Frauhover ISE achieves 35.9% efficiency for a monolithic tandem cell

The Freiburg, Germany-based Fraunhofer Institute for Solar Energy Systems ISE has achieved a new efficiency world record with a monolithic tandem cell made of III-V semiconductors (elements from the third and fifth main groups of the periodic table) and silicon. According to the institute, an efficiency of 35.9 percent was measured under an air mass of 1.5 (corresponding to PV standard test conditions). This is the same value that research institutes NREL, CSEM and EPFL achieved back in 2017 with a III-V/Si tandem solar cell with four contacts; however, that cell had four contacts. In contrast, in the ISE’s cell architecture, »the III-V semiconductor layers are connected directly to the silicon sub-cell on the atomic level. From the outside, the record cell resembles a two-terminal conventional solar cell.« Accordingly, a key step for the improved efficiency was a new compound semiconductor made of gallium indium arsenide phosphide (GaInAsP) in the middle cell.
Because of the complex structure and the resulting production costs, III-V/Si tandem solar cells are, according to ISE estimates, for the time being only suitable for applications where a particularly good ratio of power to surface area and weight is important, »for example, in electrically powered aircraft and drones«. In the future, however, they will also be used for standard modules.
© PHOTON

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