Semiconductor solar cell (PV cell) has been widely used for generating solar electricity. However, the high cost and severe pollution limits its application. Recently the discovery of graphene may open a door to fabricate a novel solar cell with lower cost and more environmentally friendly. Our proposed solar cell device consists of a graphene strip and two semiconductor strips with different energy gaps attached to the two edges of the graphene strip on a flat plane. This structure is a two-dimensional quantum well. The energy bands of graphene can be described by a two-dimensional Dirac equation centered on hexagonal corners (Dirac points) of the honeycomb lattice Brillouin zone. The 2 D Dirac equation has been solved numerically in this paper. The results indicate that the graphene quantum well possesses very dense quantum energy states which imply that quantum well of this type can absorb sun light with more different frequencies. If we use graphene quantum well to fabricate the photo voltaic cell, the efficiency of converting solar energy to electricity will be enhanced.