This paper reports an application of Atomic Force Microscopy (AFM) phase imaging to observe the phase separation between electron donor and acceptor materials in bulk heterojunction organic solar cells. The solar cells were fabricated using inkjet printed thin films of blended poly (3-octylthiophene-2, 5-diyl)(P3OT) and (6,6)-phenyl C71 butyric acid methyl ester (PC 71BM) as donor and acceptor materials respectively. The content PC71BM in the blended was varying from 25, 50 and 75 wt %. The AFM phase images of the thin film which contains 25 wt % PC71BM indicated that the acceptor molecules, PC71BM, are well distributed in the polymer chain of donor material, P3OT. The solar cell contains this film has the highest generated photocurrent. Hence, the phase separation between electron donor and acceptor materials in bulk heterojunction organic solar cells is one essential aspect that influences generation of photocurrent.