Coherent Dynamics Unraveling Exciton-carrier Correlations in Orthorhombic Lead Halide Perovskite

Abstract Capturing the temporal evolution and correlations among photoinduced species in semiconductors presents an exciting ground for uncovering new physics and discovering novel phenomena. In this work, we utilize ultrafast two-dimensional electronic spectroscopy (2DES) to investigate the temporal evolution and correlations among photoinduced species in orthorhombic lead halide perovskite at a cryogenic temperature of 15 K. Unlike tetragonal phase at room temperature, the orthorhombic phase shows a distinct strong excitonic absorption peak at 13350 cm−1, and thus, excitons and carriers can simultaneously be generated and temporally tracked using a broadband laser pulse. Low-temperature measurement facilitates clearer differentiation of exciton and carrier bands within 2D electronic spectra, while also enabling the identification of interactions between excitons and carriers through the observation of cross peaks immediately post-photoexcitation. Our analysis demonstrates an ultrafast population transfer from charge carriers to excitons in perovskites, associated with specific low-frequency inorganic sublattice phonons and high-frequency vibrations linked to methylammonium cation motion. Through first-principle calculations and non-adiabatic excited state dynamics simulations, we elucidate the origin and coupling of these vibrational modes, shedding light on the dynamics of “hot” carriers and electron-hole recombination. Overall, our findings elucidate the detailed mechanism underlying the evolution of electronically coupled excitons and carriers in orthorhombic perovskite, contributing to a deeper understanding of exciton-carrier interactions and their modulation by lattice vibrations in complex condensed matter systems.