JPH01282291A - Thin-film el element - Google Patents

Abstract

PURPOSE:To obtain a thin-film EL element, equipped with an electrode, positive hole injection layer, light-emitting layer using a rare earth complex as a light- emitting material and electrode and capable of providing emission with high brightness and clear color at a low applied voltage. CONSTITUTION:The objective element obtained by forming a (semi)transparent electrode 2 made of indium tin oxide, SnO2, ZnO, etc., normally of 50mm-1mum thickness on a substrate 1 consisting of glass, plastic, quartz, etc., then forming a positive hole injecting layer 4, consisting of a positive hole transmitter (preferably aromatic amine compound) and having function to transmit positive holes injected from the electrode 2 to a light-emitting layer thereon, forming a light- emitting layer 5 using a light-emitting material preferably consisting of a fluorescent rare earth complex thereon and further forming a back electrode 3 made of a metal, such as gold, Al, Mg or In, normally of 50-200nm thickness thereon.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an EL device having a hole injection layer and a light emitting layer, which is a thin film that can emit light of high brightness and bright colors with a low applied voltage. This invention relates to an EL (electroluminescence) element.

[Prior art and problems to be solved] EL devices have the characteristics of high visibility due to their self-luminescence, and excellent impact resistance because they are completely solid-state devices. Z-S: EL elements using Mn are widely used. However, in such @@EL element, the applied voltage for one light emission is 2.
Since nearly 00V is required, the driving method is complicated.

On the other hand, since organic thin film EL elements can significantly reduce the applied voltage, organic thin film EL elements using various materials are being developed. Vinset et al. have already fabricated an EL device using atracene as a light emitter and a vapor-deposited film with a film thickness of about 0.6 μm, and obtained blue photopic visible light emission at an applied voltage of 30 V (Thin). 5olid F days ms, 94
(1982) 1) However, this device has problems in that its brightness is insufficient and the applied voltage still has to be high.

In addition, in recent years, organic EL elements that emit light with a brightness of 5 to 90 cd/■2 just by applying a low voltage of about 10 V have been developed using thin films using the LB method (Langmuir-Prodgett method). (For example, Japanese Patent Application Laid-Open No. 61-43
682), however, this organic EL element is LB
Since a laminated film of electron-accepting and electron-donating luminescent substances is produced by stacking monomolecular films by the method, there are problems in that the structure is complex, the manufacturing is complicated, and it lacks practicality.

Therefore, in order to solve these problems, we developed an electrode/
A laminated type with hole injection layer/emitting layer/electrode has been developed, for example, JP-A-59-194393, Appl.
Phys, Lett, 51(12), 21 S.
ep.

It was introduced in 1987. Of these, App
I, Phys, Lett, 51(12),
An EL device uses an aluminum complex of 8-hydroxyquinoline as a light emitting material and a diamine compound as a hole injection material.

It is an excellent device that can obtain a luminance of 1000 cd/m'' with an applied voltage of 10 V or less.

However, the product of these electrodes/hole injection layer/light emitting layer/electrode! J-type thin film EL elements have a wide emission spectrum, resulting in poor color vividness and difficulty in faithfully expressing the three primary colors of blue, green, and red. Furthermore, in the thin film EL device described in JP-A-59-194393, it is necessary to set the film thickness between the electrodes to 1 g+w or less. Therefore, especially in a large-area EL device,
This has major problems in that pinholes are likely to occur and productivity is low.

In addition, EL elements have also been developed that have a double-structured light-emitting layer and use a rare earth complex as the light-emitting organic compound, and can emit light with sufficiently high brightness even at low voltages (for example, Japanese Patent Laid-Open No. 51-37887 No.), Shikashi.

This thin film EL device is not a laminated type having an electrode/hole injection layer/light emitting layer/m-pole;
When a rare earth complex is used as a luminescent material in a single-layer EL element, there is no disclosure regarding improvement in the saturation of the color emitted by the element, that is, the brightness of the color.

The present invention has been made in view of the above circumstances, and is a multilayer EL device having a hole injection layer and a light emitting layer, which is a thin film that exhibits a high brightness and a sharp spectrum and emits clear colors when a low voltage is applied. The purpose is to provide EL elements.

[Means for Solving Problems] In order to achieve the above object, the present inventor has continued to conduct intensive research, and as a result, the present inventor has developed a luminescent material for a stacked EL element having an electrode, a hole injection layer, a luminescent layer, and an electrode. The present inventors have discovered that the use of rare earth complexes, particularly fluorescent rare earth complexes, has a significant effect on the saturation of the color emitted by the device, leading to the completion of the present invention.

That is, the thin 111 EL device of the present invention is an EL device comprising an electrode, a hole injection layer 9, a light emitting layer, and an electrode,
The structure uses a rare earth complex as the luminescent material of the luminescent layer.

The present invention will be explained in detail below.

The thin film EL device of the present invention is an AC (alternating current) drive type and a D
It can be used for any C (DC) drive type, but
The following description will be made regarding the DC drive type with reference to FIG.

In FIG. 1, l represents a substrate, which is made of glass, plastic, quartz, or the like. 2 and 3 are electrodes sandwiching the hole injection layer 4 and the light emitting layer 5;
One electrode 2 is formed on the substrate 1 and includes ITO (insium tin oxide), 5nOx (stannic oxide),
A transparent or semi-transparent electrode is made of Z, , O (zinc oxide) or the like. This electrode 2 is usually 50 mm to IJ, L
From the viewpoint of transparency, it is preferable that the film thickness of the grave is 50 to 200 rows.
It functions as a counter electrode and uses metals such as gold, aluminum, magnesium, and indium. This back electrode 3 usually has a thickness of 50 to 200 nm.

Note that, depending on the type of thin film EL element, it is also possible to use the electrode 2 on the substrate l side as a metal back electrode and the other electrode 3 as a transparent or semitransparent electrode.

The hole injection N4 is made of a hole transfer compound and has a function of transferring holes injected from the electrode (anode) 2 to the light emitting layer. As this hole transfer compound, 10'
When the layer is placed between electrodes applying an electric field of ~lO6 volts, it is preferred to use a compound having a hole transfer coefficient of at least 610"'c"/V-Sec;
Particularly preferred are aromatic amine compounds.

Preferable examples of hole transport compounds include amine compounds that are solid at room temperature and in which at least one nitrogen atom is trisubstituted with a substituent.

In this case, at least one of the trisubstituted groups is an aryl group or a substituted aryl group.

Examples of useful substituents on aryl groups include alkyl groups with 1 to 5 carbon atoms, such as methyl, ethyl, propyl, butyl and amyl; halogen atoms, such as chlorine and fluorine. : and alkoxy groups having 1 to 5 carbon atoms, such as methoxy, ethoxy, propoxy, butyl and amyl groups.

In the present invention, it is necessary to form the hole transport compound into a thin film, and the hole transport compound formed into a thin film includes those having the following formula structure.

Q' and Q2 in the above formula are groups separately containing a nitrogen atom and at least three carbon rings, at least one of which is aromatic, for example a phenyl group. Carbocycles may also be saturated rings, such as cyclohexyl and cyclohebutyl groups.

G is a linking group, such as a cycloalkylene group, such as a cyclohexylene group, an arylene group, such as a phenylene group; an alkylene group, such as a propylene group; or a C-
It is a C bond. Specific examples within the scope of the above structural formulas include, among others:

1.1-bis(4-di-p-tolylaminophenyl)-4-7enylcyclohexane having the structure of the following formula; 1.1-bis(4-di-p-tolylaminophenyl) having the structure of the following formula ) cyclohexane; 1,1-bis(4-
p-)-lylaminophenyl)cyclohexane; and a compound having the structure of the following formula (in the above formula, n is a !i number from 2 to 4) 0 For example, 4.
4-bis(diphenylamino)quadsophenyl.

Examples include bis(4-dimethylamino-2-methylphenyl)phenylmethane and N,N,N-tri(p-tolyl)amine.

Furthermore, a rare earth complex is used as the luminescent material of the luminescent layer 5. There are no limitations as long as it is a rare earth complex, but from the point of view of EL luminous efficiency, fluorescent rare earth complexes are preferred, and the following rare earth complexes are particularly preferred.

Among these, R1 and R2 each independently represent an alkyl group having 1 to 15 carbon atoms, such as a methyl group, an ethyl group, a propyl group, a butyl group, an i-propyl group, a t-butyl group, an i-butyl group, Examples include s-butyl group, octyl group, and nonyl group.

Halogenated alkyl groups having 1 to 15 carbon atoms (here, halogen means chlorine, fluorine, bromine, etc.), such as trifluoromethyl group, beptafluoroprobyl group,
Examples include trichloromethyl group, tribromomethyl group, dichloromethyl group, chloromethyl group, difluoromethyl group, fluoromethyl group, dibromomethyl group, and bromomethyl group.

Aryl groups of 6 to 14 carbon atoms, e.g.

Examples include phenyl group, naphthyl group, tolyl group, xylyl group, and anthryl group.

5- or 6-membered heterocyclic groups containing one heteroatom, such as nitrogen, oxygen or sulfur, such as a pyrrolyl group,
It is a furyl group, a thienyl group, a pyridyl group, etc., and R1 has the same meaning as hydrogen or the group R8.

Rani M is a rare earth element, C1 (cerium), T
b (terbium), S, (samarium), El (europium), H, (holmium), Pr (praseodymium), ad (gadolium), E, (erbium).

There are Tm (thulium), etc.

Examples of the rare earth complex in this example include E, and BF.
A (benzoyl trifluoroacetone) [E,
(BFA)3].

This is shown as a structural formula: It is expressed as

Among these, Rr, R2, Rx, and M have the same meanings as above. Moreover, TOPO is tri-n-octylphosphine oxyto.

For example, the rare earth complex in this example is 1.

Examples include [Tb(TTA)3(TOPO)*], which is composed of TIl, TTA (thenoyl trifluoroacetone), and TOPO (tri-ro-octylphosphine oxyto).

This is shown as a structural formula.

[Margin below] It is expressed as

Here, R1, Rt, R3, and M have the same meanings as above.

The rare earth complexes in this example include E, TTA, and Ph.
[ E u (T T
A):l (Phen) ], S, and Ndō FA
(2-naphthoyl triple oacetone) and Phen
)] and [C-(
Examples include T T A )s(Phen) 1 and the like.

[Hereinafter, blank space] When [C, (T T A ) i (Phen)] is shown as a structural formula, it is expressed as follows.

Specific examples of the rare earths in (1) to (2) above can be expressed as linear (1-1) to (6-6).

[Left below] (1-i) [M(8FA)3] (1-4)(
3-1) [M(TTA)3] (3-4)(
4-1) [M(NTFA)3] (4-4)
(5-1) (5” Here, 1M represents a rare earth element, and the above (1-1) to (
1.10-phenanthroline and trioctylphosphine oxyto can also be added to 6-6).

Further, other preferable examples of rare earth complexes include the following.

Trisbipyridine rare earth 2a salt represented by the structural formula.

Among these, M is a trivalent rare earth ion, A is an anion,
Examples include perchlorate ion, phosphorus hexafluoride ion, fluoroborate ion, iodine ion, bromide ion, chloride ion, and acetate ion.

[btT's color] Among these, M is a trivalent ion of a rare earth element (f is a terbium ion). A is an anion, which is the same as that listed in (■).

Bispyridine rare earth complex salt represented by the structural formula.

Of these, M is a trivalent ion of two rare earth elements.

Bipyridine rare earth complex salt represented by the structural formula.

Of these, M is a trivalent ion of rare earth.

A thin film EL device having the above configuration is produced by the following procedure.

First, a transparent electrode 2 is formed as a thin film on a substrate 1 by vapor deposition or sputtering. Next, a hole injection layer 4 made of a thin film of a hole transport compound is formed on the upper surface of the transparent electrode 2. At this time, the sH conversion is performed by a vapor deposition method under five-order conditions.

(Vaporization conditions) Boat heating conditions: 50 to 400°C Vacuum degree: io-'-101Pa Vapor deposition rate: 0, 1 to 50 ne/see Substrate temperature knee substrate -200°C Film thickness: 100 nm to 5 JLs Next, hole injection A light emitting layer 5 made of a thin film of a light emitting material is formed on the upper surface of the layer 4. The thinning at this time is performed by a spin cord method, a casting method, an LB method, a vapor deposition method, or the like, and from the viewpoint of film uniformity and removal of pinholes, it is preferable to form a film using a vapor deposition method.

Regarding the formation order of the hole injection layer 4 and the light emitting layer 5, it is also possible to form the light emitting layer 5 by vapor deposition and then forming the hole injection layer 4 by vapor deposition in the reverse order of the above. 1i3jf formed in this way
The iEL element has a structure in which the electrode 2/light emitting layer 5/hole injection layer 4/electrode 3 are laminated in this order.

Thereafter, a back electrode 3 is formed as a fii film on the upper surface of the light emitting layer 5 or the hole injection layer 4 by a vapor deposition method, a sputtering method, or the like.

(Example 1) I
A transparent support substrate was prepared by forming a TO film with a thickness of 50 nm using the vapor deposition method, and this transparent support substrate was fixed to a substrate holder of a vapor deposition device (manufactured by Japan Vacuum Technology Co., Ltd.) and placed in a resistance heating boat made of molybdenum. [E u (TT A )3 (Phe
n)] in 200 @g and put N, N, N' into another boat.
, N'-tetraphenyl-(1,l'-biphenyl)4
．． 4'-diamine (TPD) and the vacuum layer is
The pressure was reduced to -4P.

Here, CE u(T T A )z (Phen)l
An aqueous solution of Eu chloride was adjusted to pH 5.5, and extracted with TTA and a solution of Phen dissolved in a 1:1 mixed solution of acetone and benzene. Furthermore, the solvent was removed under reduced pressure and [E u(T T A ) x(
Phen)] was obtained and purified.

Further, heating the resistance heating boat to 140 degrees Celsius,
The complex was deposited on a transparent support substrate at a deposition rate of 1.0 nm/see to obtain a phosphor thin film with a film thickness of 1.0 nm/see. At this time, the substrate temperature was room temperature.

Furthermore, another boat was heated to 210 degrees Celsius, and TPD was deposited at a deposition rate of 1 Onu/sec to form a hole injection layer with a thickness of 500 n- on the phosphor thin film.

The substrate temperature at this time was room temperature.

This was taken out from the vacuum layer, a stainless steel mask was placed on top of the thin film, it was fixed again on the substrate holder, 20 mg of gold was placed in a resistance heating boat made of molybdenum, and the pressure of the vacuum layer was reduced to 2xlO-'P. Thereafter, the boat was heated to 1400 degrees Celsius, and a gold electrode with a thickness of 100 ni was formed on the light emitter thin film to serve as a counter electrode. This element has a gold electrode as a positive electrode, ITO? When 22 V DC was applied using the Li electrode as the negative electrode, a current of 1.5 A flowed and red light was emitted.

The maximum emission wavelength at this time was 618n, and the emission brightness was 43.
6 cd/m". CIE chromaticity coordinates are X zero 0.6
5. It is y-0.34 and is a clear red color.

(Example 2) An EL device was produced in the same manner as in Example 1. However, the light emitting thin film material is S JN F T A ) 3 (Phen)
] was used.

Here, [S m(N T F A )z(Phen)1
To adjust the pH of an aqueous solution of S1 chloride to 5.5, add N to it.
Extraction was performed by mixing FTA and Phen dissolved in a cyclohexane solution. Further, the solvent was removed under reduced pressure to obtain [S m (N T F A ) + (Phen), which was purified.

Additionally, during the vapor deposition, the boat was heated to 160 degrees Celsius.

When a DC voltage of 31V was applied to this element, the current was 25V.
mA flow, red luminescence was obtained.

At this time, the maximum emission wavelength was 6540 Rin, and the emission brightness was 20
It was 0 cd/m'. CIE chromaticity coordinates are X=0.
66, y=0.323, and the color was clear red.

(Example 3) An EL device was produced in the same manner as in Example 1.

However, the luminescent thin film material is [Tゎ(TTA)3
(TOP Oz)] was used.

Here, [T b (T T A )s (T O P O) *
P) is an aqueous solution of TIl chloride adjusted to 14.5, and to this is added 2 x 10-' mol/i of TOPO, sx 10-
'Add and mix mol/i TTA in hexane solution,
After that, extraction was performed. Furthermore, the solvent was removed under reduced pressure,
[T b (T T A )s (obtain T OP OLl,
This was purified.

During vapor deposition, the boat was heated to 140 degrees Celsius to form a 700 nm thick phosphor thin film. When a DC voltage of 13 V was applied to this element, a current of 1.5 mA flowed and yellow-green light was emitted. The maximum emission wavelength at this time is 545 nm
The luminance was 985 cd/@'', the CIE chromaticity coordinates were xxo, 34.y=0.56, and the color was clear yellow-green.

(Example 4) An EL device was produced in the same manner as in Example 1. However, the light-emitting thin film material used was [C, (T T A 3) Phenl].

Here, [C, (T T A ) + (Phen)] is obtained by adjusting the aqueous solution of C11 chloride to pH 4.5, and adding TTA to this.
and Phen dissolved in a 1=1 mixed solution of acetone and benzene were mixed and extracted. Furthermore, the solvent was removed under reduced pressure and [C, (T T A ) + (Phen)
] was obtained and purified.

Further, during vapor deposition, the boat was heated to 145 degrees Celsius to form a 600 nm thick phosphor thin film. When a DC voltage of 34 V was applied to this element, a current of 40 mA flowed and blue-violet light was emitted.

The maximum emission wavelength at this time is 400n, and the emission brightness is 18
0 cd/ys", the CIE chromaticity coordinates are x=0.
17. y-0.02 and a clear blue-purple color.

As a result of the above, the thin 11EL element having a hole injection layer and a light emitting layer according to the present invention emits the three primary colors of red, blue, and green with high brightness and sharp spectrum in good saturation simply by applying a low voltage. It has been found. This has made it possible to realize color displays made of thin film EL elements that clearly display various colors. It has also been found that manufacturing of thin film EL elements is easy and productivity can be improved.

[Effects of invention As described above, according to the thin film EL element of the present invention.

It has the effect of being able to emit light with high brightness and clear colors just by applying a low voltage.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the DC drive type of the thin film EL device of the present invention. 1: Substrate 2: Transparent electrode 3: Back electrode 4: Hole injection layer 5: Light emitting layer

Claims (1)

[Claims] EL comprising an electrode, a hole injection layer, a light emitting layer and an electrode
1. A thin film EL device, characterized in that a rare earth complex is used as a light emitting material in the light emitting layer.