The relative importance of domain size, domain purity and domain interfaces to the performance of bulk-heterojunction organic photovoltaics

The domain size, domain purity and interfacial width between domains for a bulk heterojunction are controllably altered through use of Cahn–Hilliard modeling and their relative effect on OPV performance is predicted using Monte Carlo modeling. It is found that locally sharp, well-connected domains of only 4 nm extent out perform morphologies with broadened interfaces and/or impure domains even when domain sizes were at the ‘optimum’ size of ∼10 nm. More generally, these data provide information on the most effective method to optimize the as-cast bulk heterojunction morphology depending upon initial domain purity and the nature of interfaces between domains. Further, it indicates why morphology optimization is more effective for some blends than others. It is shown that the quench depth of the blend can be used as a general technique to control the interfacial structure of the morphology and realize substantial increases in short circuit photocurrent.