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

A pair of isomers, IDT-BOF containing S & sdot;& sdot;& sdot;O/F & sdot;& sdot;& sdot;H noncovalently configurational locks and IDT-BFO containing F & sdot;& sdot;& sdot;H/O & sdot;& sdot;& sdot;H noncovalently configurational locks, with an acceptor-pi-donor-pi-acceptor (A-pi-D-pi-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 pi bridge, and 3-(dicyanomethylidene)indan-1-one as the A unit. Owing to the S & sdot;& sdot;& sdot;O/F & sdot;& sdot;& sdot;H or F & sdot;& sdot;& sdot;H/O & sdot;& sdot;& sdot;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 %).