The formation of interfacial wrinkles at the metal contacts on organic thin films

The basic mechanism leading to the morphology change in the active layer was explored systematically. We found that the wrinkles appearing at the cathode surface under post-annealing processes are more prominent than those under pre-annealing processes, which is strongly related to the roughness increase of the active layer. Due to thermal-induced instability from the aluminum (Al) layer with the device under post-annealing processes, a net compressive strain develops from the thermal expansion mismatch between the layers. Furthermore, an analysis of the mechanical properties shows that the enlarged nano-dimension roughness of the active layer is dominated by the final-bottom morphology of the compressed Al layer which depends on the annealing sequence.