Although C₆₀ derivatives, in particular [6,6]phenyl-C61-butyric acid methyl ester (PCBM), are a key component for developing highly efficient bulk heterojunction solar cells (BHJSCs). However, they suffer from poor absorption in the visible region. For a widening of the solar spectrum coverage and an improvement of the absorption efficiencies, C₆₀ derivatives are often coupled with dyes that act as light-harvesting antennae.

Fullerene bisadducts are promising electron-accepting materials because of the increased open-circuit voltage of BHJSCs based on these compounds compared with those based on PCBM. That led Angela Sastre-Santos, Universidad Miguel Hernández de Elche, Alicante, Spain, and co-workers to synthetize C₆₀ bisadducts connected with the strong absorber perylenediimide (PDI) in a cyclic fashion.

A double click reaction plus a double Prato reaction afforded the C₆₀-PDI dyads. A fast energy transfer rate was obtained by Shunichi Fukuzumi, Osaka University, Japan, and co-workers for PDICl₄-C₆₀ systems. This result and the enhancement of molar absorption coefficient by PDI anchorage will be highly valuable for the use of PDICl₄-C₆₀ systems as acceptors in BHJSCs.

• Macrocyclic Dyads Based on C₆₀ and Perylenediimides Connected by Click Chemistry,
  Sara Pla, Luis Martín-Gomis, Kei Ohkubo, Shunichi Fukuzumi, Fernando Fernández-Lázaro, Ángela Sastre-Santos,
  Asian J. Org. Chem. 2014.
  DOI: 10.1002/ajoc.201300235