Formation, Transformation, and Synergistic Interplay of Crystalline Orientation in Conjugated Polymers via Solution‐State Aggregation Control

Controlling and achieving desired crystal orientations (i.e., edge-on and face-on) in donor-acceptor (D-A) conjugated polymers is pivotal to enhancing their optoelectronic performance. Here, four diketopyrrolopyrrole (DPP)-based polymers with different donor units (DPP3T, DPPTTT, DPP4T, and DPP5T) are developed to investigate the formation, transformation, and synergistic interplay of crystallite orientation. Three strategies were employed to probe these three aspects: (i) drop-casting from different solvents to investigate the orientation formation governed by their solution-state aggregation, (ii) thermal and solvent vapor annealing to achieve reversible orientation transformation, and (iii) blending to realize the orientation interplay between two polymers. During drop-casting, DPPs with increased donor lengths and enhanced solution-state aggregation favor the formation of edge-on over face-on orientation, where these two orientations in DPP3T can be further reversibly switched by thermal and solvent vapor annealing. Remarkably, by blending DPP3T and DPP5T with weak and strong solution aggregation, respectively, DPP5T could strengthen solution-aggregates of DPP3T and drive them to form edge-on DPP3T/DPP5T cocrystals. The charge mobilities of these DPPs correlate well with their crystalline structures. This study establishes the connection among solution-state aggregates, solid-state crystalline orientations, and charge-transport properties in conjugated copolymers, contributing a deep understanding of their crystalline behavior for applications in optoelectronic devices.