Fraunhofer ISE reports 69% record efficiency of GaAs PV cell

30 Jun 2021

As Fraunhofer Gesellschaft opens ‘ENIQ’ showroom on EUREF campus in Berlin, Germany.

Researchers from the Fraunhofer Institute for Solar Energy Systems (ISE) have this week reported (at the 48th IEEE Photovoltaic Specialists Conference) how they have achieved a record conversion efficiency of 68.9% with a photovoltaic cell under monochromatic laser light.

To do this, the research team used a very thin photovoltaic cell made of gallium arsenide and applied a highly reflective, conductive mirror on the backside. The work is described in Physica Status Solidi Rapid Research Letters.

Specifically, the ISE researchers achieved a record conversion efficiency of 68.9 % for a III-V semiconductor photovoltaic cell based on gallium arsenide exposed to laser light of 858 nm. This is the highest efficiency achieved to date for the conversion of light into electricity, they said.

This success was made possible with a special thin film technology in which the solar cell layers are first grown on a gallium arsenide substrate which is then subsequently removed. A conductive, highly reflective mirror is applied to the back surface of the remaining semiconductor structure, just a few micrometers thick.

‘Two distinct advantages’

“This thin film approach has two distinct advantages for the efficiency,” said physicist Dr. Henning Helmers, head of the Fraunhofer ISE research team. “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.”

The research group investigated thin film photovoltaic cells with back-surface reflectors made of gold and an optically optimized combination of ceramic and silver, with the latter showing the best results. An n-GaAs/p-AlGaAs heterostructure was developed as absorber, which shows particularly low charge carrier losses due to recombination.

“This is an impressive result that shows the potential of photovoltaics for industrial applications beyond solar power generation,” commented Prof. Andreas Bett, institute director of Fraunhofer ISE. Optical power transmission has manifold applications.

“Examples are the structural monitoring of wind turbines; the monitoring of high-voltage lines, fuel sensors in aircraft tanks, or passive optical networks; the optical supply of implants from outside the body; or a wireless power supply for applications in the Internet of Things,” he said.

Fraunhofer-Gesellschaft opens ENIQ showroom in Berlin

Fraunhofer Energy Research has a new location: the showroom ENIQ - Energy Intelligence by Fraunhofer is located on the EUREF campus in Berlin, Germany.

The facility functions as an interactive platform to serve the transfer of knowledge. Stakeholders from business, politics and society can discuss relevant topics with scientists, initiate projects and create innovations. Event formats for different tar-get groups are complemented by an exhibition area where innovative demonstrators and exhibits from Fraunhofer Energy Research are on display.

“With the opening of ENIQ on the EUREF campus in Berlin-Schöneberg, the Fraunhofer-Gesellschaft is taking a new approach to expanding knowledge transfer in the field of energy research. We are delighted with this successful facility, which has the potential to bring technical innovations even faster to the relevant target groups for the advancement of the energy transition," commented Andreas Feicht, State Secretary at the Federal Ministry for Economic Affairs and Energy at the inauguration on June 29, 2021.