Berlin 2015 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 43: Ultra-fast phenomena
HL 43.3: Vortrag
Mittwoch, 18. März 2015, 10:00–10:15, EW 202
Ultrafast exciton dissociation and coherent polaron formation in polymer fullerene blends observed by femtosecond spectroscopy — •Ephraim Sommer1, Antonietta De Sio1, Carlo A. Rozzi2, Margherita Maiuri3, Julien Rehault3, Giulio Cerullo3, and Christoph Lienau1 — 1Institut für Physik, Carl von Ossietzky Universität, 26129 Oldenburg, Germany — 2Istituto Nanoscienze Consiglio Nazionale delle Ricerche (CNR), Centro S3, via Campi 213a, 41125 Modena, Italy — 3Istituto di Fotonica e Nanotecnologie CNR, Dipartimento di Fisica, Politecnico di Milano, 20133 Milano, Italy
Blends of conjugated polymers (P3HT) and fullerene (PCBM) derivatives are prototype systems of organic photovoltaic devices. The primary charge-generation mechanism involves a light-induced electron transfer from the polymer to the fullerene acceptor.
Here we show ultrabroadband (500-1400nm) pump probe measurements with sub 15-fs time resolution of a pristine polymer thin-film and a blend of P3HT and PCBM, which reveal direct signatures of ultrafast charge dissociation. In particular we trace the dynamics of the interface excitons in the blended material. We find that they dissociate into charge transfer excitons within about 50fs [1]. In addition we find in both pristine and blended films evidence for an ultrafast buildup of polaron pair states. We analyze and discuss the ultrafast polaron pair dynamics on the basis of pump probe and coherent two-dimensional spectroscopy.
[1] S. M. Falke et al. Science 344, 1001-1005 (2014)