Recently, the National Renewable Energy Laboratory (NREL) in the United States has developed the world's most efficient solar cells, with a maximum energy conversion efficiency of 47.1%. Although these efficiency records are often broken, the 47.1% conversion efficiency solar cell can at present be called the most efficient solar cell in the world. The latest research results were published on Nature Energy on April 13th.
Solar cells continue to make progress on the path to improving their conversion efficiency, and the correct combination of materials can enhance the ability of solar cells to convert sunlight into electricity. John Geisz, the lead scientist of the NREL's high-efficiency crystal photovoltaic cell team, said: "This new device demonstrates the huge potential of multi-junction solar cells."
Multi-junction solar cells are a type of high-efficiency solar cells. Each cell has multiple thin films made by molecular beam epitaxy or organic metal chemical vapor deposition, and these different semiconductors with different characteristic band gaps can absorb energy from specific frequencies of electromagnetic waves in the spectrum.
So far, research has proven that silicon is the gold standard for solar cell efficiency, and the efficiency of single-junction solar cells that use only silicon currently has the highest efficiency of 33%. The efficiency limitation of 33% can be broken through by changing materials, adding more nodal points, and implementing a series of engineering technologies between the two nodes. For example, the conversion efficiency of some three-junction solar cells may exceed 45% under sunlight concentration.
The newly developed solar cell by NREL is a III-V type six-junction structure, where "III-V" refers to the position of the light absorption element on the periodic table, and III-V materials have a wide range of light absorption characteristics. Each of the six connection points in the cell has been designed specifically, and they are composed of six different types of photoactive layers that can capture light from specific parts of the solar spectrum.
Through modern engineering and nanotechnology, the device contains about 140 layers of different III-V material layers in total to support the performance of these connection points, but its width is only one-third of a human hair.
To explore the performance of this III-V type six-junction solar cell, NERL scientists tested it with concentrated light, which was 143 times greater than the intensity of natural sunlight. The test results showed that their new solar cell had a record-breaking conversion efficiency of 47.1% under concentrated light.
Although the test was conducted under concentrated light, which corresponds to a lower efficiency than what may actually be achieved in practical use, the team said that a device that focuses sunlight on the cell can be constructed using reflectors. The team also tested this new type of cell with normal sunlight exposure, and its conversion efficiency still reached 39.2%. While 39.2% conversion efficiency may seem not outstanding, it has still set a new world record for conversion efficiency under sunlight exposure.
To break through the 50% efficiency limit, the main obstacle is reducing the internal resistance that hinders the flow of current in the solar cell, according to John Geisz of NREL.
The significance of this research is that the difference in conversion efficiency in normal sunlight and concentrated light indicates the possible existence of an economical way to deploy these six-junction III-V type solar cells. By using mirrors that concentrate light onto the new solar cells, which are relatively low-cost, it is possible to greatly reduce the cost of using this technology. With the concentration, fewer semiconductors will be used. At the same time, concentrating sunlight can also improve the efficiency of the cell.
According to Ryan France, one of the co-developers of the multi-junction cell and a scientist at NREL, it is highly possible to exceed the efficiency potential of solar cells beyond 50%. In fact, achieving the same effect may ultimately require only the order of magnitude of the original semiconductor materials or even 1/1000 compared to the materials used in the NREL research. This would make solar power generation more affordable for everyone.
In addition, this breakthrough in solar cell technology could also have positive impacts on other industries, such as aerospace, where high-efficiency solar cells could be used to power spacecraft.
Overall, the development of the world's most efficient solar cells by the NREL is a significant step forward in the renewable energy industry. With the potential to exceed the 50% efficiency limit, the future of solar energy looks brighter than ever before.
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