We investigated multistacked solar cells with a structure of metal/a-si:H (n-i-p)/poly-Si (n-p)/metal. This cell consists of two component cells; top n-i-p junction a-Si:H cell and a bottom n-p junction poly-Si cell. The solar cell conversion influencing factors were investigated in terms of film thickness, doping concentration, minority carrier lifetime, diffusion length, surface recombination, surface potential, AR coating, and circuit parameters of solar cells. The optimization of material and solar cell was carried out by using a PC-1D simulator. The main stream lines of the studies were the p-n junction poly-Si bottom cell, the p-i-n junction top a-Si:H cell, and the equivalent circuit examination. The optimized simulation results indicates that the 22% efficiency of multistacked solar cells can be achieved by optimizing parameters in each layer.