The main objective of this paper is to design and simulate a high efficiency quad junction PIN solar structure using group III-nitride material system. Out of the nitride family, Indium Gallium Nitride alloy possesses a direct and wide energy band gap ranging from 0.7 eV for Indium Nitride up to 3.4 eV for Gallium Nitride, because of which it covers most of the solar spectrum thus serving as a wide band gap top cell in a mechanically stacked or a bounded multi-junction hybrid solar cell. Hence this material is chosen here to design wide band gap Quad junction device. The PIN structure is built as a quad layer solar cell cascaded using tunnel junctions. For InxGa1-xN, the mole fraction values of Indium (x) are altered for the individual cell layer. The mole fraction variation leads to the change in the grading of the concentration of Indium along the depth of the structure. Variable bandgap is achieved by varying the grading, thus making the multijunction cell to be a wide energy bandgap structure. For each cell, the parameters are modelled numerically and simulated for mole fraction values (x) of 0.365, 0.525, 0.70 and 0.93. The individual cell analysis is performed and then the structure is cascaded together to form a 100 cm2 area quad junction solar cell for which the performance analysis is obtained as voltage to be 1.17 V/cm2 and current to be 3.18 mA/cm2 which accounts to a maximum conversion efficiency of 33.63% for 100Watt/cm2, 1.5AM one sun spectrum illumination.