Ambient-Air Sulfurization Process for Cu₂ZnSnS₄ Thin Film Solar Cells: Self-Creating Inert Atmosphere Using Sulfur Vapor

Sulfurization is an inevitable process for depositing high-quality Cu2ZnSnS4 (CZTS) thin films, which usually are implemented under high vacuum or inert atmosphere. In this work, a novel ambient-air sulfurization was designed for fabricating a CZTS absorber, with the aim to eliminate the requirement of complex vacuum equipment. The sulfur powder and oxides precursor films were enclosed in a quartz container, in which the inert atmosphere was self-created during the annealing. The sulfurization mechanism was studied carefully through varying the amount of sulfur powder. Finally, the optimized CZTS thin films showed a pure Kesterite phase, large grains, and a suitable band gap. The device fabricated with the ambient-air sulfurized CZTS thin films exhibited an efficiency of 3% with Voc = 0.52 V, Jsc = 12.61 mA/cm2, and FF = 46.6%. This study offers a facile sulfurization route for CZTS thin films, and the successful design principle could be applied in other absorber materials.