Electrical and optical properties of yttrium-doped zinc oxide by spray pyrolysis for solar cell applications

A low-cost transparent conducting oxide (TCO) suitable for terawatt-scale solar cells is reported. The zinc oxide TCO is prepared by spray pyrolysis deposition and is doped with an abundant group IIIB element, yttrium (ZnO:Y). The deposition was carried out at 475°C on quartz substrate. The dependence of the electrical, structural and optical properties of ZnO:Y on deposition and post-annealing conditions was investigated. The important variables for low-resistivity ZnO:Y include Y concentration in the spray solution, post-annealing ambient and type of solvent. The lowest resistivity obtained so far is 1.14 × 10^-2 Ω-cm for a ZnO:Y film deposited from a solution containing 100 mM Zn precursor, 0.4 mM Y precursor, methanol as the solvent, and post-annealed in vacuum at 500°C for 60 minutes. The transmittance of ZnO:Y is high above 85% in the visible range. The Zn/O ratio in ZnO:Y and its correlation to the resistivity of ZnO:Y suggest that Zn interstitials and O vacancies play a significant role in controlling the electrical properties of ZnO:Y.