On the convergence of the algorithm for simulating organic solar cells

This paper analyzes the convergence of the numerical solution of a set of equations which contains Poisson and current continuity equations required to simulate organic solar cells under illumination and bias applied. Due to the strong nonlinearity, choosing appropriate initial guesses is a key parameter in obtaining the convergence. To establish such initial guesses, we analyzed the behavior of electrostatic potential, and electron and hole concentration profiles along the active layer as a function of generation rate of photo-induced e-h pairs, charge mobility and thickness. Based on these results, we propose simple functions to obtain the starting values for reaching the solution in an optimized number of iterations. By using this approach, the convergence can be successfully achieved for a wide range of physical parameters such as generation rate of photo-induced e-h pairs, charge mobility, and thickness. For an organic solar cell with an active layer thickness of around 120 nm, the results show that the solution at equilibrium condition, under illumination without bias applied, and under illumination with bias applied requires around 7, 9 and 5 iterations, respectively. Although the analysis was carried out using physical parameters of one of the most studied material pair: P3HT and PCBM, our proposal can be used for arbitrary organic semiconductor.