The innovation in this Phase II SBIR is the development of a technology which will enable the manufacture of a lightweight, low cost, high radiation resistance InP based solar cells with high efficiency suitable for space power systems. The key technological step is the application of a production-worthy epitaxial liftoff (ELO) process to a multijunction solar cell structure fabricated on a large area ( 3-inch and 4-inch)InP substrates. Our focus will be on the improvement of the efficiency of dual junction to greater than 23% and a pathway towards InP based triple junction. The number of substrate reusage will also be investigated to determine the impact of cost savings due to the high cost of InP substrates. Radiation testing of the ELO InP solar cells will be performed and compared to standard InP solar cells.