Germany based Fraunhofer Institute for Solar Energy Systems (ISE) has announced that it has achieved a record efficiency of 31.3% for a silicon-based multi-junction solar cell made of III-V and silicon material.
This means ISE has surpassed its own record set in November 2016 when it achieved a record efficiency of 30.2% for the same size of 4 cm² and the same cell design, which for this was higher than the theoretical limit of 29.4% for silicon solar cells. ISE did not say what was improved compared to the earlier record.
It stated, "The outer appearance of the new solar cell looks no different than a conventional silicon solar cell. With a simple front and rear contact, the record solar cell can be integrated into photovoltaic modules in the same manner."
The III-V silicon multi-junction solar cell consists of a sequence of subcells stacked on top of each other. So-called "tunnel diodes" internally connect the three subcells made of gallium-indium-phosphide (GaInP), gallium-arsenide (GaAs)and silicon (Si), which span the absorption range of the sun's spectrum. The GaInP top cell absorbs radiation between 300 and 670 nm. The middle GaAs subcell absorbs radiation between 500 and 890 nm and the bottom Si subcell between 650 and 1180 nm, respectively. The III-V layers are first epitaxially deposited on a GaAs substrate and then bonded to a silicon solar cell structure. Subsequently the GaAs substrate is removed, and a front and rear contact as well as an antireflection coating are applied.