Copper zinc tin sulfide (Cu2ZnSnS4, CZTS) is highly abundant in nature. It is an important absorber material for the development of low-cost and sustainable next-generation I2-II-IV-VI4 thin-film solar cells because it has a the tunable direct band gap energy, inexpensive constituent elements, and a large absorption coefficient in the visible wavelength region. This work develops an efficient one-step vacuum-based approach to depositing CZTS films without the need to supply excess sulfur during/after deposition or to perform any post-sulfurization treatment. This one-step RF sputtering process produces CZTS films that are crystalline, phase-pure, dense, smooth, and continuous. Air Mass 1.5 G power conversion efficiencies of as high as 6% have been achieved with an antireflection coating, demonstrating that this new approach has great potential as a low-cost alternative for high-efficiency CZTS solar cell production.