A team of researchers from the California Institute of Technology have invented a new type of solar cell whose active ingredients are nanometer-sized silicon wires. The solar cell they prototyped thus uses only a small fraction of the silicon used to make conventional solar cell, the rest being made of a polymer.
Harry Atwater, Howard Hughes Professor, professor of applied physics and materials science, and director of Caltech’s Resnick Institute said: “These solar cells have, for the first time, surpassed the conventional light-trapping limit for absorbing materials.”
The light trapping capability of a material measures how much light it is able to absorb. The silicon wire arrays CalTech researchers invented do absorb up to 96 percent of the incident sunlight, measuring a single wavelength, and 85% of the total spectrum. Atwater also says: :”We’ve surpassed previous optical microstructures developed to trap light”. He had also been involved in other solar power harvesting in the past like the one here.
The silicon wires Atwater and his colleagues invented can convert between 90 and 100 percent of the photons they absorb into electrons, having a near-perfect internal quantum efficiency. “High absorption plus good conversion makes for a high-quality solar cell,” says Atwater. “It’s an important advance […] Light comes into each wire, and a portion is absorbed and another portion scatters. The collective scattering interactions between the wires make the array very absorbing,” he says.
Although the wires cover only between 2 and 10 percent of the solar cell’s surface area, the resulted cell “is independently a high-efficiency, high-quality solar cell.” When brought together in an array, however, they’re even more effective, because they interact to increase the cell’s ability to absorb light.
Each wire measures between 30 and 100 microns in length and only 1 micron in diameter. “The entire thickness of the array is the length of the wire,” notes Atwater. “But in terms of area or volume, just 2 percent of it is silicon, and 98 percent is polymer.”
By combining cheap polymers with expensive but little silicon, efficiency is created not only in terms of performance, but also price. Up-scaling the entire technology could change the rules of the game in the solar industry, thanks to this discovery.