From Solution to Thin Film: Molecular Assembly of -Conjugated Systems and Impact on (Opto)electronic Properties

The assembly of conjugated organic molecules from solutionto solid-stateplays a critical role in determining the thin film morphology andoptoelectronic properties of solution-processed organic electronicsand photovoltaics. During evaporative solution processing, pi-conjugatedsystems can assemble via various forms of intermolecular interactions,forming distinct aggregate structures that can drastically tune thecharge transport landscape in the solid-state. In blend systems composedof donor polymer and acceptor molecules, assembly of neat materialscouples with phase separation and crystallization processes, leadingto complex phase transition pathways which govern the blend film morphology.In this review, we provide an in-depth review of molecular assemblyprocesses in neat conjugated polymers and nonfullerene small moleculeacceptors and discuss their impact on the thin film morphology andoptoelectronic properties. We then shift our focus to blend systemsrelevant to organic solar cells and discuss the fundamentals of phasetransition and highlight how the assembly of neat materials and processingconditions can affect blend morphology and device performance.