Ultrafast Spectral Dynamics of CsPb(Br_<i>x</i>Cl_1–<i>x</i>)₃ Mixed-Halide Nanocrystals

In this work we investigated the spectral dynamics of cesium lead mixed-halide, CsPb­(Br_<i>x</i>Cl_1–<i>x</i>)₃ perovskite nanocrystals probed with complementary spectral techniques: time-resolved photoluminescence and transient absorption spectroscopy. Mixed-halide perovskite nanocrystals were synthesized via a hot-injection method followed by anion exchange reactions. Our results show that increased Cl content in perovskite nanocrystals (<i>a</i>) diminished the photoluminescence quantum yield and gave rise to rapid radiative recombination of carriers; (<i>b</i>) resulted in rapid thermalization of hot carriers and low carrier temperatures, which suggests weaker hot-phonon bottleneck and Burstein–Moss effects; (<i>c</i>) decreased the bandgap renormalization energy, which suggests high exciton binding energy and poor charge extraction in Cl substituted perovskite nanocrystals; and (<i>d</i>) increased the number of carriers undergoing Auger losses, where Auger processes dominate over trap-assisted recombination. These findings provide a generalized framework to guide researchers as to when mixed-halide perovskite nanocrystals would be useful for optoelectronic technologies and when they would be detrimental to device performance