This paper reports the theoretical design and projected the performance of InxGa1-xN MJ solar cells for high efficiency. The design and performance evaluation are made by developing a simulation model which optimizes the design of MJ solar cells for high efficiency. The efficiency was optimized by optimizing the band gap and n-side thickness of different cells while keeping the current mismatch between different cells below 0.2%. The efficiency is found to be varied from 24.94% for single junction to 45.22% for six junctions. Further increase of junction does not significantly increase the efficiency. Use of concentrator increases the efficiency. The calculation of the photocurrent density and open circuit voltage of each junction has done under AM 1.5 and assumed that each junction absorbs the solar photons that are not absorbed by the preceding one.