  The performance of solution-processed solar cells strongly depends on the
geometrical structure and roughness of the photovoltaic layers formed during
film drying. During the drying process, the interplay of crystallization and
liquid-liquid demixing leads to the structure formation on the nano- and
microscale and to the final rough film. In order to better understand how the
film structure can be improved by process engineering, we aim at theoretically
investigating these systems by means of phase-field simulations. We introduce
an evaporation model based on the Cahn-Hilliard equation for the evolution of
the fluid concentrations coupled to the Allen-Cahn equation for the
liquid-vapour phase transformation. We demonstrate its ability to match the
experimentally measured drying kinetics and study the impact of the parameters
of our model. Furthermore, the evaporation of solvent blends and solvent-vapour
annealing are investigated. The dry film roughness emerges naturally from our
set of equations, as illustrated through preliminary simulations of spinodal
decomposition and film drying on structured substrates.
