ABSTRACT We report on a new chemical bath deposition kinetics for the zinc sulfide oxide Zn(S,O) buffer layer as used in Cu(In,Ga)Se2 (CIGS)‐based solar cells. The new approach allows at high rates a better control of the growth kinetics, the step coverage on the rough CIGS surface, and the S/(S+O) ratio in the film. Layer thicknesses as needed for buffer layer applications can be grown at moderate temperatures of 60–80 °C within 5–8 min. Applying this high‐rate Zn(S,O) buffer in CIGS/Zn(S,O)/(Zn,Mg)O/ZnO:Al devices, we realized highly efficient small area solar cells, 30 × 30 cm2 submodules, and 60 × 120 cm2 full‐size modules. Copyright © 2012 John Wiley & Sons, Ltd. The paper reports on a new reaction kinetics for the so‐called chemical bath deposition of the zinc sulfide oxide Zn(S,O) buffer layer in Cu(In,Ga)Se2 (CIGS)‐based solar cells. The new approach allows industrially relevant growth rates. Applying the high‐rate Zn(S,O) buffer layer in CIGS/Zn(S,O)/(Zn,Mg)O/ZnO:Al devices, highly efficient small area solar cells up to 19.1% and 60 ×120 cm2 modules up to 13.1% were realized. I‐V curve of a champion 60 × 120 cm2 Cu(In,Ga)Se2 module with a high‐rate Zn(S,O) buffer (Aperture area efficiency ηap = 13.1%, VOC/cell = 653 mV, FF = 71.0%, jSC = 28.4 mA/cm2, Pmax = 83.7 W, Aperture area Aap = 6374 cm2).