title: Direct observation of ultrafast long-range charge separation at polymer-fullerene heterojunctions.
abstract: In polymeric semiconductors, charge carriers are polarons, which means that the excess charge deforms the molecular structure of the polymer chain that hosts it. This results in distinctive signatures in the vibrational modes of the polymer. Here, we probe polaron photogeneration dynamics at polymer:fullerene heterojunctions by monitoring its time-resolved resonance-Raman spectrum following ultrafast photoexcitation. We conclude that polarons emerge within 300 fs. Surprisingly, further structural evolution on ≲ 50-ps timescales is modest, indicating that the polymer conformation hosting nascent polarons is not significantly different from that near equilibrium. We interpret this as suggestive that charges are free from their mutual Coulomb potential because we would expect rich vibrational dynamics associated with charge-pair relaxation. We address current debates on the photocarrier generation mechanism at molecular heterojunctions, and our work is, to our knowledge, the first direct probe of molecular conformation dynamics during this fundamentally important process in these materials.
authors: Département de Physique and Regroupement Québécois sur les Matériaux de Pointe, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, Canada H3C 3J7.
authors: Françoise
authors: F
authors: Provencher
authors: Département de Physique and Regroupement Québécois sur les Matériaux de Pointe, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, Canada H3C 3J7.
authors: Nicolas
authors: N
authors: Bérubé
authors: Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire OX11 0QX, UK.
authors: Anthony W
authors: AW
authors: Parker
authors: Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire OX11 0QX, UK.
authors: Gregory M
authors: GM
authors: Greetham
authors: Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire OX11 0QX, UK.
authors: Michael
authors: M
authors: Towrie
authors: Department of Materials, Centre for Plastic Electronics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
authors: Christoph
authors: C
authors: Hellmann
authors: Département de Physique and Regroupement Québécois sur les Matériaux de Pointe, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, Canada H3C 3J7.
authors: Michel
authors: M
authors: Côté
authors: Department of Materials, Centre for Plastic Electronics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
authors: Natalie
authors: N
authors: Stingelin
authors: 1] Département de Physique and Regroupement Québécois sur les Matériaux de Pointe, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, Canada H3C 3J7 [2] Department of Physics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
authors: Carlos
authors: C
authors: Silva
authors: Department of Chemistry, University of Cyprus, P.O. Box 20537, Nicosia 1678, Cyprus.
authors: Sophia C
authors: SC
authors: Hayes