Extracting Recombination Parameters from Impedance Measurements on Organic Solar Cells

Nongeminate recombination in organic solar cells is one of the main causes of reduced device performances. The quantification, and the subsequent reduction, of nongeminate recombination losses requires the development of methods, which allow an accurate and reliable determination of the charge-carrier density, mobility, and lifetime. Here, we present a method, based on the charge-density dependence of the recombination current, to determine the recombination parameters from impedance measurements of organic solar cells. We show that the use of the difference between the capacitance under illumination and the capacitance in the dark for the calculation of the charge density present in the active layer, allows the identification of the dominant recombination mechanism and the subsequent determination of either the charge-carrier lifetime or the bimolecular recombination coefficient