JP3967946B2 - Organic electroluminescence device - Google Patents

Description

【００２９】
また電子輸送層１２を構成する電子輸送材料としては、電子を輸送する能力を有し、陰極２からの電子注入効果を有するとともに、発光層３に対して優れた電子注入効果を有し、さらにホールの電子輸送層１２への移動を防止し、かつ薄膜形成能力の優れた化合物を挙げることができる。具体的には、フルオレン、バソフェナントロリン、バソクプロイン、アントラキノジメタン、ジフェノキノン、オキサゾール、オキサジアゾール、トリアゾール、イミダゾール、アントラキノジメタン、４，４’−Ｎ，Ｎ’−ジカルバゾールビフェニル（ＣＢＰ）等やそれらの化合物、金属錯体化合物もしくは含窒素五員環誘導体を挙げることができる。上記の金属錯体化合物としては、具体的には、トリス（８−ヒドロキシキノリナート）アルミニウム、トリ（２−メチル−８−ヒドロキシキノリナート）アルミニウム、トリス（８−ヒドロキシキノリナート）ガリウム、ビス（１０−ヒドロキシベンゾ［ｈ］キノリナート）ベリリウム、ビス（１０−ヒドロキシベンゾ［ｈ］キノリナート）亜鉛、ビス（２−メチル−８−キノリナート)（ｏ−クレゾラート）ガリウム、ビス（２−メチル−８−キノリナート)（１−ナフトラート）アルミニウム等があるが、これらに限定されるものではない。また上記の含窒素五員環誘導体としては、オキサゾール、チアゾール、オキサジアゾール、チアジアゾールもしくはトリアゾール誘導体が好ましい。具体的には、２，５−ビス（１−フェニル）−１，３，４−オキサゾール、２，５−ビス（１−フェニル）−１，３，４−チアゾール、２，５−ビス（１−フェニル）−１，３，４−オキサジアゾール、２−（４’−ｔｅｒｔ−ブチルフェニル）−５−（４”−ビフェニル）１，３，４−オキサジアゾール、２，５−ビス（１−ナフチル)−１，３，４−オキサジアゾール、１，４−ビス［２−（５−フェニルチアジアゾリル）］ベンゼン、２，５−ビス（１−ナフチル）−１，３，４−トリアゾール、３−（４−ビフェニルイル）−４−フェニル−５−（４−ｔ−ブチルフェニル)−１，２，４−トリアゾール等があるが、これらに限定されるものではない。さらに、ポリマー有機発光素子に使用されるポリマー材料も使用することができる。例えば、ポリパラフェニレン及びその誘導体、フルオレン及びその誘導体等である。
【００３０】
この電子輸送層１２にはアルカリ金属、アルカリ土類金属、希土類をドープしてもよい。例えばセシウムをバソフェナントロリンにモル比１：１の割合でドープして電子輸送層１２を形成したものを挙げることができる。
【００３１】
また、有機電界発光素子を構成する他の部材、例えば、積層された素子を保持する基板１０、陽極１、陰極２等には、従来から使用されているものをそのまま用いることができる。また有機電界発光素子から光を取り出す面上に、光散乱層、マイクロレンズ、プリズム等を配置することもできる。
【００３２】
上記の基板１０としては、発光層３で発光された光が基板１０を通して出射されるものである場合には、光透過性を有するものが使用されるが、無色透明のものの他に、多少着色されているものや、スリガラス状のものであってもよい。例えば、ソーダライムガラス、無アルカリガラスなどの透明ガラス板、ポリエステル、ポリオレフィン、ポリアミド、エポキシ樹脂、フッ素系樹脂などの樹脂から任意の方法で作製されたプラスチックフィルムやプラスチック板などを用いることができる。またさらに、基板１０内に基板１０の母材と屈折率の異なる粒子、粉体、泡等を含有することによって、光拡散効果を有するものを使用することも可能である。また、発光層３で発光された光を基板１０を通さずに出射させる場合には、基板１０は必ずしも光透過性を有するものでなくてもかまわない。そして有機電界発光素子の発光特性、寿命特性等を損なわない限り、任意の基板１０を用いることができるものであり、特に通電時の有機電界発光素子の発熱による温度上昇を低減するために、熱伝導性の高い基板１０を用いることもできるものである。
【００３３】
上記の陽極１は素子にホールを注入するための電極であり、この陽極１としては、仕事関数の大きい金属、合金、電気伝導性化合物、あるいはこれらの混合物からなる電極材料を用いるのが好ましく、特に仕事関数が４ｅＶ以上の電極材料を用いるのが好ましい。このような電極材料としては、具体的には、金などの金属、ＣｕＩ、ＩＴＯ（インジウム−スズ酸化物）、ＳｎＯ₂、ＺｎＯ、ＩＺＯ（インジウム−亜鉛酸化物）等の導電性透明材料があげられる。例えばこれらの電極材料を基板１０の上に真空蒸着法やスパッタリング法等の方法で成膜することによって、陽極１を薄膜として作製することができる。発光層３における発光を陽極１を透過させて基板１０から外部に照射する場合には、陽極１の光透過率を７０％以上にすることが好ましい。また、陽極１のシート抵抗は数百Ω／□以下であることが好ましく、特に１００Ω／□以下であることが好ましい。さらに陽極１の膜厚は、陽極１の光透過率、シート抵抗等の特性を上記のように制御するために、材料により異なるが、通常５００ｎｍ以下に設定するのが好ましく、より好ましくは１０〜２００ｎｍの範囲である。
【００３４】
上記の陰極２は、発光層３中に電子を注入するための電極であり、この陰極２としては、仕事関数の小さい金属、合金、電気伝導性化合物及びこれらの混合物からなる電極材料を用いることが好ましく、仕事関数が５ｅＶ以下の電極材料を用いるのが好ましい。このような電極材料としては、アルカリ金属、アルカリ金属のハロゲン化物、アルカリ金属の酸化物、アルカリ土類金属、希土類等や、これらと他の金属との合金などを用いることができるものであり、例えばナトリウム、ナトリウム−カリウム合金、リチウム、マグネシウム、マグネシウム−銀混合物、マグネシウム−インジウム混合物、アルミニウム−リチウム合金、Ａｌ／ＬｉＦ混合物などを例として挙げることができる。これらの他にアルミニウム、Ａｌ／Ａｌ₂Ｏ₃混合物なども使用可能である。またアルカリ金属の酸化物、アルカリ金属のハロゲン化物、あるいは金属酸化物を下地として用い、上記の仕事関数が５ｅＶ以下である材料（あるいはこれらを含有する合金）を１層以上積層して陰極２を作製することもできる。例えば、アルカリ金属／Ａｌの積層、アルカリ金属のハロゲン化物／アルカリ土類金属／Ａｌの積層、Ａｌ₂Ｏ₃／Ａｌの積層などを例として挙げることができる。またＩＴＯ、ＩＺＯなどに代表される透明電極で陰極２を作製し、発光層３で発光した光を陰極２の側から取り出す構成に形成するようにしてもよい。さらに、陰極２の界面の電子輸送層１２にリチウム、ナトリウム、セシウム、カルシウム等のアルカリ金属、アルカリ土類金属をドープしてもよい。
【００３５】
陰極２は、例えば上記の電極材料を、真空蒸着法やスパッタリング法等の方法により、薄膜に形成することによって作製することができる。また、発光層３における発光を陰極２を透過させて外部に照射する場合には、陰極２は光透過率を７０％以上にすることが好ましい。ここで、陰極２の膜厚は、陰極２の光透過率等の特性を上記のように制御するために、材料により異なるが、通常５００ｎｍ以下に設定するのが好ましく、好ましくは１００〜２００ｎｍの範囲とするのがよい。また、陰極金属の形成の際、蒸発源からの熱輻射の影響を抑えるためには、さらに薄い５０〜１００ｎｍの範囲とするのがよい。蒸着速度を速くした場合、この厚みはより厚くても構わない。さらにより好ましくは厚みを２５〜５０ｎｍの範囲とするのがよい。何故ならば、発光面積が大きくなると、短絡による発光停止という問題が生じ易くなるが、陰極金属の膜厚を薄くすることにより、短絡部分の陰極金属が短絡時の刺激により取り除かれ、その部分のみが光らなくなるオープンモードとなり、発光部分全体の発光停止という不良を抑えることができるのである。さらに、陰極２の上にＡｌ等の金属をスパッタで積層したり、フッ素系化合物、フッ素系高分子、その他の有機分子など高分子を、蒸着、スパッタ、ＣＶＤ、プラズマ重合、塗布した後に紫外線硬化させる方法、熱硬化、その他の方法で形成することも可能である。
【００３６】
【実施例】
次に、本発明を実施例によって具体的に説明する。尚、使用した発光性有機材料のエネルギーギャップ、電子親和力（ＥＡ）、イオン化ポテンシャル（ＩＰ）の値を表１にまとめて示し、発光層３ａ，３ｂ，３ｃの構成を表２にまとめて示す。
【００３７】
（実施例１）
基板１０として、厚み０．７ｍｍの透明ガラス板を用い、この基板１０の一方の表面に、ＩＴＯ（インジウム−スズ酸化物）をスパッタしてシート抵抗７Ω／□の透明電極からなる陽極１を形成した。そしてこれをアセトン、純水、イソプロピルアルコールで１５分間超音波洗浄した後、乾燥させた。
【００３８】
次に、この基板１０を真空蒸着装置にセットし、１×１０^-6Ｔｏｒｒ（１．３３×１０^-4Ｐａ）の減圧下、４，４’−ビス［Ｎ−（ナフチル）−Ｎ−フェニル−アミノ］ビフェニル（株式会社同仁化学研究所製：以下α−ＮＰＤと略す）を１０００Å厚に蒸着し、陽極１の上にホール輸送層１１を形成した。
【００３９】
次に、ホール輸送層１１の上に、α−ＮＰＤとＤＳＡ誘導体（出光興産社製「ＢＣｚＶＢｉ」：化学式１）をモル比９４：６の割合で１００Å厚に共蒸着し、発光性有機物質としてＢＣｚＶＢｉをドープした発光層３ａを形成した。またこの上にジスチリルビフェニル誘導体（出光興産社製「ＤＰＶＢｉ」：化学式２）とルブレン（化学式３）をモル比９８：２の割合で５０Å厚に共蒸着し、発光性有機物質としてルブレンをドープした発光層３ｂを形成した。さらにこの上にＤＰＶＢｉとＢＣｚＶＢｉをモル比９４：６の割合で４００Å厚に共蒸着し、発光性有機物質としてＢＣｚＶＢｉをドープした発光層３ｃを形成した。尚、上記の有機層の蒸着速度はいずれも１〜２Å／ｓに設定した。
【００４０】
【化２】

【００４１】
【化３】

【００４２】
【化４】

【００４３】
次に、発光層３ｃの上に、バソフェナントロリン（株式会社同仁化学研究所製：ＢＣＰ）とＣｓをモル比１：１で共蒸着して膜厚２００Åの電子輸送層１２を形成し、最後に、電子輸送層１２の上にＡｌを１０Å／ｓの蒸着速度で厚み１５００Å蒸着して陰極２を形成することによって、図１のような構成の有機電界発光素子を得た。
【００４４】
（実施例２）
α−ＮＰＤとシグマアルドリッチジャパン（Sigma Aldrich Japan K.K.）製：「クマリン６」をモル比９８：２で膜厚１００Åに共蒸着することによって、発光性有機物質としてクマリン６をドープした発光層３ａを形成し、ＤＰＶＢｉとイーストマンコダック社製「ＤＣＪＴＢ」をモル比９８：２で膜厚５０Åに共蒸着することによって、発光性有機物質としてＤＣＪＴＢをドープした発光層３ｂを形成し、ＤＰＶＢｉとＢＣｚＶＢｉをモル比９４：６で膜厚４００Åに共蒸着することによって、発光性有機物質としてＢＣｚＶＢｉをドープした発光層３ｃを形成するようにした他は、実施例１と同様にして、図１のような構成の有機電界発光素子を得た。
【００４５】
（比較例１）
ＤＰＶＢｉとルブレンをモル比９８：２で膜厚１００Åに共蒸着することによって、発光性有機物質としてルブレンをドープした発光層３ａを形成し、発光層３ｂは形成せずに、発光層３ｃは実施例１と同様に形成した。その他は実施例１と同様にして、有機電界発光素子を得た。
【００４６】
（比較例２）
α−ＮＰＤとルブレンをモル比９８：２で膜厚１００Åに共蒸着することによって、発光性有機物質としてルブレンをドープした発光層３ａを形成し、ＤＰＶＢｉとＢＣｚＶＢｉをモル比９４：６で膜厚４００Åに共蒸着することによって、発光性有機物質としてＢＣｚＶＢｉをドープした発光層３ｂを形成し、ＤＰＶＢｉとルブレンをモル比９８：２で膜厚１００Åに共蒸着することによって、発光性有機物質としてルブレンをドープした発光層３ｃを形成するようにした他は、実施例１と同様にして、有機電界発光素子を得た。
【００４７】
（比較例３）
α−ＮＰＤとＢＣｚＶＢｉをモル比９４：６で膜厚４００Åに共蒸着することによって、発光性有機物質としてＢＣｚＶＢｉをドープした発光層３ａを形成し、ＤＰＶＢｉとクマリン６をモル比９８：２で膜厚１００Åに共蒸着することによって、発光性有機物質としてクマリン６をドープした発光層３ｂを形成し、ＤＰＶＢｉとＤＣＪＴＢをモル比９８：２で膜厚５０Åに共蒸着することによって、発光性有機物質としてＤＣＪＴＢをドープした発光層３ｃを形成するようにした他は、実施例１と同様にして、有機電界発光素子を得た。
【００４８】
【表１】

【００４９】
上記の実施例１〜２及び比較例１〜３について、発光素子３ａ，３ｂ，３ｃのそれぞれの組成をまとめて、表２に示す。
【００５０】
【表２】

【００５１】
また、上記の実施例１〜２及び比較例１〜３について、発光素子３ａ，３ｂ，３ｃにドープした発光性有機材料のエネルギーギャップ、電子親和力（ＥＡ）、イオン化ポテンシャル（ＩＰ）をまとめて表３に示す。
【００５２】
【表３】

【００５３】
上記のようにして実施例１〜２及び比較例１〜３で得た有機電界発光素子について、発光色度、消費電力、量子効率、素子半減寿命を測定し、結果を表４に示した。
【００５４】
有機電界発光素子の色度は、ＣＩＥ色度座標で評価した。測定は、有機電界発光素子を電源（東陽テクニカ社製「ＫＥＹＴＨＬＥＹ２３６モデル」）に接続し、マルチチャンネルアナライザー（浜松ホトニクス株式会社製「ＰＭＡ−１０」）を用いて、輝度２００ｃｄ／ｍ²の条件で行なった。尚、輝度の測定はトプコン株式会社製「ＢＭ−５Ａ」で行なった。
【００５５】
有機電界発光素子の消費電力の測定は、有機電界発光素子を電源（東陽テクニカ社製「ＫＥＹＴＨＬＥＹ２３６モデル」）に接続し、２００ｃｄ／ｍ²の条件で発光させた状態における値から算出した。
【００５６】
有機電界発光素子の量子効率は、有機電界発光素子の発光スペクトル、輝度、印加電圧、電流量から定法に基づき算出した。
【００５７】
有機電界発光素子の半減寿命の測定は、初期の発光輝度が２００ｃｄ／ｍ²になる電流値を予め決定し、次いで定電流電源を用いて有機電界発光素子に所定の電流を通電して、輝度が初期の半分の１００ｃｄ／ｍ²になるまでの時間を計測することによって行ない、この時間を半減寿命とした。
【００５８】
【表４】

【００５９】
表４にみられるように、実施例１〜２の有機電界発光素子は、消費電力が少ないと共に量子効率が高く、発光効率が優れるものであり、また半減寿命が長く、長寿命化と高い発光効率を実現できることが確認された。
【００６０】
【発明の効果】
上記のように本発明の請求項１に係る有機電界発光素子は、陽極と陰極の間に、発光性有機物質がドープされた有機材料よりなる発光層を備えた有機電界発光素子において、異なる発光性有機物質がドープされた有機材料よりなる少なくとも三層の発光層を備え、最も陽極側に位置する発光層及び最も陰極側に位置する発光層にドープされている発光性有機物質のエネルギーギャップの値が、これら以外の発光層にドープされている発光性有機物質のエネルギーギャップの値より大きくなるようにしたので、発光層にドープする発光性有機物質のエネルギーギャップをこのように規定することによって、陰極側に位置する発光層から陽極側に位置する発光層に効率よくエネルギーを移動させることができ、有機電界発光素子の長寿命化と高い発光効率を実現することができるものである。
【００６１】
また、最も陽極側に位置する発光層にドープされている発光性有機物質の電子親和力（ＥＡ）の値（単位ｅＶ）が、この発光層に隣接する発光層にドープされている発光性有機物質のＥＡの値よりも０．０５ｅＶ以上小さくなるようにしたので、発光層にドープする発光性有機物質の電子親和力（ＥＡ）をこのように規定することによって、陰極から注入された電子が発光層を通過して陽極側に通過してしまうことを防ぐことができ、有機電界発光素子の長寿命化と高い発光効率を実現することができるものである。
【００６２】
また請求項２の発明は、請求項１において、最も陰極側に位置する発光層にドープされている発光性有機物質の電子親和力（ＥＡ）の値が、この発光層に隣接する発光層にドープされている発光性有機物質のＥＡの値以下になるようにしたので、発光層にドープする発光性有機物質の電子親和力（ＥＡ）をこのように規定することによって、陰極から注入された電子が最も陰極側に位置する発光層から隣接する発光層に効率よく注入されることになり、有機電界発光素子の長寿命化と高い発光効率を実現することができるものである。
【００６３】
また請求項３の発明は、請求項１又は２において、最も陰極側に位置する発光層にドープされている発光性有機物質のイオン化ポテンシャル（ＩＰ）の値（単位ｅＶ）が、この発光層に隣接する発光層にドープされている発光性有機物質のＩＰの値よりも０．０５ｅＶ以上大きくなるようにしたので、発光層にドープする発光性有機物質のイオン化ポテンシャル（ＩＰ）をこのように規定することによって、陽極から注入されたホールが発光層を通過して陰極側に通過してしまうことを防ぐことができ、有機電界発光素子の長寿命化と高い発光効率を実現することができるものである。
【００６４】
また請求項４の発明は、請求項１乃至３のいずれかにおいて、最も陽極側に位置する発光層にドープされている発光性有機物質のイオン化ポテンシャル（ＩＰ）の値が、この発光層に隣接する発光層にドープされている発光性有機物質のＩＰの値以上になるようにしたので、発光層にドープする発光性有機物質のイオン化ポテンシャル（ＩＰ）をこのように規定することによって、陽極から注入されたホールが最も陽極側に位置する発光層から隣接する発光層に効率よく注入されるようにすることができ、有機電界発光素子の長寿命化と高い発光効率を実現することができるものである。
【図面の簡単な説明】
【図１】有機電界発光素子の一例の概略構成を示す正面図である。
【図２】同上の発光層の概略構成を示す正面図である。
【符号の説明】
１ 陽極
２ 陰極
３ 発光層
３ａ，３ｂ，３ｃ 発光層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic electroluminescent element used for a flat panel display, a backlight for a liquid crystal display, an illumination light source, and the like.
[0002]
[Prior art]
As light emitters used in flat panel displays, backlights for liquid crystal displays, illumination light sources, etc., flat panel displays are made thinner, electronic devices equipped with liquid crystal displays are made smaller and thinner, or the shape of lighting fixtures is liberalized. In recent years, there has been an increasing demand for thin, lightweight, and highly efficient products. An organic electroluminescence element (organic electroluminescence element) has attracted attention as a device that can meet such a demand.
[0003]
The fact that the organic electroluminescence device emits light at a low voltage is the fact that C.E. W. Tang et al. (Appl. Phys. Lett., 51, 12, 913 (1987)) showed for the first time an element having a structure in which two thin films were laminated between electrodes. And after this, the organic electroluminescent element is 100 to 100000 cd / m at a low voltage of about 10 V such as a battery. ² Focusing on the industry because of its ability to emit light with high brightness, the ability to emit a large number of colors with a combination of materials that make up a phosphor, and the ability to use it as a very thin surface emitter In addition, organic electroluminescence devices having various thin film configurations obtained by improving the device configuration have been studied.
[0004]
Here, the basic element configuration of the organic electroluminescent element is anode / organic light emitting layer / cathode, but in addition, the configuration of anode / hole transport layer / organic light emitting layer / electron transport layer / cathode, and anode / hole Structure of injection layer / hole transport layer / organic light emitting layer / electron transport layer / cathode, structure of anode / hole injection layer / organic light emitting layer / electron transport layer / electron injection layer / cathode, anode / hole injection layer / organic The thing of various structures, such as a structure of a light emitting layer / electron injection layer / cathode, is mentioned.
[0005]
And the optimization of each said layer is examined for the purpose of improving the luminous efficiency of an organic electroluminescent element. In other words, various device configurations have been studied focusing on the ionization potential and electron affinity of each layer, and hole-electron recombination efficiency is improved by blocking holes and electrons at the interface between the organic light-emitting layer and the carrier transport layer. Many device configurations for realizing confinement of excitons in an organic light emitting layer have been proposed. For example, in Japanese Patent Laid-Open No. 2000-68057, an organic light emitting layer is formed in a plurality of layers so that the ionization potential of each organic light emitting layer increases from the anode to the cathode, and the electron affinity of the organic light emitting layer is specified. By doing so, an attempt has been made to realize a long life and high luminous efficiency. In Japanese Patent Laid-Open No. 10-74584, an attempt is made to increase luminous efficiency by defining the magnitude relationship between the electron affinity and ionization potential of the host material forming the hole transport layer and the electron transport layer.
[0006]
[Problems to be solved by the invention]
As described above, in the past, attempts have been made to define the electron affinity and ionization potential for the host material that forms a plurality of light-emitting layers, but no study has been made on the light-emitting organic material doped in the light-emitting layer. In this respect, studies on extending the life and increasing the luminous efficiency of the organic electroluminescence device have been insufficient.
[0007]
The present invention has been made in view of the above points, and provides an organic electroluminescent device that achieves a long lifetime and high luminous efficiency by defining a luminescent organic material that is doped into a light emitting layer. It is for the purpose.
[0008]
[Means for Solving the Problems]
The organic electroluminescent device according to claim 1 of the present invention is an organic electroluminescent device comprising a light emitting layer made of an organic material doped with a luminescent organic material between an anode and a cathode. It has at least three light emitting layers made of a doped organic material, and the energy gap value of the light emitting organic material doped in the light emitting layer located closest to the anode and the light emitting layer located closest to the cathode is determined by these values. It is characterized by being larger than the value of the energy gap of the luminescent organic material doped in the luminescent layer other than the above.
[0009]
Ma The The electron affinity (EA) value (unit eV) of the light emitting organic material doped in the light emitting layer located closest to the anode side is the EA of the light emitting organic material doped in the light emitting layer adjacent to the light emitting layer. It is characterized by being 0.05 eV or more smaller than the value of.
[0010]
And claims 2 The invention of claim 1 The electron affinity (EA) value of the light emitting organic material doped in the light emitting layer located closest to the cathode side is the value of the EA of the light emitting organic material doped in the light emitting layer adjacent to the light emitting layer. It is characterized by the following.
[0011]
And claims 3 The invention of claim 1 Or 2 In which the ionization potential (IP) value (unit: eV) of the light-emitting organic material doped in the light-emitting layer located closest to the cathode is doped in the light-emitting layer adjacent to the light-emitting layer It is characterized by being 0.05 eV or more larger than the value of IP.
[0012]
And claims 4 The invention of claim 1 to claim 1 3 In any of the above, the ionization potential (IP) value of the light emitting organic material doped in the light emitting layer located closest to the anode side is equal to that of the light emitting organic material doped in the light emitting layer adjacent to the light emitting layer. It is more than the value of IP.
[0013]
Here, the electron affinity (Electron Affinity) corresponds to the absolute value of the value representing the conduction band level of the organic material with respect to the vacuum level, and the ionization potential (Ionization Potential) is the valence electron of the organic material with respect to the vacuum level. Corresponds to the absolute value of the band level. The energy gap corresponds to the difference between the ionization potential and the electron affinity in each organic substance.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0015]
The organic electroluminescent element according to the present invention includes a plurality of organic light emitting layers 3 made of an organic material doped with a light emitting organic substance (fluorescent substance) between an anode 1 and a cathode 2. As the laminated structure of the organic electroluminescent element of the present invention, any layer can be used as long as the plural light emitting layers 3 between the anode 1 and the cathode 2 correspond to the present invention. FIG. 1 shows an example of an organic electroluminescent device. An anode 1 made of a transparent conductive film or the like is laminated on the surface of a substrate 10, and a plurality of organic layers are formed on the surface of the anode 1 via a hole transport layer 11. The light emitting layer 3 is laminated, and the cathode 2 is further laminated on the light emitting layer 3 via the electron transport layer 12. An organic electroluminescence element, that is, an organic electroluminescence element (organic EL element) can be formed based on this structure. When a positive voltage is applied to the anode 1 and a negative voltage is applied to the cathode 2, the electron transport layer 12 is formed. The electrons injected into the light emitting layer 3 through the hole and the holes injected into the light emitting layer 3 through the hole transport layer 11 are combined in the light emitting layer 3 to emit light. Here, by forming the light emitting layer 3 with a structure of three or more layers, an organic electroluminescent device having high luminous efficiency in an arbitrary color tone can be obtained. A light emission color that is difficult to realize with a single light emitting layer 3 can be obtained easily and optionally as required.
[0016]
In the present invention, the light emitting layer 3 made of an organic material doped with a light emitting organic substance is formed by laminating a plurality of layers. In the embodiment shown in FIG. 1, three light emitting layers 3a, 3b, 3c are formed. Are formed in a laminated structure. The present invention relates to the energy gap of the light emitting organic material doped in the light emitting layer 3a closest to the anode 1 as the light emitting organic material doped in each of the light emitting layers 3a, 3b, 3c formed in a plurality of layers of three or more layers. And the energy gap value of the light emitting organic material doped in the light emitting layer 3c closest to the cathode 2 are selected to be larger than the energy gap values of the light emitting organic materials doped in the other light emitting layers 3b. It is what I did.
[0017]
As the light-emitting organic substance that can be used for the light-emitting layer 3 in the present invention, any known arbitrary substances can be exemplified. For example, anthracene, naphthalene, pyrene, tetracene, coronene, perylene, phthaloperylene, naphthaloperylene, diphenylbutadiene, tetraphenylbutadiene, coumarin, oxadiazole, bisbenzoxazoline, bisstyryl, cyclopentadiene, quinoline metal complex, tris (8-hydroxy Quinolinato) aluminum complex, tris (4-methyl-8-quinolinato) aluminum complex, tris (5-phenyl-8-quinolinato) aluminum complex, aminoquinoline metal complex, benzoquinoline metal complex, tri- (p-terphenyl) -4-yl) amine, 1-aryl-2,5-di (2-thienyl) pyrrole derivative, pyran, quinacridone, rubrene, distilbenzene derivative, distilarylene derivative, and these Although it has a group consisting of a luminescent compound in a part of the molecule, it is not limited to this. In addition to fluorescent dye-derived compounds typified by these compounds, light-emitting materials capable of phosphorescence emission from a triplet state can be suitably used.
[0018]
As the host material of the light emitting layer 3, either an electron transporting material or a hole transporting material can be used. They can also be used as a mixture, and in a state having a concentration gradient in the layer, the proportion of the hole transporting material is large on the anode 1 side, and the electron transporting property becomes closer to the cathode 2 side. It can also be used in such a way that the proportion of the material increases. The electron transporting host material and the hole transporting host material are not particularly limited, but from the material constituting the hole transporting layer 11 described later and the material constituting the electron transporting layer 12, It can be appropriately selected and used.
[0019]
The host material of the light emitting layer 3 may be either electron transporting or hole transporting. For example, the light emitting layer 3a closest to the anode 1 is the hole transporting host material, and the other light emitting layers 3b and 3c are electron transporting. Forming using a host material, forming the light emitting layers 3a and 3b near the anode 1 with a hole transporting host material, and forming the light emitting layer 3c closest to the cathode 2 with an electron transporting host material, The light emitting layer 3a closest to the anode 1 is a hole transporting host material, the intermediate light emitting layer 3b is a mixture of a hole transporting host material and an electron transporting host material, and the light emitting layer 3c closest to the cathode 2 is an electron transporting property. The light emitting layers 3a, 3b, 3c are all formed of an electron transporting host material, or the light emitting layers 3a, 3b, 3c are all formed of an electron transporting host material. Hole transportable host material May be formed with a mixture, or as it can be or is formed with a host material having a density gradient as described above. From the viewpoint of device lifetime, it is preferable to provide at least one light emitting layer 3 made of a hole transporting host material and at least one light emitting layer 3 made of an electron transporting host material, but the present invention is not limited to this. Moreover, it is preferable to optimize the combination of the host material and the light-emitting organic material from the viewpoint of carrier injection into the doped light-emitting organic material and energy transfer. For this purpose, the host used in the light-emitting layer 3 is preferable. The material may be different in each light emitting layer 3, and the configuration can be arbitrarily set from the viewpoint of the performance of the element, the manufacturing process, and the like.
[0020]
In the present invention, as described above, the light emitting layer 3a closest to the anode 1 and the light emitting layer 3c closest to the cathode 2 have the energy gap value of the light emitting organic material doped to the other light emitting layers 3b. The light emitting organic material to be doped in each light emitting layer 3 is selected so as to be larger than the value of the energy gap of the light emitting organic material. As a result, the light emitting layer 3 positioned on the cathode 2 side is selected as the anode. 1 Energy is efficiently transferred to the light emitting layer 3 located on the side, and the light emission efficiency of the organic electroluminescent element can be improved.
[0021]
In the present invention, the electron affinity (EA) value of the luminescent organic material doped in the luminescent layer 3b adjacent to the luminescent layer 3a is used as the luminescent organic material doped in the luminescent layer 3a located closest to the anode 1 ( Preferably, the EA value is smaller than the unit eV) by 0.05 eV or less. If this condition is not satisfied, electrons injected from the cathode 2 easily pass through the light emitting layer 3 to the anode 1 side, and the chromaticity stability, lifetime, luminous efficiency, etc. of the organic electroluminescent element are lowered. This is not preferable because it may cause The difference in electron affinity (EA) between the light emitting layer 3a closest to the anode 1 and the light emitting organic material 3b adjacent to the light emitting layer 3a should be large, and the upper limit of the difference between the two is not particularly set. Although not practical, the upper limit is about 1.2 eV.
[0022]
In the present invention, as the light emitting organic material doped in the light emitting layer 3c located closest to the cathode 2, the value of the electron affinity (EA) of the light emitting organic material doped in the light emitting layer 3b adjacent to the light emitting layer 3c is determined. However, it is preferable to select from those having a small EA value. By satisfying this condition, electrons injected from the cathode 2 are efficiently injected from the light emitting layer 3c to the light emitting layer 3b, and the lifetime and the light emission efficiency of the organic electroluminescence device can be increased.
[0023]
Further, in the present invention, as the luminescent organic material doped in the luminescent layer 3c located closest to the cathode 2, the value of the ionization potential (IP) of the luminescent organic material doped in the luminescent layer 3b adjacent to the luminescent layer 3c. It is preferable to select one having an IP value larger by 0.05 eV or more than (unit eV). If this condition is not satisfied, holes injected from the anode 1 will easily pass through the light emitting layer 3 to the cathode 2 side, and the chromaticity stability, lifetime, luminous efficiency, etc. of the organic electroluminescent element will be reduced. This is not preferable because it may cause The difference in ionization potential (IP) between the light emitting layer 3c closest to the cathode 2 and the light emitting layer 3b adjacent to the light emitting layer 3b should be large, and the upper limit of the difference between the two is not particularly set. Although not practical, the upper limit is about 1.2 eV.
[0024]
In the present invention, the ionization potential (IP) value of the luminescent organic material doped in the luminescent layer 3b adjacent to the luminescent layer 3a as the luminescent organic material doped in the luminescent layer 3a located closest to the anode 1 side. It is preferable to select one having a larger IP value. By satisfying this condition, holes injected from the anode 1 are efficiently injected from the light emitting layer 3a to the light emitting layer 3b, and the lifetime and the light emission efficiency of the organic electroluminescent element can be increased.
[0025]
The relationship between the electron affinity (EA) and the ionization potential (IP) of the light-emitting organic material that satisfies the above conditions is illustrated for the light-emitting layers 3a, 3b, and 3b having a three-layer structure as shown in FIG. For example, as shown in FIG. 2, when the EA values of the light emitting organic materials doped in the light emitting layers 3a, 3b, 3c are L1, L2, L3, and IP are H1, H2, H3, the light emitting layers 3a, 3b, The energy gaps of 3c are H1-L1, H2-L2, and H3-L3, respectively. And from said conditions of an energy gap, it is H1-L1> H2-L2, and H3-L3> H2-L2. Further, from the above conditions of electron affinity (EA), L2-L1 ≧ 0.05 and L2-L3 ≧ 0. Furthermore, from the above conditions of the ionization potential (IP), H3-H2 ≧ 0.05 and H1-H2 ≧ 0. By selecting a light emitting organic material to be doped in each light emitting layer 3 so as to satisfy such conditions, electrons injected from the cathode 2 may pass to the anode 1 side or injected from the anode 1. It is possible to prevent holes from passing to the cathode 2 side at the interface between the light emitting layer 3b and the light emitting layer 3a or at the interface between the light emitting layer 3c and the light emitting layer 3b. The balance can be improved, and the chromaticity stability, life, luminous efficiency, etc. of the organic electroluminescent element can be improved. In addition, each light emitting layer 3 comprised in three or more layers may be in contact with adjacent light emitting layers 3, or a non-light emitting layer such as an insulating layer is formed between adjacent light emitting layers 3. May be.
[0026]
Moreover, in this invention, the luminescent organic substance doped to each light emitting layer 3 may be single 1 type, and may use multiple types together. When doping a plurality of kinds of light-emitting organic substances, one or more pairs of light-emitting organic substances to be doped in the arbitrary light-emitting layer 3 and the light-emitting layer 3 adjacent thereto have the above-mentioned energy gap and electron affinity. (EA) and the condition of ionization potential (IP) should just be satisfy | filled. Further, in the above description, the light emitting layer 3 has a three-layer structure as an example, but it goes without saying that the present invention can be similarly applied even when the light emitting layer 3 has four or more layers. For the other light emitting layer 3 sandwiched between the light emitting layer 3 closest to the anode 1 and the light emitting layer 3 closest to the cathode 2, the energy gap of the light emitting organic material doped in the light emitting layer 3 closer to the cathode 2 side. Is preferably set to be larger, but is not limited to this order. As a method for doping a luminescent organic substance, a method in which a host material and a luminescent organic substance are co-evaporated, a method in which a host material and a luminescent organic substance are alternately deposited, or a luminescent substance is deposited after the host material is deposited. There are a method of diffusing a luminescent organic substance in the host material by vapor deposition, a method of forming a luminescent layer 3 by applying a solution in which the host material and the luminescent organic substance are dissolved by spin coating, etc. Any method can be used as long as it is a method in which a light-emitting organic substance is allowed to coexist.
[0027]
On the other hand, as a material constituting the hole transport layer 11 (or hole injection layer), it has the ability to transport holes, has a hole injection effect from the anode 1, and has an excellent hole injection effect for the light emitting layer 3. In addition, a compound that prevents the movement of electrons to the hole transport layer 11 and has an excellent ability to form a thin film can be used. Specifically, phthalocyanine derivatives, naphthalocyanine derivatives, porphyrin derivatives, N, N′-bis (3-methylphenyl)-(1,1′-biphenyl) -4,4′-diamine (TPD), 4,4 ′ -Aromatic diamine compounds such as bis [N- (naphthyl) -N-phenyl-amino] biphenyl (α-NPD), oxazole, oxadiazole, triazole, imidazole, imidazolone, stilbene derivative, pyrazoline derivative, tetrahydroimidazole, poly Arylalkanes, butadiene, 4,4 ′, 4 ″ -tris (N- (3-methylphenyl) N-phenylamino) triphenylamine (m-MTDATA), and polyvinylcarbazole, polysilane, polyethylenedioside thiophene (PEDOT) ), PTPDES ([Chemical 1]), etc. Child materials including but not limited to.
[0028]
[Chemical 1]

[0029]
The electron transport material constituting the electron transport layer 12 has the ability to transport electrons, has an electron injection effect from the cathode 2, and has an excellent electron injection effect for the light emitting layer 3. A compound that prevents the movement of holes to the electron transport layer 12 and has an excellent ability to form a thin film can be given. Specifically, fluorene, bathophenanthroline, bathocuproine, anthraquinodimethane, diphenoquinone, oxazole, oxadiazole, triazole, imidazole, anthraquinodimethane, 4,4′-N, N′-dicarbazole biphenyl (CBP) And their compounds, metal complex compounds, and nitrogen-containing five-membered ring derivatives. Specific examples of the metal complex compound include tris (8-hydroxyquinolinate) aluminum, tri (2-methyl-8-hydroxyquinolinate) aluminum, tris (8-hydroxyquinolinato) gallium, Bis (10-hydroxybenzo [h] quinolinato) beryllium, bis (10-hydroxybenzo [h] quinolinato) zinc, bis (2-methyl-8-quinolinato) (o-cresolate) gallium, bis (2-methyl-8) -Quinolinato) (1-naphtholato) aluminum, but is not limited thereto. The nitrogen-containing five-membered ring derivative is preferably an oxazole, thiazole, oxadiazole, thiadiazole or triazole derivative. Specifically, 2,5-bis (1-phenyl) -1,3,4-oxazole, 2,5-bis (1-phenyl) -1,3,4-thiazole, 2,5-bis (1 -Phenyl) -1,3,4-oxadiazole, 2- (4′-tert-butylphenyl) -5- (4 ″ -biphenyl) 1,3,4-oxadiazole, 2,5-bis ( 1-naphthyl) -1,3,4-oxadiazole, 1,4-bis [2- (5-phenylthiadiazolyl)] benzene, 2,5-bis (1-naphthyl) -1,3,4 -Triazole, 3- (4-biphenylyl) -4-phenyl-5- (4-t-butylphenyl) -1,2,4-triazole, and the like, but is not limited thereto. Polymer materials used in polymer organic light emitting devices can also be used. In example, polyparaphenylene and its derivatives, fluorene and its derivatives.
[0030]
The electron transport layer 12 may be doped with alkali metal, alkaline earth metal, or rare earth. For example, cesium may be doped with bathophenanthroline at a molar ratio of 1: 1 to form the electron transport layer 12.
[0031]
Moreover, what is conventionally used can be used as it is for other members constituting the organic electroluminescent element, for example, the substrate 10 holding the stacked elements, the anode 1 and the cathode 2. In addition, a light scattering layer, a microlens, a prism, or the like can be disposed on a surface from which light is extracted from the organic electroluminescent element.
[0032]
As said board | substrate 10, when the light light-emitted by the light emitting layer 3 is radiate | emitted through the board | substrate 10, what has a light transmittance is used, In addition to a colorless and transparent thing, it is somewhat colored Or a ground glass. For example, a transparent glass plate such as soda lime glass or non-alkali glass, a plastic film or a plastic plate produced by an arbitrary method from a resin such as polyester, polyolefin, polyamide, epoxy resin, or fluorine resin can be used. Furthermore, it is possible to use a material having a light diffusing effect by containing particles, powder, bubbles or the like having a refractive index different from that of the base material of the substrate 10 in the substrate 10. Further, when the light emitted from the light emitting layer 3 is emitted without passing through the substrate 10, the substrate 10 does not necessarily have to be light transmissive. An arbitrary substrate 10 can be used as long as the light emission characteristics, life characteristics, etc. of the organic electroluminescent element are not impaired, and in order to reduce the temperature rise due to the heat generation of the organic electroluminescent element particularly during energization, A highly conductive substrate 10 can also be used.
[0033]
The anode 1 is an electrode for injecting holes into the device. As the anode 1, it is preferable to use an electrode material made of a metal, an alloy, an electrically conductive compound, or a mixture thereof having a high work function. In particular, it is preferable to use an electrode material having a work function of 4 eV or more. Specific examples of such electrode materials include metals such as gold, CuI, ITO (indium-tin oxide), SnO. ₂ , ZnO, IZO (indium-zinc oxide), and other conductive transparent materials. For example, the anode 1 can be formed as a thin film by depositing these electrode materials on the substrate 10 by a method such as vacuum deposition or sputtering. When light emitted from the light emitting layer 3 is transmitted through the anode 1 and irradiated from the substrate 10 to the outside, the light transmittance of the anode 1 is preferably set to 70% or more. The sheet resistance of the anode 1 is preferably several hundred Ω / □ or less, and particularly preferably 100 Ω / □ or less. Furthermore, although the film thickness of the anode 1 varies depending on the material in order to control the light transmittance, sheet resistance and other characteristics of the anode 1 as described above, it is usually preferably set to 500 nm or less, more preferably 10 to 10 nm. The range is 200 nm.
[0034]
The cathode 2 is an electrode for injecting electrons into the light emitting layer 3, and as the cathode 2, an electrode material made of a metal, an alloy, an electrically conductive compound, or a mixture thereof having a low work function is used. It is preferable to use an electrode material having a work function of 5 eV or less. Examples of such electrode materials include alkali metals, alkali metal halides, alkali metal oxides, alkaline earth metals, rare earths, alloys of these with other metals, and the like. Examples include sodium, sodium-potassium alloy, lithium, magnesium, magnesium-silver mixture, magnesium-indium mixture, aluminum-lithium alloy, Al / LiF mixture, and the like. Besides these, aluminum, Al / Al ₂ O _Three Mixtures and the like can also be used. Further, the cathode 2 is formed by laminating one or more layers of materials (or alloys containing them) having the work function of 5 eV or less using an alkali metal oxide, an alkali metal halide, or a metal oxide as a base. It can also be produced. For example, alkali metal / Al laminate, alkali metal halide / alkaline earth metal / Al laminate, Al ₂ O _Three As an example, a laminate of / Al can be given. Alternatively, the cathode 2 may be formed with a transparent electrode typified by ITO, IZO, etc., and the light emitted from the light emitting layer 3 may be extracted from the cathode 2 side. Further, the electron transport layer 12 at the interface of the cathode 2 may be doped with an alkali metal such as lithium, sodium, cesium, or calcium, or an alkaline earth metal.
[0035]
The cathode 2 can be produced, for example, by forming the above electrode material into a thin film by a method such as a vacuum deposition method or a sputtering method. Further, when the light emitted from the light emitting layer 3 is transmitted through the cathode 2 and irradiated outside, the cathode 2 preferably has a light transmittance of 70% or more. Here, although the film thickness of the cathode 2 varies depending on the material in order to control the characteristics such as the light transmittance of the cathode 2 as described above, it is preferably set to 500 nm or less, preferably 100 to 200 nm. It should be a range. Further, when the cathode metal is formed, in order to suppress the influence of thermal radiation from the evaporation source, it is preferable to set the thickness in the range of 50 to 100 nm. When the deposition rate is increased, this thickness may be larger. Even more preferably, the thickness is in the range of 25-50 nm. This is because when the light emitting area is increased, the problem of light emission stop due to a short circuit is likely to occur, but by reducing the film thickness of the cathode metal, the cathode metal in the short circuit part is removed by the stimulation at the time of the short circuit, and only that part. This is an open mode in which the light does not shine, and it is possible to suppress the failure of stopping the light emission of the entire light emitting portion. Furthermore, a metal such as Al is laminated on the cathode 2 by sputtering, or a polymer such as a fluorine compound, a fluorine polymer, or other organic molecules is deposited, sputtered, CVD, plasma polymerized, applied, and then cured by UV. It is also possible to form it by the method of making it, thermosetting, and other methods.
[0036]
【Example】
Next, the present invention will be specifically described with reference to examples. The values of the energy gap, electron affinity (EA), and ionization potential (IP) of the light-emitting organic material used are shown together in Table 1, and the structures of the light emitting layers 3a, 3b, and 3c are shown together in Table 2.
[0037]
Example 1
A transparent glass plate having a thickness of 0.7 mm is used as the substrate 10, and an anode 1 made of a transparent electrode having a sheet resistance of 7Ω / □ is formed on one surface of the substrate 10 by sputtering ITO (indium-tin oxide). did. This was ultrasonically washed with acetone, pure water, and isopropyl alcohol for 15 minutes, and then dried.
[0038]
Next, the substrate 10 is set in a vacuum deposition apparatus, and 1 × 10 ^-6 Torr (1.33 × 10 ^-Four Pa), 4,4′-bis [N- (naphthyl) -N-phenyl-amino] biphenyl (manufactured by Dojindo Laboratories Co., Ltd .; hereinafter abbreviated as α-NPD) was deposited to a thickness of 1000 mm, and the anode A hole transport layer 11 was formed on 1.
[0039]
Next, α-NPD and a DSA derivative (“BCzVBi” manufactured by Idemitsu Kosan Co., Ltd .: Chemical formula 1) are co-deposited on the hole transport layer 11 at a molar ratio of 94: 6 to a thickness of 100 mm to obtain a light-emitting organic substance. A light emitting layer 3a doped with BCzVBi was formed. Further, a distyryl biphenyl derivative (“DPVBi” manufactured by Idemitsu Kosan Co., Ltd .: Chemical formula 2) and rubrene (Chemical formula 3) and a rubrene (chemical formula 3) are co-evaporated in a molar ratio of 98: 2 on top of this, and rubrene is doped as a light-emitting organic substance. The light emitting layer 3b was formed. Further, DPVBi and BCzVBi were co-evaporated at a molar ratio of 94: 6 to a thickness of 400 mm thereon to form a light emitting layer 3c doped with BCzVBi as a light emitting organic material. In addition, the vapor deposition rate of said organic layer was set to 1-2 Å / s.
[0040]
[Chemical 2]

[0041]
[Chemical 3]

[0042]
[Formula 4]

[0043]
Next, on the light emitting layer 3c, bathophenanthroline (manufactured by Dojindo Laboratories Co., Ltd .: BCP) and Cs are co-evaporated at a molar ratio of 1: 1 to form an electron transport layer 12 having a thickness of 200 mm. Then, Al was deposited on the electron transport layer 12 at a thickness of 1500 Å at a deposition rate of 10 Å / s to form the cathode 2, thereby obtaining an organic electroluminescent device having a configuration as shown in FIG. 1.
[0044]
(Example 2)
α-NPD and Sigma Aldrich Japan KK: “Coumarin 6” is co-evaporated at a molar ratio of 98: 2 to a film thickness of 100 mm to form a luminescent layer 3a doped with Coumarin 6 as a luminescent organic substance. Then, by co-evaporating DPVBi and “DCJTB” manufactured by Eastman Kodak Co. in a molar ratio of 98: 2 to a film thickness of 50 mm, a light emitting layer 3b doped with DCJTB as a light emitting organic material is formed, and DPVBi and BCzVBi are formed. As in Example 1, except that the light emitting layer 3c doped with BCzVBi as a light emitting organic material is formed by co-evaporation at a molar ratio of 94: 6 to a film thickness of 400 mm, as shown in FIG. An organic electroluminescent device having the structure was obtained.
[0045]
(Comparative Example 1)
By co-evaporating DPVBi and rubrene at a molar ratio of 98: 2 to a film thickness of 100 mm, the luminescent layer 3a doped with rubrene as the luminescent organic material is formed, and the luminescent layer 3c is formed without forming the luminescent layer 3b. Formed as in Example 1. Other than that was carried out similarly to Example 1, and obtained the organic electroluminescent element.
[0046]
(Comparative Example 2)
By co-evaporating α-NPD and rubrene at a molar ratio of 98: 2 to a film thickness of 100 mm, a light emitting layer 3a doped with rubrene as a luminescent organic material is formed, and DPVBi and BCzVBi are formed at a molar ratio of 94: 6. The light emitting layer 3b doped with BCzVBi is formed as a luminescent organic material by co-evaporation at 400 、, and rubrene as a luminescent organic material is formed by co-evaporation of DPVBi and rubrene at a molar ratio of 98: 2 at a film thickness of 100 Å. An organic electroluminescent element was obtained in the same manner as in Example 1 except that the light emitting layer 3c doped with was formed.
[0047]
(Comparative Example 3)
By co-evaporating α-NPD and BCzVBi at a molar ratio of 94: 6 to a film thickness of 400 mm, a light emitting layer 3a doped with BCzVBi as a luminescent organic material is formed, and DPVBi and coumarin 6 are formed at a molar ratio of 98: 2. By co-evaporating to a thickness of 100 mm, a luminescent layer 3b doped with coumarin 6 is formed as a luminescent organic material, and by co-evaporating DPVBi and DCJTB in a molar ratio of 98: 2 to a thickness of 50 mm, As in Example 1, an organic electroluminescent element was obtained except that the light emitting layer 3c doped with DCJTB was formed.
[0048]
[Table 1]

[0049]
Table 2 shows the compositions of the light-emitting elements 3a, 3b, and 3c for Examples 1 to 2 and Comparative Examples 1 to 3 described above.
[0050]
[Table 2]

[0051]
For Examples 1 to 2 and Comparative Examples 1 to 3, the energy gap, electron affinity (EA), and ionization potential (IP) of the light emitting organic material doped in the light emitting elements 3a, 3b, and 3c are collectively shown. 3 shows.
[0052]
[Table 3]

[0053]
With respect to the organic electroluminescent elements obtained in Examples 1-2 and Comparative Examples 1-3 as described above, the luminescence chromaticity, power consumption, quantum efficiency, and element half-life were measured, and the results are shown in Table 4.
[0054]
The chromaticity of the organic electroluminescent element was evaluated by CIE chromaticity coordinates. The measurement was performed by connecting the organic electroluminescence device to a power source (“KEYTHLEY236 model” manufactured by Toyo Technica Co., Ltd.) and using a multi-channel analyzer (“PMA-10” manufactured by Hamamatsu Photonics Co., Ltd.) with a luminance of 200 cd / m. ² It performed on condition of this. The luminance was measured with “BM-5A” manufactured by Topcon Corporation.
[0055]
The power consumption of the organic electroluminescent device is measured by connecting the organic electroluminescent device to a power source (“KEYTHLEY 236 model” manufactured by Toyo Technica Co., Ltd.) and 200 cd / m. ² It calculated from the value in the state made to light-emit on the conditions of.
[0056]
The quantum efficiency of the organic electroluminescent device was calculated based on a conventional method from the emission spectrum, luminance, applied voltage, and current amount of the organic electroluminescent device.
[0057]
Measurement of the half-life of the organic electroluminescent element is that the initial luminance is 200 cd / m. ² A predetermined current value is determined in advance, and then a predetermined current is applied to the organic electroluminescent element using a constant current power source. The luminance is 100 cd / m, which is half of the initial luminance. ² This was done by measuring the time until it became a half-life.
[0058]
[Table 4]

[0059]
As seen in Table 4, the organic electroluminescent elements of Examples 1 and 2 have low power consumption, high quantum efficiency, excellent light emission efficiency, long half life, long life and high light emission. It was confirmed that efficiency could be realized.
[0060]
【The invention's effect】
As described above, the organic electroluminescent device according to claim 1 of the present invention is different from the organic electroluminescent device having a light emitting layer made of an organic material doped with a luminescent organic material between an anode and a cathode. A light-emitting organic substance doped with a light-emitting organic substance doped with a light-emitting layer located on the most anode side and a light-emitting layer located on the most cathode side. Since the value is larger than the value of the energy gap of the light emitting organic material doped in the light emitting layer other than these, by defining the energy gap of the light emitting organic material doped in the light emitting layer in this way The energy can be efficiently transferred from the light emitting layer located on the cathode side to the light emitting layer located on the anode side. In which it is possible to realize an optical efficiency.
[0061]
Ma The The electron affinity (EA) value (unit eV) of the light emitting organic material doped in the light emitting layer located closest to the anode side is the EA of the light emitting organic material doped in the light emitting layer adjacent to the light emitting layer. Since the electron affinity (EA) of the light-emitting organic material doped in the light-emitting layer is defined in this manner, electrons injected from the cathode pass through the light-emitting layer. Thus, the organic electroluminescence device can be prevented from passing to the anode side, and the lifetime of the organic electroluminescence device can be increased and high luminous efficiency can be realized.
[0062]
And claims 2 The invention of claim 1 The electron affinity (EA) value of the light emitting organic material doped in the light emitting layer located closest to the cathode side is the value of the EA of the light emitting organic material doped in the light emitting layer adjacent to the light emitting layer. Since the electron affinity (EA) of the light-emitting organic material doped in the light-emitting layer is defined in this manner, electrons injected from the cathode are adjacent to the light-emitting layer located closest to the cathode side. As a result, the organic electroluminescence device can be efficiently injected into the light emitting layer, and the lifetime of the organic electroluminescence device can be increased and high light emission efficiency can be realized.
[0063]
And claims 3 The invention of claim 1 Or 2 In which the ionization potential (IP) value (unit: eV) of the light-emitting organic material doped in the light-emitting layer located closest to the cathode is doped in the light-emitting layer adjacent to the light-emitting layer Since the ionization potential (IP) of the light-emitting organic material doped in the light-emitting layer is defined in this manner, holes injected from the anode are formed in the light-emitting layer. It is possible to prevent the organic electroluminescence device from passing through and to the cathode side, and to realize a long life and high luminous efficiency of the organic electroluminescence device.
[0064]
And claims 4 The invention of claim 1 to claim 1 3 In any of the above, the ionization potential (IP) value of the light emitting organic material doped in the light emitting layer located closest to the anode side is equal to that of the light emitting organic material doped in the light emitting layer adjacent to the light emitting layer. Since the value is equal to or greater than the value of IP, by defining the ionization potential (IP) of the light-emitting organic material doped in the light-emitting layer in this way, the light-emitting layer in which holes injected from the anode are located on the most anode side Can be efficiently injected into the adjacent light emitting layer, and the lifetime of the organic electroluminescent device can be extended and high luminous efficiency can be realized.
[Brief description of the drawings]
FIG. 1 is a front view showing a schematic configuration of an example of an organic electroluminescent element.
FIG. 2 is a front view showing a schematic configuration of the light emitting layer.
[Explanation of symbols]
1 Anode
2 Cathode
3 Light emitting layer
3a, 3b, 3c Light emitting layer

Claims (4)

In an organic electroluminescent device having a light emitting layer made of an organic material doped with a light emitting organic substance between an anode and a cathode, at least three light emitting layers made of an organic material doped with different light emitting organic substances The energy gap value of the light emitting organic material doped in the light emitting layer located closest to the anode side and the light emitting layer located closest to the cathode side of the light emitting organic material doped in other light emitting layers rather greater than the value of the energy gap, and most value of the electron affinity of the light-emitting organic material that is doped in the light emitting layer located on the anode side (EA) (unit eV) is doped into the light emitting layer adjacent to the light-emitting layer the organic electroluminescent device characterized by small Ikoto than 0.05eV than the value of EA luminous organic material being. The electron affinity (EA) value of the light emitting organic material doped in the light emitting layer located closest to the cathode side is less than or equal to the EA value of the light emitting organic material doped in the light emitting layer adjacent to the light emitting layer. the organic electroluminescence device according to claim 1, characterized in that. The value (unit eV) of the ionization potential (IP) of the light emitting organic material doped in the light emitting layer located closest to the cathode side is the IP of the light emitting organic material doped in the light emitting layer adjacent to the light emitting layer. The organic electroluminescent element according to claim 1, wherein the organic electroluminescent element is 0.05 eV or more larger than the value of . The ionization potential (IP) value of the light emitting organic material doped in the light emitting layer located closest to the anode side is equal to or greater than the IP value of the light emitting organic material doped in the light emitting layer adjacent to the light emitting layer. the organic electroluminescence device according to any one of claims 1 to 3, characterized in that there.

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