PV Efficiency Hits 25%

There is a new world record in solar cell efficiency. The University of New South Wales’ ARC Photovoltaic Centre of Excellence just broke their previous world record of 24.7 percent by delivering the first silicon solar cell to achieve a 25 percent efficiency rate.

A revision of the international standard by which solar cells are measured, has delivered the significant 25 per cent record to the team led by Martin Green and Stuart Wenham, professors at UNSW, widening their lead on the rest of the world.

According to Green the new world mark in converting incident sunlight into electricity was one of six new world records claimed by UNSW for its silicon solar technologies.

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

"Since the weights of the colors in sunlight change during the day, solar cells are measured under a standard color spectrum defined under typical operational meteorological conditions," he said. "Improvements in understanding atmospheric effects upon the color 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 others made lesser gains.

UNSW's world-leading silicon cell is now six per cent more efficient than the next-best technology, according to Green. The new record also inches the UNSW team closer to the 29 percent theoretical maximum efficiency possible for first-generation silicon photovoltaic cells.

Anita Ho-Baillie, head of the 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.

Green added, "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."

Wenham said the focus of the Centre is now improving mainstream production, adding "Our main efforts now are focused on getting these efficiency improvements into commercial production. 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, Jianhua Zhao and Aihua Wang, who have since left the Centre to establish China Sunergy, one of the world's largest photovoltaic manufacturers.

For more information, visit: www.unsw.edu.au