Strong Optical, Electrical, and Raman in-Plane Anisotropy in Corrugated Two-Dimensional Perovskite

Combining the unique properties of hybrid halide perovskites and in-plane anisotropic potential of two-dimensional materials, corrugated layered perovskites are excellent candidates for novel optoelectronic devices. Here, we report strong in-plane anisotropy in a two-dimensional hybrid halide perovskite with corrugated inorganic sheets. We assigned the angle-dependent Raman spectra to particular orientations of the crystals where the method applied is suitable for fast determination of the in-plane crystallographic axes. We demonstrated strong in-plane anisotropy of the optoelectronic properties: electrical measurements showed that changes of photoconductivity and angle-resolved reflectance spectroscopy exhibited variation of the band structure. Employing first-principles calculations, we confirmed the observed anisotropy of the dielectric response. Photoluminescence spectroscopy revealed an anomalous energy shift of ∼20 meV dependent on the relative orientation of the crystals and polarization of the excitation light. Using temperature-dependent analysis of the photoluminescence spectra, we obtained the anisotropic exciton–phonon coupling strength as well as the angle-dependent average phonon energy involved, which contributes to the shift of the photoluminescence peak maximum. This discovery of the in-plane anisotropic behavior in layered 2D perovskites could be expected to spur new functionalities in optical and optoelectronic device applications.