Investigation on the facet-dependent anisotropy in halide perovskite single crystals

Metal halide perovskite (MHP) single crystals (SCs) are proven to possess superior optoelectronic properties compared to those of their polycrystalline thin film analogues. With the advancement and progress in the study of MHP SCs, it is found that the properties at the surface and bulk of SCs are significantly different. However, there are only a few studies present for the facet-dependent performance of MHP SCs. In this work, we have systematically investigated the anisotropic properties of naturally exposed facets ((100) and (112)) in MAPbI3 SCs. We studied the influence of temperature and illumination on the properties of these facets. It was found that hysteresis at the (112) facet is higher than that at the (100) facet because of the higher trap density of 1.17 × 1013 cm-3 at this facet as compared to the trap density of 2.11 × 1012 cm-3 for the (100) facet. Although there exist different kinds of defects at both the facets, the ion migration mechanism remains the same at both facets, which is confirmed by the obtained almost same activation energy of 0.378 and 0.308 eV for (100) and (112) facets, respectively, for ion migration. The photocurrent, responsivity, and EQE values further confirm anisotropic properties of both the facets in MAPbI3 SCs although they are the same from the crystallography point of view. Thus, this study provides a detailed and systematic investigation of the facet-dependent properties in MHP SCs.