High Transmission and Low Resistivity Cadmium Tin Oxide Thin Films Deposited by Sol-Gel

Transparent conducting cadmium tin oxide (CTO) thin films were obtained from a mixture of CdO and SnO2 precursor solutions by the dip-coating sol-gel technique. The thin films studied in this work were made with 7 coats (~200 nm) on corning glass and quartz substrates. Each coating was deposited at a withdrawal speed of 2 cm/min, dried at 100°C for 1 hour and then sintered at 550°C for 1 hour in air. In order to decrease the resistivity values of the films, these were annealed in a vacuum atmosphere and another set of films were annealed in an Ar/CdS atmosphere. The annealing temperatures (Ta) were 450°C, 500°C and 550°C, as well as 600°C and 650°C, when corning glass and quartz substrates were used, respectively. X-Ray diffraction (XRD) patterns of the films annealed in a vacuum showed that there is only the presence of CTO crystals for 450°C≤ Ta ≤ 600°C and CTO+SnO2 crystals for Ta=650°C. The films annealed in Ar/CdS atmosphere were only constituted of CTO crystals independent of the Ta. The minimum resistivity value obtained was ~4 x 10 -4 cm (Rsheet= 20 /□) for the films deposited on quartz and annealed at Ta=600°C under an Ar/CdS atmosphere. The films deposited on quartz showed the higher optical transmission (~90%) with respect to the films deposited on corning glass substrates (~85%) in the Uv-vis region. For their optical and electrical characteristics, these films are good candidates as transparent electrodes in solar cells.