Decoding Solution Aggregation and Thermal Cycling Pathways in Conjugated Polymer Inks Via Advanced X‐Ray Scattering

Conjugated polymers are cornerstone materials for optoelectronics, offering highly tunable optoelectronic properties and excellent compatibility with scalable coating. In both laboratory and industrial settings, polymer inks are often subjected to multiple heating and cooling cycles for dissolution and storage, yet the structural and functional consequences of such thermal cycling remain poorly understood. Here, a new characterization framework is established to decode the solution‐state aggregation dynamics of various conjugated polymers under thermal cycling. By integrating variable temperature X‐ray scattering, grazing‐incidence X‐ray scattering, and microscopy, it is demonstrated that single thermal cycle promotes aggregate compactness and ordered molecular packing, leading to enhanced crystallinity and charge mobility. Conversely, excessive cycling leads to over‐aggregation and disrupted chain alignment, ultimately degrading electrical performance. Notably, aggregation pathways vary with polymer structure: SY‐PPV and PM6 form larger aggregates upon cycling, while IDTBT tends to fragment with the poorest tolerance. These behaviors are linked to polymers’ intrinsic structural order, with disordered systems being more thermally sensitive. Furthermore, solvent‐specific studies reveal that o ‐xylene suppresses excessive aggregation in PM6, yielding improved morphological stability and electrical performance. This work establishes a mechanistic understanding of how thermal history governs polymer aggregation and device functionality, offering guidance for robust and sustainable organic electronics manufacturing.