Australian scientists develop world’s most efficient silicon photovoltaic cells

Solar energy has long been considered the magic solution for many of mankind's energy problems. Not only is it free, it is also abundant, and as far as humans are concerned, virtually inexhaustible. However, the high costs of solar cells and their low efficiencies in converting sunlight into electricity have not made them commercially viable.

Now, a new solar cell has breached the magical 25 per cent energy efficiency mark for those of the unconcentrated silicon variety.
The University of New South Wales (UNSW) Photovoltaic Centre of Excellence already held the world record of 24.7 per cent for silicon solar cell efficiency. Now 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.

New research has led to revisions in how incident light efficiency is calculated.  As a result, their record-holding design has reached the 25-per cent mark, a "magic" number according to many industry experts.  The cell, designed by Professors Martin Green and Stuart Wenham has a wide lead over competitive offerings, according to the Centre.  UNSW holds six solar world records now.

Centre Executive Research Director Professor Green described how the new research improved the understanding of the efficiency.  He states, "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. 

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 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."

UNSW's world-leading silicon cell is now 6 per cent more efficient than the next-best technology, Green said. The new record also inches the UNSW team closer to the 29 per cent theoretical maximum efficiency possible for first-generation silicon photovoltaic cells. Dr Anita Ho-Baillie, who heads the centre's high efficiency cell research effort, says the new research is a big boost "because our cells push the boundaries of response into the extremities of the spectrum."

She states, "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."

Professor Green states, "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."

The biggest goal of UNSW is now to adapt the ultra-high efficiency cells for mass production which should lead to more cost reductions.  ARC Centre Director, Professor Stuart Wenham, adds, "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."