The article investigates the ionic transport mechanisms in methylammonium lead iodide (CH₃NH₃PbI₃) solar cells, which have shown rapid improvements in power conversion efficiency but exhibit unusual behaviors such as current-voltage hysteresis and low-frequency giant dielectric response. The study combines first-principles calculations with kinetic measurements to derive activation energies for ionic migration and compare them with experimental data. The results indicate that iodide ion vacancies play a crucial role in ion migration, with an activation energy of 0.6 eV, in agreement with kinetic measurements. This suggests that hybrid halide perovskites are mixed ionic-electronic conductors, which has significant implications for solar cell device architectures and stability. The findings highlight the importance of understanding ionic transport in these materials to improve solar cell performance and address stability issues.The article investigates the ionic transport mechanisms in methylammonium lead iodide (CH₃NH₃PbI₃) solar cells, which have shown rapid improvements in power conversion efficiency but exhibit unusual behaviors such as current-voltage hysteresis and low-frequency giant dielectric response. The study combines first-principles calculations with kinetic measurements to derive activation energies for ionic migration and compare them with experimental data. The results indicate that iodide ion vacancies play a crucial role in ion migration, with an activation energy of 0.6 eV, in agreement with kinetic measurements. This suggests that hybrid halide perovskites are mixed ionic-electronic conductors, which has significant implications for solar cell device architectures and stability. The findings highlight the importance of understanding ionic transport in these materials to improve solar cell performance and address stability issues.