Designing high-performance nonfused ring electron acceptors via side-chain engineering

The side-chain has a significant influence 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. In this work, we designed and synthesized three brand-new nonfused ring electron acceptors (NFREAs) OC4-4Cl-Ph, OC4-4Cl-Th, and OC4-4Cl-C8 with hexylbenzene, hexylthiophene, and octyl side chains on the pi-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 may effectively form interpenetrating networks that resemble nanofibrils, which can facilitate exciton dissociation and charge transport. Finally, OC4-4Cl-C8-based devices can be created a marvellously power conversion efficiency (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 validated that side-chain engineering is an efficient way to achieve high-performance NFREAs. In this work, we designed and synthesized three brand-new nonfused ring electron acceptors (NFREAs) OC4-4Cl-Ph, OC4-4Cl-Th and OC4-4Cl-C8 and can be modularly synthesized. The OC4-4Cl-C8 exhibited longer exciton diffusion distances and the corresponding blend film displayed faster hole transfer and diffusion-mediated processes, weaker bimolecular recombination, and more efficient exciton transport. Finally, photovoltaic devices based on OC4-4Cl-C8 can generate an excellent PCE of 16.56%.image

Automated summary

In this work, three new nonfused ring electron acceptors (NFREAs) were designed and synthesized. It was found that OC4-4Cl-C8 exhibited better optical properties and aggregation behaviors, leading to higher photovoltaic performance. Therefore, side-chain engineering is an efficient strategy to optimize the performance of organic solar cells.