JPH09293588A - Electric field luminous element, and driving method for it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving method for an electric field luminous element having a long luminous life, by restraining the polarization of an EL(electro- luminescence) layer consisting of an organic compound. SOLUTION: An EL layer 7 is interposed between anode and cathode electrodes 3 and 6, and is constituted of a TPD(triphenyldiamine derivative) coat 4 and an ALq3 coat (trisaluminium complex coat) 5 laminated. At first, before operating an electric field luminous element 1, voltage in a direction reverse to that of a luminous electric field, is applied by a voltage applying means 9. Consequently in emitting light, the orientation polarization of a functional group in an organic compound constituting the EL layer 7, or the ion polarization of an ionic impurity can be restrained previously. Resultantly, the deterioration of the luminous characteristic of the EL layer can be restrained, to prolong the luminous life of the electric field luminous element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescence device and a driving method thereof, and more particularly to an organic electroluminescence device that can be used in a flat display.

[0002]

2. Description of the Related Art In recent years, an electroluminescent device using an organic compound for an electroluminescent layer has reached a practical stage. The organic electroluminescent element using such an organic compound is a self-luminous element, and thus does not require a backlight unlike a liquid crystal display device. Therefore, the organic electroluminescent element can be used for a thin flat display. As an example of this organic electroluminescence device, there is known a structure in which an electroluminescent layer containing, for example, a quinacridone derivative as an organic compound is sandwiched between an anode electrode and a cathode electrode. As another example, there is one in which an electroluminescent layer is formed by stacking a plurality of organic compound layers.

[0003]

However, the organic electroluminescent device has the following problems. The display life of the organic electroluminescent device is still shorter than that of the liquid crystal display device. Therefore, in order to use the organic electroluminescent device as a flat display, development of an electroluminescent material having a longer light emission life, a device structure, and the like is desired.

By the way, the light emission life of the organic electroluminescence device is influenced not only by the external environment but also by the constituent molecules of the electroluminescence layer and a trace amount of impurities existing in the electroluminescence layer. For example, a polar group of a molecule forming the electroluminescence layer may be oriented (orientation polarization) by an electric field generated by a forward voltage applied during light emission. Alternatively, an electric field generated by a forward voltage may cause ionic impurities existing in the electroluminescent layer to cause ionic polarization.
Since the internal electric field of the electroluminescent layer in which the orientation polarization and the ionic polarization are generated is in the opposite direction to the electric field generated by the forward voltage required for light emission, the voltage applied during light emission cannot effectively contribute. . Due to such a mechanism, the light emitting characteristics of the organic electroluminescent device deteriorate.

The problem to be solved by the present invention is what kind of means should be taken to obtain an organic electroluminescence device having a long light emission life.

[0006]

According to the first aspect of the present invention,
In the electroluminescent element, an organic electroluminescent layer that emits light at a predetermined voltage, and an anode electrode provided on one surface side of the organic electroluminescent layer,
A cathode electrode provided on the other surface side, a forward voltage applied in the forward direction that is the direction of the electric field that emits light from the organic electroluminescent layer, and a reverse voltage that the direction of the electric field is the reverse direction of the forward direction. And a voltage applying means for supplying the voltage.

According to the first aspect of the invention, it has an effect of suppressing deterioration of the light emitting characteristics with time. That is, when a reverse voltage is applied between the anode electrode and the cathode electrode by the voltage applying means, when a forward voltage is applied, polar groups of the organic compound forming the organic electroluminescence layer and ionic impurities existing in the layer are formed. Can suppress the occurrence of orientation polarization and ionic polarization. When a reverse voltage is applied, polar groups and ionic impurities form an internal electric field close to the forward direction. Therefore, when a forward voltage is applied, the internal electric field cannot be immediately inverted, and deterioration of the light emitting characteristics of the electroluminescent layer can be suppressed.

According to a second aspect of the present invention, the voltage applying means applies a forward voltage and a reverse voltage at a predetermined duty ratio between the anode electrode and the cathode electrode during light emission driving. Is a feature. According to the second aspect of the present invention, the forward voltage and the reverse voltage are applied to the electroluminescence layer at the time of driving the light emission, so that it has an effect of suppressing the deterioration of the light emission characteristics of the electroluminescence layer. At this time, by appropriately setting the duty ratio of the forward voltage and the reverse voltage, it is possible to effectively suppress the deterioration of the light emission characteristics.

According to a third aspect of the invention, the organic electroluminescence layer has an electron transport layer and a hole transport layer.

According to the third aspect of the present invention, only a forward voltage is applied as in a DC driven organic electroluminescence layer that transports holes from the anode electrode to the hole transport layer and transports electrons from the cathode electrode to the electron transport layer. The light-emission life of the device that emits light can be significantly extended.

According to a fourth aspect of the present invention, the electroluminescent layer comprises a triphenyldiamine derivative film provided on the anode electrode side and a tris (8-quinolinolate) aluminum complex film provided on the cathode electrode side. The feature is that

According to a fifth aspect of the present invention, the electroluminescent layer is provided on the anode electrode side.
At least polyvinylcarbazole and 2,5-bis (1-
It is characterized by comprising a mixed film containing naphthyl) oxadiazole and a tris (8-quinolinolate) aluminum complex film provided on the cathode electrode side.

According to a sixth aspect of the present invention, there is provided a method for driving an electroluminescent device, wherein an anode electrode is formed on one surface side of the organic electroluminescence layer and a cathode electrode is formed on the other surface side of the organic electroluminescence layer. Between the cathode electrode and the cathode electrode, a forward voltage applied in the forward direction, which is the direction of the electric field that emits light through the organic electroluminescent layer, and a reverse voltage applied in the opposite direction to the forward direction are selectively supplied. It is characterized by that.

In the invention of claim 6, when a reverse voltage is applied between the anode electrode and the cathode electrode by the voltage applying means, the polarity of the organic compound forming the organic electroluminescence layer is applied when the forward voltage is applied. It is possible to prevent the ionic impurities existing in the base or layer from causing orientational polarization or ionic polarization. That is, when a reverse voltage is applied, polar groups and ionic impurities form an internal electric field close to the forward direction. Therefore, when a forward voltage is applied, the internal electric field cannot be immediately inverted, and deterioration of the light emitting characteristics of the electroluminescent layer can be suppressed.

According to a seventh aspect of the present invention, the reverse voltage is supplied to the organic electroluminescent layer in advance before the organic electroluminescent layer emits light.

According to the seventh aspect of the present invention, by supplying a reverse voltage in advance before light emission, it is possible to suppress deterioration with time even when light is emitted by applying a forward voltage to the organic electroluminescent layer.

According to an eighth aspect of the present invention, the reverse voltage is supplied to the organic electroluminescent layer during the light emission period of the organic electroluminescent layer.

According to the eighth aspect of the invention, continuous light emission can be performed for a long time by applying a reverse voltage during the light emission holding period.

According to a ninth aspect of the present invention, the product of the voltage value of the forward voltage and its application time is substantially equal to the product of the voltage value of the reverse voltage and its application time. There is.

According to the ninth aspect of the present invention, since the products of the voltage values and the application times in the forward direction and the reverse direction are substantially equal to each other, the electric fields received by the organic electroluminescent layers cancel each other out. It is possible to suppress deterioration over time.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, details of an electroluminescent device and a method of driving the same according to the present invention will be described based on embodiments shown in the drawings. (Embodiment 1) FIG. 1 is a sectional explanatory view of an electroluminescence device according to Embodiment 1 of the present invention. Hereinafter, the configuration of the electroluminescent device of this embodiment will be described with reference to FIG. In the figure, 1 is
2 shows an electroluminescent device. In this electroluminescent device 1, an anode electrode 3 is formed on a glass substrate 2, and a triphenyldiamine derivative (hereinafter referred to as TPD) film 4, a tris (8-quinolinolate) aluminum film are sequentially formed on the anode electrode 3. Complex (hereinafter referred to as Alq3) film 5
Is formed, and the cathode electrode 6 is formed on the Alq3 film 5. The anode electrode 3 has a sheet resistance of 5
It is made of ITO (indium tin oxide) of 0 ohm or less, and is formed over substantially the entire surface of the glass substrate 2. Note that T
The PD film 4 and the Alq3 film 5 form an electroluminescence (hereinafter referred to as EL) layer 7. Further, the lead wires 8 and 9 are connected to the anode electrode 3 and the cathode electrode 6, respectively.
The voltage applying means 10 is connected via.

The thickness of the TPD film 4 is set to about 50 nm. As TPD, N, N'-diphenyl-N, N'-bis (3
-Methyl) -1,1'-biphenyl-4,4'diamine was used. This T
The PD film 4 functions as a hole (hole) transport layer. The structural formula of this compound is shown below.

[0023]

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The film thickness of the Alq3 film 5 was set to about 50 nm. This Alq3 film 5 functions as an electron transport layer and a light emitting layer. The structural formula of Alq3 is shown below.

[0025]

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The cathode electrode 6 is made of magnesium (Mg)
And indium (In) are co-evaporated at a molar ratio of 30: 1 to form MgIn. The thickness of the cathode electrode 6 was set to about 300 nm.

The voltage applying means 10 outputs a forward voltage in which the direction of the electric field to be emitted is a forward direction and a reverse voltage in which the forward direction is a reverse direction between the anode electrode 3 and the cathode electrode 6 by switching operation. Is set to. In the electroluminescent device 1 of the present embodiment, before emitting light (before shipping)
The reverse voltage of −10 V was applied to the device for 1 second or longer.

Next, the measurement results of the voltage-luminance characteristics of the electroluminescent device of this embodiment and the comparative example will be described. This measurement is
A forward voltage of 10 V is applied for 1 hour to the electroluminescent device 1 of the present embodiment that has been subjected to the reverse voltage application process and the unprocessed element that has not been subjected to the reverse voltage application process (the structure is the same as that of this embodiment). After that, the voltage-luminance characteristics of the device were examined. As a result, the light emission starting voltage of the electroluminescent device of the present embodiment was decreased by 0.5 V as compared with the untreated device. Also, 100 cd
Half life of constant voltage driving at a brightness of / m ² (1
Time to drop from 00 cd / m ² to 50 cd / m ² )
Was about 1 hour for the untreated element, while it was about 100 hours for the electroluminescent element of the present embodiment. Further, the luminous efficiency of the electroluminescent device of the present embodiment was higher than that of the untreated device by 0.31 m / W.

As described above, in the electroluminescent device of this embodiment, by applying the reverse voltage,
It is possible to reduce polarization (orientation polarization or ionic polarization of constituent molecules) that may occur when a forward voltage is applied. Further, by performing such a treatment, an internal electric field in the same direction as the electric field formed by the forward voltage required for light emission can be formed in the EL layer 7 in advance. Therefore, in the electroluminescent device of the present embodiment, the driving voltage can be lowered and the light emission life can be extended.

(Embodiment 2) FIG. 2 is a drive voltage waveform diagram for explaining a drive method used in Embodiment 2 of the present invention. The structure of the electroluminescent device of this embodiment is the same as that of the above-described first embodiment. The driving method of this embodiment is characterized in that a reverse voltage is applied at a constant time interval during light emission driving.

In the driving method of the present embodiment, the frequency of 1 K is applied between the anode electrode and the cathode electrode during light emission driving.
Hz, a rectangular wave AC electric field with a duty ratio of 1: 1 (-10
V and +8 V) were applied. And 100 cd \ m
The emission half-life at a brightness of ² (time average value) was measured. As a result, in the comparative example in which the DC constant voltage drive of 8 V was performed, the light emission half-life was about 1 hour, whereas the drive method of this embodiment extended the light emission half-life to about 200 hours. .

As described above, in this embodiment, since the reverse voltage is applied at a constant time interval, the orientation polarization (dipole polarization) and the ionic polarization caused by the application of the forward voltage are reduced, and the forward voltage is reduced. Can be effectively applied to the element. In addition, a large amount of current does not flow in the electroluminescent element while the reverse voltage is applied, and since no light-emission drive voltage is applied during this period, the amount of heat generated is reduced, and Deterioration can be suppressed.

In this embodiment, a voltage having a frequency of 1 KHz is applied during driving, but a DC voltage of 100 KH is applied.
Up to an alternating voltage of z can be applied. Further, the duty ratio is not limited to the above value. The value of the reverse voltage is preferably high as long as electrical damage to the element is minimized. Further, the application time of the reverse voltage is preferably short as long as it can suppress the polarization generated while applying the forward voltage. Therefore, the optimum application time can be set by a combination with the strength of the applied reverse voltage. More specifically, the product of the voltage value V1 (V1> 0) of the forward voltage and the application time t1 thereof is calculated as the voltage value V2 (V2 <V2) of the reverse voltage.
It is more desirable to set the product of 0) and its application time t2 to be substantially equal.

(Embodiment 3) FIG. 3 is a sectional explanatory view showing a sectional structure of a display device as a flat display in which the electroluminescent device according to the present invention is incorporated. In this embodiment, the present invention is applied to a transmissive liquid crystal display element. Reference numeral 11 in the drawing is a display device, and the display device 11 includes an address light element 12 as an electroluminescent element,
The liquid crystal display element 13 and the backlight system 14 are generally included.

The address optical element 12 is, as shown in FIG. 3, an address substrate 1 made of glass or polymer film.
5, a plurality of row electrodes 16 as anode electrodes
Groups are arranged in parallel in the row direction.
The row electrode 16 is transparent to the visible light wavelength range (401 nm to 800 nm) of the backlight system 14, and is, for example, ITO (indium tin oxide).
And tin oxide (SnO ₂ ), magnesium oxide (MgO)
And the like. Polyvinylcarbazole (hereinafter referred to as PVCz) and 2,5-bis (1) are formed on the upper surfaces of the plurality of row electrodes 16 and the address substrate 15.
-Naphthyl) -oxadiazole (hereinafter referred to as BND) and a single layer of the first organic film 17 having a hole-transporting property.
Is formed with a film thickness of about 1000Å. An electron transporting second organic film 18 made of Alq3 or the like is formed on the first organic film 17 with a film thickness of about 500Å. The first organic film 17 and the second organic film 18 are E
It constitutes the L layer 19. The structural formulas of PVCz and BND are shown below.

[0036]

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[0037]

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Further, as shown in FIG. 3, on the upper surface of the second organic film 18, column electrodes as cathode electrodes, which are parallel to each other in the column direction intersecting (orthogonal to) the row electrodes 16 with the EL layer 19 interposed therebetween. Twenty groups are formed. This column electrode 20 is
The work function is low with respect to the row electrode 16, and for example,
Metal electrodes such as MgIn, AlLi, and MgIn-Al,
It can be selected from n-type amorphous silicon (a-Si), n-type silicon carbide, etc., which have a transparency in the visible light and ultraviolet light wavelength ranges.

Then, the EL layer 19 and the terminal portion 20A
A protective film 21 having a light-transmitting property is formed so as to cover the column electrode 20 in a portion other than. Although not shown,
The terminal portions of the row electrodes 16 are not covered with the protective film 21 and are exposed. As the protective film 21, it is possible to use, for example, a silicon nitride film or a silicon oxide film, which is transparent to light in the visible light wavelength range and the ultraviolet light wavelength range. The protective film 21 is for preventing oxidation of the column electrodes 20 and preventing characteristic deterioration due to moisture, but it is not always necessary depending on the physical properties of each member of the address light element 12.

The address optical element 12 thus configured
In the above, when a predetermined voltage is applied between the row electrode 16 and the column electrode 20, ultraviolet light (350 to 350) as signal light is emitted from a portion of the first organic film 17 near the interface with the second organic film 18. Light of a predetermined wavelength range between 400 nm) is emitted. The wavelength range of the signal light and the backlight system 1
It is preferable that the wavelength range of the irradiation light (visible light) of No. 4 is as far as possible, and the signal light is 350 to 400 nm.
It is desirable to set so that the ultraviolet light in the wavelength range of is output. The row electrodes 16 and the column electrodes 20 extend to the edge of the address substrate 15, the terminal portions are exposed from the protective film 21 and the voltage application means is connected to the driving IC (not shown) as described above. ) Is connected with. In this way, the matrix-driven address optical element 12 is constructed.

The liquid crystal display element 13 to be combined with the address light element 12 having such a structure is the address light element 12
The display area has an area similar to that of the light emitting area. The configuration of the liquid crystal display element 13 will be described below with reference to FIG.

The liquid crystal display device 13 includes a pair of front transparent substrate 22 and rear transparent substrate 23, twisted nematic liquid crystal 25 sealed by a sealing material 24 between these transparent substrates, and these transparent substrates 22, It has a linear polarization axis arranged on the outer surface side of 23, comprises a pair of front polarizing plate 26 and rear polarizing plate 27, and uses a TN cell having optical activity. Further, in this embodiment, one transparent rear drive electrode 28 made of ITO is formed over the entire display area on the inner surface of the rear transparent substrate 23 which faces the rear transparent substrate 23. A photoconductive layer 29 is formed on the surface of the rear drive electrode 28. Further, a post-alignment film 30 is formed so as to cover the photoconductive layer 29.

The photoconductive layer 29 is made of a material that absorbs photons in a specific wavelength range to generate conductive carriers. Examples of such a photoconductive layer 29 include ZnO, amorphous silicon (a-Si), Amorphous selenium (a-S
e), ZnS, SrTiO ₃ , GaN, CdS, SnO _x
Inorganic semiconductors such as, charge transfer complexes such as polyvinylcarbazole, organic photocarrier generation layers (perylenes, quinones, phthalocyanines, etc.) and organic carrier transport layers (arylamines, hydrazines, oxazoles, etc.)
A material such as an organic composite material in which and are stacked can be used. In such a material, a photon in a specific wavelength region is absorbed, and a conductive carrier composed of an electron-hole pair is generated,
The impedance of the region where the photons are absorbed sharply decreases, so that the region becomes electrically conductive.
In particular, in this embodiment, ZnO is used because the photoconductive layer 29 has a light absorption characteristic for signal light (ultraviolet light) and has a peak of spectral sensitivity sensitive to the wavelength range of ultraviolet light. ZnO
Usually has no absorption in the visible light range.

On the other hand, on the inner surface facing the front transparent substrate 22,
A color filter layer 31 having a predetermined color arrangement is formed over the entire display area. Further, on the surface of the color filter layer 31, one front drive electrode 33 made of ITO is formed on the entire surface with a protective film 32 made of a transparent silicon nitride film interposed therebetween. Further, a pre-alignment film 34 is formed so as to cover the pre-driving electrode 33. The liquid crystal display element 13 and the address light element 12 described above have a dot arrangement of the address light element 12 (a portion where the row electrode 16 and the column electrode 20 intersect each other) with respect to the color arrangement of the color filter layer 31. The arrangement is such that the signal light is incident on the photoconductive layer 29 while maintaining the spatial frequency. Further, as shown in FIG. 3, a rear polarizing plate 27, which is a constituent member of the liquid crystal display element 13, is provided on the lower surface of the address light element 12, and the backlight system 14 is disposed behind it. This backlight system 14
Is roughly composed of a light source 35 that emits visible light and a light guide plate 36 made of acrylic or the like.

Next, a method of driving the display device 11 having the above structure will be described. FIG. 4 shows a method of driving the display device 11, and shows the timing of the drive voltage Vd waveform and the light emission pulse at each pixel address. FIG. 4B shows the electrodes 33 and 28 of the liquid crystal display element 13.
3 shows the timing of the driving voltage Vd applied to the liquid crystal 25 and the photoconductive layer 29 between the address photoelements 1 and 2.
The pulse train is synchronized with the “one scanning line selection time” determined by the line-sequential driving method for the second row electrode 16 and the second column electrode 20. The polarity of the drive voltage Vd is not inverted at least within the scanning time of all the scanning lines. Then, this drive voltage Vd
As shown in FIG. 4A, one scanning time is divided into at least two (not necessarily equal to each other), and "HI"
An electric potential, a "LOW" electric potential (zero electric potential in the figure) is applied. Hereinafter, the “HI” potential is referred to as a writing time potential, and the “LOW” potential is referred to as an erasing time potential. As shown in the figure, it is desirable that the first half of the selected one scanning time is the erasing time and the latter half is the writing time. FIG. 4 (c),
(D) and (e) are row electrodes 16 driven line-sequentially,
A pulse of a specific dot portion d in the XY matrix formed of the column electrodes 20 is shown. FIG.
(C) shows a light emission pulse of a certain dot part d on the first select line, (d) shows a pulse of a certain dot part d on the second select line, and (e) shows a pulse on a third select line. A pulse of a certain dot portion d is shown. Here, one of the row electrode 16 or the column electrode 20 is used as a select line.

The electrodes 16 and 2 of the selected select line
As shown in (c) to (e) of the same drawing, the crossing portion of 0 outputs an optical pulse having a sufficient output for the erase time at the time of selection. This light pulse has a wavelength range of 350 nm to 400 nm, and upon incidence on the photoconductive layer 29, electron-hole pairs are generated in the photoconductive layer 29 and exhibit conductivity. At this time, since the value of Vd is the “LOW” potential, the electric field accumulated in the liquid crystal 25 during the previous scanning time is erased.

Next, at the writing time, light energy based on desired data corresponding to each pixel of the selected select line is output. In the figure, an example of pulse height modulation is shown, but pulse width modulation may be used. At this time, since the value of Vd is the “HI” potential, a desired electric field according to the write data is applied to the liquid crystal 25, and gradation display can be performed. While the other select lines are being driven, no pulse is given to the dot part d,
Since only the driving electric field Vd repeats HI / LOW, a desired electric field is maintained. Then, each select line is set so that the negative voltage Vc is applied as the reverse voltage except during the period in which the erase pulse and the write data pulse are output.

The matrix driving method of this embodiment has been described above, but by using such a method, data writing, holding time, and even erasing can be freely performed. This has substantially the same drive characteristics without crosstalk as that of the liquid crystal display device using the TFT.

The main advantage of this embodiment is that, in the address light element 12, the reverse voltage (negative voltage) is applied to the EL layer 19 when it is not selected. Therefore, when the forward voltage is applied. It is possible to reduce the polarization that can occur (orientation polarization or ionic polarization of the constituent molecules of the EL layer 19). Further, by carrying out such a driving method, an internal electric field in the same direction as the electric field formed by the forward voltage required for light emission can be formed in the EL layer 19 in advance. Therefore, by using the driving method of the present embodiment,
The drive voltage of the address light element 12 can be lowered,
In addition, the light emission life can be extended.

Other advantages of this embodiment are listed below.
In the present embodiment, the light (visible light) emitted from the backlight system 14 to the liquid crystal display element 13 is the photoconductive layer 29.
Therefore, the liquid crystal display performance is not impaired because it is not absorbed by and no photoelectromotive force is generated. In addition, in this embodiment, a virtually static drive potential can be applied to the liquid crystal layer. Further, structurally, there is no area occupied by the active element, so that the transmittance of display light is significantly improved, and a high aperture ratio can be achieved. Further, since the row electrodes 16 and the column electrodes 20 of the address light element 12 have a simple striped structure, the processing thereof is extremely easy, and the lithography process may be performed only a few times throughout the display device. When forming the light emitting layer 19, the first organic film 17 and the second organic film 18 only have to be vapor-deposited or applied in order, so that the manufacture of the address optical element 12 becomes very simple. Further, although the rear drive electrode 28 is shown to be covered with the photoconductive layer 29, in actuality, a structure in which the rear drive electrode 28, the photoconductive layer 29, the rear alignment film 30 and the like are sequentially formed may be used, and therefore, a liquid crystal display The number of steps of the element 13 can be significantly reduced as compared with the conventional one. Moreover, since the structure is simple, the yield is extremely high, and it is easy to achieve a large screen. Further, since there is no occupied area of active elements in one pixel, there is an advantage that high definition can be supported. Moreover, by using the organic EL material as the light emitting layer as in this embodiment, it is possible to realize low voltage driving of about 5 to 10 V and low power consumption.
Incidentally, this driving voltage is almost the same as that of the liquid crystal display element using the TFT as an active element, which is much smaller than that of the display using plasma, and is a display device excellent in portability.

In addition, in this embodiment, the EL layer 1
Since 9 is used as a signal light generating means and is not used as display light, relatively weak light emission is sufficient, and the life of the EL layer 19 can be extended.
Further, in this embodiment, the signal light is 350 nm to
Ultraviolet light in the wavelength range between 400 nm was used, but it is out of the visible light wavelength range used for liquid crystal display, for example, 801n.
A wavelength range of infrared light such as m to 1 mm may be used, and a photoconductive layer having a peak of photovoltaic may be set in this wavelength range.
In addition, in this embodiment, since the EL layer 19 is made of a flexible organic material, the flexible substrates 15, 22, and 23 made of a resin having a thickness of 100 μm, for example, are used to improve flexibility. It is also possible to provide a display device having the same.
Furthermore, the rear polarizing plate 27 is the backlight system 1.
Although the visible light from 4 is linearly polarized and emitted, the signal light of the address light element 12 can reach the photoconductive layer 29 without being polarized by the polarizing plates 26 and 27, and thus emits extremely weak light. do it. When the light source 35 emits light in the wavelength range where electrical conductivity is generated in the photoconductive layer 29, a filter that blocks light in the wavelength range and transmits visible light may be provided on the lower surface of the rear polarizing plate 27. . Furthermore, the color filter layer 31 applied to this embodiment may have a stripe arrangement or a mosaic arrangement. By using the organic EL element as the address light element 12 as described above, it is possible to make the device thinner, and to irradiate the signal light only to the region corresponding to a predetermined dot of the photoconductive layer only through the column electrode and the row electrode. be able to.

(Fourth Embodiment) FIGS. 5 to 7 show a fourth embodiment of the present invention. Reference numeral 41 in the drawing is a display device.
The display device 41 is roughly composed of an address light element 42 which is a first light emitting element and an EL display element 43 which is a second light emitting element and is a display element.

As shown in FIGS. 5 and 6, the address optical element 42 has a plurality of row electrodes 45 arranged in the row direction on the rear surface of the address substrate 44 made of glass or a polymer film having a thickness of 100 μm and having flexibility. Are arranged parallel to each other. The row electrode 45 functions as an anode electrode, and may be an electrode material that is light transmissive and has a predetermined work function. For example, ITO or tin oxide can be used. PVCz and B are formed on the plurality of row electrodes 45 and the address substrate 44 (rear surface).
A first organic film 46 as a hole transport layer and a substantial light emitting layer is formed by mixing ND and a white light emitting material. A second organic film 47 as an electron transport layer made of Alq3 is laminated on the first organic film 46 (rear surface) so as to be bonded. The first organic film 46 and the second organic film 47 form a signal light generation layer 48.

On the second organic film 47 (rear surface),
A plurality of column electrodes 49 arranged in parallel in the column direction orthogonal to the row direction and intersecting the row electrodes 45 via the signal light generation layer 48 are formed. The column electrode 49 functions as a cathode electrode, has a low work function with respect to the anode electrode, and is a metal electrode such as MgIn, AlLi, or MgIn-Al having opacity to visible light or ultraviolet light. In addition, n-type amorphous silicon (a-S) that is transparent to visible and ultraviolet light wavelength regions
i), n-type silicon carbide or the like.

The address optical element 42 thus configured
In, in the case where a predetermined voltage is applied between the row electrode 45 and the column electrode 49, white light as signal light is emitted from a portion of the first organic film 46 near the interface with the second organic film 47. . The row electrodes 45 and the column electrodes 49 extend to the edge of the address substrate 44 and are connected to a driving IC (not shown). In this way, the matrix-driven address optical element 2 is constructed.

The EL display element 43 has a display area having an area which is approximately the same as the area over the entire light emitting area of the address light element 42 described above. The EL display element 43 is formed on the front surface side of the address substrate 44. First, on the front surface of the address substrate 44, a plurality of rear drive electrodes 50 as cathode electrodes are formed of, for example, transparent ITO. After that, the drive electrode 50 is arranged and formed so as to face each of the above-mentioned row electrodes 45 and overlap in a plan view.

On the address substrate 44 and the rear drive electrode 50, the photoconductive layer 51 is formed so as to cover the entire display area.
Are formed. The photoconductive layer 51 is made of a material that absorbs photons to generate conductive carriers, and is, for example,
In this embodiment, the photoconductive layer 51 is formed using amorphous silicon (a-Si). Then, on the surface layer of the photoconductive layer 51, a doped layer 51A formed by doping an n-type impurity (for example, phosphorus) is formed. A third organic film 52 as an electron transport layer, which is made of Alq3 which is the same material as the second organic film 47 described above, is formed on the entire surface of the doped layer 51A. The doped layer 51A
Has a function of facilitating injection of electrons into the third organic film 52. Then, a fourth organic film 53 as a hole transport layer is formed on the upper surface of the third organic film 52. The fourth organic film 53 is made of PVCz and BND, and corresponds to each dot portion (the portion where the row electrode 45 and the column electrode 49 of the address light element 42 overlap with each other through the signal light generation layer 48 (light emitting region)). Part), R (red), G (green), B (blue) to form a predetermined color arrangement.
The luminescent materials for causing each of the luminescence of the above are mixed. In the figure, 53R, 53G and 53B are respectively R and
The dot portions of the fourth organic film 53 corresponding to G and B are shown. As a method of forming the fourth organic film 53, PV is used.
A method of applying a mixed material of Cz and BND and then impregnating a luminescent dye corresponding to each dot portion, a method of forming a pattern of an organic film preliminarily mixed with a luminescent pigment for each color according to a color arrangement, and the like are used. be able to. The third organic film 52 and the fourth organic film 53 thus formed constitute a display light generating layer 54. Furthermore, the fourth organic film 53
A transparent front drive electrode 55 as an anode electrode made of ITO is formed on the entire upper surface of the display area.

The operation of the entire display device will be described below. First, in the address light element 42, when a predetermined voltage is applied between the row electrode 45 and the column electrode 49 selected by line-sequential scanning, white light as signal light is generated from the signal light generating layer 48 as a photoconductive layer. It is irradiated toward 51. At this time, since the signal light generation layer 48 and the photoconductive layer 51 are sufficiently close to each other, the signal light can be incident on the photoconductive layer 51 while maintaining a practically sufficient spatial frequency. Therefore, the signal light emitted from a predetermined address does not enter the photoconductive layer 51 and the doped layer 51A in the adjacent dot regions to excite the photoconductive layer 51. The photoconductive layer 51 and the doped layer 51A in the portion where the signal light is incident are in a state in which electron-hole pairs are generated and charges can be injected into the third organic film 52 as described above. As a result, the voltage applied between the front drive electrode 55 and the rear drive electrode 50 is applied to a predetermined dot portion of the display light generation layer 54 composed of the third organic film 52 and the fourth organic film 53. Will be done.

A DC drive voltage, a pulse voltage, an AC voltage or the like can be used between the drive electrodes. As a result, as described above, due to the light emission of the EL display element 43, display light colored by various light emitting materials is generated in the front direction, and at the same time, return light is generated in the rear direction, which is indicated by a dashed arrow r in FIG. To do. This return light r is incident on the photoconductive layer 51 and the doped layer 51A, so that the photoconductive layer 51 and the doped layer 51A are re-excited to newly generate electron-hole pairs. Therefore, the photoconductive layer 51 includes the third organic film 52.
A state in which charges can be injected is retained. Therefore, in the state where the drive voltage is continuously applied to the display light generating layer 54,
The electric charge is continuously injected into the display light generating layer 25. While in this state, the display light generation layer 54 can be continuously driven for a sufficiently long time for one frame period, so that the row electrode 45 and the column electrode 49 on the address light element 42 side are not selected. However, the display light generation layer 54
Will continue to emit light. Therefore, the light emission is maintained by the line-sequential scanning until the second scanning. Note that new display light emission can be performed by releasing the voltage applied to the rear drive electrode 50 immediately before the second scan.

Next, a driving method of the display device of this embodiment will be described with reference to FIG. FIG. 7 shows a driving method of the display device 41, and shows timings of a driving voltage waveform of the EL display element 43 and a pulse at each pixel address of the address optical element 42. FIGS. 7A to 7C
Shows the timing of the drive voltage applied to the display light generating layer 54, the photoconductive layer 29, and the doped layer 51A between the electrodes 50 and 55 of the EL display element 43. The timing of this drive voltage is a pulse train synchronized with the "one scanning line selection time" determined by the line-sequential drive method of the row electrode 45 and the column electrode 49 of the address optical element 42. As the drive voltage, a positive voltage Vd (light emission drive pulse) is applied during one scanning line selection time, and a negative voltage (Vdc) is applied during the other time. FIGS. 7D, 7E, and 7F show pulses of a specific dot portion d in the XY matrix composed of the row electrodes 45 and the column electrodes 49 which are line-sequentially driven. Note that FIG. 4D shows a write data pulse of a dot portion d1 on the first select line, FIG. 4E shows a write data pulse of a dot portion d2 on the second select line, and FIG. Indicates a write data pulse of a dot portion d3 on the third select line. Here, one of the row electrode 45 and the column electrode 49 is used as a select line.

Each of the selected intersections of these select lines outputs the light energy of the light amount based on the desired data, as shown in FIGS. The address optical element 42 makes each light incident on the corresponding region of the photoconductive layer 51, and electrons corresponding to the amount of light are stored in the photoconductive layer 51.
Generates hole pairs. Since the drive voltage Vd is constantly applied between the rear drive electrode 50 and the front drive electrode 55 corresponding to the select line except when erasing, charges generate display light according to the light quantity of the address optical element 42. The display light generating layer 54 injected into the layer 54 emits gradation light. Here, in the display light generating layer 54, the photoconductive layer 51 exhibits conductivity by the feedback light even when the select line is not selected. Therefore, since the photoconductive layer 51 continues to inject charges from the post-driving electrode 50 for substantially one frame period, the display light generation layer 54 can maintain light emission.

Further, the reverse voltage Vrc is applied to each select line of the address light element 42 during the non-selection period, and the EL display element 43 is applied with the reverse voltage Vdc at the time of erasing the previous data. It Although FIG. 7 shows an example in which pulse height modulation is performed and gradation light emission is performed, gradation light emission may be performed by pulse width modulation.

In the present embodiment, as described above, when the address light element 42 and the EL display element 43 are driven, a reverse voltage (an electric field generated by a forward voltage applied to cause light emission and a reverse electric field) is generated. (Voltage generated) is applied at a predetermined interval and at a predetermined duty ratio with respect to the pulse of the light emission drive voltage.
The light emission life of the L display element 43 can be significantly extended.

The first to fourth embodiments have been described above, but the present invention is not limited to these, and various changes accompanying the gist of the configuration can be made. For example, in the above-described embodiment, as the organic EL layer, TPD, Alq
3, PVCz, BND, etc. were used as constituent materials. In addition,
The present invention can be applied when an organic material whose constituent molecules cause orientational polarization under the influence of an electric field is used, or when a material layer contains a functional group or an impurity that causes ionic polarization. it can. Incidentally, when there is a difference in electronegativity of the constituent atoms of the organic EL layer, polarization always occurs when placed in an electric field (especially in a strong electric field). Specifically, C-O, C-N, C = O, C = N, CN-C, C-
_{F, NO, NO 2 -C,} C-S, C-OH, C-CO
OH, functional groups such as C-CH ₃ is believed to affect the polarization. Therefore, the present invention can be applied to an electroluminescence device using an organic EL layer containing these various functional groups.

In each of the embodiments, the organic electroluminescent layer is a single organic material having a hole transporting property and an electron transporting property or a single layer composed of a plurality of organic materials, and the same level is used instead of the anode electrode and the cathode electrode. If a pair of electrodes having a work function is used, light can be emitted even with a reverse voltage and can be emitted for a long time.

In the third embodiment, the TN liquid crystal mode using the polarizing plates 26 and 27 is used. However, the present invention is not limited to this, and the ferroelectric liquid crystal mode, antiferroelectric liquid crystal mode, STN (super twist nematic) liquid crystal mode, And so on. Further, as a reflective LCD, multicolor display may be performed without using a color filter by elliptically polarized light due to birefringence of liquid crystal, or multicolor display may be performed by mixing dichroic dyes in liquid crystal. Further, only the front polarizing plate may be arranged without using the rear polarizing plate, and a configuration such as a polymer dispersed liquid crystal mode in which the polarizing plate is not used may be used. In addition, an elliptically polarizing phase difference plate may be appropriately arranged at a predetermined position.

As described above, in the first embodiment, the reverse voltage is applied in advance before driving the light emission, so that in the second embodiment, the forward voltage and the reverse voltage are alternately alternated at a predetermined duty ratio during continuous light emission. By applying the voltage, or in the third and fourth embodiments, by applying a reverse voltage when not selected, deterioration over time due to internal polarization of the electroluminescent layer can be suppressed.
In the electroluminescent elements 3 and 4, it is even more effective if the reverse electric field is applied in advance.

In each of the above-described embodiments, the reverse electric field is applied after forming the organic electroluminescent layer, but the reverse electric field may be applied when the organic electroluminescent layer is formed. By using such a method, it is possible to obtain an electroluminescence device having a longer emission life.

[0069]

As is apparent from the above description, according to the present invention, there is an effect of realizing an electroluminescence device having a long light emission life. In addition, it is possible to reduce the light emission drive voltage and save power consumption.

[Brief description of drawings]

FIG. 1 is an explanatory cross-sectional view of a first embodiment of an electroluminescent device according to the present invention.

FIG. 2 is a waveform diagram showing a drive voltage according to the second embodiment of the present invention.

FIG. 3 is a cross-sectional view of Embodiment 3 of an electroluminescent device according to the present invention.

FIG. 4 is a timing chart showing drive timing of the third embodiment.

FIG. 5 is a cross-sectional view of Embodiment 4 of an electroluminescent device according to the present invention.

FIG. 6 is a perspective view of a fourth embodiment.

FIG. 7 is a timing chart showing drive timing according to the fourth embodiment.

[Explanation of symbols]

 1 Electroluminescent Device 3 Anode Electrode 4 TPD Film 5 Alq3 Film 6 Cathode Electrode 10 Voltage Applying Means

Claims (9)

[Claims] 1. An organic electroluminescence layer which emits light at a predetermined voltage, an anode electrode provided on one surface side of the organic electroluminescence layer, a cathode electrode provided on the other surface side, and the organic electroluminescence layer. A forward voltage that is applied in the forward direction that is the direction of the electric field that emits light through the luminescent layer, and a voltage applying unit that supplies the reverse voltage whose direction of the electric field is the reverse direction of the forward direction. Light emitting element. 2. The voltage applying means applies the forward voltage and the reverse voltage at a predetermined duty ratio between the anode electrode and the cathode electrode during light emission driving. The electroluminescent device according to claim 1. 3. The electroluminescent device according to claim 1, wherein the organic electroluminescence layer has an electron transport layer and a hole transport layer. 4. The electroluminescent layer comprises a triphenyldiamine derivative film provided on the anode electrode side and a tris (8) provided on the cathode electrode side.
-Quinolinolate) aluminum complex film, and the electroluminescent element according to claim 3. 5. The electroluminescent layer is provided on the cathode electrode side, and a mixed film provided on the anode electrode side and containing at least polyvinylcarbazole and 2,5-bis (1-naphthyl) oxadiazole. The electroluminescent element according to claim 3, comprising a tris (8-quinolinolate) aluminum complex film. 6. A method for driving an electroluminescence device, comprising an anode electrode formed on one surface side of an organic electroluminescence layer and a cathode electrode formed on the other surface side thereof, wherein the anode electrode and the cathode electrode are formed. In between, an electric field characterized by selectively supplying a forward voltage applied in the forward direction, which is the direction of the electric field that emits light through the organic electroluminescent layer, and a reverse voltage applied in the opposite direction to the forward direction. Driving method of light emitting element. 7. The method of driving an electroluminescent device according to claim 6, wherein the reverse voltage is supplied to the organic electroluminescent layer in advance before the organic electroluminescent layer emits light. 8. The reverse voltage is applied to the organic electroluminescent layer during the light emitting period of the organic electroluminescent layer.
Alternatively, the method of driving the electroluminescent device according to claim 7. 9. The product of claim 6, wherein the product of the voltage value of the forward voltage and its application time is substantially equal to the product of the voltage value of the reverse voltage and its application time. Item 9. A method for driving an electroluminescent element according to any one of items 8.