Elucidating the Free Carrier and Exciton Ultrafast Dynamics in 2D Perovskites with Alternating Cations in the Interlayer Space

An emerging class of two-dimensional (2D) layered perovskites with alternating cations in the interlayer space (ACI) offers tunable dimensionality and enhanced chemical stability, furnishing new opportunities for perovskite-based optoelectronic devices. In order to optimize the macroscopic device performance, a fundamental understanding of the fate and dynamics of photogenerated charge carriers (e.g., free carriers or excitons) is essential. Terahertz spectroscopy unveils unique intrinsic features of distinct ultrafast processes involving photoexcited states. Our study focused on the dynamics of charge carriers in 2D ACI perovskites with varying layers (n). Our results reveal photogenerated charge carrier transitions from excitons to free carriers mediated by increasing the thickness of the interlayer space cation, going from ACI-1 (n = 1) to ACI-3 (n = 3) structures. Further, we examine the transport of photogenerated charge carriers. While n = 1 exhibits a strong excitonic character, a remarkable high charge carrier mobility was recorded with a layer of n ≥ 2.