Influence of the Curing and Annealing Temperatures on the Properties of Solution Processed Tin Oxide Thin Films

Abstract

We report the effect of the curing (Tcuring) and annealing (Tanneal) temperatures on the structural, electrical, and optical properties of solution processed tin oxide. Tanneal was varied from 300 to 500 °C, and Tcuring from 200 °C to Tanneal. All Tanneal lead to a polycrystalline phase, but the amorphous phase was observed at Tanneal = 300 °C and Tcuring ranging from 250 to 300 °C. This could be explained by the melting point of the precursor (SnCl2), occurring at 250 °C. The crystallinity can be effectively controlled by the annealing temperature, but the curing temperature dramatically affects the grain size. We can reach grain sizes from 5–10 nm (Tcuring = 200 °C and Tanneal = 300 °C) to 30–50 nm (Tcuring = 500 °C and Tanneal = 500 °C). At a fixed Tanneal, Hall mobilities, carrier concentration, and conductivity increased with the curing temperature. The Hall mobility was in the range of 1 to 9.4 cm2/Vs, the carrier concentration was 1018 to 1019 cm−3, and the conductivity could reach ~20 S/cm when the grain size was 30–50 nm. The optical transmittance, the optical bandgap, the refractive index, and the extinction coefficient were also analyzed and they show a correlation with the annealing process.