Thin-film solar cells that are considered as the second generation of solar cells are known for their low cost and acceptable efficiency. In this technology, semiconductor layers with a thickness of micrometer are deposited on thick enough substrates to maintain physical consistency. The relatively low processing temperature helps use substrates of different materials. Compared with crystalline solar cells, which are mainly made up of rigid flat plates, it is also possible to make thin-film cells on flexible or non-flat substrates. In this study, a method was first proposed to calculate the efficiency of such cells without the need for 3D simulation, and then it is investigated using non-flat conical and paraboloid substrates as a novel method to enhance the light trapping. As a result, a significant increase in the efficiency of the studied non-flat cells was observed and reported in comparison with the flat cells. In addition, the paraboloid shape shows a better performance than that of the conical, to use as the cell's substrate. (C) 2019 Elsevier Ltd. All rights reserved.