Annealing of ZnO and SnO2 transparent conductive oxides

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Transparent Conductive Oxide (TCO) are used in different field [1], especially as antireflective layers on the surface of solar cells [2,3].But in the solar cells process, annealing steps are often used , i.e ; the front metallic contacts of solar cells are obtained by serigraphy at high temperature (800 – 830°C). In this case what happen in TCOs used as antireflective layers ?. In this work we present the comparison of changes in physical properties of two TCOs: tin oxide SnO2 and zinc oxide ZnO when they are annealed at low and high temperatures. These films are deposited by the Atmospheric Pressure Chemical Vapour Deposition APCVD technique. Tin oxide is deposited from tin dichloride (SnCl2, 2H2O) precursor and zinc oxide is obtained by the use of zinc acetylacetonate Zn(C5H7O2)2. The electrical and optical properties of tin oxide and zinc oxide are determined by the four points probes method and spectrophotometry measurement. The values of the resistivity of tin oxide and zinc oxide are 10-4 Ω.cm and 10-3 Ω.cm respectively. These films present an optical transmission higher than 80%. The scanning electronic microscopy images show that the films have a polycrystalline aspect. A post annealing of these TCOs at 450°C improves their electrical properties, while an annealing at higher temperature damage them.