  Perovskite solar cells (PSC) are promising potential competitors to
established photovoltaic technologies due to their superior efficiency and
low-cost solution processability. However, the limited understanding of the
crystallization behaviour hinders the technological transition from lab-scale
cells to modules. In this work, we perform Phase Field (PF) simulations of the
doctor-bladed film formation to obtain mechanistic and morphological
information that is experimentally challenging to access. PF simulations are
validated extensively using in- and ex-situ experiments for different solvent
evaporation rates. The well-known transition from a film with many pinholes,
for a low evaporation rate, to a smooth film, for high evaporation rates, is
recovered in simulation and experiment. From the simulation, the transition can
be assigned to the change in the ratio of evaporation to crystallization rate
because of two distinct mechanisms. Firstly, for larger evaporation rates,
nuclei appear at higher concentrations, which favors nucleation as compared to
growth. Secondly, the growth of the crystals is confined in a thinner film,
which limits their vertical size. Both effects are expected to be valid
independent of the specific chemistry of the chosen experimental system, as
long as the evaporation time of the solvent is comparable to the
crystallization time.
