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

The demand for energy is growing globally, and there is an urgent need to exploit the full potential of climate-neutral energy sources such as solar power to reduce greenhouse gas emissions and fight climate change. In this regard, lead halide perovskites emerge as an excellent candidate for highly efficient solar cells. However, these perovskites are unstable under continuous illumination where a process called ion migration occurs. Ion migration can cause phase instabilities, hampering the long-term performance of the corresponding devices and preventing commercialization. Thus, understanding the origin of and manipulating the ion migration in these materials are crucial for exploiting their full potential. Ion migration arises in part because of the soft nature of these semiconductors. At the same time, the softness leads to large strain under various conditions, which could provide a solution for stabilizing these perovskites. Yet, a complete picture of the role of strain on ion migration remains elusive. Unveiling the connection between the dynamically disordered perovskite lattice and the optoelectronic properties can provide concrete guidelines for compositional engineering toward a rational design of mixed-halide devices, where targeted strain engineering strategies can be used as fabrication routes to obtain phase-stable and band-gap-tunable materials.