Abstract
Lead halide perovskite nanocrystals (NCs) are promising materials for light-emitting applications. These NCs exhibit high photoluminescence quantum yields, are tunable throughout the visible wavelength region by varying halide composition, and can be easily synthesized using low-cost solution-based methods at ambient conditions. It is important to understand the mechanism by which NCs grow and the impact of growth on the eventual photophysics of the NCs. In this work, we develop a new transient absorption spectrometer that can measure the excited state dynamics of NCs in situ, during their synthesis. We report on the evolving excited state properties of MAPbI3 and MAPbBr3 NCs during their nucleation and growth using a ligand-mediated synthesis in a non-polar solvent. New insights into the evolution of the NC surface during growth are provided by analyzing features in the transient spectra that originate from the Stark effect, caused by trapped carriers at the surface.