Nano-scaled dielectric and metallic structures are popular light tapping structures in thin-film solar cells. However, a large parasitic absorption in those structures is unavoidable. Most schemes based on such structures also involve the textured active layers that may bring undesirable degradation of the material quality. Here we propose a novel light trapping structure based on the prism structured SiO2 for thin-film solar cells, and a fiat active layer is introduced purposefully. Such a light trapping structure is imposed by the geometrical shape optimization to gain the best optical benefit. A self-consistent simulation method including the solutions of Maxwell, drift diffusion and Poisson equations is adopted for modeling the optical and electrical performance of the solar cell. By examining our scheme, it is disclosed that the conversion efficiency of the flat a-Si:H thin-film solar cell (8.1%) can be promoted to an impressive value (10.74%) that is higher than previous reports. As the method proposed in this work is also applicable to design the thin-film solar cell systems with other materials, this proposal would provide useful guides for developing high-performance thin-film solar cells. (C) 2015 Elsevier Ltd. All rights reserved.