Large Area Multijunction III-V Space Solar Cells Over 31% Efficiency

This paper explores development and progress for large area III/N multijunction space solar cells with efficiencies at or above 31 %. XTJ Prime SuperCells with area over 70 cm², average 30.7% AMO efficiency with a maximum of 31.9%. Post radiation testing indicates an EOL efficiency of 26.7% for 1e15 1 MeVe-/cm²fluences after ECSS annealing. Upright Metamorphic triple junction (UMM3J) devices were developed with breakthroughs in optimizing cell design and uniformity on 150 mm wafers, and demonstrated SuperCell build of average AM0 efficiency at 31.3% for 73.5 cm²cells in area with best efficiency at 31.5%. UMM3J devices were also evaluated under typical GEO and interplanetary environments for low-irradiance and low-temperature (LILT). Finally, next generation space solar cell UMM4J devices were investigated, and high quality 1.9 eV subcells were demonstrated.

I. Introduction

Lattice matched GaInP/GaInAs/Ge triple junction (3J) solar cells with slightly different types of architectures have been the dominant product for space missions. Currently, Spectrolab is flying XTJ 29.5% SuperCells on orbit on multiple spacecraft from the state-of-the-art 150 mm diameter wafer process line. Here a SuperCell refers to any epitaxial III/V multijunction solar cell we produce from two cells per 150 mm wafer. Recently, we introduced an improved variant of the XTJ family designated the XTJ Prime [1]. This improved variant of lattice matched devices is the only currently qualified cell achieving over 3 Watts per cell in SuperCell sizes. Spectro lab's guiding principle continues to be addressing the space photovoltaic marketplace with increasing value through improved end-of-life cost for power (EOL $/W). This aim is more than increased efficiency alone. It addresses bothmission total power needs as well as the totalcost to provide that power on orbit.