  Nonequilibrium processes occurring in functional materials can significantly
impact device efficiencies and are often difficult to characterize due to the
broad range of length and time scales involved. In particular, mixed halide
hybrid perovskites are promising for optoelectronics, yet the halides
reversibly phase separate when photo-excited, significantly altering device
performance. By combining nanoscale imaging and multiscale modeling, we
elucidate the mechanism underlying this phenomenon, demonstrating that local
strain induced by photo-generated polarons promotes halide phase separation and
leads to nucleation of light-stabilized iodide-rich clusters. This effect
relies on the unique electromechanical properties of hybrid materials,
characteristic of neither their organic nor inorganic constituents alone.
Exploiting photo-induced phase separation and other nonequilibrium phenomena in
hybrid materials, generally, could enable new opportunities for expanding the
functional applications in sensing, photoswitching, optical memory, and energy
storage.
