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 Cs
0.05
(FA
0.83
MA
0.17
)
0.95
PbI
3–
x
Br
x
perovskite structures
by employing conventional and microsecond time-resolved open-loop
Kelvin probe force microscopy (KPFM). Our results indicate strong
negative charge carrier trapping upon illumination and very slow (>1
s) relaxation of charges at the grain boundaries. The fast electronic
recombination and transport dynamics on the microsecond scale probed
by time-resolved open-loop KPFM show diffusion of charge carriers
toward grain boundaries and indicate locally higher recombination
rates because of intrinsic compositional 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, charge accumulation,
recombination properties, and the final device performance. Our findings
extend the current understanding of complex charge carrier dynamics
in stable multication OIHP structures.
Nanoscale investigation of operational stability in perovskite films. Scanning probe microscopy is employed to reveal signs of early-stage degradation caused by the formation of local charge imbalance across the film microstructure.
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