Cadmium tin oxide thin films deposited by RF magnetron sputtering for photovoltaic applications

Cadmium tin oxide (CTO) thin films were deposited by radio frequency (RF) magnetron sputtering from a CdO:SnO2 target onto glass substrates at temperatures from ambient to 300 °C. As-deposited films exhibited amorphous structure and high sheet resistance. Single phase cadmium stannate (Cd2SnO4) thin films with cubic spinel structure having both random and preferred orientation along (4 0 0) were obtained after annealing in Ar/CdS atmosphere. The randomly-oriented single phase Cd2SnO4 thin films showed a high mobility of >50 cm2 V−1 s−1 and carrier density of ∼7 × 1020 cm−3. The thermal expansion coefficient of Cd2SnO4 films was determined to be 5.6 × 10−6 cm/cm/K. The dependence of optical and electrical properties of the as-deposited and annealed CTO thin films on oxygen content in the sputtering gas, substrate temperature and annealing temperature were reported. 16% (AM 1.5) conversion efficiency was achieved for CdTe thin film solar cells using Cd2SnO4 films as the window layer.

► We report a reproducible method for the preparation of high quality Cd2SnO4 films.
► The dependence of CTO film properties on sputter and anneal conditions is studied.
► Single phase Cd2SnO4 thin films with random orientation show best properties.
► The coefficient of thermal expansion of Cd2SnO4 films is determined.