Nature Inspired Nanotexturing Gives Graphene Boost In Light Absorption

Nature has long provided examples of what can be achieved through a little nanoengineering. Take the colour of many butterflies. The brilliant blues that you sometimes see are often the result of ‘structural colouration’ whereby the nanoscopic structure of the butterfly wings interacts with light in such a way that certain colours are absorbed while others are strongly reflected back into the dazzled eye of the observer. These naturally occuring nanostructures also serve other purposes however, mostly in the effective reflection of heat and high energy dangerous light. Silver ants also display this property through the adoption of triangular-shaped hairs on their bodies that dissipate the high heats of the Sahara, keeping the ant cool.

Functional nanostructures exist in nature, for example in the wings of a butterfly to protect it from heat while also giving rise to many of the wonderful wing colours that we see (Photo Credit: AP Photo/Kirsty Wigglesworth)

By fine-tuning the texture of the surface of a material on the nanoscale, the same scale as the wavelengths of light we see in, scientists can tailor the heat and light absorption of a material to optimise it for a range of uses. When it comes to absorbing as much light as possible, for example in solar energy devices, nature provides us with even more inspiration, for example in the eyes of moths, which are patterened in such a way that the little light available in very dim conditions is funnelled into the moth’s eye, allowing it to see in low-level lighting with little light being reflected. The light that is absorbed is also of a range of wavelengths, or ‘broadband’ light. Such properties would be hugely beneficial in solar energy harvesting, where solar panels could potentially increase their efficiency by absorbing more light across the entire solar spectrum.

Using nature as inspiration, a team of scientists working in the Advanced Technology Institute based at my new place of work, the University of Surrey, have engineered graphene to increase its light absorbance from 3% to 95% simply by ‘nanotexturising’ the surface. Traditionally graphene is terrible at absorbing light, but is a brilliant conductor of heat and electricity along its plane. These properties of conduction have always been desirable in solar cells, but graphene has always had to work with other materials that are capable of absorbing much more light. This research could eliminate that, bringing us a step closer to thin, light, transparent, flexible graphene solar cells. Furthermore, if they can work in such low-level light conditions, they could even be used indoors in smart windows or smart wallpaper that can harvest any wasted light and use it to power other appliances.

The graphene is nanotextured by growing it on a titanium metal surface that has been sputtered with tiny particles to disrupt the otherwise smooth surface. This results in a bumpy nanostructure that closely resembles the size and shape of the moths’ eyes that they were initially modelled on.

By incorporating this technology into existing solar cells, the efficiency will not only increase because of the enhanced levels of light absorption, but also because of the wide broadband wavelengths of light that can be absorbed by it. Once again showing that nature is one brilliant nanoengineer, constantly providing us with inspiration for groundbreaking research.