title: Direct Observation of Electron-Phonon Coupling and Slow Vibrational Relaxation in Organic-Inorganic Hybrid Perovskites.
abstract: Quantum and dielectric confinement effects in Ruddlesden-Popper 2D hybrid perovskites create excitons with a binding energy exceeding 150 meV. We exploit the large exciton binding energy to study exciton and carrier dynamics as well as electron-phonon coupling (EPC) in hybrid perovskites using absorption and photoluminescence (PL) spectroscopies. At temperatures <75 K, we resolve splitting of the excitonic absorption and PL into multiple regularly spaced resonances every 40-46 meV, consistent with EPC to phonons located on the organic cation. We also resolve resonances with a 14 meV spacing, in accord with coupling to phonons with mixed organic and inorganic character. These assignments are supported by density-functional theory calculations. Hot exciton PL and time-resolved PL measurements show that vibrational relaxation occurs on a picosecond time scale competitive with that for PL. At temperatures >75 K, excitonic absorption and PL exhibit homogeneous broadening. While absorption remains homogeneous, PL becomes inhomogeneous at temperatures <75K, which we speculate is caused by the formation and subsequent dynamics of a polaronic exciton.
authors.affiliation: Departments of †Chemistry, ‡Physics and Astronomy, §Materials Science and Engineering, and ∥Electrical and Systems Engineering, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Straus
authors.affiliation: Departments of †Chemistry, ‡Physics and Astronomy, §Materials Science and Engineering, and ∥Electrical and Systems Engineering, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Hurtado Parra
authors.affiliation: Departments of †Chemistry, ‡Physics and Astronomy, §Materials Science and Engineering, and ∥Electrical and Systems Engineering, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Natasha
authors.initials: N
authors.lastname: Iotov
authors.affiliation: Departments of †Chemistry, ‡Physics and Astronomy, §Materials Science and Engineering, and ∥Electrical and Systems Engineering, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Julian
authors.initials: J
authors.lastname: Gebhardt
authors.affiliation: Departments of †Chemistry, ‡Physics and Astronomy, §Materials Science and Engineering, and ∥Electrical and Systems Engineering, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Rappe
authors.affiliation: Departments of †Chemistry, ‡Physics and Astronomy, §Materials Science and Engineering, and ∥Electrical and Systems Engineering, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Subotnik
authors.affiliation: Departments of †Chemistry, ‡Physics and Astronomy, §Materials Science and Engineering, and ∥Electrical and Systems Engineering, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: James M
authors.initials: JM
authors.lastname: Kikkawa
authors.affiliation: Departments of †Chemistry, ‡Physics and Astronomy, §Materials Science and Engineering, and ∥Electrical and Systems Engineering, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Cherie R
authors.initials: CR
authors.lastname: Kagan