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Scientists at Melbourne's Monash University have developed a new generation of solar cells which they say could lead to significant improvements in solar panel efficiency.

A report in the journal Nature Chemistry details the Melbourne team's research.

The technology they are developing uses dye sensitised solar cells containing electrolytes made out of an iron-based organometallic compound called ferrocene. Ferrocene is also called a "sandwich compound", because it sandwiches an iron atom between two organic rings to form a highly stable compound structure.

Their research into solar cells using this 'iron sandwich' is published today in the journal Nature Chemistry.

Dye sensitized solar cell technology has been around for more than 20 years. Until now the cells have worked by using iodide based electrolytes, and a chemical compound dye to absorb sunlight.

Solar cells based on this technology have proved to be viable low-cost alternatives to conventional silicon solar cells. They're found in products such as flexible back pack solar panels used to charge cell phone batteries.

Lead author, Monash PhD student Torben Daeneke, together with Dr Udo Bach, Professor Leone Spiccia, and colleagues, have replaced the traditional iodide electrolyte with a ferrocene compound.
Rising solar energy efficiencies

Bach says the solar cells using the ferrocene compound electrolytes were found to have energy conversion efficiencies approaching that of iodide.

"Extensive research around the world since 1991 has improved the energy conversion efficiency of traditional iodide electrolytes to about 12 per cent."

"But in just 2 years of work, a single PhD student at Monash was able to achieve energy conversion efficiencies of 7.5 per cent using ferrocene compound electrolytes."

"And since the paper was submitted for publication, that's gone up to 8 per cent," says Bach.

Silicon based solar cells achieve energy conversion efficiencies of 20 per cent.
Iodide problems

Improvements in the performance of iodide based electrolytes by small adjustments in the types of chemicals used for the electrolyte are petering out.

Bach says while there are other ways to try and improve them, they still have limitations because of their complex chemistry and corrosive nature.

"Previous efforts to use non corrosive ferrocene type metal compounds as the electrolyte have resulted in poor performance with far less conversion efficiency," he says.

"What's different this time was our decision to exclude oxygen during the assembly process."

Bach explains that they have overcome the problem of electrolytes decomposing in oxygen, by constructing the cells in an environment filled with an inert gas.

"Another problem with ferrocene is its strong charge recombination effect which causes charge carriers generated through photon conversion to recombine before their energy can be collected."

Bach says a number of specific changes were made to suppress this recombination effect.

"We included additives to cut down recombination, customized the semi conductor layer and used an organic dye with stronger light absorbing properties, developed by researchers at the University of Melbourne."

One of the great advantages of ferrocene, is the ease with which its structure can be altered, a property that could be used to further improve its efficiency.

Bach says research will now focus on improving the system to fine tune the electrochemical properties, slightly modify the chemical structure and evaluate the stability of the ferrocene based solar cell.

Dr Ashraf Uddin from the University of New South Wales School of Photovoltaic and Renewable Energy says the Melbourne-based researchers seem to be addressing an important issue in improving the energy conversion efficiencies of ferrocene electrolytes. But he raises several potential obstacles.

"We also need to know more about the product's reliability, the sort of durability or life span the cells are likely to have. And then there's the issue of production costs."

Uddin says these types of solar cells could do more than recharge cell phones and laptop computers.

"They could be included in the body work of cars or on the walls of buildings to help generate electricity."

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