Analytical Model for Photocurrent in Organic Solar Cells as a Function of the Charge-Transport Figure of Merit Including Second-Order Recombination

We develop an analytical model for the photocurrent of organic solar cells based on carrier drift and including second-order charge recombination, in which the figure of merit theta(o) naturally appears. This approach provides expressions for the fill-factor-theta(o) and alpha-theta(o) relations, where a is the exponent of the function of the short-circuit current versus light intensity (J(SC) proportional to I-alpha). A correlation between the reduction factor of Langevin recombination and the dissociation probability of charge transfer states (P) is also discussed. Photocurrent curves of a polymer device obtained at different temperatures (100-300 K) are fitted by the model, whose fitting parameters are in agreement with the literature.