The influence of strain on phase stability in mixed-halide perovskites

Lead halide perovskites are at the forefront of semiconductor research because of the tremendous efficiency increase of the corresponding devices together with low-cost fabrication. In sharp contrast with conventional semiconductors (e.g., silicon), they exhibit a soft and disordered lattice that directly affects their optoelectronic properties, making them particularly susceptible to strain. This perspective highlights the most common strategies to manipulate strain in lead halide perovskites at different length scales, focusing on how compressive and tensile strain affect ion migration and thereby undesired phase segregation in mixed-halide perovskites. We emphasize the role of the reduced unit cell volume and the polarizability of the lattice in the suppression of phase segregation. Finally, we highlight some of the most puzzling questions about the phase segregation mechanism, we propose targeted experiments for filling the gap in understanding, and we discuss the potential of using the apparent weaknesses of this class of materials (softness and phase segregation) as a strength.