Production of Homogeneous Cu2ZnSnS4 by Splat Solidification in Microgravity

Abstract

Cu2ZnSnS4 is used for chalcopyrite thin film solar cells with a high absorption coefficient and 1.5eV band-gap energy because elements of Cu2ZnSnS4 are non-toxic and abundant in the Earth's crust. High performance chalcopyrite thin film solar cells with homogeneous composition and structure are expected to be produced by laser ablation of Cu2ZnSnS4 bulk. In order to synthesize the homogeneous Cu2ZnSnS4 bulk, the Cu2ZnSnS4 melt was solidified by splat solidification using braking of a drop tower. For the ground-based experiments, the melt sample was pushed by pressurized Ar gas that had a force equal to that of deceleration force of the drop tower, and was blown against Cu chill block to solidify. The solidified sample had homogeneous composition and no grain boundary; in contrast, the samples that were solidified by pressurized Ar gas and air-cooled in normal gravity had heterogeneous composition and grain boundaries.