A variable series resistance mechanism to explain the negative capacitance observed in impedance spectroscopy measurements of nanostructured solar cells

A simple model for conductivity modulation in a recombination diode is discussed to explain the observation of negative capacitance at forward bias observed in many optoelectronic devices. We formulate the basic recombination-modulation model in terms of an equivalent circuit for small ac perturbation and discuss the application of the results in measurements of impedance spectroscopy of dye-sensitized solar cells, organic solar cells and related systems.