Theoretically, the maximum efficiency of the highest-grade crystalline silicon solar cells is approximately 30 percent, because much of the sunlight that hits a solar cell is lost as heat. In practice, however, the most efficient solar cells on the market today operate at about 23 percent efficiency – that is, they convert about 23 percent of the energy hitting the cell into electricty. But Solar3D, a Santa Barbara-based solar energy technology startup, claims to be developing a breakthrough silicon solar cell technology that, according to preliminary tests, is capable of achieving an efficiency of 25.47 percent.
The company’s design concept for a three-dimensional solar cell utilizes light management techniques used in the fiber optics industry. Instead of allowing sunlight to bounce off the surface, Solar3D uses a top light-collecting layer, made of silicon dioxide or another similar material. This material, like a similar material being developed on a nano-scale at Northwestern University, does not absorb sunlight itself; instead, it guides it into three-dimensional micro-photovoltaic structures, each a few micrometers wide.
From here, the technology works like a funnel trapping sunlight, giving the photovoltaic material more time to convert it into electricity. Instead of passing through the photovoltaic material just once, the photons “bounce around” until nearly all of them are converted into electricity. Further efficiency improvements are achieved by running the electrical contacts under the light collectors, rather than across the top of the cell, like most photovoltaic cells. This prevents the wires from shading the cells, blocking the absorption of sunlight.
Solar3D predicts that its “next generation solar cell” will be dramatically more efficient and less expensive than existing technologies. Although still in the preliminary phases of product development, Solar3D is working on completing a prototype and finding a partner in the semiconductor industry to fabricate and help commercialize the product. According to Solar3D President and CEO Jim Nelson, recent tests of multiple micro three-dimensional photovoltaic structures have exceeded the company’s expectations.
“If the results of the simulations hold up in fabrication, as we expect, our cell’s performance will be the highest conversion efficiency achieved in silicon solar cells,” Nelson said. “Our objective has always been to change the world by providing affordable solar power. At this level of conversion efficiency and expected manufacturing cost, we intend to do just that. It will be continuing increases in solar cell efficiency, along with decreases in manufacturing costs, that will drive solar electricity to economic parity with current methods of power generation. With the efficiency that comes from our new design, we take a giant step in that direction.”
Solar3D’s technology was invented by Nadir Dagli, an electrical engineer trained at the Massachusetts Institute of Technology, and an expert in photonics and nanophotonics for high-speed telecommunication devices. He has been a professor of electrical and computer engineering at the University of California at Santa Barbara since 1987.