Backbone Tuning Enhances the Solution Aggregation to Refine Fibrillization Network Morphology for Efficient All-Chlorinated Polymer Donor

An ideal nanoscale interpenetrating network morphology that is formed spontaneously upon a prepared active layer film is the key to efficient exciton dissociation and charge transport. Here, a new strategy is described for optimization of morphology by enhancing polymer solution aggregation ability to effectively improve device performance. Polymers PBDQx-Cl, PBDQx-TCl, and PBDQx-2TCl were designed and synthesized systematically by tuning the polymer backbones. Structural manipulation has been found to have a profound effect on the regulation of electronic structure and solution aggregation behavior. Compared with PBDQx-Cl and PBDQx-TCl, PBDQx-2TCl exhibits enhanced solution aggregation ability and contributes to a fibrous phase separation in primitive pure film morphology. After blending with BTP-eC9, evolution of a nanoscale fibrillization interpenetrating network morphology is gradually demonstrated, in which the phase separation and microstructure form are collectively refined, which can provide more interface regions and charge transport channels. The resulting PBDQx-2TCl:BTP-eC9 micromorphologically meets the requirements for efficient exciton splitting, charge transfer, and decreased recombination loss. Thus, among the three polymers, the device based on PBDQx-2TCl:BTP-eC9 shows the highest PCE of 16.17% with superior J SC of 26.49 mA cm –2 and FF of 74.28%. These results demonstrate that the well-refined fibrillar network morphology can be achieved by adjusting the aggregation ability of a polymer solution. This in turn promotes a deeper understanding of the relationships between micromorphology and solution aggregation behavior.