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

TL;DR

This paper introduces a coupled phase field and fluid dynamics model for the morphology evolution in organic solar cells during drying, along with a preconditioning technique for efficient numerical solution.

Contribution

It develops a novel preconditioned iterative solver for large coupled systems in a complex morphology evolution model.

Findings

Preconditioned solver achieves parameter-robust iteration counts.

Model qualitatively replicates drying-induced morphology changes.

Finite-element discretization effectively handles complex coupled equations.

Abstract

We present a model for the morphology evolution of printed organic solar cells which occurs during the drying of a mixture of polymer, the non-fullerene acceptor and the 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.