Slowing down of carrier dynamics via temperature-controlled phase transition in two-dimensional ferroelectric CuInP2S6

The relaxation and recombination of photoexcited carriers directly determine the performance of optoelectronic devices and photocatalysts, and ferroelectric materials with spontaneous polarization may offer a unique route for modulating carrier lifetimes. Two-dimensional CuInP2S6 (CIPS) exhibits ferroelectricity at room temperature. However, the mechanism by which the temperature-induced ferroelectric-to-paraelectric phase transition modulates the carrier dynamics in CIPS remains unclear. Herein, second-harmonic generation measurements are combined with broadband ultrafast spectroscopy to directly resolve temperature-induced phase transition in CIPS, clarifying how carrier dynamics evolve in the ferroelectric phase vs the paraelectric phase. Near the phase-transition region, the carrier lifetime exhibits a sudden and nearly twofold increase when transitioning from the paraelectric phase to the ferroelectric phase. By contrast, the carrier lifetime is only weakly affected by temperature outside this region. Electronic structure calculations and Raman spectroscopy indicate that the change in carrier lifetime is related not only to the intrinsic polarization field in the ferroelectric phase but is also closely associated with phase transition-induced modifications in the electron and phonon structures. The findings of this study provide a mechanistic basis for developing temperature-tunable and polarization-controlled behaviors for a broad range of light-related applications.