JP3945293B2 - Luminescent material, organic electroluminescent element, and display device - Google Patents

Description

で表される有機金属錯体からなる発光材料である。これは、以下の（１）又は（２）の特徴を有しており、更に以下の（３）〜（４）及び（６）を望ましい特徴とするものである。
【００２５】
（１）発光材料は有機金属錯体であり、その中心金属は周期表第６周期の重金属であるタングステンである。
（２）上記中心金属の電子配置は、（Ｘｅ）４ｆ⁰５ｄ⁰６ｓ⁰もしくは（Ｘｅ）４ｆ¹⁴５ｄ⁰６ｓ⁰である閉殻構造である。
（３）ＬＵＭＯ（最低非占有分子軌道）は、中心金属の非占有ｄ軌道と配位子の非占有π^＊軌道から構成される。
（４）上記中心金属としてＬａ³⁺、Ｃｅ⁴⁺、Ｈｆ⁴⁺、Ｔａ⁵⁺、Ｗ⁶⁺、Ｒｅ⁷⁺、Ｈｇ²⁺、Ｔｌ³⁺、Ｐｂ⁴⁺ 及びＢｉ⁵⁺ のうち、特にＷ ⁶⁺ が選択され、主たる配位子は配位子１つ当たり２つの共有結合で中心金属と結合している。
（５）参考迄に述べると、上記中心金属がＬａ³⁺、Ｃｅ⁴⁺、Ｈｆ⁴⁺、Ａｕ⁺又はＨｇ²⁺である場合、主たる配位子は配位子１つ当たり１つの共有結合で中心金属と結合している。
（６）配位子の分子構造は、上記（４）の場合は下記の化学式（１）、および上記（５）の場合は下記の化学式（２）に示された分子及びその誘導体であるが、特に化学式（１）の中で一番最初に挙げたものである。
【００２６】
【化３】
化学式（１）：

化学式（２）：

【００２７】
上記の特徴のうち、（１）又は／及び（２）は、高効率で青色の燐光発光を実現するために必要不可欠である。
【００２８】
燐光発光には基底一重項状態であるＳ⁰、励起一重項状態であるＳ¹、及び励起三重項状態であるＴ¹が関与している。そして、スピン禁制であるＳ¹→Ｔ¹及びＴ¹→Ｓ⁰の遷移が効率よく起こらなければならない。このスピン禁制を解くためには、大きなスピン軌道相互作用が必要である。そして、スピン軌道相互作用は原子番号の４乗に比例するため、重金属ほど有利になる。これが、上記（１）の特徴である。
【００２９】
更に、青色発光を得るために、発光分子のＨＯＭＯ（最高占有分子軌道）−ＬＵＭＯ（最低非占有分子軌道）のエネルギーギャップは２．７ｅＶ以上必要である。これまで報告されている燐光材料である有機金属錯体は、その中心金属がＩｒ³⁺、Ｐｔ²⁺などであり、電子状態は５ｄ軌道が開殻構造になっている。この場合、配位子場分裂によってｄ軌道は分裂し、占有されたｄ軌道と空のｄ軌道との間のｄ−ｄ遷移によって、ＨＯＭＯ−ＬＵＭＯのギャップは制限される。配位子場分裂のエネルギーは２．５ｅＶより大きくすることは期待できないので、開殻構造の電子状態を有する錯体では、青色発光に必要なＨＯＭＯ−ＬＵＭＯのエネルギーギャップを確保することは非常に困難であると考えられる。
【００３０】
そこで、本発明の発光材料では、中心金属の電子配置は、（Ｘｅ）４ｆ⁰５ｄ⁰６ｓ⁰もしくは（Ｘｅ）４ｆ¹⁴５ｄ⁰６ｓ⁰である閉殻構造とする。これが上記（２）の特徴である。この場合、ＨＯＭＯのエネルギーレベルは配位子によって決まり、ＬＵＭＯは中心金属の非占有５ｄ軌道よりなる。従って、青色発光に必要なエネルギーギャップを確保できるものと考えられる。
【００３１】
更に望ましくは、ＬＵＭＯには配位子の非占有π^＊軌道が寄与していると、遷移確率を高める上で有利である。これが、上記（３）の特徴である。
【００３２】
上記（４）、（５）は、中心金属の価数と配位数からくる要請によるものである。たとえば、Ｗ⁶⁺は６配位が安定であるから、２座の配位子を有する場合には、配位子１つ当たり２つの共有結合で中心金属と結合している必要がある。Ｈｆ⁴⁺であれば８配位が安定であるから、２座の配位子を有する場合には、配位子１つ当たり１つの共有結合と１つの配位結合で中心金属と結合している必要がある。
【００３３】
具体的な配位子の分子構造は、上記（３）を満たすように共役系の大きさを調節すればよい。また、合成の難易も考慮に入れる必要がある。
【００３４】
以上に示したような分子を発光層に用いることにより、高効率の有機電界発光素子を作ることができる。
【００３５】
層構造は、効率、信頼性等を考慮して、適切に設計したものを用いることができる。
【００３６】
また、本発明は、このような有機電界発光素子を青色発光素子として好適に用いた表示装置に係るものでもある。
【００３７】
このような表示装置では、前述したように、高効率に発光する有機電界発光素子を青色発光素子として用いることから、他の赤色発光素子及び緑色発光素子と組み合わせることで、効率の高いフルカラー表示が可能になる。
【００３８】
以下、本発明の有機電界発光素子及びこれを用いた表示装置の構成例を図面に基づいて詳細に説明する。
【００３９】
この有機電界発光素子及びこれを用いた表示装置は、図１又は図２に示したものと同様の構造からなっていてよい。
【００４０】
図１に示す発光素子は、基板１０と、この基板１０上に設けられた有機電界発光素子１Ａの各構成層とを備えている。即ち、基板１０上に、下部電極６、有機層２、４及び上部電極７を順次積層してなり、基板１０側または上部電極７側から発光光５を取り出す構成となっている。尚、この図においては、基板１０上に１画素分の有機電界発光素子１Ａを設けた構成を示しているが、この表示装置２１は、例えば図３に示したと同様に複数の画素を備え、複数の有機電界発光素子が各画素に配列形成されていることとする。
【００４１】
次に、この表示装置２１を構成する各部の詳細な構成を、基板１０、下部電極６及び上部電極７、有機層２、４の順に説明する。
【００４２】
基板１０は、ガラス、シリコン、プラスチック基板、さらにはＴＦＴ（Thin Film Transistor）が形成されたＴＦＴ基板などからなる。特に、この表示装置２１が、基板１０側から発光光５を取り出す透過型である場合には、この基板１０は光透過性を有する材料で構成されることとする。
【００４３】
また、基板１０上に形成された下部電極６は、陽極または陰極として用いられるものである。尚、図面においては、代表して下部電極６が陽極である場合を例示した。
【００４４】
この下部電極６は、表示装置２１の駆動方式によって適する形状にパターンニングされていることとする。例えば、この表示装置２１の駆動方式が単純マトリクス方式である場合には、この下部電極６は例えばストライプ状に形成される。また、表示装置２１の駆動方式が画素毎にＴＦＴを備えたアクティブマトリクス方式である場合には、下部電極６は複数配列された各画素に対応させてパターン形成され、同様に各画素に設けられたＴＦＴに対して、これらのＴＦＴを覆う層間絶縁膜に形成されたコンタクトホール（図示省略）を介してそれぞれが接続される状態で形成されることとする。
【００４５】
一方、下部電極６上に有機層を介して設けられる上部電極７は、下部電極６が陽極である場合には陰極として用いられ、下部電極６が陰極である場合には陽極として用いられる。尚、図面においては、上部電極７が陰極である場合が示されている。
【００４６】
そして、この表示装置２１が、単純マトリクス方式である場合には、図３のように上部電極７は例えば下部電極６のストライプと交差するストライプ状に形成され、これらが交差して積層された部分が有機電界発光素子となる。また、この表示装置２１が、アクティブマトリクス方式である場合には、この上部電極７は、基板１０上の一面を覆う状態で成膜されたベタ膜状に形成され、各画素に共通の電極として用いられることとする。尚、表示装置２１の駆動方式としてアクティブマトリクス方式を採用する場合には、有機電界発光素子の開口率を確保するために、上部電極７側から発光光５を取り出す上面発光型とすることが望ましい。
【００４７】
ここで、下部電極６（または上部電極７）を構成する陽極材料としては、仕事関数がなるべく大きなものがよく、たとえば、ニッケル、金、白金、パラジウム、セレン、ロジウム、ルテニウム、イリジウム、レニウム、タングステン、モリブデン、クロム、タンタル、ニオブや、これらの合金、酸化物、あるいは、酸化錫、ＩＴＯ（Indium Tin Oxide）、酸化亜鉛、酸化チタン等が好ましい。
【００４８】
一方、上部電極７（または下部電極６）を構成する陰極材料としては、仕事関数がなるべく小さなものがよく、例えば、マグネシウム、カルシウム、インジウム、リチウム、アルミニウム、銀やこれらの合金が好ましい。
【００４９】
ただし、この有機電界発光層で生じた発光光５を取り出す側となる電極は、上述した材料の中から、光透過性を有する材料を適宜選択して用いることとし、特に、有機電界発光素子の発光光５の波長領域において３０％より多くの光を透過する材料が好ましく用いられる。
【００５０】
発光を基板側又は上面側、或いはこれらの双方のいずれから取り出すかによって、基板、電極材料及び積層する順序を適切に選択すればよい。
【００５１】
図２に示す発光素子１Ｂにおいて、正孔注入層１の正孔注入材料としては、ＰＰＶ（ポリフェニレンビニレン）などの伝導性ポリマー、フタロシアニン銅、スターバースト型アミンなどの材料を単層もしくは積層して用いることができる。
【００５２】
正孔輸送層２に用いられる正孔輸送材料は、トリフェニルアミン多量体もしくはその誘導体などの既知の材料を用いることができる。
【００５３】
さらに、発光層３（又は図１にも示した電子輸送層４に混合可能な発光材料）は、後述の化学式（３）で表されるＷ錯体を用いる。これは、適当な濃度でＴＡＺ（トリアゾール誘導体）などのワイドギャップなホスト材料にドープしてもよい。
【００５４】
電子輸送層４の電子輸送材料には、Ａｌｑ₃（トリス（８−キノリノール）アルミニウム）、ＴＡＺ、ＯＸＤ（オキサジアゾール誘導体）などの既知の材料を用いることができる。この電子輸送層には本発明の発光材料をドープして、電子輸送性発光層としてもよい。
【００５５】
電子輸送性発光層と陰極の間に、酸化リチウム、酸化セシウム、フッ化ストロンチウムなどのアルカリ金属酸化物、アルカリ金属弗化物、アルカリ土類酸化物、アルカリ土類弗化物からなるバッファ層を挿入すると、電子の注入効率が上がり、より好ましい。
【００５６】
上記したような材料による多層膜の作製は、真空蒸着やスピンコートなどの周知の方法を用いることができる。
【００５７】
なお、本発明の発光素子を駆動するときは、大気中の水分や酸素等による影響を排除し、安全性を高めるために、あらかじめ、例えばフッ化マグネシウムやＳｉＮｘなどで封止したり、あるいは、周囲空間を乾燥した不活性ガスでパージするか真空に引いた状態にしておくことが望ましい。
【００５８】
【実施例】
以下、実施例に基づいて本発明を具体的に説明する。
【００５９】
実施例１
膜厚が１９０ｎｍのＩＴＯが形成されているガラス基板上に、正孔注入層として２−ＴＮＡＴＡ（４，４’，４”−トリス（Ｎ，Ｎ−（２−ナフチル）フェニルアミノ）トリフェニルアミン）を３５ｎｍ、正孔輸送層としてα−ＮＰＢ（４，４’−ビス［Ｎ−（１−ナフチル）−Ｎ−フェニルアミノ］ビフェニル）を３０ｎｍ、発光層として下記の化学式（３）で表されるＷ錯体を８重量％ＴＡＺにドープした層を２５ｎｍ、電子輸送層としてＡｌｑ₃を２５ｎｍ、バッファ層として酸化リチウムを０．５ｎｍ、陰極としてアルミニウム２００ｎｍ、真空蒸着で順次形成し、有機電界発光素子を作製した。
【００６０】
【化４】
化学式（３）：

【００６１】
こうして作製された有機電界発光素子の特性を測定した。ＥＬスペクトルには４６０ｎｍにピークがあり、ＣＩＥ色度座標上での座標は（0.14,0.11）であった。発光の量子効率は６％と高効率であった。
【００６２】
比較例１
発光層として、下記の化学式（４）で表されるＺｎ錯体をドープした以外は、実施例１と同様にして有機電界発光素子を作製した。
【００６３】
【化５】
化学式（４）：

【００６４】
こうして作製された有機電界発光素子の特性を測定した。ＥＬスペクトルには４６０ｎｍにピークがあり、ＣＩＥ色度座標上での座標は（0.14,0.18）であった。発光の量子効率は１％と低効率であった。
【００６５】
以上に述べた本発明の実施の形態及び実施例は、本発明の技術的思想に基づいて種々に変形可能である。
【００６６】
【発明の作用効果】
本発明は、上記したように、これまで実現不可能だった高効率の青色発光素子を実現する燐光発光材料の分子設計を提供し、これを実現するものである。この燐光材料を発光材料として用いることによって、これまで不可能だった高効率の青色発光素子を実現するとともに、高効率フルカラー表示装置を可能にする。
【図面の簡単な説明】
【図１】有機電界発光素子の要部概略断面図である。
【図２】同、他の有機電界発光素子の要部概略断面図である。
【図３】同、有機電界発光素子を用いたフルカラーの平面ディスプレイの構成図である。
【符号の説明】
１…正孔注入層、２…正孔輸送層、３…発光層（発光材料）、４…電子輸送層、
５…発光光、６…透明電極（陽極）、７…陰極、１０…基板、１４…保護膜、
１５ａ、１５ｂ…有機層、２０…電源[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light emitting material used for a display element for a display device such as a color display, a self-luminous organic electroluminescent element using the light emitting material, and a display device combining the light emitting elements. .
[0002]
[Prior art]
In recent years, especially in multimedia-oriented products, the importance of human-machine interfaces has increased. In order to operate the machine more comfortably and efficiently, it is necessary to extract a sufficient amount of information from the machine without error, in a concise and instantaneous manner. For this reason, research has been conducted on various display devices including displays. Has been done.
[0003]
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 an interface for many miniaturized products such as a laptop information processing device, a small television receiver, a clock, a calculator, and the like.
[0004]
This liquid crystal display has been studied as a slick interface from a small size to a large-capacity display device, taking advantage of the fact that the liquid crystal is driven at a low voltage and has a low power consumption.
[0005]
However, since this liquid crystal display is a light receiving type, a backlight is indispensable, and driving the backlight requires a larger electric power than that of the liquid crystal. Therefore, even though a storage battery or the like is built in, there is a problem in that there is a limit in use such as power supply being limited and operation time being shortened.
[0006]
Furthermore, since the liquid crystal display is a display based on the orientation state of the liquid crystal molecules, the contrast changes depending on the angle even within the viewing angle. For this reason, the viewing angle is narrow and the large display such as a large display can be used. Is not suitable. In addition, since the alignment speed of liquid crystal molecules is slow, it is not suitable for displaying moving images.
[0007]
On the other hand, from the viewpoint of the driving method, the active matrix method of the liquid crystal display shows a response speed sufficient for handling moving images, but uses a TFT (thin film transistor) driving circuit, so that the screen size can be increased due to pixel defects. It is difficult and is not a good idea from the viewpoint of cost reduction. In contrast to the active matrix method, the simple matrix method, which is another driving method, is low in cost and relatively easy to increase the screen size, but provides a response speed sufficient for handling moving images. I can't.
[0008]
For such a liquid crystal element, a display element 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.
[0009]
Among these, the plasma display element utilizes plasma luminescence in gas for display, and is suitable for an increase in size and capacity. However, it has problems in terms of thickness reduction and cost, and further requires a high voltage bias for driving, which is not suitable for portable devices.
[0010]
As for the inorganic electroluminescent element, a green light emitting display or the like has been commercialized, but, like the plasma display element, several hundred volts are required for AC bias driving, and thus it has not been accepted by users. However, as a result of subsequent technological advances, the R, G, and B primary colors required for color displays have been successfully emitted today, but inorganic materials are indispensable for the structure, so the emission wavelength due to molecular design, etc. Such control is impossible, and full colorization is expected to be difficult.
[0011]
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, it was observed that when a strong fluorescent anthracene single crystal was injected into a carrier, a unique light emission phenomenon (due to the induction of luminescence) occurred. Since then, organic electroluminescence devices have been the subject of research for a long time, but because of the low brightness, single color, and the use of a single crystal, it is technically mainly in terms of carrier injection into organic materials. Emphasis was put on and did not leave the basic research stage.
[0012]
However, since Tang et al. Of Eastman Kodak in 1987 announced an organic thin film electroluminescent device having an amorphous light emitting layer capable of low voltage drive and high luminance emission, R, G, B in various directions. Three primary colors of light emission, stability, brightness increase, layered structure and manufacturing method and research have been actively conducted in various fields, and it has reached today.
[0013]
An organic electroluminescent element using an organic light emitting material is one in which an organic electroluminescent layer containing an organic light emitting material is sandwiched between an anode and a cathode, at least one of which is light transmissive, and a DC voltage is applied. Causes light emission.
[0014]
1 to 3 show examples of conventional organic electroluminescent elements (organic EL elements), respectively.
[0015]
FIG. 1 shows a substrate 10 made of translucent glass or the like, an anode 6 such as translucent ITO (Indium Tin Oxide), an organic layer 15a composed of a hole transport layer 2 and an electron transport layer 4, and a cathode. 7 is a single heterostructure organic electroluminescent element 1A having a laminated structure in which 7 is sequentially laminated, and this laminated structure is sealed by a protective layer. In this case, light emission 5 having a predetermined wavelength is generated from the interface between the hole transport layer 2 and the electron transport layer 4 by application of a DC voltage from the power source 20.
[0016]
FIG. 2 shows an organic structure comprising a translucent anode 6 and, if necessary, a hole injection layer 1, a hole transport layer 2, a light emitting layer 3, and an electron transport layer 4 on a translucent substrate 10. This is a double heterostructure organic electroluminescent device 1B having a laminated structure in which a layer 15b and a cathode 7 are sequentially laminated, and this laminated structure is sealed by a protective layer. In this case, by applying a DC voltage 20 between the anode 6 and the cathode 7, holes injected from the anode 6 pass through the hole transport layer 2, and electrons injected from the cathode 7 become electron transport layer 4. Then, each reaches the light emitting layer 3. As a result, electron / hole recombination occurs in the light emitting layer 3 to generate singlet excitons, and light emission 5 having a predetermined wavelength is generated from the singlet excitons.
[0017]
FIG. 3 is a configuration example of the flat display 21 using the organic electroluminescent element. As shown in the figure, in the case of a full color display, for example, organic layers 15 (15a, 15b) capable of emitting three primary colors of red (R), green (G), and blue (B) are disposed between the cathode 7 and the anode 6. It is arranged in. The cathode 7 and the anode 6 can be provided in stripes crossing each other, and are selected by the luminance signal circuit 24 and the control circuit 25 with a built-in shift register, and a signal voltage is applied to each of them, thereby the selected cathode The organic layer at the position (pixel) where the anode 7 and the anode 6 intersect is configured to emit light.
[0018]
In the case of FIG. 1, a light emitting material is included in the electron transport layer, and a two-layer structure of the electron transport layer 4 and the hole transport layer 2 that also serves as the light emitting layer is obtained by CWTang, SAVanSlyke, and CHChen according to J. of Appl. 65-9,3610-3616 (1989), and a patent application (Japanese Patent Laid-Open No. 63-264692) has been filed.
[0019]
Here, in order to realize a full color display, stable high color purity R, G, B light emitting elements are indispensable. Therefore, in the field of organic electroluminescence devices, research and development of luminescent material devices having chromaticity of NTSC (National Television System Committee) standard or sRGB (Standard RGB) is actively conducted.
[0020]
Until now, organic materials with fluorescent properties have been used exclusively as light-emitting materials, but Forrest et al. Recently announced high-efficiency organic electroluminescent devices using phosphorescent materials composed of Pt and Ir complexes. Has become active.
[0021]
[Problems to be solved by the invention]
However, all of the complexes such as Pt, Ir, and Ru that have been published so far are blue-green to red light-emitting materials, and there are no reports on elements of blue materials that are indispensable for realizing a full color display.
[0022]
For this reason, in a display device using an organic electroluminescent element, full color display using a phosphorescent material capable of emitting blue light with high efficiency cannot be realized.
[0023]
Accordingly, the present invention provides a phosphorescent material capable of emitting blue light with high efficiency, an organic electroluminescent element including the material in a light emitting layer, and a display device capable of high-efficiency full color display by using the phosphor. It is for the purpose.
[0024]
[Means for Solving the Problems]
That is, the luminescent material of the present invention for achieving such an object is
[Chemical 2]
Chemical formula (3):

It is a luminescent material which consists of organometallic complex represented by these. This has the following features (1) or (2), and the following (3) to (4) and (6) are desirable features.
[0025]
(1) The light emitting material is an organometallic complex, and the central metal is tungsten , which is a heavy metal of the sixth periodic table.
(2) The electron arrangement of the central metal is a closed shell structure of (Xe) 4f ⁰ 5d ⁰ 6s ⁰ or (Xe) 4f ¹⁴ 5d ⁰ 6s ⁰ .
(3) LUMO (lowest unoccupied molecular orbital) is composed of an unoccupied d orbital of the central metal and an unoccupied π ^* orbital of the ligand.
(4) La ³⁺ as the central ^{metal, Ce 4+, Hf 4+, Ta} 5+, W 6+, Re 7+, Hg 2+, Tl 3+, Pb 4+ and Bi ^{5 +} of, in particular W ⁶⁺ is selected and the main ligand is bound to the central metal by two covalent bonds per ligand.
(5) For reference, when the central metal is La ³⁺ , Ce ⁴⁺ , Hf ⁴⁺ , Au ⁺ or Hg ²⁺ , the main ligand is one covalent bond per ligand. It is combined with the central metal.
(6) the molecular structure of the ligand, the (4) following chemical formula in the case of (1), and in the case of (5) is a molecule and its derivatives have been shown in the following formula (2) In particular, it is the first listed in the chemical formula (1) .
[0026]
[Chemical 3]
Chemical formula (1):

Chemical formula (2):

[0027]
Among the above features, (1) and / or (2) are indispensable for realizing blue phosphorescence with high efficiency.
[0028]
Phosphorescence emission involves the ground singlet state S ⁰ , the excited singlet state S ¹ , and the excited triplet state T ¹ . Then, the transitions of S ¹ → T ¹ and T ¹ → S ⁰ , which are spin forbidden, must occur efficiently. In order to solve this spin forbidden, a large spin orbit interaction is required. And since the spin-orbit interaction is proportional to the fourth power of the atomic number, a heavy metal is more advantageous. This is the feature (1) above.
[0029]
Furthermore, in order to obtain blue light emission, the energy gap of HOMO (highest occupied molecular orbital) -LUMO (lowest unoccupied molecular orbital) of the light emitting molecule is required to be 2.7 eV or more. Organometallic complexes, which are phosphorescent materials reported so far, have a central metal of Ir ³⁺ , Pt ^2+, etc., and the electronic state of the 5d orbit has an open shell structure. In this case, the d orbitals are split by ligand field splitting, and the HOMO-LUMO gap is limited by the dd transition between the occupied d orbitals and the empty d orbitals. Since the energy of ligand field splitting cannot be expected to be higher than 2.5 eV, it is very difficult to secure the HOMO-LUMO energy gap necessary for blue light emission with a complex having an open-shell electronic state. It is thought that .
[0030]
Therefore, in the light-emitting material of the present invention, the electron arrangement of the central metal is a closed shell structure in which (Xe) 4f ⁰ 5d ⁰ 6s ⁰ or (Xe) 4f ¹⁴ 5d ⁰ 6s ⁰ is used. This is the feature (2) above. In this case, the energy level of HOMO is determined by the ligand, and LUMO consists of unoccupied 5d orbitals of the central metal. Therefore, it is considered that an energy gap necessary for blue light emission can be secured.
[0031]
More desirably, the unoccupied π ^* orbital of the ligand contributes to LUMO, which is advantageous in increasing the transition probability. This is the feature (3) above.
[0032]
The above (4) and (5) are due to requests from the valence and coordination number of the central metal. For example, since W ⁶⁺ is stable in 6-coordination, when it has a bidentate ligand, it needs to be bound to the central metal by two covalent bonds per ligand. Hf ⁴⁺ is stable in 8-coordination, so when it has a bidentate ligand, it binds to the central metal with one covalent bond and one coordination bond per ligand. Need to be.
[0033]
The specific molecular structure of the ligand may be adjusted by adjusting the size of the conjugated system so as to satisfy the above (3). It is also necessary to take into account the difficulty of synthesis.
[0034]
By using the molecules as described above for the light emitting layer, a highly efficient organic electroluminescent device can be produced.
[0035]
The layer structure can be appropriately designed in consideration of efficiency, reliability, and the like.
[0036]
The present invention also relates to a display device that suitably uses such an organic electroluminescent element as a blue light emitting element.
[0037]
In such a display device, as described above, an organic electroluminescent element that emits light with high efficiency is used as a blue light emitting element. Therefore, by combining with other red light emitting elements and green light emitting elements, high-efficiency full color display can be achieved. It becomes possible.
[0038]
Hereinafter, the organic electroluminescent element of this invention and the structural example of a display apparatus using the same are demonstrated in detail based on drawing.
[0039]
This organic electroluminescent element and a display device using the same may have the same structure as that shown in FIG. 1 or FIG.
[0040]
The light emitting element shown in FIG. 1 includes a substrate 10 and each constituent layer of the organic electroluminescent element 1A provided on the substrate 10. That is, the lower electrode 6, the organic layers 2, 4 and the upper electrode 7 are sequentially stacked on the substrate 10, and the emitted light 5 is extracted from the substrate 10 side or the upper electrode 7 side. In addition, in this figure, although the structure which provided the organic electroluminescent element 1A for 1 pixel on the board | substrate 10 is shown, this display apparatus 21 is provided with several pixel like FIG. 3, for example, It is assumed that a plurality of organic electroluminescent elements are arranged in each pixel.
[0041]
Next, the detailed structure of each part which comprises this display apparatus 21 is demonstrated in order of the board | substrate 10, the lower electrode 6, the upper electrode 7, and the organic layers 2 and 4. FIG.
[0042]
The substrate 10 is made of glass, silicon, a plastic substrate, a TFT substrate on which a TFT (Thin Film Transistor) is formed, or the like. In particular, in the case where the display device 21 is a transmissive type that takes out the emitted light 5 from the substrate 10 side, the substrate 10 is made of a material having optical transparency.
[0043]
The lower electrode 6 formed on the substrate 10 is used as an anode or a cathode. In the drawings, the case where the lower electrode 6 is an anode is shown as an example.
[0044]
It is assumed that the lower electrode 6 is patterned into a suitable shape depending on the driving method of the display device 21. For example, when the driving method of the display device 21 is a simple matrix method, the lower electrode 6 is formed in a stripe shape, for example. Further, when the driving method of the display device 21 is an active matrix method in which a TFT is provided for each pixel, the lower electrode 6 is formed in a pattern corresponding to each of a plurality of arranged pixels and similarly provided in each pixel. The TFTs are formed in a state of being connected to each other through a contact hole (not shown) formed in an interlayer insulating film covering these TFTs.
[0045]
On the other hand, the upper electrode 7 provided on the lower electrode 6 via an organic layer is used as a cathode when the lower electrode 6 is an anode, and is used as an anode when the lower electrode 6 is a cathode. In the drawing, the case where the upper electrode 7 is a cathode is shown.
[0046]
When the display device 21 is a simple matrix system, the upper electrode 7 is formed in a stripe shape intersecting with the stripe of the lower electrode 6 as shown in FIG. Becomes an organic electroluminescent element. When the display device 21 is an active matrix system, the upper electrode 7 is formed in a solid film shape so as to cover one surface of the substrate 10 and is used as a common electrode for each pixel. Shall be used. In the case where the active matrix method is adopted as the driving method of the display device 21, it is desirable to use a top emission type in which the emitted light 5 is extracted from the upper electrode 7 side in order to ensure the aperture ratio of the organic electroluminescent element. .
[0047]
Here, the anode material constituting the lower electrode 6 (or the upper electrode 7) preferably has a work function as large as possible. For example, nickel, gold, platinum, palladium, selenium, rhodium, ruthenium, iridium, rhenium, tungsten Molybdenum, chromium, tantalum, niobium, alloys thereof, oxides, or tin oxide, ITO (Indium Tin Oxide), zinc oxide, titanium oxide, and the like are preferable.
[0048]
On the other hand, the cathode material constituting the upper electrode 7 (or the lower electrode 6) should have a work function as small as possible. For example, magnesium, calcium, indium, lithium, aluminum, silver, and alloys thereof are preferable.
[0049]
However, for the electrode on the side from which the emitted light 5 generated in the organic electroluminescent layer is extracted, a light-transmitting material is appropriately selected from the materials described above, and in particular, an organic electroluminescent element is used. A material that transmits more than 30% of light in the wavelength region of the emitted light 5 is preferably used.
[0050]
The substrate, the electrode material, and the stacking order may be appropriately selected depending on whether the light emission is extracted from the substrate side, the upper surface side, or both.
[0051]
In the light-emitting element 1B shown in FIG. 2, as a hole injection material of the hole injection layer 1, a conductive polymer such as PPV (polyphenylene vinylene), a material such as phthalocyanine copper, a starburst amine, or the like is laminated. Can be used.
[0052]
As the hole transport material used for the hole transport layer 2, a known material such as a triphenylamine multimer or a derivative thereof can be used.
[0053]
Furthermore, the light-emitting layer 3 (or mixable-emitting material or the electron transport layer 4 shown in FIG. 1) is Ru with a W complex represented by the below-mentioned formula (3). This may be doped into a wide gap host material such as TAZ (triazole derivative) at an appropriate concentration.
[0054]
As the electron transport material of the electron transport layer 4, a known material such as Alq ₃ (tris (8-quinolinol) aluminum), TAZ, OXD (oxadiazole derivative) can be used. This electron transport layer may be doped with the light emitting material of the present invention to form an electron transporting light emitting layer.
[0055]
When a buffer layer made of an alkali metal oxide such as lithium oxide, cesium oxide, or strontium fluoride, an alkali metal fluoride, an alkaline earth oxide, or an alkaline earth fluoride is inserted between the electron transporting light emitting layer and the cathode The electron injection efficiency is more preferable.
[0056]
A multilayer film made of the above-described materials can be formed using a known method such as vacuum deposition or spin coating.
[0057]
When driving the light emitting device of the present invention, in order to eliminate the influence of moisture, oxygen, etc. in the atmosphere and improve safety, it is sealed in advance with, for example, magnesium fluoride or SiNx, or It is desirable that the surrounding space be purged with a dry inert gas or evacuated.
[0058]
【Example】
Hereinafter, the present invention will be specifically described based on examples.
[0059]
Example 1
2-TNATA (4,4 ′, 4 ″ -tris (N, N- (2-naphthyl) phenylamino) triphenylamine as a hole injection layer on a glass substrate on which ITO having a thickness of 190 nm is formed ) Is 35 nm, α-NPB (4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl) is 30 nm as the hole transport layer, and the light emitting layer is represented by the following chemical formula (3). An organic electroluminescent device is formed by sequentially forming a W complex doped with 8 wt% TAZ with 25 nm, Alq ₃ 25 nm as an electron transport layer, lithium oxide 0.5 nm as a buffer layer, aluminum 200 nm as a cathode, and vacuum deposition. Was made.
[0060]
[Formula 4]
Chemical formula (3):

[0061]
The characteristics of the organic electroluminescence device thus fabricated were measured. The EL spectrum had a peak at 460 nm, and the coordinates on the CIE chromaticity coordinates were (0.14, 0.11). The quantum efficiency of light emission was as high as 6%.
[0062]
Comparative Example 1
An organic electroluminescent element was produced in the same manner as in Example 1 except that the light emitting layer was doped with a Zn complex represented by the following chemical formula (4).
[0063]
[Chemical formula 5]
Chemical formula (4):

[0064]
The characteristics of the organic electroluminescence device thus fabricated were measured. The EL spectrum had a peak at 460 nm, and the coordinates on the CIE chromaticity coordinates were (0.14, 0.18). The quantum efficiency of light emission was as low as 1%.
[0065]
The embodiments and examples of the present invention described above can be variously modified based on the technical idea of the present invention.
[0066]
[Effects of the invention]
As described above, the present invention provides a molecular design of a phosphorescent material that realizes a high-efficiency blue light-emitting element that has been impossible to realize so far, and realizes this. By using this phosphorescent material as a light-emitting material, a highly efficient blue light-emitting element that has been impossible until now is realized, and a high-efficiency full-color display device is enabled.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a main part of an organic electroluminescent element.
FIG. 2 is a schematic cross-sectional view of a main part of another organic electroluminescent element.
FIG. 3 is a configuration diagram of a full-color flat display using organic electroluminescent elements.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Hole injection layer, 2 ... Hole transport layer, 3 ... Light emitting layer (luminescent material), 4 ... Electron transport layer,
5 ... emitted light, 6 ... transparent electrode (anode), 7 ... cathode, 10 ... substrate, 14 ... protective film,
15a, 15b ... organic layer, 20 ... power supply

Claims (9)

[Chemical 1]
Chemical formula (3):

A light emitting material comprising an organometallic complex represented by the formula:   An organic electroluminescent device comprising at least a hole transport layer and a luminescent layer sandwiched between an anode and a cathode, wherein the luminescent layer contains the luminescent material according to claim 1. . The organic electroluminescent element according to claim 2 , wherein an electron transport layer is provided between the cathode and the light emitting layer. The organic electroluminescent element according to claim 2 , wherein at least one of the anode and the cathode is made of a light transmissive material. The organic electroluminescent element according to claim 4 , wherein the cathode is made of a light transmissive material. The organic electroluminescent element according to claim 4 , wherein the cathode is made of an alloy of magnesium and silver. A display device in which the organic electroluminescent elements according to claim 2 are arranged in a plurality of pixels. The organic light emitting element emitting layer containing a light emitting material as claimed in claim 1 having a display device according to claim 7. The display device according to claim 7 , wherein the organic electroluminescent element is provided as a blue light emitting element in a part of the plurality of pixels.

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