Benchmarking the Electronic Processes at the Planar Organic Heterojunction Solar Cells

While there exist several models for organic heterojunction solar cells, there is still a need for one that is both general and flexible to compare the relative importance of the plethora of potential processes. We describe a modeling framework that allows one to compare the relative importance of different physical processes, taking place in organic heterojunction-based photocell, on equal footing. The framework is based on rate equations, making it easy to modify and include processes not explicitly introduced here. To apply this approach, we fabricated several heterojunction devices. Applying this new methodology for a given device structure, we used a single set of parameters to fit four different experiments extending over a wide range of applied voltage and 5 orders of magnitude of light intensity. As an example, and as a result of the self-consistency of the joint modeling and experiment, we find that the charge generation and charge recombination do not take place through the same set of interface states (i.e., much can be gained through material and morphology design). In addition, by including the detailed balance between charge transfer excitons' generation and dissociation, we found that the bimolecular Langevin recombination through the charge transfer excitons is not strong enough to account for the losses in the photocells.