August 5, 2011 - Rice University’s James Tour’s Lab has created thin films from graphene that eliminate expensive, brittle indium tin oxide (ITO) films for touchscreen displays, solar panels, and LED lights. The see-through graphene-hybrid film is flexible, allowing integration into body-wearable electronics or building integrated photovoltaics (BIPV), among other commercial applications.
Rice University’s hybrid graphene/aluminum mesh material. (Credit: Yu Zhu, Rice University)
The Tour Lab’s thin film combines a single-layer sheet of highly conductive graphene with a fine grid of metal nanowire. The combination outperformed ITO and competing materials at the Lab, offering better transparency and lower electrical resistance. The hybrid works better than pure graphene, which interacts too much with its substrate, Tour said. The fine metal mesh maintains conductivity without blocking transparency, added postdoctoral researcher Yu Zhu. The gaps in the nanowires make them unsuitable stand-alone components in conductive electrodes. The researchers settled on a grid of 5um aluminum nanowires.
Standard roll-to-roll (R2R) and ink-jet printing could produce the metal grids on a commercial scale. Roll-to-roll graphene production is also becoming more readily available from nanomaterials manufacturing companies. Tour believes the ITO replacement can be scaled up immediately.
An electron microscope image of a hybrid electrode developed at Rice University shows solid connections after 500 bends. (Credit: Tour Lab, Rice University.)
In tests, the hybrid film’s conductivity decreased 20%-30% with the initial 50 bends, but after that the material stabilizes. "There were no significant variations up to 500 bending cycles," Zhu said. More rigorous bending test should be performed by commercial users, he added.
The film also proved environmentally stable. When the research paper was submitted in late 2010, test films had been exposed to the environment in the lab for six months without deterioration. After a year, they remain so.
Yu Zhu holds a sample of a transparent electrode that merges graphene and a fine aluminum grid. Clockwise from top right: James Tour, Zhu, Zheng Yan, and Zhengzong Sun. (Credit: Jeff Fitlow, Rice University.)
The Office of Naval Research Graphene MURI program, the Air Force Research Laboratory through the University Technology Corporation, the Air Force Office of Scientific Research and the Lockheed Martin Corp./LANCER IV program supported the research.
The research was reported in the online edition of ACS Nano. James Tour is Rice’s T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science. Yu Zhu is lead author on the paper. Rice graduate students Zhengzong Sun and Zheng Yan and former postdoctoral researcher Zhong Jin are co-authors of the paper.