Abstract
In the last decade, hybrid organic-inorganic halide perovskites have emerged as a new type of semiconductor for photovoltaics and other optoelectronic applications. Unlike standard, tetrahedrally bonded semiconductors (e.g., Si and GaAs), the ionic thermal fluctuations in the halide perovskites (i.e., structural dynamics) are strongly coupled to the electronic dynamics. Therefore, it is crucial to obtain accurate and detailed knowledge about the nature of the atomic motions within the crystal. This has proved to be challenging due to low thermal stability and the complex, temperature-dependent structural phase sequence of the halide perovskites. Here, these challenges are overcome and a detailed analysis of the low-frequency lattice mode symmetries is provided in the low-temperature orthorhombic phase of methylammonium-lead iodide. Raman measurements using linearly and circularly polarized light at 1.16 eV excitation are combined with density functional perturbation theory (DFPT). By performing an iterative analysis of Raman polarization-orientation dependence and DFPT mode analysis, the crystal orientation is determined. Subsequently, accounting for birefringence effects detected using circularly polarized light excitation, the symmetries of all of the observed Raman-active modes at 10 K are assigned.
| Original language | English |
|---|---|
| Article number | 051601(R) |
| Number of pages | 6 |
| Journal | Physical Review Materials |
| Volume | 4 |
| Issue number | 5 |
| DOIs | |
| Publication status | Published - 4 May 2020 |
Funding
The authors would like to thank Dr. Tsachi Livneh (NRC) for fruitful discussions, Dr. Ishay Feldman (WIS) for performing x-ray diffraction measurements, and Dr. Lior Segev (WIS) for developing the Raman software. This work was primarily supported by the NSF-BSF program, under NSF Grant No. DMR-1719353 and BSF Grant No. 2016650. R.S. acknowledges FGS-WIS for financial support. O.Y. acknowledges funding from: ISF (1861/17), BSF (2016650), ERC (850041-ANHARMONIC), Benoziyo Endowment Fund, Ilse Katz Institute, Henry Chanoch Krenter Institute, Soref New Scientists Start up Fund, Carolito Stiftung, Abraham & Sonia Rochlin Foundation. Z.D. and L.G. acknowledge support from the US NSF, under Grant No. DMR-1719353. J.Z. acknowledges support from a VIEST Fellowship at the University of Pennsylvania. A.M.R. acknowledges support from the Office of Naval Research under Grant No. N00014-17-1-2574. The authors acknowledge computational support from the High-Performance Computing Modernization Office of the U.S. Department of Defense.