title: Role of the Charge-Transfer State in Reduced Langevin Recombination in Organic Solar Cells: A Theoretical Study.
abstract: Reduced Langevin recombination has been observed in organic solar cells (OSCs) for many years, but its origin is still unclear. A recent work by Burke et al. (Adv. Energy Mater.2015, 5, 1500123-1) was inspired by this reduced Langevin recombination, and they proposed an equilibrium model of charge-transfer (CT) states that correlates the open-circuit voltage of OSCs with experimentally available device parameters. In this work, we extend Burke et al.'s CT model further and for the first time directly correlate the reduced Langevin recombination with the energetic and dynamic behavior of the CT state. Recombination through CT states leads in a straightforward manner to a decrease in the Langevin reduction factor with increasing temperature, without explicit consideration of the temperature dependence of the mobility. To verify the correlation between the CT states and reduced Langevin recombination, we incorporated this CT model and the reduced Langevin model into drift-diffusion simulations of a bilayer OSC. The simulations not only successfully reproduced realistic current-voltage (J-V) characteristics of the bilayer OSC, but also demonstrate that the two models consistently lead to same value of the apparent Langevin reduction factor.
authors.affiliation: NanoSYD, Mads Clausen Institute, University of Southern Denmark , Alsion 2, DK-6400 Sønderborg, Denmark.
authors.forename: Yiming
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Institute of Solid State Physics, Graz University of Technology and NAWI Graz , Petersgasse 16, 8010 Graz, Austria.
authors.forename: Karin
authors.initials: K
authors.lastname: Zojer
authors.affiliation: NanoSYD, Mads Clausen Institute, University of Southern Denmark , Alsion 2, DK-6400 Sønderborg, Denmark.
authors.forename: Benny
authors.initials: B
authors.lastname: Lassen
authors.affiliation: NanoSYD, Mads Clausen Institute, University of Southern Denmark , Alsion 2, DK-6400 Sønderborg, Denmark.
authors.forename: Jakob
authors.initials: J
authors.lastname: Kjelstrup-Hansen
authors.affiliation: NanoSYD, Mads Clausen Institute, University of Southern Denmark , Alsion 2, DK-6400 Sønderborg, Denmark.
authors.forename: Horst-Günter
authors.initials: HG
authors.lastname: Rubahn
authors.affiliation: NanoSYD, Mads Clausen Institute, University of Southern Denmark , Alsion 2, DK-6400 Sønderborg, Denmark.
authors.forename: Morten
authors.initials: M
authors.lastname: Madsen