  Understanding the nature of the photoexcitation and ultrafast charge dynamics
pathways in organic halide perovskite nanocubes and their aggregation into
superlattices is key for the potential applications as tunable light emitters,
photon harvesting materials and light-amplification systems. In this work, we
apply two-dimensional coherent electronic spectroscopy (2DES) to track in real
time the formation of near-infrared optical excitons and their ultrafast
relaxation in CH(NH2)2PbI3 nanocube superlattices. Our results unveil that the
coherent ultrafast dynamics is limited by the combination of the inherent short
exciton decay time ~40 fs and the dephasing due to the coupling with selective
optical phonon modes at higher temperatures. On the picosecond timescale, we
observe the progressive formation of long-lived localized trap states. The
analysis of the temperature dependence of the excitonic intrinsic linewidth, as
extracted by the anti-diagonal components of the 2D spectra, unveils a dramatic
change of the excitonic coherence time across the cubic to tetragonal
structural transition. Our results offer a new way to control and enhance the
ultrafast coherent dynamics of photocarrier generation in hybrid halide
perovskite synthetic solids.
