Solar cells are expected to become an absolutely clean and inexhaustible energy source for human beings. However, to achieve this, three conditions need to be met: cheap manufacturing components; cheap manufacturing methods with low energy consumption; high conversion effectiveness. According to a recent report by the American Physicists Organization Network, American scientists have now developed a new technology to manufacture high-quality nanowire solar cells at a low cost. Related research was published in the journal Nature. Nanotechnology.

The scientific research team led by Yang Peidong of the Materials Science Division of the Lawrence Berkeley Laboratory under the Department of Energy for the first time used solution-based cation exchange chemical technology to manufacture high-quality semiconductor cadmium sulfide as the core and copper sulfide as the shell. Core / shell nanowire solar cell. The open circuit voltage and filling value of these cheap and easy-to-manufacture batteries (the two together determine the maximum energy that solar cells can produce) are higher than traditional flat solar cells, and their energy conversion efficiency is 5.4%, which can be compared with traditional solar energy. The battery is comparable.

Traditional solar cell manufacturing is too complicated

Existing solar cells are generally made of ultra-pure single-crystal silicon circles, and the thickness of this very expensive material is required to be about 100 microns to absorb as much sunlight as possible, which makes the manufacture of silicon-based flat solar cells Into a complex, energy-intensive and expensive process.

Therefore, scientists hope to use semiconductor nanowires (the width of which is only one-thousandth of human hair, but the length can be extended to the millimeter level) instead of silicon wafers to manufacture solar cells. Compared with traditional solar cells, nanowire solar cells have several advantages: the ability to separate and accumulate charges is stronger; they can be made of materials with abundant reserves rather than silicon that requires strict treatment. However, to date, the conversion efficiency of nanowire solar cells has been low, dwarfing their advantages and limiting their development.

The core of all solar cells is two separate layers of material: a layer with rich electrons acts as a negative electrode; a layer with rich electron holes acts as a positive electrode. When they absorb the photons in the sun, they use the energy of the photons to make electron-hole pairs. Then, these electron-hole pairs will be separated at the P-N junction (the interface between the positive and negative electrodes), and the energy is used as electricity. Collect it.

A year ago, the Yang Peidong team developed a very inexpensive method that used silicon to replace the planar PN junction of a traditional solar cell with a spherical PN junction. In the spherical PN junction, with the P-type silicon nanowire as the core, the N-type silicon layer forms a shell around it. This geometry effectively turns a single nanowire into a photovoltaic cell, and also greatly enhances the light-harvesting ability of silicon-based photovoltaic thin films.

New nanowire battery is cheap and high quality

Now, they use this method, through the solution-based cation exchange reaction (developed by the laboratory director Paul Alivisatos, mainly used to manufacture quantum dots and nanorods), using cadmium sulfide and copper sulfide The core / shell nanowires are out.

Yang Peidong explained: "Scientists used to use physical vapor transport to synthesize cadmium sulfide nanowires. However, the wet chemical method we used this time allowed us to obtain nanowires of higher quality and longer length, and the newly generated single The diameter of crystalline cadmium sulfide nanowires is between 100 nanometers and 400 nanometers, up to 50 millimeters. "

The scientists then immersed the generated cadmium sulfide nanowires in a copper chloride solution and kept them at 50 degrees Celsius for 5 seconds to 10 seconds. Subsequently, the cation exchange reaction converted the outermost layer of cadmium sulfide into a copper sulfide shell.

Yang Peidong said: "In the past, the open circuit voltage and filling value of nanowire solar cells were much lower than that of flat solar cells. The reasons for its lack of performance include the surface recombination problems of P-N junctions and the difficulty in treating P —Control the quality of the N junction. The new method provides us with a simple and inexpensive method of manufacturing high-quality nanomaterials. It also avoids the high-temperature doping and deposition processes required for the gas-phase manufacturing process, making the manufacturing cost lower and regeneration Sex is better. "

Scientists believe that they can improve the energy conversion efficiency of this solar cell nanowire by increasing the number of copper sulfide shell materials. If you want to commercialize this technology, you need to increase the conversion efficiency to at least 10%.

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