Halide alloying in metal halide perovskites is a useful tool for optoelectronic applications requiring a specific bandgap. However, mixed-halide perovskites show ion migration in the perovskite layer, leading to phase segregation and reducing the long-term stability of the devices. Here, we study the ion migration process in methylammonium-based mixed-halide perovskites with varying ratios of bromide to iodide. We find that the mixed-halide perovskites show two separate halide migration processes, in contrast to pure-phase perovskites, which show only a unique halide migration component. Compared to pure-halide perovskites, these processes have lower activation energies, facilitating ion migration in mixed versus pure-phase perovskites, and have a higher density of mobile ions. Under illumination, we find that the concentration of mobile halide ions is further increased and notice the emergence of a migration process involving methylammonium cations. Quantifying the ion migration processes in mixed-halide perovskites shines light on the key parameters allowing the design of bandgap-tunable perovskite solar cells with long-term stability.

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European Research Council (ERC) , The Netherlands Organisation for Scientific Research (NWO)
ACS Appl.Energy Mater.
Hybrid Solar Cells

McGovern, L, Grimaldi, G, Futscher, M.H, Hutter, E.M, Muscarella, L.A, Schmidt, M.C, & Ehrler, B. (2021). Reduced Barrier for Ion Migration in Mixed-Halide Perovskites. ACS Appl.Energy Mater., 4(12), 13431–13437. doi:10.1021/acsaem.1c03095