JP4052024B2 - Organic electroluminescence element and display device - Google Patents

Description

【００３３】
【化４】

【００３４】
【化５】

【００３５】
これらの化合物は、Ｔｅｔｒａｈｅｄｒｏｎ Ｌｅｔｔｅｒｓ ４１（２０００）４２６１〜４２６４およびＪ．Ａｍ．Ｃｈｅｍ．Ｓｏｃ．１９９７，１１９，７２９１〜７３０２ Ａｎｇｅｗ．Ｃｈｅｍ．，Ｉｎｔ．Ｅｄ．Ｅｎｇｌ．，３６（１９９７）１７４０等に記載の合成方法により容易に合成することができる。
【００３６】
また、本発明者等は、リン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１，２，３−トリフェニルベンゼン化合物をホスト化合物として用いて、有機エレクトロルミネッセンス素子を作製した場合に、素子の発光輝度および寿命が改善されることを見出した。
【００３７】
本発明のホスト化合物とは、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。本発明におけるリン光性化合物は、ドーパント化合物の一種である。
【００３８】
本発明のリン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、リン光量子収率が、２５℃において０．００１以上の化合物である。好ましくは０．０１以上である。更に好ましくは０．１以上である。
【００３９】
上記リン光量子収率は、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。溶液中でのリン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リン光性化合物とは、任意の溶媒のいずれかにおいて上記リン光量子収率が達成されれば良い。
【００４０】
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る。より好ましくはイリジウム錯体系化合物である。
【００４１】
以下に、本発明で用いられるリン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。
【００４２】
【化６】

【００４３】
【化７】

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【化８】

【００４５】
また、別の形態では、ホスト化合物とリン光性化合物の他に、リン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、ホスト化合物とリン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などが挙げられる。
【００４６】
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出来る。
【００４７】
以下、エレクトロルミネッセンス素子（ＥＬ素子）について説明する。
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、エレクトロルミネッセンス素子（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、必要に応じ発光層の他に、正孔輸送層、電子輸送層、陽極バッファー層およ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。
【００４８】
具体的には、
（ｉ）陽極／発光層／陰極
（ii）陽極／正孔輸送層／発光層／陰極
（iii）陽極／発光層／電子輸送層／陰極
（iv）陽極／正孔輸送層／発光層／電子輸送層／陰極
（ｖ）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／陰極などで示される構造がある。
【００４９】
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法など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又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。
【００５０】
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、樹脂など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のち、これをスピンコート法など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。
【００５１】
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。
【００５２】
ここで、本発明に記載のリン光性化合物は、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。
【００５３】
これらのリン光性化合物としては、前記のようなリン光量子収率が、２５℃において０．００１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リン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リン光性化合物をもちいてリン光性化合物の発光、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ＥＬ素子を得ることができる。従って、用いられるリン光性化合物のリン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。
【００５４】
例えば、３５０ｎｍ〜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、緑の領域にリン光をもったイリジウム錯体を用いる事で緑領域に電界発光する有機ＥＬ素子を得ることが出来る。
【００５５】
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とリン光性化合物の他に、リン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とリン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出来る。
【００５６】
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。
【００５７】
一般式（１）〜（６）で表される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。又、Ｔｇは１００度以上であることが好ましい。又、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。
【００５８】
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ＥＬ素子を構成するその他の層について説明する。
【００５９】
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、電子注入層又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など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も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。
【００６０】
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などが挙げられる。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。
【００６１】
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号明細書に記載されている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号公報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）などが挙げられる。
【００６２】
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。
【００６３】
また、ｐ型−Ｓｉ、ｐ型−ＳｉＣなど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法など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、上記材料の一種又は二種以上からなる一層構造であってもよく、同一組成又は異種組成の複数層からなる積層構造であってもよい。
【００６４】
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。
【００６５】
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など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などが挙げられる。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。
【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、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（Ａｌｑ₃）、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）など、及びこれらの金属錯体の中心金属がＩｎ、Ｍｇ、Ｃｕ、Ｃａ、Ｓｎ、Ｇａ又は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、又はそれらの末端がアルキル基やスルホン酸基など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など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。
【００６８】
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法など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一種又は二種以上からなる一層構造であってもよいし、あるいは、同一組成又は異種組成の複数層からなる積層構造であってもよい。
【００６９】
又、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リン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３５０ｎｍから４４０ｎｍ、更に好ましくは３９０ｎｍ〜４１０ｎｍの範囲にある蛍光性化合物が用いられる。
【００７０】
本発明の有機ＥＬ素子に好ましく用いられる基板は、ガラス、プラスチックなど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。本発明のエレクトロルミネッセンス素子に好ましく用いられる基板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。
【００７１】
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。
【００７２】
次に、該有機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ＥＬ素子の作製法について説明する。
【００７３】
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など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。
【００７４】
さらに、陽極と発光層または正孔注入層の間、および、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。
【００７５】
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。
【００７６】
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。
【００７７】
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。
【００７８】
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。
【００７９】
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、および「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）層などのような機能層を有していても良い。
【００８０】
バッファー層は、陰極バッファー層または陽極バッファー層の少なくとも何れか１つの層内に本発明の化合物の少なくとも１種が存在して、発光層として機能してもよい。
【００８１】
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。
【００８２】
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などの金属、ＣｕＩ、インジウムチンオキシド（ＩＴＯ）、ＳｎＯ₂、ＺｎＯなどの導電性透明材料が挙げられる。
【００８３】
上記陽極は、蒸着やスパッタリングなどの方法により、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１０ｎｍ〜２００ｎｍの範囲で選ばれる。
【００８４】
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（Ａｌ₂Ｏ₃）混合物、インジウム、リチウム／アルミニウム混合物、希土類金属などが挙げられる。これらの中で、電子注入性及び酸化など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（Ａｌ₂Ｏ₃）混合物、リチウム／アルミニウム混合物などが好適である。上記陰極は、これらの電極物質を蒸着やスパッタリングなどの方法により、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素子の陽極又は陰極のいずれか一方が、透明又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。
【００８５】
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、蒸着法などがあるが、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などの点から、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、会合構造などにより異なるが、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。
【００８６】
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など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など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。
【００８７】
【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。
【００８８】
実施例１
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Ａｌｑ₃を２００ｍｇ入れ、真空蒸着装置に取付けた。
【００８９】
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。
【００９０】
次いで、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、Ａｌｑ₃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、電子注入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、表１に示す比較用有機ＥＬ素子ＯＬＥＤ１−１を作製した。
【００９２】
上記有機ＥＬ素子ＯＬＥＤ１−１の比較化合物を表１に記載の化合物に替えた以外は有機ＥＬ素子ＯＬＥＤ１−１と同様にして、有機ＥＬ素子ＯＬＥＤ１−２〜１−７を作製した。発光色は青色から緑色を示した。
【００９３】
【化９】

【００９４】
【化１０】

【００９５】
これらの素子を温度２３度、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／ｍ²）および輝度の半減する時間を測定した。発光輝度は有機ＥＬ素子ＯＬＥＤ１−１を１００とした時の相対値で表し、輝度の半減する時間は有機エレクトロルミネッセンス素子ＯＬＥＤ１−１の輝度が半減する時間を１００とした相対値で表した。結果を表１に示す。発光輝度［ｃｄ／ｍ²］については、ミノルタ製ＣＳ−１０００を用いて測定した。
【００９６】
【表１】

【００９７】
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が改善され、特に輝度の半減する時間が大きく改善されているのが分かる。
【００９８】
実施例２（ホスト）
本発明の化合物６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エレクトロルミネッセンス素子ＯＬＥＤ２−１を作製した。
【００９９】
これらの素子を温度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。
【０１００】
上記有機エレクトロルミネッセンス素子ＯＬＥＤ２−１の、ＤＣＭ−２をＱｄ−２またはＢＣｚＶＢｉに替えることによって、それぞれ、緑色または青色の発光が得られた。
【０１０１】
【化１１】

【０１０２】
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ＢＣＰ２００ｍｇを入れ真空蒸着装置に取付けた。
【０１０３】
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。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。
【０１０４】
【化１２】

【０１０５】
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、表２に示す比較用有機ＥＬ素子ＯＬＥＤ３−１を作製した。
【０１０６】
上記有機ＥＬ素子ＯＬＥＤ３−１のＢＣＰを表２に記載の化合物に替えた以外は有機エレクトロルミネッセンス素子ＯＬＥＤ３−１と同様にして、有機エレクトロルミネッセンス素子ＯＬＥＤ３−２〜９を作製した。
【０１０７】
これらの素子を温度２３度、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／ｍ²）、および輝度の半減する時間を測定した。発光輝度は有機エレクトロルミネッセンス素子ＯＬＥＤ３−１を１００とした時の相対値で表し、輝度の半減する時間は有機エレクトロルミネッセンス素子ＯＬＥＤ３−１の輝度が半減する時間を１００とした相対値で表した。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。
【０１０８】
【表２】

【０１０９】
表２より、本発明の化合物を用いた有機ＥＬ素子は、点灯開始時の発光輝度、発光効率及び輝度の半減する時間が改善されているのが分かる。特に、輝度の半減する時間が改善されているのが分かる。
【０１１０】
実施例４（陰極バッファー層）
実施例３で作製した有機エレクトロルミネッセンス素子ＯＬＥＤ３−４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エレクトロルミネッセンス素子（ＯＬＥＤ４−１）を作製した。
【０１１１】
実施例３と同様に点灯開始時の発光輝度（ｃｄ／ｍ²）、および輝度の半減する時間を測定したところ、有機エレクトロルミネッセンス素子ＯＬＥＤ３−１との相対比較で、発光輝度１４２、輝度の半減する時間３２０となった。また、有機エレクトロルミネッセンス素子ＯＬＥＤ３−３〜９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。
【０１１２】
実施例５（三色の発光）
実施例３で用いた有機エレクトロルミネッセンス素子の発光層をＤＰＶＢｉからそれぞれＡｌｑ₃またはＡｌｑ₃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、有機エレクトロルミネッセンス素子を作製し、点灯開始時の発光輝度（ｃｄ／ｍ²）および輝度の半減する時間を測定した。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エレクトロルミネッセンス素子において、点灯開始時の発光輝度（ｃｄ／ｍ²）および輝度の半減する時間の改善が確認された。
【０１１３】
なお、Ａｌｑ₃を発光層に用いた場合は緑色の発光が得られ、Ａｌｑ₃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。
【０１１４】
実施例６
有機ＥＬ素子ＯＬＥＤ６−１〜６−９を以下のように作製した。
【０１１５】
〈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。
【０１１６】
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（リン光性化合物）を１００ｍｇ入れ、さらに別のモリブデン製抵抗加熱ボートにＡｌｑ₃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、Ａｌｑ₃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。
【０１１７】
【化１３】

【０１１８】
次に、ＬｉＦ０．５ｎｍおよびＡｌ１１０ｎｍを蒸着して陰極を形成し、有機ＥＬ素子ＯＬＥＤ６−１を作製した。
【０１１９】
上記において、発光層のＣＢＰを表３にしめ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ＯＬＥＤ６−２〜６−９を作製した。
【０１２０】
〈有機ＥＬ素子ＯＬＥＤ６−１〜６−９の発光輝度および発光寿命の評価〉
有機ＥＬ素子ＯＬＥＤ６−１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リン光性化合物からの緑色の発光を示した。有機ＥＬ素子ＯＬＥＤ６−１〜６−９の温度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および輝度の半減する時間を測定した。発光輝度は有機エレクトロルミネッセンス素子ＯＬＥＤ６−１を１００とした時の相対値で表し、輝度の半減する時間も有機エレクトロルミネッセンス素子ＯＬＥＤ６−１を１００とした時の相対値で表した。発光輝度［ｃｄ／ｍ²］については、ミノルタ製ＣＳ−１０００を用いて測定した。
【０１２１】
【表３】

【０１２２】
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エレクトロルミネッセンス素子は、発光輝度が高く、発光寿命が長いことから、有機ＥＬ素子として非常に有用であることがわかった。
【０１２３】
リン光性化合物をＩｒ−１２またはＩｒ−９に変更した以外は有機ＥＬ素子ＯＬＥＤ６−１〜６−９と同様にして作製した有機ＥＬ素子においても同様の効果が得られた。なお、Ｉｒ−１２を用いた素子からは青色の発光が、Ｉｒ−９を用いた素子からは赤色の発光がえられた。
【０１２４】
実施例７
上記実施例６で作製した有機ＥＬ素子ＯＬＥＤ６−１の電子輸送層ＢＣＰを表４にしめ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ＯＬＥＤ７−１〜７−９を作製した。
【０１２５】
〈有機ＥＬ素子ＯＬＥＤ６−１およびＯＬＥＤ７−１〜７−９の発光輝度および発光寿命の評価〉
有機ＥＬ素子ＯＬＥＤ６−１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リン光性化合物からの緑色の発光を示した。有機ＥＬ素子ＯＬＥＤ６−１の温度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および輝度の半減する時間を測定した。発光輝度は有機エレクトロルミネッセンス素子ＯＬＥＤ６−１を１００とした時の相対値で表し、輝度の半減する時間も有機エレクトロルミネッセンス素子ＯＬＥＤ６−１を１００とした時の相対値で表した。発光輝度［ｃｄ／ｍ²］については、ミノルタ製ＣＳ−１０００を用いて測定した。
【０１２６】
【表４】

【０１２７】
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）に用いたエレクトロルミネッセンス素子は、発光輝度が高く、発光寿命が長いことから、有機ＥＬ素子として非常に有用であることがわかった。
【０１２８】
リン光性化合物をＩｒ−１２またはＩｒ−９に変更した以外は有機ＥＬ素子ＯＬＥＤ７−１〜７−９と同様にして作製した有機ＥＬ素子においても同様の効果が得られた。なお、Ｉｒ−１２を用いた素子からは青色の発光が、Ｉｒ−９を用いた素子からは赤色の発光がえられた。
【０１２９】
実施例８
実施例６で作製したそれぞれ赤色、緑色、青色発光有機エレクトロルミネッセンス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。
【０１３０】
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）。前記複数画素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それぞれ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。
【０１３１】
該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。
【０１３２】
【発明の効果】
本発明により、発光輝度の向上および耐久性の両立を達成した有機エレクトロルミネッセンス素子、および発光輝度の高い、長寿命な表示装置が得られた。
【図面の簡単な説明】
【図１】作製したフルカラー表示装置の表示部の模式図。
【符号の説明】
Ａ 表示部
３ 画素
５ 走査線
６ データ線[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic electroluminescence (hereinafter also abbreviated as organic EL) element and a display device. More specifically, the present invention relates to an organic electroluminescence element having excellent emission luminance and a display device having the organic electroluminescence element of the present invention.
[0002]
[Prior art]
As a light-emitting electronic display device, there is an electroluminescence display (ELD). As a component of ELD, an inorganic electroluminescent element and an organic electroluminescent element are mentioned. Inorganic electroluminescent elements have been used as planar light sources, but an alternating high voltage is required to drive the light emitting elements. An organic electroluminescence element has a structure in which a light emitting layer containing a compound that emits light is sandwiched between a cathode and an anode, and injects electrons and holes into the light emitting layer to recombine excitons. It is an element that emits light by utilizing light emission (fluorescence / phosphorescence) generated when this exciton is deactivated, and can emit light at a voltage of several volts to several tens of volts. Therefore, it has a wide viewing angle, high visibility, and since it is a thin-film type complete solid-state device, it is attracting attention from the viewpoints of space saving and portability.
[0003]
However, for organic EL elements for practical use in the future, development of organic EL elements that emit light efficiently and with high luminance with lower power consumption is desired.
[0004]
Various organic EL elements have been reported so far. For example, Appl. Phys. Lett. , Vol. 51, 913 or a combination of a hole injection layer described in JP-A-59-194393 and an organic light-emitting layer, a hole injection layer described in JP-A-63-295695, an electron injection transport layer, , Jpn. Journal of Applied Physics, vol. 127, no. 2 A combination of the hole transfer layer, the light emitting layer, and the electron transfer layer described on pages 269 to 271 is disclosed. However, a device with higher luminance is demanded, and further improvement in energy conversion efficiency and light emission quantum efficiency is expected. In addition, a problem that the light emission life is short has been pointed out.
[0005]
The cause of this deterioration in luminance over time has not been fully elucidated, but the electroluminescent device that emits light decomposes the organic compound itself that constitutes the thin film by the light emitted by itself and the heat generated at that time. Factors derived from organic compounds, which are organic EL element materials, such as crystallization of organic compounds, have also been pointed out.
[0006]
Moreover, at present, electron transport materials have little knowledge, and in combination with the use of antibonding orbitals, no useful high-performance electron transport materials that can withstand practical use have been found. For example, the research group at Kyushu University includes 2- (4-biphenyl) -5- (4-t-butylphenyl) -1,3,4-oxadizole (t-BuPBD), which is an oxadiazole derivative, 1,3-bis (4-t-butylphenyl-1,3,4-oxadizodyl) biphenylene (OXD-1), 1,3-bis (4) which are oxadiazole dimer derivatives with improved thin film stability -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 produced a white light emitting device by using a triazole-based electron transport material having excellent electron blocking properties (Science, 3 March 1995, Vol. 267, p. 1332). Further, JP-A-5-331459 describes that phenanthroline derivatives are useful as electron transport materials.
[0007]
However, the conventional electron transporting material has a low thin film forming ability and easily crystallizes, so that there is a problem that the light emitting element is destroyed, and the element performance that can withstand practical use cannot be expressed.
[0008]
In addition, a technique has been reported in which the luminous efficiency is improved by forming the luminous layer with a host compound and a small amount of phosphor. For example, in Japanese Patent No. 3093796, a small amount of a phosphor is doped into a stilbene derivative, a distyrylarylene derivative or a tristyrylarylene derivative to achieve improvement in light emission luminance and a longer device lifetime.
[0009]
An 8-hydroxyquinoline aluminum complex as a host compound, a device having an organic light-emitting layer doped with a small amount of phosphor (Japanese Patent Laid-Open No. 63-264692), an 8-hydroxyquinoline aluminum complex as a host compound, An element having an organic light emitting layer doped with a quinacridone dye (Japanese Patent Laid-Open No. 3-255190) is known. As described above, the emission luminance is improved by doping a phosphor having a high fluorescence quantum yield as compared with the conventional device.
[0010]
However, the light emission from the small amount of the phosphor to be doped is light emission from the excited singlet, and when the light emission from the excited singlet is used, the generation ratio of the singlet exciton and the triplet exciton is 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 an organic EL device using phosphorescence emission from an excited triplet was reported from Princeton University (MA Baldo et al., Nature, 395, 151-154 (1998)), room temperature. In recent years, research on phosphorescent materials has been actively conducted (for example, MA Baldo et al., Nature, 403, 17, 750-753 (2000), US Pat. No. 6,097). , No. 147). When the excited triplet is used, the upper limit of the internal quantum efficiency is 100%. In principle, the luminous efficiency is up to four times that of the excited singlet, and almost the same performance as a cold cathode tube is obtained. It can be applied to and is attracting attention.
[0011]
Of course, the host when using the phosphorescent compound as a dopant needs to have an emission maximum wavelength in a region shorter than the emission maximum wavelength of the phosphorescent compound. I know that there is.
[0012]
The 10th International Works on Inorganic and Organic Electroluminescence (EL'00, Hamamatsu) reports on several phosphorescent compounds. For example, Ikai et al. Uses a hole transporting compound as a host of a phosphorescent compound. In addition, M.M. E. Thompson et al. Use various electron transport materials as a host of phosphorescent compounds doped with a novel iridium complex. Furthermore, Tsutsui et al. Have obtained high luminous efficiency by introducing a hole blocking layer.
[0013]
Japanese Patent Application Laid-Open No. 2001-192651 describes an example in which a benzene derivative containing a condensed arylene group is used as a host of a phosphorescent compound, but in this case as well, the initial characteristics such as emission luminance are relatively good. However, it has been found that there is a problem with the light emission lifetime.
[0014]
The hole blocking layer is structurally the same as the electron transport layer used in a normal organic EL device, but the function of holes leaking from the light emitting layer to the cathode side rather than the electron transport function. It is named as a hole block layer because it has a powerful function of preventing movement, and can be interpreted as a kind of electron transport layer. Therefore, in this 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.
[0015]
Examples of the host compound of the phosphorescent compound include C.I. Adachi et al. , Appl. Phys. Lett. 77, page 904 (2000), etc., but a new approach is required for the properties required for the host compound to obtain a high-brightness organic electroluminescence device. .
[0016]
However, none of the reports has obtained a configuration that can achieve both improvement in light emission luminance and durability of the device.
[0017]
[Problems to be solved by the invention]
Therefore, the present invention has been made for the purpose of achieving both improvement in light emission luminance and durability of the device using a 1,2,3-triphenylbenzene compound. -Use of a triphenylbenzene compound as a host compound for phosphorescence emission and / or use of a 1,2,3-triphenylbenzene compound as an electron transport material (hole blocker) to improve emission luminance and durability The present invention provides an organic electroluminescent element that achieves both compatibility and a display device with high emission luminance and long life using the organic electroluminescent element of the present invention.
[0018]
[Means for Solving the Problems]
The above object of the present invention has been achieved by the following constitutions.
[0019]
1. The organic electroluminescent element which has a light emitting layer containing a host compound and a phosphorescent compound, A host compound is a compound represented by the said General formula (1), The organic electroluminescent element characterized by the above-mentioned.
[0021]
  2. General formula (1)soWherein the compound represented is contained in an electron transport layer1The organic electroluminescent element of description.
[0023]
  3. The phosphorescent compound is an iridium compound, an osmium compound or a platinum compound,1The organic electroluminescent element of description.
[0024]
  4. The phosphorescent compound is an iridium compound,3The organic electroluminescent element of description.
[0025]
  5. 1 to4A display device comprising the organic electroluminescence element according to any one of the above.
  6). An organic electroluminescence device having a light emitting layer and an electron transport layer, wherein the light emitting layer contains a phosphorescent compound, and the electron transport layer contains a compound represented by the general formula (1). element.
[0026]
The present invention will be described in more detail. First, the compounds represented by general formula (1) and general formula (2) will be described.
[0027]
  In the general formulas (1) and (2), R₁~ R_ThreeAnd R₁₁, R₁₂Represented byBaseAs 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.)ButNamed,AlkylThe group may be further substituted with an arbitrary substituent. Also adjacentAlkylGroups may be condensed with each other to form a ring.
[0028]
  R₁~ R_ThreeAnd R₁₁, R₁₂Represented byBaseOf these, particularly preferred are alkyl groups orIs waterIt is an elementary atom.
[0029]
In general formula (1) and general formula (2), Ar₁~ Ar_ThreeAnd Ar₁₁~ Ar₁₄Of the substituted or unsubstituted phenyl groups represented by₁~ R_ThreeThe substituent described in the above can be applied.
[0030]
The compound of the present invention is a compound having strong fluorescence in a solid state, is excellent in electroluminescence, and can be effectively used as a light emitting material. In addition, since the electron injection property and the electron transport property from the metal electrode are very excellent, in the device using another light emitting material or the compound of the present invention as a light emitting material, the compound of the present invention is converted into an electron transporting material ( When used as a hole blocker), it exhibits excellent luminous efficiency.
[0031]
  Specific belowOf the present inventionCompoundAnd related compoundsExamples of the present inventionCompound ofIs not limited to these.
[0032]
[Chemical Formula 3]

[0033]
[Formula 4]

[0034]
[Chemical formula 5]

[0035]
These compounds are described in Tetrahedron Letters 41 (2000) 4261-4264 and J. Am. Am. Chem. Soc. 1997, 119, 7291-7302 Angew. Chem. , Int. Ed. Engl. 36 (1997) 1740 and the like.
[0036]
In addition, as a result of intensive studies on the host compound of the phosphorescent compound, the present inventors made an organic electroluminescence device using the 1,2,3-triphenylbenzene compound of the present invention as the host compound. In some cases, it has been found that the light emission luminance and lifetime of the device are improved.
[0037]
The host compound of the present invention is a compound having the largest mixing ratio (mass) in the 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 types 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. Furthermore, if a light emitting layer is comprised from 3 types of compound A, compound B, and compound C, and the mixing ratio is A: B: C = 5: 10: 85, compound A and compound B are dopant compounds, Compound C is a host compound. The phosphorescent compound in the present invention is a kind of dopant compound.
[0038]
The phosphorescent compound of the present invention is a compound in which light emission from an excited triplet is observed, and is a compound having a phosphorescence quantum yield of 0.001 or more at 25 ° C. Preferably it is 0.01 or more. More preferably, it is 0.1 or more.
[0039]
The phosphorescence quantum yield can be measured by the method described in Spectroscopic II, page 398 (1992 edition, Maruzen) of Experimental Chemistry Course 4 of the 4th edition. Although the phosphorescence quantum yield in a solution can be measured using various solvents, the phosphorescence quantum yield used in the present invention is only required to achieve the phosphorescence quantum yield in any solvent.
[0040]
A complex compound containing a Group VIII metal in the periodic table of elements is preferable, and an iridium, osmium, or platinum complex compound is more preferable. More preferred are iridium complex compounds.
[0041]
Specific examples of the phosphorescent compound used in the present invention are shown below, but are not limited thereto. These compounds are described, for example, in Inorg. Chem. 40, 1704-1711, and the like.
[0042]
[Chemical 6]

[0043]
[Chemical 7]

[0044]
[Chemical 8]

[0045]
In another embodiment, in addition to the host compound and the phosphorescent compound, at least one 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, electroluminescence as an organic EL element can be emitted from the fluorescent compound by energy transfer from the host compound and the phosphorescent compound. Preferred as the fluorescent compound is one 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, squalium dyes, oxobenzanthracene dyes, fluorescein dyes, rhodamine dyes, pyrylium dyes, perylene dyes, stilbene dyes , Polythiophene dyes, or rare earth complex phosphors.
[0046]
The fluorescence quantum yield here can also be measured by the method described in page 362 (1992 version, Maruzen) of Spectroscopic II of the Fourth Edition Experimental Chemistry Course 7.
[0047]
Hereinafter, the electroluminescence element (EL element) will be described.
In a broad sense, the light emitting layer in an EL element refers to a layer that emits light when a current is passed through an electrode composed of a cathode and an anode. Specifically, it refers to a layer containing a fluorescent compound that emits light when an electric current is passed through an electrode composed of a cathode and an anode. Usually, an electroluminescence element (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 electron transport layer, an anode buffer layer, a cathode buffer layer, and the like in addition to the light emitting layer as required, and has a structure sandwiched between a cathode and an anode.
[0048]
In particular,
(I) Anode / light emitting layer / cathode
(Ii) Anode / hole transport layer / light emitting layer / cathode
(Iii) Anode / light emitting layer / electron transport layer / cathode
(Iv) Anode / hole transport layer / light emitting layer / electron transport layer / cathode
(V) There is a structure represented by anode / anode buffer layer / hole transport layer / light emitting layer / electron transport layer / cathode buffer layer / cathode.
[0049]
As a method of forming a light emitting layer using the above compound, there is a method of forming a thin film by a known method such as a vapor deposition method, a spin coat method, a cast method, an LB method, etc. preferable. Here, the molecular deposition film refers to a thin film formed by deposition from the gas phase state of the compound or a film formed by solidification from the molten state or liquid phase state of the compound. Normally, this molecular deposited film can be distinguished from a thin film (molecular accumulated film) formed by the LB method by a difference in aggregated structure and higher order structure and a functional difference resulting therefrom.
[0050]
Further, as described in JP-A-57-51781, this light-emitting layer is prepared by dissolving the above compound as a light-emitting material together with a binder such as a resin in a solvent, and then using this as a spin coating method or the like. It can be obtained by coating with a thin film.
[0051]
There is no restriction | limiting in particular about the film thickness of the light emitting layer formed in this way, Although it can select suitably according to a condition, Usually, it is the range of 5 nm-5 micrometers.
[0052]
Here, the phosphorescent compound described in the present invention is specifically a heavy metal complex compound as described above, preferably a complex system having a group VIII metal as a central metal in the periodic table of elements. A compound, and more preferably an osmium, iridium or platinum complex compound.
[0053]
As these phosphorescent compounds, the phosphorescence quantum yield as described above is 0.001 or more at 25 ° C., and the phosphorescence emission maximum wavelength is longer than the fluorescence maximum wavelength of the fluorescent compound serving as the host. Thus, for example, the emission maximum of the phosphorescent compound using the phosphorescent compound having a wavelength longer than the emission maximum wavelength of the fluorescent compound serving as the host, that is, utilizing the triplet state, the fluorescence maximum of the host compound. An EL element that emits electroluminescence at a wavelength longer than the wavelength can be obtained. Accordingly, the phosphorescent maximum wavelength of the phosphorescent compound to be used is not particularly limited, and in principle can be obtained by selecting a central metal, a ligand, a ligand substituent, and the like. The emission wavelength can be changed.
[0054]
For example, a fluorescent compound having a fluorescence maximum wavelength in the 350 nm to 440 nm region is used as a host compound, and an organic EL element that emits light in the green region is obtained by using, for example, an iridium complex having phosphorescence in the green region. I can do it.
[0055]
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. The fluorescent compound B may contain at least one kind of fluorescent compound B, and electroluminescence as an 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
[0056]
The color emitted by the fluorescent compound of the present specification is shown in FIG. 4.16 on page 108 of “New Color Science Handbook” (edited by the Japan Society for Color Science, University of Tokyo Press, 1985). It is determined by the color when the result measured by Minolta) is applied to the CIE chromaticity coordinates.
[0057]
The molecular weight of the host compounds represented by the general formulas (1) to (6) is preferably 600 to 2000. If the molecular weight is in this molecular weight range, Tg (glass transition temperature) is increased, and thermal stability is improved. The device life is improved. More preferably, the molecular weight is 800-2000. Moreover, it is preferable that Tg is 100 degree | times or more. In addition, when the molecular weight is within this range, the light emitting layer can be easily produced by a vacuum deposition method, and the production of the organic EL element becomes easy. Furthermore, the thermal stability of the fluorescent compound in the organic EL element is also improved.
[0058]
Next, other layers constituting the 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.
[0059]
The hole injection layer and the hole transport layer have a function of transmitting the 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. Therefore, a lot of holes are injected into the light emitting layer with a lower electric field, and the electrons injected into the light emitting layer from the cathode, the electron injection layer, or the electron transport layer are converted into the light emitting layer and the hole injection layer or the hole transport layer. Due to the barrier of electrons existing at the interface, the device has excellent light emitting performance, such as being accumulated at the interface in the light emitting layer and improving the light emission efficiency. The material of the hole injection layer and hole transport layer (hereinafter referred to as hole injection material and hole transport material) has a property of transmitting the holes injected from the anode to the light emitting layer. If it is a thing, there will be no restriction | limiting in particular, In the conventionally known thing used for the hole injection layer of an electroluminescent material, and the hole injection layer of a EL element, and a hole transport layer, it is conventionally used as a hole charge injection transport material. Any one can be selected and used.
[0060]
The hole injection material and the hole transport material have either hole injection or transport or electron barrier properties, and may be either organic or inorganic. Examples of the hole injection material and hole transport material include triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, and oxazoles. Derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aniline copolymers, and conductive polymer oligomers, particularly thiophene oligomers. 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 can be used. preferable.
[0061]
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; Bis (4-di-p-tolylaminophenyl) cyclohexane; N, N, N ′, N′-tetra-p-tolyl-4,4′-diaminobiphenyl; 1,1-bis (4-di-p- Tolylaminophenyl) -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 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 further described in US Pat. No. 5,061,569 Having two condensed aromatic rings in the molecule, for example, 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (NPD), JP-A-4-3 4,4 ′, 4 ″ -tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine in which three triphenylamine units described in Japanese Patent No. 8688 are linked in a starburst type ( MTDATA).
[0062]
Furthermore, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used.
[0063]
In addition, 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, or an LB method. Can be formed. Although there is no restriction | limiting in particular about the film thickness of a positive hole injection layer and a positive hole transport layer, Usually, it is about 5 nm-5 micrometers. The hole injection layer and hole transport layer may have a single layer structure composed of one or more of the above materials, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions.
[0064]
Furthermore, the electron transport layer used as necessary only needs to have a function of transmitting electrons injected from the cathode to the light emitting layer, and the material thereof is selected from any conventionally known compounds. Can be used.
[0065]
Examples of materials used for this electron transport layer (hereinafter referred to as electron transport materials) include heterocyclic tetracarboxylic acid anhydrides such as nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, naphthalene perylene, carbodiimides, Examples include fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, and oxadiazole derivatives. Furthermore, in the above oxadiazole derivative, a thiadiazole derivative in which the 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 an electron transport material.
[0066]
Furthermore, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used.
[0067]
Further, metal complexes of 8-quinolinol derivatives such as tris (8-quinolinol) aluminum (Alq_Three), 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 metal complexes in which the central metal of these metal complexes is replaced with In, Mg, Cu, Ca, Sn, Ga or Pb are also used as electron transport materials. Can be used. In addition, metal-free or metal phthalocyanine, or those having terminal ends substituted with an alkyl group or a sulfonic acid group can be preferably used as the electron transport material. In addition, the distyrylpyrazine derivative exemplified as the material of the light emitting layer can also be used as an electron transport material, and similarly to the hole injection layer and the hole transport layer, inorganic such as n-type-Si and n-type-SiC. A semiconductor can also be used as an electron transport material.
[0068]
The electron transport layer can be formed by forming the above compound by a known thin film forming method such as a vacuum deposition method, a spin coating method, a casting method, or an LB method. Although the film thickness as an electron carrying layer does not have a restriction | limiting in particular, Usually, it selects in 5 nm-5 micrometers. The electron transport layer may have a single layer structure composed of one or two 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.
[0069]
Further, in the present invention, the fluorescent compound is not limited to the light emitting layer alone, and the hole transport layer adjacent to the light emitting layer, or the fluorescent compound serving as a host compound of the phosphorescent compound in the electron transport layer; At least one fluorescent compound having a fluorescent maximum wavelength may be contained in the same region, whereby the luminous efficiency of the EL element can be further increased. As the fluorescent compound contained in these hole transport layer and electron transport layer, the fluorescence maximum wavelength is in the range of 350 nm to 440 nm, more preferably in the range of 390 nm to 410 nm, as in the light emitting layer. A compound is used.
[0070]
The substrate preferably used for the organic EL device of the present invention is not particularly limited in the kind of glass, plastic and the like, and is not particularly limited as long as it is transparent. Examples of the substrate preferably used in the electroluminescent device of the present invention include glass, quartz, and a light transmissive plastic film.
[0071]
Examples of the light transmissive plastic film include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide, polyetheretherketone, polyphenylene sulfide, polyarylate, polyimide, and polycarbonate (PC). And a film made of cellulose triacetate (TAC), cellulose acetate propionate (CAP), or the like.
[0072]
Next, a suitable example for producing the organic EL element will be described. As an example, a method for manufacturing an EL element composed of the anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / electron injection layer / cathode will be described.
[0073]
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 film thickness of 1 μm or less, preferably 10 to 200 nm. An anode is produced. Next, a thin film comprising a hole injection layer, a hole transport layer, a light emitting layer, and an electron transport layer / electron injection layer, which is a device material, is formed thereon.
[0074]
Furthermore, a buffer layer (electrode interface layer) may be present between the anode and the light emitting layer or hole injection layer and between the cathode and the light emitting layer or electron injection layer.
[0075]
The buffer layer is a layer provided between the electrode and the organic layer in order to lower the driving voltage and improve the luminous efficiency. “The organic EL element and its forefront of industrialization (published by NTS Corporation on November 30, 1998) 2) Chapter 2 “Electrode Materials” (pages 123 to 166) in detail, and includes an anode buffer layer and a cathode buffer layer.
[0076]
The details of the anode buffer layer are also described in JP-A-9-45479, 9-260062, and 8-288069. Specific examples thereof include a phthalocyanine buffer layer represented by copper phthalocyanine, vanadium oxide. And an oxide buffer layer, an amorphous carbon buffer layer, and a polymer buffer layer using a conductive polymer such as polyaniline (emeraldine) or polythiophene.
[0077]
The details of the cathode buffer layer are also described in JP-A-6-325871, JP-A-9-17574, JP-A-10-74586, and the like. Specifically, a metal buffer layer represented by strontium, aluminum and the like, Examples thereof include an alkali metal compound buffer layer typified by lithium fluoride, an alkaline earth metal compound buffer layer typified by magnesium fluoride, an oxide buffer layer typified by aluminum oxide and lithium oxide, and the like.
[0078]
The buffer layer is preferably a very thin film, and depending on the material, the film thickness is preferably in the range of 0.1 to 100 nm.
[0079]
Further, in addition to the basic constituent layer, a layer having other functions may be laminated as required. For example, JP-A-11-204258, JP-A-11-204359, and “Organic EL device and its industrialization front line ( It may have a functional layer such as a hole blocking layer described on page 237 of “November 30, 1998, NTS Corporation”.
[0080]
The buffer layer may function as a light emitting layer when at least one of the compounds of the present invention is present in at least one of the cathode buffer layer and the anode buffer layer.
[0081]
Next, the electrode of the organic EL element will be described. The electrode of the organic EL element consists of a cathode and an anode.
[0082]
As the anode in the organic EL element, an electrode material made of a metal, an alloy, an electrically conductive compound, or a mixture thereof having a high work function (4 eV or more) is preferably used. Specific examples of such electrode materials include metals such as Au, CuI, indium tin oxide (ITO), SnO.₂And conductive transparent materials such as ZnO.
[0083]
The anode may be formed by a thin film of these electrode materials by a method such as vapor deposition or sputtering, and a pattern having a desired shape may be formed by a photolithography method, or (100 μm) when pattern accuracy is not so required. As described above, a pattern may be formed through a mask having a desired shape when the electrode material is deposited or sputtered. When light emission is extracted from the anode, it is desirable that the transmittance is greater than 10%, and the sheet resistance as the anode is preferably several hundred Ω / □ or less. Further, although the film thickness depends on the material, it is usually selected in the range of 10 nm to 1 μm, preferably 10 nm to 200 nm.
[0084]
On the other hand, as the cathode, a material having a low work function (4 eV or less) metal (referred to as an electron injecting metal), an alloy, an electrically conductive compound, and a mixture thereof as an electrode material is used. Specific examples of such electrode materials include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al₂O_Three) Mixtures, indium, lithium / aluminum mixtures, rare earth metals and the like. Among these, a mixture of an electron injecting metal and a second metal which is a stable metal having a larger work function value than this from the viewpoint of durability against electron injecting and oxidation, for example, a magnesium / silver mixture, magnesium / Aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al₂O_Three) Mixtures, lithium / aluminum mixtures and the like are preferred. The cathode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition 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 addition, in order to transmit light emission, if either one of the anode or the cathode of the organic EL element is transparent or translucent, the light emission efficiency is improved, which is convenient.
[0085]
Next, a method for manufacturing the organic EL element will be described.
As the thinning method, there are a spin coating method, a casting method, a vapor deposition method and the like as described above, but a vacuum vapor deposition method is preferable because a homogeneous film can be easily obtained and pinholes are hardly generated. When a vacuum deposition method is employed 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, etc., but generally a boat heating temperature of 50 to 450 ° C., vacuum Degree 10^-6-10^-3It is desirable to select appropriately within the ranges of Pa, vapor deposition rate of 0.01 to 50 nm / second, substrate temperature of −50 to 300 ° C., and film thickness of 5 nm to 5 μm.
[0086]
As described above, a method such as vapor deposition or sputtering of a thin film made of a desired electrode material, for example, an anode material, on a suitable substrate so as to have a film thickness of 1 μm or less, preferably 10 to 200 nm. After forming an anode by forming a thin film of each layer comprising a hole injection layer, a hole transport layer, a light emitting layer, and an electron transport layer / electron injection layer as described above on the anode, A desired organic EL device can be obtained by forming a thin film made of a cathode material to a thickness of 1 μm or less, preferably 50 to 200 nm by a method such as vapor deposition or sputtering, and providing a cathode. . The organic EL device is preferably produced from the hole injection layer to the cathode in this manner consistently by a single evacuation. However, the production order is reversed so that the cathode, the electron injection layer, the light emitting layer, It is also possible to produce the hole injection layer and the anode in this order. In the case of applying a DC voltage to the organic EL device thus obtained, 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. Further, even when a voltage is applied with 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 alternating current waveform to be applied may be arbitrary.
[0087]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, the aspect of this invention is not limited to this.
[0088]
Example 1
After patterning on a substrate (made by NH Techno Glass Co., Ltd .: NA-45) with a 150 nm ITO film on glass as the anode, the transparent support substrate provided with this ITO transparent electrode was ultrasonically cleaned with i-propyl alcohol. Then, it was dried with dry nitrogen gas, and UV ozone cleaning was performed for 5 minutes. This transparent support substrate was fixed to a substrate holder of a commercially available vacuum deposition apparatus, while 200 mg of α-NPD was put in a molybdenum resistance heating boat, and 200 mg of Comparative Compound 1 was put in another molybdenum resistance heating boat. Add 200 mg of bathocuproine (BCP) to a resistance heating boat made of molybdenum, and add Alq to another resistance heating boat made of molybdenum._Three200 mg was added and attached to a vacuum deposition apparatus.
[0089]
The vacuum chamber is then 4 × 10^-FourAfter reducing the pressure to Pa, the heating boat containing α-NPD was energized and heated, and deposited at a film thickness of 50 nm on a transparent support substrate at a deposition rate of 0.1 to 0.3 nm / sec. Provided. The substrate temperature during vapor deposition was room temperature.
[0090]
Next, the heating boat containing the comparative compound 1 was energized and heated to provide a 30 nm light emitting layer at a deposition rate of 0.1 to 0.3 nm / sec. Further, the heating boat containing BCP was heated by energization to provide a hole blocking layer having a thickness of 10 nm. Furthermore, Alq_ThreeThe heating boat containing was energized and heated to provide an electron transport layer having a thickness of 20 nm at a deposition rate of 0.1 to 0.3 nm / sec.
[0091]
Next, a vacuum chamber is opened, and a stainless steel rectangular perforated mask is placed on the electron injection layer. On the other hand, 3 g of magnesium is put into a molybdenum resistance heating boat, and 0.02 of silver is put into a tungsten vapor deposition basket. Put 5g and again vacuum tank 2 × 10^-FourAfter depressurizing to Pa, power was applied to the magnesium-containing boat 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. The organic EL element OLED1-1 for comparison shown in Table 1 was produced by vapor-depositing silver to obtain a cathode made of the mixture of magnesium and silver.
[0092]
Organic EL elements OLED1-2 to 1-7 were produced in the same manner as the organic EL element OLED1-1 except that the comparative compounds of the organic EL element OLED1-1 were changed to the compounds shown in Table 1. The emission color was blue to green.
[0093]
[Chemical 9]

[0094]
Embedded image

[0095]
These elements are continuously lit by applying a DC voltage of 10 V in a dry nitrogen gas atmosphere at a temperature of 23 ° C., and light emission luminance (cd / m at the start of lighting)²) And the time to reduce the luminance by half. The light emission luminance is expressed as a relative value when the organic EL element OLED1-1 is 100, and the time when the luminance is halved is expressed as a relative value when the time when the luminance of the organic electroluminescence element OLED1-1 is halved is 100. The results are shown in Table 1. Luminance [cd / m²] Was measured using Minolta CS-1000.
[0096]
[Table 1]

[0097]
From Table 1, the organic EL device using the compound of the present invention has improved emission luminance at the start of lighting, and particularly greatly improved the time to reduce the luminance by half, compared with the organic EL device using a comparative compound having a similar structure. You can see that.
[0098]
Example 2 (Host)
Organic electroluminescent element OLED2-1 was produced by the same method as Example 1 except using the light emitting layer with a film thickness of 30 nm which vapor-deposited the compound 6 of this invention and DCM-2 by the mass ratio of 100: 1.
[0099]
When these devices were applied with a DC voltage of 10 V in a dry nitrogen gas atmosphere at a temperature of 23 degrees, red light emission was obtained.
[0100]
Green or blue light emission was obtained by changing DCM-2 of the organic electroluminescent element OLED2-1 to Qd-2 or BCzVBi, respectively.
[0101]
Embedded image

[0102]
Example 3 (Electron Transport Material)
After patterning on a substrate (made by NH Techno Glass Co., Ltd .: NA-45) with a 150 nm ITO film on glass as the anode, the transparent support substrate provided with this ITO transparent electrode was ultrasonically cleaned with i-propyl alcohol. Then, it was dried with dry nitrogen gas, and UV ozone cleaning was performed for 5 minutes. This transparent support substrate is fixed to a substrate holder of a commercially available vacuum deposition apparatus. Meanwhile, 200 mg of m-MTDATXA is put into a molybdenum resistance heating boat, and 200 mg of DPVBi is put into another molybdenum resistance heating boat. 200 mg of BCP was put in a resistance heating boat made of molybdenum and attached to a vacuum deposition apparatus.
[0103]
The vacuum chamber is then 4 × 10^-FourAfter depressurizing to Pa, energize and heat the heating boat containing m-MTDATXA, deposit it on a transparent support substrate at a film thickness of 25 nm at a deposition rate of 0.1 to 0.3 nm / sec, and further contain DPVBi. Further, the heating boat was energized and heated, and vapor deposition was performed at a deposition rate of 0.1 to 0.3 nm / sec with a film thickness of 20 nm to provide a light emitting layer. The substrate temperature during vapor deposition was room temperature. Then, the heating boat containing 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.
[0104]
Embedded image

[0105]
Next, a vacuum chamber is opened, and a stainless steel rectangular perforated mask is placed on the electron transport layer. On the other hand, 3 g of magnesium is placed in a molybdenum resistance heating boat, and 0.02 of silver is placed in a tungsten vapor deposition basket. Put 5g and again vacuum tank 2 × 10^-FourAfter depressurizing to Pa, power was applied to the magnesium-containing boat 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. The organic EL element OLED3-1 for comparison shown in Table 2 was produced by vapor-depositing silver to form a cathode made of the mixture of magnesium and silver.
[0106]
Organic electroluminescent elements OLED3-2 to 9 were produced in the same manner as organic electroluminescent element OLED3-1 except that the BCP of organic EL element OLED3-1 was changed to the compounds shown in Table 2.
[0107]
These elements are continuously lit by applying a DC voltage of 10 V in a dry nitrogen gas atmosphere at a temperature of 23 ° C., and light emission luminance (cd / m at the start of lighting)²), And the time to reduce the luminance by half. The light emission luminance is expressed as a relative value when the organic electroluminescence element OLED3-1 is 100, and the time when the luminance is halved is expressed as a relative value when the time when the luminance of the organic electroluminescence element OLED3-1 is halved is 100. The results are shown in Table 2. In all elements, the emission color was blue.
[0108]
[Table 2]

[0109]
From Table 2, it can be seen that the organic EL device using the compound of the present invention has improved the light emission luminance at the start of lighting, the light emission efficiency, and the time to reduce the luminance by half. In particular, it can be seen that the time for halving the luminance is improved.
[0110]
Example 4 (cathode buffer layer)
Except that the cathode of the organic electroluminescence element OLED3-4 produced in Example 3 was replaced with Al, and a cathode buffer layer was provided by depositing lithium fluoride with a thickness of 0.5 nm between the electron transport layer and the cathode. Thus, an organic electroluminescence element (OLED4-1) was produced.
[0111]
As in Example 3, the light emission luminance at the start of lighting (cd / m²), And the time when the luminance is reduced by half, the light emission luminance 142 and the time when the luminance is reduced by half are 320 in comparison with the organic electroluminescence element OLED3-1. Similarly, organic electroluminescent elements OLED3-3 to 9-9 were more effective when a cathode buffer layer was introduced.
[0112]
Example 5 (Three colors of light emission)
The light emitting layer of the organic electroluminescence element used in Example 3 was changed from DPVBi to Alq._ThreeOr Alq_ThreeAnd DCM-2 were replaced with a light emitting layer deposited at a mass ratio of 100: 1 in the same manner to produce an organic electroluminescence device, and the light emission luminance (cd / m at the start of lighting)²) And the time to reduce the luminance by half. As a result, as in Example 3, in the organic electroluminescence device using the compound of the present invention for the electron transport layer, the emission luminance (cd / m at the start of lighting)²) And an improvement in the time to reduce the luminance by half.
[0113]
Alq_ThreeIs used for the light emitting layer, green light emission is obtained, and Alq_ThreeAnd DCM-2 were co-evaporated at 100: 1, and red light emission was obtained.
[0114]
Example 6
Organic EL elements OLED6-1 to 6-9 were produced as follows.
[0115]
<Production of organic EL element>
After patterning on a substrate (NA-45 manufactured by NH Techno Glass Co., Ltd.) having a film of 150 nm of ITO (indium tin oxide) formed on a glass substrate of 100 mm × 100 mm × 1.1 mm as an anode, this ITO transparent electrode was provided. The transparent support substrate was ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and subjected to UV ozone cleaning for 5 minutes.
[0116]
This transparent support substrate is fixed to a substrate holder of a commercially available vacuum deposition apparatus, while 200 mg of α-NPD is put into a molybdenum resistance heating boat, and 200 mg of CBP is put into another resistance heating boat made of molybdenum. 200 mg bathocuproin (BCP) is put into a resistance heating boat, 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._Three200 mg was added and attached to a vacuum deposition apparatus. The vacuum chamber is then 4 × 10^-FourAfter depressurizing to Pa, the heating boat containing α-NPD was energized and heated, and deposited on a transparent support substrate at a deposition rate of 0.1 nm / sec to provide a 45 nm thick hole transport layer. Further, 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 have a film thickness of 20 nm. A light emitting layer was provided. In addition, the substrate temperature at the time of vapor deposition was room temperature. Further, an electron transport layer that also serves as a hole blocking function with a film thickness of 10 nm is provided by energizing and heating the heating boat containing BCP and depositing on the light emitting layer at a deposition rate of 0.1 nm / sec. It was. In addition, Alq_ThreeThe heating boat containing was heated by energizing, and was deposited on the electron transport layer at a 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.
[0117]
Embedded image

[0118]
Next, LiF 0.5nm and Al110nm were vapor-deposited, the cathode was formed, and the organic EL element OLED6-1 was produced.
[0119]
Organic EL elements OLED6-2 to 6-9 were produced in exactly the same manner except that the CBP of the light emitting layer was replaced with the compounds shown in Table 3 above.
[0120]
<Evaluation of light emission luminance and light emission lifetime of organic EL elements OLED6-1 to 6-9>
In the organic EL element OLED6-1, current started to flow at an initial driving voltage of 3 V, and green light was emitted from the phosphorescent compound that is a dopant of the light emitting layer. The luminance of the organic EL elements OLED6-1 to 6-9 and the time for halving the luminance when a 9 V DC voltage was applied in a dry nitrogen gas atmosphere at 23 ° C. were measured. The light emission luminance is expressed as a relative value when the organic electroluminescence element OLED6-1 is set to 100, and the time during which the luminance is reduced by half is also expressed as a relative value when the organic electroluminescence element OLED6-1 is set as 100. Luminance [cd / m²] Was measured using Minolta CS-1000.
[0121]
[Table 3]

[0122]
As is apparent from Table 3, the electroluminescence device using the compound of the present invention as a host has a high emission luminance and a long emission lifetime, and thus was found to be very useful as an organic EL device.
[0123]
The same effect was obtained also in the organic EL device produced in the same manner as the organic EL devices OLED6-1 to 6-9 except that the phosphorescent compound was changed to Ir-12 or Ir-9. Note that blue light was emitted from the element using Ir-12, and red light was emitted from the element using Ir-9.
[0124]
Example 7
Organic EL elements OLED7-1 to 7-9 were produced in exactly the same manner except that the electron transport layer BCP of the organic EL element OLED6-1 produced in Example 6 was replaced with the compounds shown in Table 4.
[0125]
<Evaluation of Luminous Luminance and Luminous Life of Organic EL Elements OLED6-1 and OLEDs 7-1 to 7-9>
In the organic EL element OLED6-1, current started to flow at an initial driving voltage of 3 V, and green light was emitted from the phosphorescent compound that is a dopant of the light emitting layer. When the organic EL element OLED6-1 was applied with a 9 V DC voltage in a dry nitrogen gas atmosphere at a temperature of 23 ° C., the light emission luminance and the time to reduce the luminance by half were measured. The light emission luminance is expressed as a relative value when the organic electroluminescence element OLED6-1 is set to 100, and the time during which the luminance is reduced by half is also expressed as a relative value when the organic electroluminescence element OLED6-1 is set as 100. Luminance [cd / m²] Was measured using Minolta CS-1000.
[0126]
[Table 4]

[0127]
As is apparent from Table 4, the electroluminescence device using the compound of the present invention for the electron transport layer (hole blocking layer) is very useful as an organic EL device because of its high emission luminance and long emission lifetime. I found out.
[0128]
The same effect was obtained also in the organic EL device produced in the same manner as the organic EL devices OLED7-1 to 7-9 except that the phosphorescent compound was changed to Ir-12 or Ir-9. Note that blue light was emitted from the element using Ir-12, and red light was emitted from the element using Ir-9.
[0129]
Example 8
The red, green, and blue light-emitting organic electroluminescence elements produced in Example 6 were juxtaposed on the same substrate, and the active matrix type full-color display device shown in FIG. 1 was produced.
[0130]
FIG. 1 shows only a schematic diagram of a display portion of the produced full-color display device. That is, a wiring portion including a plurality of scanning lines 5 and data lines 6 and a plurality of juxtaposed pixels 3 (light emission color is a red region pixel, a green region pixel, a blue region pixel, etc.) on the same substrate. The scanning line 5 and the plurality of data lines 6 in 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 lattice shape 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 system provided with an organic EL element corresponding to each emission color, a switching transistor as an active element, and a driving transistor, and a scanning signal is applied from a scanning line 5. Then, an image data signal is received from the data line 6 and light is emitted according to the received image data. In this way, full-color display is possible by appropriately juxtaposing the red, green, and blue pixels.
[0131]
By driving the full-color display device, a clear full-color moving image display with high luminance was obtained.
[0132]
【The invention's effect】
According to the present invention, an organic electroluminescence element that achieves both improvement in emission luminance and durability, and a display device with high emission luminance and a long lifetime are obtained.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a display portion of a full color display device manufactured.
[Explanation of symbols]
A display
3 pixels
5 scanning lines
6 data lines

Claims (6)

The organic electroluminescent element which has a light emitting layer containing a host compound and a phosphorescent compound, A host compound is a compound represented by following General formula (1), The organic electroluminescent element characterized by the above-mentioned.

[Wherein, Ar _{1 to} Ar ₃ each independently represents a substituted or unsubstituted phenyl group, and R _{1 to} R ₃ each independently represents a hydrogen atom, a substituted alkyl group or an unsubstituted alkyl group. However, at least one represents a substituted alkyl group or an unsubstituted alkyl group. Adjacent R _{1 to} R ₃ may be condensed with each other to form a ring. ] The organic electroluminescence device according to claim 1, wherein the compound represented by the general formula (1) is contained in the electron transport layer. The organic electroluminescence device according to claim 1, wherein the phosphorescent compound is an iridium compound, an osmium compound or a platinum compound. The organic electroluminescent device according to claim 3, wherein the phosphorescent compound is an iridium compound. A display device comprising the organic electroluminescence element according to claim 1. An organic electroluminescence device having a light emitting layer and an electron transport layer, wherein the light emitting layer contains a phosphorescent compound, and the electron transport layer contains a compound represented by the following general formula (1): element.

[Wherein Ar ₁ ~ Ar _Three Each independently represents a substituted or unsubstituted phenyl group, R ₁ ~ R _Three Each independently represents a hydrogen atom, a substituted alkyl group or an unsubstituted alkyl group. However, at least one represents a substituted alkyl group or an unsubstituted alkyl group. Adjacent R ₁ ~ R _Three May be condensed with each other to form a ring. ]

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