  Metal halide perovskites are an emerging class of crystalline semiconductors
of great interest for application in optoelectronics. Their properties are
dictated not only by their composition, but also by their crystalline structure
and microstructure. While significant efforts were dedicated to the development
of strategies for microstructural control, significantly less is known about
the processes that govern the formation of their crystalline structure in thin
films, in particular in the context of crystalline orientation. In this work,
we investigate the formation of highly oriented triple cation perovskite films
fabricated by utilizing a range of alcohols as an antisolvent. Examining the
film formation by in-situ grazing-incidence wide-angle X-ray scattering reveals
the presence of a short-lived highly oriented crystalline intermediate, which
we identify as FAI-PbI2-xDMSO. The intermediate phase templates the
crystallisation of the perovskite layer, resulting in highly oriented
perovskite layers. The formation of this DMSO containing intermediate is
triggered by the selective removal of DMF when alcohols are used as an
antisolvent, consequently leading to differing degrees of orientation depending
on the antisolvent properties. Finally, we demonstrate that photovoltaic
devices fabricated from the highly oriented films, are superior to those with a
random polycrystalline structure in terms of both performance and stability.
