Artificial leaves enhance light to energy conversion

Left: SEM image of the top view of a fabricated artificial leaf (light harvesting structures), where the white bar corresponds to a length of 200 nm. Right: Diagram illustrating the artificial leaves and the size scales involved.  Credit: D. Gomez

Modern society is, to a very large extent, built on the products of the organic chemical industry. On a daily basis, these products are used for making pharmaceuticals, plastics, health and cosmetics products and for several items in the housing, transportation and telecommunication industries.

However, the chemical industry relies heavily on fossil fuel derived energy for carrying out these chemical processes. A more sustainable and desirable prospect is to harvest sunlight for doing chemistry and thus transform this industry into a solar chemical manufacturing industry.

This project aims to create novel ways to harvest solar energy for driving chemical reactions instead of generating electrical power. To this end, a team of researchers from CSIRO and the National Institute for Materials Science design in Japan, have fabricated nano-sized structures that are capable of harvesting light and converting it into chemical potential energy.

They have used the high-resolution electron beam lithography tool at MCN to create structures capable of efficiently harvesting light for driving chemical transformations, with some assessment of their performance carried out by collaborators in Japan. The artificial leaves, or light harvesting devices, are made out of a light harvesting components in direct contact with an electron filter. Each element is made of aluminum wires with a cross section of tens of nanometers. The spacing between the light harvesting elements is a critical parameter, with its magnitude is in the hundreds of nanometers, which is controlled with a 10nm resolution.

Through this project the team have demonstrated up to two orders of magnitude improvement in the rate of the chemical reaction of a test model using their light-harvesting system. They have achieved this by using a very simple configuration of nanostructures and anticipate that more spectacular light-to-chemical energy transformations can be achieved with more sophisticated nanoparticle deigns.

The team is currently creating more sophisticated nanoparticle systems that are capable of absorbing nearly 100% of the incident light across the visible spectrum. This will translate into much higher light-to-chemical energy transformation efficiencies and they envisage that these light-harvesting technologies could be used for developing a sustainable and solar driven fine chemicals manufacturing industry in the not too distant future.