2, Oak Ridge National Laboratory, Oakridge, Tennessee, United States
3, California State University, Northridge, Northridge, California, United States
Inorganic cesium lead halide, CsPbX3 (X = Cl, Br, I), perovskite nanocrystals (NCs) have recently driven a paradigm shift in light-harvesting and light-emitting technologies due to their tunable optical bandgaps, bright photoluminescence (PL), and higher stabilities than methylammonium-based perovskites. Whereas research efforts in the literature has primarily focused on the synthesis and surface properties of these materials, to successfully implement CsPbX3 in applications it is imperative to understand their carrier dynamic processes, which are controlled by their size, shape, and composition. These processes, which include carrier generation, carrier cooling, and carrier recombination by radiative and nonradiative pathways, ultimately determine the efficiency of optoelectronic technologies. In this work we show the impact of morphology and composition on the carrier dynamics of CsPbBr3 NCs. We compared the ultrafast dynamics of CsPbBr3 bulk films, nanocubes, and nanowires with transient absorption spectroscopy (TAS) and time-resolved photoluminescence (TrPL) and observed the fastest exciton decay lifetime of the films relative to the nanocubes and nanowires. In order to study the impact of composition on the relaxation dynamics of CsPbX3 NCs, we partially substituted bromide ions with chloride ions via anion exchange reactions and examined their ultrafast dynamics with TAS and TrPL. We observed that incorporation of chloride ions increased the rates of carrier cooling and carrier recombination through Auger and trap states.