By Ucilia Wang, contributor, Renewable Energy World network
February 21, 2011 -- One way to boost solar cell performance is to effectively trap light, and many companies have come up approaches to minimize reflection and keep the photons bouncing around the semiconductors. A new entrant, Solar3D, is investing a way to do this by creating "trenches" and optics on top.
The Santa Barbara, CA, company is in the early stage of technology development. It's still designing components of the device and determining the types of materials to use. The goal is to fabricate a prototype cell by the end of this year, said Jim Nelson, CEO of Solar3D.
The company wants to develop a silicon solar cell with an array of tiny 3D structures that look like trenches for trapping light, Nelson said. The trenches, which don't exist in conventional solar cells, add more surface areas to capture light, increasing power output, he said. The substrate and the trenches will be made with silicon. There also will be an optical element on top of the trenches to help increase the amount of light capture. The optical element could be made of silicon oxide or some other composite material, Nelson said.
"The light comes down and hits the (optical element), which forces it into the trenches at an angle so that it will bounce back and forth, for four times at least, to get the most energy out," Nelson said.
The company is also investigating putting the electrical contact lines underneath the optical element rather than on top of the silicon cell. This placement is meant to make sure more light is caught and funnel it to the 3D trenches below.
By Solar3D's own assumption, such design will push a silicon solar cell's efficiency close to its theoretical maximum of 29%, Nelson said. More computer simulation and calculations will have to be done to nail down the designs and likely efficiency targets, however. Solar3D recently upgraded its simulation software.
SunPower holds the world record for being able to produce a solar cell with 24% efficiency, though the typical efficiency of cells rolling off its production lines could be a few percentage points lower. SunPower is using the more expensive monocrystalline silicon, while most of the solar cells today use multicrystalline silicon and generally have efficiencies of 15-18%.
Nelson said the goal is a process to make the solar cell that requires minimal additional equipment and costs. "Our technology guys feel they can engineer something that can be a dropped into existing facilities with minimum capital investments," he said. Solar3D just announced a mass-scale manufacturing design for 3D solar cells.
There is no clear indication whether the company can even come close to delivering on its promise, though its 3D solar cell idea is intriguing. The 3D solar cell concept isn't new. In a 2007 research paper, Georgia Tech's scientists described "tower structures" on the silicon substrate, as well as other features that 3DSolar mentions on its website, that were designed to trap more light. SUSS Microtec and Rolith are collaborating on a process to create 3D solar cells with nanolithography.
Solar3D is starting out at a time when venture capitalists are shying away from startups, which are likely to require hundreds of millions of dollars to bring their technologies into commercialization. Investors also are weary of simplistic pitches about how a novel technology can dramatically boost solar cell performance without incurring much more additional manufacturing costs than what current processes require.
But then, Nelson said Solar3D doesn't want to raise venture capital at all. "One option we will never touch is the venture capital option," said Nelson who, unlike many solar startup CEOs, doesn't have a technical background. Instead, he comes from the private equity world.
"There have been billions of dollars that VCs have put into green energy, but green energy has never been for them. They should've never done it. The payback is too long and so different than what American venture capitalists are used to," Nelson said.
Nelson is mum about how much money the company has raised for developing this technology. Solar3D actually started out as a software developer called MachineTalker Inc., in the early 2000s, he said. The company went public to raise money but the technology never got commercialized. About a year and a half ago, key investors interested in cleantech decided to look into funding solar technology development. The company's director of technology, Changwan Son, joined Solar3D last fall.
They have enough money to complete the prototype cell, Nelson said. He will then look for a manufacturing partner as an investor and to help Solar3D finalize the process for making the 3D device. The company might do another public offering to raise money; its shares are currently traded on the Over the Counter Bulletin Board market.
Solar3D employs about a dozen people, with 5 full-time workers on technology development, Nelson said. The company hopes to contract with manufacturers to make its technology and maybe license its know-how as well, he added.
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