GalnNAs material has been studied as a candidate for the fourth-layer in multi-junction solar cells. However, the material quality of GalnNAs has inhibited its practical use in commercial photovoltaics. While improvements in GalnNAs material using rapid thermal annealing and hydrogenation have been reported, in this thesis, the main focus is on 1he effects of hydrogenation on GalnNAs solar cells. The selective passivation impurities/defects and nitrogen-nitrogen clusters by hydrogenation in GalnNAs bulk and solar cell samples is presented. A comparison of reference and hydrogenated solar cells show improvements in the material quality and device performance after passivation.