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 α-${\theta }_o$ relations, where α is the exponent of the function of the short-circuit current versus light intensity ($J_{\mathrm{SC}}$ ∝ $I^{\alpha }$). 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.

• Received 4 November 2019
• Revised 11 May 2020
• Accepted 10 July 2020

DOI:https://doi.org/10.1103/PhysRevApplied.14.034046