New record solar efficiency claimed for silicon-based multijunction cell

Germany’s Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) and Dutch research institute AMOLF announced last week that they have fabricated a multijunction solar cell with a record efficiency of 36.1%.

The two research institutes presented the new record at the European Photovoltaic Solar Energy Conference (EU PVSEC) in Lisbon late last week, believing it to be the highest efficiency ever reached for a solar cell based on silicon.

The new record is a huge step for silicon-based solar technology, which is used widely across the planet but suffers from a fundamental efficiency limit of 29.4%.

However, according to Fraunhofer ISE, this limitation can be overcome by coating the solar cells with additional materials to create what is known as ‘multijunction’ solar cells.

These multijunction cells boast multiple light absorption layers stacked one atop the other, so that each layer effectively absorbs a specific part of the sunlight’s colour spectrum, resulting in increased efficiency.

“This new record is the result of a unique collaboration between Fraunhofer ISE and AMOLF that started in 2020,” explained Albert Polman, who led the AMOLF-part of the project.

“The Fraunhofer team is world-renowned for the fabrication of ultra-high efficiency solar cells based on silicon and III-V semiconductors such as GaInP or GaAs. The AMOLF team has built up many years of experience in optimizing the management of light in solar cells.

“In this project, we brought this knowledge together, with this unique result. The solar cells have travelled between Freiburg and Amsterdam for the different processing steps, in this way building up the full solar cell.”

The record-breaking fabrication utilises silicon TOPCon solar cell with two semiconductor layers composed of gallium indium phosphide (GaInP) and Gallium Indium Arsenide Phosphide (GaInAsP) that were developed at Fraunhofer ISE.

The layer stack was then coated with a specially designed metal/polymer nanocoating designed at AMOLF and fabricated jointly at AMOLF and Fraunhofer ISE.

Additionally, the back reflector of the solar cell improves the trapping of light inside the cell, enabling efficiency to be increased beyond 36% for the first time.

Naturally, given the many added steps of this record-breaking solar cell, such an ultra-high efficiency silicon-based solar cell is more expensive than conventional solar cells. However, Fraunhofer ISE believes that such cells could be of particular benefit in locations where available space is limited and a large amount of solar power must be generated within a small area.

Additional potential applications include for use in solar-powered electric cars, consumer products, and drones.

“It is a great achievement of the researchers in both teams to combine the best processes available to jointly realize a new efficiency record for a silicon-basedmultijunction solar cell,” said Frank Dimroth, from Fraunhofer ISE.

“Both, the new back reflector from AMOLF and the improved GaInAsP middle cell from Fraunhofer contributed to this outstanding result.”