(775b) Impact of the Active Layer Morphology on Bimolecular Recombination Dynamics in Organic Solar Cells

Mehraeen, S., University of Illinois
Coropceanu, V., Georgia Institute of Technology
Brédas, J. L., Georgia Institute of Technology
We present a reaction-diffusion model to describe the impact of the morphology of the active layer and charge-transfer (CT) lifetime on the bimolecular recombination kinetics in organic solar cells. The morphologies we consider, range from a bilayer with flat interface to a bilayer with rough interface and bulk heterojunctions with coarse and fine intercalated domains of donor and acceptor molecules. Using the reaction-diffusion model in kinetic Monte Carlo simulations, we find that only the density of states affects the order of bimolecular recombination kinetics. The results show that the morphology of the active layer only influences the charge carrier lifetime and the average delay time between the exciton dissociation and the onset of bimolecular recombination. The results also show that the same effect on the charge recombination dynamics obtained by a change in the donor or acceptor domain size, can be achieved by a change in the degree of disorder. Overall, our results reveal that the intrinsic lifetime of the CT states in conjunction with active layer morphology and nature of disorder can explain experimentally observed deviation of recombination dynamics from Langevin model.