Buildings may soon be able to generate their own electricity from roofs, walls, windows – even benchtops – that come with in-built solar power capabilities.
How would you like to turn most of the surfaces in your home into mini power stations while maintaining their beauty and serviceability? A collaboration between Australian research institutions and industry is moving towards this goal by commercialising solar cell technology that can harness solar energy from walls, windows and steel roof sheeting, improving the energy efficiency of buildings.
The collaboration, known as the Victorian Organic Solar Cell Consortium, was boosted by a A$3.4 million grant from the Victorian and Commonwealth governments late last year. Its members include Monash University, the University of Melbourne, CSIRO, and industry partners BlueScope Steel, Securency International, Bosch and Innovia Films. The stakes are potentially high.
The project aims to develop a commercial process to produce what are known as dye-sensitised solar cells and organic solar cells that are printed on flexible materials. It combines original and applied research, but the emphasis is on commercialising technology.
Professor Yi-Bing Cheng, a materials engineering specialist from Monash, holds a thin piece of plastic printed with parallel whitish strips of colour between his fingers and says the "objective is to prove the concept is industrially viable". In the two-pronged project, Professor Cheng is a leader of the Monash team, which focuses on dye-sensitised cells, while counterparts at the University of Melbourne are working on organic solar cells.
Both technologies are aimed at developing more flexibly deployable alternatives to traditional silicon solar photovoltaic cells. The dye-sensitised version, based on nanotechnology, works like this: a thin layer of titanium oxide (about 20 microns) is laid on a base, and highly light-absorbing dye molecules are adsorbed onto this titanium oxide surface.
Because titanium oxide particles are extremely small and porous, they create a very large surface for the dye molecules to attach to, effectively making tiny nano-sized stacks. So pronounced is this effect that the titanium oxide film has 300 times the surface area of its actual footprint.
The dye molecules have the capacity to create electricity. When a photon from sunlight strikes a dye molecule it creates an electron, which is carried by the semiconducting titanium oxide and out through an external circuit to power lights or other electrical devices. The circuit then delivers the spent electrons back to the solar cell, where they react with an electrolyte and regenerate the dye molecules, preparing them to generate another electron.
Dye-sensitised cells have been around for about 20 years, but the Monash project has some significant points of difference from the 'traditional' technology. At Monash, ferrocene – an iron-based organometallic compound – and cobalt compounds are replacing iodide to create the electrolyte that returns spent electrons to the cell. These new electrolytes increase the generation efficiency of the solar cells and have the potential to greatly expand the life span of the solar cells.
Traditional dye-sensitised solar cells were sandwiched between panes of glass but the Monash project is developing the capacity to print them on plastic or metal. Industry partners include Securency International, a creator of polymer banknotes, and Innovia Films, manufacturers of polymer substrate. BlueScope Steel has invested a significant amount of money and aims to use the commercialised solar cell technology to print on its steel roofing products.
In the battle for the title of most efficient converter of solar energy into electricity, silicon-based cells are still ahead in one way. They can convert between 15 and 18 per cent of solar energy into electricity, while lab-scale dye-sensitised cells manage about 12 per cent.
But Udo Bach, Associate Professor of Materials Engineering at Monash and one of the project leaders, says those figures do not tell the whole story. "Silicon needs to be highly pure and highly crystallised, whereas the materials we use have far less stringent requirements." As a result, far less energy is used in producing the cells, meaning dye-sensitised cells take less than a year to produce the energy it took to manufacture them. With silicon cells, the payback time is more than three years.
Leone Spiccia, Professor of Chemistry at Monash and also a group leader, points out another advantage of dye-sensitised cells. Silicon-based cells work well when the sun is high but shut down when the light falls below certain levels. Meanwhile, dye-sensitised cells "harvest light from any direction so can work in diffuse light". They will produce energy from lower levels of light than silicon cells, Professor Spiccia says.
Professor Cheng says dye-sensitised cells are produced from low-cost materials and have few environmental side-effects with manufacture and disposal. "Different colour dyes can be used, meaning the solar cells can be different colours, even transparent," he adds.
The possibility of a colour range and capacity to work from diffuse and weak light sources make dye-sensitised cells particularly exciting. It means cells can be integrated into a range of surfaces, including walls, benchtops and windows, both inside and outside buildings, to boost their energy efficiency.
They could even be used to create novel features. "The possibility of using the cells to create different patterns and shapes (inside buildings) is very appealing," Professor Cheng says.
Monash has done some work on improving the dye used in the process, but the main focus of the project now is to improve the printing process of the cells to industrial levels. "Our project aims to show we can mass-produce cells efficiently. The cost of any solar cell technology will be dependent on how quickly you can produce," Associate Professor Bach says.
Professor Cheng says the project team is looking at buying machines that will enable continuous printing, pushing commercialisation closer. At Monash there are between 10 and 15 researchers involved, and if one considers the organic cell project (with which Monash cooperates on a weekly basis) and industrial partners, the total research force is between 40 and 50 people.
"Around the world there aren't too many projects with this scale of concerted effort," Professor Cheng says. He considers the overall global effort is too small to make the kinds of leaps that would push the technology to widespread adoption. But in Australia, there is work underway to create a united front of solar researchers who could make use of the research money made available with the introduction of the carbon tax.
The flexible solar cells project is impressive in the breadth of its expertise – synthetic, physical and inorganic chemistry, materials science and engineering and microscopy and advanced spectroscopy, to name a few fields. "We are working at the interface of different scientific disciplines, and that's exciting and particularly rewarding," Professor Spiccia says.
