Drift-Diffusion and Analytical Modeling of the Recombination Mechanisms in Organic Solar Cells: Effect of the Nonconstant Charge Distribution Inside the Active Layer

In this work, we use a drift-diffusion simulation to analyze the effects of nonuniform charge distribution on the recombination rate in organic solar cells. We compare these results with those obtained with an open-circuit voltage decay analytical model. We propose an improvement to this model to account for the effects of the nonuniform charge distribution. The new model produces a better fit and a more accurate parameter evaluation, without the computational effort needed by the drift-diffusion simulation. The new model also permits to quantify the amount of charge accumulated at the electrode/organic interfaces, gaining further information about the electronic band structure of the solar cell, in particular the alignment between electrode work functions ad organic transport bands.