Rational Design of Thermally Stable, Bicontinuous Donor/Acceptor Morphologies with Conjugated Block Copolymer Additives

The bicontinuous microemulsion (BμE) phase is an equilibrium morphology characterized by cocontinuous domains, high interfacial areas, and nanoscale domain dimensions. These characteristics make the BμE potentially suitable for use in organic photovoltaic applications. Here, we use a combination of simulations and experiments to investigate the equilibrium morphologies formed by a ternary blend of conjugated polymer, all-conjugated diblock copolymer, and fullerene derivative PCBM. Using coarse-grained simulations, we identify the blend compositions that are most likely to result in donor/acceptor morphologies resembling the BμE. Experimentally, we probe these compositions through transmission electron microscopy and grazing-incidence X-ray scattering measurements. We demonstrate that all-conjugated block copolymer additives can be used to produce thermally stable, cocontinuous donor/acceptor morphologies at higher additive contents and longer annealing times than previously reported. These results demonstrate that conjugated BCP compatibilizers can be used as a means to achieve equilibrium, cocontinuous morphologies in donor/acceptor blends.