采用热处理方法提高MEH-PPV单层聚合物有机发光二极管发光性能的研究

Enhancement of the Luminescence Performance of Polymer Light-emitting Diodes with Single Layer Structure by Heat Treatment

对以MEH PPV为发光层的单层聚合物有机发光二极管 (OLED)器件在最佳条件下进行真空热处理 ,并用金相显微镜观察施加电压后器件的阴极表面形貌。发现处理后的器件阴极表面的气泡及黑斑明显减少。器件的发光性能显著提高。与未经处理的器件相比 ,最大相对发光强度提高了一个数量级、启亮电压降低了2 0V ,半寿命提高了 1 2 7倍。初步分析表明热处理方法提高器件发光性能的主要原因在于有效地减少了器件在工作过程中由于焦耳热产生的某些气体 ,从而减少阴极表面气泡及黑斑的出现 ,另一方面 ,热处理方法也增强了有机发光层与阴极接触界面的结合力 。

Heat treatment at the optimum condition on MEH-PPV OLED device with single-layer structure was performed. The surface morphology of the Al back electrode of the device after being operated at 12.0V is observed by Metallovert. It is found that the bubbles and black spots on the Al electrode surface was reduced and the luminescence performance of the device was improved obviously after the heat treatment. Compared with the unannealed device, the turn-on voltage of the annealed one is reduced by 2.0V, the maximum EL intensity is increased by ten times, the relative energy efficiency is improved by ten times at the same drive voltage, the half decay time is increased by 12.7 times. We analysised the reason of this result and considered that this is mainly because the bubbles and black spots caused by the evolved gases which were probably produced by the electrolysis of water coming from the humid air were reduced effectively by heat treatment , on the other hand, heat treatment also changes the characteristics of the interface between the light emitting polymer layer and the cathode by promoting the formation of the C-Al or C-O-Al chemical bond, this can enhance the interfacial adhesion and as a result, the electron injection is improved.