Fabrication of a novel SnO2:Al/ZnO:F bi-layer for opto-electronic applications

Single layered aluminium doped tin oxide (ATO), fluorine doped zinc oxide (FZO) and bi-layered ATO/FZO thin films were deposited onto preheated glass substrates (T_s = 340 ± 5 °C) using a low-cost and simplified spray pyrolysis technique. The structural, optical, electrical and surface morphological properties of the bi-layered ATO/FZO thin films were studied and compared with that of the single layered films. The average optical transmittance of the bi-layer film in the visible range was found to be around 80 %. The bi-layered ATO/FZO films possessed both better transmittance in the visible range and sharp absorption edge, the unique desirable features of ATO and FZO films, respectively. The optical band gap (E_g) value of the bi-layer coating (3.22 eV) was found to lie between the E_g values of single layered ATO (3.71 eV) and FZO (3.20 eV) films. Sheet resistance values of ATO and FZO single layer films were 3.47 and 11.2 kΩ/sq., respectively. The bi-layered ATO/FZO thin films exhibited a sheet resistance of 4.42 kΩ/sq. which was very much close to that of ATO films and three times less than that of FZO film. The AFM images showed the good packing density and homogeneity of the surface of the bi-layer films. The annealing studies clearly showed that the ATO over layer remarkably improved the thermal stability of the bi-layered film.