Ligang Yuan

Orientation arrangement of methylammonium ions in hybrid organic−inorganic perovskite is still under debate because their tendency for alignment is expected to give rise to either ferroelectric or anti-ferroelectric behavior, which may influence the perovskite device performance. To resolve the debate surrounding the alignment of the organic cations in perovskite materials, we studied the dipole orientation by analysing the dielectric properties of the material. The dielectric permittivity has been investigated as a function of temperature with the data analysed using the Kirkwood–Fröhlich–Onsager theory. From these results, we provide experimental evidence of the anti-parallel arrangement of methylammonium ions in hybrid organic−inorganic perovskite.

We study the circular photogalvanic effect in the organometal halide perovskite solar cell absorber CH3NH3PbI3. The calculated photocurrent density for a system with broken inversion symmetry is about 10⁻⁹ A/W, comparable to the previously studied quantum well and bulk Rashba systems. The circular photogalvanic effect relies on inversion symmetry breaking, so that by tuning the optical penetration depth, the degree of inversion symmetry breaking can be probed at different depths from the sample surface. We propose that measurements of this effect may clarify the presence or absence of inversion symmetry, which remains a controversial issue and has been argued to play an important role in the high conversion efficiency of this material.