Abstract
The performance of organic semiconductors is critically governed by the evolution of their supramolecular structure during film processing. Molecular packing, polymorphism, crystal orientation, and phase separation strongly influence charge transport, doping efficiency, and device performance. Consequently, understanding the kinetics of structure formation has become a key challenge in the rational design of organic electronic materials. Recent advances in synchrotron radiation, high-brilliance X-ray sources, fast area detectors, and microfocused beams have enabled operando studies of structural evolution with unprecedented spatial and temporal resolution. Small- and wide-angle X-ray scattering (SAXS/WAXS), grazing-incidence WAXS (GIWAXS), and complementary methods now allow direct observation of nucleation, crystal growth, polymorphic transitions, molecular orientation, and hierarchical self-assembly during solution processing, solvent treatment, thermal annealing, and electrochemical doping. Examples will be presented demonstrating how in situ characterization reveals the mechanisms governing structure–property relationships in polymer semiconductors. In particular, polymorphism in PBTTT with single-ether side chains has been shown to produce two distinct supramolecular organizations—a liquid-crystalline phase with enhanced backbone planarization and π-stacking, and a crystalline phase exhibiting increased backbone torsion. These structural differences lead to markedly different doping efficiencies and charge transport, resulting in superior thermoelectric and electrochemical performance of the liquid-crystalline phase. Such studies highlight the importance of monitoring structural evolution in real time to understand how processing conditions determine the final electronic functionality. The combination of time-resolved X-ray scattering with complementary techniques such as fast chip calorimetry provides a comprehensive multiscale picture of supramolecular structure formation. These methodologies offer powerful tools for optimizing processing protocols, controlling polymorphism and molecular ordering, and accelerating the development of high-performance organic semiconductors for flexible electronics.