Australia’s University of New South Wales (UNSW) announced last week that a recalibration of the international standard by which solar cells are measured revealed that they had created the first silicon solar cell to achieve the “magic” efficiency milestone of 25%.

Physics dictates that the theoretical maximum efficiency for first-generation silicon photovoltaic cells will be around 29%.

The UNSW ARC Photovoltaic Centre of Excellence already held the world record of 24.7% for silicon solar cell efficiency. UNSW’s world-leading silicon cell is now 6% more efficient than the next-best technology, Centre Executive Research Director and Scientia Professor Martin Green said.

Green said the jump in performance leading to the milestone resulted from new knowledge about the composition of sunlight.

“Since the weights of the colours in sunlight change during the day, solar cells are measured under a standard colour spectrum defined under typical operational meteorological conditions,” he said.

“Improvements in understanding atmospheric effects upon the colour content of sunlight led to a revision of the standard spectrum in April. The new spectrum has a higher energy content both down the blue end of the spectrum and at the opposite red end with, dare I say it, relatively less green.”

The recalibration of the international standard, done by the International Electrochemical Commission in April, gave the biggest boost to UNSW technology while the measured efficiency of other technologies made lesser gains.

Dr. Anita Ho-Baillie, who heads the Centre’s high-efficiency cell research effort, said the UNSW technology benefited greatly from the new spectrum “because our cells push the boundaries of response into the extremities of the spectrum.”

“Blue light is absorbed strongly, very close to the cell surface where we go to great pains to make sure it is not wasted. Just the opposite, the red light is only weakly absorbed and we have to use special design features to trap it into the cell,” she said.

“These light-trapping features make our cells act as if they were much thicker than they are. This already has had an important spin-off in allowing us to work with CSG Solar to develop commercial ‘thin-film’ silicon-on-glass solar cells that are over 100 times thinner than conventional silicon cells,” Green said.

ARC Centre Director, Professor Stuart Wenham said the focus of the Centre is now improving mainstream production. “Our main efforts now are focussed on getting these efficiency improvements into commercial production,” he said. “Production compatible versions of our high efficiency technology are being introduced into production as we speak.”

The world-record-holding cell was fabricated by former Centre researchers Dr. Jianhua Zhao and Dr. Aihua Wang, who have since left the Centre to establish China Sunergy, one of the world’s largest photovoltaic manufacturers.

“China was the largest manufacturer of solar cells internationally in 2007 with 70 per cent of the output from companies with our former UNSW students either Chief Executive Officers or Chief Technical Officers,” said Green.