The role of halide oxidation in perovskite halide phase separation

Summary Halide perovskites display full solid solubility for Br:I and Cl:Br compositions at equilibrium, yet initially homogeneous distributions often partition into Br- and I-rich (Cl- and Br-) regions under non-equilibrium conditions (e.g., illumination), imposing a major obstacle to operationally stable bandgap tunability critical for applications such as tandem photovoltaics and light emitting diodes. Halide oxidation plays a major role in the physical demixing of alloyed halide compositions in perovskite films; this step appears to initiate halide segregation, ultimately directed by several underlying thermodynamic and kinetic driving forces operating in both concert and competition. Notably, the potential energy needed to oxidize the halide, determined by their relative oxidation potentials (I−