The distribution of an energy gap gradient can influence photovoltaic conversion, which in turn influences the performance of solar cells. On the other hand, controlling the energy gap gradient can influence the range of the absorption spectrum, and thus the overall solar photovoltaic conversion efficiency is affected. To control the energy gap of a CuIn1-xGaxSe2 (CIGS) solar cell, this study employs a non-vacuum stack coating technique. The chemical composition of the ink is regulated and a multilayer stack is coated to investigate (1) the distribution range of the energy gap and (2) the variability of conversion efficiency in multilayer stack and single-layer composition conditions, in order to determine the feasibility of using a coating stack design to change and control an energy gap. The effect of film composition on crystallinity is tested through high-temperature selenylation. Finally, a miniature solar module is prepared and the conversion efficiency is found to improve from 5.02% to 7.08%, and the feasibility of energy gap control is demonstrated. (C) 2017 Elsevier Ltd. All rights reserved.