JPH11219788A - EL device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroluminescence element with excellent luminescent characteristics and durability. SOLUTION: A hole injection layer 14 of 4,4',4''-tris[N-phenyl-N-(1-naphthyl) amino] triphenylamine is formed on an anode electrode 13, and a hole transporting layer 15 of α-NPD is laminated on the hole injection layer 14. This element 11 is structured by laminating an electron transporting layer 16 and a cathode electrode 17 on its top. Since the hole injection layer 14 has high hole injection efficiency and thermal stability, this element 11 with excellent luminescent characteristics and high durability can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an electroluminescent device, and more particularly, to an electroluminescent device using an organic material which causes electroluminescence (hereinafter, referred to as EL).

[0002]

2. Description of the Related Art Conventionally, an electroluminescent device having a structure as shown in FIG. 7 has been known. As shown in FIG. 1, the electroluminescent device 1 has an anode electrode 3 made of transparent ITO (indium tin oxide) on a glass substrate 2,
A hole transport layer 4, an electron transport layer 5, and a cathode electrode 6 made of MgIn are laminated.

Here, the hole transport layer 4 is made of N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1'biphenyl-4,4'-
Diamine (hereinafter referred to as TPD) is thermally stabilized N, N'-di (1-naphthyl) -N, N'-diphenyl-1,1'-biphenyl-4,4'-diamine (hereinafter referred to as TPD) , Α-NPD).

[0004] TPD has the following structural formula:

Embedded image It is represented by

[0005] α-NPD has the following structural formula:

Embedded image It is represented by

In such an electroluminescent device 1, FIG.
Between the anode electrode 3 and the hole transport layer 4 as shown in FIG.
Another layer capable of transporting holes (hereinafter referred to as hole injection layer)
It is known that the performance of the element can be improved by interposing 7. As a material for forming the hole injection layer 7, 4,4 ', 4 "-tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine (hereinafter, MTDAT)
A) is known.

[0007] MTDATA has the following structural formula:

Embedded image It is represented by

[0008]

In an electroluminescent device using such an organic material, it is important that the organic material has thermal stability. The glass transition temperature (Tg) of α-NPD forming the hole transport layer 4 is around 100 ° C., and the glass transition temperature (Tg) of TPD is 62 ° C. It is stable. However, the MTDA forming the hole injection layer 7
The glass transition temperature (Tg) of TA is around 75 ° C., and the thermal stability is lower than that of the hole transport layer 4.
Under such circumstances, in order to maintain the stability of the characteristics when the electroluminescent device 1 is driven, it is desired to form the hole injection layer 7 with a thermally stable hole injection material. Further, it is desired to improve the stability of quality in the manufacturing process of the electroluminescent device 1 by making the hole injection layer 7 thermally stable.

The problem to be solved by the present invention lies in what means should be taken to obtain a durable electroluminescent device having good hole injection efficiency.

[0010]

According to the first aspect of the present invention,
An organic material layer is interposed between the anode electrode and the cathode electrode, the organic material layer including a hole injection layer bonded to the anode electrode, and a hole transport layer bonded to the hole injection layer. An electroluminescent device, wherein the organic material layer and the hole injection layer have a structural formula

Embedded image And 4,4 ', 4 "-tris [N-phenyl-N- (1-naphthyl) amino] triphenylamine.

The 4,4 ', 4 "-tris [N-phenyl-N- (1-naphthyl) amino] triphenylamine which forms the hole injection layer according to the first aspect of the present invention has a glass transition temperature ( Tg)
= 117 ° C. and melting point (Tm) = 248 ° C. Since it is thermally stable, it has excellent durability. In addition, since the hole injecting property is equivalent to that of MTDATA, the hole injecting efficiency is good, and an electroluminescent element having good emission characteristics can be formed.

According to a second aspect of the present invention, in the electroluminescent device according to the first aspect, the organic material layer includes the hole transport layer and an electron transport layer bonded to the hole transport layer.

According to a third aspect of the present invention, in the electroluminescent device according to the first or second aspect, the hole transport layer is formed of N, N'-di (1-naphthyl) -N, N It is characterized by comprising '-diphenyl-1,1'-biphenyl-4,4'-diamine (α-NPD).

According to the third aspect of the present invention, since the hole transport layer (α-NPD) has thermal stability similarly to the hole injection layer, when a high voltage and a high current are applied, a high temperature is applied. The durability near the anode electrode can be improved. Therefore, the durability of the electroluminescent device can be improved.

According to a fourth aspect of the present invention, in the electroluminescent device according to the second or third aspect, a light emitting layer is interposed between the hole transport layer and the electron transport layer. It is characterized by.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the electroluminescent device according to the present invention will be described below based on embodiments shown in the drawings. (Embodiment 1) FIG. 1 is an explanatory sectional view showing Embodiment 1 of an electroluminescent device according to the present invention. As shown in the figure, in an electroluminescent element 11 of the present embodiment, an anode electrode 13 made of transparent ITO is formed on a glass substrate 12. On the anode electrode 13, 4,4 ', 4 "-tris [N-
The hole injection layer 14 made of phenyl-N- (1-naphthyl) amino] triphenylamine (hereinafter referred to as α-TPNATA) is formed by a vacuum evaporation method so as to have a thickness of 30 nm. The α-TPNATA was synthesized from tris (4-iodophenyl) amine synthesized from triphenylamine and N-phenyl-1-naphthylamine by an Ullmann reaction, and purified by column chromatography to obtain the final product. Was found to be able to be recovered at a yield of 10%. By the way, α-TPNATA
As a result of thermal analysis, a glass transition point Tg of 117 ° C. and a melting point (Tm) of 248 ° C. were observed.

Α-TPNATA has the structural formula

Embedded image It is represented by

On the hole injection layer 14, a hole transport layer 15 made of α-NPD is formed by a vacuum evaporation method so as to have a thickness of 30 nm. Then, an electron transport layer 16 made of beryllium (bis (10-hydroxybenzo [h] quinolinenanate)) (hereinafter referred to as Bebq2) is formed on the hole transport layer 15 by a vacuum evaporation method so as to have a thickness of 50 nm. Is formed.

Bebq2 has the structural formula

Embedded image It is represented by

On the electron transport layer 16, for example, MgIn
Are formed to constitute the electroluminescent device 11 of the present embodiment.

Here, α-TPNAT is added to the hole injection layer 14.
A of the present embodiment using A and MTDA instead of α-TPNATA of the present embodiment for the hole injection layer in the hole injection layer.
An electroluminescent device using TA (Comparative Example 1) was prepared with an area of 2 × 2 [mm 2], and the luminescence characteristics were evaluated based on the measurement results of luminescence in room temperature and air.
A DC power supply is connected to the anode and cathode electrodes of each electroluminescent element, and a voltage is applied for about 1 second while changing the voltage by 0.1 V, the current value of each voltage is measured, and light is emitted by a luminance meter. Was measured for strength. Measured voltage V
[V], current density J [A / m2], luminance L [cd / mm2], and luminous efficiency η [lm / W] assuming a perfect diffusion surface
Is calculated by the following equation (1). η = π · L / (V · J) (1) This value is plotted on a logarithmic graph, and is then 300 [cd /
m2].

The electroluminescent device of this embodiment and Comparative Example 1
At 300 [cd / m2] were almost the same as shown in Table 1 below. Note that the values in parentheses in Table 1 indicate the ratio of standard deviation × 3 at eight measurement points.

[Table 1]

By the way, looking at the limit of the power at which the electroluminescent element is destroyed by the high voltage and the high current, as shown in FIG. 3, in Comparative Example 1, 9.946 [V] × 108.75 [mA / cm2] = 1
In contrast to 0.7491 [W / cm2], as shown in FIG. 2, in the electroluminescent device of the present embodiment, 10.432 [V] × 1251 [mA / cm2] = 13.0.
It was found to have durability up to 50 [W / cm2]. At a high voltage and a high current, the heat generated by the anode electrode melts the hole injection layer immediately above the anode electrode and destroys the element. The melting point of MTDATA is 203 ° C., compared to α- used in the present embodiment.
Since the melting point of TPNATA is as high as 248 ° C., it can be seen that the durability of the electroluminescent element is improved. in this way,
By using α-TPNATA for the hole injection layer 14, it becomes possible to realize an element that can withstand higher voltage and higher current.

Although the first embodiment has been described above, the electroluminescent device in which α-TPNATA can be used as the hole injection layer is a device having an organic multilayer structure including at least the hole transport layer 15 and the electron transport layer 16. Therefore, the hole transporting layer 15 can also exert the above-described effects with a hole transporting substance other than α-NPD of the present embodiment, for example, TPD. The Bebq2 used for the electron transport layer 16
May be another electron transporting material, for example, aluminum tri (8-quinolate) (hereinafter, referred to as Alq3). Al
q3 is a structural formula

Embedded image It is represented by Further, the hole transport layer 15 and the electron transport layer 16
Of course, a configuration in which a light emitting layer is interposed between the light emitting element and the light emitting element may be used. Further, for the purpose of producing an electroluminescent element having heat resistance, α-TPNATA may be used as the hole transport layer.

(Embodiment 2) FIG. 4 is an explanatory sectional view showing an embodiment 2 of an electroluminescent device according to the present invention. As shown in the figure, an electroluminescent element 11 of the present embodiment has an anode electrode 13 made of transparent ITO on a glass substrate 12.
Are formed. On the anode electrode 13, α-T
The hole injection layer 14 made of PNATA is formed by a vacuum evaporation method so as to have a thickness of 30 nm. Hole injection layer 1
4 is provided with a hole transport layer 15 of α-NPD for 30 n.
It is formed by a vacuum evaporation method so as to have a film thickness of m. On the hole transport layer 15, a light emitting layer 18 formed by co-evaporation of Bebq2 and quinacridone (hereinafter, referred to as Qd) is formed to have a thickness of 22 nm.

Qd is a structural formula

Embedded image It is represented by

An electron transport layer 16 of Bebq2 is formed on the light emitting layer 18 by a vacuum evaporation method so as to have a thickness of 50 nm. Then, a cathode electrode 17 made of, for example, MgIn is formed on the electron transport layer 16 to constitute the electroluminescent device 11 of the present embodiment.

Using the electroluminescent device of the present embodiment and Comparative Example 1 described above, the same measurement as in the above-described Embodiment 1 was performed. As a result, the same evaluation as that of the Embodiment 1 was obtained in the light emission characteristics and heat resistance. I was able to. FIG. 5 is a graph showing the results of measuring the light emission characteristics of the electroluminescent device 11 of the present embodiment.

Next, the luminance of the electroluminescent device 1 of Comparative Example 2 shown in FIG. 6 will be compared. This electroluminescent element 1 is composed of an anode electrode 3 made of ITO, a MTDA
A hole injection layer 7 of TA, a hole transport layer 4 of α-NPD, a light emitting layer 8 of co-evaporated TPD and rubrene, Be
An electron transport layer 5 made of bq2 and a cathode electrode 6 made of Mg-In are sequentially laminated. When luminance of the comparative example 2 and the electroluminescent element 11 of this embodiment were measured at the same current density, as shown in Table 2 below,
It showed almost the same value.

[Table 2]

However, as shown in the same table, at the highest luminance, the value of the electroluminescent element 11 of the present embodiment was higher than that of the comparative example 2 by 10% or more. It can be understood that this is a result in which the difference in heat resistance of the lowermost layer of the organic layer appears as it is at the highest luminance at the limit of destruction if the devices have the same efficiency at the light emitting interface. That is, MTDATA is transferred to the hole injection layer 7.
Electroluminescent element 1 of Comparative Example 2 used for α-TPNAT
Electroluminescent device 1 of this embodiment using A as hole injection layer 14
1 difference. In the case of devices having the same luminous efficiency, M
If α-TPNATA is used instead of TDATA, a more durable electroluminescent element can be obtained.

Also in this embodiment, the same effect can be obtained by using, for example, TPD in addition to α-NPD. Further, an electron transporting substance other than Bebq2, for example, Alq3 may be used for the electron transporting layer 16. further,
As a substance to be co-evaporated together with the electron transporting substance on the light emitting layer 18, for example, coumarin or the like can be used other than Qd. Furthermore, the same effect can be obtained in an electroluminescent element in which co-evaporation is performed not with an electron transporting substance but with a hole transporting substance.

[0032]

As is apparent from the above description, according to the present invention, the hole injection efficiency is high, the emission characteristics are good,
In addition, an electroluminescent element having durability can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional explanatory view showing Embodiment 1 of an electroluminescent element according to the present invention.

FIG. 2 is a graph showing light emission characteristics of the electroluminescent device of Embodiment 1.

FIG. 3 is a graph showing light emission characteristics of Comparative Example 1.

FIG. 4 is an explanatory sectional view showing Embodiment 2 of the electroluminescent device according to the present invention.

FIG. 5 is a graph showing light emission characteristics of the electroluminescent device of Embodiment 2.

FIG. 6 is an explanatory sectional view showing Comparative Example 2.

FIG. 7 is an explanatory sectional view showing a conventional example.

FIG. 8 is an explanatory sectional view showing another conventional example.

[Explanation of symbols]

 Reference Signs List 11 electroluminescent element 13 anode electrode 14 hole injection layer (α-TPNATA) 15 hole transport layer 16 electron transport layer 17 cathode electrode 18 light emitting layer

Claims (4)

[Claims] An organic material layer is interposed between an anode electrode and a cathode electrode, wherein the organic material layer is connected to the anode electrode, and a hole injection layer is connected to the hole injection layer. And wherein the organic material layer and the hole injection layer have a structural formula: An electroluminescent device comprising: 4,4 ', 4 "-tris [N-phenyl-N- (1-naphthyl) amino] triphenylamine represented by the formula: 2. The method according to claim 1, wherein the organic material layer includes an electron transport layer bonded to the hole transport layer.
An electroluminescent device according to claim 1. 3. The method according to claim 1, wherein the hole transport layer is made of N, N′-di (1-naphthyl) -N, N′-diphenyl-1,1′-biphenyl-4,4′-diamine. The electroluminescent device according to claim 1 or 2, wherein 4. The electroluminescent device according to claim 2, wherein a light emitting layer is interposed between the hole transport layer and the electron transport layer.