Growing Nanopillars on Aluminum Foil to Fabricate Solar Cells

The U.S. researchers have developed a new type of solar cell technology. The solar cell can be made by growing upright nanopillars on aluminum foil. The entire cell can be produced after being encapsulated in a transparent colloidal polymer. Flexible solar cells cost less than traditional silicon solar cells.

Ali Jewey, a professor of electrical engineering and computer science at the University of California, who led the study, said that nanocolumn technology allows researchers to use cheaper, lower-quality materials than traditional silicon and thin-film batteries. More importantly, this technology is more suitable for making a curlable solar panel on thin aluminum foil, thereby reducing manufacturing costs. Once successful, its production costs will be as low as 1/10 of monocrystalline silicon solar panels.

The solar cell is made by embedding a uniform 500-nm-high cadmium sulfide into a cadmium telluride thin film, both of which are commonly used semiconductors in thin-film solar cells. According to a report published by Nature and Materials by Jerway and his colleagues, this type of battery converts light energy into electricity with an efficiency of up to 6%. Previously, some scientists used this design idea of ​​the column, but the method is relatively expensive, and the photoelectric conversion efficiency is less than 2%.

In conventional solar cells, silicon absorbs light and generates free electrons. These electrons must reach the circuit before they are trapped in defects or impurities in the material. This requires the use of extremely pure and expensive crystalline silicon for the production of high-efficiency photovoltaic devices.

The nanopillars take on the responsibility of silicon. The material around the nanocolumns absorbs light and generates electrons, which are transported by the nanocolumns to the circuit. This design increases efficiency in two ways: tightly packed nanopillars capture the light between the columns, helping the surrounding materials absorb more light; the electrons travel through the nanopillars at very short distances, so there is not much chance of being trapped For material defects. This means that low-quality, inexpensive materials can be used.

Scientists use different nanostructures to make such solar cells. For example, a Harvard professor of chemistry, Charles Ripoll, has developed a nanowire with different silicon cores and concentric silicon layers; Yang Peidong of the University of California, Berkeley, has developed a dye-sensitized solar cell with zinc oxide nanowires. . The photoelectric conversion efficiency of these nanowire solar cells has reached 4%.

For the first time, nano-pillar batteries made by Jerway and his colleagues used oxidized aluminum foil to create periodically distributed 200-nanometer-wide holes, which serve as templates for the upright growth of cadmium sulfide crystals. Then, cadmium telluride and the top electrode were decorated with thin films of copper and gold. They are connected to the battery via a glass plate, or they are bent at the top of the polymer solution.

Wang Zhonglin, a professor of materials and engineering at the Georgia Institute of Technology, commented that integrating nanomaterials engineering design with various flexible substrate technologies for fabricating flexible, flexible, high-efficiency solar cells is an exciting development. Athena Nozick, a physical chemist at the National Renewable Energy Laboratory responsible for research on solar cells, said that the battery will compete with flexible thin film solar cells made of silicon, cadmium telluride and other materials. It may not be its flexibility but its cost advantage.

Currently, researchers are exploring the use of materials that increase conversion efficiency. For example, the top copper-gold layer is now only 50% transparent. If all light is allowed to pass through, the efficiency can be doubled. Therefore, researchers are planning to use transparent conductive materials such as indium oxide. In addition, the use of other semiconductor materials as nano-pillars and their surrounding materials is also under consideration by researchers. Such a fabrication process can be applied to a wider range of semiconductor materials. Other material combinations may also improve efficiency. More importantly, It is possible to avoid the toxicity of cadmium.