Nanopillars form cheap, flexible solar cells
Berkeley, CA – Researchers at the Lawrence Berkeley National Laboratory and the University of California at Berkeley have demonstrated a way to fabricate efficient solar cells from low-cost and flexible materials.
The new design grows optically active semiconductors in arrays of nanoscale pillars, each a single crystal.
Computer simulations have indicated that, compared to flat surfaces, nanopillar semiconductor arrays should be far more sensitiveand efficient.
“Unfortunately, early attempts to make photovoltaic cells based on pillar-shaped semiconductors grown from the bottom up yielded disappointing results. Light-to-electricity efficiencies were less than one to two percent,” says Berkeley's Professor Ali Javey, adding: “Epitaxial growth on single crystalline substrates was often used, which is costly.”
Javey devised a new process to make large-scale modules of dense, highly ordered arrays of single-crystal nanopillars. Inside a quartz furnace his group grew pillars of electron-rich cadmium sulfide on aluminum foil.
In the same furnace they submerged the nanopillars in a layer of hole-rich cadmium telluride, which acted as a window to collect the light. This formed 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 device was measured at six percent - less than the 10 to 18 percent of mass-produced commercial cells, but higher than most photovoltaic devices based on nanostructured materials.
A flexible solar cell was achieved by removing the aluminum substrate, substituting an indium bottom electrode, and embedding the 3D array in clear plastic.
“There are lots of ways to improve 3-D nanopillar photovoltaics for higher performance, and ways to simplify the fabrication process as well, but the method is already hugely promising as a way to lower the cost of efficient solar cells,” said Javey.
Details are published in Nature.