The effects of different solvents on the morphology of poly(2-methoxy-5-(2-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV): N,N′-bis(1-ethylpropyl)-3,4,9,10-perylene bis(tetracarboxyl diimide) (EP-PTC) blend film and the performance of solar cells based on MEH-PPV: EP-PTC blend film were studied. The results show that the phase separation in the blend film using non-aromatic solvents is of micron (0.5—5 μm) size, which leads to low charge separation efficiency and consequently the low power conversion efficiency of the assembled solar cell; whereas the phase separation in the blend film using aromatic solvents is of nano-size, which increases the interface area of the two phases obviously and consequently increases the ratio of charge separation significantly. The power conversion efficiency of solar cells based on MEH-PPV: EP-PTC blend film using aromatic solvents is improved 30 times of magnitude compared with that of solar cell based on the blend film using non-aromatic solvents.