Researchers find new way to grow microwires
1 min read
Researchers from the Massachusetts Institute of Technology (MIT) and Penn State have found a way of producing nanowires made of silicon in quantity and in a highly controlled way. According to Tonio Buonassisi, MIT professor of mechanical engineering, the breakthrough method could be scaled up to an industrial scale process and potentially lead to practical commercial applications such as sensors, batteries and solar cells.
While prototypes of solar cells made from such wires have previously been produced by several researchers, these methods have serious limitations according to Buonassisi, as most provide little control over the exact sizes and spacing of the wires. In contrast, Buonassisi claims the new process is simple, allows precise control over the wire dimensions and spacing and can be carried out on any 3d surface.
The method involves heating and intentionally contaminating the surface of a silicon wafer with copper, which diffuses into the silicon. Then, when the silicon slowly cools, the copper diffuses out to form droplets on the surface. When it is placed in an atmosphere of silicon tetrachloride gas, silicon microwires begin to grow outward wherever there is a copper droplet on the surface. Silicon in the gas dissolves into these copper droplets, and then after reaching a sufficient concentration, begins to precipitate out at the bottom of the droplet onto the silicon surface below. This build up of silicon gradually elongates to form microwires approximately 10 to 20micrometers across. The whole process can be carried out repeatedly on an industrial manufacturing scale and according to Buonassisi, could potentially be adapted to a continuous process.
Although the research is still in the development stage, Buonassisi believes it demonstrates potential for a solar cell based on such wires at a significantly lower cost. "This is still in a very early stage," he said. "More work remains to be done to find the best combinations of temperature profiles, copper concentrations and surface patterning for various applications. It also remains to be determined what thickness and spacing of wires produces the most efficient solar cells."
