JP2005026003A - Manufacturing method for organic el device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method capable of realizing a long life and high brightness of an organic EL device. <P>SOLUTION: First, a hole injection layer application solution is applied on a substrate 10 in which an electrode layer 11 composed of ITO is formed to form a coating film. Then, a luminous layer application solution is applied on the coating film to form a coating film. Second, the substrate 10 is housed in a pressurizing tank, and the coating film is dried and solidified under a constant pressurizing/heating condition to form a first organic layer 12 and a second organic layer together. Thereby, a mixture layer 20 is formed in the interface of the organic layers 12, 13. LiF and Al are deposited on it for forming an electrode layer 15 to obtain the organic EL device 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００２４】
このように溶液の乾燥温度を１８０℃以上とした場合には、用いた溶剤の沸点に拘わらず素子寿命の飛躍的な改善が認められた。ここで、もし素子寿命が溶剤の乾燥除去効率に依存すると仮定すると、表１において沸点１１０℃のトルエンを用い且つ乾燥温度が１４０℃の場合、及び、沸点１３８℃のｍ−キシレンを用い且つ乾燥温度が１４０℃の場合にも、半減寿命が１０００ｈｒを超えることが予想されるが、結果はそれに反する。また、ｍ−キシレンとのアナロジーから推定すれば、溶媒沸点と乾燥温度が略同じであるｐ−シメンを用い且つ乾燥温度が１８０℃の場合には、大きな寿命改善効果は期待できないはずであるが、この予想に反する結果が得られた。
【００２５】
また、この実験は上述したように加圧条件で実施したものであるが、減圧条件としたこと以外は同様にして（つまり従来の方法で）有機ＥＬ素子を製造し、その寿命評価を行ったところ、表１に示すような十分な寿命改善効果は得られなかった。
【００２６】
すなわち、加熱工程における溶媒の乾燥除去効率を高めるべく、塗膜の周囲を減圧してももちろん構わないものの、逆に加圧することがより好適である。つまり、加熱工程が、少なくとも二つの塗膜の周囲を大気圧よりも大きな圧力となるように加圧する加圧ステップを有すると有用である。
【００２７】
この場合、塗膜同士が互いに加圧されて両者の界面における密着性がより高められると考えられる。ただし、作用はこれに限定されない。よって、層同士の密着性が更に向上されるので、層間剥離の発生及びそれに起因し得る素子劣化が一層抑制され得る。
【００２８】
具体的には、加圧ステップでは、圧力が好ましくは０．９８〜１９６０ｋＰａ（０．０１〜２０ｋｇｆ／ｃｍ^２）、より好ましくは４．９〜１９６０ｋＰａ（０．０５〜２０ｋｇｆ／ｃｍ^２）、特に好ましくは１９６〜１９６０ｋＰａ（２〜２０ｋｇｆ／ｃｍ^２）の範囲内の値となるように加圧することが望ましい。
【００２９】
この圧力が０．９８ｋＰａ未満であると、加圧による密着性向上効果が十分に奏されない傾向にある。一方、この圧力が１９６０ｋＰａを超えると、加圧による効果が飽和してしまい、印加圧力に応じた密着性の向上が認められない傾向にある。
【００３０】
【発明の実施の形態】
以下、本発明の実施形態について詳細に説明する。なお、図示の便宜上、図面の寸法比率は図示の値に限定されず、また説明のものと必ずしも一致しない。さらに、上下左右等の位置関係については、特に明示しない限り、図面における位置関係に基づくものとする。
【００３１】
図１は、本発明の製造方法により製造される有機ＥＬ素子の一例を示す模式断面図である。有機ＥＬ素子１は、透明ガラス等の透光性材料から成る基板１０上に、電極層１１（電極）、第１有機層１２、第２有機層１３、第３有機層１４、及び電極層１５（電極）が順次形成されたものである。
【００３２】
本形態の有機ＥＬ素子１において、電極層１１，１５は、それぞれホール注入電極（陽極）及び電子注入電極（陰極）として機能する。また、第１有機層１２、第２有機層１３、及び第３有機層１４は、それぞれホール注入層、発光層、及び電子注入層として機能するものである。
【００３３】
基板１０、電極層１１、第１有機層１２、第２有機層１３、第３有機層１４、及び電極層１５を構成する材料としては、例えば、本出願人による特開２００３−１４２２６８号公報に記載されている各種材料を用いることができる。
【００３４】
ここで、各有機層１２，１３，１４の構成材料をより具体的に例示すると、ホール注入層としてはＰＶＫ（ポリ（Ｎ−ビニルカルバゾール）：Ｔｇ＝２２４℃）、ＰＥＤＯＴ（ポリ（３，４−エチレンジオキシチオフェン）：Ｔｇ＝１９０℃）、Ｃｕフタロシアニン等が挙げられ、発光層としてはＭＥＨ−ＰＰＶ（ポリ（２−メトキシ−５−エチルヘキシルオキシ−ｐ−フェニレンビニレン）Ｔｇ＝８０℃）、その他ホストポリマーにドーパントを混合した分子分散型ポリマー発光材料が挙げられ、電子注入層としては下記式（１）で表されるオキサジアゾール誘導体（Ｔｇ＝１３７℃）、Ａｌｑ３（トリス（８−キノリノラト）アルミニウム：Ｔｇ＝１６０℃）、Ｂｐｈｅｎ（バソフェナントロリン：Ｔｇ＝８６℃）等が挙げられる。
【００３５】
【化１】

【００３６】
なお、有機ＥＬ素子１においては、図示の如く、第１有機層１２及び第２有機層１３との間の界面領域に両者の混合層２０が形成されている。この混合層２０については、後述する有機ＥＬ素子１の製造手順についての説明で詳しく言及する。
【００３７】
また、各有機層１２，１３，１４に用いる有機材料の種類やその塗布溶媒等に応じて電極層１１をホール注入用電極（陽極）とし、且つ電極層１５を電子注入用電極（陰極）として用いてもよい。さらに、ホール注入層としての第１有機層１２及び電子注入層としての第３有機層１４は必ずしも必要ではなく、また、有機層１２，１３，１４の三層構造に限られず、後述するように、例えば第１有機層１２及び第２有機層１３（ホール注入層と発光層）、又は、第２有機層１３及び第３有機層１４（発光層と電子注入層）から成る二層構造としてもよい。前者の場合には発光層が電子輸送性を有すると好ましく、後者の場合には発光層がホール輸送性を有することが好ましい。
【００３８】
またさらに、必要に応じてその他の有機層として、ホール輸送層、電子輸送層等を更に設けた積層構造としてもよい。さらにまた、各有機層１２，１３，１４は単層でも複層でもよく、複層の場合、各有機層１２，１３，１４を構成する複数の層を異なる機能層としてもよいし、同種の機能層としても構わない。また、電極層１１と第１有機層１２との界面を改質したり、電荷注入性を改善するためのバッファ層（緩衝層）を更に設けたりしてもよい。
【００３９】
このような構成を有する有機ＥＬ素子１を作製する方法について以下に説明する。図２は、本発明の製造方法により有機ＥＬ素子１を製造する手順の一例を示すフロー図である。ここでは、ホール注入層としての第１有機層１２及び発光層としての第２有機層１３から成る二層構造を有する有機ＥＬ素子１を製造する際の手順について述べる。
【００４０】
まず、透明ガラス等の基板１０を用意すると共に、ＰＥＤＯＴ／ＰＳＳ（ポリ（３，４−エチレンジオキシチオフェン）／ポリスチレンスルホン酸）を塗布溶媒としての水に１．０ｗｔ％濃度となるように溶解してホール注入層塗布溶液を調製する。また、ＭＥＨ−ＰＰＶを塗布溶媒としてのｍ−キシレンに１．５ｗｔ％濃度となるように溶解して発光層塗布溶液を調製する。
【００４１】
次に、基板１０上に電極層１１としてのＩＴＯ電極をスパッタ法等により形成した（ステップＳ１）後、その上に、ホール注入層塗布溶液をスピンコート法によって所定の膜厚（例えば５００Å）となるように一定回転数（例えば２０００ｒｐｍ）で成膜し、第１有機層１２用の塗膜を形成する（ステップＳ２）。ひき続き、その塗膜上に発光層塗布溶液をスピンコート法によって所定の膜厚（例えば８００Å）となるように一定回転数（例えば２０００ｒｐｍ）で成膜し、第２有機層１３用の塗膜を形成する（ステップＳ３）。これにより、第１有機層１２用の塗膜と第２有機層１３用の塗膜との間に、両者が混合されて成り且つ最終的に混合層２０とされる領域が形成される。
【００４２】
それから、それらの塗膜が形成された基板１０を、ヒーター等の加熱手段を備える加熱槽内に載置し、槽内を窒素ガス等の不活性ガス環境とし、一定圧力に保持した状態で且つ一定温度で加熱し、二層の塗膜を同時に乾燥・固化させ、第１有機層１２及び第２有機層１３を一括して形成せしめる（ステップＳ４；加熱工程、加圧ステップ）。このとき、両有機層１２，１３の界面領域に混合層２０が形成されるものと考えられる。
【００４３】
このとき、槽内の圧力が大気圧よりも大きな圧力、好ましくは０．９８〜１９６０ｋＰａ（０．０１〜２０ｋｇｆ／ｃｍ^２）、より好ましくは４．９〜１９６０ｋＰａ（０．０５〜２０ｋｇｆ／ｃｍ^２）、特に好ましくは１９６〜１９６０ｋＰａ（２〜２０ｋｇｆ／ｃｍ^２）の範囲内の値となるように圧力調整を行う。また、加熱温度が好ましくはＭＥＨ−ＰＰＶのガラス転移点（Ｔｇ）よりも高い温度、より好ましくはそのＴｇよりも高く且つそのＴｇ＋２００℃以下となるように、ヒーター等の出力調整を行う。
【００４４】
この例では、具体的には加熱温度が８０℃より高い温度、より好ましくは８０℃より高く且つ２８０℃（８０℃＋２００℃）以下であることが望ましい。ただし、ＭＥＨ−ＰＰＶの熱分解が十分に抑制される加熱時間であれば、ＰＥＤＯＴ／ＰＳＳのＴｇ（１９０℃）より高い温度で加熱してもよい。
【００４５】
ここで、ＭＥＨ−ＰＰＶを溶解させる溶媒としては、他の有機溶媒、例えばトルエン等を用いてもよい。また、ホール注入層としての第１有機層１２を形成させる材料として下記式（２）で表されるＰＴＰＤＰＥＳを用いる場合には、その溶媒としてはモノクロロベンゼン等を例示できる。この場合、第２有機層１３用の構成材料であるＭＥＨ−ＰＰＶの溶媒としてモノクロロベンゼンを使用することも不可能ではないが、ＰＴＰＤＰＥＳ溶液とＭＥＨ−ＰＰＶ溶液との過度の混合を避ける観点から、ＭＥＨ−ＰＰＶの溶媒としては、モノクロロベンゼンと異なる例えば上記のトルエンを用いることが好ましい。
【００４６】
【化２】

【００４７】
次に、その基板１０を加熱槽から取り出し、第２有機層１３上に、Ｃａ及びＡｌを所定厚さ（例えば、Ｃａ：６０Å、Ａｌ：２５００Å）で順次真空蒸着等して電極層１５を形成させて有機ＥＬ素子１を得る（ステップＳ５）。なお、各有機層や電極層の劣化を防止すべく、有機ＥＬ素子１上を封止板等により封止することが好ましい。
【００４８】
図３は、本発明の製造方法により有機ＥＬ素子１を製造する手順の他の例を示すフロー図である。この手順は、発光層としての第２有機層１３及び電子注入層としての第３有機層１４から成る二層構造を有する有機ＥＬ素子１を製造する際のものであり、ホール注入層塗布溶液に代えて電子注入層塗布溶液を調製し、且つ、ステップＳ２〜Ｓ４の代わりにそれぞれステップＳ６〜Ｓ８を実施すること以外は、図２に示す手順と同様である。電子注入層塗布溶液は、上記式（１）で表されるオキサジアゾール誘導体を塗布溶媒としての２−エトキシエタノールに０．５ｗｔ％濃度となるように溶解して調製する。
【００４９】
ステップＳ６においては、基板１０に設けられた電極層１１の上に、発光層塗布溶液をスピンコート法によって所定の膜厚（例えば５００Å）となるように一定回転数（例えば３５００ｒｐｍ）で成膜し、第２有機層１３用の塗膜を形成する。また、ステップＳ７においては、その塗膜上に、電子注入層塗布溶液をスピンコート法によって所定の膜厚（例えば５０〜１００Å）となるように一定回転数（例えば１５００ｒｐｍ）で成膜する。これにより、両塗膜の界面領域に混合層２０と同様の混合領域が形成される。
【００５０】
さらに、ステップＳ８（加熱工程、加圧ステップ）においては、それらの塗膜が形成された基板１０を、ヒーター等の加熱手段を備える加熱槽内に載置し、槽内を窒素ガス等の不活性ガス環境とし、一定圧力に保持した状態で且つ一定温度で加熱し、二層の塗膜を同時に乾燥・固化させ、第２有機層１３及び第３有機層１４を一括して形成せしめる。この際、両有機層１３，１４の界面領域に混合層が形成され得る。
【００５１】
このステップＳ８における加熱条件及び圧力条件は、前述したステップＳ４におけるのと同様である。ただし、ただし、ＭＥＨ−ＰＰＶの熱分解が十分に抑制される加熱時間であれば、好ましくは上記式（１）で表されるオキサジアゾール誘導体のＴｇである１３７℃より高い温度、より好ましくは１３７℃より高く且つ２８０℃（８０℃＋２００℃）の温度で加熱してもよい。
【００５２】
ここで、電子注入層としての第３有機層１４を形成させる材料として上述したＡｌｑ３やＢｐｈｅｎを用いる場合、その溶媒としては、上記式（１）で表されるオキサジアゾール誘導体と同様に２−エトキシエタノール等を用いることができる。
【００５３】
図４は、本発明の製造方法により有機ＥＬ素子１を製造する手順の更に他の例を示すフロー図である。この手順は、図１に示す三つの有機層１２，１３，１４を有する有機ＥＬ素子１を製造する際のものであり、ステップＳ２，Ｓ３を実施した後にステップＳ７を実施し、且つ、その後のステップＳ４に代えてステップＳ９を実施すること以外は、図２に示す手順と同様である。
【００５４】
ステップＳ９においては、各有機層１２，１３，１４用の各塗膜が形成され且つ隣接する塗膜間に混合領域が形成された基板１０を上述した加熱槽内に載置し、槽内を窒素ガス等の不活性ガス環境とし、一定圧力に保持した状態で且つ一定温度で加熱し、三層の塗膜を同時に乾燥・固化させ、第１有機層１２、第２有機層１３及び第３有機層１４を一括して形成せしめる。この際、各有機層１２，１３，１４の各界面領域に混合層が形成され得る。このステップＳ９における加熱条件及び圧力条件は、前述したステップＳ４におけるのと同様である。
【００５５】
このようにして製造された有機ＥＬ素子１及び本発明によるその製造方法によれば、各有機層１２，１３，１４用の塗膜を連続して形成し、各塗膜間に混合領域を生成させたものを、ステップＳ４，Ｓ８，Ｓ９において同時に加熱・加圧処理して混合層２０等を形成せしめるので、各有機層１２，１３，１４同士の密着性が高められる。よって、各有機層１２，１３，１４間の界面における被着面積が増大し、その結果、発光効率が高められて有機ＥＬ素子１の輝度を格段に向上できる。
【００５６】
また、隣接する有機層１２，１３，１４同士の密着性が高まるので、経時劣化による界面剥離の発生を十分に抑止できる。よって、素子劣化が抑えられ、素子寿命を延長させることが可能となる。したがって、塗布形成された有機層を備える有機ＥＬ素子１の動作安定性及び信頼性を格別に向上させることができる。
【００５７】
ここで、図５は、有機ＥＬ素子１における混合層２０近傍の要部を模式的に示す断面図である。本発明の製造方法によれば、同図に示す如く、下層である第１有機層１２の表層に、上層である第２有機層１３を構成する有機物質１３ａが言わば「染み込んだ」状態で存在する混合層２０が形成されるものと推定される。このような形態が生起されることにより、前述した有機層１２，１３間の密着性が格段に高められる。また、図３及び図４に示す手順で作製される有機ＥＬ素子１においても、これと同様にして混合層が形成され各有機層１２，１３，１４間の密着性が向上される。
【００５８】
これに対し、図６は、従来の湿式法により製造される有機ＥＬ素子の有機層境界部の要部を模式的に示す断面図であり、参考のために図５と対比して示す。同図に示すように、各有機層を個別に塗布・乾燥して得られる従来の素子では、有機層５２の最上部に不活性ガス下での加熱を行っても 微量の酸素により酸化皮膜５２ａを生じる。このような有機層５２の表面改質により、下層である有機層５２と上層である有機層を構成する有機物質５３ａとは、全体として単に接している程度に積層されているものと推定される。このような形態により界面剥離が比較的生じ易くなることが、素子の信頼性及び寿命の低下を来たし易くする要因の一つと想定される。ただし、各作用は上記のものに限定されない。
【００５９】
また、各有機層１２，１３，１４を形成する際に、加熱乾燥に加えて加圧処理を施して塗膜を乾燥・固化させるので、形成される各層間の密着性、及び、電極層１１が形成された基板１０と各有機層１２，１３，１４との密着性が更に高められる。これにより、各有機層１２，１３，１４の界面剥離を更に有効に防止して素子劣化が抑制され、素子寿命を一層延長させることができる。
【００６０】
また、各有機層１２，１３，１４間に混合層が形成される結果、層間のエネルギー障壁が見かけ上連続的に変化する状態が生起され、もって電子及びキャリアの注入効率が高まってエネルギー効率が向上されることによっても素子寿命が延長され得る。さらに、各有機層１２，１３，１４を個別に乾燥する工程を省略できるので、有機ＥＬ素子１の製造プロセスが簡略化され、生産効率を向上でき、且つ、製造コストを低減できる利点がある。
【００６１】
なお、本発明は上述した実施形態に限定されるものではなく、その要旨を変更しない限度において様々な変形が可能である。例えば、各有機層１２，１３，１４を形成する際の溶液塗布法としては、スピンコート法以外に、キャスト法、ディップコート法、スプレーコート法等を用いてもよい。
【００６２】
さらに、各有機層１２，１３，１４を全て加熱又は加熱・加圧処理する必要はなく、これらのうち少なくともいずれか二層をそのように処理してもよい。またさらに、加圧処理を行わなくてもよい。なお、有機ＥＬ素子１への入熱を軽減してサーマルバジェットを改善する観点からは、加熱又は加熱・加圧処理する層数は二層以上で極力少ない方が望ましい。一方、各層間の密着性、及び電極層１１が形成された基板１０と各有機層１２，１３，１４との密着性をより高めて寿命延長を図る観点からは、加熱又は加熱・加圧処理する層数は多い方が望ましい。
【００６３】
【実施例】
以下、実施例により本発明の内容をより具体的に説明するが、本発明はそれらの実施例に限定されるものではない。
【００６４】
〈実施例１〉
まず、透明ガラス製の基板１０を用意すると共に、１ｗｔ％濃度のＰＥＤＯＴ／ＰＳＳを用い、ホール注入層塗布溶液を調製した。また、ＭＥＨ−ＰＰＶを塗布溶媒としてのｍ−キシレンに３ｗｔ％濃度となるように溶解して発光層塗布溶液を調製した。またＡｌｑ３を塗布溶媒としてのジメチルアセトアミドに１．０ｗｔ％濃度となるように溶解して電子注入層塗布溶液を調製した。
【００６５】
次に、基板１０上にＩＴＯ電極を蒸着法により形成した後、その上に、ホール注入層塗布溶液をスピンコート法によって膜厚５００Åとなるように回転数２０００ｒｐｍで成膜し、続けて、発光層塗布溶液をスピンコート法によって膜厚８００Åとなるように回転数２０００ｒｐｍで成膜し、更にその塗膜上に電子注入層塗布溶液をスピンコート法によって膜厚が１００Åとなるように回転数１０００ｒｐｍで成膜した。
【００６６】
次いで、これらの膜が形成されたガラス基板を加圧槽内に収容し、１８０℃及び３０ｋＰａで一定時間加熱・加圧処理を施し、発光層及び電子注入層を一括して形成した。その後、そのガラス基板を加熱層から取り出し、電子注入層上にＬｉＦを５Å、陰極としてＡｌも２５００Åの厚さとなるように真空蒸着して、有機ＥＬ素子を得た。この有機ＥＬ素子の特性を測定評価したところ、電流効率５ｃｄ／Ａ（＠１００ｃｄ／ｍ^２）、輝度半減寿命２０００時間（１００ｃｄ／ｍ^２駆動時）であることが確認された。
【００６７】
〈実施例２〉
１８０℃、大気圧で一定時間加熱処理を施した以外は実施例１と同様にして有機ＥＬ素子を作製した。この有機ＥＬ素子の特性を測定評価したところ、電流効率５ｃｄ／Ａ（＠１００ｃｄ／ｍ^２）、輝度半減寿命１５００時間（１００ｃｄ／ｍ^２駆動時）であることが確認された。
【００６８】
〈比較例１〉
ホール注入層をスピンコート法によって形成した後、乾燥処理を２００℃で５分行い、次いで、その塗膜上に発光層を乾燥処理１８０℃で１時間にて形成した後、電子注入層を１８０℃で１時間にて形成したこと以外は、実施例１と同様にして有機ＥＬ素子を作製した。この有機ＥＬ素子の特性を測定評価したところ、電流効率１ｃｄ／Ａ（＠１００ｃｄ／ｍ^２）、輝度半減寿命１００時間（１００ｃｄ／ｍ^２駆動時）であることが確認された。
【００６９】
〈比較例２〉
ホール注入層をスピンコート法によって形成した後、乾燥処理を２００℃で５分行い、次いで、その塗膜上に発光層を乾燥処理１８０℃で１時間にて形成した後、Ａｌｑ３層を真空蒸着により形成したこと以外は、実施例１と同様にして有機ＥＬ素子を作製した。この有機ＥＬ素子の特性を測定評価したところ、電流効率１ｃｄ／Ａ（＠１００ｃｄ／ｍ^２）、輝度半減寿命３００時間（１００ｃｄ／ｍ^２駆動時）であった。
【００７０】
〈物性評価〉
まず、参考として実施例１と同様の塗布溶液を用いその溶液をＳｉウェハー上に塗布及び加熱乾燥して形成した発光層の表面形態を原子間力顕微鏡（ＡＦＭ）により観察した。図７は、ノンコンタクトモードで測定されたその発光層表面の形状を示す三次元スペクトルである。図７より、発光層表面は、高さ（深さ）が数ｎｍ〜数十ｎｍ程度の微小凹凸が多数形成されていることが確認された。
【００７１】
さらに、実施例１と同様の塗布溶液を用いその溶液をＳｉウェハー上に塗布し、次いでＡｌｑ３層を塗布形成した後、加熱処理を行い、本発明によるサンプルを作製した。図８は、その本発明によるサンプルについてＤＦＭモード（ダイナミクフォースモード）で測定された表面形状を示す二次元スペクトルである。同図において白く視認される部分が凸部を示す。また、図８では、図７に近似した表面形状が認められ、発光層上にＡｌｑ３層の痕跡が認められない表面形状が観測された。これより、Ａｌｑ３層は内部に染み込み発光層と混合層を形成しているものと考えられる。
【００７２】
また、図９は、図８と同じサンプルをオージェ電子分光法により観察した発光層表面上のＡｌ分布を示すものである。これより、発光層の窪み部分にＡｌが多く分布していることが判明した。
【００７３】
一方、比較例２と同様の塗布溶液を用いその溶液をＳｉウェハー上に塗布し加熱処理を施し、次いでＡｌｑ３層の蒸着を行い、従来方法によるサンプルを作製した。図１０は、その従来方法によるサンプルについてＤＦＭモード（ダイナミクフォースモード）で測定された表面形状を示す二次元スペクトルである。同図において、白く視認される部分が凸部を示す。図１０では、図７及び図８とは異なる表面形状が認められ、発光層上にＡｌｑ３層として認識される表面形状が観測された。これより、Ａｌｑ３層は内部に染み込むことなく、別層としてのＡｌｑ３層が発光層上に形成されたものと考えられる。
【００７４】
さらに、図１１は、図１０と同じサンプルをオージェ電子分光法により観察した発光層表面上のＡｌ分布を示すものである。これより、Ａｌｑ３層の均一な分布が観測された。
【００７５】
【発明の効果】
以上説明したように、本発明の有機ＥＬ素子の製造方法によれば、有機層の形成に湿式法を用いた場合にも、製造される有機ＥＬ素子の寿命を格段に改善でき、これにより、素子の動作安定性及び信頼性を向上できる。また、有機層間の密着性を高めることができるので、有機ＥＬ素子の発光効率ひいては輝度を向上させることが可能となる。
【図面の簡単な説明】
【図１】本発明の製造方法により製造される有機ＥＬ素子の一例を示す模式断面図である。
【図２】本発明の製造方法により有機ＥＬ素子１を製造する手順の一例を示すフロー図である。
【図３】本発明の製造方法により有機ＥＬ素子１を製造する手順の他の例を示すフロー図である。
【図４】本発明の製造方法により有機ＥＬ素子１を製造する手順の更に他の例を示すフロー図である。
【図５】有機ＥＬ素子１における混合層２０近傍の要部を模式的に示す断面図である。
【図６】従来の湿式法により製造される有機ＥＬ素子の有機層境界部の要部を模式的に示す断面図である。
【図７】ノンコンタクトモードで測定されたその発光層表面の形状を示す三次元スペクトルである。
【図８】本発明によるサンプルについてＤＦＭモード（ダイナミクフォースモード）で測定された表面形状を示す二次元スペクトルである。
【図９】図８と同じサンプルをオージェ電子分光法により観察した発光層表面上のＡｌ分布を示すものである。
【図１０】従来方法によるサンプルについてＤＦＭモード（ダイナミクフォースモード）で測定された表面形状を示す二次元スペクトルである。
【図１１】図１０と同じサンプルをオージェ電子分光法により観察した発光層表面上のＡｌ分布を示すものである。
【符号の説明】
１…有機ＥＬ素子、１０…基板、１１，１５…電極層、１２…第１有機層、１３…第２有機層、１３ａ…有機物質、１４…第３有機層、２０…混合層、Ｓ１〜Ｓ９…ステップ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an organic EL (Electro Luminescence) element.
[0002]
[Prior art]
Since the announcement of the stacked organic EL device using the vacuum evaporation method by Kodak Company, the development of organic EL displays has been actively conducted and is now being put into practical use. Such a stacked organic EL element is formed by vacuum-vaporizing a low molecular weight dye. However, when such a vacuum deposition method is used, it is extremely difficult to obtain a thin film that is homogeneous and has few defects, and it takes a long time to form a plurality of organic layers, resulting in a decrease in the throughput of device manufacturing. There is a problem of end up.
[0003]
On the other hand, in order to further increase the productivity, a wet method in which a solution obtained by dissolving an organic material constituting an organic layer in an appropriate solvent (solvent) is applied and then the solvent is removed has been actively studied. Examples of a method for forming a coating type organic EL element using such a wet method include a method of sequentially forming a transparent electrode layer as an anode, a hole injection layer, a light emitting layer, and an electrode layer as a cathode on a glass substrate. it can. In the element having this configuration, an organic material such as PEDOT / PSS (poly (3,4-ethylenedioxythiophene) / polystyrene sulfonic acid) excellent in solubility or dispersibility in an aqueous solvent is frequently used as the hole injection layer. ing. In addition, a method using an organic solvent (non-aqueous solvent) as a coating solution for forming a hole injection layer is generally performed.
[0004]
When such a wet method is used, the coating film for the hole injection layer formed on the transparent electrode layer is usually dried, and then the coating film is formed and dried to form the light emitting layer. Will continue to be implemented. In particular, the organic EL element is severely deteriorated due to the presence of moisture. Therefore, when an aqueous solution such as PEDOT / PSS is used for forming the hole injection layer, a drying process is essential before the formation of the light emitting layer. Tend to. In addition, even when an organic solvent solution is used, if the organic solvent remains, it may easily cause a partial loss of the organic layer, which causes a disadvantage that a dark spot is generated when the organic EL element emits light. A drying process was performed every time the organic layer was formed.
[0005]
As such a solvent drying method, there is a reduced pressure drying method (for example, see Patent Document 1) in which the solvent is evaporated on the substrate on which the solution is applied in order to increase the removal efficiency in a reduced pressure environment. Further, a heat drying method has been proposed in order to increase the unevenness at the interface between the organic layer and the deposited layer and increase the light emitting area at the interface while promoting the drying of the solvent (see, for example, Patent Document 2). .
[0006]
[Patent Document 1]
JP 1997-97679 A
[Patent Document 2]
JP 2002-31567 A
[0007]
[Problems to be solved by the invention]
However, so far, no matter what coating drying method is used, an organic EL element having an organic layer formed by a wet method has a lifetime (generally, the time when the luminance is halved when continuously driven at a constant current). ) Is shorter than an organic EL element having the same structure formed by vapor deposition. Although the degree varies depending on the light emitting material and the brightness, those formed by the wet method tend to have a lifetime that is almost orders of magnitude shorter than those formed by the vapor deposition method. In particular, those using a blue light emitting material include those having a lifetime of only about 1/100 of the vapor deposition method. Further, some of the conventional coating-type organic EL elements still have insufficient light emission luminance, and their application to practical surface-emitting displays by further improving the luminance is eagerly desired.
[0008]
Therefore, the present invention has been made in view of such circumstances, and even when a wet method is used for forming an organic layer, the lifetime of the manufactured organic EL element can be extended and the luminous efficiency can be improved. It aims at providing the manufacturing method of an organic EL element.
[0009]
[Means for Solving the Problems]
In order to solve the above-described problem, a method for manufacturing an organic EL element according to the present invention is a method for manufacturing an organic EL element having a plurality of organic layers between electrodes, and includes at least two organic layers among the plurality of organic layers. A coating process in which each solution (coating solution) in which each material constituting the material is dissolved or dispersed in a solvent is continuously applied on a substrate, and at least two coating films formed by such coating are simultaneously applied. And a heating step of forming at least two organic layers by heating.
[0010]
In such a manufacturing method, after the formation of the coating film by continuously applying a plurality of coating solutions in the coating process is performed, in the heating process, the coating films are collectively heat-treated to form a plurality of organic layers. Is formed. Specifically, when the plurality of organic layers are at least a light emitting layer and an electron injection layer, for example, after forming a coating film for the light emitting layer on the substrate, the electron injection is further performed on the substrate without drying it. A coating film for the layer is continuously formed. Then, these coating films are heated at the same time to form a light emitting layer and an electron injection layer in a lump.
[0011]
By carrying out like this, a part of adjacent coating film contacts in the state before drying, and a mixed layer is formed in the interface area | region of coating films by those fluidity | liquidity. Usually, the organic layer constituting the organic EL element and the coating film for forming the organic layer are extremely thin (for example, on the order of several hundred to several thousand liters). It is presumed that there is no mixing, and a state occurs in which one of the surfaces is so narrow that the other soaks into the other. However, the action is not limited to this. Therefore, each organic layer exhibits its function sufficiently, and the adhesion is remarkably enhanced by the formation of such a mixed layer.
[0012]
As a result, the contact area in the vicinity of the interface is increased, and a continuous composition change of both layer components to both electrodes occurs. Since the light emission of the organic EL element tends to depend on the electron / hole coupling efficiency in the vicinity of the interface of the organic layer, the contact area between the layers at the site increases and a continuous composition change occurs. Thus, the luminous efficiency is enhanced by an effective carrier confinement effect. In addition, since the adhesion between the organic layers is improved, delamination is sufficiently suppressed, and element degradation due to the occurrence of such delamination is suppressed.
[0013]
Furthermore, in order to sufficiently prevent the previously formed film from being attacked by the coating film for forming the adjacent organic layer, each material constituting at least two organic layers formed in succession is provided. It is preferable to use different solvents to be dissolved.
[0014]
Moreover, it is suitable when a pressurization process has a heating step which heats an organic layer. When heat treatment is performed together with pressurization in this way, it becomes easier to obtain the same adhesion improvement effect in a shorter time.
[0015]
Specifically, in the heating step, it is more preferable to heat to a temperature higher than the glass transition point of the material constituting the organic layer. In particular, when other organic layers are already formed, it is more preferable to heat to a temperature higher than the lowest glass transition point (Tg) of these organic layers. It is desirable to heat to temperature.
[0016]
In principle, the heating temperature depends on the amount of the material constituting the organic layer, and may be heated at a temperature higher than the Tg of the material that is the main component, and is preferably Tg + 200 ° C. or lower. More specifically, for example, when the dopant is 5% or less and the remaining 95% is made of a host material, even if the dopant has a higher Tg than the host material, the host material which is the main component It is only necessary to heat at a temperature equal to or higher than the Tg, and it is not necessary to heat at a temperature higher than the higher Tg (in this case, the Tg of the dopant).
[0017]
Further, the host material may be composed of a plurality of components. Even in such a case, the host material may be heat-treated at a temperature higher than the Tg of the main component, and may be heated at the lowest Tg + 200 ° C. or less. Good. However, it should be noted that heating at a temperature lower than the decomposition temperature of the material constituting the organic layer is required. When heat treatment is performed at a temperature equal to or higher than the decomposition temperature of either the dopant or the host material, the organic layer does not function at all due to decomposition of the organic layer, and light emission does not occur. Therefore, it is important to control the heat treatment at a temperature that does not cause decomposition of the organic layer during the production.
[0018]
More specifically, in view of the above-described characteristics of the materials constituting the organic layer, it is usually preferable to perform the heat treatment at 200 ± 100 ° C., and more preferably at 200 ± 50 ° C.
[0019]
In this way, the fluidity of the organic layer in the pressurizing step is enhanced, and an effect equivalent to the modification effect by the annealing treatment is achieved, so that the adhesion between the organic layer and other layers is further increased. Enhanced. Moreover, when the heating temperature of the organic layer exceeds its Tg + 200 ° C., the organic layer tends to be thermally decomposed.
[0020]
In addition, the inventors of the present invention initially conducted research from the viewpoint of promoting the drying / removal of the solvent in the wet method. As a result, the effect of the heating temperature and the organic EL element formed by the film forming process at that temperature were investigated. We have found that lifetime has an unexpected relationship. That is, as a matter of course, the higher the heating temperature and the reduced pressure around the boiling point of the solvent, the more the drying of the solvent is promoted. However, as described above, this does not lead to an improvement in device lifetime. On the other hand, the present inventors manufactured organic EL devices by carrying out a drying process not only under reduced pressure conditions but also under pressurized conditions in order to broadly explore the pressure dependence of heating conditions. .
[0021]
The specific manufacturing procedure of the organic EL element at this time is as follows. First, an ITO electrode layer (anode) is formed on a glass substrate, and PEDOT / PSS (poly (3,4-ethylenedioxythiophene) / polystyrene sulfonic acid) is formed thereon as a hole injection layer. A coating solution prepared by dissolving MEH-PPV (poly (2-methoxy-5-ethylhexyloxy-p-phenylenevinylene) in various solvents as a light emitting layer material was applied by spin coating. The substrate was placed in a pressure vessel, and the light-emitting layer was formed by drying and removing the solvent at various heating temperatures under a pressure of 30 kPa in a nitrogen atmosphere. An Al electrode layer (cathode) was formed to obtain an organic EL element.
[0022]
The various organic EL elements obtained were evaluated for their life characteristics. Table 1 summarizes the results. In addition, the time described in the table indicates that the initial luminance of the organic EL element is 100 cd / m. ² And the time from the start of driving until the luminance reaches the initial half value, that is, “half-life”.
[0023]
[Table 1]

[0024]
Thus, when the drying temperature of the solution was 180 ° C. or higher, a dramatic improvement in the device life was recognized regardless of the boiling point of the solvent used. Here, if it is assumed that the lifetime of the element depends on the dry removal efficiency of the solvent, in Table 1, when toluene having a boiling point of 110 ° C. is used and the drying temperature is 140 ° C., and using m-xylene having a boiling point of 138 ° C. and drying is performed. Even when the temperature is 140 ° C., the half-life is expected to exceed 1000 hr, but the result is contrary to this. In addition, if estimated from an analogy with m-xylene, when p-cymene having a solvent boiling point and a drying temperature of about the same is used and the drying temperature is 180 ° C., a great life improvement effect should not be expected. The result was contrary to this expectation.
[0025]
Moreover, although this experiment was implemented on pressurization conditions as mentioned above, the organic EL element was manufactured similarly (that is, by the conventional method) except having made it the decompression condition, and the lifetime evaluation was performed. However, a sufficient life improvement effect as shown in Table 1 was not obtained.
[0026]
That is, in order to increase the drying and removal efficiency of the solvent in the heating step, it is of course possible to reduce the pressure around the coating film. That is, it is useful that the heating process includes a pressurizing step for pressurizing the surroundings of at least two coating films so that the pressure is higher than the atmospheric pressure.
[0027]
In this case, it is considered that the coating films are pressurized with each other and the adhesion at the interface between them is further enhanced. However, the action is not limited to this. Accordingly, the adhesion between the layers is further improved, so that the occurrence of delamination and the element deterioration that can be caused by the delamination can be further suppressed.
[0028]
Specifically, in the pressurizing step, the pressure is preferably 0.98 to 1960 kPa (0.01 to 20 kgf / cm. ² ), More preferably 4.9 to 1960 kPa (0.05 to 20 kgf / cm) ² ), Particularly preferably 196 to 1960 kPa (2 to 20 kgf / cm ² It is desirable to pressurize so that the value is within the range of
[0029]
If this pressure is less than 0.98 kPa, there is a tendency that the effect of improving adhesion by pressurization is not sufficiently exhibited. On the other hand, when this pressure exceeds 1960 kPa, the effect of pressurization is saturated, and there is a tendency that an improvement in adhesion according to the applied pressure is not recognized.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail. For convenience of illustration, the dimensional ratios in the drawings are not limited to the values shown in the drawings, and do not necessarily match those described. Further, the positional relationship such as up, down, left and right is based on the positional relationship in the drawings unless otherwise specified.
[0031]
FIG. 1 is a schematic cross-sectional view showing an example of an organic EL element produced by the production method of the present invention. The organic EL element 1 includes an electrode layer 11 (electrode), a first organic layer 12, a second organic layer 13, a third organic layer 14, and an electrode layer 15 on a substrate 10 made of a translucent material such as transparent glass. (Electrodes) are sequentially formed.
[0032]
In the organic EL element 1 of this embodiment, the electrode layers 11 and 15 function as a hole injection electrode (anode) and an electron injection electrode (cathode), respectively. The first organic layer 12, the second organic layer 13, and the third organic layer 14 function as a hole injection layer, a light emitting layer, and an electron injection layer, respectively.
[0033]
As a material constituting the substrate 10, the electrode layer 11, the first organic layer 12, the second organic layer 13, the third organic layer 14, and the electrode layer 15, for example, Japanese Patent Laid-Open No. 2003-142268 by the present applicant is disclosed. Various materials described can be used.
[0034]
Here, when the constituent materials of the organic layers 12, 13, and 14 are illustrated more specifically, PVK (poly (N-vinylcarbazole): Tg = 224 ° C.), PEDOT (poly (3,4) are used as the hole injection layer. -Ethylenedioxythiophene): Tg = 190 ° C.), Cu phthalocyanine, and the like. As the light emitting layer, MEH-PPV (poly (2-methoxy-5-ethylhexyloxy-p-phenylenevinylene) Tg = 80 ° C.), Other examples include a molecular dispersion type polymer light emitting material in which a dopant is mixed with a host polymer. The electron injection layer includes an oxadiazole derivative (Tg = 137 ° C.) represented by the following formula (1), Alq3 (tris (8-quinolinolato). ) Aluminum: Tg = 160 ° C.), Bphen (vasophenanthroline: Tg = 86 ° C.) and the like.
[0035]
[Chemical 1]

[0036]
In the organic EL element 1, a mixed layer 20 of both is formed in the interface region between the first organic layer 12 and the second organic layer 13 as shown in the figure. The mixed layer 20 will be described in detail in the description of the manufacturing procedure of the organic EL element 1 described later.
[0037]
Further, the electrode layer 11 is used as a hole injection electrode (anode) and the electrode layer 15 is used as an electron injection electrode (cathode) depending on the type of organic material used for each organic layer 12, 13, 14 and the coating solvent. It may be used. Further, the first organic layer 12 as the hole injection layer and the third organic layer 14 as the electron injection layer are not necessarily required, and are not limited to the three-layer structure of the organic layers 12, 13, and 14, and will be described later. For example, a two-layer structure composed of the first organic layer 12 and the second organic layer 13 (hole injection layer and light emitting layer) or the second organic layer 13 and the third organic layer 14 (light emitting layer and electron injection layer) may be used. Good. In the former case, the light emitting layer preferably has an electron transporting property, and in the latter case, the light emitting layer preferably has a hole transporting property.
[0038]
Furthermore, it is good also as a laminated structure which further provided the hole transport layer, the electron carrying layer, etc. as another organic layer as needed. Furthermore, each organic layer 12, 13, and 14 may be a single layer or a plurality of layers. In the case of a plurality of layers, a plurality of layers constituting each of the organic layers 12, 13, and 14 may be different functional layers. It does not matter as a functional layer. Further, the interface between the electrode layer 11 and the first organic layer 12 may be modified, or a buffer layer (buffer layer) may be further provided to improve charge injection properties.
[0039]
A method for producing the organic EL element 1 having such a configuration will be described below. FIG. 2 is a flowchart showing an example of a procedure for manufacturing the organic EL element 1 by the manufacturing method of the present invention. Here, a procedure for manufacturing the organic EL element 1 having a two-layer structure including the first organic layer 12 as the hole injection layer and the second organic layer 13 as the light emitting layer will be described.
[0040]
First, a substrate 10 such as transparent glass is prepared, and PEDOT / PSS (poly (3,4-ethylenedioxythiophene) / polystyrene sulfonic acid) is dissolved in water as a coating solvent so as to have a concentration of 1.0 wt%. Then, a hole injection layer coating solution is prepared. Also, MEH-PPV is dissolved in m-xylene as a coating solvent so as to have a concentration of 1.5 wt% to prepare a light emitting layer coating solution.
[0041]
Next, an ITO electrode as the electrode layer 11 is formed on the substrate 10 by sputtering or the like (step S1), and then a hole injection layer coating solution is formed thereon with a predetermined film thickness (for example, 500 mm) by spin coating. The film is formed at a constant rotational speed (for example, 2000 rpm) so as to form a coating film for the first organic layer 12 (step S2). Subsequently, a light-emitting layer coating solution is formed on the coating film by a spin coating method at a predetermined rotation speed (for example, 2000 rpm) so as to have a predetermined film thickness (for example, 800 mm), and the coating film for the second organic layer 13 Is formed (step S3). Thereby, between the coating film for the 1st organic layer 12 and the coating film for the 2nd organic layer 13, the area | region which both consist of and is made into the mixed layer 20 finally is formed.
[0042]
Then, the substrate 10 on which those coating films are formed is placed in a heating tank equipped with a heating means such as a heater, the inside of the tank is an inert gas environment such as nitrogen gas, and is maintained at a constant pressure and Heating at a constant temperature, the two-layer coating film is simultaneously dried and solidified to form the first organic layer 12 and the second organic layer 13 together (step S4; heating step, pressure step). At this time, it is considered that the mixed layer 20 is formed in the interface region between the organic layers 12 and 13.
[0043]
At this time, the pressure in the tank is larger than atmospheric pressure, preferably 0.98 to 1960 kPa (0.01 to 20 kgf / cm ² ), More preferably 4.9 to 1960 kPa (0.05 to 20 kgf / cm) ² ), Particularly preferably 196 to 1960 kPa (2 to 20 kgf / cm ² ) Adjust the pressure so that the value is within the range. The output of the heater or the like is adjusted so that the heating temperature is preferably higher than the glass transition point (Tg) of MEH-PPV, more preferably higher than the Tg and lower than the Tg + 200 ° C.
[0044]
In this example, specifically, it is desirable that the heating temperature is higher than 80 ° C., more preferably higher than 80 ° C. and not higher than 280 ° C. (80 ° C. + 200 ° C.). However, heating may be performed at a temperature higher than the Tg (190 ° C.) of PEDOT / PSS as long as the heating time is enough to prevent thermal decomposition of MEH-PPV.
[0045]
Here, as a solvent for dissolving MEH-PPV, another organic solvent such as toluene may be used. Moreover, when using PTPDPES represented by the following formula (2) as a material for forming the first organic layer 12 as the hole injection layer, monochlorobenzene or the like can be exemplified as the solvent. In this case, it is not impossible to use monochlorobenzene as a solvent for MEH-PPV, which is a constituent material for the second organic layer 13, but from the viewpoint of avoiding excessive mixing of the PTPDPES solution and the MEH-PPV solution, As a solvent for MEH-PPV, for example, the above toluene different from monochlorobenzene is preferably used.
[0046]
[Chemical 2]

[0047]
Next, the substrate 10 is taken out of the heating tank, and the electrode layer 15 is formed on the second organic layer 13 by sequentially vacuum-depositing Ca and Al at a predetermined thickness (for example, Ca: 60 mm, Al: 2500 mm). Thus, the organic EL element 1 is obtained (step S5). In addition, in order to prevent deterioration of each organic layer or electrode layer, it is preferable to seal the organic EL element 1 with a sealing plate or the like.
[0048]
FIG. 3 is a flowchart showing another example of the procedure for manufacturing the organic EL element 1 by the manufacturing method of the present invention. This procedure is for manufacturing an organic EL element 1 having a two-layer structure including a second organic layer 13 as a light emitting layer and a third organic layer 14 as an electron injection layer. Instead, the procedure is the same as that shown in FIG. 2 except that an electron injection layer coating solution is prepared and steps S6 to S8 are performed instead of steps S2 to S4. The electron injection layer coating solution is prepared by dissolving the oxadiazole derivative represented by the above formula (1) in 2-ethoxyethanol as a coating solvent so as to have a concentration of 0.5 wt%.
[0049]
In step S6, a light emitting layer coating solution is formed on the electrode layer 11 provided on the substrate 10 by a spin coating method at a predetermined rotation speed (for example, 3500 rpm) so as to have a predetermined film thickness (for example, 500 mm). Then, a coating film for the second organic layer 13 is formed. In step S7, an electron injection layer coating solution is formed on the coating film at a constant rotation speed (for example, 1500 rpm) so as to have a predetermined film thickness (for example, 50 to 100 mm) by spin coating. As a result, a mixed region similar to the mixed layer 20 is formed in the interface region between the two coating films.
[0050]
Further, in step S8 (heating step, pressurizing step), the substrate 10 on which the coating film is formed is placed in a heating tank equipped with a heating means such as a heater, and the inside of the tank is free of nitrogen gas or the like. In an active gas environment, heated at a constant temperature while maintaining a constant pressure, the two layers of the coating film are simultaneously dried and solidified to form the second organic layer 13 and the third organic layer 14 together. At this time, a mixed layer can be formed in the interface region between the organic layers 13 and 14.
[0051]
The heating conditions and pressure conditions in step S8 are the same as in step S4 described above. However, if the heating time is such that the thermal decomposition of MEH-PPV is sufficiently suppressed, the temperature is preferably higher than 137 ° C., which is the Tg of the oxadiazole derivative represented by the above formula (1), more preferably You may heat at the temperature higher than 137 degreeC and 280 degreeC (80 degreeC +200 degreeC).
[0052]
Here, when Alq3 or Bphen described above is used as a material for forming the third organic layer 14 as the electron injection layer, as the solvent, as in the oxadiazole derivative represented by the above formula (1), 2- Ethoxyethanol or the like can be used.
[0053]
FIG. 4 is a flowchart showing still another example of the procedure for manufacturing the organic EL element 1 by the manufacturing method of the present invention. This procedure is for manufacturing the organic EL element 1 having the three organic layers 12, 13, and 14 shown in FIG. 1. After performing Steps S2 and S3, Step S7 is performed, and then The procedure is the same as that shown in FIG. 2 except that step S9 is performed instead of step S4.
[0054]
In step S9, the substrate 10 in which the coating films for the organic layers 12, 13, and 14 are formed and the mixed region is formed between the adjacent coating films is placed in the heating tank described above, and the inside of the tank is filled. In an inert gas environment such as nitrogen gas, heated at a constant temperature and at a constant temperature, the three-layer coating film is simultaneously dried and solidified, and the first organic layer 12, the second organic layer 13 and the third organic layer The organic layer 14 is formed in a lump. At this time, a mixed layer may be formed in each interface region of each organic layer 12, 13, 14. The heating conditions and pressure conditions in step S9 are the same as in step S4 described above.
[0055]
According to the organic EL device 1 manufactured in this way and the manufacturing method according to the present invention, a coating film for each of the organic layers 12, 13, and 14 is continuously formed, and a mixed region is generated between the coating films. Since what was made to heat and pressurize at the same time in step S4, S8, and S9 and form the mixed layer 20 grade | etc., The adhesiveness of each organic layer 12,13,14 is improved. Therefore, the deposition area at the interface between the organic layers 12, 13, and 14 is increased. As a result, the light emission efficiency is increased and the luminance of the organic EL element 1 can be significantly improved.
[0056]
Further, since the adhesion between the adjacent organic layers 12, 13, and 14 is enhanced, the occurrence of interface peeling due to deterioration with time can be sufficiently suppressed. Therefore, element deterioration can be suppressed and the element life can be extended. Therefore, the operational stability and reliability of the organic EL element 1 including the organic layer formed by coating can be significantly improved.
[0057]
Here, FIG. 5 is a cross-sectional view schematically showing a main part in the vicinity of the mixed layer 20 in the organic EL element 1. According to the manufacturing method of the present invention, as shown in the figure, the organic material 13a constituting the second organic layer 13 that is the upper layer exists in a state of being soaked in the surface layer of the first organic layer 12 that is the lower layer. It is presumed that the mixed layer 20 is formed. By causing such a form, the adhesiveness between the organic layers 12 and 13 described above is remarkably enhanced. Also in the organic EL element 1 manufactured by the procedure shown in FIGS. 3 and 4, a mixed layer is formed in the same manner, and the adhesion between the organic layers 12, 13 and 14 is improved.
[0058]
On the other hand, FIG. 6 is a cross-sectional view schematically showing the main part of the organic layer boundary part of the organic EL element manufactured by the conventional wet method, and is shown in comparison with FIG. 5 for reference. As shown in the figure, in the conventional element obtained by individually applying and drying each organic layer, even if the uppermost portion of the organic layer 52 is heated under an inert gas, the oxide film 52a is formed by a small amount of oxygen. Produce. By such surface modification of the organic layer 52, it is presumed that the lower organic layer 52 and the organic substance 53a constituting the upper organic layer are laminated so as to be in contact with each other as a whole. . It is assumed that interfacial delamination is relatively easy to occur due to such a form as one of the factors that tend to reduce the reliability and lifetime of the element. However, each action is not limited to the above.
[0059]
Moreover, when forming each organic layer 12,13,14, in addition to heat-drying, since a coating process is performed and a coating film is dried and solidified, the adhesiveness between each formed layers and the electrode layer 11 are formed. The adhesion between the substrate 10 on which is formed and the organic layers 12, 13, and 14 is further enhanced. Thereby, interface peeling of each organic layer 12, 13, 14 can be further effectively prevented, element deterioration can be suppressed, and the element life can be further extended.
[0060]
Further, as a result of the mixed layer being formed between the organic layers 12, 13, and 14, a state in which the energy barrier between the layers is apparently continuously changed is generated, thereby increasing the injection efficiency of electrons and carriers and increasing the energy efficiency. By improving the device life, the device life can be extended. Furthermore, since the step of individually drying the organic layers 12, 13, and 14 can be omitted, there is an advantage that the manufacturing process of the organic EL element 1 can be simplified, the production efficiency can be improved, and the manufacturing cost can be reduced.
[0061]
In addition, this invention is not limited to embodiment mentioned above, A various deformation | transformation is possible in the limit which does not change the summary. For example, as a solution coating method for forming the organic layers 12, 13, and 14, a cast method, a dip coating method, a spray coating method, or the like may be used in addition to the spin coating method.
[0062]
Furthermore, it is not necessary to heat or heat / press all the organic layers 12, 13, and 14, and at least any two of them may be treated as such. Furthermore, the pressurizing process may not be performed. In addition, from the viewpoint of reducing the heat input to the organic EL element 1 and improving the thermal budget, the number of layers to be heated or heated / pressurized is preferably two or more and as small as possible. On the other hand, from the viewpoint of further improving the adhesion between each layer and the adhesion between the substrate 10 on which the electrode layer 11 is formed and each organic layer 12, 13, 14, and extending the life, heating or heating / pressurizing treatment is performed. A larger number of layers is desirable.
[0063]
【Example】
Hereinafter, the content of the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.
[0064]
<Example 1>
First, a transparent glass substrate 10 was prepared, and a hole injection layer coating solution was prepared using 1 wt% concentration PEDOT / PSS. Further, MEH-PPV was dissolved in m-xylene as a coating solvent so as to have a concentration of 3 wt% to prepare a light emitting layer coating solution. Further, Alq3 was dissolved in dimethylacetamide as a coating solvent so as to have a concentration of 1.0 wt% to prepare an electron injection layer coating solution.
[0065]
Next, an ITO electrode is formed on the substrate 10 by vapor deposition, and then a hole injection layer coating solution is formed thereon at a rotational speed of 2000 rpm so as to have a film thickness of 500 mm, followed by light emission. The layer coating solution is formed at a rotational speed of 2000 rpm so as to have a film thickness of 800 mm by a spin coating method, and the electron injection layer coating solution is further formed on the coating film at a rotational speed of 1000 rpm so that the film thickness becomes 100 mm. The film was formed.
[0066]
Next, the glass substrate on which these films were formed was housed in a pressure vessel, and subjected to heat and pressure treatment at 180 ° C. and 30 kPa for a certain period of time to form a light emitting layer and an electron injection layer in a lump. Thereafter, the glass substrate was taken out from the heating layer, and vacuum-deposited on the electron injection layer so that LiF had a thickness of 5 mm and Al as the cathode had a thickness of 2500 mm to obtain an organic EL element. When the characteristics of this organic EL element were measured and evaluated, the current efficiency was 5 cd / A (@ 100 cd / m ² ), Luminance half-life 2000 hours (100 cd / m ² (During driving).
[0067]
<Example 2>
An organic EL device was produced in the same manner as in Example 1 except that heat treatment was performed at 180 ° C. and atmospheric pressure for a certain period of time. When the characteristics of this organic EL element were measured and evaluated, the current efficiency was 5 cd / A (@ 100 cd / m ² ), Luminance half-life 1500 hours (100 cd / m) ² (During driving).
[0068]
<Comparative example 1>
After the hole injection layer is formed by spin coating, a drying process is performed at 200 ° C. for 5 minutes, and then a light emitting layer is formed on the coating film at a drying process of 180 ° C. for 1 hour, and then an electron injection layer is formed at 180 ° C. An organic EL element was produced in the same manner as in Example 1 except that it was formed at 1 ° C. for 1 hour. When the characteristics of this organic EL element were measured and evaluated, the current efficiency was 1 cd / A (@ 100 cd / m ² ), Luminance half life 100 hours (100 cd / m ² (During driving).
[0069]
<Comparative example 2>
After the hole injection layer is formed by the spin coating method, the drying treatment is performed at 200 ° C. for 5 minutes, and then the light emitting layer is formed on the coating film at 180 ° C. for 1 hour, and then the Alq3 layer is vacuum deposited. An organic EL device was produced in the same manner as in Example 1 except that the step was performed. When the characteristics of this organic EL element were measured and evaluated, the current efficiency was 1 cd / A (@ 100 cd / m ² ), Luminance half life 300 hours (100 cd / m ² Driving).
[0070]
<Evaluation of the physical properties>
First, as a reference, the same coating solution as in Example 1 was used, and the surface form of the light-emitting layer formed by coating and heating and drying the solution on a Si wafer was observed with an atomic force microscope (AFM). FIG. 7 is a three-dimensional spectrum showing the shape of the light emitting layer surface measured in the non-contact mode. From FIG. 7, it was confirmed that the surface of the light emitting layer was formed with a large number of minute irregularities having a height (depth) of about several nm to several tens of nm.
[0071]
Further, the same coating solution as in Example 1 was used, and the solution was applied onto a Si wafer, and then an Alq3 layer was applied and formed, followed by heat treatment to prepare a sample according to the present invention. FIG. 8 is a two-dimensional spectrum showing the surface shape of the sample according to the present invention measured in the DFM mode (dynamic force mode). In the same figure, a portion visually recognized as white indicates a convex portion. Moreover, in FIG. 8, the surface shape approximated to FIG. 7 was recognized, and the surface shape in which the trace of the Alq3 layer was not recognized on the light emitting layer was observed. From this, it is considered that the Alq3 layer penetrates into the inside to form a light emitting layer and a mixed layer.
[0072]
FIG. 9 shows the Al distribution on the surface of the light emitting layer obtained by observing the same sample as FIG. 8 by Auger electron spectroscopy. From this, it was found that a large amount of Al was distributed in the recessed portion of the light emitting layer.
[0073]
On the other hand, using the same coating solution as in Comparative Example 2, the solution was coated on a Si wafer, subjected to heat treatment, and then an Alq3 layer was deposited to prepare a sample by a conventional method. FIG. 10 is a two-dimensional spectrum showing the surface shape measured in the DFM mode (dynamic force mode) for the sample according to the conventional method. In the same figure, the part visually recognized as white shows a convex part. In FIG. 10, a surface shape different from those in FIGS. 7 and 8 was recognized, and a surface shape recognized as an Alq3 layer was observed on the light emitting layer. From this, it is considered that the Alq3 layer as a separate layer was formed on the light emitting layer without penetrating the Alq3 layer.
[0074]
Further, FIG. 11 shows the Al distribution on the surface of the light emitting layer obtained by observing the same sample as FIG. 10 by Auger electron spectroscopy. From this, a uniform distribution of the Alq3 layer was observed.
[0075]
【The invention's effect】
As described above, according to the method for producing an organic EL element of the present invention, even when a wet method is used for forming an organic layer, the lifetime of the produced organic EL element can be remarkably improved. The operational stability and reliability of the element can be improved. Moreover, since the adhesiveness between organic layers can be improved, it becomes possible to improve the luminous efficiency of the organic EL element and hence the luminance.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an example of an organic EL element produced by the production method of the present invention.
FIG. 2 is a flowchart showing an example of a procedure for manufacturing an organic EL element 1 by the manufacturing method of the present invention.
FIG. 3 is a flowchart showing another example of the procedure for manufacturing the organic EL element 1 by the manufacturing method of the present invention.
FIG. 4 is a flowchart showing still another example of the procedure for manufacturing the organic EL element 1 by the manufacturing method of the present invention.
5 is a cross-sectional view schematically showing a main part in the vicinity of the mixed layer 20 in the organic EL element 1. FIG.
FIG. 6 is a cross-sectional view schematically showing a main part of an organic layer boundary part of an organic EL element manufactured by a conventional wet method.
FIG. 7 is a three-dimensional spectrum showing the shape of the light emitting layer surface measured in a non-contact mode.
FIG. 8 is a two-dimensional spectrum showing the surface shape of a sample according to the present invention measured in DFM mode (dynamic force mode).
9 shows the Al distribution on the surface of the light emitting layer obtained by observing the same sample as FIG. 8 by Auger electron spectroscopy.
FIG. 10 is a two-dimensional spectrum showing a surface shape measured in a DFM mode (dynamic force mode) for a sample according to a conventional method.
11 shows the Al distribution on the surface of the light emitting layer obtained by observing the same sample as FIG. 10 by Auger electron spectroscopy.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Organic EL element, 10 ... Board | substrate, 11, 15 ... Electrode layer, 12 ... 1st organic layer, 13 ... 2nd organic layer, 13a ... Organic substance, 14 ... 3rd organic layer, 20 ... Mixed layer, S1- S9 ... Step.

Claims (6)

A method for producing an organic EL device comprising a plurality of organic layers between electrodes,
An application step of continuously applying each solution formed by dissolving or dispersing each material constituting at least two organic layers of the plurality of organic layers on a substrate;
A heating step of simultaneously heating at least two coating films formed by the coating to form the at least two organic layers;
The manufacturing method of an organic EL element provided with. In the heating step, the material is heated to a temperature higher than the lowest glass transition point among the materials constituting the at least two organic layers.
The manufacturing method of the organic EL element of Claim 1. In the heating step, the material is heated to the lowest glass transition point + 200 ° C. or lower among the materials constituting the at least two organic layers.
The manufacturing method of the organic EL element of Claim 1 or 2. The heating step includes a pressurizing step of pressurizing the periphery of the at least two coatings so as to be a pressure greater than atmospheric pressure.
The manufacturing method of the organic EL element as described in any one of Claims 1-3. In the pressurizing step, pressurization is performed so that the pressure becomes a value within a range of 0.98 to 1960 kPa.
The manufacturing method of the organic EL element of Claim 4. A different solvent is used as a solvent in which each material constituting the at least two organic layers formed in succession is dissolved.
The manufacturing method of the organic EL element as described in any one of Claims 1-4.

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