Organic solar cells are promising sources of electrical power due to their efficiency, low cost, and potential renewable energy applications. There are several reports on green organic solar cells using the environment- friendly water- soluble polymer. Here, we report the organic solar cells with a bilayer structure containing water- soluble polymer. The water-soluble conjugated polythiophene, PTEBS:Na+, was used as an electron donor and PCBM in organic solvent was used as an electron acceptor. The bilayer consisted of PTEBS: Na+/PCBM showed UV- vis absorption maximum at 460 nm. The AFM morphology of the bilayer was also investigated.