title: Tracking the coherent generation of polaron pairs in conjugated polymers.
abstract: The optical excitation of organic semiconductors not only generates charge-neutral electron-hole pairs (excitons), but also charge-separated polaron pairs with high yield. The microscopic mechanisms underlying this charge separation have been debated for many years. Here we use ultrafast two-dimensional electronic spectroscopy to study the dynamics of polaron pair formation in a prototypical polymer thin film on a sub-20-fs time scale. We observe multi-period peak oscillations persisting for up to about 1 ps as distinct signatures of vibronic quantum coherence at room temperature. The measured two-dimensional spectra show pronounced peak splittings revealing that the elementary optical excitations of this polymer are hybridized exciton-polaron-pairs, strongly coupled to a dominant underdamped vibrational mode. Coherent vibronic coupling induces ultrafast polaron pair formation, accelerates the charge separation dynamics and makes it insensitive to disorder. These findings open up new perspectives for tailoring light-to-current conversion in organic materials.
authors.affiliation: Institut für Physik, Carl von Ossietzky Universität, Oldenburg 26129, Germany.|Center of Interface Science, Carl von Ossietzky Universität, Oldenburg 26129, Germany.
authors.forename: Antonietta
authors.initials: A
authors.lastname: De Sio
authors.affiliation: Istituto Nanoscienze-CNR, Centro S3, via Campi 213a, Modena 41125, Italy.
authors.forename: Filippo
authors.initials: F
authors.lastname: Troiani
authors.affiliation: IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Milano 20133, Italy.
authors.forename: Margherita
authors.initials: M
authors.lastname: Maiuri
authors.affiliation: IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Milano 20133, Italy.
authors.forename: Julien
authors.initials: J
authors.lastname: Réhault
authors.affiliation: Institut für Physik, Carl von Ossietzky Universität, Oldenburg 26129, Germany.|Center of Interface Science, Carl von Ossietzky Universität, Oldenburg 26129, Germany.
authors.forename: Ephraim
authors.initials: E
authors.lastname: Sommer
authors.affiliation: Institut für Theoretische Physik and IQST, Universität Ulm, Ulm 89069, Germany.
authors.forename: James
authors.initials: J
authors.lastname: Lim
authors.affiliation: Institut für Theoretische Physik and IQST, Universität Ulm, Ulm 89069, Germany.
authors.forename: Susana F
authors.initials: SF
authors.lastname: Huelga
authors.affiliation: Institut für Theoretische Physik and IQST, Universität Ulm, Ulm 89069, Germany.
authors.forename: Martin B
authors.initials: MB
authors.lastname: Plenio
authors.affiliation: Istituto Nanoscienze-CNR, Centro S3, via Campi 213a, Modena 41125, Italy.
authors.forename: Carlo Andrea
authors.identifier: http://orcid.org/0000-0001-6429-4835
authors.initials: CA
authors.lastname: Rozzi
authors.affiliation: IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Milano 20133, Italy.
authors.forename: Giulio
authors.initials: G
authors.lastname: Cerullo
authors.affiliation: Istituto Nanoscienze-CNR, Centro S3, via Campi 213a, Modena 41125, Italy.|Dipartimento di Scienze Fisiche, Matematiche e Informatiche, Università di Modena e Reggio Emilia, via Campi 213a, Modena 41125, Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: Molinari
authors.affiliation: Institut für Physik, Carl von Ossietzky Universität, Oldenburg 26129, Germany.|Center of Interface Science, Carl von Ossietzky Universität, Oldenburg 26129, Germany.|Research Center Neurosensory Science, Carl von Ossietzky Universität, Oldenburg 26111, Germany.
authors.forename: Christoph
authors.identifier: http://orcid.org/0000-0003-3854-5025
authors.initials: C
authors.lastname: Lienau