Low-LUMO 56π-electron fullerene acceptors bearing electron-withdrawing cyano groups for small-molecule organic solar cells

- 56π-Electron fullerene derivatives possessing low LUMO levels were synthesized by using electron-withdrawing cyano groups.
- Controlled introduction of the cyano group prevents formation of undesired poly(cyano)-adducts.
- LUMO levels of the products are tunable by changing electrophiles in the second stage reaction.
- Low-LUMO fullerenes served as electron acceptors in organic solar cells containing a low-bandgap small-molecule donor.
- Power conversion efficiency of 2.0% was obtained in the p-n heterojunction organic solar cell.