Schematic structure of the nano-wire photocell
Researchers from the Technical University of Eindhoven (Netherlands) set a new record efficiency photovoltaic nanowire: 17.8%. This is a relatively new type of solar cell, which was invented less than a decade ago. For a short time he was able to come close to the effectiveness of the traditional types of single-layer solar cells.
Such rapid progress indicates that the nanowire solar cells - a very promising technology. This Inventors say from the outset. "Focus" photons through the nanowire looks so tempting that you can dream of a radical increase in efficiency.
Solar cell with standing nanofibers gallium arsenide. Photo: Nanotechnology Center Niels Bohr Institute (Denmark)
Unlike other types of photocells, photocells nanowire does not consist of layers of dense solid, and the fibers of the vertical grating thickness of about 200 nanometers each.
In 2013, Peter Krogstrup from the Niels Bohr Institute of Nanotechnology Centre (Denmark), together with scientists from the Federal Polytechnic School of Lausanne (Switzerland) have constructed a prototype solar cell with standing nanofibers gallium arsenide. In normal sunlight with solar cell removed the current corresponding to 180 mA per square centimeter of surface. In fact, standing nanofibers are concentrated light from an area 15 times greater than their total cross sections.
Such phenomenal performance are explained by resonance waves of visible light, which is less than the length of the standing section of the fiber. Faced with standing fibers adjacent waves are in resonance. Grid standing fibers as the vacuum "sucks" an ambient light.
If we accept the "cheating" with resonance, the nanofibers generally have to overcome a fundamental limit of Shockley-Kvayssera, which is 33.7% of the cells with one pn junction, 42% for two-layer cell, 49% for three-layer and 68% for a hypothetical cell with an infinite the number of layers.
Record efficiency of different types of solar cells, 1976-2016
Shortly after the first prototypes of other scientists began experimenting with real nanowire solar cells. The efficiency of such cells began to grow rapidly.
Now a group of researchers from the Technical University of Eindhoven for the first time demonstrated in real conditions nanowire solar cell efficiency of 17.8%. According to the researchers, this is not the limit. Authors of scientific work Dick van Dam and Cui Yingchao believe that record will fall quickly. They predict that the line efficiency of 20% will be overcome in the next two years. Increased efficiency due to the theoretical work of physicists, who have calculated better shape and diameter of the nanofibers, as well as their relative position. Their achievement - is to optimize the "forest" of nanofibres, which reduced the number of defects.
Previous record achievement for this type of solar cells was 15.3%. This result showed researchers from Lund University (Sweden). It is believed that the theoretical limit of efficiency for a nanowire solar cell is 46%, ie much higher than the fundamental limit of Shockley-Kvayssera traditional elements, which do not operate a resonance effect.
Scientists emphasize that another advantage of nanowire solar cells is their theoretical cheapness of mass production, even in comparison with run-decades of manufacturing technology, traditional photocells. An important advantage that manufacture of new cells is required five times less material. It is not only cheaper and more energy efficient. The less material - the fewer defects and defective parts. At least theoretically.
To nanowire solar cells have become commercially attractive, they have to catch up with the usual elements of cost and efficiency. To do this, bring the efficiency of at least 25% and improve the technical process for their manufacture. A further reduction in price can be achieved by switching from the use of rare metals such gallium arsenide and indium phosphide, to the more common silicon. Another way to reduce the cost of - the invention of process technology for the production of solar cells without the use of a thick substrate.
For his work on the calculation and production of nanowire solar cells with efficiency rekorodnym Dick van Dam October 17, 2016 he received his doctorate (PhD) in the Technical University of Eindhoven. Unfortunately, his doctoral dissertation to be published in the public domain. Before conducting an independent review and publication of a scientific paper in the Official Journal of the author refrains from disclosing the technical details of the invention.
In a press release the University emphasizes that Dr. van Dam known as a winner of the television quiz season Met het Mes op Tafel, which combines poker and erudition.