Porous-lift-off germanium membranes as lightweight, flexible, and cost-effective template for III-V space solar cells: a review

Abstract

The growing demand for low-cost, lightweight, and high-efficiency space technologies has driven the search for photovoltaic solutions which minimize material use without sacrificing performance. III-V multijunction solar cells remain the state of the art for space power applications due to their exceptional efficiency and radiation resistance. Among III-V solar cells architectures, Germanium (Ge)-based structure remains widely used; however, their broader deployment is limited by reliance on thick and expensive Ge substrates. Germanium membranes, however, offer a promising path to address these limitations through substrate reuse strategies. This review highlights progress in the development of Ge membrane as a transformative platform for space photovoltaics, with a focus on porous Ge-based lift-off approaches while reusing Ge substrate. These methods enable the fabrication of detachable, monocrystalline Ge membrane through pore etching, epitaxial growth, porous transformation, layer lift-off and substrate reuse, significantly reducing Ge consumption and device weight. Two main fabrication routes for porous Ge formation are discussed: lithography-based dry etching using Ge-On-Nothing approach and electrochemical etching. The fundamentals of pore formation, thermal reorganization of porous, and subsequent III-V epitaxy are reviewed. Key challenges related to process uniformity, detachment scalability, and industrial integration are examined, and potential strategies for scalable manufacturing are outlined. Azmat Ali and colleagues review progress on porous-lift-off Germanium (Ge) membranes as lightweight, cost-effective and reusable templates for III-V space solar cells. They identify key bottlenecks in membrane uniformity, scalability, and industrial integration, and outline strategies for scalable manufacturing and Ge-substrate reuse.