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.