Fabrication of flexible Al-doped ZnO films via sol-gel method

1% Al-doped ZnO transparent and conducting thin films on flexible polyimide (PI) substrates were successfully synthesized by the conventional sol-gel spin coating method. All the films with different number of layers (9, 10 and 11) retained a hexagonal wurtzite structure of ZnO and showed preferential c-axis orientation. Good adhesion was evidenced by dense microstructure and homogeneously distributed grains of the films on flexible PI substrates. The average transmittances reached 70% for all the films above a cut-off wavelength of ∼500 nm originated from PI substrates. Comparing to the resistance of films annealed in air, the electrical conductivity could be enhanced by further vacuum (P∼10−2 Pa) post-annealing, and lowest resistivity of 2.52×10−1 Ωcm was obtained in the film with 10 layers.