Lattice Compression Increases the Activation Barrier for Phase Segregation in Mixed-Halide Perovskites

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Publication date
DOI http://dx.doi.org/10.1021/acsenergylett.0c01474
Reference L.A. Muscarella, E.M. Hutter, F. Wittmann, Y.W. Woo, Y.-K. Jung, L. McGovern, J. Versluis, A. Walsh, H.J. Bakker and B. Ehrler, Lattice Compression Increases the Activation Barrier for Phase Segregation in Mixed-Halide Perovskites, ACS Energy Lett. 5, 3152-3158 (2020)
Groups Hybrid Solar Cells, Ultrafast Spectroscopy

The bandgap tunability of mixed-halide perovskites makes them promising candidates for light emitting diodes and tandem solar cells. However, illuminating mixed-halide perovskites results in the formation of segregated phases enriched in a single-halide. This segregation occurs through ion migration, which is also observed in single-halide compositions, and whose control is thus essential to enhance the lifetime and stability. Using pressure-dependent transient absorption spectroscopy, we find that the formation rates of both iodide- and bromide-rich phases in MAPb(BrxI1-x)3 reduce by two orders of magnitude on increasing the pressure to 0.3 GPa. We explain this reduction from a compression-induced increase of the activation energy for halide migration, which is supported by first-principle calculations. A similar mechanism occurs when the unit cell volume is reduced by incorporating a smaller cation. These findings reveal that stability with respect to halide segregation can be achieved either physically through compressive stress or chemically through compositional engineering.