JP2004014440A - Organic electroluminescent element and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element with a high luminous brightness and durability, and a display device using it. <P>SOLUTION: The organic electroluminescent element having an electron transport layer and a luminous layer contains a compound expressed in a chemical formula [1]. In the formula, R<SB>1</SB>and R<SB>2</SB>independently denote a substituent, Ar denotes a bivalent arylene group, n is an integer of 0 to 8, p is an integer of 1 to 4, q is an integer of 1 to 4, R3 to R6 denote a hydrogen atom or a substituent, and Ar1 and Ar2 independently denote an aryl group. <P>COPYRIGHT: (C)2004,JPO

Description

【００２８】
で表されることが好ましい。
本発明の化合物は、固体状態において強い蛍光を持つ化合物であり、電場発光性にも優れており、発光材料として有効に使用できる。また、金属電極からの優れた電子注入性及び電子輸送性に非常に優れているため、他の発光材料または本発明の化合物を発光材料として用いた素子において、本発明の化合物を電子輸送材料（またはホールブロッカー）として使用した場合優れた発光効率を示す。
【００２９】
以下に具体的な化合物の例を挙げるが、本発明はこれらに限定されるものではない。
【００３０】
【化３】

【００３１】
【化４】

【００３２】
【化５】

【００３３】
【化６】

【００３４】
【化７】

【００３５】
【化８】

【００３６】
【化９】

【００３７】
【化１０】

【００３８】
【化１１】

【００３９】
本発明の化合物は、特開２００１−９３６７０及びＪ．Ａｍ．Ｃｈｅｍ．Ｓｏｃ．１２０，ｐ．９７１４（１９９８）記載の方法に準じて合成することができる。
【００４０】
また、本発明者等はりん光性化合物のホスト化合物について鋭意検討を重ねた結果、本発明の含ホウ素カルバゾール化合物をホスト化合物として用いて、有機ＥＬ素子を作製した場合に、素子の発光輝度及び寿命が改善されることを見出した。
【００４１】
本発明においてホスト化合物とは、２種以上の化合物で構成される発光層中において、混合比（質量）の最も多い化合物であり、それ以外の化合物はドーパント化合物という。例えば、発光層を化合物Ａ、化合物Ｂという２種で構成しその混合比がＡ：Ｂ＝１０：９０であれば化合物Ａがドーパント化合物であり、化合物Ｂがホスト化合物である。更に、発光層を化合物Ａ、化合物Ｂ、化合物Ｃの３種から構成し、その混合比がＡ：Ｂ：Ｃ＝５：１０：８５であれば、化合物Ａ、化合物Ｂがドーパント化合物であり、化合物Ｃがホスト化合物である。本発明におけるりん光性化合物はドーパント化合物の一種である。
【００４２】
本発明のりん光性化合物とは励起三重項からの発光が観測される化合物であり、りん光量子収率が２５℃において０．００１以上の化合物である。りん光量子収率は好ましくは０．０１以上であり、更に好ましくは０．１以上である。
【００４３】
上記りん光量子収率は、第４版実験化学講座７の分光ＩＩの３９８ページ（１９９２年版、丸善）に記載の方法により測定できる。溶液中でのりん光量子収率は種々の溶媒を用いて測定できるが、本発明に用いられるりん光性化合物とは、任意の溶媒のいずれかにおいて上記りん光量子収率が達成されればよい。
【００４４】
本発明に用いられるりん光性化合物は、好ましくは元素の周期律表でＶＩＩＩ属の金属を含有する錯体系化合物であり、さらに好ましくは、イリジウム、オスミウム、または白金錯体系化合物であり、より好ましくはイリジウム錯体系化合物である。
【００４５】
以下に、本発明で用いられるりん光性化合物の具体例を示すが、これらに限定されるものではない。これらの化合物は、例えば、Ｉｎｏｒｇ．Ｃｈｅｍ．４０巻、１７０４−１７１１に記載の方法等により合成できる。
【００４６】
【化１２】

【００４７】
【化１３】

【００４８】
【化１４】

【００４９】
また、別の形態では、ホスト化合物とりん光性化合物の他に、りん光性化合物からの発光の極大波長よりも長波な領域に、蛍光極大波長を有する蛍光性化合物を少なくとも１種含有する場合もある。この場合、ホスト化合物とりん光性化合物からのエネルギー移動で、有機ＥＬ素子としての電界発光は蛍光性化合物からの発光が得られる。蛍光性化合物として好ましいのは、溶液状態で蛍光量子収率が高いものである。ここで、蛍光量子収率は０．１以上、特に０．３以上が好ましい。具体的には、クマリン系色素、ピラン系色素、シアニン系色素、クロコニウム系色素、スクアリウム系色素、オキソベンツアントラセン系色素、フルオレセイン系色素、ローダミン系色素、ピリリウム系色素、ペリレン系色素、スチルベン系色素、ポリチオフェン系色素または希土類錯体系蛍光体等が挙げられる。
【００５０】
ここでの蛍光量子収率も、前記第４版実験化学講座７の分光ＩＩの３６２ページ（１９９２年版、丸善）に記載の方法により測定することができる。
【００５１】
以下、有機ＥＬ素子について説明する。
有機ＥＬ素子における発光層は、広義の意味では、陰極と陽極からなる電極に電流を流した際に発光する層のことを指す。具体的には、陰極と陽極からなる電極に電流を流した際に発光する蛍光性化合物を含有する層のことを指す。通常、有機ＥＬ素子は一対の電極の間に発光層を挟持した構造をとる。本発明の有機ＥＬ素子は、必要に応じ発光層、電子輸送層の他に、正孔輸送層、陽極バッファー層及び陰極バッファー層等を有し、陰極と陽極で挟持された構造をとる。
【００５２】
具体的には、
（ｉ）陽極／発光層／電子輸送層／陰極
（ｉｉ）陽極／正孔輸送層／発光層／電子輸送層／陰極
（ｉｉｉ）陽極／陽極バッファー層／正孔輸送層／発光層／電子輸送層／陰極バッファー層／陰極等で示される構造がある。
【００５３】
上記化合物を用いて発光層を形成する方法としては、例えば蒸着法、スピンコート法、キャスト法、ＬＢ法等の公知の方法により薄膜を形成する方法があるが、特に分子堆積膜であることが好ましい。ここで、分子堆積膜とは、上記化合物の気相状態から沈着され形成された薄膜や、該化合物の溶融状態または液相状態から固体化され形成された膜のことである。通常、この分子堆積膜はＬＢ法により形成された薄膜（分子累積膜）と、凝集構造、高次構造の相違やそれに起因する機能的な相違により区別することができる。
【００５４】
また、この発光層は、特開昭５７−５１７８１号に記載されているように、樹脂等の結着材と共に発光材料として上記化合物を溶剤に溶かして溶液とした後、これをスピンコート法等により塗布して薄膜形成することにより得ることができる。
【００５５】
このようにして形成された発光層の膜厚については特に制限はなく、状況に応じて適宜選択することができるが、通常は５ｎｍ〜５μｍの範囲である。
【００５６】
ここで、本発明に記載のりん光性化合物は、具体的には、前述のように、重金属錯体系化合物であり、好ましくは元素の周期律表でＶＩＩＩ属の金属を中心金属とする錯体系化合物であり、さらに好ましくは、オスミウム、イリジウムまたは白金錯体系化合物である。
【００５７】
これらのりん光性化合物としては、前記のようなりん光量子収率が、２５℃において０．００１以上、好ましくは０．０１以上である他、前記ホストとなる蛍光性化合物の蛍光極大波長よりも長いりん光発光極大波長を有するものであり、これにより、例えば、ホストとなる蛍光性化合物の発光極大波長より長波のりん光性化合物を用いてりん光性化合物の発光、即ち三重項状態を利用した、ホスト化合物の蛍光極大波長よりも長波において電界発光する有機ＥＬ素子を得ることができる。従って、用いられるりん光性化合物のりん光発光極大波長としては特に制限されるものではなく、原理的には、中心金属、配位子、配位子の置換基等を選択することで得られる発光波長を変化させることができる。
【００５８】
例えば、３５０〜４４０ｎｍの領域に蛍光極大波長を有する蛍光性化合物をホスト化合物として用い、例えば、緑の領域にりん光を持ったイリジウム錯体を用いることで緑領域に電界発光する有機ＥＬ素子を得ることができる。
【００５９】
また、別の形態では、前記のように、ホスト化合物としての蛍光性化合物Ａとりん光性化合物の他に、りん光性化合物からの発光の極大波長よりも長波な領域に、蛍光極大波長を有するもう一つの蛍光性化合物Ｂを少なくとも１種含有する場合もあり、蛍光性化合物Ａとりん光性化合物からのエネルギー移動で、有機ＥＬ素子としての電界発光は蛍光性化合物Ｂからの発光を得ることもできる。
【００６０】
本明細書の蛍光性化合物が発光する色は、「新編色彩科学ハンドブック」（日本色彩学会編、東京大学出版会、１９８５）の１０８頁の図４．１６において、分光放射輝度計ＣＳ−１０００（ミノルタ製）で測定した結果をＣＩＥ色度座標に当てはめたときの色で決定される。
【００６１】
ホスト化合物の分子量は６００〜２０００であることが好ましく、この分子量範囲にあると、Ｔｇ（ガラス転移温度）が上昇し、熱安定性が向上し、素子寿命が改善される。より好ましくは分子量が８００〜２０００である。また、Ｔｇは１００度以上であることが好ましい。また、この範囲内の分子量であると発光層を真空蒸着法により容易に作製することができ、有機ＥＬ素子の製造が容易になる。さらに、有機ＥＬ素子中における蛍光性化合物の熱安定性もよくなる。
【００６２】
次に正孔注入層、正孔輸送層、電子注入層、電子輸送層等発光層と組み合わせて有機ＥＬ素子を構成するその他の層について説明する。
【００６３】
正孔注入層、正孔輸送層は、陽極より注入された正孔を発光層に伝達する機能を有し、この正孔注入層、正孔輸送層を陽極と発光層の間に介在させることにより、より低い電界で多くの正孔が発光層に注入され、そのうえ、発光層に陰極、電子注入層または電子輸送層より注入された電子は、発光層と正孔注入層もしくは正孔輸送層の界面に存在する電子の障壁により、発光層内の界面に累積され発光効率が向上する等発光性能の優れた素子となる。この正孔注入層、正孔輸送層の材料（以下、正孔注入材料、正孔輸送材料という）については、前記の陽極より注入された正孔を発光層に伝達する機能を有する性質を持つものであれば特に制限はなく、従来、光導伝材料において、正孔の電荷注入輸送材料として慣用されているものや有機ＥＬ素子の正孔注入層、正孔輸送層に使用される公知のものの中から任意のものを選択して用いることができる。
【００６４】
上記正孔注入材料、正孔輸送材料は、正孔の注入もしくは輸送、電子の障壁性のいずれかを有するものであり、有機物，無機物のいずれであってもよい。この正孔注入材料、正孔輸送材料としては、例えばトリアゾール誘導体、オキサジアゾール誘導体、イミダゾール誘導体、ポリアリールアルカン誘導体、ピラゾリン誘導体及びピラゾロン誘導体、フェニレンジアミン誘導体、アリールアミン誘導体、アミノ置換カルコン誘導体、オキサゾール誘導体、スチリルアントラセン誘導体、フルオレノン誘導体、ヒドラゾン誘導体、スチルベン誘導体、シラザン誘導体、アニリン系共重合体、また、導電性高分子オリゴマー、特にチオフェンオリゴマー等が挙げられる。正孔注入材料、正孔輸送材料としては、上記のものを使用することができるが、ポルフィリン化合物、芳香族第三級アミン化合物及びスチリルアミン化合物、特に芳香族第三級アミン化合物を用いることが好ましい。
【００６５】
上記芳香族第三級アミン化合物及びスチリルアミン化合物の代表例としては、Ｎ，Ｎ，Ｎ′，Ｎ′−テトラフェニル−４，４′−ジアミノフェニル；Ｎ，Ｎ′−ジフェニル−Ｎ，Ｎ′−ビス（３−メチルフェニル）−〔１，１′−ビフェニル〕−４，４′−ジアミン（ＴＰＤ）；２，２−ビス（４−ジ−ｐ−トリルアミノフェニル）プロパン；１，１−ビス（４−ジ−ｐ−トリルアミノフェニル）シクロヘキサン；Ｎ，Ｎ，Ｎ′，Ｎ′−テトラ−ｐ−トリル−４，４′−ジアミノビフェニル；１，１−ビス（４−ジ−ｐ−トリルアミノフェニル）−４−フェニルシクロヘキサン；ビス（４−ジメチルアミノ−２−メチルフェニル）フェニルメタン；ビス（４−ジ−ｐ−トリルアミノフェニル）フェニルメタン；Ｎ，Ｎ′−ジフェニル−Ｎ，Ｎ′−ジ（４−メトキシフェニル）−４，４′−ジアミノビフェニル；Ｎ，Ｎ，Ｎ′，Ｎ′−テトラフェニル−４，４′−ジアミノジフェニルエーテル；４，４′−ビス（ジフェニルアミノ）クオードリフェニル；Ｎ，Ｎ，Ｎ−トリ（ｐ−トリル）アミン；４−（ジ−ｐ−トリルアミノ）−４′−〔４−（ジ−ｐ−トリルアミノ）スチリル〕スチルベン；４−Ｎ，Ｎ−ジフェニルアミノ−（２−ジフェニルビニル）ベンゼン；３−メトキシ−４′−Ｎ，Ｎ−ジフェニルアミノスチルベンゼン；Ｎ−フェニルカルバゾール、さらには、米国特許第５，０６１，５６９号に記載されている２個の縮合芳香族環を分子内に有するもの、例えば４，４′−ビス〔Ｎ−（１−ナフチル）−Ｎ−フェニルアミノ〕ビフェニル（ＮＰＤ）、特開平４−３０８６８８号に記載されているトリフェニルアミンユニットが３つスターバースト型に連結された４，４′，４″−トリス〔Ｎ−（３−メチルフェニル）−Ｎ−フェニルアミノ〕トリフェニルアミン（ＭＴＤＡＴＡ）等が挙げられる。
【００６６】
さらにこれらの材料を高分子鎖に導入した、またはこれらの材料を高分子の主鎖とした高分子材料を用いることもできる。
【００６７】
また、ｐ型−Ｓｉ、ｐ型−ＳｉＣ等の無機化合物も正孔注入材料、正孔輸送材料として使用することができる。この正孔注入層、正孔輸送層は、上記正孔注入材料、正孔輸送材料を、例えば真空蒸着法、スピンコート法、キャスト法、ＬＢ法等の公知の方法により、薄膜化することにより形成することができる。正孔注入層、正孔輸送層の膜厚については特に制限はないが、通常は５ｎｍ〜５μｍ程度である。この正孔注入層、正孔輸送層は、上記材料の１種または２種以上からなる一層構造であってもよく、同一組成または異種組成の複数層からなる積層構造であってもよい。
【００６８】
さらに、必要に応じて用いられる電子輸送層は、陰極より注入された電子を発光層に伝達する機能を有していればよく、その材料としては従来公知の化合物の中から任意のものを選択して用いることができる。
【００６９】
この電子輸送層に用いられる材料（以下、電子輸送材料という）の例としては、ニトロ置換フルオレン誘導体、ジフェニルキノン誘導体、チオピランジオキシド誘導体、ナフタレンペリレン等の複素環テトラカルボン酸無水物、カルボジイミド、フレオレニリデンメタン誘導体、アントラキノジメタン及びアントロン誘導体、オキサジアゾール誘導体等が挙げられる。さらに、上記オキサジアゾール誘導体において、オキサジアゾール環の酸素原子を硫黄原子に置換したチアジアゾール誘導体、電子吸引基として知られているキノキサリン環を有するキノキサリン誘導体も、電子輸送材料として用いることができる。
【００７０】
さらにこれらの材料を高分子鎖に導入した、またはこれらの材料を高分子の主鎖とした高分子材料を用いることもできる。
【００７１】
また、８−キノリノール誘導体の金属錯体、例えばトリス（８−キノリノール）アルミニウム（Ａｌｑ）、トリス（５，７−ジクロロ−８−キノリノール）アルミニウム、トリス（５，７−ジブロモ−８−キノリノール）アルミニウム、トリス（２−メチル−８−キノリノール）アルミニウム、トリス（５−メチル−８−キノリノール）アルミニウム、ビス（８−キノリノール）亜鉛（Ｚｎｑ）等、及びこれらの金属錯体の中心金属がＩｎ、Ｍｇ、Ｃｕ、Ｃａ、Ｓｎ、ＧａまたはＰｂに置き替わった金属錯体も、電子輸送材料として用いることができる。その他、メタルフリー若しくはメタルフタロシアニン、またはそれらの末端がアルキル基やスルホン酸基等で置換されているものも、電子輸送材料として好ましく用いることができる。また、発光層の材料として例示したジスチリルピラジン誘導体も、電子輸送材料として用いることができるし、正孔注入層、正孔輸送層と同様に、ｎ型−Ｓｉ、ｎ型−ＳｉＣ等の無機半導体も電子輸送材料として用いることができる。
【００７２】
この電子輸送層は、上記化合物を、例えば真空蒸着法、スピンコート法、キャスト法、ＬＢ法等の公知の薄膜形成法により製膜して形成することができる。電子輸送層としての膜厚は、特に制限はないが、通常は５ｎｍ〜５μｍの範囲で選ばれる。この電子輸送層は、これらの電子輸送材料１種または２種以上からなる一層構造であってもよいし、あるいは、同一組成または異種組成の複数層からなる積層構造であってもよい。
【００７３】
また、本発明においては、蛍光性化合物は発光層のみに限定することはなく、発光層に隣接した正孔輸送層、または電子輸送層に前記りん光性化合物のホスト化合物となる蛍光性化合物と同じ領域に蛍光極大波長を有する蛍光性化合物を少なくとも１種含有させてもよく、それにより更に有機ＥＬ素子の発光効率を高めることができる。これらの正孔輸送層や電子輸送層に含有される蛍光性化合物としては、発光層に含有されるものと同様に蛍光極大波長が３５０〜４４０ｎｍ、更に好ましくは３９０〜４１０ｎｍの範囲にある蛍光性化合物が用いられる。
【００７４】
本発明の有機ＥＬ素子に好ましく用いられる基盤は、ガラス、プラスチック等の種類には特に限定はなく、また、透明のものであれば特に制限はない。本発明の有機ＥＬ素子に好ましく用いられる基盤としては例えばガラス、石英、光透過性プラスチックフィルムを挙げることができる。
【００７５】
光透過性プラスチックフィルムとしては、例えばポリエチレンテレフタレート（ＰＥＴ）、ポリエチレンナフタレート（ＰＥＮ）、ポリエーテルスルホン（ＰＥＳ）、ポリエーテルイミド、ポリエーテルエーテルケトン、ポリフェニレンスルフィド、ポリアリレート、ポリイミド、ポリカーボネート（ＰＣ）、セルローストリアセテート（ＴＡＣ）、セルロースアセテートプロピオネート（ＣＡＰ）等からなるフィルム等が挙げられる。
【００７６】
次に、有機ＥＬ素子を作製する好適な例を説明する。例として、前記の陽極／正孔注入層／正孔輸送層／発光層／電子輸送層／電子注入層／陰極からなる有機ＥＬ素子の作製法について説明する。
【００７７】
まず適当な基板上に、所望の電極用物質、例えば陽極用物質からなる薄膜を、１μｍ以下、好ましくは１０〜２００ｎｍの範囲の膜厚になるように、蒸着やスパッタリング等の方法により形成させて陽極を作製する。次に、この上に素子材料である正孔注入層、正孔輸送層、発光層、電子輸送層／電子注入層からなる薄膜を形成させる。
【００７８】
さらに、陽極と発光層または正孔注入層の間、及び、陰極と発光層または電子注入層との間にはバッファー層（電極界面層）を存在させてもよい。
バッファー層とは、駆動電圧低下や発光効率向上のために電極と有機層間に設けられる層のことで、「有機ＥＬ素子とその工業化最前線（１９９８年１１月３０日エヌ・ティー・エス社発行）」の第２編第２章「電極材料」（第１２３頁〜第１６６頁）に詳細に記載されており、陽極バッファー層と陰極バッファー層とがある。
【００７９】
陽極バッファー層は、特開平９−４５４７９号、同９−２６００６２号、同８−２８８０６９号等にもその詳細が記載されており、具体例として、銅フタロシアニンに代表されるフタロシアニンバッファー層、酸化バナジウムに代表される酸化物バッファー層、アモルファスカーボンバッファー層、ポリアニリン（エメラルディン）やポリチオフェン等の導電性高分子を用いた高分子バッファー層等が挙げられる。
【００８０】
陰極バッファー層は、特開平６−３２５８７１号、同９−１７５７４号、同１０−７４５８６号等にもその詳細が記載されており、具体的にはストロンチウムやアルミニウム等に代表される金属バッファー層、フッ化リチウムに代表されるアルカリ金属化合物バッファー層、フッ化マグネシウムに代表されるアルカリ土類金属化合物バッファー層、酸化アルミニウム、酸化リチウムに代表される酸化物バッファー層等が挙げられる。
【００８１】
上記バッファー層はごく薄い膜であることが望ましく、素材にもよるが、その膜厚は０．１〜１００ｎｍの範囲が好ましい。
【００８２】
さらに上記基本構成層の他に必要に応じてその他の機能を有する層を積層してもよく、例えば特開平１１−２０４２５８号、同１１−２０４３５９号、及び「有機ＥＬ素子とその工業化最前線（１９９８年１１月３０日エヌ・ティー・エス社発行）」の第２３７頁等に記載されている正孔阻止（ホールブロック）層等のような機能層を有していてもよい。
【００８３】
次に有機ＥＬ素子の電極について説明する。有機ＥＬ素子の電極は、陰極と陽極からなる。
【００８４】
この有機ＥＬ素子における陽極としては、仕事関数の大きい（４ｅＶ以上）金属、合金、電気伝導性化合物及びこれらの混合物を電極物質とするものが好ましく用いられる。このような電極物質の具体例としてはＡｕ等の金属、ＣｕＩ、インジウムチンオキシド（ＩＴＯ）、ＳｎＯ_２、ＺｎＯ等の導電性透明材料が挙げられる。
【００８５】
上記陽極は、蒸着やスパッタリング等の方法により、これらの電極物質の薄膜を形成させ、フォトリソグラフィー法で所望の形状のパターンを形成してもよく、あるいはパターン精度をあまり必要としない場合は（１００μｍ以上程度）、上記電極物質の蒸着やスパッタリング時に所望の形状のマスクを介してパターンを形成してもよい。この陽極より発光を取り出す場合には、透過率を１０％より大きくすることが望ましく、また、陽極としてのシート抵抗は数百Ω／□以下が好ましい。さらに膜厚は材料にもよるが、通常１０ｎｍ〜１μｍ、好ましくは１０〜２００ｎｍの範囲で選ばれる。
【００８６】
一方、陰極としては、仕事関数の小さい（４ｅＶ以下）金属（電子注入性金属と称する）、合金、電気伝導性化合物及びこれらの混合物を電極物質とするものが用いられる。このような電極物質の具体例としては、ナトリウム、ナトリウム−カリウム合金、マグネシウム、リチウム、マグネシウム／銅混合物、マグネシウム／銀混合物、マグネシウム／アルミニウム混合物、マグネシウム／インジウム混合物、アルミニウム／酸化アルミニウム（Ａｌ_２Ｏ_３）混合物、インジウム、リチウム／アルミニウム混合物、希土類金属等が挙げられる。これらの中で、電子注入性及び酸化等に対する耐久性の点から、電子注入性金属とこれより仕事関数の値が大きく安定な金属である第二金属との混合物、例えばマグネシウム／銀混合物、マグネシウム／アルミニウム混合物、マグネシウム／インジウム混合物、アルミニウム／酸化アルミニウム（Ａｌ_２Ｏ_３）混合物、リチウム／アルミニウム混合物等が好適である。上記陰極は、これらの電極物質を蒸着やスパッタリング等の方法により、薄膜を形成させることにより、作製することができる。また、陰極としてのシート抵抗は数百Ω／□以下が好ましく、膜厚は通常１０ｎｍ〜１μｍ、好ましくは５０〜２００ｎｍの範囲で選ばれる。なお、発光を透過させるため、有機ＥＬ素子の陽極または陰極のいずれか一方が、透明または半透明であれば発光効率が向上するので好都合である。
【００８７】
次に有機ＥＬ素子の作製方法について説明する。
薄膜化の方法としては、前記の如くスピンコート法、キャスト法、蒸着法等があるが、均質な膜が得られやすく、かつピンホールが生成しにくい等の点から、真空蒸着法が好ましい。薄膜化に、真空蒸着法を採用する場合、その蒸着条件は、使用する化合物の種類、分子堆積膜の目的とする結晶構造、会合構造等により異なるが、一般にボート加熱温度５０〜４５０℃、真空度１０^−６〜１０^−３Ｐａ、蒸着速度０．０１〜５０ｎｍ／秒、基板温度−５０〜３００℃、膜厚５ｎｍ〜５μｍの範囲で適宜選ぶことが望ましい。
【００８８】
前記の様に、適当な基板上に、所望の電極用物質、例えば陽極用物質からなる薄膜を、１μｍ以下、好ましくは１０〜２００ｎｍの範囲の膜厚になるように、蒸着やスパッタリング等の方法により形成させて陽極を作製した後、該陽極上に前記の通り正孔注入層、正孔輸送層、発光層、電子輸送層／電子注入層からなる各層薄膜を形成させた後、その上に陰極用物質からなる薄膜を１μｍ以下、好ましくは５０〜２００ｎｍの範囲の膜厚になるように、例えば蒸着やスパッタリング等の方法により形成させ、陰極を設けることにより、所望の有機ＥＬ素子が得られる。この有機ＥＬ素子の作製は、一回の真空引きで一貫してこの様に正孔注入層から陰極まで作製するのが好ましいが、作製順序を逆にして、陰極、電子注入層、発光層、正孔注入層、陽極の順に作製することも可能である。このようにして得られた有機ＥＬ素子に、直流電圧を印加する場合には、陽極を＋、陰極を−の極性として電圧５〜４０Ｖ程度を印加すると、発光が観測できる。また、逆の極性で電圧を印加しても電流は流れずに発光は全く生じない。さらに、交流電圧を印加する場合には、陽極が＋、陰極が−の状態になったときのみ発光する。なお、印加する交流の波形は任意でよい。
【００８９】
【実施例】
以下、実施例を挙げて本発明を詳細に説明するが、本発明の態様はこれに限定されない。
【００９０】
実施例１（発光材料）
陽極としてガラス上にＩＴＯを１５０ｎｍ成膜した基板（ＮＨテクノグラス社製：ＮＡ−４５）にパターニングを行った後、このＩＴＯ透明電極を設けた透明支持基板をｉ−プロピルアルコールで超音波洗浄し、乾燥窒素ガスで乾燥し、ＵＶオゾン洗浄を５分間行った。この透明支持基板を、市販の真空蒸着装置の基板ホルダーに固定し、一方、モリブデン製抵抗加熱ボートにα−ＮＰＤを２００ｍｇ入れ、別のモリブデン製抵抗加熱ボートに比較化合物１を２００ｍｇ入れ、別のモリブデン製抵抗加熱ボートにバソキュプロイン（ＢＣＰ）を２００ｍｇ入れ、さらに別のモリブデン製抵抗加熱ボートにＡｌｑ_３を２００ｍｇ入れ、真空蒸着装置に取付けた。次いで、真空槽を４×１０^−４Ｐａまで減圧した後、α−ＮＰＤの入った前記加熱ボートに通電して加熱し、蒸着速度０．１〜０．３ｎｍ／ｓｅｃで透明支持基板に膜厚５０ｎｍで蒸着し、正孔輸送層を設けた。蒸着時の基板温度は室温であった。ついで、比較化合物１の入った前記加熱ボートに通電して加熱し、蒸着速度０．１〜０．３ｎｍ／ｓｅｃで３０ｎｍの発光層を設けた。更に、ＢＣＰの入った前記加熱ボートを通電して加熱し、膜厚１０ｎｍの正孔阻止層を設けた。更に、Ａｌｑ_３の入った前記加熱ボートを通電して加熱し、蒸着速度０．１〜０．３ｎｍ／ｓｅｃで膜厚２０ｎｍの電子輸送層を設けた。
【００９１】
次に、真空槽をあけ、電子輸送層の上にステンレス鋼製の長方形穴あきマスクを設置し、一方、モリブデン製抵抗加熱ボートにマグネシウム３ｇを入れ、タングステン製の蒸着用バスケットに銀を０．５ｇ入れ、再び真空槽を２×１０^−４Ｐａまで減圧した後、マグネシウム入りのボートに通電して蒸着速度１．５〜２．０ｎｍ／ｓｅｃでマグネシウムを蒸着し、この際、同時に銀のバスケットを加熱し、蒸着速度０．１ｎｍ／ｓｅｃで銀を蒸着し、前記マグネシウムと銀との混合物から成る陰極とすることにより、有機ＥＬ素子１−１を作製した。
【００９２】
上記有機ＥＬ素子１−１の比較化合物１を表１に記載の化合物に替えた以外は有機ＥＬ素子１−１と同様にして、有機ＥＬ素子１−２〜１−１２を作製した。全ての有機ＥＬ素子の発光色は青色から緑色であった。
【００９３】
これらの有機ＥＬ素子を２３℃、乾燥窒素ガス雰囲気下で１０Ｖ直流電圧印加による連続点灯を行い、点灯開始時の発光輝度（ｃｄ／ｍ^２）及び耐久性の指標として輝度の半減時間を測定した。発光輝度は有機ＥＬ素子１−１を１００とした相対値で表し、輝度の半減時間は有機ＥＬ素子１−１の輝度の半減時間を１００とした相対値で表した。測定結果を表１に示す。発光輝度［ｃｄ／ｍ^２］については、ミノルタ製ＣＳ−１０００を用いて測定した。
【００９４】
【化１５】

【００９５】
【化１６】

【００９６】
【化１７】

【００９７】
【表１】

【００９８】
表１より、本発明の化合物を用いた有機ＥＬ素子は、類似構造を有する比較化合物を用いた有機ＥＬ素子に比べ、点灯開始時の発光輝度及び輝度の半減時間が改善されているのが分かる。
【００９９】
実施例２（ホスト化合物）
本発明の化合物１とＤＣＭ−２を１００：１の質量比で蒸着した膜厚３０ｎｍの発光層を使用する以外は、実施例１と同様の方法で有機ＥＬ素子２−１を作製した。
【０１００】
この有機ＥＬ素子を２３℃度、乾燥窒素ガス雰囲気下で１０Ｖ直流電圧印加すると、赤色の発光が得られた。
【０１０１】
上記有機ＥＬ素子２−１の、ＤＣＭ−２をＱｄ−２またはＢＣｚＶＢｉに替えることによって作製した有機ＥＬ素子２−２、２−３からはそれぞれ、緑色または青色の発光が得られた。
【０１０２】
【化１８】

【０１０３】
実施例３（電子輸送材料）
陽極としてガラス上にＩＴＯを１５０ｎｍ成膜した基板（ＮＨテクノグラス社製：ＮＡ−４５）にパターニングを行った後、このＩＴＯ透明電極を設けた透明支持基板をｉ−プロピルアルコールで超音波洗浄し、乾燥窒素ガスで乾燥し、ＵＶオゾン洗浄を５分間行った。この透明支持基板を、市販の真空蒸着装置の基板ホルダーに固定し、一方、モリブデン製抵抗加熱ボートに、ｍ−ＭＴＤＡＴＸＡを２００ｍｇ入れ、別のモリブデン製抵抗加熱ボートにＤＰＶＢｉを２００ｍｇ入れ、また別のモリブデン製抵抗加熱ボートにＢＣＰを２００ｍｇ入れ真空蒸着装置に取付けた。
【０１０４】
次いで、真空槽を４×１０^−４Ｐａまで減圧した後、ｍ−ＭＴＤＡＴＸＡの入った前記加熱ボートに通電して加熱し、蒸着速度０．１〜０．３ｎｍ／ｓｅｃで透明支持基板に膜厚２５ｎｍで蒸着し、さらに、ＤＰＶＢｉの入った前記加熱ボートに通電して加熱し、蒸着速度０．１〜０．３ｎｍ／ｓｅｃで膜厚２０ｎｍで蒸着し、発光層を設けた。蒸着時の基板温度は室温であった。
【０１０５】
ついで、ＢＣＰの入った前記加熱ボートに通電して加熱し、蒸着速度０．１〜０．３ｎｍ／ｓｅｃで３０ｎｍの電子輸送層を設けた。
【０１０６】
次に、真空槽をあけ、電子輸送層の上にステンレス鋼製の長方形穴あきマスクを設置し、一方、モリブデン製抵抗加熱ボートにマグネシウム３ｇを入れ、タングステン製の蒸着用バスケットに銀を０．５ｇ入れ、再び真空槽を２×１０^−４Ｐａまで減圧した後、マグネシウム入りのボートに通電して蒸着速度１．５〜２．０ｎｍ／ｓｅｃでマグネシウムを蒸着し、この際、同時に銀のバスケットを加熱し、蒸着速度０．１ｎｍ／ｓｅｃで銀を蒸着し、前記マグネシウムと銀との混合物からなる陰極とすることにより、有機ＥＬ素子３−１を作製した。
【０１０７】
有機ＥＬ素子３−１のＢＣＰを表２に記載の化合物に替えた以外は有機ＥＬ素子３−１と同様にして、有機ＥＬ素子３−２〜３−１２を作製した。
【０１０８】
これらの有機ＥＬ素子を２３℃、乾燥窒素ガス雰囲気下で１０Ｖ直流電圧印加による連続点灯を行い、点灯開始時の発光輝度（ｃｄ／ｍ^２）、及び輝度の半減時間を測定した。発光輝度は有機ＥＬ素子３−１を１００とした相対値で表し、輝度の半減時間は有機ＥＬ素子３−１の輝度の半減時間を１００とした相対値で表した。測定結果を表２に示す。なお全ての素子において発光色は青色だった。
【０１０９】
【化１９】

【０１１０】
【表２】

【０１１１】
表２より、本発明の化合物を用いた有機ＥＬ素子は、類似構造を有する比較化合物を用いた有機ＥＬ素子に比べ、点灯開始時の発光輝度及び輝度の半減する時間が改善されているのが分かる。
【０１１２】
実施例４（陰極バッファー層）
実施例３で作製した有機ＥＬ素子３−５の陰極をＡｌに置き換え、電子輸送層と陰極の間にフッ化リチウムを膜厚０．５ｎｍ蒸着して陰極バッファー層を設けた以外は同様にして有機ＥＬ素子４−１を作製した。
【０１１３】
実施例３と同様にこの有機ＥＬ素子を点灯開始時の発光輝度（ｃｄ／ｍ^２）、及び輝度の半減時間を測定したところ、有機ＥＬ素子３−１を１００とした相対値の比較で、発光輝度３１５、輝度の半減時間４２０となった。また、有機ＥＬ素子３−６〜３−１２についても、同様に、陰極バッファー層を導入するとさらに効果的であった。
【０１１４】
実施例５（三色の発光）
実施例３で用いた有機ＥＬ素子の発光層をＤＰＶＢｉから、それぞれＡｌｑ_３またはＡｌｑ_３とＤＣＭ−２を１００：１の質量比で蒸着した発光層に置き替えた以外は同様にして、有機ＥＬ素子を作製し、点灯開始時の発光輝度（ｃｄ／ｍ^２）及び輝度の半減時間を測定した。その結果、実施例３と同様に、本発明の化合物を電子輸送層に用いた有機ＥＬ素子は点灯開始時の発光輝度（ｃｄ／ｍ^２）及び輝度の半減時間の改善が確認された。
【０１１５】
なお、Ａｌｑ_３を発光層に用いた場合は緑色の発光が得られ、Ａｌｑ_３とＤＣＭ−２を１００：１で共蒸着した発光層からは赤色の発光が得られた。
【０１１６】
実施例６
有機ＥＬ素子６−１〜６−８を以下のようにして作製した。
【０１１７】
〈有機ＥＬ素子の作製〉
陽極として１００ｍｍ×１００ｍｍ×１．１ｍｍのガラス基板上にＩＴＯ（インジウムチンオキシド）を１５０ｎｍ成膜した基板（ＮＨテクノグラス社製ＮＡ−４５）にパターニングを行った後、このＩＴＯ透明電極を設けた透明支持基板をイソプロピルアルコールで超音波洗浄し、乾燥窒素ガスで乾燥し、ＵＶオゾン洗浄を５分間行なった。
【０１１８】
この透明支持基板を、市販の真空蒸着装置の基板ホルダーに固定し、一方、モリブデン製抵抗加熱ボートに、α−ＮＰＤを２００ｍｇ入れ、別のモリブデン製抵抗加熱ボートにＣＢＰを２００ｍｇ入れ、別のモリブデン製抵抗加熱ボートにバソキュプロイン（ＢＣＰ）を２００ｍｇ入れ、別のモリブデン製抵抗加熱ボートにＩｒ−１（りん光性化合物）を１００ｍｇ入れ、さらに別のモリブデン製抵抗加熱ボートにＡｌｑ_３を２００ｍｇ入れ、真空蒸着装置に取付けた。次いで、真空槽を４×１０^−４Ｐａまで減圧した後、α−ＮＰＤの入った前記加熱ボートに通電して加熱し、蒸着速度０．１ｎｍ／ｓｅｃで透明支持基板に蒸着し、膜厚４５ｎｍの正孔輸送層を設けた。さらに、ＣＢＰとＩｒ−１の入った前記加熱ボートに通電して加熱し、それぞれ蒸着速度０．１ｎｍ／ｓｅｃ、０．０１ｎｍ／ｓｅｃで前記正孔輸送層上に共蒸着して膜厚２０ｎｍの発光層を設けた。なお、蒸着時の基板温度は室温であった。さらに、ＢＣＰの入った前記加熱ボートに通電して加熱し、蒸着速度０．１ｎｍ／ｓｅｃで前記発光層の上に蒸着して膜厚１０ｎｍの正孔阻止の役割も兼ねた電子輸送層を設けた。その上に、さらに、Ａｌｑ_３の入った前記加熱ボートに通電して加熱し、蒸着速度０．１ｎｍ／ｓｅｃで前記電子輸送層の上に蒸着して更に膜厚４０ｎｍの電子注入層を設けた。なお、蒸着時の基板温度は室温であった。
【０１１９】
次に、フッ化リチウム０．５ｎｍ及びＡｌを１１０ｎｍ蒸着して陰極を形成し、有機ＥＬ素子６−１を作製した。
【０１２０】
発光層のＣＢＰを表３に示す化合物に置き換えた以外は全く同じ方法で、有機ＥＬ素子６−２〜６−９を作製した。
【０１２１】
【化２０】

【０１２２】
〈有機ＥＬ素子６−１〜６−９の発光輝度及び半減時間の評価〉
有機ＥＬ素子６−１では、初期駆動電圧３Ｖで電流が流れ始め、発光層のドーパントであるりん光性化合物からの緑色の発光を示した。作製した有機ＥＬ素子について、２３℃、乾燥窒素ガス雰囲気下で９Ｖ直流電圧を印加した時の発光輝度及び発光寿命の指標として輝度の半減時間を測定した。発光輝度は有機ＥＬ素子６−１を１００とした相対値で表し、輝度の半減時間は有機ＥＬ素子６−１を１００とした相対値で表した。測定結果を表３に示す。発光輝度［ｃｄ／ｍ^２］については、ミノルタ製ＣＳ−１０００を用いて測定した。
【０１２３】
【表３】

【０１２４】
表３から明らかなように、本発明の化合物をホストに用いた有機ＥＬ素子は、発光輝度が高く、半減時間が長いことから、有機ＥＬ素子として非常に有用であることが分かった。
【０１２５】
りん光性化合物をＩｒ−１１またはＩｒ−９に変更した以外は有機ＥＬ素子６−１〜６−９と同様にして作製した有機ＥＬ素子６−１０、６−１１においても同様の効果が得られた。なお、Ｉｒ−１１を用いた有機ＥＬ素子６−１０からは青色の発光が、Ｉｒ−９を用いた有機ＥＬ素子６−１１からは赤色の発光が得られた。
【０１２６】
実施例７
実施例６で作製した有機ＥＬ素子６−１の電子輸送層に用いたＢＣＰを表４に示す化合物に置き換えた以外は全く同じ方法で、有機ＥＬ素子７−１〜７−９を作製した。
【０１２７】
〈有機ＥＬ素子６−１、７−１〜７−９の発光輝度及び半減時間の評価〉
有機ＥＬ素子６−１では、初期駆動電圧３Ｖで電流が流れ始め、発光層のドーパントであるりん光性化合物からの緑色の発光を示した。これらの有機ＥＬ素子を２３℃、乾燥窒素ガス雰囲気下で９Ｖ直流電圧を印加した時の発光輝度及び輝度の半減時間を測定した。発光輝度は有機エレクトロルミネッセンス素子６−１を１００とした相対値で表し、輝度の半減時間も有機ＥＬ素子６−１を１００とした相対値で表した。測定結果を表４に示す。発光輝度［ｃｄ／ｍ^２］については、ミノルタ製ＣＳ−１０００を用いて測定した。
【０１２８】
【表４】

【０１２９】
表４から明らかなように、本発明の化合物を電子輸送層（正孔阻止層）に用いた有機ＥＬ素子は、発光輝度が高く、半減時間が長いことから、有機ＥＬ素子として非常に有用であることが分かった。
【０１３０】
りん光性化合物をＩｒ−１１またはＩｒ−９に変更した以外は有機ＥＬ素子７−１〜７−９と同様にして作製した有機ＥＬ素子７−１０、７−１１においても同様の効果が得られた。なお、Ｉｒ−１１を用いた有機ＥＬ素子７−１０からは青色の発光が、Ｉｒ−９を用いた有機ＥＬ素子７−１１からは赤色の発光が得られた。
【０１３１】
実施例８
実施例６で作製したそれぞれ赤色、緑色、青色発光の有機ＥＬ素子を同一基板上に並置し、図１に示すアクティブマトリクス方式フルカラー表示装置を作製した。
【０１３２】
図１には作製したフルカラー表示装置の表示部の模式図のみを示した。即ち同一基板上に、複数の走査線５及びデータ線６を含む配線部と、並置した複数の画素３（発光の色が赤領域の画素、緑領域の画素、青領域の画素等）とを有し、配線部の走査線５及び複数のデータ線６は、それぞれ導電材料からなり、走査線５とデータ線６は格子状に直交して、直交する位置で画素３に接続している（詳細は図示せず）。複数の画素３は、それぞれの発光色に対応した有機ＥＬ素子、アクティブ素子であるスイッチングトランジスタと駆動トランジスタが設けられたアクティブマトリクス方式で駆動されており、走査線５から走査信号が印加されると、データ線６から画像データ信号を受け取り、受け取った画像データに応じて発光する。この様に各赤、緑、青の画素を適宜、並置することによって、フルカラー表示が可能となる。
【０１３３】
フルカラー表示装置を駆動することにより、輝度の高い鮮明なフルカラー動画表示が得られた。
【０１３４】
【発明の効果】
本発明により、発光輝度及び耐久性の高い有機エレクトロルミネッセンス素子及びそれを用いた表示装置を提供することができた。
【図面の簡単な説明】
【図１】フルカラー表示装置の表示部の模式図である。
【符号の説明】
３　画素
５　走査線
６　データ線[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an organic electroluminescence device and a display device, and more particularly, to an organic electroluminescence device and a display device having excellent emission luminance.
[0002]
[Prior art]
As a light emitting type electronic display device, there is an electroluminescence display (ELD). ELD components include inorganic electroluminescent elements and organic electroluminescent (hereinafter abbreviated as organic EL) elements. Inorganic electroluminescent devices have been used as flat light sources, but require a high AC voltage to drive the light emitting devices. An organic EL element generally has a configuration in which a light-emitting layer containing a compound that emits light is sandwiched between a cathode and an anode, and electrons and holes are injected into the light-emitting layer and recombined to form excitons ( Exciton), and emits light by utilizing light emission (fluorescence / phosphorescence) when the exciton is deactivated. The element can emit light at a voltage of about several volts to several tens of volts. Since it is a self-luminous type, it has a wide viewing angle and high visibility, and because it is a thin-film type solid-state element, it is attracting attention from the viewpoint of space saving and portability.
[0003]
However, there is a demand for an organic EL device that emits light with high efficiency and low power consumption efficiently and efficiently for an organic EL device for practical use in the future. Until now, various organic EL devices have been reported. For example, Appl. Phys. Lett. , Vol. 51, 913 or a combination of a hole injection layer and an organic light emitting layer described in JP-A-59-194393, a hole injection layer and an electron injection-transport layer described in JP-A-63-295695. , Jpn. Journalof Applied Physics, vol. 127, no. 2, pages 269-271, each of which discloses a combination of a hole transport layer, a light emitting layer, and an electron transport layer. However, an organic EL device having higher luminance is required, and further improvement in energy conversion efficiency and emission quantum efficiency is expected. In addition, it has been pointed out that the light emission lifetime is short. Although the cause of the luminance degradation over time is not completely elucidated, the light emitting organic EL element decomposes the organic compound itself that constitutes the thin film due to the light emitted by itself and the heat generated at that time. Factors derived from the organic compound as the organic EL device material, such as crystallization of the organic compound, have been pointed out.
[0004]
Since the light emitting material for organic EL is an organic compound, a very wide range of compounds are being studied. In addition to a typical combination of elements such as carbon, nitrogen, oxygen, and sulfur, other characteristic elements are used. Containing compounds are also being investigated. For example, examples of using a compound containing boron have been reported, and are described in JP-A-2000-290645, JP-A-2000-294373, JP-A-2001-72971, and JP-A-2001-93670. There was a problem with the brightness.
[0005]
Further, at present, there is little knowledge of electron transporting materials, and there is no useful high-performance electron transporting material that can withstand practical use due to the use of antibonding orbitals. For example, a research group at Kyushu University has begun studying 2- (4-biphenyl) -5- (4-t-butylphenyl) -1,3,4-oxadizole (t-BuPBD), which is an oxadiazole derivative. Oxadiazole dimer derivatives 1,3-bis (4-t-butylphenyl-1,3,4-oxadizodyl) biphenylene (OXD-1) and 1,3-bis (4 -T-butylphenyl-1,3,4-oxadizolyl) phenylene (OXD-7) (Jpn. J. Appl. Phys. Vol. 31 (1992), p. 1812). In addition, a research group at Yamagata University has manufactured a white light-emitting device by using a triazole-based electron transporting material having excellent electron blocking properties (Science, 3 March 1995, Vol. 267, p. 1332). Further, Japanese Patent Application Laid-Open No. 5-331559 describes that a phenanthroline derivative is useful as an electron transport material.
[0006]
However, the conventional electron transport material has a low ability to form a thin film and is easily crystallized, so that there is a problem that the light emitting element is destroyed, and the element performance that can withstand practical use cannot be exhibited. JP-A-9-87616, JP-A-9-194487, and JP-A-2000-188604 as examples of organic electroluminescent materials that solve these problems, examples in which a compound containing a silicon atom in a molecule is used as a light emitting material or an electron transport material Is described, but it is not sufficient to achieve both luminous efficiency and luminous life.
[0007]
In addition, a method has been reported in which the light-emitting layer is composed of a host compound and a small amount of a phosphor to achieve an improvement in luminous efficiency. For example, in Japanese Patent No. 3093796, a stilbene derivative, a distyrylarylene derivative, or a tristyrylarylene derivative is doped with a small amount of a fluorescent substance, thereby improving emission luminance and extending the life of the element.
[0008]
Also, an element having an organic light emitting layer in which an 8-hydroxyquinoline aluminum complex is used as a host compound and a small amount of a fluorescent substance is doped therein (Japanese Patent Application Laid-Open No. 63-264691), and a quinacridone using an 8-hydroxyquinoline aluminum complex as a host compound An element having an organic light emitting layer doped with a system dye (Japanese Patent Application Laid-Open No. 3-255190) is known. As described above, by doping the phosphor having a high fluorescence quantum yield, the emission luminance is improved as compared with the conventional device. However, the light emission from the doped small amount of phosphor is light emission from an excited singlet. When light emission from an excited singlet is used, the generation ratio between a singlet exciton and a triplet exciton is 1: 1. 3, the generation probability of the luminescent excited species is 25%, and the light extraction efficiency is about 20%. Therefore, the limit of the external extraction quantum efficiency (ηext) is 5%. However, since Princeton University reported an organic EL device using phosphorescence emission from an excited triplet (MA Baldo et al., Nature, 395, 151-154 (1998)), the temperature was kept at room temperature. Research into phosphorescent materials has become active (eg, MA Baldo et al., Nature, 403, 17, 750-753 (2000), US Pat. No. 6,097,147). When the excited triplet is used, the upper limit of the internal quantum efficiency is 100%, so that the luminous efficiency is up to four times in principle compared to the case of the excited singlet, and the performance almost equal to that of the cold cathode tube is obtained. It is also applicable to applications and is attracting attention.
[0009]
When a phosphorescent compound is used as a dopant, the host must have an emission maximum wavelength in a shorter wavelength region than the emission maximum wavelength of the phosphorescent compound, but other conditions that must be satisfied It turns out that there is.
[0010]
The 10th International Works on Inorganic and Organic Electroluminescence (EL '00, Hamamatsu) reports several reports on phosphorescent compounds. For example, Ikai et al. Use a hole transporting compound as a host for a phosphorescent compound. Further, M. E. FIG. Tompson et al. Use various electron transporting materials as a host of a phosphorescent compound and dope them with a novel iridium complex. Further, Tsutsui et al. Obtain high luminous efficiency by introducing a hole blocking layer. The hole blocking layer is structurally the same as the electron transporting layer used in a normal organic EL device, but has a function of a hole leaking from the light emitting layer to the cathode side more than the electron transporting function. It is called a hole block layer because it has a strong function of preventing movement, and can be interpreted as a kind of electron transport layer. Therefore, in the present application, the hole block layer is also referred to as an electron transport layer, and the material (hole blocker) used in the layer is also referred to as an electron transport material.
[0011]
As for the host compound of the phosphorescent compound, for example, C.I. Adachi et al. , Appl. Phys. Lett. 77, p. 904 (2000), etc., it is necessary to take a newer approach to the properties required for the host compound to obtain a high-luminance organic EL device.
[0012]
However, none of the reports has obtained a configuration capable of achieving both improvement in light emission luminance and durability of the device.
[0013]
[Problems to be solved by the invention]
An object of the present invention is to provide an organic electroluminescent element having high emission luminance and high durability, and a display device using the same.
[0014]
[Means for Solving the Problems]
The above object of the present invention has been achieved by the following constitutions.
[0015]
1. An organic electroluminescent device having an electron transport layer and a light emitting layer, comprising a compound represented by the general formula (1).
[0016]
2. 2. The organic electroluminescent device according to the above 1, wherein the compound represented by the general formula (1) is contained in an electron transport layer.
[0017]
3. 2. The organic electroluminescent device according to the above 1, wherein the compound represented by the general formula (1) is contained in a light emitting layer.
[0018]
4. 4. The organic electroluminescent device according to the above item 3, wherein the light emitting layer contains a host compound and a phosphorescent compound, and the host compound is a compound represented by the general formula (1).
[0019]
5. 5. The organic electroluminescent device according to the above 4, wherein the phosphorescent compound is an iridium compound, an osmium compound or a platinum compound.
[0020]
6. 6. The organic electroluminescent device according to the above item 5, wherein the phosphorescent compound is an iridium compound.
[0021]
7. A display device comprising the organic electroluminescence element according to any one of the above items 1 to 6.
[0022]
Hereinafter, the present invention will be described in detail.
The present inventor has examined in detail the compatibility between emission luminance and durability. As a result, the present inventors have found that a boron-containing carbazole compound having a specific structure is used as a host compound for phosphorescence, and / or that a boron-containing carbazole compound having a specific structure is electron-transported. It has been found that an organic electroluminescence device having high emission luminance and high durability and a display device using the same can be obtained by using the material as a material (hole blocker).
[0023]
The compound represented by Formula (1) will be described.
R ₁ And R ₂ Examples of the substituent represented by are an alkyl group (methyl group, ethyl group, i-propyl group, hydroxyethyl group, methoxymethyl group, trifluoromethyl group, t-butyl group, cyclopentyl group, cyclohexyl group, benzyl group, etc. ), Alkenyl group (vinyl group, propenyl group, styryl group, etc.), alkynyl group (ethynyl group, etc.), aryl group (phenyl group, naphthyl group, p-tolyl group, p-chlorophenyl group, etc.), alkyloxy group (methoxy, etc.) Group, ethoxy group, i-propoxy group, butoxy group, etc., aryloxy group (phenoxy group, etc.), alkylthio group (methylthio group, ethylthio group, i-propylthio group, etc.), arylthio group (phenylthio group, etc.), halogen atom (Fluorine atom, chlorine atom, bromine atom, iodine atom, etc.), amino group (dimethylamino group, A cyano group, a nitro group, a heterocyclic group (a pyrrole group, a pyrrolidyl group, a pyrazolyl group, an imidazolyl group, a pyridyl group, a benzimidazolyl group, a benzothiazolyl group, a benzoxazolyl group, and the like). No. Examples of the aromatic group include the above-mentioned aryl group and heteroaryl group (pyrrole group, pyrazolyl group, imidazolyl group, pyridyl group, benzimidazolyl group, benzothiazolyl group, benzoxazolyl, etc.). It may be substituted with a substituent. Adjacent substituents may be condensed with each other to form a ring.
[0024]
R ₃ ~ R ₆ Represents a hydrogen atom or a substituent, and specific examples thereof include the aforementioned R ₁ Is synonymous with R ₃ Or R ₄ Represents a substituent, and a particularly preferred substituent is an alkyl group.
[0025]
The divalent arylene group represented by Ar is a residue obtained by removing two hydrogen atoms or two substituents from an arbitrary position of an aromatic compound, and the arylene group is composed of hydrocarbon. May be a heterocyclic ring containing a hetero atom, or may be condensed.
[0026]
Ar ₁ And Ar ₂ The aryl group represented by may be an aromatic hydrocarbon ring group or an aromatic heterocyclic group, and may further form a condensed ring. Specific examples include a phenyl group, a 1-naphthyl group, a 9-anthryl group, a 9-phenanthryl group, a 2-pyridyl group, a 4-quinolyl group, and a 2-thienyl group. Note that Ar ₁ Or Ar ₂ Either of the
[0027]
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[0028]
Is preferably represented by
The compound of the present invention is a compound having strong fluorescence in a solid state, has excellent electroluminescence, and can be effectively used as a luminescent material. In addition, since the compound of the present invention has excellent electron injecting and electron transporting properties from a metal electrode, the compound of the present invention can be used as an electron transporting material ( Or when used as a hole blocker).
[0029]
Hereinafter, specific examples of the compound will be described, but the present invention is not limited thereto.
[0030]
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[0031]
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[0032]
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[0033]
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[0034]
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[0035]
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[0036]
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[0037]
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[0038]
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[0039]
The compounds of the present invention are described in JP 2001-93670 A and J. Am. Chem. Soc. 120, p. 9714 (1998).
[0040]
Further, the present inventors have conducted intensive studies on the host compound of the phosphorescent compound. It has been found that the life is improved.
[0041]
In the present invention, the host compound is a compound having the largest mixing ratio (mass) in a light emitting layer composed of two or more compounds, and the other compounds are referred to as dopant compounds. For example, if the light-emitting layer is composed of two kinds of compound A and compound B and the mixing ratio is A: B = 10: 90, compound A is a dopant compound and compound B is a host compound. Further, the light emitting layer is composed of three kinds of compound A, compound B and compound C, and if the mixing ratio is A: B: C = 5: 10: 85, compound A and compound B are dopant compounds, Compound C is the host compound. The phosphorescent compound in the present invention is a kind of a dopant compound.
[0042]
The phosphorescent compound of the present invention is a compound that emits light from an excited triplet, and has a phosphorescence quantum yield of 0.001 or more at 25 ° C. The phosphorescence quantum yield is preferably at least 0.01, more preferably at least 0.1.
[0043]
The phosphorescence quantum yield can be measured by the method described in Spectroscopy II, 4th Edition, pp. 398 (1992 edition, Maruzen) of Experimental Chemistry Course 7. Although the phosphorescence quantum yield in a solution can be measured using various solvents, the phosphorescent compound used in the present invention only needs to achieve the above-mentioned phosphorescence quantum yield in any arbitrary solvent.
[0044]
The phosphorescent compound used in the present invention is preferably a complex-based compound containing a metal belonging to Group VIII in the periodic table of elements, more preferably iridium, osmium, or a platinum complex-based compound, more preferably Is an iridium complex-based compound.
[0045]
Hereinafter, specific examples of the phosphorescent compound used in the present invention are shown, but the invention is not limited thereto. These compounds are described, for example, in Inorg. Chem. 40, 1704-1711.
[0046]
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[0047]
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[0048]
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[0049]
In another embodiment, in addition to the host compound and the phosphorescent compound, a case where at least one kind of fluorescent compound having a fluorescence maximum wavelength is contained in a region longer than the maximum wavelength of light emission from the phosphorescent compound. There is also. In this case, by the energy transfer from the host compound and the phosphorescent compound, the electroluminescence as the organic EL element can be obtained from the fluorescent compound. Preferred as the fluorescent compound is a compound having a high fluorescence quantum yield in a solution state. Here, the fluorescence quantum yield is preferably 0.1 or more, particularly preferably 0.3 or more. Specifically, coumarin dyes, pyran dyes, cyanine dyes, croconium dyes, squarium dyes, oxobenzanthracene dyes, fluorescein dyes, rhodamine dyes, pyrylium dyes, perylene dyes, stilbene dyes , A polythiophene dye or a rare earth complex phosphor.
[0050]
The fluorescence quantum yield here can also be measured by the method described in Spectroscopy II, page 362 (1992 edition, Maruzen) of the 4th edition of Experimental Chemistry Course 7.
[0051]
Hereinafter, the organic EL device will be described.
The light emitting layer in the organic EL element refers to a layer which emits light when a current is applied to an electrode composed of a cathode and an anode in a broad sense. Specifically, it refers to a layer containing a fluorescent compound that emits light when an electric current is applied to an electrode composed of a cathode and an anode. Usually, an organic EL element has a structure in which a light emitting layer is sandwiched between a pair of electrodes. The organic EL device of the present invention has a hole transport layer, an anode buffer layer, a cathode buffer layer, and the like in addition to a light emitting layer and an electron transport layer, if necessary, and has a structure sandwiched between a cathode and an anode.
[0052]
In particular,
(I) anode / light-emitting layer / electron transport layer / cathode
(Ii) anode / hole transport layer / light-emitting layer / electron transport layer / cathode
(Iii) There are structures represented by anode / anode buffer layer / hole transport layer / emission layer / electron transport layer / cathode buffer layer / cathode and the like.
[0053]
As a method for forming a light-emitting layer using the above compound, for example, there is a method for forming a thin film by a known method such as a vapor deposition method, a spin coating method, a casting method, and an LB method. preferable. Here, the molecular deposition film refers to a thin film formed by depositing the compound from a gaseous state or a film formed by solidifying the compound from a molten state or a liquid state. In general, this molecular deposition film can be distinguished from a thin film (molecule accumulation film) formed by the LB method by a difference in an aggregated structure and a higher-order structure and a functional difference resulting therefrom.
[0054]
Further, as described in JP-A-57-51781, this light-emitting layer is prepared by dissolving the above compound as a light-emitting material in a solvent together with a binder such as a resin in a solvent and then spin-coating. To form a thin film.
[0055]
The thickness of the light emitting layer formed in this way is not particularly limited and can be appropriately selected depending on the situation, but is usually in the range of 5 nm to 5 μm.
[0056]
Here, the phosphorescent compound according to the present invention is specifically a heavy metal complex-based compound as described above, and preferably a complex-based compound having a metal of Group VIII as a central metal in the periodic table of the elements. Compounds, more preferably osmium, iridium or platinum complex compounds.
[0057]
These phosphorescent compounds have a phosphorescence quantum yield as described above of not less than 0.001 at 25 ° C., preferably not less than 0.01, and a fluorescence maximum wavelength of the fluorescent compound serving as the host. It has a long maximum wavelength of phosphorescence emission, so that, for example, using a phosphorescent compound having a longer wavelength than the emission maximum wavelength of the fluorescent compound serving as a host, the light emission of the phosphorescent compound, that is, utilizing the triplet state Thus, an organic EL device that emits electroluminescence at a longer wavelength than the maximum fluorescence wavelength of the host compound can be obtained. Therefore, the phosphorescent maximum wavelength of the phosphorescent compound used is not particularly limited, and can be obtained by selecting a central metal, a ligand, a substituent of the ligand, and the like in principle. The emission wavelength can be changed.
[0058]
For example, by using a fluorescent compound having a maximum fluorescence wavelength in a region of 350 to 440 nm as a host compound and using, for example, an iridium complex having phosphorescence in a green region, an organic EL device which emits light in the green region is obtained. be able to.
[0059]
In another embodiment, as described above, in addition to the fluorescent compound A as the host compound and the phosphorescent compound, the fluorescent maximum wavelength is set in a region longer than the maximum wavelength of light emission from the phosphorescent compound. May contain at least one other fluorescent compound B, and the electroluminescence as the organic EL element obtains light emission from the fluorescent compound B by energy transfer from the fluorescent compound A and the phosphorescent compound. You can also.
[0060]
The color emitted by the fluorescent compound of the present specification is shown in FIG. 4.16 on page 108 of the “New Edition of Color Science Handbook” (edited by The Japan Society of Color Science, The University of Tokyo Press, 1985), and is shown in FIG. (Minolta) is determined by the color when the result of measurement is applied to the CIE chromaticity coordinates.
[0061]
The molecular weight of the host compound is preferably from 600 to 2,000. When the molecular weight is in this range, Tg (glass transition temperature) increases, thermal stability improves, and the life of the device improves. More preferably, the molecular weight is from 800 to 2,000. Further, Tg is preferably at least 100 degrees. Further, when the molecular weight is within this range, the light emitting layer can be easily formed by a vacuum evaporation method, and the production of the organic EL device becomes easy. Further, the thermal stability of the fluorescent compound in the organic EL device is improved.
[0062]
Next, other layers constituting an organic EL element in combination with a light emitting layer such as a hole injection layer, a hole transport layer, an electron injection layer, and an electron transport layer will be described.
[0063]
The hole injection layer and the hole transport layer have a function of transmitting holes injected from the anode to the light emitting layer, and the hole injection layer and the hole transport layer are interposed between the anode and the light emitting layer. Due to this, many holes are injected into the light emitting layer at a lower electric field, and furthermore, electrons injected from the cathode, the electron injection layer or the electron transport layer into the light emitting layer are separated from the light emitting layer and the hole injection layer or the hole transport layer. An element having excellent light-emitting performance, such as improved luminous efficiency, is accumulated at the interface in the light-emitting layer due to the barrier of electrons existing at the interface. The material of the hole injection layer and the hole transport layer (hereinafter, referred to as a hole injection material and a hole transport material) has a property of transmitting the holes injected from the anode to the light emitting layer. There is no particular limitation as long as the material is a conventional photoconductive material, a material commonly used as a hole charge injection / transport material, a hole injection layer of an organic EL device, and a known material used for a hole transport layer. Any one of them can be selected and used.
[0064]
The hole injecting material and the hole transporting material have any of hole injecting or transporting and electron barrier properties, and may be any of an organic substance and an inorganic substance. Examples of the hole injection material and the hole transport material include a triazole derivative, an oxadiazole derivative, an imidazole derivative, a polyarylalkane derivative, a pyrazoline derivative and a pyrazolone derivative, a phenylenediamine derivative, an arylamine derivative, an amino-substituted chalcone derivative, and oxazole. Derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aniline-based copolymers, conductive polymer oligomers, especially thiophene oligomers, and the like. As the hole injecting material and the hole transporting material, those described above can be used, and porphyrin compounds, aromatic tertiary amine compounds and styrylamine compounds, particularly aromatic tertiary amine compounds may be used. preferable.
[0065]
Representative examples of the aromatic tertiary amine compound and styrylamine compound include N, N, N ', N'-tetraphenyl-4,4'-diaminophenyl; N, N'-diphenyl-N, N' -Bis (3-methylphenyl)-[1,1'-biphenyl] -4,4'-diamine (TPD); 2,2-bis (4-di-p-tolylaminophenyl) propane; 1,1- Bis (4-di-p-tolylaminophenyl) cyclohexane; N, N, N ', N'-tetra-p-tolyl-4,4'-diaminobiphenyl; 1,1-bis (4-di-p- Tolaminophenyl) -4-phenylcyclohexane; bis (4-dimethylamino-2-methylphenyl) phenylmethane; bis (4-di-p-tolylaminophenyl) phenylmethane; N, N'-diphenyl-N, N -Di (4-methoxyphenyl) -4,4'-diaminobiphenyl; N, N, N ', N'-tetraphenyl-4,4'-diaminodiphenyl ether; 4,4'-bis (diphenylamino) quadri Phenyl; N, N, N-tri (p-tolyl) amine; 4- (di-p-tolylamino) -4 '-[4- (di-p-tolylamino) styryl] stilbene; 4-N, N-diphenyl Amino- (2-diphenylvinyl) benzene; 3-methoxy-4'-N, N-diphenylaminostilbenzene; N-phenylcarbazole, and two of those described in U.S. Pat. No. 5,061,569. Having a condensed aromatic ring in the molecule thereof, for example, 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (NPD), JP-A-4-3086 8,4,4 ', 4 "-tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine (MTDATA) in which three triphenylamine units described in No. 8 are linked in a starburst type ) And the like.
[0066]
Further, a polymer material in which these materials are introduced into a polymer chain, or a polymer material in which these materials are used as a polymer main chain, can also be used.
[0067]
Further, inorganic compounds such as p-type Si and p-type SiC can also be used as the hole injection material and the hole transport material. The hole injection layer and the hole transport layer are formed by thinning the hole injection material and the hole transport material by a known method such as a vacuum deposition method, a spin coating method, a casting method, and an LB method. Can be formed. The thickness of the hole injection layer and the hole transport layer is not particularly limited, but is usually about 5 nm to 5 μm. The hole injecting layer and the hole transporting layer may have a single-layer structure composed of one or more of the above materials, or may have a laminated structure composed of a plurality of layers having the same composition or different compositions.
[0068]
Furthermore, the electron transporting layer used as needed may have a function of transmitting electrons injected from the cathode to the light emitting layer, and any material may be selected from conventionally known compounds. Can be used.
[0069]
Examples of materials used for the electron transport layer (hereinafter, referred to as electron transport materials) include nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, heterocyclic tetracarboxylic anhydrides such as naphthalene perylene, carbodiimide, Examples include fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, and oxadiazole derivatives. Further, in the oxadiazole derivative, a thiadiazole derivative in which an oxygen atom of the oxadiazole ring is substituted with a sulfur atom, and a quinoxaline derivative having a quinoxaline ring known as an electron withdrawing group can also be used as the electron transport material.
[0070]
Further, a polymer material in which these materials are introduced into a polymer chain, or a polymer material in which these materials are used as a polymer main chain, can also be used.
[0071]
Further, a metal complex of an 8-quinolinol derivative, such as tris (8-quinolinol) aluminum (Alq), tris (5,7-dichloro-8-quinolinol) aluminum, tris (5,7-dibromo-8-quinolinol) aluminum, Tris (2-methyl-8-quinolinol) aluminum, tris (5-methyl-8-quinolinol) aluminum, bis (8-quinolinol) zinc (Znq), and the like, and the central metals of these metal complexes are In, Mg, Cu , Ca, Sn, Ga or Pb can also be used as the electron transport material. In addition, metal-free or metal phthalocyanine, or those whose terminals are substituted with an alkyl group, a sulfonic acid group, or the like can be preferably used as the electron transporting material. Further, the distyrylpyrazine derivative exemplified as the material of the light emitting layer can be used as the electron transporting material, and similarly to the hole injection layer and the hole transport layer, inorganic materials such as n-type Si and n-type SiC can be used. Semiconductors can also be used as electron transport materials.
[0072]
The electron transporting layer can be formed by forming the above compound by a known thin film forming method such as a vacuum evaporation method, a spin coating method, a casting method, and an LB method. The thickness of the electron transport layer is not particularly limited, but is usually selected in the range of 5 nm to 5 μm. The electron transport layer may have a single-layer structure composed of one or more of these electron transport materials, or may have a laminated structure composed of a plurality of layers having the same composition or different compositions.
[0073]
Further, in the present invention, the fluorescent compound is not limited to only the light emitting layer, a hole transport layer adjacent to the light emitting layer, or a fluorescent compound to be a host compound of the phosphorescent compound in the electron transport layer and At least one kind of fluorescent compound having a maximum fluorescence wavelength may be contained in the same region, whereby the luminous efficiency of the organic EL device can be further increased. As the fluorescent compound contained in the hole transport layer or the electron transport layer, the fluorescent compound having a fluorescence maximum wavelength in the range of 350 to 440 nm, more preferably 390 to 410 nm, as in the light emitting layer. Compounds are used.
[0074]
The substrate preferably used for the organic EL device of the present invention is not particularly limited in the type of glass, plastic, and the like, and is not particularly limited as long as it is transparent. Examples of the substrate preferably used for the organic EL device of the present invention include glass, quartz, and a light-transmitting plastic film.
[0075]
Examples of the light-transmitting plastic film include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide, polyetheretherketone, polyphenylene sulfide, polyarylate, polyimide, and polycarbonate (PC). , Cellulose triacetate (TAC), cellulose acetate propionate (CAP) and the like.
[0076]
Next, a preferred example of manufacturing an organic EL device will be described. As an example, a method of manufacturing an organic EL device including the above-described anode / hole injection layer / hole transport layer / emission layer / electron transport layer / electron injection layer / cathode will be described.
[0077]
First, a thin film made of a desired electrode material, for example, an anode material, is formed on a suitable substrate by a method such as vapor deposition or sputtering so as to have a thickness of 1 μm or less, preferably in the range of 10 to 200 nm. Make the anode. Next, a thin film composed of a hole injection layer, a hole transport layer, a light emitting layer, and an electron transport layer / electron injection layer, which are element materials, is formed thereon.
[0078]
Further, a buffer layer (electrode interface layer) may be provided between the anode and the light emitting layer or the hole injection layer and between the cathode and the light emitting layer or the electron injection layer.
The buffer layer is a layer provided between the electrode and the organic layer for lowering the driving voltage and improving the luminous efficiency. The “organic EL device and the forefront of its industrialization (published by NTT Corporation on November 30, 1998) )), Vol. 2, Chapter 2, "Electrode Materials" (pages 123 to 166), and includes an anode buffer layer and a cathode buffer layer.
[0079]
The details of the anode buffer layer are also described in JP-A-9-45479, JP-A-9-260062, JP-A-8-288069 and the like. Specific examples thereof include a phthalocyanine buffer layer represented by copper phthalocyanine, and vanadium oxide. And a polymer buffer layer using a conductive polymer such as polyaniline (emeraldine) or polythiophene.
[0080]
The details of the cathode buffer layer are also described in JP-A-6-325871, JP-A-9-17574, and JP-A-10-74586. Specifically, a metal buffer layer represented by strontium, aluminum, and the like; Examples thereof include an alkali metal compound buffer layer represented by lithium fluoride, an alkaline earth metal compound buffer layer represented by magnesium fluoride, an oxide buffer layer represented by aluminum oxide and lithium oxide.
[0081]
The buffer layer is desirably an extremely thin film, and the thickness is preferably in the range of 0.1 to 100 nm, depending on the material.
[0082]
In addition to the above basic constituent layers, layers having other functions may be laminated as necessary. For example, JP-A-11-204258, JP-A-11-204359, and "Organic EL Device and Its Industrialization Frontier ( And a functional layer such as a hole blocking (hole block) layer described on page 237 of November 30, 1998, NTT Corporation).
[0083]
Next, the electrodes of the organic EL element will be described. The electrodes of the organic EL element are composed of a cathode and an anode.
[0084]
As the anode in this organic EL element, a metal, an alloy, an electrically conductive compound, or a mixture thereof having a large work function (4 eV or more) is preferably used as an electrode material. Specific examples of such an electrode material include metals such as Au, CuI, indium tin oxide (ITO), and SnO. ₂ , ZnO and the like.
[0085]
The anode may be formed by forming a thin film of these electrode substances by a method such as vapor deposition or sputtering and forming a pattern of a desired shape by a photolithography method, or (100 μm Above), a pattern may be formed through a mask having a desired shape at the time of vapor deposition or sputtering of the electrode material. When light is extracted from the anode, the transmittance is desirably greater than 10%, and the sheet resistance of the anode is preferably several hundred Ω / □ or less. Further, the thickness depends on the material, but is usually selected in the range of 10 nm to 1 μm, preferably 10 to 200 nm.
[0086]
On the other hand, as a cathode, a metal having a small work function (4 eV or less) (referred to as an electron injecting metal), an alloy, an electrically conductive compound, and a mixture thereof are used as an electrode material. Specific examples of such an electrode material include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O ₃ ) Mixtures, indium, lithium / aluminum mixtures, rare earth metals and the like. Among them, from the viewpoint of electron injecting property and durability against oxidation, etc., a mixture of an electron injecting metal and a second metal which is a stable metal having a large work function, such as a magnesium / silver mixture, magnesium / Aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O ₃ Mixtures, lithium / aluminum mixtures and the like are preferred. The cathode can be manufactured by forming a thin film from these electrode substances by a method such as evaporation or sputtering. Further, the sheet resistance as the cathode is preferably several hundred Ω / □ or less, and the film thickness is usually selected in the range of 10 nm to 1 μm, preferably 50 to 200 nm. In order to transmit light, it is convenient if one of the anode and the cathode of the organic EL element is transparent or translucent, since luminous efficiency is improved.
[0087]
Next, a method for manufacturing an organic EL element will be described.
Examples of the method for thinning include the spin coating method, the casting method, and the vapor deposition method as described above, but the vacuum vapor deposition method is preferable because a uniform film is easily obtained and pinholes are hardly generated. When a vacuum deposition method is used for thinning, the deposition conditions vary depending on the type of compound used, the target crystal structure of the molecular deposition film, the association structure, and the like. Degree 10 ^-6 -10 ^-3 It is desirable to appropriately select Pa, a deposition rate of 0.01 to 50 nm / sec, a substrate temperature of −50 to 300 ° C., and a thickness of 5 nm to 5 μm.
[0088]
As described above, a thin film made of a desired electrode substance, for example, an anode substance, is formed on an appropriate substrate by a method such as vapor deposition or sputtering so as to have a thickness of 1 μm or less, preferably 10 to 200 nm. To form an anode, and a layer thin film including a hole injection layer, a hole transport layer, a light emitting layer, and an electron transport layer / electron injection layer is formed on the anode as described above, and then formed thereon. A desired organic EL element can be obtained by forming a thin film made of a material for a cathode to a thickness of 1 μm or less, preferably 50 to 200 nm, for example, by a method such as vapor deposition or sputtering, and providing a cathode. . In the production of this organic EL device, it is preferable to consistently produce the hole injection layer to the cathode in this manner by one evacuation, but the production order is reversed, and the cathode, the electron injection layer, the light emitting layer, A hole injection layer and an anode can be formed in this order. When a DC voltage is applied to the organic EL element obtained in this manner, light emission can be observed by applying a voltage of about 5 to 40 V with the positive polarity of the anode and the negative polarity of the cathode. Also, even if a voltage is applied in the opposite polarity, no current flows and no light emission occurs. Further, when an AC voltage is applied, light is emitted only when the anode is in the + state and the cathode is in the-state. The waveform of the applied AC may be arbitrary.
[0089]
【Example】
Hereinafter, the present invention will be described in detail with reference to Examples, but embodiments of the present invention are not limited thereto.
[0090]
Example 1 (luminescent material)
After patterning a substrate (made by NH Techno Glass Co., Ltd .: NA-45) on which 150 nm of ITO was formed on glass as an anode, the transparent support substrate provided with the ITO transparent electrode was subjected to ultrasonic cleaning with i-propyl alcohol. After drying with dry nitrogen gas, UV ozone cleaning was performed for 5 minutes. This transparent support substrate was fixed to a substrate holder of a commercially available vacuum evaporation apparatus, while 200 mg of α-NPD was put in a molybdenum resistance heating boat, 200 mg of Comparative Compound 1 was put in another molybdenum resistance heating boat, and another 200 mg of bathocuproine (BCP) is put into a molybdenum resistance heating boat, and Alq is put into another molybdenum resistance heating boat. ₃ Was placed in a vacuum evaporation apparatus. Then, the vacuum chamber was 4 × 10 ^-4 After reducing the pressure to Pa, the heating boat containing α-NPD was energized and heated, and was deposited on the transparent support substrate at a deposition rate of 0.1 to 0.3 nm / sec with a thickness of 50 nm to form a hole transport layer. Provided. The substrate temperature during vapor deposition was room temperature. Next, the heating boat containing the comparative compound 1 was heated by supplying electricity to the heating boat, and a 30 nm light emitting layer was provided at a deposition rate of 0.1 to 0.3 nm / sec. Further, the heating boat containing BCP was energized and heated to provide a hole blocking layer having a thickness of 10 nm. Furthermore, Alq ₃ Was heated by supplying electricity to the heating boat, and an electron transport layer having a thickness of 20 nm was provided at a deposition rate of 0.1 to 0.3 nm / sec.
[0091]
Next, a vacuum chamber was opened, and a stainless steel rectangular perforated mask was set on the electron transport layer. Meanwhile, 3 g of magnesium was placed in a molybdenum resistance heating boat, and silver was placed in a tungsten deposition basket in a volume of 0.1 g. 5 g, and the vacuum chamber was again filled with 2 × 10 ^-4 After reducing the pressure to Pa, the boat containing magnesium was energized to deposit magnesium at a deposition rate of 1.5 to 2.0 nm / sec. At this time, the silver basket was heated at the same time and the deposition rate was 0.1 nm / sec. An organic EL device 1-1 was produced by depositing silver to form a cathode made of a mixture of magnesium and silver.
[0092]
Organic EL elements 1-2 to 1-12 were produced in the same manner as in the organic EL element 1-1, except that the comparative compound 1 of the organic EL element 1-1 was changed to the compound shown in Table 1. The emission colors of all the organic EL elements were from blue to green.
[0093]
These organic EL elements were continuously lit by applying a DC voltage of 10 V under a dry nitrogen gas atmosphere at 23 ° C., and the light emission luminance (cd / m) at the start of lighting was obtained. ² ) And the half-life of luminance was measured as an index of durability. The emission luminance was represented by a relative value when the organic EL element 1-1 was set to 100, and the luminance half-life was represented by a relative value when the luminance half-life of the organic EL element 1-1 was set to 100. Table 1 shows the measurement results. Emission luminance [cd / m ² ] Was measured using Minolta CS-1000.
[0094]
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[0095]
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[0096]
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[0097]
[Table 1]

[0098]
From Table 1, it can be seen that the organic EL device using the compound of the present invention has improved emission luminance and half-time of luminance at the start of lighting as compared to the organic EL device using the comparative compound having a similar structure. .
[0099]
Example 2 (host compound)
An organic EL device 2-1 was produced in the same manner as in Example 1, except that a 30 nm-thick light emitting layer in which the compound 1 of the present invention and DCM-2 were deposited at a mass ratio of 100: 1 was used.
[0100]
When a 10 V DC voltage was applied to the organic EL device at 23 ° C. in a dry nitrogen gas atmosphere, red light emission was obtained.
[0101]
Green or blue light was emitted from the organic EL elements 2-2 and 2-3 produced by replacing DCM-2 with Qd-2 or BCzVBi in the organic EL element 2-1.
[0102]
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[0103]
Example 3 (Electron transport material)
After patterning a substrate (made by NH Techno Glass Co., Ltd .: NA-45) on which 150 nm of ITO was formed on glass as an anode, the transparent support substrate provided with the ITO transparent electrode was subjected to ultrasonic cleaning with i-propyl alcohol. After drying with dry nitrogen gas, UV ozone cleaning was performed for 5 minutes. This transparent support substrate was fixed to a substrate holder of a commercially available vacuum evaporation apparatus, while 200 mg of m-MTDATXA was put in a molybdenum resistance heating boat, 200 mg of DPVBi was put in another molybdenum resistance heating boat, and another. A molybdenum resistance heating boat was charged with 200 mg of BCP and attached to a vacuum evaporation apparatus.
[0104]
Then, the vacuum chamber was 4 × 10 ^-4 After reducing the pressure to Pa, the heating boat containing m-MTDATXA was energized and heated, and was deposited on the transparent support substrate at a deposition rate of 0.1 to 0.3 nm / sec with a film thickness of 25 nm, and further containing DPVBi. The heating boat was energized and heated to deposit a 20 nm-thick film at a deposition rate of 0.1 to 0.3 nm / sec to provide a light-emitting layer. The substrate temperature during vapor deposition was room temperature.
[0105]
Next, the heating boat containing the BCP was energized and heated to provide a 30 nm electron transport layer at a deposition rate of 0.1 to 0.3 nm / sec.
[0106]
Next, a vacuum chamber was opened, and a stainless steel rectangular perforated mask was set on the electron transport layer. Meanwhile, 3 g of magnesium was placed in a molybdenum resistance heating boat, and silver was placed in a tungsten deposition basket in a volume of 0.1 g. 5 g, and the vacuum chamber was again filled with 2 × 10 ^-4 After reducing the pressure to Pa, the boat containing magnesium was energized to deposit magnesium at a deposition rate of 1.5 to 2.0 nm / sec. At this time, the silver basket was heated at the same time and the deposition rate was 0.1 nm / sec. An organic EL device 3-1 was produced by depositing silver to form a cathode made of a mixture of magnesium and silver.
[0107]
Organic EL elements 3-1 to 3-12 were produced in the same manner as in the organic EL element 3-1 except that the BCP of the organic EL element 3-1 was changed to the compounds shown in Table 2.
[0108]
These organic EL elements were continuously lit by applying a DC voltage of 10 V under a dry nitrogen gas atmosphere at 23 ° C., and the light emission luminance (cd / m) at the start of lighting was obtained. ² ), And the half-life of the luminance were measured. The emission luminance was represented by a relative value when the organic EL element 3-1 was set to 100, and the half-life time of the luminance was represented by a relative value when the half-life time of the luminance of the organic EL element 3-1 was set to 100. Table 2 shows the measurement results. The light emission color was blue in all the devices.
[0109]
Embedded image

[0110]
[Table 2]

[0111]
From Table 2, it can be seen that the organic EL device using the compound of the present invention has improved emission luminance at the start of lighting and the time for halving the luminance as compared to the organic EL device using the comparative compound having a similar structure. I understand.
[0112]
Example 4 (cathode buffer layer)
The same procedure was performed except that the cathode of the organic EL element 3-5 produced in Example 3 was replaced with Al, and lithium fluoride was deposited to a thickness of 0.5 nm between the electron transport layer and the cathode to provide a cathode buffer layer. Organic EL device 4-1 was produced.
[0113]
In the same manner as in Example 3, this organic EL element emitted light at the start of lighting (cd / m ² ) And the half-life of the luminance were measured. As a result, a relative value was set to 100 with respect to the organic EL element 3-1. As a result, the emission luminance was 315 and the luminance half-life was 420. Similarly, for the organic EL elements 3-6 to 3-12, it was more effective to introduce a cathode buffer layer.
[0114]
Example 5 (Three-color light emission)
The light emitting layer of the organic EL device used in Example 3 was changed from DPVBi to Alq, respectively. ₃ Or Alq ₃ An organic EL device was manufactured in the same manner except that the light-emitting layer was formed by vapor-depositing DCM and DCM-2 at a mass ratio of 100: 1. ² ) And half-time of luminance were measured. As a result, as in Example 3, the organic EL device using the compound of the present invention for the electron transport layer exhibited an emission luminance (cd / m) at the start of lighting. ² ) And the half-life of the luminance were improved.
[0115]
In addition, Alq ₃ When green light was used for the light emitting layer, green light emission was obtained. ₃ And DCM-2 at a ratio of 100: 1, red light was emitted from the light emitting layer.
[0116]
Example 6
Organic EL elements 6-1 to 6-8 were produced as follows.
[0117]
<Preparation of organic EL element>
After patterning was performed on a substrate (NA-45 manufactured by NH Techno Glass Co., Ltd.) on which 150 nm of ITO (indium tin oxide) was formed on a glass substrate of 100 mm × 100 mm × 1.1 mm as an anode, the ITO transparent electrode was provided. The transparent support substrate was subjected to ultrasonic cleaning with isopropyl alcohol, dried with dry nitrogen gas, and subjected to UV ozone cleaning for 5 minutes.
[0118]
This transparent support substrate was fixed to a substrate holder of a commercially available vacuum evaporation apparatus, while 200 mg of α-NPD was put in a molybdenum resistance heating boat, 200 mg of CBP was put in another molybdenum resistance heating boat, and another molybdenum was heated. 200 mg of bathocuproine (BCP) is put into a resistance heating boat made of aluminum, 100 mg of Ir-1 (phosphorescent compound) is put into another resistance heating boat made of molybdenum, and Alq is put into another resistance heating boat made of molybdenum ₃ Was placed in a vacuum evaporation apparatus. Then, the vacuum chamber was 4 × 10 ^-4 After the pressure was reduced to Pa, the heating boat containing α-NPD was energized and heated, and was vapor-deposited on a transparent support substrate at a vapor deposition rate of 0.1 nm / sec to provide a hole transport layer having a thickness of 45 nm. Furthermore, the heating boat containing CBP and Ir-1 was energized and heated, and co-deposited on the hole transport layer at a deposition rate of 0.1 nm / sec and 0.01 nm / sec, respectively, to form a 20 nm-thick film. A light emitting layer was provided. In addition, the substrate temperature at the time of vapor deposition was room temperature. Further, an electric current is applied to the heating boat containing the BCP to heat it, and the electron boat is vapor-deposited on the light-emitting layer at a vapor deposition rate of 0.1 nm / sec. Was. On top of that, Alq ₃ The heating boat containing the gas was heated by applying an electric current, and was vapor-deposited on the electron transport layer at a vapor deposition rate of 0.1 nm / sec to further provide an electron injection layer having a thickness of 40 nm. In addition, the substrate temperature at the time of vapor deposition was room temperature.
[0119]
Next, 0.5 nm of lithium fluoride and 110 nm of Al were deposited to form a cathode, and an organic EL device 6-1 was produced.
[0120]
Organic EL devices 6-1 to 6-9 were prepared in exactly the same manner except that the CBP of the light emitting layer was replaced with the compounds shown in Table 3.
[0121]
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[0122]
<Evaluation of emission luminance and half-life of organic EL elements 6-1 to 6-9>
In the organic EL element 6-1, current began to flow at an initial driving voltage of 3 V, and emitted green light from the phosphorescent compound that was the dopant of the light emitting layer. With respect to the produced organic EL device, the half-life of luminance was measured as an index of the emission luminance and the emission life when a 9 V DC voltage was applied in a dry nitrogen gas atmosphere at 23 ° C. The emission luminance was represented by a relative value with the organic EL element 6-1 being 100, and the half-life of the luminance was represented by a relative value with the organic EL element 6-1 being 100. Table 3 shows the measurement results. Emission luminance [cd / m ² ] Was measured using Minolta CS-1000.
[0123]
[Table 3]

[0124]
As is clear from Table 3, the organic EL device using the compound of the present invention as a host has high emission luminance and a long half-life, and thus is very useful as an organic EL device.
[0125]
Similar effects can be obtained in organic EL elements 6-10 and 6-11 produced in the same manner as in organic EL elements 6-1 to 6-9, except that the phosphorescent compound is changed to Ir-11 or Ir-9. Was done. In addition, blue light emission was obtained from the organic EL element 6-10 using Ir-11, and red light emission was obtained from the organic EL element 6-11 using Ir-9.
[0126]
Example 7
Organic EL devices 7-1 to 7-9 were manufactured in exactly the same manner except that the BCP used in the electron transport layer of the organic EL device 6-1 manufactured in Example 6 was replaced with the compound shown in Table 4.
[0127]
<Evaluation of emission luminance and half-life of organic EL elements 6-1 and 7-1 to 7-9>
In the organic EL element 6-1, a current began to flow at an initial driving voltage of 3 V, and emitted green light from the phosphorescent compound that was the dopant of the light emitting layer. These organic EL devices were measured for emission luminance and luminance half-life when a 9 V DC voltage was applied at 23 ° C. in a dry nitrogen gas atmosphere. The emission luminance was represented by a relative value when the organic electroluminescent element 6-1 was set to 100, and the half-life of the luminance was also represented by a relative value when the organic EL element 6-1 was set to 100. Table 4 shows the measurement results. Emission luminance [cd / m ² ] Was measured using Minolta CS-1000.
[0128]
[Table 4]

[0129]
As is clear from Table 4, the organic EL device using the compound of the present invention for the electron transport layer (hole blocking layer) has a high emission luminance and a long half-life, and is therefore very useful as an organic EL device. I found it.
[0130]
Similar effects can be obtained in organic EL devices 7-10 and 7-11 produced in the same manner as in organic EL devices 7-1 to 7-9 except that the phosphorescent compound is changed to Ir-11 or Ir-9. Was done. In addition, blue light emission was obtained from the organic EL element 7-10 using Ir-11, and red light emission was obtained from the organic EL element 7-11 using Ir-9.
[0131]
Example 8
The red, green, and blue light emitting organic EL elements produced in Example 6 were juxtaposed on the same substrate to produce an active matrix full-color display device shown in FIG.
[0132]
FIG. 1 shows only a schematic view of the display section of the manufactured full-color display device. That is, on the same substrate, a wiring portion including a plurality of scanning lines 5 and data lines 6 and a plurality of pixels 3 (pixels in a red region, pixels in a green region, pixels in a blue region, and the like) are arranged side by side. The scanning lines 5 and the plurality of data lines 6 of the wiring portion are each made of a conductive material, and the scanning lines 5 and the data lines 6 are orthogonal to each other in a grid and are connected to the pixels 3 at orthogonal positions ( Details are not shown). The plurality of pixels 3 are driven by an active matrix method provided with an organic EL element corresponding to each emission color, a switching transistor as an active element, and a driving transistor. Receives an image data signal from the data line 6, and emits light in accordance with the received image data. By arranging the red, green, and blue pixels appropriately as described above, a full-color display can be realized.
[0133]
By driving the full-color display device, a clear full-color moving image display with high luminance was obtained.
[0134]
【The invention's effect】
According to the present invention, an organic electroluminescence element having high emission luminance and high durability and a display device using the same can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a display unit of a full-color display device.
[Explanation of symbols]
3 pixels
5 scan lines
6 Data line

Claims (7)

An organic electroluminescent device having an electron transport layer and a light emitting layer, comprising a compound represented by the following general formula (1).

(Wherein, R ₁ and R ₂ each independently represent a substituent, Ar represents a divalent arylene group, n represents an integer of 0 to 8, p represents an integer of 1 to 4, and q represents Represents an integer of 1 to 4. When p represents an integer of 2 or more, a plurality of R ₁ may be the same or different, and when q represents an integer of 2 or more, a plurality of R ₂ are the same. When p is 2 or more and a plurality of R ₁ are adjacent to each other, they may be condensed with each other to form a ring, and when q is 2 or more, When a plurality of R ₂ are adjacent to each other, they may be condensed with each other to form a ring, and may further form a ring with R ₁ and R _2. R _{3 to} R _{6 each} represent a hydrogen atom or a substituent represents, it may form a ring with _{R 3} and _{R 5} and / or _{R 4} and _{R 6.} However, at least one of _{R 3} or _{R 4} is .Ar ₁ and Ar ₂ represents a substituent each independently represent an aryl group.) The organic electroluminescence device according to claim 1, wherein the compound represented by the general formula (1) is contained in an electron transport layer. The organic electroluminescent device according to claim 1, wherein the light emitting layer contains the compound represented by the general formula (1). The organic electroluminescent device according to claim 3, wherein the light emitting layer contains a host compound and a phosphorescent compound, and the host compound is a compound represented by the general formula (1). The organic electroluminescence device according to claim 4, wherein the phosphorescent compound is an iridium compound, an osmium compound, or a platinum compound. The organic electroluminescence device according to claim 5, wherein the phosphorescent compound is an iridium compound. A display device comprising the organic electroluminescence device according to claim 1.

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