JP2005174675A - Organic electroluminescent element and light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element improved in electron transportation property, and provide a light emitting device using this. <P>SOLUTION: The organic electroluminescent element 10 is constructed to have at least a luminous layer 5 and an electron transporting layer 6 between a positive electrode 2 and a negative electrode 8, and as a main component of the electron transporting layer 6, an organic compound having as a main skeleton a substituted anthracene which is made by bonding the 9th place carbon atom of anthracene or the 9th place and the 10th place carbon atoms of anthracene with phenyl group and/or naphthyl group is used. Furthermore, this organic electroluminescent element is arranged corresponding to a plurality of picture elements, and thereby a display device of self light-emitting type is formed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an organic electroluminescent element suitable as a display element of a display device such as a self-luminous color display, and a display device using the same.

  In recent years, especially in multimedia-oriented products, the importance of human-machine interfaces has increased. In order for humans to operate a machine more comfortably and efficiently, it is necessary to extract information from the machine in a concise, instantaneous, and sufficient amount, and display it in an easy-to-understand manner. Various display devices have been studied.

  In addition, with the miniaturization of machines, the demand for miniaturization and thinning of display devices is increasing day by day. Under such circumstances, a liquid crystal display is used as a display device for an interface in many miniaturized products such as a laptop information processing device, a small television, a clock, a calculator, and the like.

  The liquid crystal display has been studied as a display device that plays a central role in an interface from a small size to a large capacity display device by taking advantage of the feature that the liquid crystal can be driven at a low voltage and has low power consumption.

  However, since the liquid crystal element is a light transmissive display element and not a self-luminous element, a backlight is indispensable for the liquid crystal display, and the light emission requires larger power than the driving of the liquid crystal element. Therefore, for example, in portable devices driven by a storage battery or the like, there is a problem in that there is a limitation in use, such as shortening the time that can be operated by one charge.

  In addition, the liquid crystal display realizes the display mainly by controlling the amount of light transmitted in the vertical direction of the screen by the orientation of the liquid crystal molecules, so the viewing angle is narrow, and the contrast changes depending on the angle within the viewing angle. This is not suitable for large area display such as a large display.

  Furthermore, there is a problem that the alignment speed of liquid crystal molecules is slow. For this reason, the method of driving a liquid crystal display by a simple matrix method is low in cost and relatively easy to increase the screen size, but cannot provide a response speed sufficient for handling moving images, Not suitable for display. Another driving method, which is a liquid crystal display driving method using an active matrix method, can achieve a response speed sufficient for handling moving images, but uses a TFT (Thin Film Transistor) driving circuit, which may cause pixel defects. It is difficult to increase the screen size, and it is not a good idea for cost reduction.

  For such a liquid crystal display, a display device using a plasma display element, an inorganic electroluminescence element, an organic electroluminescence element, or the like, which is a self-luminous element, has been studied.

  Among these, the plasma display element uses plasma light emission in a low-pressure gas for display, and a PDP (plasma display device) is suitable for an increase in size and capacity. However, it is difficult to reduce the thickness and cost of the PDP, and further, a high-voltage AC bias power source is required for driving, which is not suitable for portable devices.

  In addition, as for the inorganic electroluminescent element, a green light emitting display or the like was once commercialized. However, as with the plasma display element, since it is necessary to apply a high voltage of several hundred volts for driving by AC bias driving, It was not accepted. After that, as a result of technological progress, it has succeeded in light emission of the three primary colors R (red), G (green), and B (blue) that are necessary for color displays, but since the light-emitting material is an inorganic compound, It is impossible to control the emission wavelength by design and the like, and full color is expected to be difficult.

  On the other hand, an organic electroluminescent element utilizes electroluminescence by an organic compound, and this phenomenon has already been discovered about 30 years ago. That is, in the first half of the 1960s, when a charge carrier was injected into an anthracene single crystal having strong fluorescence, a unique phenomenon in which luminescence (luminescence) was induced was observed. Since then, organic electroluminescent devices have been the subject of research for a long time, but because of their low brightness, single color, and the use of single crystals, they are mainly technical in terms of carrier injection into organic materials. Emphasis was put on and did not leave the basic research stage.

  However, Eastman Kodak's Tang et al. Announced in 1987 an organic thin-film electroluminescent device with an amorphous light-emitting layer capable of low-voltage drive and high-luminance emission (CW Tang and SA VanSlyke, Appl. Phys. Lett. , 51, 913 (1987)), the R & D of RGB primary colors, stability, brightness increase, layered structure and manufacturing method, etc. has been actively conducted in various fields. (Hereinafter, the organic thin film electroluminescent element may be referred to as an organic EL (Electroluminescence) element).

The element structure of the organic EL element used here is that 1,1-bis (4-bis (4-tolyl) aminophenyl) cyclohexane (TAPC) and tris (8-quinolinolato) are formed on an ITO substrate as an anode. Two organic compound layers made of aluminum (III) (Alq ₃ ) are stacked, and a cathode is deposited thereon.

TAPC is a triphenylamine-based molecule, and the TAPC layer functions as a hole transport layer. The Alq ₃ layer has two functions, the Alq ₃ layer in the vicinity of the interface with the TAPC layer functions as a green light emitting layer having electron transport properties, and the Alq ₃ layer on the cathode side functions as an electron transport layer. That is, the structure of the organic electroluminescent element is substantially a three-layer structure of a hole transport layer / a light emitting layer / an electron transport layer.

  Subsequent active research and development have proposed various device structures, but the basics have not changed.

  FIG. 1 is a schematic cross-sectional view showing a basic form of an organic EL element having a multilayer structure. The organic EL element 10 includes an anode 2 made of an ITO (Indium Tin Oxide) transparent electrode, a hole injection layer 3, a hole transport layer 4, a light emitting layer 5, an electron transport on a transparent substrate 1 such as a glass substrate. The layer 6 and the cathode (for example, an aluminum electrode) 7 are sequentially formed by, for example, a vacuum deposition method.

  When a DC voltage is applied between the anode 2 and the cathode 7 of the organic EL element 10, holes are injected from the anode 2 into the hole injection layer 3, and the injected holes emit light through the hole transport layer 4. Reach layer 5. On the other hand, electrons are injected from the cathode 7, and the injected electrons reach the light emitting layer 5 through the electron transport layer 6. The holes and electrons that have reached the light emitting layer 5 are recombined there, and the light emitting material excited by the recombination reaction emits light of a predetermined wavelength, and this light is emitted from the transparent substrate 1 side. By changing the light emitting material contained in the light emitting layer 5 in various ways, light emitting elements having various emission spectral characteristics can be realized.

  Actually, there are cases where one layer serves as both a transport layer and a light emitting layer, and there are cases where the transport layer is formed of a plurality of layers.

  For the light-emitting layer 5, for example, a light-emitting substance such as anthracene, naphthalene, phenanthrene, pyrene, chrysene, perylene, butadiene, coumarin, acridine, stilbene, or the like is used.

  As the hole transport layer 4, N, N'-bis (3-methylphenyl) -N, N'-diphenylbenzidine (TPD), N, N'-di (1-naphthyl) -N, N'-diphenyl Benzidine (NPB), N, N′-bis (4′-bis (3-methylphenyl) amino-4-biphenylyl) -N, N′-diphenylbenzidine (TPTE) and the like have been used. It is a derivative of phenylamine multimer. At present, trimer and tetramer derivatives are mainly used, and the performance of materials and elements has been improved. For example, the structural formula of TPTE is represented by the following chemical formula 9.

Chemical formula 9:

On the other hand, Alq ₃ derivatives, quinolinolato complexes of Zn and Ga, triazoles, oxydiazoles, and silole derivatives have been proposed for the electron transport layer, but still exceed Alq ₃ even after 15 years from Tang's paper. The material has not been discovered.

The hole drift mobility of the hole transport material is about 10 ⁻⁴ cm ² / Vs, which is about two orders of magnitude higher than the electron drift mobility of the electron transport material. For the injection of holes from the anode 2 to the hole transport layer 4, for example, when the anode 2 is an ITO transparent electrode, starburst amine, copper phthalocyanine complex (CuPc) or the like is used as the hole injection layer 3. Can be done smoothly. Further, an appropriate hole transport layer 4 itself can be selected from a large number of candidates according to the energy level of the light emitting layer 5 and the like.

On the other hand, injection of electrons from the cathode 7 into the electron transport layer 6 is not so easy. As the cathode material, a metal material having a small work function is selected. However, considering the stability of the material and the vapor deposition characteristics, the work function has a lower limit of 3.7 eV of Mg. If the electron transport material is Alq ₃ , its lowest unoccupied orbital (LUMO) level is about 2.5 eV, so there is an energy barrier of 1.2 eV. Actually, Mg activity is too high, and alloying or co-evaporation with about 5 to 10% of Ag is performed for stabilization, so that the energy barrier is further increased.

In 1997, Tang et al. Reduced the driving voltage and increased the electron injection efficiency by inserting lithium fluoride LiF with a thickness of 1 nm or less as a buffer layer between Alq ₃ and the cathode (MgAg and Al). It was found to improve dramatically (Appl. Phys. Lett., 70, 152, (1997)).

  However, considering the balance between the hole injection efficiency and the mobility, it must be said that the electron injection efficiency and the mobility are still low and insufficient.

  For example, depending on the type of the luminescent material, the injection of electrons is insufficient or the energy barrier of the highest occupied orbit (HOMO) between the luminescent layer 5 and the electron transport layer 6 is not sufficient, so that the holes are emitted from the luminescent layer 5. May penetrate into the electron transport layer 6 to recombine holes and electrons in the electron transport layer 6 to generate undesirable light emission that lowers the color purity, and may cause a decrease in light emission efficiency.

Therefore, in order to develop an organic EL element having a low driving voltage, high power efficiency, and high color purity, a high-performance electron transport material replacing Alq ₃ is necessary.

  Now, 9,10-diphenylanthracene exhibits blue fluorescence, and the fluorescence quantum yield η is ˜1, which is well known as a fluorescence standard substance in the blue region.

  For this reason, 9,10-diphenylanthracene derivatives have been actively studied as blue light-emitting materials. Many patents relating to 9,10-diphenylanthracene derivatives have been published, most of which are blue light-emitting materials (for example, JP-A No. 2002-121547, JP-A No. 10-228982, JP-A No. 2001-335516, etc.) .)

Patent Document 1 described later proposes an organic EL element in which an electron transport layer is composed of a plurality of layers and a 9,10-diphenylanthracene derivative is contained in an electron transport layer adjacent to a light emitting layer. However, the purpose is to improve the light emitting operation lifetime, and the 9,10-diphenylanthracene derivative is not used as a main electron transporting material. Therefore, the electron transport layer adjacent to the cathode does not contain the 9,10-diphenylanthracene derivative, and the electron transport layer adjacent to the light emitting layer is also mixed at a ratio of 0.1 to 25% by volume. It is only contained as a dopant. Further, in the example in which 9,10-di (2-naphthyl) anthracene (ADN) is doped into Alq ₃ which is an electron transport material, the luminance yield is increased when the doping amount of ADN is increased from 5% by volume to 10% by volume. A downward trend is shown.

JP 2003-51388 A (pages 2 and 4-8, FIGS. 4 and 5, Tables 1 and 2)

  An object of the present invention is to provide an organic electroluminescent element having improved electron transport characteristics and a display device using the same in view of the above situation.

  That is, the present invention is an organic electroluminescent device in which at least a light emitting layer and an electron transport layer are provided between an anode and a cathode, and the main component of the electron transport layer is a carbon atom at the 9th position of anthracene. Or an organic electroluminescent device, which is an organic compound having a main skeleton of a substituted anthracene formed by bonding a phenyl group and / or a naphthyl group to the 9th and 10th carbon atoms, and from the organic electroluminescent device This also relates to a light emitting device.

Low driving voltage, high power efficiency, in order to develop an organic electroluminescent device having high color purity, although high performance electron transporting material in place of Alq ₃ is required, the host material of the light-emitting layer with Alq ₃ In some cases, considering the energy levels of the hole transport layer, the light emitting layer and the cathode, the energy level of the highest occupied orbital (HOMO) and lowest unoccupied orbital (LUMO) of the electron transport material is that of Alq ₃ (HOMO˜5 .6 eV, LUMO to 2.5 eV) is preferably about 0.2 to 0.5 eV lower.

  According to the study of the present inventors, the energy levels of many organic compounds having the substituted anthracene as a main skeleton are HOMO to 5.8 eV and LUMO to 2.7 eV, which satisfy the above-mentioned conditions. In this respect, the organic compound is ideal as an electron transport material.

In addition, the present inventor has found that when the main skeleton is the substituted anthracene by a first-principles quantum chemistry calculation, the main skeleton is aromatic with a hydrocarbon group such as an alkyl group, an aryl group having 5 to 14 carbon atoms, or a styryl group. It was found that the molecular orbital of HOMO / LUMO is in the main skeleton, and the electronic structure of HOMO / LUMO is essentially unchanged even when the group ring is substituted / modified.

That is, the organic compound having the substituted anthracene as the main skeleton can be a candidate for a high-performance electron transport material that can replace Alq ₃ as long as it does not deviate from the above energy structure.

In the organic electroluminescent element of the present invention, compared with the case where Alq ₃ is used for the electron transport layer, the electron transport property is improved, so that the drive voltage is lowered, and the power efficiency is also improved by lowering the drive voltage. Further, undesirable light emission other than in the light emitting layer is reduced, and the color purity of the light emission is improved.

  Of course, in order to be useful as an electron transport layer, it is necessary to satisfy the performance generally required as a material of an organic electroluminescence device, such as thermal stability and vapor deposition property. This can be achieved by appropriately selecting the substituent to be introduced.

  Moreover, since the light emitting device of the present invention uses the organic electroluminescent element of the present invention, it can be driven at a low voltage and has excellent power efficiency. In addition, when applied to a color display or the like, color reproducibility is improved.

  In this invention, it is good that the ratio of the said organic compound in the said electron carrying layer is 50 mass% or more.

  The main skeleton of the organic compound is 9-phenylanthracene, and the highest occupied orbital (HOMO) and lowest unoccupied orbital (LUMO) of the organic compound are mainly formed by 14 carbon atoms forming the anthracene ring. It is preferable that a part of the π orbitals be delocalized on the 1′-position, 2′-position and 6′-position carbon atom of the phenyl group.

（但し、前記一般式（１）において、Ｒ¹及びＲ²は、置換または非置換の、炭素原子数１〜１２のアルキル基またはシクロアルキル基であり、Ａr¹は、炭素原子数６〜１４のアリール基または置換アリール基である。また、ｎは０〜９の整数であり、ｍとｐの和は０〜５の整数であって、ｎ、ｍまたはｐがそれぞれ２以上のときは、Ｒ¹、Ｒ²及びＡr¹は、それぞれ同一の若しくは異なる基である。） Specifically, the organic compound may be an organic compound represented by the following general formula (1).
General formula (1):

(In the general formula (1), R ¹ and R ² are substituted or unsubstituted alkyl groups or cycloalkyl groups having 1 to 12 carbon atoms, and Ar ¹ is 6 to 14 carbon atoms.) In addition, n is an integer of 0 to 9, and the sum of m and p is an integer of 0 to 5, and when n, m, or p is 2 or more, R ¹ , R ² and Ar ¹ are the same or different groups.

  Alternatively, the main skeleton of the organic compound is 9-naphthylanthracene, and the highest occupied orbital (HOMO) and the lowest unoccupied orbital (LUMO) of the organic compound are mainly formed by 14 carbon atoms forming the anthracene ring. It is preferable that a part of the π orbitals be delocalized on the carbon atom at the bonding position of the naphthyl group to the anthracene ring and on the adjacent carbon atoms.

（但し、前記一般式（２）において、Ｒ¹及びＲ²は、置換または非置換の、炭素原子数１〜１２のアルキル基またはシクロアルキル基であり、Ａr¹は炭素原子数５〜１４のアリール基または置換アリール基である。また、ｎは０〜９の整数であり、ｍとｐの和は０〜７の整数であって、ｎ、ｍまたはｐがそれぞれ２以上のときは、Ｒ¹、Ｒ²及びＡr¹は、それぞれ同一の若しくは異なる基である。） Specifically, the organic compound may be an organic compound represented by the following general formula (2).
General formula (2):

(In the general formula (2), R ¹ and R ² are substituted or unsubstituted alkyl groups or cycloalkyl groups having 1 to 12 carbon atoms, and Ar ¹ is a group having 5 to 14 carbon atoms. N is an integer of 0 to 9, and the sum of m and p is an integer of 0 to 7, and when n, m or p is 2 or more, R is ¹ , R ² and Ar ¹ are the same or different groups.

  Alternatively, the main skeleton of the organic compound is 9,10-diphenylanthracene, and the highest occupied orbital (HOMO) and the lowest unoccupied orbital (LUMO) of the organic compound are mainly 14 carbon atoms forming the anthracene ring. Are partly delocalized on the carbon atoms at the 1′-position, 2′-position, 6′-position, 1 ″ -position, 2 ″ -position and 6 ″ -position of the phenyl group. It is good to have.

（但し、前記一般式（３）において、Ｒ¹〜Ｒ³は、置換または非置換の、炭素原子数１〜１２のアルキル基またはシクロアルキル基であり、Ａr¹及びＡr²は炭素原子数６〜１４のアリール基または置換アリール基である。また、ｎは０〜８の整数であり、ｍとｐの和およびｌとｑの和は、０〜５の整数であって、ｎ、ｍ、ｌ、ｐまたはｑがそれぞれ２以上のときは、Ｒ¹、Ｒ²、Ｒ³、Ａr¹及びＡr²は、それぞれ同一の若しくは異なる基である。） Specifically, the organic compound may be an organic compound represented by the following general formula (3).
General formula (3):

(In the general formula (3), R ^{1 to} R ³ are substituted or unsubstituted alkyl groups or cycloalkyl groups having 1 to 12 carbon atoms, and Ar ¹ and Ar ² have 6 carbon atoms. N is an integer of 0 to 8, and the sum of m and p and the sum of l and q are integers of 0 to 5, and n, m, When l, p or q is 2 or more, R ¹ , R ² , R ³ , Ar ¹ and Ar ² are the same or different groups, respectively.

  Alternatively, the main skeleton of the organic compound is 9-naphthyl-10-phenylanthracene, and the highest occupied orbital (HOMO) and lowest unoccupied orbital (LUMO) of the organic compound mainly includes 14 anthracene rings. A π orbit formed by a carbon atom, and a part thereof is a carbon atom at the bonding position of the naphthyl group to the anthracene ring and its adjacent carbon atoms, and the 1 ″ position and 2 ″ position of the phenyl group. And delocalized on the 6 ″ carbon atom.

（但し、前記一般式（４）において、Ｒ¹〜Ｒ³は、置換または非置換の、炭素原子数１〜１２のアルキル基またはシクロアルキル基であり、Ａr²及びＡr³は炭素原子数６〜１４のアリール基または置換アリール基である。また、ｎは０〜８の整数であり、ｍとｐの和は０〜７の整数、ｌとｑの和は０〜５の整数であって、ｎ、ｍ、ｌ、ｐまたはｑがそれぞれ２以上のときは、Ｒ¹、Ｒ²、Ｒ³、Ａr¹及びＡr²は、それぞれ同一の若しくは異なる基である。） Specifically, the organic compound may be an organic compound represented by the following general formula (4).
General formula (4):

(However, in the said General formula (4), R < ¹ > -R < ³ > is a substituted or unsubstituted C1-C12 alkyl group or a cycloalkyl group, and Ar < ² > and Ar < ³ > are 6 carbon atoms. And n is an integer of 0 to 8, the sum of m and p is an integer of 0 to 7, and the sum of l and q is an integer of 0 to 5. , N, m, l, p or q are each 2 or more, R ¹ , R ² , R ³ , Ar ¹ and Ar ² are the same or different groups.)

  Alternatively, the main skeleton of the organic compound is 9,10-dinaphthylanthracene, and the highest occupied orbital (HOMO) and lowest unoccupied orbital (LUMO) of the organic compound mainly includes 14 carbons forming the anthracene ring. Π orbitals formed by atoms, and some of them may be delocalized on the carbon atom at the position of bonding of the two naphthyl groups to the anthracene ring and on the adjacent carbon atoms. .

（但し、前記一般式（３）において、Ｒ¹〜Ｒ³は、置換または非置換の、炭素原子数１〜１２のアルキル基またはシクロアルキル基であり、Ａr¹及びＡr²は炭素原子数６〜１４のアリール基または置換アリール基である。また、ｎは０〜８の整数であり、ｍとｐの和およびｌとｑの和は、０〜７の整数であって、ｎ、ｍ、ｌ、ｐまたはｑがそれぞれ２以上のときは、Ｒ¹、Ｒ²、Ｒ³、Ａr¹及びＡr²は、それぞれ同一の若しくは異なる基である。） Specifically, the organic compound may be an organic compound represented by the following general formula (5).
General formula (5):

(In the general formula (3), R ^{1 to} R ³ are substituted or unsubstituted alkyl groups or cycloalkyl groups having 1 to 12 carbon atoms, and Ar ¹ and Ar ² have 6 carbon atoms. N is an integer of 0 to 8, and the sum of m and p and the sum of l and q are integers of 0 to 7, and n, m, When l, p or q is 2 or more, R ¹ , R ² , R ³ , Ar ¹ and Ar ² are the same or different groups, respectively.

  In the organic electroluminescent device according to the present invention, the light emitting layer may be a hole transporting light emitting layer. This is a single heterostructure in which a hole transport layer and an electron transport layer are stacked. Alternatively, a double hetero structure in which a hole transport layer, a light emitting layer, and an electron transport layer are sequentially stacked may be used.

  Furthermore, as a buffer layer that smoothly connects between an electrode made of an inorganic material and a charge transport layer made of an organic material, a hole injection layer is provided between the anode and the hole transport layer or the hole transporting light emitting layer. It may be provided, or a buffer layer may be provided between the cathode and the electron transport layer.

  In the light emitting device according to the present invention, the organic electroluminescent element is preferably provided corresponding to a plurality of pixels and configured as a self-luminous display device.

  Hereinafter, an organic electroluminescent element according to a preferred embodiment of the present invention and a display device as an example of a light emitting device using the same will be described in detail with reference to the drawings.

Embodiment 1
FIG. 1 is a schematic cross-sectional view of an organic electroluminescent element 10 according to Embodiment 1 of the present invention.

  In the organic electroluminescent element 10 shown in FIG. 1, a transparent anode 2, a hole injection layer 3, a hole transport layer 4, a light emitting layer 5, an electron transport layer 6, and a cathode 7 are laminated on a transparent substrate 1. And is sealed by the protective layer 8.

  In such an organic electroluminescent device 10, by applying a DC voltage between the anode 2 and the cathode 7 using a DC power supply 50, holes are injected from the anode 2 into the hole injection layer 3, The holes reach the light emitting layer 5 through the hole transport layer 4, and electrons are injected from the cathode 7, and the electrons reach the light emitting layer 5 through the electron transport layer 6. As a result, recombination of holes and electrons occurs in the light emitting layer 5, and the light emitting material excited by the recombination reaction emits light of a predetermined wavelength.

  The organic electroluminescence device 10 is a bottom emission type or substrate transmission type (bottom emission type) organic electroluminescence device in which emitted light is emitted from the transparent substrate 1 side.

  For the substrate 1, for example, a light-transmitting material such as glass or plastic can be used as appropriate. When an organic electroluminescent element is used in combination with another display element, or when a large number of organic electroluminescent elements are arranged in a matrix to form a display device or the like as will be described later, a substrate is formed between the elements. May be shared. For example, in the case of active matrix driving, a TFT (Thin Film Transistor) can be formed on a common substrate.

  The material constituting the anode 2 should have a work function as large as possible. Further, in the present embodiment, the anode 2 needs to be light transmissive, and for example, ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), tin oxide, zinc oxide, or the like is used as a constituent material.

  On the other hand, the material constituting the cathode 7 should have a work function as small as possible. For example, magnesium, calcium, indium, lithium, aluminum, silver and alloys thereof are preferable.

  Note that the cathode 7 can be formed on the transparent substrate 1 by reversing the stacking order shown in FIG. In this case, for the cathode 7, a material having optical transparency is appropriately selected from the materials described above, and more than 30% of light is emitted in the wavelength region of the emitted light of the organic electroluminescent element 10. A material that transmits light is preferably used, and its thickness is thin, for example, 50 nm or less so that light can be transmitted.

  In this case, since the anode 2 does not need to be light transmissive, for example, nickel, gold, platinum, palladium, selenium, rhodium, ruthenium, iridium, rhenium, tungsten, molybdenum, chromium, tantalum, niobium and alloys thereof, An oxide or ITO, tin oxide, zinc oxide, titanium oxide, or the like is used.

  Examples of the material for the hole injection layer 3 include conductive polymers such as polyphenylene vinylene (PPV), copper phthalocyanine complex (CuPc), starburst amine, and diphenyl, trimer, and tetramer of triphenylamine. A material such as 4,4 ′, 4 ″ -tris (N- (2-naphthyl) -N-phenylamino) triphenylamine (2-TNATA) can be appropriately selected and used as a single layer or a stacked layer.

  The material of the hole transport layer 4 includes benzidine or a derivative thereof, styrylamine or a derivative thereof, triphenylmethane or a derivative thereof, porphyrin or a derivative thereof, triazole or a derivative thereof, imidazole or a derivative thereof, oxadiazole or a derivative thereof. Derivative, polyarylalkane or derivative thereof, phenylenediamine or derivative thereof, arylamine or derivative thereof, oxazole or derivative thereof, anthracene or derivative thereof, fluorenone or derivative thereof, hydrazone or derivative thereof, stilbene or derivative thereof, or polysilane compound And heterocyclic conjugated monomers such as vinylcarbazole compounds, thiophene compounds, and aniline compounds, oligomers, polymers, and the like.

  Specifically, N, N′-di (1-naphthyl) -N, N′-diphenylbenzidine (NPB), N, N′-bis (4′-bis (3-methylphenyl) amino-4-biphenylyl ) -N, N′-diphenylbenzidine (TPTE), α-naphthylphenyldiamine, porphyrin, metal tetraphenylporphyrin, metal naphthalocyanine, 4,4 ′, 4 ″ -trimethyltriphenylamine, 4,4 ′, 4 ″ -Tris (m-tolylphenylamino) triphenylamine (m-MTDATA), N, N, N ', N'-tetrakis (p-tolyl) p-phenylenediamine, N, N, N', N'-tetra Phenylbiphenyl-4,4′-diamine, N-phenylcarbazole, 4-di-p-tolylaminostilbene, poly (paraphenylenevinylene), poly (thiophenevinylene), poly (2,2′-thienylpyrrole), etc. Can be mentioned But it is not limited thereto.

As the light emitting material, a known material can be appropriately selected and used. As an example, the red light emitting layer includes tris (8-quinolinolato) aluminum (III) (Alq ₃ ) and 4-dicyanomethylene-6- (p-dimethylaminostyryl) -2-methyl-4H-pyran (DCM). % Doped, Alq ₃ doped with a few percent of coumarin, blue emitting layer 4,4-bis (2,2-diphenylethen-1-yl) biphenyl (DPVBi), etc. be able to.

  The main constituent material of the electron transport layer 6 is the organic compound having the substituted anthracene as a main skeleton.

  A buffer layer between the electron transport layer 6 and the cathode 7 is made of an oxide or fluoride of an alkali metal element such as lithium oxide, cesium oxide or lithium fluoride, or an oxide or fluoride of an alkaline earth metal element. Inserting a layer is more preferable because the electron injection efficiency is increased.

  Fabrication of the multilayer film using the above-described materials can be performed using a known method such as vacuum deposition or spin coating.

When driving the organic EL element according to the present embodiment, in order to eliminate the influence of moisture, oxygen, etc. in the atmosphere and improve safety, for example, magnesium fluoride, silicon nitride SiN _x or the like is used in advance. It is desirable to seal with a protective layer 8 with a sealant, or to purge the surrounding space with a dry inert gas or to be in a vacuum state.

  FIG. 2 schematically shows the energy level of the laminated structure of the organic electroluminescent element 10 using a band model.

FIG. 2 shows ITO as the material of the anode 2, 2-TNATA as the material of the hole injection layer 3, TPTE as the material of the hole transport layer 4, Alq ₃ as the host material of the light emitting layer 5, and the electron transport layer. In this case, 9,10-diphenylanthracene derivative is used as the material for lithium 6, lithium oxide is used as the material for the buffer layer between the cathode 7 and the electron transport layer 6, and Mg ₉₅ Ag ₅ is used as the material for the cathode 7. is there.

In FIG. 2, E ₂ and E ₇ are the work functions of the materials of the respective layers, and H ₃ , H ₄ , H ₅ , and H ₆ indicate the levels of the highest occupied molecular orbitals (HOMO) of the materials of the respective layers. ₃ , L ₄ , L ₅ and L ₆ indicate the level of the lowest unoccupied molecular orbital (LUMO) of the material of each layer. Here, the subscript number is the layer number. Since data on the work function of lithium oxide in the buffer layer has not been obtained, the value of the work function E _Li of metal lithium is used _instead , as is generally done. The energy level value shown in FIG. 2 is an example, and changes variously depending on the material.

From FIG. 2, when the 9,10-diphenylanthracene derivative is used as the electron transport layer 6, the LUMO level is lower than that of Alq ₃ and is close to the work function of Li, so that the energy barrier against electron injection is reduced. I understand. In addition, since the material has a relatively high electron mobility, the driving voltage is lowered as a whole. Further, when the light emitting layer 5 is made of a material having a high hole transport property other than Alq ₃ , the HOMO level of the electron transport layer 6 is deep, so that holes can be effectively confined in the light emitting layer 5 and the light emission efficiency can be improved. In addition, unstable hole block materials such as bathocuproine (BCP) and bis- (2-methyl-8-quinolinolato) -4- (phenylphenolato) aluminum (III) (B-Alq) are not required.

Embodiment 2
FIG. 3 is a schematic cross-sectional view of the organic electroluminescent element 20 according to the second embodiment of the present invention.

  The basic configuration of the organic electroluminescent element 20 is the same as that of the organic electroluminescent element 10 except that the organic electroluminescent element 20 is configured as a top emission type (top emission type) element that extracts light emitted upward from the element. That is, the light-transmitting anode 2, the hole injection layer 3, the hole transport layer 4, the light emitting layer 5, the electron transport layer 6 and the cathode 7 are laminated and sealed by the protective layer 8 in exactly the same structure. It is.

  The difference is that a light reflecting layer 11 made of an appropriate metal layer such as aluminum is provided below the anode 2 made of an ITO transparent electrode or the like. For this reason, the light emitted from the light emitting layer 5 is reflected by the light reflecting layer 11 and is emitted through the cathode 7B.

  For this reason, the cathode 7B needs to be light-transmitting, and as described in Embodiment 1, light is selected from magnesium, calcium, indium, lithium, aluminum, silver, and alloys thereof having a small work function. A material having permeability is appropriately selected and used.

  Since the organic electroluminescent element 20 is based on the premise that a light-transmitting material such as ITO is used as a desirable anode material, it is necessary to provide the light reflecting layer 11. If a material having a large work function and suitable as an anode material described in the first embodiment is selected and the anode 2 is formed to be light reflective, it is not necessary to provide the light reflecting layer 11.

  Note that as in Embodiment Mode 1, a structure in which the stacking order is reversed may be employed.

  The advantage of adopting such a top emission type (top emission type) structure is that the substrate 1B does not need to be transparent, and the range of selection of the material of the substrate 1B is widened. For example, a TFT or the like is provided on the substrate 1B. Even if it is formed, the ratio (light emitting area ratio) of the light emitting portion of the organic electroluminescent element can be increased without being obstructed by the TFT or the like.

Embodiment 3
FIG. 4 is a plan view schematically showing a display device 30 in which a large number of the organic electroluminescent elements 10 shown in FIG. 1 or the organic electroluminescent elements 20 shown in FIG. 3 are formed in a matrix. In this display device 30, a lower electrode, a laminate composed of a hole injection layer 3, a hole transport layer 4, a light emitting layer 5, and an electron transport layer 6, and an upper electrode are laminated on a substrate 31. Is formed.

  Further, when the driving method of the display device 30 is an active matrix method in which a TFT is provided for each pixel, a TFT formation layer is provided between the substrate 31 and the lower electrode.

  The substrate 31 is made of a glass substrate, a silicon substrate, a plastic substrate, a TFT substrate on which a TFT is formed, or the like. In particular, when the display device 30 is a substrate transmission type (bottom emission type) that extracts emitted light from the substrate 31 side, the substrate 31 is made of a light-transmitting material.

  The lower electrode formed on the substrate 31 is used as an anode or a cathode. The lower electrode is patterned into a shape suitable for the driving method of the display device 30.

  For example, when the driving method of the display device 30 is a simple matrix method, the lower electrode is formed in a stripe shape as shown in FIG. 5, for example.

  When the driving method of the display device 30 is an active matrix method in which a TFT is provided for each pixel, the lower electrode is patterned to correspond to each of the plurality of pixels 32 arranged in the same manner. The provided TFTs (not shown) are electrically connected through contact holes (not shown) formed in an interlayer insulating film covering these TFTs.

  On the other hand, the upper electrode is used as a cathode when the lower electrode is an anode, and is used as an anode when the lower electrode is a cathode.

  When the display device 30 is a simple matrix system, the upper electrode is formed in a stripe shape that intersects with the stripe-shaped lower electrode, for example, as shown in FIG. A region where the stripe of the electrode overlaps forms one pixel 32. That is, in the intersecting region, the upper electrode, the lower electrode, and the laminate sandwiched between them form one organic electroluminescent element 10 or 20.

  Further, when the display device 30 is an active matrix system, the upper electrode is formed in a solid film shape that covers the entire surface of the substrate 31 and is used as a common electrode for each pixel 32. . When the active matrix method is adopted as the driving method of the display device 30, a top emission type (a light emitting area ratio) that can increase the ratio of the light emitting portion of the organic electroluminescent element without being obstructed by the TFT or the like ( Top emission type) is desirable.

  FIG. 5 exemplifies the structure of a flat display using an 8 × 3 RGB simple matrix driving method as an example. As shown in the figure, for example, in the case of a full-color display, three types of laminates 43a, 43b, and 43c that can emit red (R), green (G), and blue (B) light respectively have an anode 41 and a cathode. 42. Both the cathode and the anode are patterned in a stripe shape and are orthogonal to each other in a matrix shape. A signal voltage is applied to the anode 41 and the cathode 42 in a time series by control circuits 44 and 45 with a built-in shift register, and the organic electroluminescent element at the intersection is configured to emit light. The flat display having such a configuration can be used not only as a display of characters / signals but also as an image reproducing device. Further, the stripe pattern of the cathode 42 is arranged for each color of red (R), green (G), and blue (B), so that a multi-color or full-color all solid-state flat panel display can be configured.

  EXAMPLES Hereinafter, although the preferable Example of this invention is described concretely, this invention is not limited to a following example.

Example 1
A glass substrate is used as the substrate 1, an ITO layer having a thickness of 190 nm is formed thereon as the anode 2, a 2-TNATA layer is formed as the hole injection layer 3 to a thickness of 35 nm, and a TPTE as the hole transport layer 4 is formed. The layer is 30 nm, the light emitting layer 5 is Alq ₃ is 35 nm, the electron transport layer 6 is 15 nm of a 9-phenylanthracene derivative represented by the following chemical formula 6, the buffer layer is 0.5 nm of lithium oxide, and the cathode 7 is Mg ₉₅ Ag _5. Were formed sequentially by vacuum deposition, and a bottom emission type organic electroluminescence device was produced.

Chemical formula 6:

When the characteristics of the organic electroluminescent device 10 thus manufactured were measured, the driving voltage at a current density of 25 mA / cm ² was 5.47 V, the luminous efficiency was 3.5 Cd / A, and the power efficiency was 2.0 lm. / W, luminance was 900 Cd / m ² , and emission peak wavelength was 520 to 525 nm (green).

Example 2
An organic electroluminescent device was produced in the same manner as in Example 1 except that a 9,10-diphenylanthracene derivative represented by the following chemical formula 7 was used as the electron transport layer 6.

Chemical formula 7:

The characteristics of the organic electroluminescent device 10 thus fabricated were measured. The driving voltage at a current density of 25 mA / cm ² was 5.92 V, the luminous efficiency was 3.5 Cd / A, and the power efficiency was 1.8 lm. / W, luminance was 885 Cd / m ² . The emission peak wavelength was 520 to 525 nm, which was not different from Example 1.

Example 3
An organic electroluminescent element was produced in the same manner as in Example 1 except that a 9,10-diphenylanthracene derivative represented by the following chemical formula 8 was used as the electron transport layer 6.

Chemical formula 8:

The characteristics of the organic electroluminescent device 10 thus fabricated were measured. The driving voltage at a current density of 25 mA / cm ² was 5.29 V, the luminous efficiency was 3.1 Cd / A, and the power efficiency was 1.8 lm. / W, luminance was 771 Cd / m ² . The emission peak wavelength was 520 to 525 nm, which was not different from Example 1.

Comparative Example 1
As a comparative example, an organic electroluminescent element was produced in the same manner as in Example 1 except that Alq ₃ was used as the electron transport layer 6.

When the characteristics of the organic electroluminescent device 10 thus manufactured were measured, the driving voltage at a current density of 25 mA / cm ² was 6.51 V, the luminous efficiency was 3.1 Cd / A, and the power efficiency was 1.5 lm. / W, luminance was 782 Cd / m ² . The emission peak wavelength was 520 to 525 nm, which was not different from Example 1.

From the above experiment, when the current density was kept at 25 mA / cm ² , the driving voltage was lower in each of Examples 1 to 3 than in Comparative Example 1, and the efficiency of electron injection and transportation was improved. It is shown that. In Examples 1 and 2, the light emission efficiency with respect to the current is also improved, and this is considered to be because the effect of confining electrons and holes is improved by improving the electron injection and transport efficiency. The power efficiency, which is the sum of the two effects, is the best in Example 1, which is thought to be due to the fact that two units of 9-phenylanthracene structure are contained in one molecule and the electron mobility is high.

  In addition, it is a main skeleton part consisting of 9-phenylanthracene or 9,10-diphenylanthracene that plays an important role in electron transport properties, and other substituents contribute to the improvement of thermal stability. Less important for electron transport.

  As described above, the organic electroluminescent device of this example provides a light emitting device with low driving voltage and high power efficiency. By using an organic compound having 9-phenylanthracene or 9,10-diphenylanthracene as the main skeleton in the electron transport layer, the electron mobility and the efficiency of injecting electrons from the cathode are improved, and the above effect is realized.

  In addition, when combined with a light emitting layer having a high hole transporting property, the HOMO level of the electron transport layer is deepened, so that holes are effectively confined in the light emitting layer, and the light emission efficiency and the color purity are improved. Further, since unstable hole block materials such as BCP and B-Alq are not required, the reliability is improved.

  Although the present invention has been described based on the embodiments and examples, it is needless to say that the present invention is not limited to these examples and can be appropriately changed without departing from the gist of the invention. .

  It is useful for realizing organic electroluminescent elements with low driving voltage, high power efficiency, and high color purity, and is effective when used in various fields as display devices, light emitting devices, and lighting devices. Is.

It is a schematic sectional drawing of the organic electroluminescent element based on Embodiment 1 of this invention. It is explanatory drawing which shows the energy band model of the laminated structure of an organic electroluminescent element similarly. It is a schematic sectional drawing of the organic electroluminescent element based on Embodiment 2 of this invention. It is a top view of the display apparatus based on Embodiment 3 of this invention. 2 is a configuration diagram of a full-color flat display as an example of the display device. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transparent substrate, 1B ... Substrate, 2 ... Anode, 3 ... Hole injection layer, 4 ... Hole transport layer,
5 ... Light emitting layer, 6 ... Electron transport layer, 7 ... Electron injection layer, 7 ... Cathode, 7B ... Cathode (light transmissive),
8 ... Protective layer, 10 ... Organic electroluminescent device, 11 ... Light reflecting layer, 20 ... Organic electroluminescent device,
DESCRIPTION OF SYMBOLS 30 ... Display apparatus, 31 ... Board | substrate, 32 ... Pixel, 41 ... Transparent electrode (anode), 42 ... Cathode,
43 ... laminate, 44 ... control circuit, 45 ... control circuit (luminance signal circuit), 50 ... DC power supply

Claims (17)

  It is an organic electroluminescent element in which at least a light emitting layer and an electron transport layer are provided between an anode and a cathode, and the main component of the electron transport layer is a carbon atom at the 9th position of anthracene, or 9th position and 10th position. Organic electroluminescent device, which is an organic compound having a main skeleton of a substituted anthracene formed by bonding a phenyl group and / or a naphthyl group to a carbon atom at the position.   The organic electroluminescent element according to claim 1, wherein a ratio of the organic compound in the electron transport layer is 50% by mass or more.   The substituted anthracene is 9-phenylanthracene, and the highest occupied orbital (HOMO) and lowest unoccupied orbital (LUMO) of the organic compound are π orbitals formed mainly by 14 carbon atoms forming the anthracene ring. Furthermore, the organic electroluminescent element of Claim 1 which the part has delocalized on the carbon atom of 1'-position, 2'-position, and 6'-position of the said phenyl group. The organic electroluminescent element according to claim 3, wherein the organic compound is an organic compound represented by the following general formula (1).
General formula (1):

(In the general formula (1), R ¹ and R ² are substituted or unsubstituted alkyl groups or cycloalkyl groups having 1 to 12 carbon atoms, and Ar ¹ is 6 to 14 carbon atoms.) In addition, n is an integer of 0 to 9, and the sum of m and p is an integer of 0 to 5, and when n, m, or p is 2 or more, R ¹ , R ² and Ar ¹ are the same or different groups.   The substituted anthracene is 9-naphthylanthracene, and the highest occupied orbital (HOMO) and lowest unoccupied orbital (LUMO) of the organic compound are π orbitals formed mainly by 14 carbon atoms forming the anthracene ring. The organic electroluminescent device according to claim 1, wherein a part thereof is delocalized on the carbon atom at the bonding position of the naphthyl group to the anthracene ring and the adjacent carbon atoms. The organic electroluminescent element according to claim 5, wherein the organic compound is an organic compound represented by the following general formula (2).
General formula (2):

(In the general formula (2), R ¹ and R ² are substituted or unsubstituted alkyl groups or cycloalkyl groups having 1 to 12 carbon atoms, and Ar ¹ is a group having 5 to 14 carbon atoms. N is an integer of 0 to 9, and the sum of m and p is an integer of 0 to 7, and when n, m or p is 2 or more, R is ¹ , R ² and Ar ¹ are the same or different groups.   The substituted anthracene is 9,10-diphenylanthracene, and the highest occupied orbital (HOMO) and the lowest unoccupied orbital (LUMO) of the organic compound are mainly formed by 14 carbon atoms forming the anthracene ring. An orbital, and a part thereof is delocalized on the carbon atoms at the 1′-position, 2′-position, 6′-position, 1 ″ -position, 2 ″ -position and 6 ″ -position of the phenyl group. 1. The organic electroluminescent device described in 1. The organic electroluminescent element according to claim 7, wherein the organic compound is an organic compound represented by the following general formula (3).
General formula (3):

(In the general formula (3), R ^{1 to} R ³ are substituted or unsubstituted alkyl groups or cycloalkyl groups having 1 to 12 carbon atoms, and Ar ¹ and Ar ² have 6 carbon atoms. N is an integer of 0 to 8, and the sum of m and p and the sum of l and q are integers of 0 to 5, and n, m, When l, p or q is 2 or more, R ¹ , R ² , R ³ , Ar ¹ and Ar ² are the same or different groups, respectively.   The substituted anthracene is 9-naphthyl-10-phenylanthracene, and the highest occupied orbital (HOMO) and lowest unoccupied orbital (LUMO) of the organic compound is mainly formed by 14 carbon atoms forming the anthracene ring. Π orbitals, and a part of them is a carbon atom at the bonding position of the naphthyl group to the anthracene ring and its adjacent carbon atom, and the 1 ″ position, 2 ″ position and 6 ″ position of the phenyl group. The organic electroluminescent element according to claim 1, which is delocalized on a carbon atom. The organic electroluminescent element according to claim 9, wherein the organic compound is an organic compound represented by the following general formula (4).
General formula (4):

(However, in the said General formula (4), R < ¹ > -R < ³ > is a substituted or unsubstituted C1-C12 alkyl group or a cycloalkyl group, and Ar < ² > and Ar < ³ > are 6 carbon atoms. And n is an integer of 0 to 8, the sum of m and p is an integer of 0 to 7, and the sum of l and q is an integer of 0 to 5. , N, m, l, p or q are each 2 or more, R ¹ , R ² , R ³ , Ar ¹ and Ar ² are the same or different groups.)   The substituted anthracene is 9,10-dinaphthylanthracene, and the highest occupied orbital (HOMO) and lowest unoccupied orbital (LUMO) of the organic compound is mainly formed by 14 carbon atoms forming the anthracene ring. The organic compound according to claim 1, wherein the organic compound is a π orbital, and a part thereof is delocalized on the carbon atom at the bonding position of the two naphthyl groups with the anthracene ring and the carbon atoms adjacent to the carbon atom. Electroluminescent device. The organic electroluminescent element according to claim 11, wherein the organic compound is an organic compound represented by the following general formula (5).
General formula (5):

(In the general formula (3), R ^{1 to} R ³ are substituted or unsubstituted alkyl groups or cycloalkyl groups having 1 to 12 carbon atoms, and Ar ¹ and Ar ² have 6 carbon atoms. N is an integer of 0 to 8, and the sum of m and p and the sum of l and q are integers of 0 to 7, and n, m, When l, p or q is 2 or more, R ¹ , R ² , R ³ , Ar ¹ and Ar ² are the same or different groups, respectively.   The organic electroluminescent element according to claim 1, wherein the light emitting layer is a hole transporting light emitting layer.   The organic electroluminescent element according to claim 1, wherein a hole injection layer is provided between the anode and the hole transporting layer or the hole transporting light emitting layer.   The organic electroluminescent element according to claim 1, wherein a buffer layer for electron injection is provided between a cathode and the electron transport layer.   The light-emitting device which consists of an organic electroluminescent element as described in any one of Claims 1-15.   The light-emitting device according to claim 16, wherein the organic electroluminescent element is provided corresponding to a plurality of pixels and configured as a self-luminous display device.

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