  Nanoscale investigations by scanning probe microscopy have provided major
contributions to the rapid development of organic-inorganic halide perovskites
(OIHP) as optoelectronic devices. Further improvement of device level
properties requires a deeper understanding of the performance-limiting
mechanisms such as ion migration, phase segregation and their effects on charge
extraction both at the nano- and macroscale. Here, we have studied the dynamic
electrical response of Cs0.05(FA0.83-MA0.17)0.95PbI3-xBrx perovskite structures
by employing conventional and microsecond time-resolved Kelvin probe force
microscopy (KPFM). Our results indicate strong negative charge carrier trapping
upon illumination and very slow (>1s) relaxation of charges at the grain
boundaries. The fast electronic recombination and transport dynamics on the
microsecond scale probed by time-resolved KPFM show diffusion of charge
carriers towards grain boundaries and indicate locally higher recombination
rates due to intrinsic spatial heterogeneity. The nanoscale electrostatic
effects revealed are summarized in a collective model for mixed-halide CsFAMA.
Results on multilayer solar cell structures draw direct relations between
nanoscale ionic transport, electron accumulation, recombination properties and
the final device performance. Our findings extend the current understanding of
complex charge carrier dynamics in stable multi-cation OIHP structures.
