有机发光二极管(OLED)顶发射器件的透明电极

Transparent electrode for top emission organic light-emitting diode

有机发光二极管(OLED)已经成功应用于手机显示屏(小面积)及电视显示屏(大面积).对于小面积显示屏来说,由于显示面积的限制,大多采用顶发射结构.顶发射OLED(TEOLED)由于其更大的开口率,相较传统底发射器件而言,可在相同电流密度下获得更高的发光功率,但是顶发射器件中最关键的就是透明电极的制备.概括起来,根据制作方法和材料来区分,TEOLED透明电极主要分为以下几类,即(1)透明导电氧化物电极;(2)超薄复合金属电极;(3)电介质金属电介质(DMD)复合电极;(4)纳米材料电极等.一般氧化物在可见光范围光透过率很好,但是热蒸发温度很高,需要用溅射的方法来制作,从而对有机层造成损伤;复合金属电极可以用热蒸镀方式制作,方法简单易行,目前被大部分商用产品采用,但是透明度较低;纳米材料的透过率很高,且可以制成柔性电极,但是由于需要溶液加工处理,较易破坏有机层.DMD复合电极既可以具有高透光率,而且可以采用热蒸镀方法成膜,有望成为未来OLED顶发射透明电极的首选.本文对几种透明电极的发展现状和优缺点进行了综述,提出了透明电极今后可能的发展方向.

Organic light-emitting diode（OLED）has been successfully used in mobile display（small area）and television display（large area）.For small area display screens,the top emission structure is mostly adopted because of the limitation of display area.Top emission OLED（TEOLED）can get higher power efficiency at the same current density than traditional bottom emission devices because of its higher aperture-opening ratio.However,the most important part of top emission device is the preparation of transparent electrode.In summary,according to the method and material,TEOLED transparent electrode is divided into the following categories：（1）Transparent conductive oxide electrode（TCO）;（2）ultrathin composite metal electrode;（3）dielectric/metal/dielectric（DMD）composite electrode;（4）nanomaterial electrodes,etc.The general oxide has great optical transmittance in the visible light range,but the thermal evaporation temperature is very high.It needs to be fabricated by sputtering,which damages the organic layer.The composite metal electrode can be made by thermal evaporation,which is simple and easy.It is adopted by most commercial products by now,however its transparency is relatively low.Nano materials have high transparency and can be fabricated for flexible electrodes,but because of the solution processing,it is easier to destroy the organic layer.DMD composite electrode not only has high transmittance,but also can use thermal evaporation method to form film,it is expected to become better choice of top electrode for TEOLED.In order to achieve the objective of producing top emitting OLED with excellent properties,it is most important to find enough transparent,high conductive,ohmic contact,film forming process without destroying organic layer and stable electrode material.Up to now,the researchers have proposed several methods for preparing barrier layer-ITO,pulsed laser deposition transparent conducting oxide,thermal evaporated ultrathin composite metal,DMD composite,nano-materials,etc.In this paper,the applications of these materials in the TEOLED transparent electrode are reviewed.By comparing the advantages and disadvantages of thin film electrode,the research progress of TEOLED transparent electrode is reviewed.