News in Science

Boost in low-cost solar cell efficiency

Solar cells The efficiency of low-cost solar cells that could one day form exterior walls or windows of buildings has been increased by 30 per cent, say Australian researchers.

Associate Professor Kalantar-zadeh, of RMIT University, and colleagues, report their research in the journal ACS Nano.

"This kind of solar cell is considered the third generation of solar cells," says Kalantar-zadeh, whose team led an international consortium of universities and the CSIRO.

Dye-sensitised solar cells (DSSCs) use a dye-coated semiconductor, instead of silicon, to absorb sunlight. Energy is then transferred via an electrolyte to an appliance or battery.

Scientists hope that DSSCs will one day replace the more expensive silicon solar cells. Apart from being cheaper, they can use diffuse light to operate.

This makes them excellent candidates for being incorporated into building walls, windows and skylights.

Efficiency gains

DSSCs are currently are used in small portable devices like backpacks that can be used to charge mobile phones.

Before they can be used more widely, their efficiency at converting sunlight to electricity must be improved.

The current record for DSSC efficiency in applications is around eight per cent, whereas silicon cells operate at about 15 per cent.

The semiconductor used in DSSCs is usually made from titania, but Kalantar-zadeh and colleagues, including PhD student Jian Zhen Ou used a metal called niobia instead.

This generates a higher voltage when it receives energy from its dye coating, thus increasing the overall efficiency of the solar cell by 30 per cent, compared to DSSCs titania-based semiconductors.

"Our work suggests that niobia can be used as the star material in DSSCs and provides a viable solution to boost the conversion efficiency to the values that far exceed that of silicon-based solar cells," say the researchers.

'Significant' efficiency increase

Dr Greg Wilson of CSIRO Energy Transformed Flagship, which is working on applying DSSCs to buildings but was not involved with the RMIT University-led research, welcomes the findings.

"30 per cent is significant - it would push it above the 10 per cent barrier," says Wilson.

But he says the anodisation method used by Kalantar-zadeh and colleagues used an electric current to prepare the niobia, which requires more energy than methods used to produce titania-based semiconductors.

Kalantar-zadeh says to increase the efficiency of DSSCs even further his team needs to increase the thickness of the niobia-based semiconductor so they can coat it with more dye.

"At the moment the thickness of the niobia is not optimum," he says.

Kalantar-zadeh says at the moment the team is finding it difficult to increase the semiconductor thickness without the material collapsing.

Ferrocene research

Meanwhile, in other related research, a team led by Professor Feng Wang of the Swinburne University of Technology has made a further step towards improving DSSCs.

Scientists hope to use a chemical called ferrocene as a new electrolyte in DSSCs, but have long had difficulties distinguishing between two different forms of the molecule.

In a study reported online in the Journal of Organometallic Chemistry, Wang and colleagues now show it is possible to distinguish between the two ferrocene forms using their infrared 'fingerprints'.

The findings will help scientists to find the best form of ferrocene for use in DSSCs.