“…This possibility originates from the fact that C 60 has an electronic degeneracy in its cationic state because of its high symmetry I h [21,22], but C 60 hydrides usually do not because of the reduction in symmetry by the addition of hydrogen. Electron mobility in C 60 film is about 1 cm 2 V −1 s −1 [20,23,24] so that C 60 is one of the most useful electron-transport materials. However, to achieve low-cost production and large-area devices, it is necessary for C 60 materials to have a solution-processable form, such as [6,6]-phenyl C 61 -butyric acid methyl ester (PCBM) [25].…”