New, high efficiency segmented unicouples are currently being developed at the Jet Propulsion Laboratory (JPL). These unicouples incorporate a combination of state-of-the-art thermoelectric materials based on Bi₂Te₃ and novel, high ZT p-type p-type CeFe₄Sb₁₂-based alloys and n-type CoSb₃-based alloys initially developed at JPL. The maximum predicted thermal to electrical efficiency is about 15% for a hot-side temperature of 975K and a cold-side temperature of about 300K. The different challenges for the development of this unicouples are reviewed and described. Recent developments are also presented and discussed. In particular, some thermal and electrical testing results and preliminary degradation mechanism studies are reported. Future challenges to fully and further develop this technology as well potential space and terrestrial applications are discussed. The potential of thermoelectric systems based on this advanced technology is compared to state-of-the-art.