Ferroelectric Polarons in Lead Halide Perovskites
Xiaoyang Zhu a
a Department of Chemistry, Columbia University, US, Broadway, 3000, New York, United States
Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe Fall Meeting19 (NFM19)
#PERFuDe19. Halide perovskites: when theory meets experiment from fundamentals to devices
Berlin, Germany, 2019 November 3rd - 8th
Organizers: Ivan Infante, Matthew Mayer, Jörg Ackermann, Claudine Katan, Jonathan Owen, Wolfgang Tress, Uli Würfel and Simone Meloni
Keynote, Xiaoyang Zhu, presentation 094
DOI: https://doi.org/10.29363/nanoge.nfm.2019.094
Publication date: 18th July 2019

Lead halide perovskites have been demonstrated as high performance materials in solar cells and light-emitting devices. These materials are characterized by coherent band transport expected from crystalline semiconductors, but dielectric responses and phonon dynamics typical of liquids.  Here we explain the essential physics in this class of materials based on their dielectric functions and dynamic symmetry breaking on nano scales. We show that the dielectric function in the THz region may lead to dynamic and local ordering of polar nano domains by an extra electron or hole, resulting a quasiparticle which we call a ferroelectric large polaron, a concept similar to solvation in chemistry. Compared to a conventional large polaron, the collective nature of polarization in a ferroelectric large polaron may give rise to order(s)-of-magnitude larger reduction in the Coulomb potential. Using two-dimensional optical Kerr effect spectroscopy, we directly probe the energetics and local phonon responses of ferroelectric polarons. The ferroelectric polaron may explain the defect tolerance and low recombination rates of charge carriers in lead halide perovskites and the slow cooling of hot carriers, as well as providing a design principle of the “perfect” semiconductor for optoelectronics.

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