title: The Effects of the Organic-Inorganic Interactions on the Thermal Transport Properties of CH3NH3PbI3.
abstract: Methylammonium lead iodide perovskite (CH3NH3PbI3), the most investigated hybrid organic-inorganic halide perovskite, is characterized by a quite low thermal conductivity. The rotational motion of methylammonium cations is considered responsible for phonon transport suppression; however, to date, the specific mechanism of the process has not been clarified. In this study, we elucidate the role of rotations in thermal properties based on molecular dynamics simulations. To do it, we developed an empirical potential for CH3NH3PbI3 by fitting to ab initio calculations and evaluated its thermal conductivity by means of nonequilibrium molecular dynamics. Results are compared with model systems that include different embedded cations, and this comparison shows a dominant suppression effect provided by rotational motions. We also checked the temperature dependence of the vibrational density of states and specified the energy range in which anharmonic couplings occur. By means of phonon dispersion analysis, we were able to fully elucidate the suppression mechanism: the rotations are coupled with translational motions of cations, via which inorganic lattice vibrations are coupled and scatter each other.
authors.affiliation: Department of Chemical System Engineering, School of Engineering, The University of Tokyo , 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.|CREST-JST , 7 Gobancho, Chiyoda-ku, Tokyo 102-0076, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Hata
authors.affiliation: Department of Chemical System Engineering, School of Engineering, The University of Tokyo , 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.|Dipartimento di Ingegneria Civile e Ambientale, Università degli Studi di Perugia , 06125 Perugia, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Giorgi
authors.affiliation: Department of Chemical System Engineering, School of Engineering, The University of Tokyo , 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.|CREST-JST , 7 Gobancho, Chiyoda-ku, Tokyo 102-0076, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Yamashita
keywords: Thermal conductivity; hybrid organic−inorganic halide perovskites; molecular dynamics; thermoelectric materials; thermoelectrics