Lee Hyemi, Kim Aran, Cho Sung Min, Chae Heeyeop
Department of Chemical Engineering, Sungkyunkwan University, Suwon 440-746, Republic of Korea.
J Nanosci Nanotechnol. 2009 Dec;9(12):7278-82. doi: 10.1166/jnn.2009.1780.
A nanoscale organic light emitting layer of PVK/Ir(ppy)3 was formed by the gravure printing process for the fabrication of organic light emitting diodes (OLEDs) in this work. The control of the nanoscale thickness and roughness by gravure printing is known to be challenging. The thickness and roughness characteristics were investigated for various solvents and printing speeds in this work. The OLED device fabricated in this work has a layer structure of glass/ITO/PEDOT: PSS/PVK + Ir(ppy)3-active layer/LiF/Al. PVK (poly(N-vinyl carbazole)) was used as the host and Ir(ppy)3 as the green-emitting dopant. The thickness of the active layer was controlled by the multiple-printing technique. The effects of the solvent on the surface roughness and OLED brightness were investigated with three different widely used solvents, viz. chloroform (CF), chlorobenzene (CB), and 1,2-dichlorobenzene (DCB). DCB showed the smoothest surface and the best brightness. The low surface roughness obtained with DCB is attributed to its relatively low evaporation rate. We also investigated the effect of the printing speed. In the case of chloroform, the thickness was inversely proportional to the printing speed, because of its high evaporation rate. In the case of DCB, the thickness was proportional to the printing speed. When the evaporation rate is low, a higher rolling speed was preferred for the formation of a thicker layer. The evaporation rate is believed to affect the surface morphology of the active polymer material and the control of the evaporation rate is considered to be an important factor in the gravure printing of nanoscale organic layers.
在本工作中，通过凹版印刷工艺形成了用于制造有机发光二极管（OLED）的PVK/Ir(ppy)3纳米级有机发光层。众所周知，通过凹版印刷控制纳米级厚度和粗糙度具有挑战性。在本工作中，研究了各种溶剂和印刷速度下的厚度和粗糙度特性。本工作中制造的OLED器件具有玻璃/ITO/PEDOT:PSS/PVK + Ir(ppy)3活性层/LiF/Al的层结构。PVK（聚（N-乙烯基咔唑））用作主体，Ir(ppy)3用作绿色发光掺杂剂。活性层的厚度通过多次印刷技术进行控制。用三种不同的常用溶剂，即氯仿（CF）、氯苯（CB）和1,2-二氯苯（DCB），研究了溶剂对表面粗糙度和OLED亮度的影响。DCB显示出最光滑的表面和最佳的亮度。用DCB获得的低表面粗糙度归因于其相对较低的蒸发速率。我们还研究了印刷速度的影响。在氯仿的情况下，由于其高蒸发速率，厚度与印刷速度成反比。在DCB的情况下，厚度与印刷速度成正比。当蒸发速率较低时，较高的轧制速度有利于形成较厚的层。据信蒸发速率会影响活性聚合物材料的表面形态，并且控制蒸发速率被认为是纳米级有机层凹版印刷中的一个重要因素。
