Key Laboratory of Organic Optoelectronics & Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084
Improved Performance of Organic Light-Emitting Diodes with MgF2 as the Anode Buffer Layer
Key Laboratory of Organic Optoelectronics & Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084
Abstract： Organic light-emitting diodes (OLEDs) based on N,N’-bis(1-naphthyl)-N,N’-diphenyl-1,1’-biphenyl-4,4’-diamine (NPB) and tris (8-hydroxyquinoline) aluminium (Alq3) are improved by using a thin MgF2 buffer layer sandwiched between the indium tin oxide (ITO) anode and hole transporting layer (HTL) of NPB. The current-voltage curves of the OLEDs with MgF2 buffers shift to lower voltages, which can be explained by the tunnelling effect. Under 10V bias, the current density and brightness for the optimized OLED with a 1.0-nm MgF2 are 196A/m2 and 517cd/m2, respectively, while for the OLED without anode buffer layer are only 109A/m2 and 156cd/m2. The atomic force microscopy shows that the rms roughness of NPB on ITO/MgF2 is only 1/3 of NPB on bare ITO. The improved morphology of the HTL would lead to more robust OLEDs. The OLED with a 1.0-nm MgF2 layer has a long lifetime of more than five times of the MgF2-free reference device due to the combined electrical and morphological effects of the MgF2 layer.
2006, Vol. 23 
