title: Impact of charge transport on current-voltage characteristics and power-conversion efficiency of organic solar cells.
abstract: This work elucidates the impact of charge transport on the photovoltaic properties of organic solar cells. Here we show that the analysis of current-voltage curves of organic solar cells under illumination with the Shockley equation results in values for ideality factor, photocurrent and parallel resistance, which lack physical meaning. Drift-diffusion simulations for a wide range of charge-carrier mobilities and illumination intensities reveal significant carrier accumulation caused by poor transport properties, which is not included in the Shockley equation. As a consequence, the separation of the quasi Fermi levels in the organic photoactive layer (internal voltage) differs substantially from the external voltage for almost all conditions. We present a new analytical model, which considers carrier transport explicitly. The model shows excellent agreement with full drift-diffusion simulations over a wide range of mobilities and illumination intensities, making it suitable for realistic efficiency predictions for organic solar cells.
authors.affiliation: Department of Dye and Organic Solar Cells, Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstrasse 2, 79100 Freiburg, Germany.|Material Research Centre FMF, University of Freiburg, 79104 Freiburg, Germany.
authors.forename: Uli
authors.initials: U
authors.lastname: Würfel
authors.affiliation: Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany.
authors.forename: Dieter
authors.initials: D
authors.lastname: Neher
authors.affiliation: Department of Dye and Organic Solar Cells, Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstrasse 2, 79100 Freiburg, Germany.|Material Research Centre FMF, University of Freiburg, 79104 Freiburg, Germany.
authors.forename: Annika
authors.initials: A
authors.lastname: Spies
authors.affiliation: Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany.
authors.forename: Steve
authors.initials: S
authors.lastname: Albrecht