KR101338345B1 - organic electroluminescent display device - Google Patents

Abstract

The present invention relates to an organic electroluminescent device having a long lifetime.
The organic electroluminescent device of the present invention comprises a first electrode and a second electrode; A light emitting material layer positioned between the first and second electrodes and having a first highest occupied molecular orbital (HOMO) level; A first organic material layer comprising a triphenylene compound derivative having a second HOMO level and an organic compound having a third HOMO level and having a fourth HOMO level between the first electrode and the light emitting material layer, The third HOMO level is located between the first HOMO level and the second HOMO level. As such, by using a triphenylene compound derivative having a high glass transition temperature, it is possible to obtain a device having a high thermal stability and a long lifetime, and to form an organic compound having a relatively high HOMO level, thereby lowering the driving voltage.

Description

Organic electroluminescent display device

The present invention relates to an organic electroluminescent device, and more particularly, to an organic electroluminescent device having an improved lifetime.

2. Description of the Related Art Flat panel displays having excellent characteristics such as thinning, lightening, and low power consumption have been widely developed and applied to various fields.

Among them, an organic electroluminescent device or an organic electroluminescent display, also called an organic light emitting diode (OLED), injects electric charge into a light emitting layer formed between a cathode, which is an electron injection electrode, and an anode, which is a hole injection electrode. This is a device that emits light while disappearing after pairing electrons and holes. Such organic electroluminescent devices can be formed not only on a flexible substrate such as a plastic but also because they are excellent in color due to self-luminescence and are low in plasma display panel (Plasma Display Panel) and inorganic electroluminescence It has the advantage of being able to drive (less than 10V) voltage and relatively low power consumption.

1 is a diagram illustrating a structure of a general organic electroluminescent device using a band diagram.

As shown in FIG. 1, the organic electroluminescent device has an emitting material layer (EML) 14 between an anode electrode 11 serving as an anode and a cathode electrode 17 serving as a cathode. Located. To inject holes from the anode electrode 11 and electrons from the cathode electrode 17 into the light emitting material layer 14, between the anode electrode 11 and the light emitting material layer 14 and between the cathode electrode 17 and the light emission. A hole transporting layer (HTL) 13 and an electron transporting layer (ETL) 15 are positioned between the material layers 14, respectively. At this time, to inject holes and electrons more efficiently, a hole injecting layer (HIL) between the anode electrode 11 and the hole transport layer 13 and between the electron transport layer 15 and the cathode electrode 17 ( 12) and an electron injecting layer (EIL) 16.

1, the lower line is the highest energy level of the valence band, the highest occupied molecular orbital (HOMO), the upper line is the lowest energy level of the conduction band, LUMO (lowest unoccupied molecular orbital). The energy difference between the HOMO level and the LUMO level is called a band gap.

In the organic electroluminescent device having such a structure, holes (+) and cathode electrodes 17 injected from the anode electrode 11 into the light emitting material layer 14 through the hole injection layer 12 and the hole transport layer 13. Electrons (−) injected from the electron injection layer 16 and the electron transport layer 15 through the electron injection layer 16 form an exciton 18 through recombination. 18 to emit light of a color corresponding to the band gap of the light emitting material layer 14.

Here, the hole injection layer 12 and the hole transport layer 13 may be formed by depositing with a single material, such as N, N'-di-1-naphthyl-N, N'-diphenyl-1, 1'-biphenyl-4,4'diamine (hereinafter referred to as NPD) or 4,4 ', 4 "-Tris (N- (2-naphthyl) -N-phenyl-amino) -triphenylamine (hereinafter referred to as 2-TNATA) However, the glass transition temperature of NPD is about 95 degrees Celsius, and the glass transition temperature of 2-TNATA is about 110 degrees Celsius, which is not satisfactory for thermal stability. Attempts have been made to ensure higher thermal stability and longer life using triphenylene compound derivatives having a higher glass transition temperature than -TNATA.

However, when such a triphenylene compound derivative is used as the hole injection layer, a problem arises in that the driving voltage rises and the voltage rise according to the actual use time is lower than that of NPD or 2-TNATA. In addition, when the triphenylene compound derivative is used as the hole transport layer, there is a problem in that the interface property with the light emitting material layer is lowered and the luminous efficiency and lifespan characteristics are lowered.

FIG. 2A is a diagram schematically showing a band diagram of an organic EL device using NPD as a hole transport layer, and FIG. 2B is a diagram schematically showing a band diagram of an organic EL device using a triphenylene compound derivative as a hole transport layer. to be.

As shown in FIGS. 2A and 2B, the hole transport layer 23a or 23b, the light emitting material layer 24, and the electron transport layer 25 are sequentially positioned between the anode electrode 21 and the cathode electrode 27. Here, the HOMO level of the hole transport layer 23b formed of the triphenylene compound derivative is lower than the HOMO level of the hole transport layer 23a formed of NPD, and thus the energy gap g2 between the hole transport layer 23b and the light emitting material layer 24. ) Is larger than the energy gap g1 between the hole transport layer 23a and the light emitting material layer 24. That is, holes injected from the anode electrode 21 into the hole transport layer 23b are difficult to be injected into the light emitting material layer 24, and holes are accumulated at the interface between the hole transport layer 23b and the light emitting material layer 24. As a result, the driving voltage increases during light emission, and in particular, the interface characteristics are deteriorated due to the holes accumulated in the interface, and a change in the voltage increase according to the driving time causes a greater problem than the hole transport layer 23a of the NPD. .

Table 1 and Figures 3 and 4 show the characteristics of the conventional organic electroluminescent device, and shows the comparative results of Example 1 using NPD as the hole transport layer and Example 2 using the triphenylene compound derivative as the hole transport layer. Here, FIG. 3 is a graph showing the life characteristics of each organic electroluminescent device, and FIG. 4 is a graph showing a change in voltage according to driving time, and is a result measured at 4,000 nits of luminance.

Voltage (V) Efficiency (cd / A) CIE (X) CIE (Y) Life span (T ₉₀ : hr) Example 1 3.6 5.1 0.137 0.100 100 Example 2 4.4 5.0 0.139 0.099 200

As shown in Table 1, the efficiency of Example 1 is 5.1 cd / A, the CIE (X) and CIE (Y) are 0.137 and 0.100, respectively, the efficiency of Example 2 is 5.0 cd / A, and the CIE (X) and CIE ( Y) is 0.139 and 0.099, respectively, and Examples 1 and 2 show similar characteristics in efficiency and color coordinates. However, while the driving voltage of Example 1 is 3.6V, the driving voltage of Example 2 is 4.4V, which is higher than that of Example 1, and as shown in Table 1 and Figure 3, when Example 1 is 100 hours later, the luminance is reduced to 90%. On the other hand, in Example 2 after 200 hours, it can be seen that the life of Example 2 is long. In addition, in the case of the voltage rise change according to the driving time, it can be seen that the voltage rise change of Example 2 is larger than that of Example 1, as shown in FIG.

As described above, Example 2 using the triphenylene compound derivative as the hole transport layer has advantages in lifespan, compared with Example 1 using NPD as the hole transport layer, but has a high driving voltage and a large change in voltage increase with driving time. There are disadvantages.

The present invention is to solve the above-mentioned driving voltage rise and the change in voltage characteristics according to the driving time, by using a material having a relatively high glass transition temperature to provide an organic electroluminescent device having improved thermal stability and lifespan For the purpose of

The organic electroluminescent device of the present invention comprises a first electrode and a second electrode; A light emitting material layer positioned between the first and second electrodes and having a first highest occupied molecular orbital (HOMO) level; A first organic material layer comprising a triphenylene compound derivative having a second HOMO level and an organic compound having a third HOMO level and having a fourth HOMO level between the first electrode and the light emitting material layer, The triphenylene compound derivative is represented by Formula 1-1 below, in Formula 1-1, R1 and R2 each represent a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, and the third HOMO level is It is located between the first HOMO level and the second HOMO level.

Formula 1-1

The fourth HOMO level is located between the second HOMO level and the third HOMO level.

A second organic material layer is further included between the first organic material layer and the light emitting material layer, wherein the HOMO level of the second organic material layer is present between the first HOMO level and the fourth HOMO level.

The second organic material layer is formed of an organic material represented by one of Chemical Formulas 2-1 to 2-3.

2-1

2-2

Formula 2-3

The triphenylene compound derivative is represented by the following Chemical Formula 3-1.

3-1

The proportion of the triphenylene compound derivative is about 10% to about 90%, preferably about 40% to about 60%.

The organic compound having the third HOMO level is represented by one of the following Formulas 4-1 to 4-3.

Formula 4-1

Formula 4-2

Formula 4-3

The triphenylene compound derivative has a larger glass transition temperature than the organic compound having the third HOMO level.

The first electrode or the second electrode is characterized in that the transparent.

The present invention provides a long-life organic electricity by depositing a triphenylene compound derivative having a relatively high glass transition temperature together with an organic compound having a higher HOMO level than the triphenylene compound derivative to form a hole transport layer or a hole injection layer. A light emitting device can be provided. In addition, it is possible to provide an organic electroluminescent device having excellent reliability by suppressing an increase in driving voltage and a rise in driving voltage caused by real-time use.

1 is a diagram illustrating a structure of a general organic electroluminescent device using a band diagram.
FIG. 2A is a diagram schematically showing a band diagram of an organic EL device using NPD as a hole transport layer, and FIG. 2B is a diagram schematically showing a band diagram of an organic EL device using a triphenylene compound derivative as a hole transport layer. to be.
3 is a graph showing the life characteristics of a conventional organic electroluminescent device.
4 is a graph illustrating a change in voltage according to a driving time of a conventional organic electroluminescent device.
5 is a view schematically showing an organic electroluminescent device according to a first embodiment of the present invention.
6 is a view schematically showing an organic electroluminescent device according to a second embodiment of the present invention.
7 is a graph showing the life characteristics of the organic electroluminescent device according to the first and second embodiments of the present invention.
8 is a graph showing a change in voltage with respect to a driving time of the organic electroluminescent device according to the first and second embodiments of the present invention.

Hereinafter, an organic electroluminescent device according to the present invention will be described in detail with reference to the accompanying drawings.

5 is a view schematically showing an organic electroluminescent device according to a first embodiment of the present invention.

As shown in FIG. 5, an anode electrode 120 is formed of a transparent conductive material such as indium tin oxide (ITO) on the transparent substrate 110. The hole transport layer 130 is formed on the anode electrode 120. The hole transport layer 130 is formed by depositing a triphenylene compound derivative together with an organic compound having a higher HOMO level.

The basic structure of such a triphenylene compound derivative is represented by the following Chemical Formula 1, wherein R1 and R2 are each an aryl group having 6 to 30 carbon atoms substituted or unsubstituted.

Formula 1

Subsequently, the light emitting material layer 140 is formed on the hole transport layer 130, and the electron transport layer 150 and the electron injection layer 160 are continuously formed on the light emitting material layer 140. A cathode electrode 170 is formed of a metal material such as aluminum (Al) on the electron injection layer 160 to complete the light emitting diode, and an encapsulation substrate 180 on the cathode electrode 170. ) Is attached.

In this case, the organic compound used in the hole transport layer 130 together with the triphenylene compound derivative has a higher HOMO level than the triphenylene compound derivative and has a lower HOMO level than the light emitting material layer 140.

In other words, the light emitting material layer 140 has a first HOMO level, the triphenylene compound derivative has a second HOMO level, the organic compound has a third HOMO level, and the hole transport layer 130 has a fourth HOMO level. The third HOMO level of the organic compound is located between the first HOMO level and the second HOMO level. In addition, the fourth HOMO level of the hole transport layer 130 is located between the second HOMO level and the third HOMO level.

Here, the organic compound having the third HOMO level may be NPD represented by Formula 2 or 2-TNATA represented by Formula 3.

(2)

(3)

In addition, the material represented by the following formula (4) may be used in the organic compound having a third HOMO level.

Formula 4

On the other hand, the triphenylene compound derivative may be used a substance of the formula (5).

Formula 5

Triphenylene compound derivatives have a higher glass transition temperature than organic compounds having a third HOMO level, such as NPD or 2-TNATA.

As described above, in the present invention, the hole transport layer 130 may be formed with a triphenylene compound derivative having a relatively high glass transition temperature and an organic compound having a higher HOMO level, thereby improving the lifetime characteristics of the device. In addition, since holes that accumulate at the interface can be minimized by minimizing an energy barrier between the hole transport layer 130 and the light emitting material layer 140, the initial driving voltage is reduced, and the voltage increase change according to the driving time is minimized and consumed. Can lower the power.

Meanwhile, the triphenylene compound derivative and the organic compound having a higher HOMO level may be used as the hole injection layer, and the organic compound may be used as the hole transport layer, which will be described in the second embodiment.

6 is a view schematically showing an organic electroluminescent device according to a second embodiment of the present invention.

The organic electroluminescent device according to the second embodiment of the present invention has a difference in the hole injection layer 132 and the hole transport layer 134 compared with the first embodiment, and the description of the same parts as in the first embodiment will be omitted. do.

As shown in FIG. 6, a hole injection layer 132 and a hole transport layer 134 are sequentially formed between the anode electrode 120 and the light emitting material layer 140. The hole injection layer 132 is formed by depositing a triphenylene compound derivative and an organic compound having a higher HOMO level, and the hole transport layer 134 is formed of the organic compound. The basic structure of such a triphenylene compound derivative is represented by the above-mentioned formula (1), wherein in formula (1) R1 and R2 are each an aryl group having 6 to 30 carbon atoms substituted or unsubstituted.

The HOMO level of the organic compound is higher than that of the triphenylene compound derivative, lower than the light emitting material layer 140, and the HOMO level of the hole transport layer 134 is higher than the hole injection layer 132 and lower than the light emitting material layer 140. .

Herein, the organic compound may be NPD represented by Chemical Formula 6 or 2-TNATA represented by Chemical Formula 7.

6

Formula 7

Alternatively, a substance represented by the following formula (8) may be used for the organic compound.

8

On the other hand, the triphenylene compound derivative may be used a substance of the formula (9).

Formula 9

As described above, in the second embodiment of the present invention, the anode material 120 includes the organic material layer including the triphenylene compound derivative as the hole injection layer 132 and the additional organic material layer as the hole transport layer 134. It is possible to improve the interfacial characteristics with the hole injection and the light emitting material layer from the to obtain a stable device.

According to an embodiment of the present invention, an organic electroluminescent device was manufactured and its properties were measured.

In Experimental Example 1, an organic electroluminescent device was manufactured according to the first embodiment of the present invention. A hole transport layer having a hole transport layer of about 70 nm was formed by simultaneously depositing a triphenylene compound derivative and NPD on an anode electrode (120 of FIG. 5). 5 to 130, a light emitting material layer (140 in FIG. 5) and an electron transport layer (150 in FIG. 5) are deposited about 30 nm, and then an electron injection layer (160 in FIG. 5). Lithium ) About 1 nm of fluoride (LiF) was deposited, and then 100 nm of aluminum (Al) was deposited on the cathode electrode (170 of FIG. 5) to complete the device.

 In Experimental Example 2, an organic electroluminescent device was manufactured according to the second exemplary embodiment of the present invention. A hole injection of about 50 nm was performed by simultaneously depositing a triphenylene compound derivative and NPD on the anode electrode 120 (FIG. 6). A layer (132 in FIG. 6) is formed and NPD is deposited thereon to form a hole transport layer (134 in FIG. 6) of about 20 nm. The other material layer was formed under the same conditions as in Experimental Example 1 to complete the device.

On the other hand, in order to confirm the effect of the present invention, as mentioned in the prior art, 70 nm NPD is formed on the anode electrode, and the other material layer fabricated as a comparative example device formed under the same conditions as in Experimental Example 1 It was.

Table 2 and Figures 7 and 8 show the results of comparing the characteristics of the organic electroluminescent device of Experimental Example 1, Experimental Example 2 and Comparative Example. 7 is a graph showing the life characteristics of each organic electroluminescent device, and FIG. 8 is a graph showing a change in voltage with respect to a driving time of each organic electroluminescent device.

Voltage (V) Efficiency (cd / A) CIE (X) CIE (Y) Life span (T ₉₅ : hr) Voltage change (V) Experimental Example 1 3.8 5.4 0.140 0.087 350 0.52 Experimental Example 2 3.4 4.9 0.139 0.089 420 0.38 Comparative Example 3.3 5.6 0.139 0.089 130 0.25

As can be seen from Table 2, Experimental Example 1, Experimental Example 2, and Comparative Example show similar characteristics in color coordinates (CIE (X), CIE (Y)). Experimental Example 1 and Experimental Example 2 have better life characteristics than the comparative example. As shown in Table 2 and FIG. 7, Experimental Example 2 is after 420 hours, while Experimental Example 1 is 350 hours, when the luminance is reduced to 95%. After that, it can be seen that the life of Experimental Example 2 is long. On the other hand, the efficiency of Experimental Example 2 compared to Experimental Example 1 is slightly lower than 4.9 cd / A, Experimental Example 2 has a lower driving voltage (3.4V) than Experimental Example 1, and shows a level similar to the comparative example. Also, Experimental Example 2 is smaller than Experimental Example 1 in the voltage rise change with the driving time. Therefore, Experimental Example 2 is superior to Experimental Example 1 in terms of lifetime and power consumption.

The present invention is not limited to the above-described embodiments, and various changes and modifications may be made without departing from the spirit of the present invention.

110: transparent substrate 120: anode electrode
132: hole injection layer 134: hole transport layer
140: light emitting material layer 150: electron transport layer
160: electron injection layer 170: cathode electrode
180: encapsulation substrate

Claims (10)

A first electrode and a second electrode;
A light emitting material layer positioned between the first and second electrodes and having a first highest occupied molecular orbital (HOMO) level;
A first organic material layer comprising a triphenylene compound derivative having a second HOMO level and an organic compound having a third HOMO level and having a fourth HOMO level between the first electrode and the light emitting material layer,
The triphenylene compound derivative is represented by the following chemical formula, in which the R1 and R2 are substituted or unsubstituted aryl groups having 6 to 30 carbon atoms, respectively, and the third HOMO level is the first HOMO. An organic electroluminescent device positioned between the level and the second HOMO level.

The method according to claim 1,
And the fourth HOMO level is located between the second HOMO level and the third HOMO level.
The method according to claim 1,
And a second organic material layer between the first organic material layer and the light emitting material layer, wherein the HOMO level of the second organic material layer is present between the first HOMO level and the fourth HOMO level. device.
The method according to claim 3,
The second organic material layer is an organic electroluminescent device formed of an organic material represented by one of the formulas (1) to (3).
Formula 1

(2)

Formula 3

The method according to claim 1 or 3,
The triphenylene compound derivative is an organic electroluminescent device represented by the following formula.

The method according to claim 1 or 3,
The ratio of the triphenylene compound derivative is 10% to 90% organic electroluminescent device.
The method of claim 6,
The ratio of the triphenylene compound derivative is 40% to 60% organic electroluminescent device.
The method according to claim 1 or 3,
The organic compound having the third HOMO level is an organic electroluminescent device represented by one of the following formula (1) to (3).
Formula 1

(2)

Formula 3

The method according to claim 1 or 3,
And the triphenylene compound derivative has a glass transition temperature greater than that of the organic compound having the third HOMO level.
Claim 10 has been abandoned due to the setting registration fee. The method according to claim 1 or 3,
And the first electrode or the second electrode is transparent.

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