Resolving Carrier Dynamics in Metal Halide Perovskites to Elucidate Structural Transformation Mechanisms and the Impact of Structural Heterogeneity on Transport
Naomi Ginsberg a b, Milan Delor b, Connor Bischak b, Minliang Lai b, Hannah Weaver a, Dylan Lu b, QinQin Yu a, Peidong Yang b, David Limmer b
a Department of Physics, University of California, Berkeley, USA
b Department of Chemistry, University of California, Berkeley, USA
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Invited Speaker, Naomi Ginsberg, presentation 061
Publication date: 11th February 2019

The intrinsic physical properties of metal halide perovskites, such as electron-phonon coupling, combined with the inhomogeneities that result from many solution-based thin film deposition processes, motivate a strong emphasis on characterization approaches that elucidate the complex and fascinating relationships between material structure and function across multiple relevant scales. We therefore describe lessons from a spectrum of dynamic imaging measurements that address this important need. First, we show how our development of time-resolved elastic scattering microscopy—with a nanoscale sensitivity—allows us to elucidate how grain boundaries impact charge carrier migration through their lateral- and depth-dependent resistivities in a variety of thin films. While this approach may also be used to detect photoinduced demixing in mixed halide perovskites, we demonstrate the way in which A-cation selection enables the tuning of the extent of demixing at high spatial resolution via cathodoluminescence microscopy. This second approach furthermore facilitates a quantitative mechanistic analysis of the activation energy in the structural phase transition in inorganic lead halide nanostructures. We determine that the conversion from non-perovskite to perovskite phases requires only the energy required to break lead-halide bonds, requiring a disordered region between phases that suggests that the perovskite phase grows above the transition temperature from a nanoscale melt. Correlating the electronic and optical properties with structural ones at the nanoscale with these powerful dynamic imaging approaches provides highly complementary insight into the many enigmatic properties of metal halide perovskites that will need to be addressed to fully develop them into widely adopted photovoltaics.

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