All-Optical Probing of Phase Transition Dynamics in 2D Lead Halide Perovskites

Understanding and manipulating structural phase transitions in soft functional materials are crucial for their fabrication and optoelectronic applications. Here, we investigate the phase-transition dynamics of two-dimensional (2D) metal-halide perovskites (MHPs) using time-resolved vibrational-pump visible-probe (VPVP) spectroscopy, where mid-infrared laser pulses are employed to impulsively heat these materials to transition from a low-temperature phase to a high-temperature phase. We focus on three archetypal 2D lead iodide perovskites, which contain organic spacer cations of varying lengths, to explore the fundamental kinetics of the impulsively driven, temperature-induced phase transitions. Our findings reveal that the phase transitions in these materials occur on the microsecond time scale and are largely independent of the organic spacer length and the substrate, while they become faster at higher temperatures. Our results provide key insights into the structural phase transition mechanisms of 2D MHPs, shed light on the operational speed of these materials if their functions involve structural transitions between two phases, and facilitate further exploration of their functional properties in optoelectronic, ferroelectric, and ferromagnetic applications.