Caltech Silicon Wire Research for Future Solar Cells

Recent research conducted at the California Institute of Technology (Caltech) supported by BP and the Energy Frontier Research Center program of the Department of Energy, which has been funded by the Recovery Act, has led to stellar results for the field of solar energy. A team of scientists from Caltech has created an innovative flexible photovoltaic (PV) solar cell using arrays of long, thin silicon wires embedded in a polymer substrate that enhances the absorption of sunlight and efficiently converts its photons into electrons. In addition, this design has cost benefits in that the solar cell requires only a fraction of the expensive semiconductor materials required by conventional silicon solar cells. Cost-competitiveness is a critical factor for solar cells in order to achieve large-scale adoption in the energy market.

These silicon-wire arrays reportedly absorb up to 96 percent of incident sunlight at a single wavelength and 85 percent of the total exposed sunlight. Both high absorption and high conversion factors are key characteristics for a high-quality solar cell. Part of what makes this solar cell design unique is that the silicon wires, in and of themselves, have a relatively high efficiency. Thus, when these wires are assembled in an array, they are more effective, and they also interact to increase the cell's ability to absorb light. In specific, light exposures each wire leading to absorption and scattering across the array, which increases the net absorption factor.

Interestingly enough, the array is composed of only 2 percent silicon and 98 percent polymer materials, as these arrays have the thickness of a conventional crystalline solar cell, but their volume is equivalent to that of a 2?m-thick film. Since the silicon material is an expensive component of a conventional solar cell, a cell that requires just 1/50 of the amount of this semiconductor will be significantly less expensive to produce. The composite nature of these solar cells enables the attribute of flexibility, which diversifies its application base. Moreover, flexible thin films can be manufactured in a roll-to-roll process, which is an inherently lower cost process than for the production of rigid silicon wafers required for conventional solar cells.

Research discoveries of this nature have led to the formation of numerous start-up companies in the clean energy sector in the last decade. A recent survey of innovative venture-backed clean technology companies published by the Wall Street Journal ranked solar power companies in the top three in a list of growing green companies for 2010. This analysis used a wide range of factors including the track records of success for both a company's management and for the investors on its board; the amount of capital raised in the last three years, and the percentage change in a company's valuation in the 12 monthsprior toNov. 30.

Based on this selection process, Solyndra Inc. of Fremont, CA (low-cost solar PV installation); Suniva Inc. of Norcross, GA (monocrystalline silicon PV), and eSolar of Pasadena, CA (concentrated solar power) were ranked 1-3, respectively; however, they were the few solar power companies to even make the list out of the 350 venture firms surveyed, as the green energy industry has become more competitive in recent years due to increasing cleantech investments globally.

"Photo credit- www.abc.net: Conventional silicon PV solar cell."