Preconditioning for a Cahn–Hilliard–Navier–Stokes model for morphology formation in organic solar cells

We present a model for the morphology evolution of printed organic solar cells, which occurs during the drying of a mixture of polymer, non-fullerene acceptor, and solvent. Our model uses a phase field approach coupled to a Navier–Stokes equation describing the macroscopic movement of the fluid. Additionally, we incorporate the evaporation process of the solvent using an Allen–Cahn equation. The model is discretized using a finite-element approach with a semi-implicit discretization in time. The resulting (non)linear systems are coupled and of large dimensionality. We present a preconditioned iterative scheme to solve them robustly with respect to changes in the discretization parameters. We illustrate that the preconditioned solver shows parameter-robust iteration numbers and that the model qualitatively captures the behavior of the film morphology during drying.