Now, cheap, efficient, flexible solar cells made from nanopillars

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Washington, July 10 (ANI): Scientists have found a new way to make cheap, efficient, and flexible solar cells by using nanopillars made of low-cost and flexible materials.

The design by researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory and the University of California at Berkeley, grows optically active semiconductors in arrays of nanoscale pillars, each a single crystal, with dimensions measured in billionths of a meter.

"To take advantage of abundant solar energy we have to find ways to mass-produce efficient photovoltaics. Single-crystalline semiconductors offer a lot of promise, but standard ways of making them aren't economical," said Ali Javey, lead author of the study.

Solar cell basically converts light energy into charge-carrying electrons and "holes" (the absence of an electron), which flow to electrodes to produce a current.

But, unlike a typical two-dimensional solar cell, a nanopillar array offers much more surface for collecting light.

Computer simulations have indicated that, compared to flat surfaces, nanopillar semiconductor arrays should be more sensitive to light, have a greatly enhanced ability to separate electrons from holes, and be a more efficient collector of these charge carriers.

Thus, Javey created a new, controlled way to use a method called the "vapour-liquid-solid" process to make large-scale modules of dense, highly ordered arrays of single-crystal nanopillars.

Inside a quartz furnace, the researchers grew pillars of electron-rich cadmium sulfide on aluminum foil, in which geometrically distributed pores made by anodization served as a template.

And in the same furnace they submerged the nanopillars, once grown, in a thin layer of hole-rich cadmium telluride, which acted as a window to collect the light.

The two materials in contact with each other form a solar cell in which the electrons flow through the nanopillars to the aluminum contact below, and the holes are conducted to thin copper-gold electrodes placed on the surface of the window above.

The efficiency of the test device was measured at six percent, which while less than the 10 to 18 percent range of mass-produced commercial cells is higher than most photovoltaic devices based on nanostructured materials.

It is possible to make a flexible solar cell, by removing the aluminum substrate, substituting an indium bottom electrode, and embedding the 3-D array in clear plastic. (ANI)

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