Tuning Hot Carrier Cooling Dynamics by Dielectric Confinement in Two-Dimensional Hybrid Perovskite Crystals

Hot carrier (HC) cooling is a critical photophysical process that significantly influences the optoelectronic performance of hybrid perovskite-based devices. The hot carrier extraction at the device interface is very challenging because of its ultrashort lifetime. Here, ultrafast transient reflectance spectroscopy measurements and time-domain ab initio calculations show how the dielectric constant of the organic spacers can control and slow the HC 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 longer HC cooling time compared to that of (AP)₂PbI₄  ( AP = HOC₃H₆NH₃⁺) and (PEA)₂PbI₄ (PEA = C₆H₅C₂H₄NH₃⁺). The slow HC relaxation process in the former case can be ascribed 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. © 2019 American Chemical Society.