Effect of Nanocrystal Size and Carbon on Grain Growth during Annealing of Copper Zinc Tin Sulfide Nanocrystal Coatings

Abstract

Polycrystalline films were prepared by annealing coatings cast from colloidal dispersions of Cu2ZnSnS4 (CZTS) nanocrystals in sulfur vapor. This nanocrystal dispersion-based route is a promising potential low-cost approach for production of low-cost thin-film solar cells. We studied the effects of nanocrystal size, sulfur pressure, and carbon concentration on the microstructure development and grain growth during annealing. Coatings prepared from dispersions of CZTS nanocrystals with an average diameter of either 5 or 35 nm were annealed for 10–60 min at 600 °C in 50 or 500 Torr of sulfur. The CZTS nanocrystal size influenced both the rate and mechanism of grain growth. When coatings composed of 5 nm nanocrystals are annealed, abnormal grain growth forms micrometer-scale CZTS grains on the surface of the coating. In contrast, when CZTS coatings composed of 35 nm nanocrystals are annealed, grains grow uniformly via normal grain growth. Grain growth rates increased with sulfur pressure regardless of the nan...