Fraunhofer ISE Sets 68.9% Efficiency Record for Photovoltaic Cell Under Laser Light

At the 48th IEEE Photovoltaic Specialists Conference, researchers from Germany’s Fraunhofer Institute for Solar Energy System (ISE) demonstrated how they have obtained a record conversion efficiency of 68.9% with a photovoltaic cell under monochromatic light.
The cell was based on gallium arsenide exposed to laser light of 858 nanometers.
The research team said that photovoltaic devices could also be used with laser light for effective power transmission, in addition to its traditional use for solar cells.
The researchers noted that this is the highest efficiency obtained to date in converting light into electricity.
To achieve record efficiency, the research team utilized a thin photovoltaic cell made of gallium arsenide and applied a few micrometers thick, highly reflective, and conductive mirror on the back surface of the remaining semiconductor structure.
“In a photovoltaic cell, the light – absorbed by the cell structure – sets positive and negative charges free that are conducted to back and front of cell contacts to generate power,” the researchers said. The photovoltaic effect is efficient when the incident light’s energy lies slightly over the bandgap energy inherent to the semiconductor material. Therefore, high efficiencies are theoretically achievable when a monochromatic laser light as a source is matched with a suitable semiconductor compound material.
In this new form of energy transfer called power by light, the researchers said that the laser energy is transferred through the air or optical fiber to a photovoltaic cell whose properties match with the monochromatic laser light’s power and wavelength.
In comparison with traditional power transmission through copper wires, the new power by light energy transfer systems is beneficial for applications that need a galvanically isolated power supply, lightning or explosion protection, and electromagnetic compatibility, they added.
Henning Helmers, head of the research team, said, “This thin-film approach has two distinct advantages for efficiency. First of all, photons are trapped in the cell, and the absorption is maximized for photon energies close to the bandgap, 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 recycle. This extends the effective carrier lifetime, thus additionally increasing the voltage.”
Andreas Bett, Institute Director of Fraunhofer ISE, said, “Optical power transmission has manifold applications. Examples are the structural monitoring of wind turbines; monitoring of high-voltage lines, fuel sensors in aircraft tanks, or passive optical networks; optical supply of implants from outside the body, or a wireless power supply for applications on the internet of things.”
In April 2021, researchers from ISE reportedly obtained a record conversion efficiency of 26% for both sides-contacted silicon solar cells.
Mercom had earlier reported that researchers at ISE achieved a record efficiency of 25.9% for the III-V/Si tandem solar cell grown directly on silicon.