provided on the cathode 306 side, and the organic material cluster 312 serving as an electron capture region may be provided on the anode 303 side.

Similarly, in the structure shown in FIG. 4, an organic film 401 serving as a hole capturing region is provided on the cathode 306 side, and an organic film 402 serving as an electron capturing region is provided on the anode 303 side. It does not matter.

Embodiment 3 In this embodiment, a light emitting device using an EL element having a band structure different from that of FIG. 1A will be described with reference to FIG. In FIG. 5, FIG.
The only difference is that the light emitting layer 500 is the same.

The structure of this embodiment shown in FIG. 5A has an electron trapping region 501 and a hole blocking region 5 inside a light emitting layer 500.
02, characterized in that a hole trapping region 503 and an electron blocking region 504 are formed. Here, the hole blocking region is a region serving as a potential barrier for preventing the movement of the holes 109 to the cathode 101 side, and the electron blocking region is a potential barrier for preventing the movement of the electrons 108 to the anode 105 side. Area.

In this embodiment, the electron trapping region 501 and the hole blocking region 502 are formed of the same organic material, and the hole trapping region 503 and the electron blocking region 504 are formed of the same organic material. The same organic substance is an organic film or a cluster of organic substances. In this embodiment, the LUMO level and the HO
It is necessary to use an organic substance having an action of lowering the MO level and an organic substance having an action of increasing the LUMO level and the HOMO level. At this time, the electron trapping region 501 is formed by an organic substance having a function of lowering the LUMO level and the HOMO level.
In addition, a hole blocking region 502 is formed, and a hole trapping region 503 and an electron blocking region 504 are formed by an organic substance having a function of increasing the LUMO level and the HOMO level.

In this embodiment, an example is shown in which four regions, ie, the electron trapping region 501, the hole blocking region 502, the hole trapping region 503, and the electron blocking region 504 are formed inside the light emitting layer 500. , Any one or any two or three. Of course, any combination of two or three is optional.

According to the structure of the present embodiment, carriers injected from the electrode are blocked by the blocking region and remain inside the light emitting layer 500, so that the probability of being trapped in the trapping region is improved, and the recombination efficiency ( η (recombination)) is improved.
As a result, the driving voltage of the EL element is reduced, so that the power consumption of the light emitting device is reduced and the reliability is improved.

Embodiment 4 In this embodiment, a light emitting device using an EL element having a band structure different from that of FIG. 1A will be described with reference to FIG. In FIG. 6, FIG.
The only difference is that the light emitting layer 600 is the same.

The structure of this embodiment shown in FIG. 6A is characterized in that an electron capturing region 601 and a hole capturing region 602 are formed inside a light emitting layer 600, and both are formed of the same organic substance. There is. The same organic substance is an organic film or a cluster of organic substances. In this embodiment, it is necessary to use an organic substance having a function of lowering the LUMO level and increasing the HOMO level.

In the structure of this embodiment, the carriers injected from the electrodes are confined in the trapping region formed in the same layer. In this case, the band gap between the LUMO level and the HOMO level is very small. Therefore, the recombination efficiency (η (recombination)) is improved. As a result, the driving voltage of the EL element is reduced, so that the power consumption of the light emitting device is reduced and the reliability is improved.

Embodiment 5 In this embodiment, an example of the light emitting device of the present invention will be described with reference to FIG. 7A is a cross-sectional view, and FIG. 7B is a top view.

In FIG. 7A, reference numeral 701 denotes a substrate, on which a pixel portion 702 and a driving circuit 703 are formed. The pixel portion 702 and the driving circuit 703 are connected to the wiring 70
The transmission and reception of electric signals can be performed by 4-706. The substrate 701 may be made of any material as long as it is transparent to visible light.

In the pixel portion 702, a plurality of pixels (typically, pixels having a structure as shown in FIG. 3A) including a TFT and an EL element are formed in a matrix, and passivation is formed thereon. A film 707 is formed. In this embodiment, a tantalum oxide film is formed as the passivation film 707 by a sputtering method; however, a silicon nitride film may be provided as long as the film can be formed at a temperature that does not deteriorate the organic EL film.

On the wirings 704 and 706, a sealing agent 708 made of an epoxy resin is formed so as to surround the pixel portion 702 and the driving circuit 703, and the sealing agent 708 allows the printed wiring board (PWB) to be printed.
d) 709 is attached. In addition, as a material of the printed wiring board, typically, glass cloth-epoxy, epoxy-based film, glass cloth-heat resistant epoxy, ceramics, alumina, paper base-phenol or paper base-epoxy can be used. Also, a glass substrate,
A crystallized glass substrate or a plastic substrate may be used. In this embodiment, a printed wiring board in which ceramics 710 is used as a core material and sandwiched between a glass cloth and an epoxy-based base material 711 is used.

At this time, an anisotropic conductive film (typically, a resin in which metal particles are dispersed) or a metal bump (typically, a solder bump, a gold bump, a nickel bump, Copper conductors 712 and 713 are provided.
The wiring 704 or 706 and the wiring group 714 formed on the printed wiring board 709 are electrically connected via the wiring 713. Here, the wiring group is a general term for wiring formed on the front surface, the back surface, or inside the printed wiring board 709.

The wiring group 714 is formed of an FPC (Flexible P
rinted circuit) 715 to transmit electric signals transmitted to the conductors 712 and 713, and to the printed wiring board 70.
Various ICs (integrated circuits) 715, 71 connected on
6 are wires for exchanging electrical signals between
It is formed with a thickness of ２０20 μm. As the wiring group 714, a pattern made of copper foil, gold foil, silver foil, nickel foil, or aluminum foil is typically used.

In the light emitting device of this embodiment having the above structure, the electric signal transmitted to the FPC 715 is processed by the printed wiring board 709, and the processed electric signal is transmitted through the conductors 712 and 713. The data is transmitted to the pixel portion 702 or the driving circuit 703. At this time, in this embodiment, the printed wiring board 709 serves as a protection plate for protecting the EL element from external impact. Further, the printed wiring board 709 can be used as a substrate for enclosing the EL element in a closed space.

In this embodiment, the printed wiring board 709 is used.
Although an example is shown in which an IC is mounted to have a signal processing function, a wiring group is simply formed and a wiring used in the pixel portion 702 or the driving circuit 703 may be used as a redundant wiring for lowering resistance. it can. By doing so, for example, it is possible to improve the signal delay of the wiring for supplying current to the EL element or the gate wiring of the TFT.

As described above, by using the printed wiring board as one of the substrates of the light emitting device, the performance and reliability of the light emitting device can be improved. It should be noted that the configuration of the present embodiment includes the first embodiment.
Any one of the configurations 4 to 4 may be implemented in combination.

[Embodiment 6] In this embodiment, an organic EL film that can be used in the present invention will be described. A feature of the present invention is that a LUMO level or a HOMO level
An organic film or an organic film that locally changes the level is provided, and any organic film may be used as long as the condition is satisfied. Note that an organic substance cluster or an organic film which emits light through triplet excitation may be used.

More specifically, Alq3 (tris-6-quinolinato aluminum complex), DPVBi
(Distyl arylene derivative), BeBq2 (bisbenzoquinolilatoberylium complex), TPD (triphenylamine derivative), α-NPD, PPV (polyparaphenylenevinylene), PVK (polyvinylcarbazole) It is. Here, the molecular structures of the above materials which can be used as the light-emitting layer are shown below.

[0053]

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[0054]

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[0055]

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[0056]

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[0057]

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[0058]

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[0059]

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More specifically, materials such as coumarin 6, DCM1, DCM2, quinacridone, rubrene, or perylene can be used as the fluorescent dye. Here, the molecular structures of the above materials which can be used as the light-emitting layer are shown below.

[0061]

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[0062]

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[0063]

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[0064]

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[0065]

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The band structure of the present invention can be formed by appropriately combining the light emitting layer and the fluorescent substance. Note that the configuration of this embodiment can be freely combined with any of the configurations of Embodiments 1 to 6.

[Embodiment 7] A light emitting device manufactured by carrying out the present invention can be used as a display portion of various electric appliances. For example, in order to watch a TV broadcast or the like on a large screen, a display in which the light emitting device of the present invention is incorporated in a housing may be used as a display having a diagonal of 20 to 60 inches.
In addition, the display incorporating the light emitting device in the housing,
All information displays such as a display for a personal computer, a display for receiving a TV broadcast, and a display for displaying an advertisement are included.

Further, in a liquid crystal display in which a liquid crystal module (liquid crystal panel) is incorporated in a housing, the light emitting device of the present invention can be used as a light source of a backlight. Further, it may be used as a light source such as a fluorescent display lamp at a construction site. These liquid crystal displays and fluorescent display lamps are also electrical appliances.

In addition, the light emitting device of the present invention can be used as a display unit of various electric appliances. As the electric appliance of the present invention, a video camera, a digital camera,
Goggle-type displays (head-mounted displays), navigation systems, music players (typically car audio or audio components), notebook personal computers, game devices,
A portable information terminal (typically, a mobile computer, a mobile phone, a portable game machine or an electronic book), an image reproducing apparatus (typically, an apparatus having a display unit for reproducing and displaying an image recorded on a recording medium) ). In particular, it is desirable to use a light-emitting device for a portable information terminal that is often viewed from an oblique direction, since a wide viewing angle is regarded as important.
8 and 9 show specific examples of these electric appliances.

FIG. 8A shows a display in which a light emitting device is incorporated in a housing.
A display unit 2003 and the like are included. The present invention can be used for the display portion 2003. Such a display is of a light-emitting type and does not require a backlight, and can be a display portion thinner than a liquid crystal display.

FIG. 8B shows a video camera,
101, display unit 2102, voice input unit 2103, operation switch 2104, battery 2105, image receiving unit 2106
And so on. The light emitting device of the present invention can be used for the display portion 2102.

FIG. 8C shows a part (one side on the right) of the head-mounted EL display, which includes a main body 2201, a signal cable 2202, a head fixing band 2203, and a display unit 22.
04, an optical system 2205, a light emitting device 2206, and the like. The present invention can be used for the light-emitting device 2206.

FIG. 8D shows an image reproducing apparatus (specifically, a DVD reproducing apparatus) provided with a recording medium.
1, recording medium (DVD or the like) 2302, operation switch 23
03, a display unit (a) 2304, a display unit (b) 2305, and the like. The display section (a) mainly displays image information, and the display section (b) mainly displays character information. The light emitting device of the present invention can be used for these display sections (a) and (b). Note that the image reproducing device provided with the recording medium includes a home game machine and the like.

FIG. 8E shows a portable computer, which includes a main body 2401, a camera section 2402, an image receiving section 2403, operation switches 2404, a display section 2405, and the like. The light emitting device of the present invention can be used for the display portion 2405.

FIG. 8F shows a personal computer, which includes a main body 2501, a housing 2502, a display portion 2503, a keyboard 2504, and the like. The light emitting device of the present invention can be used for the display portion 2503.

If the light emission luminance is further increased in the future, it is possible to use the front light or rear light projector by enlarging and projecting the light including the output image information with a lens or an optical fiber.

In the light emitting device, since the light emitting portion consumes power, it is desirable to display information so that the light emitting portion is reduced as much as possible. Therefore, when a light emitting device is used for a portable information terminal, particularly a display portion mainly for character information such as a mobile phone or a sound reproducing device, the light emitting portion is driven to form character information with a non-light emitting portion as a background. It is desirable to do.

FIG. 9A shows a mobile phone, which includes a main body 2601, an audio output unit 2602, an audio input unit 2603,
Display unit 2604, operation switch 2605, antenna 26
06. The light emitting device of the present invention can be used for the display portion 2604. Note that the display portion 2604 can display power of the mobile phone by displaying white characters on a black background.

FIG. 9B shows a music reproducing apparatus, specifically, a car audio system.
02, including operation switches 2703 and 2704. The light emitting device of the present invention can be used for the display portion 2702.
In this embodiment, a car audio is shown, but the present invention may be applied to a portable or home sound reproducing apparatus. The display unit 2
Reference numeral 704 denotes that white characters are displayed on a black background to reduce power consumption. This is particularly effective in a portable sound reproducing device.

As described above, the applicable range of the present invention is extremely wide, and the present invention can be used for electric appliances in various fields. Further, the electric appliance of this embodiment may use any of the light emitting devices shown in Embodiments 1 to 5.

[Embodiment 8] When an electric appliance having the light emitting device of the present invention as a display portion is used outdoors, it may be viewed in a dark place or a bright place. At this time, in a dark place, it is possible to sufficiently recognize even if the luminance is not so high, but in a bright place, it may not be possible to recognize the image unless the luminance is high. E
In the case of the L light emitting device, since the luminance changes in proportion to the amount of current for operating the element, when the luminance is increased, the power consumption also increases. However, if the light emission luminance is adjusted to such a high level, the display will be large in power consumption in a dark place and the display will be unnecessarily bright.

To prepare for such a case, it is not possible to provide the EL light emitting device or the electric appliance of the present invention with a function of detecting the external brightness with a sensor and adjusting the light emission luminance according to the degree of the brightness. It is valid. That is, the light emission luminance is increased in a bright place, and the light emission luminance is decreased in a dark place. As a result, it is possible to realize an EL light emitting device that prevents an increase in power consumption and does not give a viewer a feeling of fatigue.

As a sensor for detecting external brightness, a CMOS sensor or a CCD (charge coupled device) can be used. The CMOS sensor can be integrally formed on a substrate on which an EL element is formed using a known technique, or an IC may be externally provided.
Further, an IC in which a CCD is formed may be attached to a substrate in which an EL element is formed, or a structure in which a CCD or a CMOS sensor is provided in a part of an electric appliance using an EL light emitting device as a display portion may be employed.

A control circuit for changing the amount of current for operating the light emitting element according to the signal obtained by the sensor for sensing the external brightness is provided, whereby the light emission of the EL element is controlled according to the external brightness. Brightness can be adjusted. It should be noted that such adjustment may be performed automatically or manually.

When the configuration of this embodiment is added to the EL light emitting device or the electric appliance of the present invention, it is possible to further reduce the power consumption of the EL light emitting device. Note that the configuration of this embodiment can be implemented in any of the electric appliances shown in Embodiment 7.

[0086]

According to the present invention, the driving voltage of the EL element can be reduced, and the power consumption and the reliability (lifetime) of the light emitting device can be reduced. Furthermore, it is possible to reduce the power consumption of an electric appliance using the light emitting device of the present invention for a display portion.

[Brief description of the drawings]

FIG. 1 illustrates a band structure of an EL element.

FIG. 2 illustrates a band structure of an EL element.

FIG. 3 illustrates a cross-sectional structure of a pixel and an EL element of an EL light-emitting device.

FIG. 4 is a diagram showing a cross-sectional structure of an EL element.

FIG. 5 illustrates a band structure of an EL element.

FIG. 6 illustrates a band structure of an EL element.

FIG. 7 illustrates a cross-sectional structure of an EL light-emitting device.

FIG. 8 illustrates an example of an electric appliance.

FIG. 9 illustrates an example of an electric appliance.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H05B 33/26 H05B 33/26 A

Claims (12)

[Claims] 1. A light-emitting device having a light-emitting element including a cathode, an anode, and a light-emitting layer, wherein an electron-capturing region or a hole-capturing region is provided inside the light-emitting layer. 2. A light-emitting device having a light-emitting element including a cathode, an anode, and a light-emitting layer, wherein an electron-capturing region, a hole-capturing region, an electron-blocking region, or a hole-blocking region is provided inside the light-emitting layer. A light-emitting device, characterized in that: 3. The light emitting device according to claim 2, wherein the electron blocking region is an organic cluster or an organic film forming a LUMO level higher than the LUMO level of the light emitting layer. 4. The light emitting device according to claim 2, wherein the hole blocking region is an organic cluster or an organic film forming a HOMO level lower than a HOMO level of the light emitting layer. 5. The electron capturing region according to claim 1, wherein the electron trapping region is an L lower than the LUMO level of the light emitting layer.
A light-emitting device comprising a cluster or an organic film of an organic substance forming a UMO level. 6. The light emitting device according to claim 1, wherein the hole-capturing region is higher than a HOMO level of the light emitting layer.
A light-emitting device, which is an organic substance cluster or an organic film that forms an OMO level. 7. A light-emitting device having a light-emitting element including a cathode, an anode and a light-emitting layer, wherein a region exhibiting a LUMO level lower than the LUMO level of the light-emitting layer or the light-emitting layer is provided inside the light-emitting layer. A light-emitting device including a region having a HOMO level higher than the HOMO level. 8. The light emitting device according to claim 7, wherein
The region showing a LUMO level lower than the level or a region showing a HOMO level higher than the HOMO level of the light emitting layer is a cluster or an organic film of an organic substance provided inside the light emitting layer. Light emitting device. 9. A light-emitting device having a light-emitting element including a cathode, an anode, and a light-emitting layer, wherein a region exhibiting a LUMO level lower than the LUMO level of the light-emitting layer is provided inside the light-emitting layer.
A region exhibiting a HOMO level higher than the HOMO level of the light emitting layer, a LUMO level higher than the LUMO level of the light emitting layer
A light-emitting device provided with a region showing a level or a region showing a HOMO level lower than the HOMO level of the light-emitting layer. 10. The LUM of claim 9, wherein:
A region exhibiting a LUMO level lower than the O level, a region exhibiting a HOMO level higher than the HOMO level of the light emitting layer, a region exhibiting a LUMO level higher than the LUMO level of the light emitting layer, or the light emitting layer HO lower than the HOMO level of
A light-emitting device, wherein the region exhibiting the MO level is an organic cluster or an organic film provided inside the light-emitting layer. 11. An electric appliance using the light emitting device according to claim 1 for a display unit. 12. An electric appliance using the light emitting device according to claim 1 as a light source.