Ladder-Type Thienoacenaphthopyrazine-Based Molecules: Synthesis, Properties, and Application to Construct High-Performance Polymer for Organic Solar Cells

We present a new design strategy to synthesize ladder-type thienoacenaphthopyrazine (TAP)-based monomers through two different coupling reactions from starting material 5,6-dibromoacenaphthylene-1,2-dione. By bringing varous electron-deficient groups together (such as five-membered aromatic rings, pyrazine, fluorine, and thiadiazols), this new family of molecules exhibits good stability in ambient conditions and easily tunes the electronic, photophysical and film-forming properties of polymers. The unique molecular shape with its extended pi-conjugated backbone perpendicular to the polymer chain, offers a remarkable platform for the development of a semiconducting polymer with rare geometry. The planar and enlarged conjugated backbone enables TAP-based copolymers PTAP1 and PTAP2 to exhibit distinguishing solubility properties that are different from small-molecule-based polymers, indicating the advantages of novel ladder-type monomers. Their insolubility in chloroform supports orthogonal solvent processing to fabricate layer-by-layer organic solar cells (LBL-OSCs). Owing to its shorter pi-pi stacking distance, higher hole mobility, and more favorable phase separation caused bymultifluorine substitution, polymer PTAP1-based LBL-OSC exhibits the highest efficiency of 17.14% by using Y6-BO as the electron acceptor while the efficiency for the PTAP2-based device is 14.20%. This high efficiency indicates the tremendous potential of these novel building units. [GRAPHICS] .