Coupled optical and structural properties of two-dimensional metal-halide perovskites across phase transitions

Ruddlesden-Popper (RP) metal-halide hybrid perovskites have emerged as a promising class of two-dimensional (2D) materials for optoelectronics and thermal energy storage. These materials consist of alternating layers of organic cations and inorganic octahedra. The organic cations often undergo order-to-disorder phase transitions near room temperature, leading to subtle changes in the inorganic layer that impact their optoelectronic properties. To elucidate how structural changes influence optoelectronic properties, we interrogate a series of 2D lead bromide and iodide perovskites with different-length alkylammonium cations. We find that the octahedra become either more or less distorted at the phase transition temperature, depending on the identity of the cation and halide, and that octahedral motion occurs either continuously with temperature or abruptly across a phase transition. Our study directly links structural dynamics to reversible changes in the optical properties of 2D perovskites and realizes the potential for dynamically switchable optoelectronics with hybrid materials.