27 July 2012
Breakthrough technology promises photovoltaics from any semiconductor
A new technology that could enable low cost, high efficiency solar cells to be made from virtually any semiconductor material has been developed by researchers at the US Department of Energy's Lawrence Berkeley National Laboratory and the University of California Berkeley.
The technology, they believe, opens the door to the use of plentiful, relatively inexpensive semiconductors such as metal oxides, sulfides and phosphides, which have previously been considered unsuitable for solar cells because of the difficulty in chemically tailoring their properties.
"Solar technologies today face a cost to efficiency trade off that has slowed widespread implementation," said physicist Alex Zettl, who led the research. "Our technology reduces the cost and complexity of fabricating solar cells and thereby provides what could be an important cost effective and environmentally friendly alternative that would accelerate the usage of solar energy."
The researchers have dubbed the technology 'screening-engineered field-effect photovoltaics', or SFPV, because it utilises the electric field effect, a phenomenon by which the concentration of charge carriers in a semiconductor is altered by the application of an electric field.
With the SFPV technology, a carefully designed partially screening top electrode lets the gate electric field penetrate the electrode and more uniformly modulate the semiconductor carrier concentration and type to induce a p-n junction. This enables the creation of high quality p-n junctions in semiconductors that are extremely difficult to dope by conventional chemical methods.
"Our technology requires only electrode and gate deposition, without the need for high temperature chemical doping, ion implantation, or other expensive or damaging processes," noted Zettl. "The key to our success is the minimal screening of the gate field which is achieved through geometric structuring of the top electrode. This makes it possible for electrical contact to and carrier modulation of the semiconductor to be performed simultaneously."
Under the SFPV system, the architecture of the top electrode is structured so that at least one of the electrode's dimensions is confined. "Our demonstrations show that a stable, electrically contacted p-n junction can be achieved with nearly any semiconductor and any electrode material through the application of a gate field, provided that the electrode is appropriately geometrically structured," Zettle concluded.