PARIS Ė Scientists at the U.S. Naval Research Laboratory (NRL) have developed a triple-junction solar cell design, which they claim has the potential to exceed 50 percent power conversion efficiency under concentrated illumination.
The NRL researchers have been collaborating with the scientists and engineers at Imperial College in London and MicroLink Devices Inc. (Niles, Illinois) to increase the efficiency of triple-junction solar cells much further. The world record stands at 44 percent under concentrated illumination.
Work has focused on different semiconductor materials and applied band structure engineering, via strain-balanced quantum wells. This has produced a design for a multi-junction solar cell that can achieve direct band gaps ranging from 0.7 to 1.8 electron volts with materials that are all lattice-matched to an indium phosphide substrate.
"Having all lattice-matched materials with this wide range of band gaps is the key to breaking the current world record," said Robert Walters, Ph.D., NRL research physicist. "It is well-known that materials lattice-matched to InP can achieve band gaps of about 1.4 eV and below, but no ternary alloy semiconductors exist with a higher direct band-gap."
To achieve high efficiency levels, NRL researchers said they identified InAlAsSb quaternary alloys as a high band gap material layer that can be grown lattice-matched to InP. They modeled the band structure of InAlAsSb and demonstrated that this material could potentially achieve a direct band-gap as high as 1.8eV.
With this result, and using a model that includes both radiative and non-radiative recombination, the research team said it created a solar cell design that can potentially exceed 50 percent power conversion efficiency under concentrated solar illumination.
Schematic diagram of a multi-junction solar cell formed from materials lattice-matched to InP and achieving the bandgaps for maximum efficiency
NRL said it will collaborate with MicroLink and Rochester Institute of Technology (Rochester, New York) to pursue a three-year materials and device development program aimed at realizing this solar cell technology. See related links:
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