What Is a Nanowire Battery?

American scientists have developed a new technology for cheaply manufacturing high-quality nanowire solar cells, and related research was published in the journal Nature · Nanotechnology.

Solar cells are expected to become an absolutely clean and inexhaustible source of energy for human beings. However, to do this, three conditions need to be met: cheap manufacturing components; cheap and low energy consumption manufacturing methods; high conversion effectiveness. According to a recent report from the Organization of American Physicists, scientists in the United States have developed a new technology for cheaply manufacturing high-quality nanowire solar cells. Related research has been published in the journal Nature Nanotechnology.

For the first time, a scientific research team led by Yang Peidong of the Lawrence Berkeley Laboratory Materials Science Division of the Department of Energy has used solution-based cation exchange chemistry technology to produce high-quality semiconductor cadmium sulfide cores and copper sulfide shells. Core / shell nanowire solar cells. This cheap and easy-to-manufacture battery has an open circuit voltage and a filling value (both of which determine the maximum energy that a solar cell can produce) are higher than traditional flat-panel solar cells, and its energy conversion efficiency is 5.4%, which can be compared with traditional solar cells. The battery is comparable. ^[1]

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

Therefore, scientists hope to use semiconductor nanowires (which are only one thousandth of the width of human hair, but can extend to the millimeter level) to replace solar cells with silicon wafers. Compared with traditional solar cells, nanowire solar cells have several advantages: they have a higher ability to separate and accumulate charges; they can be made of materials with abundant reserves rather than silicon that requires strict processing. However, so far, the conversion efficiency of nanowire solar cells is low, dwarfing their advantages and limiting their development.

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

One year ago, Yang Peidong's team developed a very cheap method that uses silicon and replaces the planar P-N junction of a traditional solar cell with a spherical P-N junction. In the spherical P-N junction, a P-type silicon nanowire is used as a core, and an N-type silicon layer forms a shell around it. This geometry effectively turns a single nanowire into a photovoltaic cell and also greatly improves the light-capturing capacity of silicon-based photovoltaic thin films. ^[1]

Now they use this method to make cadmium sulfide and copper sulfide through a solution-based cation exchange reaction (developed by the director of the laboratory, Paul Alivisatos, mainly for the manufacture of quantum dots and nanorods). Out of the core / shell nanowires.

Yang Peidong explained: "Scientists previously used physical vapor transport to synthesize cadmium sulfide nanowires. However, the wet chemical method we used this time allowed us to obtain higher quality and longer nanowires. Crystalline cadmium sulfide nanowires range in diameter from 100 nm to 400 nm and are up to 50 mm long. "

The scientists then immersed the resulting cadmium sulfide nanowires in a copper chloride solution and left it at 50 degrees Celsius for 5 to 10 seconds. Subsequently, the cation exchange reaction turned the outermost 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 those of flat-plate solar cells. The reasons for the lack of performance include the problem of surface recombination of P-N junctions during high temperature doping and the difficulty The quality of the N junction is controlled. The new method provides us with a simple and inexpensive method for manufacturing high-quality nanomaterials. It also circumvents the high-temperature doping and deposition processes required for the gas phase manufacturing process, making the manufacturing cost lower and recycling Sex is better. "

Scientists believe that they can improve the energy conversion efficiency of this type of solar cell nanowires by increasing the amount of copper sulfide shell materials. If they want to commercialize this technology, they need to increase the conversion efficiency to at least 10%. ^[2]