The assembly of conjugated organic molecules from solution
to solid-state
plays a critical role in determining the thin film morphology and
optoelectronic properties of solution-processed organic electronics
and photovoltaics. During evaporative solution processing, π-conjugated
systems can assemble via various forms of intermolecular interactions,
forming distinct aggregate structures that can drastically tune the
charge transport landscape in the solid-state. In blend systems composed
of donor polymer and acceptor molecules, assembly of neat materials
couples with phase separation and crystallization processes, leading
to complex phase transition pathways which govern the blend film morphology.
In this review, we provide an in-depth review of molecular assembly
processes in neat conjugated polymers and nonfullerene small molecule
acceptors and discuss their impact on the thin film morphology and
optoelectronic properties. We then shift our focus to blend systems
relevant to organic solar cells and discuss the fundamentals of phase
transition and highlight how the assembly of neat materials and processing
conditions can affect blend morphology and device performance.