Zinc oxide nanowires enable cheaper, greener components
Researchers from Lithuania’s Kaunas University of Technology (KTU) have enabled high-yield nanowire production from zinc oxide — a cheaper, more environmentally friendlier material than the rare earth elements such as indium, arsenic and gallium often used in electronics production.
By enabling electronic circuits on the molecular scale, nanowires are answering market demand for innovative, smaller, flexible electronic devices. However, assembly of nanowires into functional materials remains a problem as their synthesis is mostly limited by the surface of growth, hindering their wide application. Furthermore, many applications require properties which are contradictive and therefore cannot be effectively realised in a single material.
The new method for zinc oxide nanowires production, created at KTU’s Institute of Materials Science, tackles these problems. Thus the wider application of nanowires in innovative electronic devices, which are increasingly involving different surface materials, becomes possible.
“The new method was created while I was researching simple ways to grow metal oxide nanostructures,” said KTU researcher Dr Simas Račkauskas. “The method, which we now call combustion synthesis, allows producing high levels of a controlled nanostructure. Nanowires are being grown in the gas phase, the final product collected as powder and then dispersed in various solutions. Simple coating methods such as spraying allow placing zinc oxide nanowires on various surfaces.”
Due to their semiconductor properties, zinc oxide nanowires have potential applications in electronics and optics. The properties of zinc oxide-coated surfaces also allow their usage in medicine. At the moment, researchers are investigating two potential applications of the zinc oxide nanowires: a multifunctional antireflecting solar cell coating and multifunctional gas sensor array, sensitive and selective to gases, activated by light.
“Solar elements currently used in the market are reflecting light; thus the light, which could be turned into energy, is partly lost,” Dr Račkauskas said. “Nanowire solar cell coatings improve the performance of solar cells by reducing their reflective qualities, by transforming UV rays into light and by rendering the solar elements’ self-cleaning properties.”
Initial research reveals that by using zinc oxide nanowire coating the efficiency of solar elements is improved by 6%. The coating is water-repelling and it degrades the organic pollutants; thus the self-cleaning effect of a solar cell is achieved. The research team can produce around 100 g of zinc oxide nanoparticles per hour under laboratory conditions, costing around €8 — enough to cover the 2.5 m2 of solar elements.
The researchers are also investigating the properties of a UV sensor which can be sprayed on any surface. In the development of the sensor two materials are used: zinc oxide nanoparticles and a conductor (wire), such as graphite or metal paint. One can draw a full electronic scheme including wire and sensor on any surface, say textile, paper or plastic. According to Dr Račkauskas, a light sensor can be used like any other switch — it is just activated by light, such as a simple laser pointer beam.
“The application possibilities of such a UV sensor are virtually inexhaustible; however, we need to wait for the market demand and the further development of flexible electronics,” Dr Račkauskas said. “Our product might be interesting for functional design as it allows integrating electronics into clothing items, walls, interior design objects. Also, our UV switch can be placed in hard-to-access locations.”
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