LAUSR

Hot-carrier cooling is one of the critical photophysical processes that significantly influence the performance of hybrid perovskite-based optoelectronic devices. The extraction of hot carriers at the device interface is very challenging because of their ultrashort lifetime. Here, ultrafast transient spectroscopy measurements and time-domain ab initio calculations show how the dielectric constant of the organic spacers can control and slow the hot-carrier cooling dynamics in single-crystal 2D Ruddlesden-Popper hybrid perovskites. We find that (EA)2PbI4 (EA = HOC2H4NH3+) that correspond to a high dielectric constant organic spacer has a much longer hot-carrier cooling time compared to (AP)2PbI4 (AP = HOC3H6NH3+) and (PEA)2PbI4 (PEA = C6H5C2H4NH3+). The slow hot-carrier relaxation in the former case can be attributed to a stronger screening of the Coulomb interactions, a small nonradiative internal conversion within the conduction bands, as well as a weak electron-phonon coupling. Our findings provide a strategy to prolong the hot-carrier cooling time in low-dimensional hybrid perovskite materials by using organic spacers with reduced dielectric confinement.