High-quality cadmium stannate annealed in N2 atmosphere for low-cost thin film solar cell

Abstract

Radio frequency magnetron sputtered cadmium stannate (Cd₂SnO₄) or cadmium tin oxide (CTO) films were annealed in a nitrogen (N₂) atmosphere. The resistivity of argon/oxygen (Ar/O₂) gas sputtered CTO films decreased drastically after high temperature annealing, and the lowest resistivity of 1.73 × 10⁻⁴ Ω cm was achieved. The Cd₂SnO₄ crystal phase of CTO films deposited in Ar/O₂ gas occurred after annealing at 600 °C to 635 °C, and the optical band gap increased obviously after annealing. When the deposition atmosphere was pure Ar, the as-deposited CTO resistivity was in the order of 10⁻⁴ Ω cm. The resistivity of thin films deposited in Ar gas could decline slightly after annealing. However, the resistivity of thick films deposited under Ar gas increased drastically after annealing. No Cd₂SnO₄ crystal phase of Ar gas sputtered CTO occurred after annealing. The visible region and near infrared spectrum transmittance of CTO films increased after annealing in a N₂ atmosphere. The resistivity of CTO films deposited in Ar/O₂ and after annealing in N₂ gas at 620 °C increased slightly after chlorine treatment. Furthermore, the resistivity of films deposited in Ar/O₂ and then annealed in N₂ gas at 620 °C decreased slightly after vacuum annealing at 600 °C for 5 min.