Coupled optoelectronic simulation of organic bulk-heterojunction solar cells: Parameter extraction and sensitivity analysis

A comprehensive optoelectronic device model for organic bulk-heterojunction solar cells is presented. First the optical incoupling into a multilayer stack is calculated. From the photon absorption profile a charge transfer exciton profile is derived. In this study we consider the Onsager-Braun mechanism to calculate the dissociation of the CT excitons into free charge carriers. These free charge carriers then migrate toward the electrodes under the influence of drift and diffusion. A general problem arising in computer simulations is the number of material and device parameters, which have to be determined by dedicated experiments and simulation-based parameter extraction. In this study we analyze measurements of the short-circuit current dependence on the active layer thickness and current-voltage curves in poly(3-hexylthiophene):[6,6]-phenyl-C-61-butyric acid methyl ester based solar cells. We have identified a set of parameter values including dissociation parameters that describe the experimental data. The overall agreement of our model with experiment is good, however, a discrepancy in the thickness dependence of the current-voltage curve questions the influence of the electric field in the dissociation process. In addition transient simulations are analyzed which show that a measurement of the turn-off photocurrent can be useful for estimating charge carrier mobilities. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3259367]