Sub-Diffraction Imaging of Carrier Dynamics in Halide Perovskite Semiconductors— Effects of Passivation, Grain Boundaries and Ion Motion

We investigate photo-induced carrier dynamics in halide perovskite semiconductors using time-resolved electrostatic force microscopy (trEFM). Using mixed cation/mixed halide perovskite semiconductors, we show that surface defect passivation leads to slower trEFM dynamics, which correlate with longer time-resolved photoluminescence lifetimes. In addition, in unpassivated samples, we find that grain boundaries exhibit slower photovoltage rise times compared to grain interiors. We explain these results by combining wavelength and intensity-dependent measurements with drift-diffusion simulations to disentangle the competing roles of ion migration and carrier recombination. The results are self-consistent, and we ascribe the slower dynamics near grain boundaries to an increased contribution from mobile ions. In contrast, passivation results in slower dynamics because it dramatically suppresses the surface recombination velocity. Overall, these results demonstrate that we can image local, electronic carrier dynamics in perovskite mechanically, surpassing the diffraction limit of optical probes, while also revealing the competing influences of electronic and ionic carrier motion, and identifying opportunities for improving interfaces and process optimization.