Probing the Hot Carrier Cooling Process in Low-Dimensional Halide Perovskites through Ultrafast Spectroscopy

Halide perovskite has shown promising applications in perovskite-based optoelectronic devices, e.g., solar cells, and light-emitting diodes, owing to its superior properties including defect tolerance, long carrier diffusion distance, and significant absorption coefficient. Perovskites in nanoscale dimension to lower dimensional networks have recently emerged as having high luminescence efficiency, color purity, and stability. Owing to the soft nature of the perovskite lattice, these electronic properties are primarily governed by the carrier/exciton-phonon coupling strength.<span style="font-size:10.8333px"> </span>Understanding the role of individual phonons in modulating photophysical properties of these class of materials is largely limited to three-dimensional perovskites, (like MAPbI₃), Here in our research, we employ femtosecond Pump – push – probe and transient absorption spectroscopy in low-dimensional perovskite systems to study the influence of electron-phonons interaction in hot-carrier cooling to the fate of band-edge excitons. Furthermore, our spectroscopic approach allows us to discern the role of carrier-carrier interactions from carrier-phonon, which is otherwise difficult in conventional measurements. Our finding reveals that suppression of hot phonon bottleneck effect for systems with increasing quantum confinement (i.e., larger exciton binding energy). We predicted that electron-hole coupling within an exciton (in those confined systems) plays a dominant role in hot-carrier cooling over phonons and carrier-phonon coupling. On the other hand, band-edge electronic dynamics in low-dimensional excitonic systems studied through impulsive excitation provide direct evidence of involvement/coupling of various low-frequency phonon modes.