Rotational Dynamics of Organic Cations in the [CH<sub>3</sub>(CH<sub>2</sub>)<sub>7</sub>NH<sub>3</sub>]<sub>2</sub>PbI<sub>4</sub> Perovskite

ORAL

Abstract

The biggest challenge of the 3D high-efficiency perovskite solar cells, such as CH3NH3PbI3 and CH(NH2)2PbI3, is their device instability. 2D perovskite compounds such as butylammonium methylammonium lead iodide perovskite, [CH3(CH2)3NH3]2(CH3NH3)n-1PbnI3n+1, present a solution to this problem. Here we present our recent quasi-elastic neutron scattering on a powder sample of the 2D 1-layer system ([CH3(CH2)7NH3]2PbI4) as a function of temperature. Upon cooling, this system undergoes an orthorhombic phase(Acam) to another orthorhombic phase(Pbca) and further to a monoclinic phase(P21/a). Our group theory and density functional theory analysis show that the rotational dynamics is dominated by C3 rotation of NH3 and CH3 groups. The relaxation rate of the C3 modes decreases with decreasing temperature through the orthorhombic-to-orthorhombic transition. On the other hand, in the low-temperature monoclinic phase, the C3 rotation becomes very slow to detect. The relevance of this finding to electronic properties will also be discussed.

*The work is supported by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, under Award DE-SC0016144.

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Presenters

  • Xiao Hu

    • University of Virginia

Authors

  • Xiao Hu

    • University of Virginia

  • Depei Zhang

    • University of Virginia
    • Department of Physics, University of Virginia

  • Tianran Chen

    • University of Virginia
    • NIST Center for Neutron Research, National Institute of Standards and Technology

  • Alexander Chen

    • University of Virginia
    • Department of Chemical Engineering, University of Virginia

  • Daniel Pajerowski

    • Oak Ridge National Laboratory
    • Oak Ridge National Lab

  • Guangyong Xu

    • NIST Center for Neutron Research, National Institute of Standards and Technology
    • National Institute of Standards and Technology
    • NCNR, NIST
    • NIST Center for Neutron Research

  • Wei-Liang Chen

    • National Taiwan University
    • Center for Condensed Matter Sciences, National Taiwan University

  • Mina Yoon

    • Oak Ridge National Laboratory
    • Center for Nanophase Materials Sciences, Oak Ridge National Laboratory
    • CNMS, Oak Ridge National Lab
    • Center for Nanophase Materials Sciences, Oak Ridge National Lab

  • Yu-Ming Chang

    • National Taiwan University
    • Center for Condensed Matter Sciences, National Taiwan University
    • Center for Condensed Matter Sciences, National Taiwan University, Taiwan

  • Joshua Choi

    • University of Virginia
    • Department of Chemical Engineering, University of Virginia

  • Seunghun Lee

    • University of Virginia
    • Department of Physics, University of Virginia