title: Dielectric and Thermodynamic Signatures of Low-Temperature Glassy Dynamics in the Hybrid Perovskites CH3NH3PbI3 and HC(NH2)2PbI3.
abstract: Hybrid main group halide perovskites hold great technological promise in optoelectronic applications and present rich and complex evolution of structure and dynamics. Here we present low-temperature dielectric measurements and calorimetry of APbI3 [A = CH3NH3(+), HC(NH2)2(+)] that suggest glassy behavior on cooling. In both compounds, the dielectric loss displays frequency-dependent peaks below 100 K characteristic of a glassy slowing of relaxation dynamics, with HC(NH2)2PbI3 exhibiting greater glass fragility. Consistent with quenched disorder, the low-temperature heat capacity of both perovskites deviates substantially from the ∼T(3) acoustic phonon contribution predicted by the Debye model. We suggest that static disorder of the A-site molecular cation, potentially coupled to local distortions of the Pb-I sublattice, is responsible for these phenomena. The distinct low-temperature dynamics observed in these two perovskites suggest qualitative differences in the interaction between the molecular cation and the surrounding inorganic framework, with potential implications for defect screening and device performance at ambient temperatures.
authors.affiliation: Materials Research Laboratory, University of California , Santa Barbara, California 93106, United States.|Materials Department, University of California , Santa Barbara, California 93106, United States.
authors.forename: Douglas H
authors.initials: DH
authors.lastname: Fabini
authors.affiliation: Materials Department, University of California , Santa Barbara, California 93106, United States.|Department of Physics, Boston College , Chestnut Hill, Massachusetts 02467, United States.
authors.forename: Tom
authors.initials: T
authors.lastname: Hogan
authors.affiliation: Materials Research Laboratory, University of California , Santa Barbara, California 93106, United States.|Department of Chemistry and Biochemistry, University of California , Santa Barbara, California 93106, United States.
authors.forename: Hayden A
authors.initials: HA
authors.lastname: Evans
authors.affiliation: Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Constantinos C
authors.initials: CC
authors.lastname: Stoumpos
authors.affiliation: Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Mercouri G
authors.initials: MG
authors.lastname: Kanatzidis
authors.affiliation: Materials Research Laboratory, University of California , Santa Barbara, California 93106, United States.|Materials Department, University of California , Santa Barbara, California 93106, United States.|Department of Chemistry and Biochemistry, University of California , Santa Barbara, California 93106, United States.
authors.forename: Ram
authors.initials: R
authors.lastname: Seshadri