【０００１】
【産業上の利用分野】
本発明は，有機ＥＬ素子製作の工程で，最後に成膜する電極を，従来の真空蒸着法によらず，塗布（印刷その他等）により，大気圧下で成膜することで，その生産性を向上させる製造方法と，その製法により高品質な有機ＥＬ素子を得ることに関する。
【０００２】
【従来の技術】
有機ＥＬ素子の発光剤には，低分子材料から成るものと，高分子材料から構成されているものがある。
低分子ＥＬは，高真空にした真空蒸着室の中で，発光剤をルツボやボート等に入れ，加熱・蒸発させ，基板に成膜させる。
高分子ＥＬは発光剤を溶剤に溶かした溶液を基板等に塗布（印刷その他等）乾燥させて成膜する。
【０００３】
有機ＥＬ素子は，図１に示すように，両電極間に有機ＥＬ剤その他を１層または複数層構成して成る。有機発光剤に，低分子のものを使用している場合，有機層・電極層共に，成膜には真空蒸着法が用いられる。
【０００４】
高分子ＥＬは，有機ＥＬ剤を成膜する際，真空蒸着法ではなく，溶液の塗布（印刷等）という簡便な方法で成膜でき，カラー化の必要性からインクジェット方式等による印刷法が研究されている。印刷法は，低分子ＥＬの製造法とは違って，湿式法と呼ばれるが，塗膜の乾燥法を工夫することで，水分を除去し，性能を確保している。
この作業は，真空蒸着法に比較して，簡単であり，無駄も少ない。が，最後に，残る一方の電極を成膜するためには，蒸着という作業が残っている。このため，折角「有機ＥＬ剤の成膜」までは効率的に進められるにもかかわらず，最終工程での蒸着作業のために，低分子ＥＬ素子と同様，生産性が伸ばせない。
【０００５】
真空蒸着法の最大のメリットは，製造工程が全て乾式であり，ＥＬの最も嫌う水分・酸素が侵入しにくい という事である。
真空蒸着法（スパッタリング等の方法も含む。以下同様）は，図２に示してある様に，高真空（１０のｎ乗Ｐａ（パスカル），ｎは−４〜−６が一般的）にした空間の中で材料を加熱・蒸発させ，基板に成膜させる方法である。
その真空室内部を高真空にするのに長時間掛かるため，真空室を余り大きくできない。そのため，基板の大きさに制約が生じる。しかも蒸着作業にはエネルギーが多量に必要である。
このように真空蒸着法による成膜法は，製造に大変な労力と時間が掛かる。
【０００６】
真空蒸着法は上述のとおり，材料の歩留まり・製造のエネルギー使用効率共に悪く，また，製造過程で，基板サイズに制限が設けられるために，量産性が悪い。
これらの条件等は製品価格に転化せざるを得ないとすれば，安価にするのは，困難が伴う。
本発明はこの有機ＥＬ素子を効率よく製造し，安価かつ材料の無駄を削減し，高品質の有機ＥＬ素子を得る方法を提供する。
【０００７】
【発明が解決しようとする課題】
有機ＥＬ素子の電極を，真空蒸着をせずに，量産に適した方法で作るには，塗布（印刷その他）が最良の策である。
電極を塗布するには，導電性溶液が必要である。導電性溶液を構成するには，導電性金属粉と，金属粉を繋ぎ固定するバインダーと分散媒（希釈剤）とを混ぜて液状にする。従来の方法で塗布した場合，バインダーや分散媒が有機系の場合有機物の蒸発（揮発）ガスが有機ＥＬの薄膜を侵してしまい，素子構成が不可能であった。その理由は，導電性溶液が塗布されて加熱・乾燥するまでの過程で，導電性溶液の塗布層から有機系溶剤が徐々に蒸発，周囲に拡散する。塗布後，乾燥のための加熱は，塗布面の外表面から加熱されるために，外表面が先に乾燥し皮膜を形成する。内部の有機溶剤の蒸発したガスが皮膜に阻まれて，有機層側に移動し易くなる。有機層側に移動した有機溶剤の蒸発（揮発）したガスは有機薄膜を侵していき，生乾きの導電性溶液がその後を追う様に流動し，有機膜の厚さが４０〜９０ｎｍという薄さのために，最終的に有機層が破壊される。
（注：１ｎｍ＝０．０００００１ｍｍ）
バインダーや分散媒を無機系のものにすれば，上記のような現象は起きず，薄膜は侵されにくくなるが，中でも水系のものを有機ＥＬ剤の上に塗布することは有機ＥＬ剤が水分を嫌う事から考えても常識的に出来ない。
セラミック系では，乾燥温度が高くて（通常２００〜３００℃は必要）有機膜が熱破壊されてしまい，素子として成立しない。
【０００８】
【課題を解決するための手段】
有機溶剤は 揮発性 のものが多く，導電性溶液も，そのほとんどのものが揮発性有機溶剤を含んでおり，低温・短時間で乾燥できるようになっている。
電極の一方が成膜されている基板の上に，有機ＥＬ層まで成膜したＥＬ素子基板全体を，揮発性有機溶剤が容易に蒸発（揮発）しやすい温度以上，有機ＥＬ層が，熱破壊されない温度（ガラス転移温度。現状では一般的に約１００℃前後であるが，材料の改善により，更に高温にできる）以下の範囲内に加熱しておき，導電性溶液を，塗布（スクリーン印刷，スプレー，ディスペンサーなど）する。
【０００９】
塗布された導電性溶液は素子の加熱面に接すると，その中に含まれる有機系溶剤が接触部から直ちに蒸発し，外部へ飛散して，有機層の内部へは有機系ガスは浸透しない。これは，素子基板全体が加熱されているため基板内部の方が塗布面よりも温度が高く，加熱された有機層との境界で有機溶剤が蒸発するため，乾燥膜が生じ，導電性溶液の内部からの有機系ガスが有機層へ浸透するのを妨げる。さらに，基板側から導電性溶液層の外側（有機層との境界と反対側）に熱が徐々に伝導されていくので，導電性溶液の内側から乾燥し，有機系のガスは有機層側から外側に押し出されるため，内部に有機系ガスが残留せず，有機層も破壊せずに，導電性溶液が乾燥して電極として構成される。よって，有機膜中に有機系の蒸気（ガス）が残らず，浸透もせずに経時的な有機膜破壊は防げる。
以上は有機系の導電性溶液について述べたが，水系の場合でも，有機ＥＬ剤のガラス転移温度が１００℃を超えられるものであれば，基板の温度を１００℃に加熱すれば，上記揮発性物質と同様の現象が起こり，水分が有機ＥＬの膜内部に浸入する前に，蒸発し，乾燥膜が生成され，有機ＥＬ膜から内部へ水蒸気を浸透させず，結果として，水分の滲入と残留が妨げられる。
【００１０】
【発明の効果】
このように，基板を加熱した状態で電極用導電性溶液を塗布する方法は，有機ＥＬ膜側への有機性ガスや水分の滲入・残留も無く，有機ＥＬ素子特性に与える影響は無視できるため，高品質な有機ＥＬ素子が製造可能となった。
【００１１】
また，このように塗布（印刷その他）して成膜された電極は，真空蒸着法で成膜された膜厚に比較して容易に厚く出来る（真空蒸着の場合８０〜２００ｎｍ程度であり，厚くするには時間が掛かるが，印刷の場合，１〜３０μｍくらいの積層は短時間で容易に成膜できる）ので，電流駆動型の有機ＥＬ素子にとっては，電極の抵抗値を低くでき，高輝度化のために大電流を流しても，発熱を低く抑えることができる。発熱が少なければ，有機ＥＬ素子自体の劣化も抑えられ，長寿命となり，信頼性の高い製品がえられる。
さらに，導電性溶液を塗布する際に，有機ＥＬ剤と電極用金属の電位差を緩和するために仕事率（化学ポテンシャル）の低い金属（Ｃｓ，Ｌｉ，Ｃａなどのアルカリ金属や，アルカリ土類金属など）や，吸水・吸着作用を持つ薬品類を，該導電性溶液（或いはバインダー単体）に適量混入・撹拌し，塗布する（重ね塗りなどの方法も含む）事で，ＥＬ素子の性能を高める効果を引き出すための方策を採る事も可能である。
【００１２】
このように，本発明は，有機ＥＬ層を成膜した後，残る片方の電極を塗布（印刷その他）で成膜可能としたために，有機ＥＬ素子の基板の大きさを，真空蒸着法のように制限する必要が無く，高品質なものを，大量に，大気圧下で一貫して製造可能とした。
なお，大気圧下での作業としても，乾燥した空気，或いは窒素等で印刷機の周囲の環境を有機ＥＬ素子にとって良い状態にして製造するのに越した事は無い。
また，この様にして作成した電極で有機ＥＬ素子としては完成であるが，素子の保護と寿命の維持の為に，該電極の上から，従来行っているゲッター剤およびカバー等を取付けて使用するなど，或いは，その他の封止効果をもたらす操作を追加することは当然の事である。
【図面の簡単な説明】
【図１】有機ＥＬ素子の 基本構造 を示す図
【図２】真空蒸着室の 蒸着室内部断面 概要を示す図
【符号の説明】
１０…封止用カバー， １１…背面電極， １２…透明電極， １３…有機ＥＬ剤，１３−１…電子輸送性発光層（一般的な例），１３−２…ホール輸送層（一般的な例），１４…基板，２５…真空蒸着室，２６…被蒸着基板，２７…蒸着物質，２８…蒸発皿（るつぼ，ボート等）， ２９…電熱器[0001]
[Industrial applications]
According to the present invention, in the process of manufacturing an organic EL device, the electrode to be formed last is formed under atmospheric pressure by coating (printing or the like) without using a conventional vacuum deposition method, thereby improving the productivity. And a method for obtaining a high-quality organic EL device by the method.
[0002]
[Prior art]
The luminescent agent of the organic EL element includes a low molecular weight material and a high molecular weight material.
In the low molecular EL, a luminescent agent is put in a crucible, a boat, or the like, heated and evaporated in a vacuum evaporation chamber in a high vacuum, and a film is formed on a substrate.
The polymer EL is formed by applying (printing or the like) a solution in which a luminescent agent is dissolved in a solvent to a substrate or the like and drying it.
[0003]
As shown in FIG. 1, the organic EL device is configured by forming one or more layers of an organic EL agent and the like between both electrodes. When a low molecular weight organic light emitting agent is used, a vacuum evaporation method is used for film formation for both the organic layer and the electrode layer.
[0004]
Polymer EL can be formed by a simple method of applying a solution (printing, etc.) instead of vacuum deposition when forming an organic EL agent, and a printing method using an inkjet method or the like has been studied because of the need for colorization. Have been. The printing method is called a wet method, unlike the method of manufacturing a low-molecular EL, but by devising a method of drying a coating film, moisture is removed and the performance is secured.
This operation is simpler and less wasteful than the vacuum evaporation method. However, finally, in order to form the remaining one electrode, an operation called vapor deposition remains. For this reason, although the process up to the point of “organic EL agent film formation” can be efficiently performed, the productivity cannot be improved because of the vapor deposition work in the final step, similarly to the low-molecular EL device.
[0005]
The greatest advantage of the vacuum deposition method is that the manufacturing process is all dry, and that moisture and oxygen, which EL dislikes most, do not easily enter.
As shown in FIG. 2, the vacuum evaporation method (including methods such as sputtering, etc.) was performed under a high vacuum (10 n Pa (Pascal), where n is generally -4 to -6). In this method, a material is heated and evaporated in a space to form a film on a substrate.
Since it takes a long time to make the inside of the vacuum chamber a high vacuum, the vacuum chamber cannot be made very large. Therefore, the size of the substrate is restricted. In addition, a large amount of energy is required for the vapor deposition operation.
As described above, the film forming method by the vacuum evaporation method requires a great deal of labor and time in manufacturing.
[0006]
As described above, the vacuum vapor deposition method is inferior in both the yield of materials and the energy use efficiency in production, and the mass productivity is poor because the size of the substrate is limited in the production process.
If these conditions must be converted to product prices, it is difficult to make them cheap.
The present invention provides a method for efficiently manufacturing the organic EL element, reducing the cost and wasting material, and obtaining a high-quality organic EL element.
[0007]
[Problems to be solved by the invention]
Application (printing or the like) is the best way to make the electrodes of the organic EL element by a method suitable for mass production without performing vacuum deposition.
To apply the electrodes, a conductive solution is required. In order to form a conductive solution, a conductive metal powder, a binder for connecting and fixing the metal powder, and a dispersion medium (diluent) are mixed to form a liquid. In the case of applying by a conventional method, when the binder or the dispersion medium is an organic type, the evaporation (volatilization) gas of the organic substance invades the thin film of the organic EL, and the element cannot be configured. The reason is that in the process from the application of the conductive solution to the heating and drying, the organic solvent gradually evaporates from the coating layer of the conductive solution and diffuses to the surroundings. After the application, since the heating for drying is performed from the outer surface of the application surface, the outer surface is dried first to form a film. The gas evaporated from the organic solvent in the inside is blocked by the film and easily moves to the organic layer side. The gas evaporated (evaporated) of the organic solvent moved to the organic layer side invades the organic thin film, and the freshly dried conductive solution flows so as to follow the thin film, and the thickness of the organic film is as thin as 40 to 90 nm. Therefore, the organic layer is finally destroyed.
(Note: 1 nm = 0.000001 mm)
If the binder or the dispersion medium is made of an inorganic material, the above-mentioned phenomenon does not occur and the thin film is hardly attacked. I can't use common sense to think about hate.
In the case of ceramics, the drying temperature is high (usually, 200 to 300 ° C. is necessary), and the organic film is thermally broken, so that the device cannot be formed.
[0008]
[Means for Solving the Problems]
Many organic solvents are volatile, and most conductive solutions contain volatile organic solvents, so that they can be dried at low temperatures and in a short time.
The organic EL layer is thermally destroyed at a temperature higher than a temperature at which a volatile organic solvent easily evaporates (evaporates) on the substrate on which one of the electrodes is formed. The conductive solution is heated to a temperature below the temperature that is not required (glass transition temperature; generally about 100 ° C at present, but can be increased further by improving the material) and the conductive solution is applied (screen printing, Spray, dispenser, etc.)
[0009]
When the applied conductive solution comes into contact with the heating surface of the element, the organic solvent contained therein evaporates immediately from the contact portion and scatters to the outside, and the organic gas does not permeate into the organic layer. This is because the entire element substrate is heated and the temperature inside the substrate is higher than the coated surface, and the organic solvent evaporates at the boundary with the heated organic layer. Prevents organic gas from the inside from permeating into the organic layer. Furthermore, heat is gradually conducted from the substrate side to the outside of the conductive solution layer (the side opposite to the boundary with the organic layer), so that the heat is dried from the inside of the conductive solution and the organic gas is removed from the organic layer side. Since it is pushed out, the organic solution does not remain inside and the organic layer is not broken, and the conductive solution is dried to form an electrode. Therefore, organic vapor (gas) does not remain in the organic film and permeation of the organic film is prevented without permeation.
Although the above description has been made of the organic conductive solution, even in the case of an aqueous solution, if the glass transition temperature of the organic EL agent can exceed 100 ° C., the above-mentioned volatile property can be obtained by heating the substrate to 100 ° C. A phenomenon similar to that of a substance occurs, and water evaporates before water infiltrates into the organic EL film, and a dry film is generated. Water vapor does not permeate from the organic EL film to the inside. Is hindered.
[0010]
【The invention's effect】
As described above, the method of applying the conductive solution for an electrode while the substrate is heated does not cause infiltration or retention of the organic gas or moisture on the organic EL film side, and the influence on the organic EL element characteristics can be ignored. Thus, a high-quality organic EL device can be manufactured.
[0011]
Further, the electrode formed by coating (printing or the like) in this manner can be easily made thicker than the film thickness formed by the vacuum evaporation method (in the case of vacuum evaporation, it is about 80 to 200 nm, It takes time to print, but in the case of printing, a layer having a thickness of about 1 to 30 μm can be easily formed in a short time.) For a current-driven organic EL element, the resistance value of the electrode can be reduced and high luminance can be obtained. Therefore, even if a large current is applied for heat generation, heat generation can be kept low. If the heat generation is low, the deterioration of the organic EL element itself is suppressed, and the life is extended, and a highly reliable product is obtained.
Further, when the conductive solution is applied, a metal having a low power (chemical potential) (eg, an alkali metal such as Cs, Li, or Ca, or an alkaline earth metal) is used to reduce the potential difference between the organic EL agent and the electrode metal. Etc.) or chemicals having water-absorbing / adsorbing properties are mixed in the conductive solution (or binder alone) in an appropriate amount, stirred, and applied (including methods such as recoating) to enhance the performance of the EL element. It is also possible to take measures to bring out the effects.
[0012]
As described above, according to the present invention, after forming the organic EL layer, the other electrode can be formed by coating (printing or the like), so that the size of the substrate of the organic EL element can be reduced as in the vacuum evaporation method. It is not necessary to limit the process to high-quality products.
It should be noted that, even when working under atmospheric pressure, there is no better way to make the environment around the printing press in good condition for the organic EL element with dry air or nitrogen or the like.
The electrode thus formed is completed as an organic EL device. However, in order to protect the device and maintain its life, a conventional getter agent and a cover are used from above the electrode. It is a matter of course to add an operation for performing a sealing effect or the like.
[Brief description of the drawings]
FIG. 1 is a diagram showing a basic structure of an organic EL element. FIG. 2 is a diagram showing an outline of a cross-section inside a vapor deposition chamber of a vacuum vapor deposition chamber.
DESCRIPTION OF SYMBOLS 10 ... Cover for cover, 11 ... Back electrode, 12 ... Transparent electrode, 13 ... Organic EL agent, 13-1 ... Electron transporting light emitting layer (general example), 13-2 ... Hole transporting layer (General Examples), 14: substrate, 25: vacuum deposition chamber, 26: substrate to be deposited, 27: deposition material, 28: evaporating dish (crucible, boat, etc.), 29: electric heater