Photo-Induced Hot Carrier Cooling in Two-Dimensional Perovskite Single Crystals Studied by Transient Absorption and Time-Resolved Two-Photon Photoelectron Spectroscopy

We investigate hot carrier cooling in 2D perovskite single crystals by applying two complementary ultrafast spectroscopy techniques – transient absorption and time-resolved two-photon photoelectron spectroscopy. While photoelectron spectroscopy selectively probes only the upper layer of the material, transient absorption provides information on the whole bulk of the sample. Based on the similarity of the initial conditions we conclude that in both cases the cooling consists of two very different timescales. The fast timescale of 100-200 fs is related to the electron scattering by LO phonons and the slower timescale of 4-15 ps corresponds to the LO phonon relaxation. Both processes are significantly slower at the surface compared to the bulk.