Structural and electronic properties of cyanide-coated fullerene C-20@(CN)(n) (n=0-20): an ab initio approach

Density functional theory calculations at the LDA level have been performed to investigate the geometrical structure, stabilities and electronic properties of cyanide-coated fullerene C-20@(CN)(n), with n = 0-20 in the ground state. From the binding energy, dissociation energy and second-order energy, even-number-coated fullerenes are more stable than odd-number ones. C-20 has been successfully coated with electron-withdrawing group CN, achieving fullerene electron acceptors which have low-LUMO levels. The lowest LUMO value obtained for C-20@(CN)(12) is -5.89 eV, which is comparable with or lower than that of C-60 and C-60@(CN)(2) fullerenes. Each of the cyanide coatings makes the fullerenes more stable with a larger HOMO-LUMO gap. Designed cyanide-coated fullerene compounds are promising and progressive to achieve a wider range of donor materials and high efficiencies in organic photovoltaic devices.