Relevance of annealing on the stoichiometry and morphology of transparent thin films

Transparent thin films of SnO2, ZnO:Al, and ITO were deposited onto glass substrate by vacuum thermal evaporation technique, from 0.5 cm diameter grains (i.e. ITO, ZnO:Al (3%) and SnO2) with 99.99% purity. To improve the quality (i.e. stoichiometry and morphology) of these thin films, they were annealed at 400 degrees C in air for 2 h. Following this annealing, the samples become suitable to be used as contact electrodes for solar cells. The investigations were performed on samples having a polycrystalline structure, as revealed by Xray diffraction analysis after annealing process. Moreover, these thin films had a strong orientation with the following planes parallel to the substrate: (1 0 1) for SnO2, (0 0 2) for ZnO:Al and (2 2 2) for ITO film respectively. Atomic force microscopy (AFM) investigations of the ZnO:Al (R-rms = 2.8 nm) and ITO samples(Rms = 11 nm) show they are homogeneous and a slightly higher roughness (Rms = 51 nm) for the SnO2 thin film surface. The size and shape of the grains were also observed and investigated by scanning electron microscopy (SEM). All SnO2, ZnO:Al and ITO transparent thin films are uniform and dense. The values obtained for electrical resistivity, transmission and energy bandgap as well as conductivity and transparency properties of these thin films, make them suitable to be used as transparent contact electrodes for solar cells. (C) 2014 Elsevier B.V. All rights reserved.