Elastic deformation suppresses ion demixing in mixed-halide perovskites

We simulated the kinetics of ion demixing in mixed-halide perovskites using phenomenological Cahn-Hilliard equation. In the model we considered the chemical and the elastic part of Helmholtz free energy of the perovskite lattice, as well as the effect of free carriers generated by sample illumination. If the demixing process is accompanied by local elastic deformation caused by the dependence of the lattice parameter on the local chemical composition, the elastic contribution to the free energy is larger than the other two parts so that elastic deformation effectively suppresses the ion segregation. The demixing can take place if the internal stresses are relieved by surface elastic relaxation, or if the deformation of the lattice is plastic like around structure defects or at grain boundaries. • Spontaneous ion demixing in mixed-halide perovskites is simulated using phenomenological Cahn-Hilliard equation. • The model includes elastic deformation and free carriers created by light absorption. • From the simulation it follows that elastic deformation effectively hinders the demixing process. • The demixing take place only if the deformation is relaxed, for instance, at a rough surface or due to structure defects.