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Structural Instabilities Related to Highly Anharmonic Phonons in Halide Perovskites
journal contribution
posted on 2017-05-29, 00:00 authored by Arthur Marronnier, Heejae Lee, Bernard Geffroy, Jacky Even, Yvan Bonnassieux, Guido RomaHybrid
perovskites have emerged over the past five years as absorber
layers for novel high-efficiency low-cost solar cells combining the
advantages of organic and inorganic semiconductors. Unfortunately,
electrical transport in these materials is still poorly understood.
Employing the linear response approach of density functional theory,
we reveal strong anharmonic effects and a double-well phonon instability
at the center of the Brillouin zone for both cubic and orthorhombic
phases of inorganic CsPbI3. Previously reported soft phonon
modes are stabilized at the actual lower-symmetry equilibrium structure,
which occurs in a very flat energy landscape, highlighting the strong
competition between the different phases of CsPbI3. Factoring
these low-energy phonons into electron–phonon interactions
and band gap calculations could help better understand the electrical
transport properties in these materials. Furthermore, the perovskite
oscillations through the corresponding energy barrier could explain
the underlying ferroelectricity and the dynamical Rashba effect predicted
in halide perovskites for photovoltaics.