Simple nonfullerene acceptors achieving NIR absorption regulation via alkoxy functionalization on the π-spacers

Abstract

Non-fused ring acceptors (NFRAs) with simple molecular structure shows a bright prospect for high efficiency acceptors in commercial applications due to the easy synthesis and low cost. Herein, ethylhexyloxy is selected as the side chain on the π-spacer of the A-π-D-π-A type NFRAs, the orientation direction and amount have been carefully considered, which could regulate the band-edges of the absorption spectra ranging from 900 nm to 1120 nm. Hence, the inner alkoxy modified DTC-O_iT-4F could reach a rather narrow bandgap of 1.10 eV due to the conformation locks, while the outer derived strategy in DTC-O_oT-4F and DTC-O_oiT-4F is effective at the LUMO improving. Utilization of PBDB-T as the donor, organic solar cells are constructed with these acceptors, and power conversion efficiencies (PCEs) of 5.50 %, 10.02 % and 10.58 % are acquired for DTC-O_iT-4F, DTC-O_oT-4F and DTC-O_oiT-4F based devices, respectively. The conformation prediction, morphology study, crystallization orientation and energy loss analysis have been fully discussed in this work. In all, our studies have demonstrated that appropriate utilization of the alkoxy side chain on the π-spacer of the noncovalently locked simple A-π-D-π-A acceptors could effectively change its electronic characteristics and may offer some simple strategy for the design of high efficiency NFRAs.