Synthesis of Conjugated Wide-Bandgap Copolymers Bearing Ladder-Type Donating Units and Their Application to Non-Fullerene Polymer Solar Cells

Two new wide-bandgap conjugated copolymers, T-3MT and 2T-3MT, containing methyl-3-thiophenecarboxylate (3MT) as a weak accepting unit and indacenodithiophene (IDT) or indacenodithienothiophene (IDTT) as ladder-type donating units, were synthesized through Stille coupling polymerization. The effects of the IDT and IDTT units on the physical, optical, and electrochemical properties of these copolymers were investigated. Polymer solar cells (PSCs) were constructed using these new copolymers and different acceptor molecules for inter-comparative analysis of their performance. The PSCs bearing the as-cast active layers with 2,2-((2Z,2Z)-((4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b] dithiophene-2,7-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IM-IDT) displayed the highest PCEs of 3.78-3.96%, mainly owing to the predominant face-on orientation of blend film, and the relatively high open circuit voltage exceeding 1.0 V.