We investigated the intercalation of C-60 into poly(p-anthracene-ethynylene)-alt-poly(p-phenylene-vinylene) copolymers layers by density functional theory calculations in respect of crystal structures and electronic band structures. Based on the experimental observations, we found that the copolymer with branched side chains substituted next to the anthracene units and the linear side chains substituted to the vinylene units has a better tendency to intercalate with C-60 than the reversely substituted copolymer. The calculated electronic band structures of the intercalated phase, featured by flat in-gap states resulting from C-60 molecules, explain the experimentally observed variations of the photocurrent, photoluminescence, and electroluminescence yields with different ratio between PCBM and the two types of copolymers in the ternary blend.