Berlin 2018 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe
CPP: Fachverband Chemische Physik und Polymerphysik
CPP 23: Organic Photovoltaics I
CPP 23.4: Vortrag
Dienstag, 13. März 2018, 10:30–10:45, C 243
The Impact of Driving Force and Temperature on the Electron Transfer in Donor-Acceptor Blend Systems — T Unger1, •S Wedler1, F-J Kahle1, U Scherf3, H Bässler2, and A Köhler1,2 — 1Experimental Physics II, Uni Bayreuth — 2BIMF, Uni Bayreuth — 3Makromolekulare Chemie, Uni Wuppertal
We discuss whether electron transfer from a photoexcited polymer donor to a fullerene acceptor in an organic solar cell is tractable in terms of Marcus theory, and whether the driving force ΔG0 is crucial in this process (JPCC 2017, 121, 22739). Considering Marcus rates to be thermally activated, we measured the appearance time of the polaron signal between 12 and 295 K for the representative donor polymers PTB7, PCPDTBT and Me-LPPP blended with PCBM. In all cases, the dissociation process was faster than the temporal resolution of our experimental setup (220-400 fs), suggesting that the charge transfer is independent of ΔG0. We find that for the PCPDTBT:PCBM (ΔG0=0.2 eV) and PTB7:PCBM (ΔG0=0.3 eV) the data is mathematically consistent with Marcus theory, yet the condition of thermal equilibrium is not satisfied. For MeLPPP:PCBM in the Marcus inverted regime, the dissociation rate is inconsistent with Marcus theory but formally tractable using the Marcus-Levich-Jortner tunneling formalism which also requires thermal equilibrium. This is inconsistent with the short transfer times we observed and implies that coherent effects need to be considered. Our results imply that any dependence of the total photocurrent yield must be ascribed to the secondary escape of the initially generated CT-state from its Coulomb potential.