Simulation of ion migration across the structure of perovskite solar cells with Ag or reduced graphene oxide electrodes

Ion migration in CH₃NH₃PbI₃ perovskite solar cells was modeled using a semi-classical approach based on drift–diffusion, Poisson and continuity equations. This method provided detailed insights into the physics of ionic transport and the slow or fast ions migrating across the perovskite layer under both transient and steady-state conditions. Complementary COMSOL Multiphysics simulations mapped ion migration and accumulation across the perovskite layer and interfaces. The results revealed that ionic build-up near interfaces and grain boundaries impedes carrier transport and accelerates cell degradation. Our model captured coupled dynamics of electrons, holes, mobile ions, and trap states influenced by diffusion and drift mechanisms. Simulations showed ion density shifts over time from the Spiro side toward the TiO₂ layer. Trap distributions were analyzed under dark, light, and open-circuit conditions, showing significant variation. Comparisons of electron and hole densities highlighted reduced ion migration with RGO back contacts. Trap and ion concentration profiles demonstrated improved stability using RGO as contact material compared to Ag metallic conventional contact. Finally, Iodine and MethylAmmonium vacancies were identified as the fastest migrating ionic defects in the perovskite layer.