Connecting Optical Properties and Phase Transitions in Ruddlesden-Popper 2D Perovskites

Metal halide perovskites often exhibit dynamic processes, such as phase transitions and ion migration, near room temperature. For many applications, these dynamic processes are undesirable, yet the ability to control structural dynamics can provide new opportunities for devices that rely on dynamic processes. Here, we investigate the order-to-disorder phase transition in Ruddlesden-Popper (RP) 2D perovskites as a function of monoalkylammonium cation length using temperature-dependent absorption, photoluminescence, and X-ray diffraction. We find that changes in the optical properties of 2D perovskites are largely influenced by changes in the octahedra. We also describe a strategy to tune the phase transition temperature of RP 2D perovskites through alloying organic cations and halides. Overall, our results demonstrate the close relationship between structural dynamics and optical properties in 2D RP perovskites and new strategies to tune their structural dynamics.