Isomeric Effect of a π Bridge in an IDT‐Based Nonfused Electron Photovoltaic Acceptor.

A pair of isomers, IDT‐BOF containing S⋅⋅⋅O/F⋅⋅⋅H noncovalently configurational locks and IDT‐BFO containing F⋅⋅⋅H/O⋅⋅⋅H noncovalently configurational locks, with an acceptor‐π‐donor‐π‐acceptor (A‐π‐D‐π‐A) structure have been designed and synthesized by choosing 4,9‐dihydro‐s‐indaceno[1,2‐b : 5,6‐b′]dithiophene (IDT) as the D unit, an F/n‐hexyloxy substituted phenyl ring as π bridge, and 3‐(dicyanomethylidene)indan‐1‐one as the A unit. Owing to the S⋅⋅⋅O/F⋅⋅⋅H or F⋅⋅⋅H/O⋅⋅⋅H noncovalently configurational locks, both IDT‐BOF and IDT‐BFO have a completely planar structure. IDT‐BOF exhibits a similar LUMO to IDT‐BFO, but higher HOMO energy levels, leading to a smaller optical bandgap and red‐shifted absorption. However, IDT‐BOF‐based bulk‐heterojunction organic solar cells (BHJ‐OSCs) coupled with PBDB‐T, and PCE‐10 as donor materials both exhibited a lower PCE than that of IDT‐BFO (PBDB‐T: 5.2 vs. 6.1 %; PCE‐10: 1.7 vs. 3.2 %). Comprehensively comparing and investigating IDT‐BOF : PBDB‐T and IDT‐BFO : PBDB‐T OSCs suggested that the large phase separation and serious charge recombination of IDT‐BOF‐based OSCs contributed to its lower power conversion efficiency. Importantly, ternary solar cells based on PBDB‐T : Y5 as control devices with an additional 10 % IDT‐BFO exhibited a 5 % enhancement in the PCE compared to the control device (14.3 vs. 13.46 %). [ABSTRACT FROM AUTHOR]