The U.S. Energy Department's National Renewable Energy lLaboratory has improved the design of its solar cell by adding an additional absorber layer. NREL says this increased the conversion efficiency to 45.7% for a four-junction solar cell at 234 suns concentration. Ultra-high efficiency is achieved when the solar panel receives more than 1,000 suns of concentrated light in a conventrator photovoltaic (CPV) system.

NREL minimized the amount of defects on the cell and confined them to inactive regions. Using this technology, researchers developed a four-junction inverted metamorphic (4J IMM) cell with junctions that are lattice-mismatched to the substrate.

Additional improvements to solar cell design include broadband four-layer anti-reflection coating, a metamorphic tunnel junction interconnnect and top level performance from the GaInP top cell. The new cell has higher voltage and reduced series resistance when compared to standard GAInP subcells . Both are required for high efficiency at high solar concentrations.

NREL says this solar cell represents one of the highest photovoltaic research cell efficiencies achieved across all types of solar cells.