The efficiency of solar cells with nanowire increased to 17.8%

Researchers from the Technical University of Eindhoven (Netherlands) set a new record for the efficiency of solar cells with nanowire: 17.8%. This is a relatively new type of solar panel that was invented less than a decade ago. In such a short period of time, he managed to approach the efficiency of traditional types of single-layer solar cells.



Schematic structure of nanowire photocell

Such rapid progress indicates that nanowire solar cells are a very promising technology. The inventors have been talking about this from the beginning. "Focusing" photons through nanowires looks so tempting that you can dream about a radical increase in efficiency.



Photocell with standing nanofibers of gallium arsenide.

Unlike other types of photovoltaic cells, nanowire photovoltaic cells are not composed of solid dense layers, but of a lattice of vertical fibers about 200 nanometers thick each.

In 2013, Peter Krogstrup from the Nanotechnology Center of the Niels Bohr Institute (Denmark) together with scientists from the Federal Polytechnic School of Lausanne (Switzerland) designed a prototype photocell with an area of 1 mm2 with standing nanofibers of gallium arsenide. Under normal sunlight, the current corresponding to 24.6 mA per square centimeter of the surface was removed from the solar cell. In fact, standing nanofibers concentrated light from an area 15 times their total cross-sections.

Such phenomenal indicators are explained by the resonance of visible light waves, the length of which is less than the section of the standing fiber. When colliding with standing fibers, neighboring waves enter into resonance. The grid of standing fibers as a vacuum cleaner "sucks" into itself the surrounding light.


Note by the respected KhKnstn: The current removed from the photocell depends on the generation of charge carriers, which are excited when they absorb light photons. Ordinary sunlight is a standard value with a known spectral density of photons with a total power of 100 mW/cm2. For indium phosphide used in a 2016 study, the maximum current could be 34.5 mA/cm2.

In general, you need to understand the logic trick with a concentration of light 15 times more. The matter is the location of the nanoparticles relative to each other and the ratio of the surface area that the nanoparticle occupies relative to the unoccupied space. But that doesn't really matter, because normally the energy we get is rationed to the area of the illuminated surface. If we accept cheating with resonance, then nanofibers generally must overcome the Shockley-Quisser fundamental limit, which is 33.7% for a cell with one p-n transition, 42% for a two-layer cell, 49% for a three-layer cell and 68% for a hypothetical cell with an infinite number of layers.

Record efficiency of different types of solar cells, 1976-2016

Soon after the first prototypes, other scientists began experimenting with real nanowire photovoltaics. The efficiency of such elements began to grow rapidly.

Now a group of researchers from the Technical University of Eindhoven for the first time demonstrated in real conditions the efficiency of a nanowire photocell 17.8%. According to researchers, this is far from the limit. The authors of the study, Dick van Dam and Yingchao Cui, believe that the record will fall quickly. They predict that the 20% efficiency threshold will be overcome within two years. The increase in efficiency is due to the theoretical work of physicists who calculated the more efficient shape and diameter of nanofibers, as well as their mutual location. Their achievement is precisely in optimizing the “forest” of nanofibers, which allowed to reduce the number of defects.

The previous record achievement for this type of solar cell was 15.3%. This result was shown by researchers from Lund University (Sweden). The theoretical efficiency limit for a nanowire photovoltaic cell is thought to be 46%, well above the Shockley-Quisser fundamental limit for traditional cells where resonance is not involved.

Scientists emphasize that another advantage of nanowire photocells is their theoretical cheapness in mass production, even compared to the decades-old technology of manufacturing traditional photocells. An important advantage is that five times less material is required to make new cells. It is not only cheaper and more energy efficient. The less material - the fewer defects and defective batches. At least theoretically.

For nanowire photovoltaic cells to become commercially attractive, they must match conventional elements in cost and efficiency. To do this, it is necessary to bring the efficiency to at least 25% and improve the technical process of their manufacture. Further cheapening can be achieved by switching from the use of rare metals such as gallium arsenide and indium phosphide to more common silicon. Another way to reduce the cost is the invention of the process technology for the production of solar cells without the use of a thick substrate.

For his work on the calculation and manufacture of nanowire photocells with reconstitutive efficiency, Dick van Dam received his doctorate (PhD) from the Technical University of Eindhoven on October 17, 2016. Unfortunately, his doctoral dissertation is not publicly available. Before conducting an independent review and publishing a scientific article in the official journal, the author refrains from disclosing the technical details of the invention. published



Source: geektimes.ru/post/281778/