Designing High-performance Nonfused Ring Electron Acceptors via
Side-chain Engineering
Abstract
The side-chain has a significant effect on the optical properties and
aggregation behaviors of the organic small molecule acceptors, which
becomes an important strategy to optimize the photovoltaic performance
of organic solar cells (OSCs). In this work, we designed and synthesized
three novel nonfused ring electron acceptors (NFREAs) OC4-4Cl-Ph,
OC4-4Cl-Th and OC4-4Cl-C8 with hexylbenzene, hexylthiophene and octyl
side chains on the π-bridge units. Compared with OC4-4Cl-Ph and
OC4-4Cl-Th, OC4-4Cl-C8 with linear alkyl side chain has more red-shift
absorption, which is conducive to obtaining higher short-circuit current
density. Additionally, the OC4-4Cl-C8 film exhibits a longer exciton
diffusion distance and the D18:OC4-4Cl-C8 blend film displays faster
hole transfer, weaker bimolecular recombination, and more efficient
exciton transport. Furthermore, the D18:OC4-4Cl-C8 blend films can form
good nano fibril-like interpenetrating networks, which can facilitate
exciton dissociation and charge transport. Finally, OC4-4Cl-C8 based
devices can generate an excellent PCE of 16.56%, which is much higher
than OC4-4Cl-Ph (12.29%) and OC4-4Cl-Th based (11.00%) ones, being the
highest PCE among the NFREA based binary devices. All in all, we have
demonstrated that side-chain engineering is an efficient way to achieve
high-performance NFREAs.