(289b) Rational Design of Thermally Stable, Cocontinuous Donor/Acceptor Morphologies for Use As Organic Solar Cell Active Layers

Two of the primary challenges limiting the marketability of organic solar cells based on the blend of conjugated polymer donors and PCBM acceptors are i) the smaller device efficiency of the organic solar cell relative to the conventional silicon-based solar cell and ii) the long term thermal instability of the device active layer. The achievement of equilibrium donor/acceptor morphologies with the characteristics believed to yield high device performance characteristics could address each of these two challenges. In other contexts, recent experiments have demonstrated that the use of block copolymer compatibilizers can modify the morphology and improve the thermal stability of polymer-based donor/acceptor mixtures. Motivated by the above considerations, in this work, we present the results of a combined simulations and experiments-based approach to investigate if an additive BCP compatibilizer can be used to intelligently control the self-assembled morphologies taken on by conjugated polymer/PCBM mixtures. First, we use single chain in mean field Monte Carlo simulations to identify regions within the conjugated polymer/PCBM composition space in which addition of copolymers can lead to bicontinuous equilibrium morphologies with high interfacial areas and nanoscale dimensions. Second, we conduct experiments as directed by the simulations to achieve such morphologies based on the PTB7 + PTB7-b-PNDI + PCBM blend. We characterize the morphologies formed in experiments via a combination of transmission electron microscopy and x-ray scattering techniques and demonstrate that the morphologies from experiments agree with those predicted in simulations.  Accordingly, these results indicate that the approach utilized represents a promising approach to intelligently design the morphologies taken on by organic solar cell active layers.