An engineering research team in Japan has developed a new solar cell that may be able to raise the efficiency of photovoltaic cells above 50 percent, and theoretically as high as 63 percent under certain conditions. This is important as consumer-grade cells are hindered by a lower maximum efficiency of around 26 percent, with most cells on the market only boasting an efficiency of 12 to 18 percent. If that value can be improved, it will make for greater accessibility for consumers looking toward renewable energy sources, and drastically improve the output of commercial solar farms.
One of the major factors hampering solar cell efficiency is that single-layer cells can only absorb certain wavelengths of light, meaning that there are many wavelengths of light that aren’t collected by the cell, but are rather are absorbed by the material, converting to heat instead. This can be overcome by using multiple layers within the same cell, with each layer collecting different wavelengths. Quad-layer designs can reach 46 percent efficiency, but this form of solar cell is prohibitively expensive to produce, relegating its use to specialized markets, such as the military and space exploration.
This new process, developed by researchers at the Kobe University Graduate School of Engineering, makes use of what is called a "two-step photon up-conversion", where a lower-wavelength photon that would ordinarily have been wasted in a traditional cell is instead collected by a specialized layer that can absorb different wavelengths. The photon is absorbed into one of the layer’s molecules, and then is activated by a second incoming low-wavelength photon, adding its energy to the first photon, to transfer it (as an electron) to the device’s conduction layer — making added electricity for the device.
Being able to make use of photons that would have been otherwise wasted, the researchers have been able to push the theoretical limits of what this single-layer cell can produce to beyond what an expensive quad-layered cell can. "According to ideal theoretical predictions, the IBSC is expected to exhibit extremely high conversion efficiency, >60%, under the maximum concentration [using a solar concentrator] and 48.2% under one-sun irradiation."