Our attentions focused on the building block, AZO/PI substrate stacking for various flexible devices such as flexible OLEDs and flexible solar cells. The adhesion strength of AZO/PI interface was investigated in order to improve the reliability of such building block for the flexible device. Oxygen plasma treatment was used to modify the surface of polyimide. The surface chemical states of polyimide before and after plasma treatment were characterized by X-ray photoelectron spectroscopy (XPS).
The component ratio of polar groups as C-O-O, C=O, and new C-OH surface functionality increased after oxygen plasma treatment, but independence of the conditions of plasma treatment. The polyimide surfaces morphology was measured by atomic force microscope (AFM). The AFM images showed the roughness of the polyimide surface increased with increasing RF power in the oxygen plasma treatment.
The surface energy of PI film was calculated by using contact angle measurement. The surface energy increased significantly after plasma treatment from 27.9 to 125-131 mN/m for various treatment power and time. Only slight increase in surface energy (from 125 to 131 mN/m) was observed when higher power or longer treatment time was used. The results showed that both the surface energy of PI and adhesion energy of AZO/PI increased significantly after PI was treated by oxygen plasma. Adhesion energy increased with the increasing of RF treatment power, but the surface energy of
PI increased slightly with increasing power and treatment time. The enhanced adhesion at AZO/PI interface can be attributed to increased roughness and the formation of the new polar group such as C-OH and increased percentage of oxygenated, polar groups such as C-O and C=O on PI surface. The surface of AZO remained very smooth when deposited onto oxygen plasma-modified polyimide films.
However, the resistivity of AZO film degraded if polyimide film was treated by oxygen plasma. The increased resistivity of AZO films can be attributed to the increased surface roughness of polyimide by plasma modification and possibly the incorporation of C and O impurities during sputtering deposition.
86
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