Mesoscopic modeling of disordered morphologies of blends and block-copolymers for light-emitting diodes

Blending a semiconducting polymer with an insulator can significantly increase [1] luminous efficiency of polymer light emitting diodes. However, the limited thermodynamic stability of the disordered phase in blends motivates the search for alternatives, e.g. block-copolymers (BCPs) with semiconducting and insulating blocks. We choose as model systems blends and BCPs of poly(p-phenylene vinylene) (PPV) and polyacrylates. We obtain disordered morphologies of these materials using mesoscopic simulations. We study different compositions and vary immiscibility to mimic annealing at different temperatures. We find that disordered blends and BCPs are heterogeneous because of fluctuations and local segregation. Local segregation is stronger in BCPs than in their equivalent blends, even though the strength of immiscibility, normalized by the mean-field spinodal, is the same. Using a qualitative charge-percolation model, we link the distribution of PPV with electric conductance. We predict [2] that the annealing temperature affects the electrical percolation in disordered BCPs much stronger than in blends. The differences between blends and BCPs are enhanced at high contents of insulator. [1] Abbaszadeh et al, Nature Materials 2016, 15, 628; [2] Zhang et al, Macromolecules 2020, 53, 523