Exciton–Phonon Interaction-Induced Large In-Plane Optical Anisotropy in Two-Dimensional All-Inorganic Perovskite Crystals

Two-dimensional (2D) perovskites are an emerging class of layered materials with unique optoelectronic properties. To date, most 2D perovskites with Ruddlesden–Popper (RP) phase reported are organic– inorganic hybrid perovskites with long organic spacers. Here, we report a high-quality all-inorganic 2D perovskite, Cs2PbI2Cl2, synthesized by an aqueous method. The as-synthesized perovskite crystals exhibit large in-plane emission and reflection optical anisotropy. The maximum in-plane linear dichroic ratio is up to 9.6 for exciton emission and 2.0 for reflection at 77 K. The large in-plane optical anisotropy may be ascribed to the strong electron–phonon interaction-induced lattice distortion. The large optical anisotropy enables us to construct a polarization-sensitive photodetector based on this perovskite, for which the linear dichroic ratio of photoresponse is about 1.2. Our study provides an alternative avenue to achieve in-plane optical anisotropy in an isotropy structure and thus would be of great importance for polarization-associated applications.