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Impact of charge transport on current-voltage characteristics and power-conversion efficiency of organic solar cells

: Würfel, U.; Neher, D.; Spies, A.; Albrecht, S.


Nature Communications 6 (2015), Art. 6951
ISSN: 2041-1723
Deutsche Forschungsgemeinschaft DFG
Bundesministerium für Bildung und Forschung BMBF
Journal Article
Fraunhofer ISE ()
Solarzellen - Entwicklung und Charakterisierung; Farbstoff; Organische und Neuartige Solarzellen; Organische Solarzellen; carrier mobility; factor; equation; model; potential

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, photo-current 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.