Anharmonicity and Symmetry Breaking in 2D Hybrid Halide Perovskites

  Matan Menahem  ,  Omer Yaffe  
Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel

2D hybrid halide perovskites have been the focus of extensive study due to their easy tuneability and potential in optoelectronic applications such as solar cells and LEDs. It has been established that the electronic properties of halide perovskites are largely affected by thermal fluctuations (electron-phonon interaction). Yet, the phonons in 2D perovskites were not thoroughly studied and were mainly analyzed in the context of PbI2 lattice fluctuations.

In order to directly probe the dominant lattice vibrations and their influence on the electronic properties of 2D perovskites, we measured low frequency polarized Raman of prototypical 2D perovskite (C4H9NH3)2PbI4 as a function of temperature. Raman scattering results indicate a large anharmonic structural dynamic even at cryogenic temperature. Spectral broadening and loss of polarization dependence with increasing temperature suggest symmetry breaking and phonon-phonon scattering, which govern electron-phonon interaction.