This article implements for the first time a numerical semiconductor device simulation-based multiobjective evolutionary algorithm (MOEA) for the characteristic optimization of amorphous silicon thin-film solar cells, based upon a unified optimization framework (UOF). To calculate the device's characteristic, a set of coupled solar cell transport equations consisting of the Poisson equation, the electron-hole current continuity equations, and the photo-generation model is solved numerically. Electrical characteristics, the short-circuited current, the open-circuited voltage, and the conversion efficiency are calculated to analyze the properties of the explored solar cells. The aforementioned device simulation results are used to evaluate the fitness score and access the evolutionary quality of designing parameters via the implemented non-dominating sorting genetic algorithm (NSGA-II) in the UOF. Notably, designing parameters including the material and structural parameters, and the doping concentrations are simultaneously optimized for the explored solar cells. The simulation-based MOEA methodology is useful in optimal structure design and manufacturing of semiconductor solar cells.