Raman study on a bulk-heterojunction film of pentacene and C₆₀

We measured the 785-nm excited Raman spectrum of a pentacene:C₆₀ blend film. The 1462-, 492-, and 268-cm^-1 bands of C₆₀ showed broadening in bandwidth and downward shifts in peak wavenumbers, whereas such broadening and downward shifts were not observed for pentacene. These results indicate that there are pentacene crystallites among the amorphous C₆₀. The intensity ratio of the 1598-cm^-1 (B_3g) and the 1534-cm^-1 (A_g) bands indicates that pentacene molecules have standing orientations. The appearance of a 514-cm^-1 band (F_1u) and the splitting of the H_g bands of C₆₀ indicate symmetry lowering induced by the interaction between pentacene and C₆₀ molecules.