Study of thermal degradation of organic light emitting device structures by X-ray scattering

Abstract We report the process of thermal degradation of organic light emitting devices (OLEDs) having multilayered structure of [LiF/tris-(8-hydroxyquinoline) aluminum(Alq 3 )/ N , N ′-Bis(naphthalen-1-yl)- N , N ′-bis(phenyl)benzidine (NPB)/copper phthalocyanine (CuPc)/indium tin oxide (ITO)/SiO 2 on a glass] by synchrotron X-ray scattering. The results show that the thermally induced degradation process of OLED multilayers has undergone several evolutions due to thermal expansion of NPB, intermixing between NPB, Alq 3 , and LiF layers, dewetting of NPB on CuPc, and crystallization of NPB and Alq 3 depending on the annealing temperature. The crystallization of NPB appears at 180 °C, much higher temperature than the glass transition temperature ( T g  = 96 °C) of NPB. The results are also compared with the findings from the atomic force microscope (AFM) images.

[1]  L. G. Parratt.  Surface Studies of Solids by Total Reflection of X-Rays , 1954 .

[2]  Chihaya Adachi,et al.  Molecular design of hole transport materials for obtaining high durability in organic electroluminescent diodes , 1995 .

[3]  Hiroshi Inada,et al.  Thermally stable multilared organic electroluminescent devices using novel starburst molecules, 4,4′,4″‐Tri(N‐carbazolyl)triphenylamine (TCTA) and 4,4′,4″‐Tris(3‐methylphenylphenylamino)triphenylamine (m‐MTDATA), as hole‐transport materials , 1994 .

[4]  Ming Lu,et al.  Real-Time Observation of Temperature Rise and Thermal Breakdown Processes in Organic LEDs Using an IR Imaging and Analysis System , 2000 .

[5]  C. Tang,et al.  Organic Electroluminescent Diodes , 1987 .

[6]  Stephen R. Forrest,et al.  Thermally induced failure mechanisms of organic light emitting device structures probed by X-ray specular reflectivity , 1997 .

[7]  Jianbin Xu,et al.  Nanoscale investigation of moisture-induced degradation mechanisms of tris(8-hydroxyquinoline) aluminium-based organic light-emitting diodes , 2004 .

[8]  Jianbin Xu,et al.  Real-time visualization of thermally activated degradation of the ITO/CuPC/NPB/Alq3 stack used in one of the organic light-emitting diodes , 2004 .

[9]  L. Do,et al.  Observation of Crystallization of Vapor-deposited TPD Films by AFM and FFM , 1994 .

[10]  A. Okada,et al.  THERMAL STABILITY IN OLIGOMERIC TRIPHENYLAMINE/TRIS(8-QUINOLINOLATO) ALUMINUM ELECTROLUMINESCENT DEVICES , 1997 .

[11]  In situ energy-dispersive X-ray reflectivity measurements of structural changes in thin films for organic electroluminescent devices , 1997 .

[12]  Stephen R. Forrest,et al.  Hole Transporting Materials with High Glass Transition Temperatures for Use in Organic Light-Emitting Devices , 1998 .

[13]  Jwo-Huei Jou,et al.  Enhancing the performance of organic light-emitting devices by selective thermal treatment , 2005 .

[14]  Noritaka Yamamoto,et al.  STUDY OF INTERFACIAL DEGRADATION OF THE VAPOR-DEPOSITED BILAYER OF ALQ3/TPD FOR ORGANIC ELECTROLUMINESCENT (EL) DEVICES BY PHOTOLUMINESCENCE , 1995 .