Quadruple III-V bonded CPV cell hits 44.7% record conversion efficiency

Sep 24, 2013 - Mark Osborne - pv-tech.org

World record solar cell with 44.7% efficiency, made up of four solar subcells based on III-V compound semiconductors for use in concentrator photovoltaics. ©Fraunhofer ISE

A solar cell with 50% efficiency is no longer a pipe dream after researchers at at Fraunhofer ISE, CEA-Leti, Helmholtz Center Berlin and commercial CPV firm, Soitec reached a world record 44.7% conversion efficiency for a novel III-V-based solar cell.

Using Soitec’s commercial experience in wafer bonding techniques, researchers have developed a new multi-junction solar cell structure with four sub-cells, each optimised to absorb different spectral regions from ultraviolet through to the infrared.

The optimisation only took months from previously reporting a III-V cell with 43.6% efficiency, while increasing the efficiency by as much as 1%.

IV-characteristic for the current best four-junction solar cell under AM1.5d ASTM G173-03 spectrum at a concentration of 297 suns. The measurements were carried out at the Fraunhofer ISE CalLab. ©Fraunhofer

External Quantum Efficiency of the four-junction solar cell. The measurement was performed at the Fraunhofer ISE CalLab. ©Fraunhofer ISE

However, a IV-characteristic graph of the new cell highlights a level of variability in the cells ability to reach such high conversion efficiencies. The new record efficiency was measured at a concentration of 297 suns.

Frank Dimroth, department head and project leader in charge of this development work at Fraunhofer ISE said: “We are incredibly proud of our team which has been working now for three years on this four-junction solar cell. This four-junction solar cell contains our collected expertise in this area over many years. Besides improved materials and optimisation of the structure, a new procedure called wafer bonding plays a central role. With this technology, we are able to connect two semiconductor crystals, which otherwise cannot be grown on top of each other with high crystal quality. In this way we can produce the optimal semiconductor combination to create the highest efficiency solar cells."

“It confirms the acceleration of the roadmap towards higher efficiencies which represents a key contributor to competitiveness of our own CPV systems,” added André-Jacques Auberton-Hervé, Soitec’s Chairman and CEO.

The research partners did not say if or when the novel cell would be put into production. Soitec announced earlier in September, 2013 that it had launched a CPV module dubbed the ‘CX-M500’ that employed III-V solar cells with a 31.8% conversion efficiency providing a nominal peak power output of 2,450 Wp.