Abstract: Although the efficiency of MAPbI₃ perovskite solar cells has reached a high level, the grain boundaries of polycrystalline perovskite materials capture free carriers and hinder the further improvement of conversion efficiency.In this paper, to improve the performance of perovskite solar cells, magnesium(Mg) ion was added into MAPbI₃ perovskite to passivate the grain boundaries.The effects of Mg ions on the carrier recombination and transport characteristics of perovskite solar cell were analyzed by using the double heterojunction equivalent circuit.The results show that the efficiency of perovskite solar cells can be improved and the transport characteristics of heterojunction can be optimized by adding an appropriate amount of magnesium ions.When the perovskite solar cell was mixed with 0.5% Mg ions, the ideal factor is close to 2.The reverse saturation current density J₀ is reduced and the open circuit voltage is increased by 50 mV.The parallel resistance is nearly doubled.The significant increase of diffusion current also demonstrated an improvement of the electron injection and extraction performance, which implied the carrier transport is described by the diffusion model.