In a paper recently published in the journal Advanced Energy Materials, scientists at the George Washington University (GWU) report that they have developed a new solar cell that is capable of converting direct sunlight into electricity with an efficiency rate of 44.5%. At that rate, it can potentially be the world’s most efficient solar cell ever.
One of the features that differentiate the prototype from typical solar panels installed on rooftops or fields is its use of concentrator photovoltaic (CPV) panels. This type of panel makes use of lenses that concentrate or focus sunlight onto tiny solar cells (less than one millimeter square in size) stacked into one single device that is capable of capturing almost all of the energy available in the solar spectrum.
Another thing going for it is the material it uses. Each layer is made with specialized materials — a family of materials based on gallium antimonide (GaSb) substrates, commonly found in applications for infra-red lasers and photodetectors — this allows the stacked cell to act like a sieve, absorbing the energy of a specific set of wavelengths. By the time the light is directed through the stack, a little below 50% of the absorbed energy has been converted into electricity. Putting that into perspective, the most common solar cells today can only convert about a quarter of available solar energy into electricity.
The most important feature that gives the new design its unprecedented efficiency is its ability to absorb light from wavelengths that aren’t normally absorbed by conventional solar cells. This is made possible by the stacked structure of the cells and the stacking procedure used. The technique is referred to as ‘transfer-printing’ and it is what enables high-precision 3D assembly of the tiny devices. This, in turn, allows the device to capture almost the entire spectral range, from the shorter wavelengths to the longer ones.
As explained by lead author of the study, Matthew Lumb, “about 99% of the power contained in direct sunlight reaching the surface of Earth falls between wavelengths of 250 nm and 2500 nm”. Existing solar cells using conventional materials are not able to capture this kind of spectral range in its entirety.
“Our new device is able to unlock the energy stored in the long-wavelength photons, which are lost in conventional solar cells, and therefore provides a pathway to realizing the ultimate multi-junction solar cell,” Lumb said.
There’s one major downside, though. The new prototype is quite expensive to make. The team acknowledges this and note that while they disregarded cost, their main aim was to show that there are still ways to increase and maximize the efficiency of solar panels. Eventually, it is hoped that the technique they used for this particular solar cell can be refined and streamlined so a cost-efficient and practical product can be made commercially available.
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