Six-junction III-V solar cells with 47.1% conversion efficiency under 143 Suns concentration

Single-junction flat-plate terrestrial solar cells are fundamentally limited to about 30% solar-to-electricity conversion efficiency, but multiple junctions and concentrated light make much higher efficiencies practically achievable. Until now, four-junction III-V concentrator solar cells have demonstrated the highest solar conversion efficiencies. Here, we demonstrate 47.1% solar conversion efficiency using a monolithic, series-connected, six-junction inverted metamorphic structure operated under the direct spectrum at 143 Suns concentration. When tuned to the global spectrum, a variation of this structure achieves a 1-Sun global efficiency of 39.2%. Nearly optimal bandgaps for six junctions were fabricated using alloys of III-V semiconductors. To develop these junctions, it was necessary to minimize threading dislocations in lattice-mismatched III-V alloys, prevent phase segregation in metastable quaternary III-V alloys and understand dopant diffusion in complex structures. Further reduction of the series resistance within this structure could realistically enable efficiencies over 50%. Stacking multiple junctions with different bandgaps and operating under concentrated light allows solar cells to reach efficiencies beyond the limits of standard devices. Geisz et al. present a six-junction solar cell based on III-V materials with a 47.1% efficiency-the highest reported to date.