The effect of 2D-Langevin and trap-assisted recombination on the open circuit voltage in organic solar cells

Using drift-diffusion simulations we have clarified the effect of 2-dimensional (2D) lamellar ordering on the device performance and, in particular, the open circuit voltage in donor-acceptor type organic solar cells. The simulations are performed both in systems where direct (band-to-band) recombination dominates and in systems where trap-assisted recombination dominates. Results show that lamellar ordering reduces both the amount of direct and trap-assisted recombination, which is beneficial for device performance. The effect is particularly prominent for small lamellar thicknesses (~ 1 nm). It is furthermore shown that in the case of s-shaped current-voltage characteristics due to electrostatic injection barriers the s-shape becomes less prominent for thinner lamellar thicknesses.