Dithienoquinoxaline-Based Polymer Donor with Finely Tuned Aggregation Behaviors for Efficient Organic Solar Cells

The morphology control is of great importance for organic solar cells (OSCs). Herein, via synergistic optimizations of the molecular structure and processing conditions, we finely tuned the aggregation behavior of the polymer donor and studied its effects on the photovoltaic performance. We designed a novel wide-band gap polymer donor PBQx-TSF by incorporating sulfur atoms into fluorinated 2D benzodithiophene (BDT) units and copolymerizing them with dithieno[3,2-f:2′,3′-h]quinoxaline (DTQx). The structural modification enhances electron delocalization and thus decreases the ionization potential (5.36 eV). Importantly, we find that the preaggregation behavior of PBQx-TSF can be systematically modulated via solvent engineering. By blending nonhalogenated toluene (Tol) and halogenated chlorobenzene (CB) as the processing solvent, controllable crystallization dynamics and thus optimal morphology can be obtained. Owing to the efficient exciton dissociation and charge transport, PBQx-TSF:BTP-eC9-based OSC processed by a mixed processing solvent (0.5 Tol:0.5 CB) gives a maximum power conversion efficiency of 19.3%. This work highlights the significance of aggregation behavior for polymer donors, which offers a promising strategy for further advancing high-performance OSCs.