Advances in Dilute Nitride Multi-Junction Solar Cells for Space Power Applications

Abstract

A sub-cell with bandgap of around 1 eV is required to improve the efficiency of multi-junction solar cells beyond what is possible with legacy triple-junction architectures [1]. Solar Junction Corporation has been focused since 2007 on the development and commercialization of dilute nitride materials to be used as the 1eV sub-cell in a fully lattice matched multijunction solar cell. Initial focus on the terrestrial concentrating photovoltaics (CPV) market led to Solar Junction Corp.’s achievement of multiple world records in multi-junction solar cell efficiency with its triplejunction cells on GaAs [2], [3]. These solar cells have been available as commercial products since 2010. Solar Junction Corp. has leveraged its high-quality, manufacturable dilute nitride material to develop and introduce an entirely new class of space solar cells capable of reaching over 33% AM0 conversion efficiency in a four-junction (4J) configuration lattice matched to active Ge substrates, with a clear line of sight to 36% AM0 efficiency in five- or six-junction devices that can be manufactured more cost-effectively than devices relying on metamorphic technologies. In this paper, we review the latest performance and qualification results of Solar Junction Corp.’s lattice matched 4J-on-Ge space solar cells and CIC (Cell- Interconnect-Coverglass) products incorporating GaInNAsSb dilute nitride material. We also report on the production readiness of these advanced space solar cells manufactured using an optimized hybrid Molecular Beam Epitaxy (MBE) / Metal Organic Vapor Phase Epitaxy (MOVPE) growth process.