Influence of vacuum and Ar/CdS atmospheres-rapid thermal annealing (RTA) on the properties of Cd2SnO4 thin films obtained by sol-gel technique

Transparent conducting oxides are electrical conductive materials with low absorption of light. In recent years, considerable attention has been paid to ternary oxides such as CdIn2O4, Zn2SnO4, ZnGa2O4, and Cd2SnO4. In present work, Cd2SnO4 thin films were deposited via dip-coating; dipping solution was synthesized by sol-gel technique from the mixture of CdO and SnO2 precursor solutions. The films were obtained with 7 layers (~260 nm) on Corning glass substrates. Each coating was deposited at a withdrawal speed of 2 cm/min, dried at 100 °C for 1 h, and then sintered at 550 °C for 1 h in air. The films were subjected to rapid thermal annealing (RTA) treatments at an annealing temperature of 600 °C for 5 s, under two different atmospheres: vacuum and Ar/CdS (varying Ar pressure inside the chamber from 50 to 200 Torr). X-Ray diffraction patterns showed that all the annealed films were constituted mainly by Cd2SnO4 crystals with a very low presence of CdSnO3. All the films showed a high optical transmittance (above 80%) in the UV-Vis region. A slight decrease of transmittance occurs in the near infrared region for RTA films, but it is not as pronounced as the one observed when these films are treated using conventional annealing. The minimum resistivity value obtained was 2.87×10−3 Ωcm (1.1×102 Ω/□) corresponding to RTA films in vacuum. Electrical and optical properties of the films analyzed in present study make them attractive as electrodes for solar cells, with the advantage of requiring very short annealing times.