This article studied the a-Si:H solar cell with a randomly rough surface for high-power conversion efficiency. A full 3D numerical modeling program developed by our group including 3D FD-TD for optics and 3D Poisson and drift-diffusion solver for electronic simulation are used to model the characteristics of a textured solar cell. The balance between the optical and electrical performance of the a-Si:H solar cell is studied in this work. For model verification, a solar cell with high 9.23 % power conversion efficiency is used to examine the model and parameters. This article figured out the electrical limit for the a-Si:H solar cell and studied the influence of different roughness scales.