The approaches to establish a more robust and reproducible baseline process for 30cm x 30 cm-sized CIGS-based thin-film circuits with a Zn(O,S,OH)(x) buffer layer are reported, which also lead to an achievement of 12.93% efficiency on an aperture area of 864 cm(2). Monitoring the transparency or transmittance (%T) of dip solution as a process control parameter in the chemical bath deposition (CBD)-buffer deposition step and setting the end point of dipping the CIGS-based absorbers in the solution as the % T of 60% remarkably contribute to make our CBD-buffer deposition process more reproducible. By considering carefully the growth process of metal-organic chemical vapor deposition (MOCVD)-ZnO:B window, a thin layer of high-resistivity, intrinsic ZnO is deposited on the Zn(O,S,OH), buffer layer to simulate the film structure of MOCVD-ZnO:B window in the case of sputtered-5.7 GZO window. Achievement of the reproducibility of 85% for the CIGS-based thin-film circuits with a sputtered-5.7 GZO window confirms that the yield goal of 85% is surely attainable independent of window-layer deposition techniques, such as MOCVD and sputtering. In this study, it is emphasized how important to eliminate unknown factors in the fabrication process for CIGS-based thin-film modules to improve both reproducibility and efficiency. (C) 2002 Published by Elsevier Science B.V.