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

Abstract

One pair of isomers, IDT‐BOF containing S···O/F···H noncovalently configurational locks and IDT‐BFO containing F···H/O···H noncovalently configurational locks, were designed and synthesized with an acceptor‐π‐donor‐π‐acceptor (A‐π‐D‐π‐A) structure by choosing 4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b']dithiophene (IDT) as the D unit, 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 show completely planar structure. In comparison to IDT‐BFO, IDT‐BOF exhibits similar LUMO 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 PCE. Importantly, ternary solar cells based on PBDB‐T:Y5 as control devices by adding 10% IDT‐BFO exhibited a 5% enhancement in the PCE compared to the control device (14.3% vs. 13.6%).