German-French scientists develop ultra-thin GaAs solar cell with 19.9% efficiency

A research team from Germany’s Fraunhofer ISE and France’s Centre for Nanoscience and Nanotechnology (C2N) claim to have developed an ultra-thin solar cell based on Gallium arsenide (GaAs), which is a compound of elements belonging to the so-called III-V materials, with an efficiency of 19.9%.

The results, the scientists have explained, were obtained through a new manufacturing process that is characterized by the use of a 205-nanometer-thick absorbing GaAs layer and a nanostructured back mirror. “The guiding idea was to conceive a nanostructured back mirror to create multiple overlapping resonances in the solar cell, identified as Fabry–Perot and guided-mode resonances,” said Fraunhofer ISE.

These resonances are said to trap light in the absorber for a longer time. Simultaneously, they improve optical absorption, which is enhanced over a large spectral range that fits the solar spectrum from the visible to the infrared.

The silver back mirror was fabricated at the nanometer scale by soft nano-imprint lithography, through the application of a sol-gel derived film of titanium dioxide. “Controlling the fabrication of patterned mirrors at the nanometer scale was a key in the project,” the research team said.

It also believed that this cell technology could reach a 25% efficiency rate in the short term. It is also thought that the cell’s thickness could be further lowered without efficiency losses. The results of the research were published in “III-V Photovoltaics and Concentrator Technology,” in the scientific journal Nature Energy.