Structure Evolution of Oligomer Fused-Ring Electron Acceptors toward High Efficiency of As-Cast Polymer Solar Cells

The structure evolution of oligomer fused-ring electron acceptors (FREAs) toward high efficiency of as-cast polymer solar cells (PSCs) is reported. First, a series of FREAs (IC-(1-3)IDT-IC) based on indacenodithiophene (IDT) oligomers as cores are designed and synthesized, effects of IDT number (1-3) on their basic optical and electronic properties are investigated, and more importantly, the relationship between device performance of as-cast PSCs and donor(D)/acceptor(A) matching (absorption, energy level, morphology, and charge transport) of IC-(1-3) IDT-IC acceptors and two representative polymer donors, PTB7-Th and PDBT-T1 is surveyed. Then, the most promising D/A system (PDBT-T1/IC-1IDT-IC) with the best D/A harmony among the six D/A combinations, which yields a power conversion efficiency (PCE) of 7.39%, is found. Finally, changing the side-chains in IC-1IDT-IC from alkylphenyl to alkyl enhances the PCE from 7.39% to 9.20%.