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Nanoscale Photoexcited Carrier Dynamics in Perovskites



Samuel Berweger, Fei Zhang, Bryon Larson, Andrew Ferguson, Axel Palmstrom, Obadiah Reid, Thomas Mitchell (Mitch) Wallis, Kai Zhu, Joseph Berry, Pavel Kabos, Sanjini Nanayakkara


The excellent optoelectronic properties of lead-halide perovskite thin films are complemented by their tolerance to broad compositional variations and associated strain, which allows tuning of desired properties such as the optical bandgap. On the other hand, the resulting large variability in material properties is intimately linked to the inherent nanocrystalline structure, which makes it difficult to untangle the link between composition, processing conditions, and ultimately material properties and degradation. Here we study photoconductivity dynamics in perovskite thin films using temporally- and spectrally-resolved microwave near-field microscopy with temporal resolution as high as 5 ns and spatial resolution better than 50 nm. We study the effect of processing conditions and the evolution of degradation under exposure to ambient conditions on [(CsPbI$_3$)$_0.05}$(FAPbI$_3$)$_0.85}$(MAPbBr$_3$)$_0.15}$] and (FA$_0.7}$Cs$_0.3}$PbI$_3$) films. For the FA-Cs formulation we find that increasing the annealing temperature from 100$^\circ$C to 180$^\circ$C results in significant morphological changes and provides enhanced long-term stability of the desired $\alpha$-phase at the cost of increased trap density and spatially localized regions of reduced photoconductivity. For the mixed halide formulation we find spectral evidence of halide segregation-induced degradation below the instrument resolution limit under ambient exposure while for the FA-Cs formulation annealed at 180$^\circ$C we find a clear spatially inhomogeneous increase in the carrier lifetime associated with an increased trap density.
Journal of Physical Chemistry Letters


Berweger, S. , Zhang, F. , Larson, B. , Ferguson, A. , Palmstrom, A. , Reid, O. , Wallis, T. , Zhu, K. , Berry, J. , Kabos, P. and Nanayakkara, S. (2022), Nanoscale Photoexcited Carrier Dynamics in Perovskites, Journal of Physical Chemistry Letters, [online], (Accessed December 11, 2023)
Created March 8, 2022, Updated February 9, 2023