Oxide-induced grain growth in CZTS nanoparticle coatings

Abstract

An innovative and scalable synthesis approach to the formation of CZTS nanoparticles has been developed using aerosol spray pyrolysis. Surface-ligand-free CZTS nanoparticles with controllable size and composition are synthesized by thermally decomposing an aerosolized precursor mixture of copper, zinc, and tin thiocarbamates. After collection, the particles are dispersed in an organic solvent, coated on soda lime glass, mechanically compacted, and annealed in a low-pressure sulfur atmosphere to form CZTS thin films. The resulting thin film is highly porous and composed of small grains. We have found that growing a thin amorphous oxide layer on the surface of ligand-free Cu₂ZnSnS₄ (CZTS) nanoparticles substantially enhances uniform grain growth during heat treatment in a sulfur atmosphere. This is achieved by adding a simple annealing step in air after nanoparticle production and before coating. This process consistently results in CZTS films with higher tin content after annealing, suggesting that the presence of an oxide layer around the particles improves the retention of volatile tin sulfide phases, which is then beneficial in respect to grain growth kinetics.