Chapter 11: Modeling Organic Solar Cells: What are the Challenges Ahead?

The physics of organic solar cells is still being extensively investigated. While important questions regarding e.g. the mechanisms of exciton dissociation have been rather convincingly addressed highlighting the role of electrostatic (here emphasized) but also delocalization and entropy effects in pulling apart the charge carriers, much less is known on the molecular origin for the losses in the open circuit voltage in organic photovoltaics, although this is the main culprit for the reduced power efficiencies of these devices. Here, we review some of our own work on the energetics of charge transfer (CT) states at organic heterojunctions and discuss some of the challenges ahead of us, which call for multiscale theoretical models that account for, in a quantitative manner, the fate of CT states including the kinetics of charge separation and recombination events.