22 September 2010
Researchers from Case Western Reserve University and other institutions have created graphene-polymer solar cells that can be manufactured using solution processing.
Polymer solar cells produced via solution processing are emerging as less expensive alternatives to silicon solar cells, but polymer solar panels still have low power generation efficiency. Inorganic nanoparticles such as carbon nanotubes (CNTs) can be used in polymer solar cells to increase surface/interface area and charge separation and transport. However, Liming Dai, who is part of the research team, said that that there hasn’t been significant improvement in the overall device performance for CNT-based polymer photovoltaic cells.
Caption: Researchers created a bilayer photovoltaic device based on the solution-cast G-P3HT heterostructure with thermally evaporated C60. Photo courtesy of Liming Dai.
“As the building blocks for CNTs and other carbon nanomaterials, the two dimensional (2-D) single atomic carbon sheets of graphene show remarkable electronic, thermal and mechanical properties that are attractive for a variety of potential device applications,” Dai said. Graphene has the highest room-temperature mobility for electron and hole transport among all known carbon nanomaterials, he adds, and its one-atom thick, 2-D carbon network provides a much higher specific surface area (hence, a larger interface in a polymer matrix) than CNTs.
“The combination of graphene sheets with conjugated polymers is of great promise for polymer based photovoltaic cells,” Dai said. “However, the potential application of graphene sheets in polymer photovoltaic devices has been precluded by their poor solubility, which makes the graphene dispersion and device fabrication very difficult, if not impossible, by the traditional solution processing methods (e.g. spin- or blade-coating).”
To overcome those problems, the researchers chemically grafted CH2OH terminated regioregular poly(3-hexylthiophene) (P3HT) onto carboxylic groups of graphene oxide (GO) sheets using an esterification reaction. The resulting P3HT-G sheets are soluble in common organic solvents, which means that device fabrication by solution processing would be possible.
Michael Dustock at the Air Force Research Laboratory at Wright-Patterson Air Force Base in Ohio and Jong-Beom Baek in Ulsan National Institute of Science and Technology in South Korea were also part of the research team.
They created a bilayer photovoltaic device based on the solution-cast G-P3HT heterostructure with thermally evaporated C60 . The device had an up to 200% increase in power conversion efficiency compared to a P3HT/C60 device. The researchers aim to further improve the power conversion efficiency of the G-P3HT device, and they want to use the P3HT-G sheets to make bulk-heterojunction solar cells with high efficiencies.
Written by Nancy Lamontagne, Contributing Editor - US