Nanostructured devices (Quantum dot and Quantum well) have been proposed as a way to overcome the Shockley-Quiesser limit of a single junction solar cell as they have the potential to show three quasi Fermi levels. In this paper the material combinations that can be used in a Quantum Well solar cell to realize a multiple quasi-Fermi level device will be discussed. The calculations were done on different possible combinations of direct band gap III-V semiconductors, with the effect of strain being taken into account by applying 6 band K.p model. A detailed balance calculation was done on the materials selected to determine their maximum efficiency under 1 sun AM0. The material combination of Al 0.63In0.37 As as the barrier and InAs0.16P 0.84 as the well with InP as the substrate is found to be the best material combination giving a theoretical efficiency of 43% under 1 sun AM0, compared to the maximum three-level efficiency of 47% under the same conditions.