Fraunhofer ISE: 68.9% Efficiency For GaAs PV Cell

A research team at Germany's Fraunhofer ISE has claimed to have achieved the highest efficiency to date at 68.9% for a III-V semiconductor solar PV cell based on gallium arsenide (GaAs), by exposing it to laser light of 858 nanometers. This, they believe, is the highest efficiency achieved to date for the conversion of light into electricity.
Researchers believe very high efficiencies are theoretically possible when a monochromatic laser as light source is matched with a suitable semiconductor compound material. Fraunhofer ISE sees this its research as having thrown up an impressive result that can have potential for PV for industrial applications beyond solar power generation, for instance optical power transmission.
For their research, they used a special thin film technology in which the solar cell layers were first grown on a GaAs substrate then removed, followed by a conductive highly reflective mirror applied to the back surface of the remaining semiconductor structure, a few micrometers thick. Using ceramic and silver combination as a back-surface reflector, the team developed an n-GaAs/p-AIGaAs heterostructure to be used as an absorber. This method helps in minimizing transmission losses that usually occur due to recombination.
Talking about the benefits this approach brings in, Dr. Henning Helmers, Head of the Fraunhofer ISE research team, said, "First of all, photons are trapped in the cell and the absorption is maximized for photon energies close to the band gap, which simultaneously minimizes thermalization and transmission losses, making the cell more efficient. Secondly, the photons additionally generated internally by radiative recombination become trapped and effectively recycled. This extends the effective carrier lifetime, thus additionally increasing the voltage."
Earlier in April 2021, Fraunhofer ISE reported 35.9% efficiency for monolithic triple-junction III-V/Silicon solar cell. Before that, it achieved 34.1% efficiency for monolithic triple-junction and 24.3% for III-V semiconductor layers silicon solar cells (see 34.1%: Monolithic Triple-Junction Solar Cell Efficiency).
In August 2020, Fraunhofer ISE reported 25.9% efficiency for III-V/Si tandem solar cell grown directly on silicon, exceeding its previous efficiency of 24.3% (see 25.9% Efficiency For III-V/Si Tandem Solar Cell).