JP3994799B2 - Organic electroluminescence element and display device - Google Patents

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】

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【化５】

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【化６】

【００３４】
【化７】

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【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。
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【化１２】

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【化１３】

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【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）、ＳｎＯ₂、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（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（Ａｌ₂Ｏ₃）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０．１〜０．３ｎｍ／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、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／ｍ²）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／ｍ²］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／ｍ²）、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／ｍ²）、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ＥＬ素子を作製し、点灯開始時の発光輝度（ｃｄ／ｍ²）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／ｍ²）及び輝度の半減時間の改善が確認された。
【０１１５】
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。
【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。
【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／ｍ²］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／ｍ²］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]
BACKGROUND OF THE INVENTION
The present invention relates to an organic electroluminescence element and a display device, and more particularly to an organic electroluminescence element and a display device excellent in light emission luminance.
[0002]
[Prior art]
As a light-emitting electronic display device, there is an electroluminescence display (ELD). Examples of the constituent elements of ELD include inorganic electroluminescence elements and organic electroluminescence elements (hereinafter also abbreviated as organic EL elements). 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 EL element generally has a structure in which a light emitting layer containing a compound that emits light is sandwiched between a cathode and an anode. By injecting electrons and holes into the light emitting layer and recombining them, excitons ( Is an element that emits light by utilizing light emission (fluorescence / phosphorescence) when the exciton is deactivated, and 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, high visibility, and since it is a thin-film type complete solid-state device, it has attracted 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. 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. Journalof 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, higher-brightness organic EL elements are demanded, and further improvements in energy conversion efficiency and light emission quantum efficiency are expected. In addition, a problem that the light emission life is short has been pointed out. The cause of the deterioration in luminance over time has not been completely elucidated, but the organic EL element that emits light is decomposed by the light emitted by itself and the organic compound itself that constitutes the thin film by the heat generated at that time. Factors derived from organic compounds that are organic EL element materials, such as crystallization of organic compounds, have also been pointed out.
[0004]
Since organic EL light-emitting materials are organic compounds, a very wide range of compounds has been studied. In addition to typical combinations of carbon, nitrogen, oxygen, and sulfur, other characteristic elements can be used. Including compounds are also being considered. For example, examples of using a compound containing boron have been reported and described in JP-A-2000-290645, 2000-294373, 2001-72971, 2001-93670, etc. There was a problem with brightness.
[0005]
In addition, electron transport materials have little knowledge at present, 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). Furthermore, JP-A-5-331459 describes that phenanthroline derivatives are useful as electron transport materials.
[0006]
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. Examples of organic electroluminescent materials that solve these problems are disclosed in JP-A-9-87616, JP-A-9-194487, and JP-A-2000-186094 in which a compound containing a silicon atom in the molecule is used as a light emitting material or an electron transporting material. However, it was not sufficient for achieving both luminous efficiency and luminous lifetime.
[0007]
In addition, a method 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 phosphor is doped into a stilbene derivative, a distyrylarylene derivative or a tristyrylarylene derivative to achieve an improvement in light emission luminance and a longer device lifetime.
[0008]
Further, an element having an organic light emitting layer in which 8-hydroxyquinoline aluminum complex is used as a host compound and a small amount of phosphor is doped (Japanese Patent Laid-Open No. 63-264692), and 8-hydroxyquinoline aluminum complex is used as a host compound. An element having an organic light emitting layer doped with a system 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. 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 Princeton University has reported an organic EL device using phosphorescence emission from an excited triplet (MA Baldo et al., Nature, 395, 151-154 (1998)), at room temperature. Research on materials exhibiting phosphorescence has become active (for example, MA Baldo et al., Nature, 403, 17, 750-753 (2000), US Pat. No. 6,097,147, etc.). 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.
[0009]
Of course, the host when using a 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.
[0010]
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 transporting materials as a host for phosphorescent compounds, doped with a novel iridium complex. Furthermore, Tsutsui et al. Have obtained high luminous efficiency by introducing a hole blocking layer. The hole blocking layer is structurally the same as the electron transport layer used in a normal organic EL element, 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 the present application, the hole blocking layer is also referred to as an electron transport layer, and a material (hole blocker) used in the layer is also referred to as an electron transport material.
[0011]
Regarding the host compound of the phosphorescent compound, for example, C.I. Adachi et al. , Appl. Phys. Lett. 77, page 904 (2000) and the like. However, a new approach is required for the properties required for the host compound to obtain a high-brightness organic EL device.
[0012]
However, none of the reports has provided a configuration that can achieve 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 electroluminescence element having high emission luminance and 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 constitution.
[0015]
1. The organic electroluminescent element which has an electron carrying layer and a light emitting layer, The compound represented by the said General formula (1) is contained, The organic electroluminescent element characterized by the above-mentioned.
[0016]
2. 2. The organic electroluminescence device as described in 1 above, wherein the compound represented by the general formula (1) is contained in an electron transport layer.
[0017]
3. 2. The organic electroluminescence device as described in 1 above, wherein the light emitting layer contains a compound represented by the general formula (1).
[0018]
4). 4. The organic electroluminescence device according to 3 above, 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 electroluminescence device as described in 4 above, wherein the phosphorescent compound is an iridium compound, an osmium compound or a platinum compound.
[0020]
6). 6. The organic electroluminescence device as described in 5 above, wherein the phosphorescent compound is an iridium compound.
[0021]
7). 7. A display device comprising the organic electroluminescence element according to any one of 1 to 6 above.
[0022]
The present invention will be described in detail below.
As a result of detailed studies on the compatibility between emission luminance and durability, the present inventor has used a boron-containing carbazole compound having a specific structure as a host compound for phosphorescence emission and / or electron transporting a boron-containing carbazole compound having a specific structure. It has been found that by using it as a material (hole blocker), an organic electroluminescence element having high luminance and durability and a display device using the same can be obtained.
[0023]
The compound represented by the general formula (1) will be described.
R ₁ And R ₂ Examples of the substituent represented by formula (1) include alkyl groups (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) 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, Tilamino group, diphenylamino group, etc.), cyano group, nitro group, heterocyclic group (pyrrole group, pyrrolidyl group, pyrazolyl group, imidazolyl group, pyridyl group, benzimidazolyl group, benzothiazolyl group, benzoxazolyl group, etc.) Can be mentioned. Examples of the aromatic group include the above aryl group and heteroaryl group (pyrrole group, pyrazolyl group, imidazolyl group, pyridyl group, benzimidazolyl group, benzothiazolyl group, benzooxazolyl, etc.), and each substituent is further optional. It may be substituted with a substituent. Further, adjacent substituents may be condensed with each other to form a ring.
[0024]
R _Three ~ R ₆ Represents a hydrogen atom or a substituent, and specific examples thereof include the R ₁ It is synonymous with. R _Three Or R _Four At least one of these 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 substituents from any position of any aromatic compound, and the arylene group is composed of hydrocarbons. 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 phenyl group, 1-naphthyl group, 9-anthryl group, 9-phenanthryl group, 2-pyridyl group, 4-quinolyl group, 2-thienyl group and the like. Ar ₁ Or Ar ₂ One of the
[0027]
[Chemical 2]

[0028]
It is preferable to be represented by
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 injecting property and the electron transporting property from the metal electrode are very excellent, in the device using another light emitting material or the compound of the present invention as the 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.
[0029]
Although the example of a specific compound is given to the following, this invention is not limited to these.
[0030]
[Chemical 3]

[0031]
[Formula 4]

[0032]
[Chemical formula 5]

[0033]
[Chemical 6]

[0034]
[Chemical 7]

[0035]
[Chemical 8]

[0036]
[Chemical 9]

[0037]
[Chemical Formula 10]

[0038]
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[0039]
The compounds of the present invention are disclosed in JP-A-2001-93670 and J. Org. Am. Chem. Soc. 120, p. It can be synthesized according to the method described in 9714 (1998).
[0040]
In addition, as a result of intensive studies on the host compound of the phosphorescent compound, the present inventors have produced an organic EL device using the boron-containing carbazole compound of the present invention as the host compound. It has been found that the lifetime is improved.
[0041]
In the present invention, the host compound 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.
[0042]
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. The phosphorescence quantum yield is preferably 0.01 or more, more preferably 0.1 or more.
[0043]
The phosphorescence quantum yield can be measured by the method described in Spectrophoto II, page 398 (1992 edition, Maruzen) of the Fourth Edition Experimental Chemistry Course 7. 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 above phosphorescence quantum yield in any solvent.
[0044]
The phosphorescent compound used in the present invention is preferably a complex compound containing a group VIII metal in the periodic table of elements, more preferably an iridium, osmium, or platinum complex compound, more preferably. Is an iridium complex compound.
[0045]
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.
[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, 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 And polythiophene dyes or rare earth complex phosphors.
[0050]
The fluorescence quantum yield here can also be measured by the method described on page 362 (1992 edition, Maruzen) of Spectroscopic II of the Fourth Edition Experimental Chemistry Course 7.
[0051]
Hereinafter, the organic EL element will be described.
In a broad sense, the light emitting layer in an organic 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, the 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 structure in which a hole transport layer, an anode buffer layer, a cathode buffer layer, and the like are sandwiched between a cathode and an anode in addition to a light emitting layer and an electron transport layer as necessary.
[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 is a structure represented by anode / anode buffer layer / hole transport layer / light emitting layer / electron transport layer / cathode buffer layer / cathode.
[0053]
As a method for 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 vapor 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.
[0054]
In addition, 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, followed by spin coating or the like. It can be obtained by coating with a thin film.
[0055]
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.
[0056]
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.
[0057]
As these phosphorescent compounds, the phosphorescence quantum yield as described above is 0.001 or more, preferably 0.01 or more at 25 ° C., and more than the fluorescence maximum wavelength of the fluorescent compound serving as the host. It has a long phosphorescence maximum wavelength, and, for example, utilizes the phosphorescent compound's light emission, that is, the triplet state, using a phosphorescent compound longer than the emission maximum wavelength of the host fluorescent compound. Thus, it is possible to obtain an organic EL element that emits electroluminescence at a longer wavelength than the fluorescence maximum wavelength of the host compound. Accordingly, the phosphorescent maximum wavelength of the phosphorescent compound used is not particularly limited, and in principle, it can be obtained by selecting a central metal, a ligand, a ligand substituent, and the like. The emission wavelength can be changed.
[0058]
For example, a fluorescent compound having a fluorescence maximum wavelength in the 350 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. be able to.
[0059]
In another embodiment, as described above, in addition to the fluorescent compound A and the phosphorescent compound as the host 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.
[0060]
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.
[0061]
The molecular weight of the host compound is preferably 600 to 2000, and if it is in this molecular weight range, Tg (glass transition temperature) is increased, thermal stability is improved, and device lifetime is improved. More preferably, the molecular weight is 800-2000. Moreover, it is preferable that Tg is 100 degree | times or more. Further, when the molecular weight is within this range, the light emitting layer can be easily produced by a vacuum vapor deposition method, and the production of the organic EL element is facilitated. Furthermore, the thermal stability of the fluorescent compound in the organic EL element is also improved.
[0062]
Next, other layers constituting the 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 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, many 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 accumulation at the interface in the light emitting layer and improvement in 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 photoconductive material, what is conventionally used as a charge injection transport material of a hole, and the well-known thing used for the hole injection layer of an organic EL element, and a hole transport layer are used. Any one can be selected and used.
[0064]
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, oxazoles. Derivatives, styryl anthracene 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.
[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; 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 two more described in US Pat. No. 5,061,569 Having a condensed aromatic ring of, for example, 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (NPD), JP-A-4-3086 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]
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]
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 laminated structure composed of a plurality of layers having the same composition or different compositions.
[0068]
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.
[0069]
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.
[0070]
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.
[0071]
In addition, metal complexes of 8-quinolinol derivatives 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), etc., and the central metals of these metal complexes are In, Mg, Cu , Ca, Sn, Ga, or Pb can also be used as an electron transport material. 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 transporting 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 can be used. A semiconductor can also be used as an electron transport material.
[0072]
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 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 the light emitting layer, 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 kind of fluorescent compound having a fluorescent maximum 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 these hole transport layer and 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. A compound is used.
[0074]
The substrate preferably used in 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 organic EL device of the present invention include glass, quartz, and a light transmissive plastic film.
[0075]
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.
[0076]
Next, a suitable example for producing an organic EL element will be described. As an example, a method for producing an organic 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.
[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 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.
[0078]
Further, a buffer layer (electrode interface layer) may be present 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 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.
[0079]
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.
[0080]
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.
[0081]
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.
[0082]
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, issued by NTS Corporation”.
[0083]
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.
[0084]
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. ₂ And conductive transparent materials such as ZnO.
[0085]
The anode may be formed by forming 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 to 200 nm.
[0086]
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 (Al ₂ O _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, such as a magnesium / silver mixture, magnesium, from the viewpoint of electron injectability and durability against oxidation, etc. / Aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O _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 order to transmit light, 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.
[0087]
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 from the standpoint that 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 ^-3 It 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.
[0088]
As described above, a method such as vapor deposition or sputtering is performed on a suitable substrate so that a thin film made of a desired electrode material, for example, an anode material, has a thickness of 1 μm or less, preferably 10 to 200 nm. After forming an anode by forming a thin film of each layer consisting of a hole injection layer, a hole transport layer, a light emitting layer, 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, for example, 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 a reverse 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.
[0089]
【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.
[0090]
Example 1 (light emitting 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 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. _Three 200 mg was added and attached to a vacuum deposition apparatus. The vacuum chamber is then 4 × 10 ^-Four After 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. 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 _Three The 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 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 ^-Four After 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 1-1 was produced by vapor-depositing silver to form a cathode made of the mixture of magnesium and silver.
[0092]
Organic EL elements 1-2 to 1-12 were produced in the same manner as the organic EL element 1-1 except that the comparative compound 1 of the organic EL element 1-1 was changed to the compounds shown in Table 1. All organic EL elements emitted light from blue to green.
[0093]
These organic EL elements were continuously lit by applying a 10 V DC voltage in a dry nitrogen gas atmosphere at 23 ° C., and the light emission luminance (cd / m at the start of lighting) ² ) And a half-life of luminance as an index of durability. The light emission luminance is expressed as a relative value with the organic EL element 1-1 as 100, and the luminance half time is expressed as a relative value with the luminance half time of the organic EL element 1-1 as 100. The measurement results are shown in Table 1. 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 light emission luminance and half-time of luminance at the start of lighting compared to the organic EL device using a 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 light-emitting layer having a thickness of 30 nm obtained by depositing Compound 1 of the present invention and DCM-2 at a mass ratio of 100: 1 was used.
[0100]
When this organic EL device was applied with a DC voltage of 10 V in a dry nitrogen gas atmosphere at 23 ° C., red light emission was obtained.
[0101]
Green or blue light emission was obtained 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 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, while 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 into a resistance heating boat made of molybdenum and attached to a vacuum deposition apparatus.
[0104]
The vacuum chamber is then 4 × 10 ^-Four After 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.
[0105]
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.
[0106]
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 ^-Four After 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 3-1 was produced by vapor-depositing silver to form a cathode made of the mixture of magnesium and silver.
[0107]
Organic EL elements 3-2 to 3-12 were produced in the same manner as 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 10 V DC voltage in a dry nitrogen gas atmosphere at 23 ° C., and the light emission luminance (cd / m at the start of lighting) ² ), And a half-life of luminance. The light emission luminance was expressed as a relative value with the organic EL element 3-1 as 100, and the luminance half time was expressed as a relative value with the luminance half time of the organic EL element 3-1 as 100. The measurement results are shown in Table 2. In all elements, the emission color was blue.
[0109]
Embedded image

[0110]
[Table 2]

[0111]
From Table 2, the organic EL device using the compound of the present invention has improved light emission luminance at the start of lighting and the time to reduce the luminance by half compared to the organic EL device using a comparative compound having a similar structure. I understand.
[0112]
Example 4 (cathode buffer layer)
In the same manner except that the cathode of the organic EL device 3-5 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. Organic EL element 4-1 was produced.
[0113]
As in Example 3, the light emission luminance (cd / m) at the start of lighting of the organic EL element. ² ) And the half-life time of the luminance were measured. As a result of comparing the relative values with the organic EL element 3-1 as 100, the emission luminance was 315 and the luminance half-life was 420. Similarly, the organic EL elements 3-6 to 3-12 were more effective when a cathode buffer layer was introduced.
[0114]
Example 5 (Three colors of light emission)
The light emitting layer of the organic EL element used in Example 3 was changed from DPVBi to Alq. _Three Or Alq _Three And DCM-2 were replaced with a light-emitting layer deposited at a mass ratio of 100: 1 in the same manner, an organic EL device was produced, and the light emission luminance (cd / m at the start of lighting) ² ) And half-life of luminance. As a result, as in Example 3, the organic EL device using the compound of the present invention for the electron transport layer had an emission luminance (cd / m at the start of lighting). ² ) And an improvement in luminance half-life.
[0115]
Alq _Three Is used for the light emitting layer, green light emission is obtained, and Alq _Three And DCM-2 were co-evaporated at 100: 1, and red light emission was obtained.
[0116]
Example 6
Organic EL elements 6-1 to 6-8 were produced as follows.
[0117]
<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.
[0118]
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. _Three 200 mg was added and attached to a vacuum deposition apparatus. The vacuum chamber is then 4 × 10 ^-Four After 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 _Three The 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.
[0119]
Next, 0.5 nm of lithium fluoride and 110 nm of Al were vapor-deposited to form a cathode, and an organic EL element 6-1 was produced.
[0120]
Organic EL elements 6-2 to 6-9 were produced in exactly the same manner except that CBP in the light emitting layer was replaced with the compounds shown in Table 3.
[0121]
Embedded image

[0122]
<Evaluation of Luminous Luminance and Half-Time of Organic EL Elements 6-1 to 6-9>
In the organic EL element 6-1, current started to flow at an initial driving voltage of 3 V, and green light was emitted from the phosphorescent compound that is the dopant of the light emitting layer. About the produced organic EL element, the luminance half time was measured as an index of the light emission luminance and the light emission lifetime when 9 V DC voltage was applied at 23 ° C. in a dry nitrogen gas atmosphere. The light emission luminance was expressed as a relative value with the organic EL element 6-1 as 100, and the luminance half time was expressed as a relative value with the organic EL element 6-1 as 100. Table 3 shows the measurement results. Luminance [cd / m ² ] Was measured using Minolta CS-1000.
[0123]
[Table 3]

[0124]
As is apparent from Table 3, the organic EL device using the compound of the present invention as a host has a high emission luminance and a long half time, and thus was found to be very useful as an organic EL device.
[0125]
The same effect can be obtained in the organic EL elements 6-10 and 6-11 produced in the same manner as the organic EL elements 6-1 to 6-9 except that the phosphorescent compound is changed to Ir-11 or Ir-9. It was. Note that 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 elements 7-1 to 7-9 were prepared in exactly the same manner except that the BCP used in the electron transport layer of the organic EL element 6-1 prepared in Example 6 was replaced with the compounds shown in Table 4.
[0127]
<Evaluation of Luminous Luminance and Half-Time of Organic EL Elements 6-1 and 7-1 to 7-9>
In the organic EL element 6-1, current started to flow at an initial driving voltage of 3 V, and green light was emitted from the phosphorescent compound that is the dopant of the light emitting layer. When these organic EL elements were applied with a 9 V DC voltage at 23 ° C. in a dry nitrogen gas atmosphere, the luminance and half-life of the luminance were measured. The light emission luminance was expressed as a relative value with the organic electroluminescence element 6-1 as 100, and the luminance half time was expressed as a relative value with the organic EL element 6-1 as 100. Table 4 shows the measurement results. 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) is very useful as an organic EL device because of its high emission luminance and long half-life. I found out.
[0130]
The same effect can be obtained in the organic EL elements 7-10 and 7-11 produced in the same manner as the organic EL elements 7-1 to 7-9 except that the phosphorescent compound is changed to Ir-11 or Ir-9. It was. 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 the active matrix type full-color display device shown in FIG.
[0132]
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 in which an organic EL element corresponding to each emission color, a switching transistor as an active element, and a driving transistor are provided, and when a scanning signal is applied from the scanning line 5 The 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.
[0133]
By driving the full-color display device, a clear full-color moving image display with high brightness was obtained.
[0134]
【The invention's effect】
According to the present invention, an organic electroluminescence element having high emission luminance and 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 scanning lines
6 Data lines

Claims (7)

The organic electroluminescent element which has an electron carrying layer and a light emitting layer, The compound represented by following General formula (1) is contained, The organic electroluminescent element characterized by the above-mentioned.

(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 s} may be the same or different, and when q represents an integer of 2 or more, a plurality of R _{2 s} 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, and When a plurality of R ₂ are adjacent to each other, they may be condensed with each other to form a ring, and R ₁ and R ₂ may form a ring, and R _{3 to} R ₆ may be 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, .Ar ₁及representing at least one of the substituent of R ₃ or R ₄ Ar ₂ each independently represents 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 compound represented by the general formula (1) is contained in a light emitting layer. 4. The organic electroluminescence 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. 6. The organic electroluminescence device according to claim 5, wherein the phosphorescent compound is an iridium compound. A display device comprising the organic electroluminescence element according to claim 1.

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