The innovation in this SBIR Phase II project is the development of a unique triple junction inverted metamorphic technology (IMM), which will enable the manufacturing of very lightweight, low-cost, InGaAsP-based multijunction solar cells. The proposed IMM technology is based on ELO (epitaxial lift-off) and consists of Indium (In) and Phosphorous (P) solar cell active materials, which are designed to improve the radiation resistance properties of the triple junction solar cell while maintaining a high efficiency. Because of the intrinsic radiation hardness of InP materials, this material system is of great interest for building solar cells suitable for deployment in very demanding radiation environments, such as medium earth orbit and missions to the outer planets. Due to high launch costs, weight reduction is a key driver for the development of new space solar cell technologies. Our recently developed epitaxial lift-off (ELO) process will also be applied to this new structure, which will enable the fabrication of the IMM structure without the substrate. Cells with excellent end-of-life (EOL) performance require less area to meet specific mission power requirements. The target efficiency of the proposed IMM cell at the beginning of life (BOL) is greater than 30% at AMO 1-sun. The EOL target of the IMM cell is a degradation of less than 10% in efficiency.