Multiband solar cells are the third generation photovoltaic devices in which an increase of the power conversion efficiency is achieved through an absorption of low energy photons while preserving a large band gap that determines the open circuit voltage. The ability to absorb photons from different solar spectrum regions is due to an intermediate energy band separated from valence and conduction band. This intermediate band, acts as a stepping stone allowing low energy photons to transfer electrons from the valence band to the conduction band by a sequential two photons absorption processes. It has been demonstrated that Highly Mismatched Alloys (HMAs) offer a potential to be used as a model material system for practical realization of multiband solar cells . Thus incorporation of a low mole fraction of N into GaAs leads to formation of GaAs1 xNx that is a prototypical dilute nitride HMA alloy with a well-defined intermediate band. Currently, we are using a chemical beam epitaxy to synthesize dilute nitride HMAs. The materials are characterized by a variety of structural, optical and electrical methods to optimize their performance for multiband photovoltaic devices.