Understanding nucleation and growth kinetics of hybrid perovskite microstructures using ultrafast spectroscopy.

Understanding at which stage during the growth process does hybrid perovskite first displays its characteristic optical signature is critical for optimizing large-scale fabrication such as roll-to-roll printing and slot-die coating. Here, by spatially controlling the growth conditions of solution-processed hybrid perovskite using a thermal gradient technique, we fabricate hybrid perovskite that progressively changes from microstructures to large-grain thin films on the same substrate. Consequently, samples fabricated this way allows us to correlate how the structure and nanoscale morphology affect the overall optical response, where a combination of x-ray diffraction, scanning electron microscopy and spectral emission mapping microscopy are employed. Importantly, we conduct ultrafast broadband pump-probe microscopy to assess the carrier dynamics of our sample. Interestingly, we find that the initial nucleating microcrystals already exhibit the characteristics optical properties of large-grain thin films.