Solar panels that can commonly be seen on the roofs of houses or in some areas of the countryside to transform sunlight into clean energy only manage to turn a quarter of that available energy into electricity .
However, a team of scientists managed in 2017 to create a photoelectric plate that converts direct sunlight into electricity with an efficiency of 44.5% . The trick: this cell integrates multiple stacked cells into a single device, thus capturing almost all the energy in the solar spectrum.
This device uses photovoltaic concentrators (CPV) that use lenses to focus sunlight onto tiny microscale solar cells . Thus, due to its small size – less than a square millimeter – it uses more sophisticated materials than usual, making its manufacture much more profitable.
Multi-junction cells, the new design
Matthew Lumb , lead author of the study and scientific researcher at the George Washington University School of Engineering and Applied Sciences, explains that “about 99% of the energy contained in direct sunlight that reaches the Earth’s surface has longitudes wavelengths between 250nm and 2500nm, but conventional materials cannot capture this entire spectral range. “
However, the device designed by his team, being a multi-junction cell (due to the different layers that compose it) can “unlock the energy stored in long-wavelength photons.” In addition, it is made of materials based on gallium antimony (GaSb) substrates, which are often used in infrared lasers and photodetectors. In this way, they are assembled in a stacked structure together with conventional high-efficiency solar cells that capture shorter wavelength solar photons.
Finally, the stacking procedure is carried out using a technique known as transfer printing , which allows the three-dimensional assembly of these tiny devices with a high degree of precision.
