Stable Postfullerene Solar Cells via Direct C–HArylation Polymerization. Morphology–Performance Relationships

The scope of the environmentally benign direct C–H arylation polymerization (DARP) process is validated and significantly extended in the synthesis of a high-performance benzodithiophene-based copolymer series, PBDT(Ar)-FTTE, with previously untested and systematically varied heteroaryl (Ar) substituents. Bulk-heterojunction polymer solar cells (PSCs) containing a high-performance nonfullerene acceptor (NFA), ITIC-Th, and DARP-derived donors are fabricated and evaluated, yielding PCEs as high as 8%. The relationships between Ar-sensitive copolymer structure, BHJ morphology, and PSC performance are elucidated through in-depth characterization of structural order, phase separation, and charge transport including SCLC, AFM, GIWAXS, R-SoXS, and NEXAFS measurements which conclusively demonstrate the important effects of Ar-tunable, dimensionally smaller and well-blended copolymer domains for maximum PSC performance. Smaller BHJ copolymer domains having greater ITIC-Th miscibility definitively correlate with en...