Fabrication of Cu₂ZnSnS₄ (CZTS) Nanoparticle Inks for Growth of CZTS Films for Solar Cells.

Cu₂ZnSnS₄ (CZTS) is a promising candidate material for photovoltaic applications; hence, ecofriendly methods are required to fabricate CZTS films. In this work, we fabricated CZTS nanocrystal inks by a wet ball milling method, with the use of only nontoxic solvents, followed by filtration. We performed centrifugation to screen the as-milled CZTS and obtain nanocrystals. The distribution of CZTS nanoparticles during centrifugation was examined and nanocrystal inks were obtained after the final centrifugal treatment. The as-fabricated CZTS nanocrystal inks were used to deposit CZTS precursors with precisely controlled CZTS films by a spin-coating method followed by a rapid high pressure sulfur annealing method. Both the grain growth and crystallinity of the CZTS films were promoted and the composition was adjusted from S poor to S-rich by the annealing. XRD and Raman characterization showed no secondary phases in the annealed film, the absence of the detrimental phases. A solar cell efficiency of 6.2% (open circuit voltage: Voc = 633.3 mV, short circuit current: Jsc = 17.6 mA/cm², and fill factor: FF = 55.8%) with an area of 0.2 cm² was achieved based on the annealed CZTS film as the absorber layer.