Properties of Al-doped zinc oxide and In-doped zinc oxide bilayer transparent conducting oxides for solar cell applications

Novel aluminum and indium doped zinc oxide (ZnO) bilayer transparent conducting oxide thin films was fabricated by simple sol-gel spin coating method and post-annealed at 500 °C for an hour under nitrogen ambient for solar cell applications. The structural, electrical and optical properties of both the as-deposited and annealed bilayer thin films were characterized. X-ray diffraction studies show a hexagonal wurtzite-type structure of ZnO with (0 0 2) orientation, which enhanced with annealing. In atomic force microscopy studies, minimum surface roughness was attained for Al-doped ZnO (AZO)/In-doped ZnO (IZO) bilayer TCO film compared to IZO/AZO bilayer film. The AZO/IZO film sheet resistance improved to 0.057 M ohm/square after post-annealing, while the single layer AZO film sheet resistance degraded upon annealing in nitrogen atmosphere. All the films had an average transmittance in the visible region over 96%.