Benchmarking the Electronic Processes at the Planar Organic Heterojunction Solar Cells

While there exist many types of models, there is a lack of one that is both general and flexible to compare relative importance of the plethora of potential processes. We describe a modelling framework that allows to compare the relative importance of different physical processes, taking place in organic heterojunction based photo-cell, on equal footing. The framework is based on rate equations making it easy to modify and expand to include processes not specifically introduced here. To apply this approach, we fabricated several heterojunction devices. Using the new methodology and for a given device structure, we fitted with a single set of parameters four different experiments extending over a wide range of applied voltage and five orders of magnitude of light intensity. As an example, and as a result of the self-consistency of the joint modelling & 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, contrary to common belief, we find that an interfacial bi-molecular Langevin-like recombination through the charge transfer states is not strong enough to account for the losses in the photo-cells.