Light-Induced Phase Segregation in Halide-Perovskite Absorbers

In the few short years since the inception of single-junction perovskite solar cells, their efficiencies have skyrocketed. Perovskite absorbers have at least as much to offer tandem solar cells as they do for single-junction cells due in large part to their tunable band gaps. However, modifying the perovskite band structure via halide substitution, the method that has been most effective at tuning band gaps, leads to instabilities in the material for some compositions. Here, we discuss the thermodynamic origin and consequences of light-induced phase segregation observed in mixed-halide perovskites. We propose that, as the phase segregation is rooted in halide migration and possibly affected by lattice strain, modifying the perovskite composition and lattice structure, increasing compositional uniformity, and reducing defect concentrations could significantly improve stability.