Abstract: Co-sputtered AlxNiy thin films were used as diffusion barriers between aluminum and hydrogenated microcrystalline silicon (μc-Si:H) for flexible thin film solar cells. The stoichiometric ratio of AlxNiy showed a significant effect on the structures of the films. The obtained Al3Ni2 film was amorphous, while polycrystalline films were obtained when the ratio of aluminum to nickel was 1:1 and 2:3. An auger electron spectroscope and four-point probe system were applied to test the resistance to the interdiffusion between aluminum and silicon, as well as the conductivities of the AlxNiy barriers. The data of auger depth profile showed that the content of silicon was the minimum in the aluminum layer after sputtering for 4 min using AlNi thin film as the barrier layer. Compared to other AlxNiy alloys, the AlNi thin film possessed the lowest sheet resistance.