KR19990024361A - Electroluminescent element utilizing conjugated high molecular compound - Google Patents

Abstract

The present invention is vacuum-deposited the aromatic organic acid dianhydride of the general formula (1) on the ITO transparent electrode, and spin-coated a solution of dissolving the π-conjugated polymer compound of the general formula (2) or (3) in an organic solvent, the metal to be used as a negative electrode The present invention relates to a method for manufacturing an electroluminescent device in which the electrode is vacuum deposited to increase luminous efficiency. The present invention also vacuum-deposited an aromatic organic acid dianhydride of the following formula (1) on an ITO transparent electrode, and spin-coating a solution obtained by dissolving a π-conjugated polymer compound of the following formula (2) or (3) in an organic solvent, and The present invention relates to a method of manufacturing an electroluminescent device in which the luminous efficiency is increased by vacuum depositing a metal electrode to be used as a cathode after vacuum deposition with Alq or PBD of the following formula.

Formula 1

Wherein Ar is a benzene, naphthalene, anthracene, perylene or pyrene group.

Formula 2

In the stomach,

R ₁ is —H, —CH ₃ , —CN group,

R ₂ is — (CH ₂ ) _n CH ₃ (where n = 1-9),

(Where n = 0 to 8) or

-(OCH ₂ CH ₂ ) _n -OCH ₃ (where n = 1-10), x is 20-250.

Formula 3

In the stomach,

Ar ' or Is.

here,

R ₃ is a-(CH ₂ ) _n CH ₃ (where n = 0-7),

R ₄ is — (CH ₂ ) _n CH ₃ (where n = 0-7) or

And x is from 20 to 250.

PBD

The electroluminescent device according to the present invention can be very usefully used for flat panel display devices, solar cell devices, optical sensors and the like.

Description

Manufacturing method of electroluminescent device using conjugated polymer compound

As the industry has developed, the demand for display device performance has increased, and much research has been conducted on the development of a flat panel display device to replace a cathode ray tube (CRT) for the past 20 years. Liquid crystal displays are the most widely used flat panel display devices, but as the information and communication industry develops, the necessity of display devices having various performances has increased.

BACKGROUND ART Electroluminescent devices have mainly used inorganic materials as display devices for generating light by injecting current into thin films. However, a display device using an inorganic material has low efficiency, has a problem in producing various colors, and also has a crystal form, which makes it difficult to manufacture a device having a large area.

To solve this problem, electroluminescent devices using organic materials have been developed (CWTang, SAVanSlyke, Appl. Phys. Lett., 51, 913 (1987)), while organic light emitting devices have advantages of various colors and high luminous efficiency. In addition, due to the heat generated when the device is operating, recrystallization of the organic material occurs, causing a factor of destruction of the device, and thus has the disadvantage of low stability of the device.

In order to make up for the shortcomings of such low molecular materials, the use of high molecular materials was introduced.Burroughes et al. Made polyphenylenevinylene (PPV) transparent in 1990 by using π-conjugated high molecular compounds for electroluminescence. It was the first to announce the emission of light from a diode made by vacuum evaporation of aluminum after coating on the electrode ITO (JHBurroughes, DDC Bradley, ABBrown, RNMarks, K. Mackay, RHFriend, PLBurns). , ABHolmes, Nature, 347,539 (1990)). In particular, π-conjugated high molecular compounds have been the subject of many studies because they can combine excellent processability and electronic functionality such as semiconductors. Such a π-conjugated polymer compound has the advantage that it is easy to manufacture a thin film device having a large area by rotating coating and printing technique using processability, and also has the advantage of low driving voltage.

Electroluminescent diodes using soluble polyalkylthiophenes have been reported to increase luminous efficiency with longer alkyl chains substituted in the side chains (K. Yoshino et.al., J. Appl. Phys., 68,5976). (1990)), in order to use it commercially, the luminous efficiency of the electroluminescent device should be improved. Some of the electrons supplied to the electroluminescent device are emitted as light, and the rest are consumed through the device as current. Since the current consumed through the electroluminescent device will generate heat according to Ohm's law, it is advantageous that the current supplied is mostly used to generate light. In fact, the electroluminescent device using the π-conjugated polymer compound has been pointed out as the biggest problem that the device is destroyed by deterioration and does not have a desired operating life.

In general, two methods are used to improve the luminous efficiency of the electroluminescent device. The first method is to reduce the energy barrier by using a metal with a small work function (D. Braun, A. J. Heeger, Appl, Phys. Lett., 58,1982 (1991).

). It has been reported that the quantum efficiency increases as the work function is used from the large to the small cathode (J. Appl. Phys., 75, 1656 (1994)). In other words, when calcium (Ca) having a small work function is used, the efficiency is greatly increased than that of aluminum (Al) having a higher work function. However, metals with a small work function have defects that are fatally weak to air or moisture and are extremely limited in use.

The second method is for the electroluminescent device structure to form a double junction structure using two or more materials with different band gaps [M.Onoda, K.Yoshino, Jpn.J.Appl.Phys., 34, L 260 (1995)] H. Suzuki, S. Hoshino, J. Appl. Phys., 79,858 (1996). That is, an electron transport layer is inserted between the light emitting layer and the cathode or a hole transport layer is inserted between the light emitting layer and the anode. The electron transport layer inserted between the light emitting layer and the cathode increases efficiency by confining positive charges to the light emitting layer by allowing holes to be injected from the anode to move through the polymer compound and to accumulate at the interface before encountering a new energy barrier. Has been announced.

Similarly, the electroluminescent device having a hole transport layer inserted between the light emitting layer and the anode may facilitate the transport of holes from the anode to the π-conjugated polymer compound, thereby increasing the luminous efficiency. However, few examples have been reported of using such a hole transport layer in an electroluminescent device using a π-conjugated polymer compound as a light emitting layer, because the π-conjugated polymer compound can be used as a hole transport layer by itself. It has been thought that there is no big problem, and also in the manufacture of the electroluminescent device, a solution of π-conjugated polymer compound must be rotated on the hole transport layer, because the hole transport layer is melted and cannot be used.

On the other hand, in the electroluminescent device fabricated by vacuum deposition of organic materials, many devices having a multilayer structure as shown in Figs. 1 and 2 are known, and in almost all cases, the light emission efficiency is increased by using a device having a multilayer structure. It is known.

The present invention finds an organic material that is insoluble in a solvent for dissolving a π-conjugated polymer compound, and provides a method of increasing the efficiency of an electroluminescent device using the π-conjugated polymer compound as a light emitting layer by using the same as a hole transport layer. .

1 is an electroluminescent device consisting of a hole transport layer and a light emitting layer,

2 is an electroluminescent device consisting of a hole transport layer, a light emitting layer and an electron transport layer,

Figure 3 is indium tin oxide (ITO) / perylene benzenetetracarboxylic dianhydride (PTCDA) / polypropanoyloxy ethyl thiopene (PPET) Electroluminescence spectrum of aluminum (Al) device,

4 shows ITO / naphthalenetetracarboxylic dianhydride (NTCDA) / poly (2-methoxy, 5- (2′-ethylhexoxy) -1,4-phenylenevinylene) [poly ( Electroluminescence spectra of 2-methoxy, 5- (2'-ethylhexoxy) -1,4-phenylene vinylene) (MEH-PPV)] / Al devices.

The present invention relates to a method of manufacturing a multi-layer electroluminescent device using a? -Conjugated polymer compound as a light emitting layer and an aromatic organic acid dianhydride as a hole transporting layer. More specifically, the present invention uses an aromatic organic acid dianhydride of Formula 1 as a hole transporting layer of an electroluminescent device, and electroluminescence is improved by using a π-conjugated polymer compound of Formula 2 or Formula 3 as a light emitting layer. The manufacturing method of an element is related.

Formula 1

In the above formulae, Ar is a benzene, naphthalene, anthracene, perylene or pyrene group.

Formula 2

In the stomach,

R ₁ is —H, —CH ₃ , —CN group,

R ₂ is — (CH ₂ ) _n CH ₃ (where n = 1-9),

(Where n = 0 to 8) or

-(OCH ₂ CH ₂ ) _n -OCH ₃ (where n = 1-10), x is 20-250.

Formula 3

In the stomach,

Ar ' or Is.

here,

R ₃ is a-(CH ₂ ) _n CH ₃ (where n = 0-7),

R ₄ is — (CH ₂ ) _n CH ₃ (where n = 0-7) or

And x is from 20 to 250.

Hereinafter, the present invention will be described in detail.

The electroluminescent device is manufactured by vacuum depositing the aromatic organic acid dihydrate of Chemical Formula 1 on clean ITO, and then dissolving one or more compounds of the π-conjugated polymer compound of Chemical Formula 2 or Chemical Formula 3 on the organic layer. The solution can be prepared by spin-coating and vacuum depositing a metal electrode on the polymer layer. Side view of the completed electroluminescent device is shown in FIG.

In addition, after the hole transport layer and the π-conjugated polymer layer is coated on the ITO electrode in the same manner as above, the electron transport layer is vacuum deposited again, and a metal electrode is vacuum deposited on the electron transport layer to fabricate an electroluminescent device. Side view of the completed electroluminescent device is shown in FIG. Here, the thickness of each layer is 100-2000 kPa, and the metal electrodes which can be used are Ca, Ag, Mg, Al, Au, and the like. Mg, Ag and Al are most suitable here for ease of use and efficiency.

As described above, the electroluminescent device having a multi-layered structure in which the hole transport layer is inserted between the π-conjugated polymer light emitting layer and the anode ITO electrode has a higher luminous efficiency than the electroluminescent device having a single layer structure made of only a π-conjugated polymer compound without the hole transport layer. The effect was increased from 1.5 to 8 times. This increase in luminous efficiency cannot be explained simply by the fact that the hole transport layer makes it easier to transport holes from the anode to the π-conjugated polymer compound, because the π-conjugated polymer compound itself is a good hole transport material. Therefore, the hole transport layer material used can be said to increase the luminous efficiency because it also functions as a hole transporter and has less electrical conductivity than π-conjugated polymer compound and is not easily oxidized than π-conjugated polymer compound. have.

This increase in electroluminescence efficiency is also observed as an extension of light emission life, i.e., the use of a hole transport layer extends the operating life of about 2 to 10 times that of a single layer electroluminescent device. Observed.

That is, the present invention shows that the light emission efficiency can be increased by using a hole transport layer in the fabrication of an electroluminescent device using a π-conjugated polymer compound. This breaks the conventional notion that the π-conjugated polymer compound is mainly a p-type semiconductor, and thus there is no problem in the hole transport. Therefore, it is useful for the fabrication of electroluminescent devices using the π-conjugated polymer compound. Can be used.

This is described in more detail in the following non-limiting examples.

Example 1

The electroluminescent device was manufactured using PTCDA of the following formula as a hole transport layer and poly (3-alkylesterthiophene) (PAET) of the following formula as a light emitting layer. In fabrication of the electroluminescent device, the ITO glass electrode was first placed in acetone and iso-propyl alcohol, and then washed using an ultrasonic cleaner. The PTCDA layer was deposited at a vacuum degree of about 2 × 10 ⁻⁵ torr or less using a vacuum evaporator. At this time, the deposition rate was deposited at about 0.1 Å / s.

PTCDA

PAET

In the above formula, R is-(CH ₂ ) nCH ₃ (where n = 0-10), and x is 20-250.

The PAET layer was spin-coated on the PTCDA layer at about 2000 rpm for 20 seconds. At this time, a solution of the polymer compound was used as a solution of 40 mg of the polymer compound in 1 ml of chloroform.

Finally, aluminum was vacuum deposited on the polymer layer. The deposition was carried out at a deposition rate of 3 kW / s below about 2 × 10 ⁻⁵ torr. The electroluminescence spectrum of the fabricated electroluminescent device is shown in FIG. 3. For comparison, the electroluminescence spectrum of the electroluminescent device having the monolayer structure manufactured using only poly (alkyl ester thiophene) without the hole transport layer was shown in FIG. 3.

Example 2

The electroluminescent device is composed of NTCDA of the formula and MEH-PPV of the formula. In the fabrication of the electroluminescent device, ITO was first placed in acetone and iso-propyl alcohol, and then washed continuously using an ultrasonic cleaner. The NTCDA layer was deposited at a vacuum degree of about 2 × 10 ⁻⁵ torr or less using a vacuum evaporator. At this time, the deposition rate was about 0.1 mW / s.

NTCDA

MEH-PPV

The MEH-PPV layer was spin-coated over the NTCDA layer at about 2000 rpm for 20 seconds. At this time, the solution of the polymer compound was used a solution in which 20 mg of the polymer compound was dissolved in 1 ml of chloroform.

Finally, aluminum was vacuum deposited on the polymer layer. The deposition was carried out at a deposition rate of 3 kW / s below about 2 × 10 ⁻⁵ torr. 4 shows an electroluminescence spectrum of the fabricated electroluminescent device. For comparison, the electroluminescence spectrum of the monolayer structure made with only MEH-PPV is shown together in FIG. 4.

Example 3

Prepare an electroluminescent device as in Example 1, but before the vacuum deposition of the cathode Al as an electron transport layer material aluminum tri (8-hydroxyquinolinate) of the formula (aluminum tri (8-hydroxyquinolinate) (Alq) ] Was vacuum-deposited and Al was vacuum-deposited to produce an electroluminescent device. The increase rate of Alq is 1Å / s. The electroluminescent device thus manufactured showed an increase in luminous efficiency about 2 times as compared to the electroluminescent device of Example 1 having a two-layer structure.

Example 4

An electroluminescent device was manufactured as in Example 3, but an electroluminescent device was manufactured using the following chemical formula instead of Alq as the electron transport layer material. The deposition rate of PBD was 1 dl / s. The electroluminescent device thus produced showed an increase in luminous efficiency of about 2.5 times compared to the electroluminescent device of Example 1 having a two-layer structure.

In the above embodiment, in the electroluminescent device having the π-conjugated polymer compound as the light emitting layer, the light emission efficiency was increased by using the aromatic organic acid dihydrate.

PBD

The electroluminescent device manufactured according to the present invention can be very usefully used for flat panel display devices, solar cell devices and optical sensors.

Claims (3)

After vacuum depositing the aromatic organic acid dianhydride of the following Chemical Formula 1 on the ITO transparent electrode, rotating the solution of dissolving the π-conjugated polymer compound of the following Chemical Formula 2 or Formula 3 in an organic solvent, and vacuuming the metal electrode to be used as the negative electrode. Method of manufacturing an electroluminescent device characterized in that to increase the luminous efficiency by deposition. Formula 1 In the above formulae, Ar is a benzene, naphthalene, anthracene, perylene or pyrene group. Formula 2 In the stomach, R ₁ is —H, —CH ₃ , —CN group, R ₂ is — (CH ₂ ) _n CH ₃ (where n = 1-9), (Where n = 0 to 8) or -(OCH ₂ CH ₂ ) _n -OCH ₃ (where n = 1-10), x is 20-250. Formula 3 In the stomach, Ar ' or Is. here, R ₃ is a-(CH ₂ ) _n CH ₃ (where n = 0-7), R ₄ is — (CH ₂ ) _n CH ₃ (where n = 0-7) or And x is from 20 to 250. A vacuum-deposited aromatic organic acid dianhydride of the following formula (1) on an ITO transparent electrode, spin-coating a solution in which the π-conjugated polymer compound of the following formula (2) or (3) was dissolved in an organic solvent, and the electron transport layer was coated with Alq or After vacuum-deposited with PBD, a metal electrode to be used as a cathode is vacuum-deposited to increase the luminous efficiency. Formula 1 In the above formulae, Ar is a benzene, naphthalene, anthracene, perylene or pyrene group. Formula 2 In the stomach, R ₁ is —H, —CH ₃ , —CN group, R ₂ is — (CH ₂ ) _n CH ₃ (where n = 1-9), (Where n = 0 to 8) or -(OCH ₂ CH ₂ ) _n -OCH ₃ (where n = 1-10), x is 20-250. Formula 3 In the stomach, Ar ' or Is. here, R ₃ is a-(CH ₂ ) _n CH ₃ (where n = 0-7), R ₄ is — (CH ₂ ) _n CH ₃ (where n = 0-7) or And x is from 20 to 250. PBD The method of manufacturing an electroluminescent device according to claim 1 or 2, wherein the organic solvent is chloroform or tetrahydrofuran.