| 18 June 2012
Australian researchers say they have increased the efficiency of third-generation solar cells by at least 25%. The semiconductor in the new dye-sensitised solar cell (DSC) developed at the RMIT University in Melbourne is made from niobia instead of the traditional titania. Niobium pentoxide (Nb2O5) is an inexpensive, chemically stable and environmentally friendly material. Could this metal oxide indeed be the star material solar researchers had been looking for?
Dye-sensitised solar cells are cheaper and can work in diffuse light, making them a promising technology for building integrated photovoltaics — or BIPV. “However, disappointingly, the best reported DSCs have so far been limited to 12.3% efficiency in the laboratory,” says Kourosh Kalantar-zadeh, Ph.D., Associate Professor at RMIT’s School of Electrical and Computer Engineering. “We, for the first time, obtained high conversion efficiency that is at least 25% larger than those of the traditional DSCs of the same configuration.” His team’s niobia-based cell reached an efficiency of 4.1% compared with 3% for a titania cell with the same film thickness. Thus, boosting the solar energy conversion efficiency of DSC by roughly one quarter could represent a critical milestone in moving the technology toward commercialization. The RMIT Micro/nanoelectronics and Sensors Group Leader further believes that “it will be the mater of time to exceed 15% total efficiency.”
“The key to this remarkable achievement lies in structuring niobia into nano-architectures by using a simple, highly-controllable and large-scale producible technique,” Dr. Kalantar-zadeh explains. To attain this breakthrough, the team had to overcome one challenge: How to make niobia that allows electron conduction without scattering. “Anodization was the solution,” says the engineering professor. “It produced directional and continuous pathways for electron transfer.”
The Kalantar-zadeh team’s work as well as the corresponding paper “Elevated Temperature Anodized Nb2O5: A Photoanode Material with Exceptionally Large Photoconversion Efficiencies” published in the journal ACS Nano suggest that niobia can be used as “the star material in DSCs.” Niobia accepts more dye than titania, thus more sunlight can be absorbed. “Niobia has a more optimal electronic band structure hence increasing the produced voltage; and the produced electrons can survive longer in niobia, hence enhancing the photocurrent,” Dr. Kalantar-zadeh explains.
The Australians are confident their work can provide “a viable solution to boost the conversion efficiency of DSC to that of silicon-based solar cells.” Dr. Kalantar-zadeh says, “Our next step is to increase the nano-niobia film thickness to an optimum level so that we can fully unlock its potential. We have to go to a thickness of up to 15 microns of niobia to obtain the optimum efficiency. The maximum thickness we have reached so far is six microns.” The thicker the niobia layer, the more dye it can hold.
Written by Sandra Henderson, Research Editor, Solar Novus Today
Photo coutesy of ACS Nano
