TWI435877B - High efficient and low-voltage organic electroluminescent devices and material thereof - Google Patents

Description

High efficiency and low voltage organic electroluminescent device and material

The present invention relates to an electron transport layer material and an organic electroluminescent device using the same. Still further, the present invention relates to an organic electroluminescent device having high efficiency and low voltage and an electron transport layer material thereof.

Recently, organic semiconductors and organic conductive materials have been enthusiastically studied, and in particular, organic electric luminescent devices using light-emitting elements of organic semiconductors have made significant progress. Organic electroluminescence (OEL) is a phenomenon in which an organic substance is excited by a corresponding electric energy under a certain electric field. In 1963, Pope et al. first studied the 10~20 μm thick onion (anthracene) single wafer and first found that after applying 400 volts across the crystal, it was observed that the green onion emits blue fluorescence, which makes the study of organic electroluminescence. The first step is taken, but since the single crystal grows and the area is difficult, and the required driving voltage is too large, the luminous efficiency is inferior to that of the inorganic material, so it has no practical value. Subsequently, Helfrich and Williams and others continued their efforts to reduce the voltage to about 100 volts, and obtained an external quantum efficiency of about 5% photon/electron. However, since the thickness of the single crystal is too large, the driving voltage is also high, resulting in electrical energy conversion. The efficiency of light energy is too low. In 1982, Vincett et al. made a 50 nm thick onion film by vacuum evaporation, and further reduced the driving voltage to 30 volts to observe blue fluorescence, but the electron injection efficiency was too low and the onion film formation. The sex is not good, so its external quantum efficiency is only about 0.03%. After more than 20 years of sporadic development, there have been no major breakthroughs.

It was not until 1987 that the Eastman Kodak company Tang and Van Slyke first published organic light-emitting diodes (OLEDs) that they had a breakthrough. They used aromatic diamine (HTM-2) as a hole transport layer material, and a film-forming tris(8-hydroxyquinolateto)aluminum (III) as an electron transport layer and luminescence. The material is vacuum-deposited to form a film of 60-70 nm, and a magnesium-silver alloy with a low work function is used as a cathode to improve the injection efficiency of electrons and holes. The organic small molecule luminescent material developed by the two electrodes is placed between the two electrodes, and the power is emitted first, which generates green light with a wavelength of 530 nm, which can exhibit low driving voltage and high quantum efficiency (>1%). The effects of component stability and the like greatly improve the characteristics and practicability of the organic small molecule electroluminescent device.

Then in 1990, Friend et al. of Cambridge University in the United Kingdom subsequently published polymer light-emitting diodes (PLEDs) to spin-coat the conjugated polymer PPV (poly(p). -phenylene vinylene)) as a light-emitting layer, a polymer electroluminescent device having a single-layer structure is produced, which has a simple process, good mechanical properties of a polymer, and semiconductor-like properties, so that a conjugated polymer luminescent material is used. Research is developing rapidly.

It is worth noting that OLED not only can self-illuminate, but also does not require a backlight module, and has low driving voltage, high brightness, high contrast, wide viewing angle, fast response, simple structure, and super. Compared with the current FPD with LCD as the mainstream. The advantages of film, light weight, etc. can be effectively applied to illumination or made into display, photoelectric coupler, etc. If it is made on a soft substrate such as a plastic substrate, the device can be bent, folded and carried, and it is expected to be simple due to the simple process. Can significantly reduce costs. At present, more than 80 companies around the world have been competing to invest heavily in the development of organic electroluminescent display technology, which has become the mainstream of another display technology.

In 1997, Japan Pioneer first published a low-molecular monochromatic (green) passive display that successfully applied organic electroluminescent display technology to automotive instrument panels. Since then, organic electroluminescent display has begun to be commercialized and has been applied to small-sized panels, such as Japan's TDK Corporation in 1998, Sic Bo Technology in 2002, Samsung, NTT Do Co Mo's color mobile phone, and 2003 Kodak digital camera. Japan's Pioneer and Kodak Kodak have also collaborated on a small-volume production of OLED monochrome and multicolor displays, which have been officially applied to Motorola phones, and have been well received. Sanyo has also collaborated with Kodak to produce small sizes. The full color OLED sample is claimed to be mass-produced after 2001; Chi Mei has also released an active color display of more than 10 inches, making the organic electro-excitation technology more advanced. However, until now, OLEDs, especially in electronic transmission materials, still need further improvement, including component efficiency, thermal stability, voltage reduction, etc., which are closely related to the nature and process of the material itself. Can expect to become the trend of future displays.

At present, the most commonly used electron transport material in OLEDs is tris(8-hydroxyquinolateto)aluminum(III), but its luminous efficiency still needs to be improved. Therefore, the development of a better electronic transmission material has been a goal of the material development company, for example, the patent application of the organic electroluminescent device of the patent application No. WO2002043449 of the Japanese Toray application, wherein the representative structure of the electron transport layer material is as follows ( 1) and (2):

In this case, the structures of the compounds represented are as follows (3) and (4):

However, the problem of the inefficiency of the conventional tris(8-hydroxyquinoline)Alq3 is still to be solved. Therefore, in view of the shortcomings of the prior art, the present invention attempts to develop a novel electron transport layer material which is different from the conventional electron transport layer materials and has never been disclosed, which can improve component efficiency, lower voltage, and have higher The glass transition temperature (Tg) is easy to prepare and purify, and has industrial application value.

In view of the above, it is an object of the present invention to provide an electron transport layer material of an organic electroluminescent device having a compound structure and product characteristics different from those of the prior art.

Another object of the present invention is to provide an electron transport layer material of an organic electroluminescent device. Compared with the conventional electron transport layer material, the electron transport layer material of the present invention can improve the efficiency of the device due to the novel structure. Can effectively reduce the voltage. Moreover, this novel structure can have high Tg properties and has better thermal stability when applied to the industry. In addition, the electron transport layer materials of these novel structures have advantages such as ease of preparation and purification.

Still another object of the present invention is to provide an organic electroluminescent device having high luminous efficiency and low voltage. The electron transport layer of the organic electroluminescent device comprises the electron transport layer material of the novel structure described above.

In order to achieve the above object, the present invention provides an electron transport layer material of an organic electroluminescent device having a structure represented by the following chemical formula (I):

Wherein n is 1 or 2, and L represents a C ₆ -C ₂₀ aromatic group.

In a preferred embodiment, when n is 2, the aforementioned L may be the same C ₆ -C ₂₀ aromatic group. In another preferred embodiment, when n is 2, the aforementioned L may be a distinct C ₆ -C ₂₀ aromatic group.

In a preferred embodiment, the C ₆ -C ₂₀ aromatic group is selected from the group consisting of: 1,4-phenylene (1,4-phenylene), 1,3-phenylene (1,3-phenylene), a group consisting of 2,6-naphthalenyl, 2,7-naphthalenyl and 1,4-naphthalenyl.

In another preferred embodiment, the foregoing electron transport layer material may be a compound represented by the following chemical formula:

The compound of the present invention having the above structure has advantages of good thermal stability (i.e., high Tg), high efficiency, and ease of preparation and purification.

The present invention also provides an organic electroluminescent device comprising a layered structure arranged in the following order: a transparent substrate, an anode layer, a hole transport layer, a light emitting layer, an electron transport layer and a cathode layer; the organic electroluminescent device It is characterized in that the aforementioned electron transport layer contains the aforementioned electron transport layer material.

In a preferred embodiment, the anode layer and the cathode layer are respectively in contact with an external power source to form an electrical path.

In a preferred embodiment, and the layers other than the electron transport layer, the selection of other layers of materials is generally not known in the art, for example, the transparent substrate can be an inflexible glass with light penetrating properties. The substrate or the transparent organic polymer material having flexibility; and the anode layer may be indium tin oxide (ITO) or the like.

In a preferred embodiment, the anode layer and the hole transport layer further comprise a hole injection layer. In another preferred embodiment, the electron transport layer and the cathode layer further comprise an electron injection layer, wherein the material of the hole injection layer and the electron injection layer is also a common knowledge in the art without limitation. .

In still another preferred embodiment, the electron transport layer material can have a compound of the formula:

The following embodiments are intended to further understand the advantages of the present invention and are not intended to limit the scope of the invention.

Example 1. Synthesis of 9-(4-Bromo-naphthalen-l-yl)-phenanthrene

In a 1 L three-necked flask under nitrogen, 30 g of 9-boronic acid phenanthrene and 69.5 g of 1,4-dibromo-naphthalene, 300 ml of tetrahydrofuran (THF) were placed. After stirring and stirring, 38.7 g of potassium carbonate, 140 ml of H ₂ O, 3.9 g of tetrakis(triphenylphosphine) palladium, 600 ml of toluene were added, and the mixture was heated under reflux for 6 hours, cooled and concentrated to precipitate a solid. Recrystallization from toluene, filtration of solids, drying to obtain 25.4 g of the finished product, purity 99.0%, yield 48%.

HPLC conditions: Column: RP-8, flow rate _{= 1.0 ml / min, CH 3} CN: H 2 O = 8: 2.

¹ H NMR (400 MHz) spectral data: δ 8.341-8.362 (d, 1H), 7.875-7.920 (m, 2H), 7.555-7.737 (m, 7H), 7.366-7.456 (m, 4H), 7.284-7.308 ( m, 1H).

Example 2. Synthesis of 9-(4-boronic acid-naphthalen-1-yl)-phenanthrene

7 g of 9-(4-bromo-naphthalen-1-yl)-phenanthrene and 85 ml of tetrahydrofuran (THF) were placed in a three-necked flask under nitrogen. Cool down to -80 ° C, add 4.3 ml of n-butyl lithium, add 2.1 g of triethyl borate after 1 hour, naturally return to 0 ° C, add 4 ml of hydrochloric acid aqueous solution, add 100 ml of hexane, The solid was precipitated, and the product was filtered to give a product (yield: 62%).

HPLC conditions: Column: RP-8, flow rate _{= 1.0 ml / min, CH 3} CN: H 2 O = 8: 2.

Example 3. Synthesis of Inv-1

4 g of 2-(4-bromo-phenyl)-[1,10]phenanthroline (2-(4-bromo-phenyl)-[1,10]phenanthroline) and 5.5 were placed in a three-necked flask under nitrogen. 9-(4-boronic acid-naphthalen-1-yl-phenanthrene), dissolved in 80 ml of tetrahydrofuran, and then added 5.5 g of potassium carbonate, 20 ml of H ₂ O, 0.8 g of tetrakis(triphenylphosphine) palladium, heated under reflux for 17 hours, cooled, concentrated to precipitate a solid, recrystallized from toluene, filtered to give product 4.2 g, yield 48%. The purity is 99.2%, and after purification by sublimation, 3.2 g of product is obtained, and the purity is 99.8%.

HPLC conditions: Column: RP-8, flow rate _{= 1.0 ml / min, CH 3} CN: H 2 O = 9: 1.

¹ H NMR (400 MHz) spectral data: δ 9.262-9.268 (d, 1H), 8.788-8.832 (t, 2H), 8.511-8.531 (d, 2H), 8.343-8.364 (d, 1H), 8.258-8.278 ( d, 1H), 8.200-8.221 (d, 1H), 8.102-8.123 (d, 1H), 7.666-7.931 (m, 8H), 7.544-7.565 (d, 2H), 7.414-7.473 (q, 2H), 7.127-7.311 (m, 5H).

Example 3. Thermal stability data of electron transport layer materials

The Tg of the electron transport layer material (Inv-1) of the present invention is shown in Table 1:

As shown in Table 1, the electron transport layer material (Inv-1) of the present invention has high Tg characteristics (higher than the industry-recognized high Tg temperature of 130 ° C), and the application has better thermal stability in the industry.

Example 4. Organic electroluminescent device test data

The structure of the test element of this embodiment includes: a glass substrate 1; an ITO (anode layer) 2; a hole injection layer 3 (HIL); a hole transport layer 4 (HTL); and a light-emitting layer 5 (a main illuminant and a guest illuminant) ; electron transport layer 6; cathode 7. The cathode 4 is composed of 0.7 nm of LiF and 150 nm of Al.

The organic electroluminescent device shown in FIG. 1 is prepared by vacuum evaporation, wherein the comparative material of the electron transport layer material is tris(8-hydroxyquinoline)aluminum Alq3, the luminescent layer material is ADN, and the blue light material is The chemical structure of BD-1 is as follows:

The composition and thickness of the hole injection layer, the hole transport layer, the light-emitting layer, and the electron transport layer in the foregoing organic electroluminescent device, and the test results of the components thereof are listed in Table 2 below:

The chemical formulas of ADN, BD-1 and Alq3 in Table 2 are as follows:

As can be seen from Table 2, the electron transport layer material of the present invention has the advantages of improving the luminous efficiency and power efficiency of the organic electroluminescent device, reducing the on-voltage, and being easy to synthesize and purify, and has the potential for commercial application.

It will be apparent to those skilled in the art that various changes can be made in accordance with the embodiments of the present invention without departing from the spirit of the invention. Therefore, it is to be understood that the invention is not limited by the scope of the invention, and is intended to cover the modifications of the spirit and scope of the invention.

1‧‧‧ glass substrate

2‧‧‧ITO (anode layer)

3‧‧‧ hole injection layer

4‧‧‧ hole transport layer

5‧‧‧Lighting layer

6‧‧‧Electronic transport layer

7‧‧‧ cathode

Figure 1 is a schematic diagram of an organic electroluminescent device.

1. . . glass substrate

2. . . ITO (anode layer)

3. . . Hole injection layer

4. . . Hole transport layer

5. . . Luminous layer

6. . . Electronic transport layer

7. . . cathode

Claims (9)

An electron transport layer material of an organic electroluminescence device having the structure shown by the following chemical formula (I): Wherein n is 2 and L represents a C ₆ -C ₂₀ aromatic group. The electron transport layer material according to claim 1, wherein when n is 2, the L system is the same C ₆ -C ₂₀ aromatic group. The electron transport layer material according to claim 1, wherein when n is 2, the L system is a different C ₆ - C ₂₀ aromatic group. The electron transport layer material according to claim 1, wherein the C ₆ -C ₂₀ aromatic group is selected from the group consisting of: 1,4-phenylene (1,4-phenylene), 1,3-phenylene ( 1,3-phenylene), 2,6-naphthalenyl, 2,7-naphthalenyl and 1,4-naphthalenyl Group. The electron transport layer material according to claim 1, which is a compound represented by the following chemical formula: An organic electroluminescent device comprising a layered structure arranged in the following order: a transparent substrate, an anode layer, a hole transport layer, a light emitting layer, an electron transport layer and a cathode layer; the organic electroluminescent device is characterized by: The electron transport layer material according to any one of claims 1 to 5, which is contained in the above-mentioned electron transport layer. The device of claim 6, wherein the anode layer and the hole transport layer further comprise a hole injection layer. The device of claim 6, wherein the electron transport layer and the cathode layer further comprise an electron injection layer. The device of claim 6, wherein the anode layer and the cathode layer are respectively in contact with an external power source to form an electrical path.