Ultrafast dynamics of transient exciton state in methylammonium lead iodide perovskite at room temperature

Abstract

Metal-halide perovskites are promising materials for photovoltaics and other optoelectronic applications. Understanding their photophysical properties, especially the energy landscape and dynamics of photoexcited carriers, is essential. This work focuses on studying ultrafast dynamics of photoexcited carriers in a methylammonium lead iodide (MAPI) perovskite thin film at room temperature. We first performed steady-state spectroscopic measurements to characterize the sample and then implemented optical 2D coherent spectroscopy in the non-collinear geometry to probe the ultrafast dynamics of photoexcited carriers. A series of rephasing one-quantum 2D spectra at different waiting times revealed that a transient exciton resonance coexists with the free-carrier resonance for hundreds of femtoseconds before the excitons dissociate into free carriers. The free-carrier resonance persists for a significantly longer time, up to at least 1 ns, and exhibits the signs of spectral diffusion. We then characterized the spectral diffusion by calculating the frequency–frequency correlation function. The acquired 2D spectra revealed unique transient dynamics in MAPI perovskites that might be difficult to probe with one-dimensional techniques.