Strain gradient-engineered ion migration and vacancy formation energy in CsPbI₃ perovskite

Strain is widespread during the fabrication and operation of all-inorganic CsPbI₃ perovskite and significantly affects ion migration and vacancy formation. In this work, using atomistic simulations combined with the climbing-image nudged elastic band method and elastic dipole theory, we investigate the effects of uniform uniaxial strain on iodine-vacancy-mediated ion migration in CsPbI₃, as well as the influence of compressive strain gradients on the spatial variation of iodine-vacancy formation energy. The results show that uniform uniaxial strain induces a pronounced pathway-dependent response of ion migration in α-CsPbI₃, leading to strain-induced anisotropic migration behavior. We further find that compressive strain gradients lead to spatial inhomogeneity in iodine-vacancy formation energy, making more strongly compressed regions more favorable for vacancy formation. Theoretical analysis indicates that compressive strain lowers the vacancy formation energy, while strain gradients may further promote local vacancy accumulation in such regions. These findings deepen the understanding of how ion migration and vacancy formation respond to strain, providing a theoretical basis for improving the long-term stability of perovskite solar cells through strain engineering.