According to a report by the UK’s “Nature†magazine website recently, although thin-film solar cells are widely used, they also have “congenital deficiencyâ€: the thinner the thin film, the lower the manufacturing cost, but when it becomes thinner, it will lose its light-harvesting ability. American scientists say that when the thickness of a thin layer is equal to or less than the wavelength of visible light, its light-capturing ability will become very strong. Scientists can develop thin-film solar cells with a thickness that is only 1% of the thickness of today's commercial thin-film solar cells, but their light-trapping capability is greatly improved.
Scientists use ray-light extremum, the theoretical maximum light-harvesting value, to identify how much light a material can capture, but only if the material has a certain thickness. Currently, scientists have fabricated thin-film solar cells with a light-absorbing layer thickness of only 0.1 nanometers, but such slim films can miss a lot of light.
However, now Harry Atwater, professor of applied physics and materials science at Caltech, and colleagues pointed out in the latest issue of Nano Express that they have found a clever way to make thin layers help solar cells beyond Ray-light extremes. They found that when the thickness of the thin layer is smaller than the wavelength of visible light (400 to 700 nm), the thin layer interacts with the wave characteristics of these visible lights rather than seeing visible light as a straight ray. Atwater said: "When we make a thin layer equal to or less than the wavelength of visible light, all the rules are changed." In this way, the light absorption ability of a material no longer depends on the thickness, but on light and absorption. Wave effect between materials.
Through calculations and computer simulations, the Atwater team has proven that the trick to make a material more “light†is to create more “light states†for light to occupy. These “light states†are like slits. In the same way, it can absorb light of a specific wavelength. The amount of "photostate" of a material depends in part on the refractive index of the material. The higher the refractive index, the more "photostates" it can support.
In fact, as early as 2010, Stanford University professor Fan Yan and colleagues identified the “photometric†number as the main factor that a material can absorb in a certain amount of light. They used a material with a higher refractive index to surround a material with a low refractive index. As a result, it was found that the appearance of a high refractive index material can effectively increase the refractive index of the low refractive index material and enhance its light-harvesting ability.
The Atwater team extended the above conclusions. The latest research shows that the “light state†in the film absorber will greatly enhance its light-harvesting ability. Furthermore, the effective refractive index of the absorber can be increased in several ways, such as by surrounding the light absorbing layer with a metal or crystal structure or by embedding the light absorber in a more complex three-dimensional array. Fan Hao said: "The latest research shows that we can use a variety of different methods to effectively break the ray-optic extremum."
Robert Collins of the University of Toledo of the United States stated that the Atwater team’s research is “a very critical first stepâ€. However, he also believes that this technology still faces many challenges, such as the need for additional industrial processes to manufacture these thin films, which will lead to increased costs. (Liu Xia Editor: Lin Xiumin)
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