JP3852520B2 - Organic electroluminescence device - Google Patents

Description

〔但し、前記一般式（１）において、
Ｒ¹及びＲ⁴は互いに同一の又は異なる基であって、下記一般式（２）で表されるアリール基であり

（但し、前記一般式（２）において、Ｒ⁹、Ｒ¹⁰、Ｒ¹¹、Ｒ¹²及びＲ¹³は互いに同一の又は異なる基であって、水素原子、又はそれらの少なくとも１つが飽和又は不飽和アルコキシル基、又はアルキル基（メチル基、ターシャリーブチル基が好ましい。）である。）、
Ｒ²及びＲ³は互いに同一の又は異なる基であって、下記一般式（３）で表されるアリール基であり

（但し、前記一般式（３）において、Ｒ¹⁴、Ｒ¹⁵、Ｒ¹⁶、Ｒ¹⁷、Ｒ¹⁸、Ｒ¹⁹及びＲ²⁰は互いに同一の又は異なる基であって、水素原子、又はそれらの少なくとも１つが飽和又は不飽和アルコキシル基、又はアルキル基（メチル基、ターシャリーブチル基が好ましい。）である。）、
Ｒ⁵、Ｒ⁶、Ｒ⁷及びＲ⁸は互いに同一の又は異なる基であって、その少なくとも１つがシアノ基又はニトロ基である。〕
【００１６】
上記一般式（１）のジスチリル化合物を発光材料に用いることによって、高輝度で安定な黄色〜橙色発光が得られると共に、電気的、熱的或いは化学的にも安定性に優れた素子を提供できる。
【００１７】
【発明の実施の形態】
本発明の有機電界発光素子に用いるジスチリル化合物について説明する。
【００１８】
本発明の有機電界発光素子において、発光材料である一般式（１）で示されるジスチリル化合物は、例えば下記構造式（４）−１、（４）−２、（４）−３、（４）−４、（４）−５、（４）−６、（４）−７、（４）−８又は（４）−９のような分子構造の少なくとも１種が使用可能である。

【００１９】
図１〜図４には、本発明に基づく有機電界発光素子の例をそれぞれ示す。
【００２０】
図１は陰極３を発光光２０が透過する透過型有機電界発光素子Ａであって、発光２０は保護層４の側からも観測できる。図２は陰極３での反射光も発光光２０として得る反射型有機電界発光素子Ｂを示す。
【００２１】
図中、１は有機電界発光素子を形成するための基板であり、ガラス、プラスチック及び他の適宜の材料を用いることができる。また、有機電界発光素子を他の表示素子と組み合わせて用いる場合には、基板を共用することもできる。２は透明電極（陽極）であり、ＩＴＯ（Ｉｎｄｉｕｍ ｔｉｎ ｏｘｉｄｅ）、ＳｎＯ₂ 等を使用できる。
【００２２】
また、５は有機発光層であり、上記したジスチリル化合物を発光材料として含有している。この発光層について、有機電界発光２０を得る層構成としては、従来公知の種々の構成を用いることができる。後述するように、例えば、正孔輸送層と電子輸送層のいずれかを構成する材料が発光性を有する場合、これらの薄膜を積層した構造を使用できる。更に本発明の目的を満たす範囲で電荷輸送性能を上げるために、正孔輸送層と電子輸送層のいずれか若しくは両方が、複数種の材料の薄膜を積層した構造、または、複数種の材料を混合した組成からなる薄膜を使用するのを妨げない。また、発光性能を上げるために、少なくとも１種以上の蛍光性の材料を用いて、この薄膜を正孔輸送層と電子輸送層の間に挟持した構造、更に少なくとも１種以上の蛍光性の材料を正孔輸送層若しくは電子輸送層、またはこれらの両方に含ませた構造を使用しても良い。これらの場合には、発光効率を改善するために、正孔または電子の輸送を制御するための薄膜をその層構成に含ませることも可能である。
【００２３】
上記の構造式（３）で例示したジスチリル化合物は、電子輸送性能と正孔輸送性能の両方を持つため、素子構成中、電子輸送層を兼ねた発光層としても、或いは正孔輸送層を兼ねた発光層としても用いることが可能である。また、このジスチリル化合物を発光層として、電子輸送層と正孔輸送層とで挟み込んだ構成とすることも可能である。
【００２４】
なお、図１及び図２中、３は陰極であり、電極材料としては、Ｌｉ、Ｍｇ、Ｃａ等の活性な金属とＡｇ、Ａｌ、Ｉｎ等の金属との合金、或いはこれらを積層した構造を使用できる。透過型の有機電界発光素子においては、陰極の厚さを調節することにより、用途に合った光透過率を得ることができる。また、図４は封止・保護層であり、有機電界発光素子全体を覆う構造とすることにより、その効果が上がる。気密性が保たれれば、適宜の材料を使用することができる。また、８は電流注入用の駆動電源である。
【００２５】
本発明に基づく有機電界発光素子において、有機層が、正孔輸送層と電子輸送層とが積層された有機積層構造（シングルヘテロ構造）を有しており、正孔輸送層又は電子輸送層の形成材料として前記ジスチリル化合物が用いられてよい。或いは、有機層が、正孔輸送層と発光層と電子輸送層とが順次積層された有機積層構造（ダブルヘテロ構造）を有しており、発光層の形成材料として前記ジスチリル化合物が用いられてよい。
【００２６】
このような有機積層構造を有する有機電界発光素子の例を示すと、図３は、透光性の基板１上に、透光性の陽極２と、正孔輸送層６と電子輸送層７とからなる有機層５ａと、陰極３とが順次積層された積層構造を有し、この積層構造が保護膜４によって封止されてなる、シングルヘテロ構造の有機電界発光素子Ｃである。
【００２７】
図３に示すように発光層を省略した層構成の場合には、正孔輸送層６と電子輸送層７の界面から所定波長の発光２０を発生する。これらの発光は基板１側から観測される。
【００２８】
また、図４は、透光性の基板１上に、透光性の陽極２と、正孔輸送層１０と発光層１１と電子輸送層１２とからなる有機層５ｂと、陰極３とが順次積層された積層構造を有し、この積層構造が保護膜４によって封止されてなる、ダブルヘテロ構造の有機電界発光素子Ｄである。
【００２９】
図４に示した有機電界発光素子においては、陽極２と陰極３の間に直流電圧を印加することにより、陽極２から注入された正孔が正孔輸送層１０を経て、また陰極３から注入された電子が電子輸送層１２を経て、それぞれ発光層１１に到達する。この結果、発光層１１においては電子／正孔の再結合が生じて一重項励起子が生成し、この一重項励起子から所定波長の発光を発生する。
【００３０】
上述した各有機電界発光素子Ｃ、Ｄにおいて、基板１は、例えば、ガラス、プラスチック等の光透過性の材料を適宜用いることができる。また、他の表示素子と組み合わせて用いる場合や、図３及び図４に示した積層構造をマトリックス状に配置する場合等は、この基板を共用としてよい。、また、素子Ｃ、Ｄはいずれも、透過型、反射型のいずれの構造も採りうる。
【００３１】
また、陽極２は、透明電極であり、ＩＴＯ（indium tin oxide）やＳｎＯ₂ 等が使用できる。この陽極２と正孔輸送層６（又は正孔輸送層１０）との間には、電荷の注入効率を改善する目的で、有機物若しくは有機金属化合物からなる薄膜を設けてもよい。なお、保護膜４が金属等の導電性材料で形成されている場合は、陽極２の側面に絶縁膜が設けられていてもよい。
【００３２】
また、有機電界発光素子Ｃにおける有機層５ａは、正孔輸送層６と電子輸送層７とが積層された有機層であり、これらのいずれか又は双方に上記したジスチリル化合物が含有され、発光性の正孔輸送層６又は電子輸送層７としてよい。有機電界発光素子Ｄにおける有機層５ｂは、正孔輸送層１０と上記したジスチリル化合物を含有する発光層１１と電子輸送層１２とが積層された有機層であるが、その他、種々の積層構造を取ることができる。例えば、正孔輸送層と電子輸送層のいずれか若しくは両方が発光性を有していてもよい。
【００３３】
また、特に、正孔輸送層６又は電子輸送層７や発光層１１が本発明のジスチリル化合物からなる層であることが望ましいが、これらの層を前記ジスチリル化合物のみで形成してもよく、或いは、前記ジスチリル化合物と他の正孔又は電子輸送材料（例えば、芳香族アミン類やピラゾリン類等）との共蒸着によって形成してもよい。さらに、正孔輸送層において、正孔輸送性能を向上させるために、複数種の正孔輸送材料を積層した正孔輸送層を形成してもよい。
【００３４】
また、有機電界発光素子Ｃにおいて、発光層は電子輸送性発光層７であってよいが、電源８から印加される電圧によっては、正孔輸送層６やその界面で発光される場合がある。同様に、有機電界発光素子Ｄにおいて、発光層は層１１以外に、電子輸送層１２であってもよく、正孔輸送層１０であってもよい。発光性能を向上させるために、少なくとも１種の蛍光性材料を用いた発光層１１を正孔輸送層と電子輸送層との間に挟持させた構造であるのがよい。または、この蛍光性材料を正孔輸送層又は電子輸送層、或いはこれら両層に含有させた構造を構成してよい。このような場合、発光効率を改善するために、正孔又は電子の輸送を制御するための薄膜（ホールブロッキング層やエキシトン生成層など）をその層構成に含ませることも可能である。
【００３５】
また、陰極３に用いる材料としては、Ｌｉ、Ｍｇ、Ｃａ等の活性な金属とＡｇ、Ａｌ、Ｉｎ等の金属との合金を使用でき、これらの金属層が積層した構造であってもよい。なお、陰極の厚みや材質を適宜選択することによって、用途に見合った有機電界発光素子を作製できる。
【００３６】
また、保護膜４は、封止膜として作用するものであり、有機電界発光素子全体を覆う構造とすることで、電荷注入効率や発光効率を向上できる。なお、その気密性が保たれれば、アルミニウム、金、クロム等の単金属又は合金など、適宜その材料を選択できる。
【００３７】
上記した各有機電界発光素子に印加する電流は通常、直流であるが、パルス電流や交流を用いてもよい。電流値、電圧値は、素子破壊しない範囲内であれば特に制限はないが、有機電界発光素子の消費電力や寿命を考慮すると、なるべく小さい電気エネルギーで効率良く発光させることが望ましい。
【００３８】
次に、図５は、本発明の有機電界発光素子を用いた平面ディスプレイの構成例である。図示の如く、例えばマルチカラーディスプレイの場合は、黄（Ｙ）、緑（Ｇ）及び青（Ｂ）の３色を発光可能な有機層５（５ａ、５ｂ）が、陰極３と陽極２との間に配されている。陰極３及び陽極２は、互いに交差するストライプ状に設けることができ、輝度信号回路１４及びシフトレジスタ内蔵の制御回路１５により選択されて、それぞれに信号電圧が印加され、これによって、選択された陰極３及び陽極２が交差する位置（画素）の有機層が発光するように構成される。
【００３９】
即ち、図５は例えば８×３ＹＧＢ単純マトリックスであって、正孔輸送層と、発光層および電子輸送層のいずれか少なくとも一方とからなる積層体５を陰極３と陽極２の間に配置したものである（図３又は図４参照）。陰極と陽極は、ともにストライプ状にパターニングするとともに、互いにマトリクス状に直交させ、シフトレジスタ内蔵の制御回路１５および１４により時系列的に信号電圧を印加し、その交叉位置で発光するように構成されたものである。かかる構成のＥＬ素子は、文字・記号等のディスプレイとしては勿論、画像再生装置としても使用できる。また陰極３と陽極２のストライプ状パターンを黄（Ｙ）、緑（Ｇ）、青（Ｂ）の各色毎に配し、マルチカラーの全固体型フラットパネルディスプレイを構成することが可能となる。
【００４０】
【実施例】
以下、本発明を実施例について具体的に説明するが、本発明は以下の実施例に限定されるものではない。
【００４１】
実施例１
本実施例は、一般式（１）の上記ジスチリル化合物のうち、Ｒ¹ 、Ｒ⁴ に無置換フェニル基を、Ｒ² 、Ｒ³ に無置換ナフチル基を、Ｒ⁵ 、Ｒ⁷ にシアノ基を持った下記構造式（４）−２の化合物を正孔輸送性発光材料として用い、シングルヘテロ構造の有機電界発光素子を作製した例である。
【化４】

【００４２】
まず、真空蒸着装置中に、１００ｎｍの厚さのＩＴＯからなる陽極が一表面に形成された３０ｍｍ×３０ｍｍのガラス基板をセッティングした。蒸着マスクとして、複数の２．０ｍｍ×２．０ｍｍの単位開口を有する金属マスクを基板に近接して配置し、真空蒸着法により１０^-4Ｐａ以下の真空下で上記構造式（４）−２の化合物を例えば５０ｎｍの厚さに正孔輸送層（兼発光層）として成膜した。蒸着レートは０．１ｎｍ／秒とした。
【００４３】
さらに、電子輸送材料として下記構造式のＡｌｑ₃ （トリス（８−キノリノール）アルミニウム）を正孔輸送層に接して蒸着した。Ａｌｑ₃ からなるこの電子輸送層の膜厚も例えば５０ｎｍとし、蒸着レートは０．２ｎｍ／秒とした。
【化５】

【００４４】
陰極材料としてはＭｇとＡｇの積層膜を採用し、これも蒸着により、蒸着レート１ｎｍ／秒として例えば５０ｎｍ（Ｍｇ膜）および１５０ｎｍ（Ａｇ膜）の厚さに形成し、実施例１による図３に示した如き有機電界発光素子を作製した。
【００４５】
このように作製した実施例１の有機電界発光素子に、窒素雰囲気下で順バイアス直流電圧を加えて発光特性を評価した。発光色は黄色であり、分光測定を行った結果、図６に示すように、５７８ｎｍに発光ピークを有するスペクトルを得た。分光測定は、大塚電子社製のフォトダイオードアレイを検出器とした分光器を用いた。また、電圧−輝度測定を行ったところ、図９に示すように、８Ｖで６５００ｃｄ／ｍ² の輝度が得られた。
【００４６】
この有機電界発光素子を作製後、窒素雰囲気下に１カ月間放置したが、素子劣化は観察されなかった。また、初期輝度３００ｃｄ／ｍ² で電流値を一定に通電して連続発光し、強制劣化させた際、輝度が半減するまで４０００時間であった。
【００４７】
実施例２
本実施例は、一般式（１）の上記ジスチリル化合物のうち、Ｒ¹ 、Ｒ⁴ に無置換フェニル基を、Ｒ² 、Ｒ³ に無置換ナフチル基を、Ｒ⁵ 、Ｒ⁷ にシアノ基を持った上記構造式（４）−２の化合物を電子輸送性発光材料として用い、シングルヘテロ構造の有機電界発光素子を作製した例である。
【００４８】
まず、真空蒸着装置中に、１００ｎｍの厚さのＩＴＯからなる陽極が一表面に形成された３０ｍｍ×３０ｍｍのガラス基板をセッティングした。蒸着マスクとして、複数の２．０ｍｍ×２．０ｍｍの単位開口を有する金属マスクを基板に近接して配置し、真空蒸着法により１０^-4Ｐａ以下の真空下で、下記構造式のα−ＮＰＤ（α−ナフチルフェニルジアミン）を例えば５０ｎｍの厚さに正孔輸送層として成膜した。蒸着レートは０．１ｎｍ／秒とした。
【化６】

【００４９】
さらに、電子輸送材料として上記構造式（４）−２の化合物を正孔輸送層に接して蒸着した。上記構造式（４）−２の化合物からなる電子輸送層（兼発光層）の膜厚も例えば５０ｎｍとし、蒸着レートは０．２ｎｍ／秒とした。
【００５０】
陰極材料としてはＭｇとＡｇの積層膜を採用し、これも蒸着により、蒸着レート１ｎｍ／秒として例えば５０ｎｍ（Ｍｇ膜）および１５０ｎｍ（Ａｇ膜）の厚さに形成し、実施例２による図３に示した如き有機電界発光素子を作製した。
【００５１】
このように作製した実施例２の有機電界発光素子に、窒素雰囲気下で順バイアス直流電圧を加えて発光特性を評価した。発光色は黄色であり、実施例１と同様に分光測定を行った結果、図７に示すように、５７８ｎｍに発光ピークを有するスペクトルを得た。また、電圧−輝度測定を行ったところ、図１０に示すように、８Ｖで５９００ｃｄ／ｍ² の輝度が得られた。
【００５２】
この有機電界発光素子を作製後、窒素雰囲気下に１カ月間放置したが、素子劣化は観察されなかった。また、初期輝度３００ｃｄ／ｍ² で電流値を一定に通電して連続発光し、強制劣化させた際、輝度が半減するまで３５００時間であった。
【００５３】
実施例３
本実施例は、一般式（１）の上記ジスチリル化合物のうち、Ｒ¹ 、Ｒ⁴ に無置換フェニル基を、Ｒ² 、Ｒ³ に無置換ナフチル基を、Ｒ⁵ 、Ｒ⁷ にシアノ基を持った上記構造式（４）−２の化合物を発光材料として用い、ダブルヘテロ層構造の有機電界発光素子を作製した例である。
【００５４】
まず、真空蒸着装置中に、１００ｎｍの厚さのＩＴＯからなる陽極が一表面に形成された３０ｍｍ×３０ｍｍのガラス基板をセッティングした。蒸着マスクとして、複数の２．０ｍｍ×２．０ｍｍの単位開口を有する金属マスクを基板に近接して配置し、真空蒸着法により１０^-4Ｐａ以下の真空下で、上記構造式のα−ＮＰＤを例えば３０ｎｍの厚さに正孔輸送層として成膜した。蒸着レートは０．２ｎｍ／秒とした。
【００５５】
さらに、発光材料として上記構造式（４）−２の化合物を正孔輸送層に接して蒸着した。上記構造式（４）−２の化合物からなる発光層の膜厚も例えば３０ｎｍとし、蒸着レートは０．２ｎｍ／秒とした。
【００５６】
さらに、電子輸送材料として上記構造式のＡｌｑ₃ を発光層に接して蒸着した。Ａｌｑ₃ の膜厚を例えば３０ｎｍとし、蒸着レートは、０．２ｎｍ／秒とした。
【００５７】
陰極材料としてはＭｇとＡｇの積層膜を採用し、これも蒸着により、蒸着レート１ｎｍ／秒として例えば５０ｎｍ（Ｍｇ膜）および１５０ｎｍ（Ａｇ膜）の厚さに形成し、実施例３による図４に示した如き有機電界発光素子を作製した。
【００５８】
このように作製した実施例３の有機電界発光素子に、窒素雰囲気下で順バイアス直流電圧を加えて発光特性を評価した。発光色は黄色であり、分光測定を行った結果、図８に示すように、５７８ｎｍに発光ピークを有するスペクトルを得た。電圧−輝度測定を行ったところ、図１１に示すように、８Ｖで７５００ｃｄ／ｍ² の輝度が得られた。
【００５９】
この有機電界発光素子を作製後、窒素雰囲気下に１カ月間放置したが、素子劣化は観察されなかった。また、初期輝度３００ｃｄ／ｍ² で電流値を一定に通電して連続発光し、強制劣化させた際、輝度が半減するまで５０００時間であった。
【００６０】
実施例４
正孔輸送性材料としてα−ＮＰＤに替えて下記構造式のＴＰＤ（トリフェニルジアミン誘導体）を用いた他は層構成、成膜法とも実施例２に準拠して、有機電界発光素子を作製した。

【００６１】
本実施例の有機電界発光素子も実施例２と同様の黄色の発光を呈した。分光測定の結果、スペクトルは実施例２の有機電界発光素子のスペクトルと一致した。
【００６２】
【発明の作用効果】
本発明の有機電界発光素子によれば、発光領域を有する有機層が陽極と陰極との間に設けられている有機電界発光素子において、前記有機層に前記一般式（１）で表されるジスチリル化合物が含まれているので、高輝度で安定な黄色〜橙色発光を有する有機電界発光素子を提供することが可能となる。
【図面の簡単な説明】
【図１】本発明に基づく有機電界発光素子の要部概略断面図である。
【図２】同、有機電界発光素子の他の要部概略断面図である。
【図３】同、有機電界発光素子の他の要部概略断面図である。
【図４】同、有機電界発光素子の他の要部概略断面図である。
【図５】同、有機電界発光素子を用いたマルチカラーの平面ディスプレイの構成図である。
【図６】本発明の実施例１による有機電界発光素子の発光スペクトル図である。
【図７】同、実施例２による有機電界発光素子の発光スペクトル図である。
【図８】同、実施例３による有機電界発光素子の発光スペクトル図である。
【図９】同、実施例１による有機電界発光素子の電圧−輝度特性図である。
【図１０】同、実施例２による有機電界発光素子の電圧−輝度特性図である。
【図１１】同、実施例３による有機電界発光素子の電圧−輝度特性図である。
【符号の説明】
１…基板、２…透明電極（陽極）、３…陰極、４…保護膜、
５、５ａ、５ｂ…有機層、６…正孔輸送層、７…電子輸送層、
８…電源、１０…正孔輸送層、１１…発光層、１２…電子輸送層、
１４…輝度信号回路、１５…制御回路、２０…発光光、
Ａ、Ｂ、Ｃ、Ｄ…有機電界発光素子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic electroluminescent element (organic EL element) in which an organic layer having a light emitting region is provided between an anode and a cathode.
[0002]
[Prior art]
Lightweight and high-efficiency flat panel displays have been actively researched and developed for display on computers and televisions, for example.
[0003]
First, a cathode ray tube (CRT) is currently used most frequently as a display because of its high luminance and good color reproducibility, but it has a problem that it is bulky, heavy, and consumes high power.
[0004]
In addition, liquid crystal displays such as active matrix driving have been commercialized as lightweight and highly efficient flat panel displays. However, the liquid crystal display has a narrow viewing angle and is not self-luminous, so the backlight consumes a lot of power in an environment where the surroundings are dark, and the high-definition high-speed video signal expected to be put to practical use in the future. In addition, there are problems such as not having sufficient response performance. In particular, it is difficult to produce a display with a large screen size, and there are problems such as high cost.
[0005]
As an alternative to this, there is a possibility of a display using light-emitting diodes, but there are problems such as high manufacturing cost and difficulty in forming a matrix structure of light-emitting diodes on one substrate. As a low-priced display candidate to replace, there is a big problem until practical use.
[0006]
Recently, an organic electroluminescent element (organic EL element) using an organic light emitting material has attracted attention as a flat panel display that can solve these problems. That is, by using an organic compound as a light-emitting material, it is expected to realize a flat panel display that is self-luminous, has a high response speed, and has no viewing angle dependency.
[0007]
The structure of the organic electroluminescent element is such that an organic thin film containing a light emitting material that emits light by current injection is formed between a light transmitting positive electrode and a metal cathode. CW Tang, SA Van Slyke et al., In a research report published in Applied Physics Letters Vol. 51, No. 51, pages 913-915 (1987), As a two-layer structure, an element structure was developed that emits light by recombination of holes and electrons injected from each electrode into the organic film (single heterostructure organic EL element).
[0008]
In this element structure, either the hole transport material or the electron transport material also serves as the light emitting material, and light emission occurs in a wavelength band corresponding to the energy gap between the ground state and the excited state of the light emitting material. By adopting such a two-layer structure, the driving voltage was greatly reduced and the luminous efficiency was improved.
[0009]
Then, as described in a research report published in Japanese Journal of Applied Physics Vol. 27, No. 2, pages L269-L271 (1988) by C. Adachi, S. Tokita, T. Tsutsui, S. Saito, etc. A three-layer structure (a double heterostructure organic EL device) of a hole transport material, a light-emitting material, and an electron transport material was developed. Furthermore, Journal of Applied Physics Vol. 65, No. 9, 3610, such as CW Tang, SA Van Slyke, CH Chen As described in a research report published on page 3616 (1989), an element structure in which a light emitting material is included in an electron transport material has been developed. These studies have verified the possibility of light emission at low voltage and high brightness, and research and development have been very active in recent years.
[0010]
[Problems to be solved by the invention]
However, there are actually problems that need to be solved even in organic electroluminescent devices. Development of a stable high-luminance light-emitting element is difficult. As an electron transport material currently reported, tris (8-quinolinol) aluminum (hereinafter abbreviated as Alq ₃ ) and DCM [4-dicyanomethylene-6- (p Even in the example of red light emission doped with [dimethylaminostyryl) -2-methyl-4H-pyran], neither the maximum luminance nor the reliability is satisfactory as a display material.
[0011]
BSB-BCN, reported by T. Tsutsui, DUKim at the Inorganic and Organic electroluminescence conference (1996, Berlin), achieves a high luminance of 1000 cd / m ² or more, but it is more bright and stable yellow to orange. Realization of such a light emitting element is desired at present.
[0012]
Japanese Patent Application Laid-Open No. 7-188649 (Japanese Patent Application No. 6-148798) proposes to use a specific distyryl compound as an organic electroluminescent material, but the target emission color is blue.
[0013]
An object of the present invention is to provide an organic electroluminescent device having high luminance and stable light emission, particularly yellow to orange light emission.
[0014]
[Means for Solving the Problems]
As a result of diligent studies to solve the above-described problems, the present invention provides a highly reliable yellow-orange light-emitting element that is extremely useful for realizing a stable, high-brightness full-color display by using a specific distyryl compound as a light-emitting material. The present inventors have found that it can be provided and have reached the present invention.
[0015]
That is, the present invention relates to an organic electroluminescence device in which an organic layer having a light emitting region is provided between an anode and a cathode and includes an organic substance that emits light by current injection as a constituent element. The organic electroluminescent device is characterized in that the distyryl compound represented by 1) is contained as an organic light emitting material.
[Chemical 2]

[However, in the general formula (1),
R ¹ and R ⁴ are the same or different groups, and are aryl groups represented by the following general formula (2)

(However, in the general formula (2), R ⁹ , R ¹⁰ , R ¹¹ , R ¹² and R ¹³ are the same or different from each other, and a hydrogen atom or at least one of them is saturated or unsaturated alkoxyl. Group or an alkyl group (a methyl group or a tertiary butyl group is preferred)),
R ² and R ³ are the same or different groups, and are aryl groups represented by the following general formula (3)

(However, in the said General formula (3), R <^14> , R <^15> , R <^16> , R <^17> , R <^18> , R <^19> and R < ²⁰ > are mutually the same or different groups, Comprising: A hydrogen atom or those at least 1 thereof One is a saturated or unsaturated alkoxyl group, or an alkyl group (a methyl group or a tertiary butyl group is preferred),
R ⁵ , R ⁶ , R ⁷ and R ⁸ are the same or different groups, and at least one of them is a cyano group or a nitro group. ]
[0016]
By using the distyryl compound represented by the general formula (1) as a light emitting material, high luminance and stable yellow-orange light emission can be obtained, and an element excellent in electrical, thermal or chemical stability can be provided. .
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The distyryl compound used for the organic electroluminescence device of the present invention will be described.
[0018]
In the organic electroluminescence device of the present invention, the distyryl compound represented by the general formula (1) which is a luminescent material is, for example, the following structural formulas (4) -1, (4) -2, (4) -3, (4). -4, (4) -5, (4) -6, (4) -7, (4) -8 or (4) -9 or at least one molecular structure can be used.

[0019]
1 to 4 show examples of organic electroluminescent elements according to the present invention.
[0020]
FIG. 1 shows a transmissive organic electroluminescent element A in which emitted light 20 is transmitted through a cathode 3, and the emitted light 20 can also be observed from the protective layer 4 side. FIG. 2 shows a reflective organic electroluminescent device B that also obtains reflected light from the cathode 3 as emitted light 20.
[0021]
In the figure, reference numeral 1 denotes a substrate for forming an organic electroluminescent element, and glass, plastic and other appropriate materials can be used. Moreover, when using an organic electroluminescent element in combination with another display element, a board | substrate can also be shared. Reference numeral 2 denotes a transparent electrode (anode), and ITO (Indium tin oxide), SnO ₂ or the like can be used.
[0022]
Reference numeral 5 denotes an organic light emitting layer, which contains the above-mentioned distyryl compound as a light emitting material. About this light emitting layer, conventionally well-known various structures can be used as a layer structure from which the organic electroluminescence 20 is obtained. As will be described later, for example, when a material constituting either the hole transport layer or the electron transport layer has a light-emitting property, a structure in which these thin films are stacked can be used. Further, in order to improve the charge transport performance within the range satisfying the object of the present invention, either or both of the hole transport layer and the electron transport layer have a structure in which thin films of plural kinds of materials are laminated, or plural kinds of materials. It does not prevent the use of a thin film having a mixed composition. Further, in order to improve the light emitting performance, at least one kind of fluorescent material is used, and this thin film is sandwiched between the hole transport layer and the electron transport layer, and further, at least one kind of fluorescent material. May be used in the hole transport layer, the electron transport layer, or both. In these cases, in order to improve the luminous efficiency, a thin film for controlling the transport of holes or electrons can be included in the layer structure.
[0023]
Since the distyryl compound exemplified in the above structural formula (3) has both electron transport performance and hole transport performance, it can serve as a light-emitting layer that also serves as an electron transport layer or as a hole transport layer in the device configuration. It can also be used as a light emitting layer. Further, the distyryl compound may be used as a light emitting layer and sandwiched between an electron transport layer and a hole transport layer.
[0024]
1 and 2, reference numeral 3 denotes a cathode. As an electrode material, an alloy of an active metal such as Li, Mg, or Ca and a metal such as Ag, Al, or In, or a structure in which these are laminated. Can be used. In the transmissive organic electroluminescent device, the light transmittance suitable for the application can be obtained by adjusting the thickness of the cathode. Further, FIG. 4 shows a sealing / protecting layer, and the effect is improved by adopting a structure that covers the entire organic electroluminescent element. An appropriate material can be used as long as the airtightness is maintained. Reference numeral 8 denotes a drive power supply for current injection.
[0025]
In the organic electroluminescent device according to the present invention, the organic layer has an organic multilayer structure (single heterostructure) in which a hole transport layer and an electron transport layer are stacked, and the hole transport layer or the electron transport layer The distyryl compound may be used as a forming material. Alternatively, the organic layer has an organic stacked structure (double heterostructure) in which a hole transport layer, a light emitting layer, and an electron transport layer are sequentially stacked, and the distyryl compound is used as a material for forming the light emitting layer. Good.
[0026]
As an example of an organic electroluminescent device having such an organic laminated structure, FIG. 3 shows that a translucent anode 2, a hole transport layer 6 and an electron transport layer 7 are formed on a translucent substrate 1. An organic electroluminescence device C having a single hetero structure, which has a laminated structure in which an organic layer 5a made of a cathode and a cathode 3 are sequentially laminated, and the laminated structure is sealed by a protective film 4.
[0027]
In the case of a layer configuration in which the light emitting layer is omitted as shown in FIG. 3, light emission 20 having a predetermined wavelength is generated from the interface between the hole transport layer 6 and the electron transport layer 7. These luminescences are observed from the substrate 1 side.
[0028]
Further, FIG. 4 shows that a light-transmitting anode 2, an organic layer 5 b composed of a hole transport layer 10, a light emitting layer 11, and an electron transport layer 12, and a cathode 3 are sequentially formed on a light-transmitting substrate 1. This is an organic electroluminescent element D having a double hetero structure, which has a laminated structure in which the laminated structure is sealed by a protective film 4.
[0029]
In the organic electroluminescence device shown in FIG. 4, by applying a DC voltage between the anode 2 and the cathode 3, holes injected from the anode 2 are injected through the hole transport layer 10 and from the cathode 3. The emitted electrons reach the light emitting layer 11 through the electron transport layer 12. As a result, electron / hole recombination occurs in the light emitting layer 11 to generate singlet excitons, and light emission of a predetermined wavelength is generated from the singlet excitons.
[0030]
In each of the organic electroluminescent elements C and D described above, the substrate 1 can be appropriately made of a light transmissive material such as glass or plastic. Further, this substrate may be shared when used in combination with other display elements or when the stacked structure shown in FIGS. 3 and 4 is arranged in a matrix. In addition, each of the elements C and D can adopt either a transmission type or a reflection type structure.
[0031]
The anode 2 is a transparent electrode, and ITO (indium tin oxide), SnO ₂ or the like can be used. A thin film made of an organic material or an organometallic compound may be provided between the anode 2 and the hole transport layer 6 (or the hole transport layer 10) for the purpose of improving charge injection efficiency. In the case where the protective film 4 is formed of a conductive material such as metal, an insulating film may be provided on the side surface of the anode 2.
[0032]
Moreover, the organic layer 5a in the organic electroluminescent element C is an organic layer in which a hole transport layer 6 and an electron transport layer 7 are laminated, and either or both of them contain the above-mentioned distyryl compound and emit light. The hole transport layer 6 or the electron transport layer 7 may be used. The organic layer 5b in the organic electroluminescent device D is an organic layer in which the hole transport layer 10, the light-emitting layer 11 containing the distyryl compound, and the electron transport layer 12 are stacked. Can be taken. For example, either or both of the hole transport layer and the electron transport layer may have a light emitting property.
[0033]
In particular, the hole transport layer 6 or the electron transport layer 7 or the light emitting layer 11 is preferably a layer made of the distyryl compound of the present invention, but these layers may be formed only of the distyryl compound, or The co-deposition of the distyryl compound and other hole or electron transport materials (for example, aromatic amines, pyrazolines, etc.) may be used. Further, in the hole transport layer, in order to improve the hole transport performance, a hole transport layer in which a plurality of types of hole transport materials are stacked may be formed.
[0034]
In the organic electroluminescent device C, the light emitting layer may be the electron transporting light emitting layer 7, but depending on the voltage applied from the power supply 8, light may be emitted from the hole transporting layer 6 or its interface. Similarly, in the organic electroluminescent element D, the light emitting layer may be the electron transport layer 12 or the hole transport layer 10 in addition to the layer 11. In order to improve the light emitting performance, it is preferable that the light emitting layer 11 using at least one fluorescent material is sandwiched between the hole transport layer and the electron transport layer. Or you may comprise the structure which contained this fluorescent material in the positive hole transport layer or the electron carrying layer, or these both layers. In such a case, in order to improve luminous efficiency, a thin film (such as a hole blocking layer or an exciton generation layer) for controlling the transport of holes or electrons can be included in the layer configuration.
[0035]
The material used for the cathode 3 may be an alloy of an active metal such as Li, Mg, or Ca and a metal such as Ag, Al, or In, and may have a structure in which these metal layers are laminated. It should be noted that an organic electroluminescent element suitable for the application can be produced by appropriately selecting the thickness and material of the cathode.
[0036]
Moreover, the protective film 4 acts as a sealing film, and can improve the charge injection efficiency and the light emission efficiency by covering the entire organic electroluminescent element. In addition, as long as the airtightness is maintained, a material such as a single metal such as aluminum, gold, or chromium, or an alloy thereof can be appropriately selected.
[0037]
The current applied to each of the organic electroluminescent elements is usually a direct current, but a pulse current or an alternating current may be used. The current value and the voltage value are not particularly limited as long as they are within the range that does not destroy the element. However, considering the power consumption and life of the organic electroluminescence element, it is desirable to efficiently emit light with as little electrical energy as possible.
[0038]
Next, FIG. 5 is a configuration example of a flat display using the organic electroluminescent element of the present invention. As shown in the figure, for example, in the case of a multi-color display, an organic layer 5 (5a, 5b) capable of emitting three colors of yellow (Y), green (G), and blue (B) is formed between the cathode 3 and the anode 2. Arranged in between. The cathode 3 and the anode 2 can be provided in stripes crossing each other, and are selected by the luminance signal circuit 14 and the control circuit 15 with a built-in shift register, and a signal voltage is applied to each, thereby the selected cathode 3 and the organic layer at the position (pixel) where the anode 2 intersects are configured to emit light.
[0039]
That is, FIG. 5 shows, for example, an 8 × 3 YGB simple matrix in which a laminate 5 including a hole transport layer and at least one of a light emitting layer and an electron transport layer is disposed between the cathode 3 and the anode 2. (See FIG. 3 or FIG. 4). The cathode and the anode are both patterned in stripes, orthogonal to each other in a matrix, and applied with a signal voltage in time series by the control circuits 15 and 14 with a built-in shift register, and are configured to emit light at the crossing position. It is a thing. The EL element having such a structure can be used not only as a display of characters and symbols but also as an image reproducing device. Further, the stripe pattern of the cathode 3 and the anode 2 is arranged for each color of yellow (Y), green (G), and blue (B), so that a multi-color all-solid-type flat panel display can be configured.
[0040]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to a following example.
[0041]
Example 1
In this example, among the above distyryl compounds of the general formula (1), R ¹ and R ⁴ are unsubstituted phenyl groups, R ² and R ³ are unsubstituted naphthyl groups, and R ⁵ and R ⁷ are cyano groups. This is an example in which a single heterostructure organic electroluminescent device was produced using a compound of the following structural formula (4) -2 as a hole transporting light emitting material.
[Formula 4]

[0042]
First, a 30 mm × 30 mm glass substrate having an anode made of ITO having a thickness of 100 nm formed on one surface was set in a vacuum deposition apparatus. As a vapor deposition mask, a plurality of metal masks having 2.0 mm × 2.0 mm unit openings are arranged close to the substrate, and the above structural formula (4) -2 is applied under vacuum of 10 ⁻⁴ Pa or less by a vacuum vapor deposition method. The above compound was formed into a film having a thickness of, for example, 50 nm as a hole transporting layer (also serving as a light emitting layer). The deposition rate was 0.1 nm / second.
[0043]
Further, Alq ₃ (tris (8-quinolinol) aluminum) having the following structural formula was deposited as an electron transporting material in contact with the hole transporting layer. The film thickness of this electron transport layer made of Alq ₃ was also set to 50 nm, for example, and the deposition rate was set to 0.2 nm / second.
[Chemical formula 5]

[0044]
As the cathode material, a laminated film of Mg and Ag is adopted, and this is also formed by vapor deposition at a deposition rate of 1 nm / second, for example, to a thickness of 50 nm (Mg film) and 150 nm (Ag film). An organic electroluminescent device as shown in FIG.
[0045]
The organic electroluminescence device of Example 1 produced in this manner was subjected to evaluation of luminescence characteristics by applying a forward bias DC voltage in a nitrogen atmosphere. The emission color was yellow. As a result of spectroscopic measurement, a spectrum having an emission peak at 578 nm was obtained as shown in FIG. For the spectroscopic measurement, a spectroscope using a photodiode array manufactured by Otsuka Electronics Co., Ltd. as a detector was used. Further, when the voltage-luminance measurement was performed, a luminance of 6500 cd / m ² was obtained at 8 V as shown in FIG.
[0046]
After this organic electroluminescent device was fabricated, it was left in a nitrogen atmosphere for 1 month, but no device degradation was observed. Further, it was 4000 hours until the luminance was reduced to half when the device was subjected to continuous light emission by applying a constant current value at an initial luminance of 300 cd / m ² and forced degradation.
[0047]
Example 2
In this example, among the above distyryl compounds of the general formula (1), R ¹ and R ⁴ are unsubstituted phenyl groups, R ² and R ³ are unsubstituted naphthyl groups, and R ⁵ and R ⁷ are cyano groups. This is an example in which a single heterostructure organic electroluminescent device was produced using the compound of the above structural formula (4) -2 as an electron transporting light emitting material.
[0048]
First, a 30 mm × 30 mm glass substrate having an anode made of ITO having a thickness of 100 nm formed on one surface was set in a vacuum deposition apparatus. As a vapor deposition mask, a plurality of metal masks having 2.0 mm × 2.0 mm unit openings are arranged close to the substrate, and α-NPD of the following structural formula is applied under vacuum of 10 ⁻⁴ Pa or less by a vacuum vapor deposition method. (Α-Naphtylphenyldiamine) was formed into a film having a thickness of, for example, 50 nm as a hole transport layer. The deposition rate was 0.1 nm / second.
[Chemical 6]

[0049]
Further, the compound of the structural formula (4) -2 was deposited as an electron transport material in contact with the hole transport layer. The film thickness of the electron transport layer (also serving as the light emitting layer) made of the compound of the structural formula (4) -2 was also set to 50 nm, for example, and the deposition rate was set to 0.2 nm / second.
[0050]
As the cathode material, a laminated film of Mg and Ag is adopted, and this is also formed by vapor deposition at a deposition rate of 1 nm / second, for example, to a thickness of 50 nm (Mg film) and 150 nm (Ag film). An organic electroluminescent device as shown in FIG.
[0051]
The organic electroluminescence device of Example 2 produced in this way was subjected to forward bias DC voltage in a nitrogen atmosphere to evaluate the light emission characteristics. The emission color was yellow, and spectroscopic measurement was performed in the same manner as in Example 1. As a result, a spectrum having an emission peak at 578 nm was obtained as shown in FIG. Further, when the voltage-luminance measurement was performed, a luminance of 5900 cd / m ² was obtained at 8 V as shown in FIG.
[0052]
After this organic electroluminescent device was fabricated, it was left in a nitrogen atmosphere for 1 month, but no device degradation was observed. In addition, when the current value was constantly supplied at an initial luminance of 300 cd / m ² to continuously emit light and forcibly deteriorated, it was 3500 hours until the luminance was reduced to half.
[0053]
Example 3
In this example, among the above distyryl compounds of the general formula (1), R ¹ and R ⁴ are unsubstituted phenyl groups, R ² and R ³ are unsubstituted naphthyl groups, and R ⁵ and R ⁷ are cyano groups. This is an example in which an organic electroluminescent element having a double hetero layer structure was produced using the compound of the above structural formula (4) -2 as a light emitting material.
[0054]
First, a 30 mm × 30 mm glass substrate having an anode made of ITO having a thickness of 100 nm formed on one surface was set in a vacuum deposition apparatus. As a vapor deposition mask, a plurality of metal masks having 2.0 mm × 2.0 mm unit openings are arranged close to the substrate, and α-NPD of the above structural formula is applied under vacuum of 10 ⁻⁴ Pa or less by a vacuum vapor deposition method. Was formed as a hole transport layer to a thickness of 30 nm, for example. The deposition rate was 0.2 nm / second.
[0055]
Further, the compound of the above structural formula (4) -2 was deposited as a light emitting material in contact with the hole transport layer. The film thickness of the light emitting layer made of the compound of the structural formula (4) -2 was also set to 30 nm, for example, and the deposition rate was set to 0.2 nm / second.
[0056]
Further, Alq ₃ having the above structural formula was deposited as an electron transporting material in contact with the light emitting layer. The film thickness of Alq _{3 was} , for example, 30 nm, and the deposition rate was 0.2 nm / second.
[0057]
As a cathode material, a laminated film of Mg and Ag is adopted, and this is also formed by vapor deposition at a deposition rate of 1 nm / second, for example, to a thickness of 50 nm (Mg film) and 150 nm (Ag film). An organic electroluminescent device as shown in FIG.
[0058]
The organic electroluminescence device of Example 3 produced in this manner was subjected to evaluation of light emission characteristics by applying a forward bias DC voltage in a nitrogen atmosphere. The emission color was yellow, and as a result of spectroscopic measurement, a spectrum having an emission peak at 578 nm was obtained as shown in FIG. When the voltage-luminance measurement was performed, a luminance of 7500 cd / m ² was obtained at 8V as shown in FIG.
[0059]
After this organic electroluminescent device was fabricated, it was left in a nitrogen atmosphere for 1 month, but no device degradation was observed. Further, it was 5000 hours until the luminance was reduced to half when the device was subjected to continuous light emission by applying a constant current value at an initial luminance of 300 cd / m ² and forced degradation.
[0060]
Example 4
An organic electroluminescent device was produced in accordance with Example 2 in both the layer structure and the film forming method except that TPD (triphenyldiamine derivative) having the following structural formula was used instead of α-NPD as the hole transporting material. .

[0061]
The organic electroluminescent element of this example also emitted yellow light similar to that of Example 2. As a result of the spectroscopic measurement, the spectrum coincided with the spectrum of the organic electroluminescent element of Example 2.
[0062]
[Effects of the invention]
According to the organic electroluminescent element of the present invention, in the organic electroluminescent element in which an organic layer having a light emitting region is provided between an anode and a cathode, the organic layer has a distyryl represented by the general formula (1). Since the compound is contained, it is possible to provide an organic electroluminescent device having a high luminance and stable yellow to orange emission.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a main part of an organic electroluminescent element according to the present invention.
FIG. 2 is a schematic cross-sectional view of another main part of the organic electroluminescent element.
FIG. 3 is a schematic cross-sectional view of another main part of the organic electroluminescent element.
FIG. 4 is a schematic cross-sectional view of another main part of the organic electroluminescent element.
FIG. 5 is a configuration diagram of a multi-color flat display using organic electroluminescent elements.
6 is an emission spectrum diagram of the organic electroluminescent device according to Example 1 of the present invention. FIG.
7 is an emission spectrum diagram of the organic electroluminescent element according to Example 2. FIG.
8 is an emission spectrum diagram of the organic electroluminescent element according to Example 3. FIG.
9 is a voltage-luminance characteristic diagram of the organic electroluminescent element according to Example 1. FIG.
10 is a voltage-luminance characteristic diagram of the organic electroluminescent element according to Example 2. FIG.
11 is a voltage-luminance characteristic diagram of the organic electroluminescent element according to Example 3. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Transparent electrode (anode), 3 ... Cathode, 4 ... Protective film,
5, 5a, 5b ... organic layer, 6 ... hole transport layer, 7 ... electron transport layer,
8 ... Power source, 10 ... Hole transport layer, 11 ... Light emitting layer, 12 ... Electron transport layer,
14 ... luminance signal circuit, 15 ... control circuit, 20 ... emitted light,
A, B, C, D: Organic electroluminescence device

Claims (8)

In an organic electroluminescent device in which an organic layer having a light emitting region is provided between an anode and a cathode, the organic layer contains a distyryl compound represented by the following general formula (1) as an organic light emitting material. An organic electroluminescent element characterized by the above.

[However, in the general formula (1),
R ¹ and R ⁴ are the same or different groups, and are aryl groups represented by the following general formula (2)

(However, in the general formula (2), R ⁹ , R ¹⁰ , R ¹¹ , R ¹² and R ¹³ are the same or different from each other, and a hydrogen atom or at least one of them is saturated or unsaturated alkoxyl. Group, or an alkyl group).
R ² and R ³ are the same or different groups, and are aryl groups represented by the following general formula (3)

(However, in the said General formula (3), R <^14> , R <^15> , R <^16> , R <^17> , R <^18> , R <^19> and R < ²⁰ > are mutually the same or different groups, Comprising: A hydrogen atom or those at least 1 thereof One is a saturated or unsaturated alkoxyl group, or an alkyl group).
R ⁵ , R ⁶ , R ⁷ and R ⁸ are the same or different groups, and at least one of them is a cyano group or a nitro group. ] The organic layer has an organic laminated structure in which a hole transport layer and an electron transport layer are laminated, and the distyryl compound is used as a material for forming the hole transport layer. Organic electroluminescent device. The organic layer has an organic laminated structure in which a hole transport layer and an electron transport layer are sequentially laminated, and the distyryl compound is used as a material for forming the electron transport layer. Organic electroluminescent device. The organic layer has an organic laminated structure in which a hole transport layer, a light emitting layer, and an electron transport layer are laminated, and the distyryl compound is used as a material for forming the light emitting layer. The described organic electroluminescent device. In the organic electroluminescent element in which an organic layer having a light emitting region is provided between an anode and a cathode, the following structural formulas (4) -1, (4) -2, (4) -3, ( 4) -4, (4) -5, (4) -6, (4) -7, (4) -8, or (4) -9 or at least one distyryl compound represented by (4) -9 is included as an organic light emitting material. An organic electroluminescent device characterized in that

The organic layer has an organic multilayer structure in which a hole transport layer and an electron transport layer are stacked, and the distyryl compound is used as a material for forming the hole transport layer. Organic electroluminescent device. The organic layer has an organic multilayer structure in which a hole transport layer and an electron transport layer are sequentially stacked, and the distyryl compound is used as a material for forming the electron transport layer. Organic electroluminescent device. The organic layer has an organic laminated structure in which a hole transport layer, a light emitting layer, and an electron transport layer are laminated, and the distyryl compound is used as a material for forming the light emitting layer. The described organic electroluminescent device.

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