Two efficiency records set for monolithic silicon triple solar cells

September 02, 2019 //By Christoph Hammerschmidt
Two efficiency records set for monolithic silicon triple solar cells
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE have succeeded in further increasing the efficiency of monolithic triple-junction solar cells made of III-V semiconductors and silicon. By combining several absorber materials, these multi-junction solar cells make much better use of the solar spectrum than conventional silicon solar cells.

The researchers at Fraunhofer ISE improved the world record for a monolithic multiple-junction solar cell produced by wafer bonding to 34.1 %. A new efficiency record of 24.3 % was set for a silicon solar cell with directly deposited semiconductor layers.

Monolithic multiple-junction solar cells are considered to be promising for the further development of the silicon solar cells that dominate today. This is because they can be used to achieve significantly higher efficiencies for converting sunlight into electricity. Andreas Bett, director of Fraunhofer ISE, believes that an efficiency of 36 % is possible. According to Bett, the physical limit of a pure silicon solar cell of 29.4 % would thus be significantly exceeded. The high efficiency makes it possible to generate more power per area and thus save materials for solar cells and module materials.

For the highly efficient multi-junction solar cell, thin layers of III-V semiconductors a few micrometers thick are applied to a silicon solar cell. In order to optimally use the energy of sunlight, the different layers absorb different spectral ranges of sunlight: gallium indium phosphide between 300 - 660 nm (visible light), aluminum gallium arsenide between 600 - 840 nm (near infrared light) and silicon between 800 - 1200 nm (longer wavelength light). Like normal silicon solar cells, the new triple solar cells are equipped with contacts on the front and back so that the solar cells can be easily integrated into solar modules.

Picture: 
Triple-junction solar cell

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