Multi-layered Ni-63 betavoltaic cell was investigated for improving the current density and the source efficiency. The model of betavoltaic cells, which typically consist of Ni-63 radioisotope source, semiconductors, and electrodes, was built using MCNP6, and the emission and absorption behaviours of beta particles throughout the cell were analysed with changing geometrical shape of the betavoltaic cell and thickness of radioisotope source layer in order to achieve the improved current density and efficiency of the cell. The result showed that the fluence of beta particles generally increases with the increase of radioisotope thickness up to 10 mu m in both rectangular and cylindrical geometry, while it remains nearly constant above the specific thickness because of the self-absorption effect. Moreover, the results showed that current density of betavoltaic cell could be achieved in cylindrical geometry (1.67A/cm(2)) comparing with rectangular one (1.54A/cm(2)) based on the optimum thickness of Ni-63 radioisotope thickness with the consideration of self-absorption. Copyright (c) 2015 John Wiley & Sons, Ltd.