Analysis of the dynamic short-circuit resistance in organic bulk-heterojunction solar cells: relation to the charge carrier collection efficiency

• This work studies the charge carrier collection in organic BHJ solar cells.
• Recombination losses determine the I–V curve dynamic resistance in short-circuit.
• Model considering drift-driven collection and monomolecular recombination.
• Good agreement with experimental I–V curves measured at different illumination.
• Characterization of the active layer quality by effective mobility–lifetime products.

This work studies the charge carrier collection efficiency in organic bulk-heterojunction solar cells based on polymer:fullerene blends. An equivalent circuit with a specific recombination term is proposed to describe the behavior of this type of devices. It is experimentally shown that this recombination term determines the slope of the current–voltage characteristic at the short-circuit condition. The variation of this dynamic resistance with the light intensity can be interpreted considering a dominant first-order recombination process. Finally, an analytical model under a constant electric field approximation is presented that can be used to calculate the charge carrier collection efficiency of the device. This model can be also used to estimate an effective mobility–lifetime product, which is characteristic of the quality of the active layer.

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