Interrogating the Effects of Surface Passivation on Electronic and Ionic Carrier Dynamics in Lead Halide Perovskite via Sub-Diffraction-Limited Imaging

We use time-resolved electrostatic force microscopy (trEFM) to probe the effects of surface passivation on electronic and ionic carrier dynamics in mixed cation, mixed halide perovskites. We see a dependence of carrier dynamics on the local perovskite morphology; grain interiors exhibit faster dynamics than grain boundaries. Additionally, we see that surface passivation results slower dynamics on the whole. We employ drift diffusion modeling to explore the competing effects of photocarrier generation, carrier recombination, and ion motion on the evolution of the surface photovoltage. We understand that a locally higher density of mobile lattice defects at grain boundaries results in slower surface photovoltage evolution, and thus trEFM dynamics. Further, we see that a strong suppression in the surface recombination velocity (SRV) explains the slower dynamics following surface passivation. We observe an inverse, linear correlation between the measured trEFM dynamics and the calculated SRV through surface passivation with various chemicals: (3-aminopropyl)trimethoxysilane, [3-(2-aminoethyamino)propyl]trimethoxysilane, and phenethylammonium iodide; confirming our drift-diffusion simulations. Overall, we show that trEFM is capable of imaging local, electronic carrier recombination dynamics and nanoscale variations in ion motion in a sub-diffraction-limited regime, thus, surpassing the spatial resolution of optical probes.